Add transport keys for reintroduced contact.

Add DB method for checking whether there's anything to send

See merge request briar/briar!1485

bramble-android/build.gradle

@@ -15,8 +15,8 @@ android {
 	defaultConfig {
 		minSdkVersion 16
 		targetSdkVersion 30
-		versionCode 10305
-		versionName "1.3.5"
+		versionCode 10303
+		versionName "1.3.3"
 		consumerProguardFiles 'proguard-rules.txt'
 
 		testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
@@ -42,18 +42,18 @@ configurations {
 
 dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
-	tor 'org.briarproject:tor-android:0.3.5.15'
+	tor 'org.briarproject:tor-android:0.3.5.13@zip'
 	tor 'org.briarproject:obfs4proxy-android:0.0.12-dev-40245c4a@zip'
 
-	annotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 
 	compileOnly 'javax.annotation:jsr250-api:1.0'
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
-	testImplementation "junit:junit:$junit_version"
-	testImplementation "org.jmock:jmock:$jmock_version"
-	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation 'junit:junit:4.12'
+	testImplementation "org.jmock:jmock:2.8.2"
+	testImplementation "org.jmock:jmock-junit4:2.8.2"
+	testImplementation "org.jmock:jmock-legacy:2.8.2"
 }
 
 def torBinariesDir = 'src/main/res/raw'

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothPluginFactory.java

@@ -47,7 +47,7 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	private final BackoffFactory backoffFactory;
 
 	@Inject
-	public AndroidBluetoothPluginFactory(@IoExecutor Executor ioExecutor,
+	AndroidBluetoothPluginFactory(@IoExecutor Executor ioExecutor,
 			@WakefulIoExecutor Executor wakefulIoExecutor,
 			AndroidExecutor androidExecutor,
 			AndroidWakeLockManager wakeLockManager,

bramble-android/src/main/java/org/briarproject/bramble/plugin/file/AndroidRemovableDrivePlugin.java

@@ -0,0 +1,42 @@
+package org.briarproject.bramble.plugin.file;
+
+import android.app.Application;
+import android.net.Uri;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.PROP_URI;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
+
+@Immutable
+@NotNullByDefault
+class AndroidRemovableDrivePlugin extends RemovableDrivePlugin {
+
+	private final Application app;
+
+	AndroidRemovableDrivePlugin(Application app, int maxLatency) {
+		super(maxLatency);
+		this.app = app;
+	}
+
+	@Override
+	InputStream openInputStream(TransportProperties p) throws IOException {
+		String uri = p.get(PROP_URI);
+		if (isNullOrEmpty(uri)) throw new IllegalArgumentException();
+		return app.getContentResolver().openInputStream(Uri.parse(uri));
+	}
+
+	@Override
+	OutputStream openOutputStream(TransportProperties p) throws IOException {
+		String uri = p.get(PROP_URI);
+		if (isNullOrEmpty(uri)) throw new IllegalArgumentException();
+		return app.getContentResolver().openOutputStream(Uri.parse(uri));
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/plugin/file/AndroidRemovableDrivePluginFactory.java

@@ -0,0 +1,47 @@
+package org.briarproject.bramble.plugin.file;
+
+import android.app.Application;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static java.util.concurrent.TimeUnit.DAYS;
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.ID;
+
+@Immutable
+@NotNullByDefault
+public class AndroidRemovableDrivePluginFactory implements
+		SimplexPluginFactory {
+
+	private static final int MAX_LATENCY = (int) DAYS.toMillis(14);
+
+	private final Application app;
+
+	@Inject
+	AndroidRemovableDrivePluginFactory(Application app) {
+		this.app = app;
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public int getMaxLatency() {
+		return MAX_LATENCY;
+	}
+
+	@Nullable
+	@Override
+	public SimplexPlugin createPlugin(PluginCallback callback) {
+		return new AndroidRemovableDrivePlugin(app, MAX_LATENCY);
+	}
+}

bramble-android/src/main/java/org/briarproject/bramble/plugin/tcp/AndroidLanTcpPluginFactory.java

@@ -37,7 +37,7 @@ public class AndroidLanTcpPluginFactory implements DuplexPluginFactory {
 	private final Application app;
 
 	@Inject
-	public AndroidLanTcpPluginFactory(@IoExecutor Executor ioExecutor,
+	AndroidLanTcpPluginFactory(@IoExecutor Executor ioExecutor,
 			@WakefulIoExecutor Executor wakefulIoExecutor,
 			EventBus eventBus,
 			BackoffFactory backoffFactory,

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPluginFactory.java

@@ -58,7 +58,7 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 	private final File torDirectory;
 
 	@Inject
-	public AndroidTorPluginFactory(@IoExecutor Executor ioExecutor,
+	AndroidTorPluginFactory(@IoExecutor Executor ioExecutor,
 			@WakefulIoExecutor Executor wakefulIoExecutor,
 			Application app,
 			NetworkManager networkManager,

bramble-android/src/main/java/org/briarproject/bramble/util/AndroidUtils.java

@@ -10,20 +10,17 @@ import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.File;
-import java.io.IOException;
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
-import java.util.Scanner;
 
 import javax.annotation.Nullable;
 
 import static android.content.Context.MODE_PRIVATE;
 import static android.os.Build.VERSION.SDK_INT;
-import static java.lang.Runtime.getRuntime;
 import static java.util.Arrays.asList;
 import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 
@@ -121,17 +118,4 @@ public class AndroidUtils {
 	public static String[] getSupportedImageContentTypes() {
 		return new String[] {"image/jpeg", "image/png", "image/gif"};
 	}
-
-	@Nullable
-	public static String getSystemProperty(String propName) {
-		try {
-			Process p = getRuntime().exec("getprop " + propName);
-			Scanner s = new Scanner(p.getInputStream());
-			String line = s.nextLine();
-			s.close();
-			return line;
-		} catch (SecurityException | IOException e) {
-			return null;
-		}
-	}
 }

bramble-android/witness.gradle

@@ -1,43 +1,42 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
-        'com.android.tools.analytics-library:protos:27.1.3:protos-27.1.3.jar:0d9e6cff60b318baac250b6f5bb076a8161103338bf2749cdf1db8a5a13a1f12',
-        'com.android.tools.analytics-library:shared:27.1.3:shared-27.1.3.jar:10d2a51d8f89ff4ac849888e5a9c60b10e879c30d78545ec1da4d3df7bd56ae4',
-        'com.android.tools.analytics-library:tracker:27.1.3:tracker-27.1.3.jar:589b355a2ba796cbc0a2b2295737de6661f078262e5f87cd6f540b8d011e5ebb',
+        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
+        'com.android.tools.analytics-library:protos:27.1.1:protos-27.1.1.jar:13f77e73762e58ab372d140b3a6be6903aea9775b62dd14fbc62d4cc7069c9a4',
+        'com.android.tools.analytics-library:shared:27.1.1:shared-27.1.1.jar:82930a52001410e97d809930b670f4de3002286975f046b9de5f6b777b06d366',
+        'com.android.tools.analytics-library:tracker:27.1.1:tracker-27.1.1.jar:31bc5a00be0055bac89c9b2f34751883e987cd89e3ac1783720645c164f591d9',
         'com.android.tools.build:aapt2-proto:4.1.0-alpha01-6193524:aapt2-proto-4.1.0-alpha01-6193524.jar:17e75523e1e92dd4f222c7368ee41df9e964a508232f591e265d0c499baf9dca',
-        'com.android.tools.build:apksig:4.1.3:apksig-4.1.3.jar:a851980c678ff7a6785388b9a9e8cc094788ce3c4a985ad2b19c2028fd3c631a',
-        'com.android.tools.build:apkzlib:4.1.3:apkzlib-4.1.3.jar:475903065e7e83a8c1ba78d267c97a54dc5a04d768b535093850423d7b11f2c8',
-        'com.android.tools.build:builder-model:4.1.3:builder-model-4.1.3.jar:2624a1436c3ab39dd91d3ecf9409a594b0f89ea5cab255f2e9ff11f5ee03d274',
-        'com.android.tools.build:builder-test-api:4.1.3:builder-test-api-4.1.3.jar:3d2af66726b06b53b8d6d497efcee39ff9f77eb2f8d2cce38b31502383a40d2c',
-        'com.android.tools.build:builder:4.1.3:builder-4.1.3.jar:a40426cd6d68f6a722ef4950058c075e4547025e8c2fd78e732ad89f15176f84',
-        'com.android.tools.build:gradle-api:4.1.3:gradle-api-4.1.3.jar:11b1fb9de658bdcf9290b1c1517060d0c4d93f2b27975934989ca4ac890bc077',
-        'com.android.tools.build:manifest-merger:27.1.3:manifest-merger-27.1.3.jar:ce8d4009b1f1584777a7ffa1da3b0551dc316bc8e08112e442c352af70f46f2d',
-        'com.android.tools.ddms:ddmlib:27.1.3:ddmlib-27.1.3.jar:8f76e8236d2b9eebf26378746dad025c4c7c056a02e133dae4ddef47b283c710',
-        'com.android.tools.external.com-intellij:intellij-core:27.1.3:intellij-core-27.1.3.jar:652814fa099b4746fb6f10e19718e476952e8b5bac24e17d914f90650ad21808',
-        'com.android.tools.external.com-intellij:kotlin-compiler:27.1.3:kotlin-compiler-27.1.3.jar:8d7a78d5efd213c5e467e42bd205582aad73ffc77ee5dc18eb1361c9af72f125',
-        'com.android.tools.external.org-jetbrains:uast:27.1.3:uast-27.1.3.jar:aea53944a1ac6a05f12297b55290e8cbecfe54c4166260cfba4405823bfe1c78',
-        'com.android.tools.layoutlib:layoutlib-api:27.1.3:layoutlib-api-27.1.3.jar:23875ce0a8429f33a4e86cc358f658faa0ba9c576f5f05760e544b453d67d04b',
-        'com.android.tools.lint:lint-api:27.1.3:lint-api-27.1.3.jar:97666be32bcadacd944416ea334a9575ef8f4ad0c8f333151491ff4a7df43e1c',
-        'com.android.tools.lint:lint-checks:27.1.3:lint-checks-27.1.3.jar:b2d71ae84a31490fe9ff26c706163fe245b2aea98e3eb747214c1085df444708',
-        'com.android.tools.lint:lint-gradle-api:27.1.3:lint-gradle-api-27.1.3.jar:e54131c287a2954e6ed78a3351e5e10e35a1da2f09ac443bf44b705c71b63a4d',
-        'com.android.tools.lint:lint-gradle:27.1.3:lint-gradle-27.1.3.jar:6a79e48943649d63665db7b17dbaff7af93e94ab9b15072f1a4d90486294ee9f',
-        'com.android.tools.lint:lint-model:27.1.3:lint-model-27.1.3.jar:acb9e792db7000e38e3c3ca21a9b14f2de6549d7a3fc92a97ffba3d06345e5bf',
-        'com.android.tools.lint:lint:27.1.3:lint-27.1.3.jar:5a2e69d0901a3a476a5b2d5001de755868113145f5f6aa557750cfad5389a44b',
-        'com.android.tools:annotations:27.1.3:annotations-27.1.3.jar:904dd771883496d5dfc86619ab2555968ea4e8a29d7a5f4f7cae6fbf5429f8f5',
-        'com.android.tools:common:27.1.3:common-27.1.3.jar:17ab4728e3ea50f047dd5937f0faf35f2c5416962ed74891057087ddc328bf96',
-        'com.android.tools:dvlib:27.1.3:dvlib-27.1.3.jar:cead1c0c356cbe43e6855b0330fe09ef4bec2c72e22bdb4c6e7cf7e6b1dfbc37',
-        'com.android.tools:repository:27.1.3:repository-27.1.3.jar:99de1a178855b56b8cd91a56296f1e0a9399c445e6acc51f1d2927947cc472cb',
-        'com.android.tools:sdk-common:27.1.3:sdk-common-27.1.3.jar:b591e2aa0f1be600795f5c9e2bf81cba9b052bee452fc86c3362b5dd9e427a14',
-        'com.android.tools:sdklib:27.1.3:sdklib-27.1.3.jar:ad6c08a45fe2904d05656bdddf9f623fa5c1d16bbd7b8d6a270a0734136ae02e',
-        'com.android:signflinger:4.1.3:signflinger-4.1.3.jar:f3103b55ccdc8dd9ee2517eb26af93b904d41303726594372d0df59d51156e5c',
-        'com.android:zipflinger:4.1.3:zipflinger-4.1.3.jar:48569896c0497268308a8014c66eb0f2bace2b9e2fc9390f3012823fb86387d5',
-        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
+        'com.android.tools.build:apksig:4.1.1:apksig-4.1.1.jar:e0a69da9e5a03986d608b45bbf954ef0e6a0b3f58c1b8315bd169ec08b279e72',
+        'com.android.tools.build:apkzlib:4.1.1:apkzlib-4.1.1.jar:ba4b5e419b6be0130eae7f8301c3a551ad3976f487d2e0c6852ebb175ac41127',
+        'com.android.tools.build:builder-model:4.1.1:builder-model-4.1.1.jar:e95c99cc298ad67b8deb6ced99c51abc8f59afebedad044b1a10dde14646a4dd',
+        'com.android.tools.build:builder-test-api:4.1.1:builder-test-api-4.1.1.jar:464f596ab261c051c3847406748e843770dea123f6fa5fee8a9390644e709b7a',
+        'com.android.tools.build:builder:4.1.1:builder-4.1.1.jar:0f78d4759d2f7b57b95865522ec34596ba419b9982f3b25e3449213f9c98b80d',
+        'com.android.tools.build:gradle-api:4.1.1:gradle-api-4.1.1.jar:d42e6b539e4c1353ad3546e75ec8ce11a017b97481023e8ea18577eefe374358',
+        'com.android.tools.build:manifest-merger:27.1.1:manifest-merger-27.1.1.jar:7a45fa143687859bb2e5a961dcf6ee88094d3853de0cb543dc03dbcb0f4b554b',
+        'com.android.tools.ddms:ddmlib:27.1.1:ddmlib-27.1.1.jar:da6e4bd834b6a85dae8019039849d8bd96933347dfbf460df74913ddade6e40a',
+        'com.android.tools.external.com-intellij:intellij-core:27.1.1:intellij-core-27.1.1.jar:2591a7363c4443c59bf9f793730acafce9d6ec3076e2f46716edaf53a41b6fb6',
+        'com.android.tools.external.com-intellij:kotlin-compiler:27.1.1:kotlin-compiler-27.1.1.jar:5054ae770ba788f110303c65abd6b1fa28eccf52dee1274510e201b2b81885c8',
+        'com.android.tools.external.org-jetbrains:uast:27.1.1:uast-27.1.1.jar:54cd8f6886a9d2f5641659dd5c91f626629672cd48301f7f0bd6aad9bd448714',
+        'com.android.tools.layoutlib:layoutlib-api:27.1.1:layoutlib-api-27.1.1.jar:8a9a22e3b309521ea83b724e5a89cfdac6076f52d675c0e17d77b05527bc0f8c',
+        'com.android.tools.lint:lint-api:27.1.1:lint-api-27.1.1.jar:c1d8176094cb0478786070d40533efb578ebc53529a82f6ef5bee879bdca418b',
+        'com.android.tools.lint:lint-checks:27.1.1:lint-checks-27.1.1.jar:3899c91e00bd059b40c31a9ca00cd0f8303191947608735ae1b657323693fb61',
+        'com.android.tools.lint:lint-gradle-api:27.1.1:lint-gradle-api-27.1.1.jar:26aa89d38b9825cc73229daa82a68875801c8b8491f30497ce62aff1f206eb0d',
+        'com.android.tools.lint:lint-gradle:27.1.1:lint-gradle-27.1.1.jar:f7355823ead869f4d28184ba28b7a0c693b507519a2d3705bb9848a0f35b3756',
+        'com.android.tools.lint:lint-model:27.1.1:lint-model-27.1.1.jar:bc23c0c413bdfca59dac2cd56b870d8360d009e9ec0d365e71f774bcf127971d',
+        'com.android.tools.lint:lint:27.1.1:lint-27.1.1.jar:2f6038a5398a42bd591883c3f5e5894f4ec52ca1c3683bf94fa8553c1700af81',
+        'com.android.tools:annotations:27.1.1:annotations-27.1.1.jar:ff28c504d2acb9fd1a5ffbd97ae85cf59ee18c76927525aad250509bccf2cab1',
+        'com.android.tools:common:27.1.1:common-27.1.1.jar:63d9a2a9ad6d278db319f3749b9f50bdf5457ef7020074a1bebe124e714b535c',
+        'com.android.tools:dvlib:27.1.1:dvlib-27.1.1.jar:998a54201fc1cefee5f2399215e95c42b1f64f9e1d8f4452eb8255c68ba5440f',
+        'com.android.tools:repository:27.1.1:repository-27.1.1.jar:d25b74ccabf4d876903efb375e9af6fb380d8ae0445bb74bbdcc225c1e37fa1d',
+        'com.android.tools:sdk-common:27.1.1:sdk-common-27.1.1.jar:4473ae97d0ef7061ee1de61041d5aa97405ae08e44c09cf7bb278b42e4b97c7c',
+        'com.android.tools:sdklib:27.1.1:sdklib-27.1.1.jar:08e6b83961ac9724b3c1e3d0eff971f13be6701292c77914b8794480f3391250',
+        'com.android:signflinger:4.1.1:signflinger-4.1.1.jar:0c66825988873ec2d51057fa463f54a8f18fc7326ff4530b9da363b71e97ce60',
+        'com.android:zipflinger:4.1.1:zipflinger-4.1.1.jar:0a8c3e52ac13dd031236f9fb5ba4408b1d5dcd12325a05440b36da09d8881446',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
         'com.google.code.gson:gson:2.8.5:gson-2.8.5.jar:233a0149fc365c9f6edbd683cfe266b19bdc773be98eabdaf6b3c924b48e7d81',
-        'com.google.dagger:dagger-compiler:2.33:dagger-compiler-2.33.jar:aa8a0d8370c578fd6999802d0d90b9829377a46d2c1141e11b8f737970e7155e',
-        'com.google.dagger:dagger-producers:2.33:dagger-producers-2.33.jar:5897f0b6eef799c2adfe3ccacc58c0fb374d58acb063c3ebe5366c38a8bce5c8',
-        'com.google.dagger:dagger-spi:2.33:dagger-spi-2.33.jar:e2dcab2221b8afb9556ef0a1c83b0bd5f42552e254322a257330f754cdbbb9d4',
-        'com.google.dagger:dagger:2.33:dagger-2.33.jar:d8798c5b8cf6b125234e33af5c6293bb9f2208ce29b57924c35b8c0be7b6bdcb',
+        'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
+        'com.google.dagger:dagger-producers:2.24:dagger-producers-2.24.jar:f10f45b95191954d5d6b043fca9e62fb621d21bf70634b8f8476c7988b504c3a',
+        'com.google.dagger:dagger-spi:2.24:dagger-spi-2.24.jar:c038445d14dbcb4054e61bf49e05009edf26fce4fdc7ec1a9db544784f68e718',
+        'com.google.dagger:dagger:2.24:dagger-2.24.jar:550a6e46a6dfcdf1d764887b6090cea94f783327e50e5c73754f18facfc70b64',
         'com.google.errorprone:error_prone_annotations:2.2.0:error_prone_annotations-2.2.0.jar:6ebd22ca1b9d8ec06d41de8d64e0596981d9607b42035f9ed374f9de271a481a',
         'com.google.errorprone:error_prone_annotations:2.3.2:error_prone_annotations-2.3.2.jar:357cd6cfb067c969226c442451502aee13800a24e950fdfde77bcdb4565a668d',
         'com.google.errorprone:javac-shaded:9-dev-r4023-3:javac-shaded-9-dev-r4023-3.jar:65bfccf60986c47fbc17c9ebab0be626afc41741e0a6ec7109e0768817a36f30',
@@ -51,7 +50,7 @@ dependencyVerification {
         'com.google.jimfs:jimfs:1.1:jimfs-1.1.jar:c4828e28d7c0a930af9387510b3bada7daa5c04d7c25a75c7b8b081f1c257ddd',
         'com.google.protobuf:protobuf-java:3.10.0:protobuf-java-3.10.0.jar:161d7d61a8cb3970891c299578702fd079646e032329d6c2cabf998d191437c9',
         'com.googlecode.json-simple:json-simple:1.1:json-simple-1.1.jar:2d9484f4c649f708f47f9a479465fc729770ee65617dca3011836602264f6439',
-        'com.squareup:javapoet:1.13.0:javapoet-1.13.0.jar:4c7517e848a71b36d069d12bb3bf46a70fd4cda3105d822b0ed2e19c00b69291',
+        'com.squareup:javapoet:1.11.1:javapoet-1.11.1.jar:9cbf2107be499ec6e95afd36b58e3ca122a24166cdd375732e51267d64058e90',
         'com.squareup:javawriter:2.5.0:javawriter-2.5.0.jar:fcfb09fb0ea0aa97d3cfe7ea792398081348e468f126b3603cb3803f240197f0',
         'com.sun.activation:javax.activation:1.2.0:javax.activation-1.2.0.jar:993302b16cd7056f21e779cc577d175a810bb4900ef73cd8fbf2b50f928ba9ce',
         'com.sun.istack:istack-commons-runtime:3.0.7:istack-commons-runtime-3.0.7.jar:6443e10ba2e259fb821d9b6becf10db5316285fc30c53cec9d7b19a3877e7fdf',
@@ -63,21 +62,21 @@ dependencyVerification {
         'javax.annotation:jsr250-api:1.0:jsr250-api-1.0.jar:a1a922d0d9b6d183ed3800dfac01d1e1eb159f0e8c6f94736931c1def54a941f',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
         'javax.xml.bind:jaxb-api:2.3.1:jaxb-api-2.3.1.jar:88b955a0df57880a26a74708bc34f74dcaf8ebf4e78843a28b50eae945732b06',
-        'junit:junit:4.13.2:junit-4.13.2.jar:8e495b634469d64fb8acfa3495a065cbacc8a0fff55ce1e31007be4c16dc57d3',
-        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
-        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
+        'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
         'net.sf.jopt-simple:jopt-simple:4.9:jopt-simple-4.9.jar:26c5856e954b5f864db76f13b86919b59c6eecf9fd930b96baa8884626baf2f5',
         'net.sf.kxml:kxml2:2.3.0:kxml2-2.3.0.jar:f264dd9f79a1fde10ce5ecc53221eff24be4c9331c830b7d52f2f08a7b633de2',
-        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
+        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
+        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
         'org.apache.commons:commons-compress:1.12:commons-compress-1.12.jar:2c1542faf343185b7cab9c3d55c8ae5471d6d095d3887a4adefdbdf2984dc0b6',
         'org.apache.httpcomponents:httpclient:4.5.6:httpclient-4.5.6.jar:c03f813195e7a80e3608d0ddd8da80b21696a4c92a6a2298865bf149071551c7',
         'org.apache.httpcomponents:httpcore:4.4.10:httpcore-4.4.10.jar:78ba1096561957db1b55200a159b648876430342d15d461277e62360da19f6fd',
         'org.apache.httpcomponents:httpmime:4.5.6:httpmime-4.5.6.jar:0b2b1102c18d3c7e05a77214b9b7501a6f6056174ae5604e0e256776eda7553e',
+        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.bouncycastle:bcpkix-jdk15on:1.56:bcpkix-jdk15on-1.56.jar:7043dee4e9e7175e93e0b36f45b1ec1ecb893c5f755667e8b916eb8dd201c6ca',
         'org.bouncycastle:bcprov-jdk15on:1.56:bcprov-jdk15on-1.56.jar:963e1ee14f808ffb99897d848ddcdb28fa91ddda867eb18d303e82728f878349',
         'org.briarproject:obfs4proxy-android:0.0.12-dev-40245c4a:obfs4proxy-android-0.0.12-dev-40245c4a.zip:8ab05a8f8391be2cb5ab2b665c281a06d9e3a756bd0f95a40a36ca927866ea82',
-        'org.briarproject:tor-android:0.3.5.15:tor-android-0.3.5.15.jar:560c5070166300b396cb2f28d82d9f639ee1fb5479096a3cef67da56d39937ad',
+        'org.briarproject:tor-android:0.3.5.13:tor-android-0.3.5.13.zip:e0978db136731dae07774b722970cdae1e462fb5adc82845dd80a7e2d87f356c',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
         'org.checkerframework:checker-qual:2.5.2:checker-qual-2.5.2.jar:64b02691c8b9d4e7700f8ee2e742dce7ea2c6e81e662b7522c9ee3bf568c040a',
         'org.checkerframework:checker-qual:2.8.1:checker-qual-2.8.1.jar:9103499008bcecd4e948da29b17864abb64304e15706444ae209d17ebe0575df',
@@ -86,31 +85,26 @@ dependencyVerification {
         'org.codehaus.mojo:animal-sniffer-annotations:1.18:animal-sniffer-annotations-1.18.jar:47f05852b48ee9baefef80fa3d8cea60efa4753c0013121dd7fe5eef2e5c729d',
         'org.glassfish.jaxb:jaxb-runtime:2.3.1:jaxb-runtime-2.3.1.jar:45fecfa5c8217ce1f3652ab95179790ec8cc0dec0384bca51cbeb94a293d9f2f',
         'org.glassfish.jaxb:txw2:2.3.1:txw2-2.3.1.jar:34975dde1c6920f1a39791142235689bc3cd357e24d05edd8ff93b885bd68d60',
-        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
-        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
-        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
+        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
+        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
         'org.jetbrains.kotlin:kotlin-reflect:1.3.72:kotlin-reflect-1.3.72.jar:a188d9367de1c4ee9479db630985c0597b20709c83161b1430d24edb27e38c40',
         'org.jetbrains.kotlin:kotlin-stdlib-common:1.3.72:kotlin-stdlib-common-1.3.72.jar:5e7d1552863e480c1628b1cc39ce230ef829f5b7230106215a05acda5172203a',
-        'org.jetbrains.kotlin:kotlin-stdlib-common:1.4.20:kotlin-stdlib-common-1.4.20.jar:a7112c9b3cefee418286c9c9372f7af992bd1e6e030691d52f60cb36dbec8320',
         'org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.72:kotlin-stdlib-jdk7-1.3.72.jar:40566c0c08d414b9413ba556ff7f8a0b04b98b9f0f424d122dd2088510efccc4',
         'org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.3.72:kotlin-stdlib-jdk8-1.3.72.jar:133da70cfc07b56094282eac5c59bccd59f167ee2ead22e5282876d8bc10bf95',
         'org.jetbrains.kotlin:kotlin-stdlib:1.3.72:kotlin-stdlib-1.3.72.jar:3856a7349ebacd6d1be6802b2fed9c4dc2c5a564ea92b6b945ac988243d4b16b',
-        'org.jetbrains.kotlin:kotlin-stdlib:1.4.20:kotlin-stdlib-1.4.20.jar:b8ab1da5cdc89cb084d41e1f28f20a42bd431538642a5741c52bbfae3fa3e656',
-        'org.jetbrains.kotlinx:kotlinx-metadata-jvm:0.1.0:kotlinx-metadata-jvm-0.1.0.jar:9753bb39efef35957c5c15df9a3cb769aabf2cdfa74b47afcb7760e5146be3b5',
         'org.jetbrains.trove4j:trove4j:20160824:trove4j-20160824.jar:1917871c8deb468307a584680c87a44572f5a8b0b98c6d397fc0f5f86596dbe7',
         'org.jetbrains:annotations:13.0:annotations-13.0.jar:ace2a10dc8e2d5fd34925ecac03e4988b2c0f851650c94b8cef49ba1bd111478',
-        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
-        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
-        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
-        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
-        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
+        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
+        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
+        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
+        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
         'org.jvnet.staxex:stax-ex:1.8:stax-ex-1.8.jar:95b05d9590af4154c6513b9c5dc1fb2e55b539972ba0a9ef28e9a0c01d83ad77',
-        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
+        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
         'org.ow2.asm:asm-analysis:7.0:asm-analysis-7.0.jar:e981f8f650c4d900bb033650b18e122fa6b161eadd5f88978d08751f72ee8474',
         'org.ow2.asm:asm-commons:7.0:asm-commons-7.0.jar:fed348ef05958e3e846a3ac074a12af5f7936ef3d21ce44a62c4fa08a771927d',
         'org.ow2.asm:asm-tree:7.0:asm-tree-7.0.jar:cfd7a0874f9de36a999c127feeadfbfe6e04d4a71ee954d7af3d853f0be48a6c',
         'org.ow2.asm:asm-util:7.0:asm-util-7.0.jar:75fbbca440ef463f41c2b0ab1a80abe67e910ac486da60a7863cbcb5bae7e145',
+        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
         'org.ow2.asm:asm:7.0:asm-7.0.jar:b88ef66468b3c978ad0c97fd6e90979e56155b4ac69089ba7a44e9aa7ffe9acf',
-        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
     ]
 }

bramble-api/build.gradle

@@ -7,13 +7,13 @@ apply plugin: 'witness'
 apply from: 'witness.gradle'
 
 dependencies {
-	implementation "com.google.dagger:dagger:$dagger_version"
+	implementation "com.google.dagger:dagger:2.24"
 	implementation 'com.google.code.findbugs:jsr305:3.0.2'
 
-	testImplementation "junit:junit:$junit_version"
-	testImplementation "org.jmock:jmock:$jmock_version"
-	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation 'junit:junit:4.12'
+	testImplementation "org.jmock:jmock:2.8.2"
+	testImplementation "org.jmock:jmock-junit4:2.8.2"
+	testImplementation "org.jmock:jmock-legacy:2.8.2"
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }

bramble-api/src/main/java/org/briarproject/bramble/api/Consumer.java

@@ -0,0 +1,9 @@
+package org.briarproject.bramble.api;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface Consumer<T> {
+
+	void accept(T t);
+}

bramble-api/src/main/java/org/briarproject/bramble/api/client/BdfIncomingMessageHook.java

@@ -32,28 +32,31 @@ public abstract class BdfIncomingMessageHook implements IncomingMessageHook {
 
 	/**
 	 * Called once for each incoming message that passes validation.
+	 * <p>
+	 * If an unexpected exception occurs while handling data that is assumed
+	 * to be valid (e.g. locally created metadata), it may be sensible to
+	 * rethrow the unexpected exception as a DbException so that delivery is
+	 * attempted again at next startup. This will allow delivery to succeed if
+	 * the unexpected exception was caused by a bug that has subsequently been
+	 * fixed.
 	 *
 	 * @param txn A read-write transaction
-	 * @return Whether or not this message should be shared
-	 * @throws DbException Should only be used for real database errors.
-	 * If this is thrown, delivery will be attempted again at next startup,
-	 * whereas if a FormatException is thrown, the message will be permanently
-	 * invalidated.
-	 * @throws FormatException Use this for any non-database error
-	 * that occurs while handling remotely created data.
-	 * This includes errors that occur while handling locally created data
-	 * in a context controlled by remotely created data
-	 * (for example, parsing the metadata of a dependency
-	 * of an incoming message).
-	 * Never rethrow DbException as FormatException!
+	 * @throws DbException if a database error occurs while delivering the
+	 * message. Delivery will be attempted again at next startup. Throwing
+	 * this exception has the same effect as returning
+	 * {@link DeliveryAction#DEFER}.
+	 * @throws FormatException if the message is invalid in the context of its
+	 * dependencies. The message and any dependents will be marked as invalid
+	 * and deleted along with their metadata. Throwing this exception has the
+	 * same effect as returning {@link DeliveryAction#REJECT}.
 	 */
-	protected abstract boolean incomingMessage(Transaction txn, Message m,
-			BdfList body, BdfDictionary meta) throws DbException,
-			FormatException;
+	protected abstract DeliveryAction incomingMessage(Transaction txn,
+			Message m, BdfList body, BdfDictionary meta)
+			throws DbException, FormatException;
 
 	@Override
-	public boolean incomingMessage(Transaction txn, Message m, Metadata meta)
-			throws DbException, InvalidMessageException {
+	public DeliveryAction incomingMessage(Transaction txn, Message m,
+			Metadata meta) throws DbException, InvalidMessageException {
 		try {
 			BdfList body = clientHelper.toList(m);
 			BdfDictionary metaDictionary = metadataParser.parse(meta);

bramble-api/src/main/java/org/briarproject/bramble/api/db/DatabaseComponent.java

@@ -118,6 +118,18 @@ public interface DatabaseComponent extends TransactionManager {
 	KeySetId addTransportKeys(Transaction txn, PendingContactId p,
 			TransportKeys k) throws DbException;
 
+	/**
+	 * Returns true if there are any acks or messages to send to the given
+	 * contact over a transport with the given maximum latency.
+	 * <p/>
+	 * Read-only.
+	 *
+	 * @param eager True if messages that are not yet due for retransmission
+	 * should be included
+	 */
+	boolean containsAnythingToSend(Transaction txn, ContactId c,
+			int maxLatency, boolean eager) throws DbException;
+
 	/**
 	 * Returns true if the database contains the given contact for the given
 	 * local pseudonym.
@@ -150,6 +162,16 @@ public interface DatabaseComponent extends TransactionManager {
 	boolean containsPendingContact(Transaction txn, PendingContactId p)
 			throws DbException;
 
+	/**
+	 * Returns true if the database contains keys for communicating with the
+	 * given contact over the given transport. Handshake mode and rotation mode
+	 * keys are included, whether activated or not.
+	 * <p/>
+	 * Read-only.
+	 */
+	boolean containsTransportKeys(Transaction txn, ContactId c, TransportId t)
+			throws DbException;
+
 	/**
 	 * Deletes the message with the given ID. Unlike
 	 * {@link #removeMessage(Transaction, MessageId)}, the message ID,
@@ -180,6 +202,18 @@ public interface DatabaseComponent extends TransactionManager {
 	Collection<Message> generateBatch(Transaction txn, ContactId c,
 			int maxLength, int maxLatency) throws DbException;
 
+	/**
+	 * Returns a batch of messages for the given contact containing the
+	 * messages with the given IDs, for transmission over a transport with
+	 * the given maximum latency.
+	 * <p/>
+	 * If any of the given messages are not in the database or are not visible
+	 * to the contact, they are omitted from the batch without throwing an
+	 * exception.
+	 */
+	Collection<Message> generateBatch(Transaction txn, ContactId c,
+			Collection<MessageId> ids, int maxLatency) throws DbException;
+
 	/**
 	 * Returns an offer for the given contact for transmission over a
 	 * transport with the given maximum latency, or null if there are no
@@ -426,6 +460,27 @@ public interface DatabaseComponent extends TransactionManager {
 	MessageStatus getMessageStatus(Transaction txn, ContactId c, MessageId m)
 			throws DbException;
 
+	/**
+	 * Returns the IDs of all messages that are eligible to be sent to the
+	 * given contact, together with their raw lengths. This may include
+	 * messages that have already been sent and are not yet due for
+	 * retransmission.
+	 * <p/>
+	 * Read-only.
+	 */
+	Map<MessageId, Integer> getUnackedMessagesToSend(Transaction txn,
+			ContactId c) throws DbException;
+
+	/**
+	 * Returns the total length, including headers, of all messages that are
+	 * eligible to be sent to the given contact. This may include messages
+	 * that have already been sent and are not yet due for retransmission.
+	 * <p/>
+	 * Read-only.
+	 */
+	long getUnackedMessageBytesToSend(Transaction txn, ContactId c)
+			throws DbException;
+
 	/**
 	 * Returns the next time (in milliseconds since the Unix epoch) when a
 	 * message is due to be deleted, or {@link #NO_CLEANUP_DEADLINE}
@@ -483,6 +538,16 @@ public interface DatabaseComponent extends TransactionManager {
 	Collection<TransportKeySet> getTransportKeys(Transaction txn, TransportId t)
 			throws DbException;
 
+	/**
+	 * Returns the contact IDs and transport IDs for which the DB contains
+	 * at least one set of transport keys. Handshake mode and rotation mode
+	 * keys are included, whether activated or not.
+	 * <p/>
+	 * Read-only.
+	 */
+	Map<ContactId, Collection<TransportId>> getTransportsWithKeys(
+			Transaction txn) throws DbException;
+
 	/**
 	 * Increments the outgoing stream counter for the given transport keys.
 	 */

bramble-api/src/main/java/org/briarproject/bramble/api/keyagreement/event/KeyAgreementStartedEvent.java

@@ -3,7 +3,7 @@ package org.briarproject.bramble.api.keyagreement.event;
 import org.briarproject.bramble.api.event.Event;
 
 /**
- * An event that is broadcast when a BQP protocol begins.
+ * An event that is broadcast when a BQP protocol completes.
  */
 public class KeyAgreementStartedEvent extends Event {
 }

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/TransportConnectionWriter.java

@@ -22,6 +22,11 @@ public interface TransportConnectionWriter {
 	 */
 	int getMaxIdleTime();
 
+	/**
+	 * Returns true if the transport is lossy and cheap.
+	 */
+	boolean isLossyAndCheap();
+
 	/**
 	 * Returns an output stream for writing to the transport connection.
 	 */

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/duplex/AbstractDuplexTransportConnection.java

@@ -79,6 +79,11 @@ public abstract class AbstractDuplexTransportConnection
 			return plugin.getMaxIdleTime();
 		}
 
+		@Override
+		public boolean isLossyAndCheap() {
+			return false;
+		}
+
 		@Override
 		public OutputStream getOutputStream() throws IOException {
 			return AbstractDuplexTransportConnection.this.getOutputStream();

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/file/FileConstants.java

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.api.plugin;
+package org.briarproject.bramble.api.plugin.file;
 
 public interface FileConstants {
 

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/file/RemovableDriveConstants.java

@@ -0,0 +1,11 @@
+package org.briarproject.bramble.api.plugin.file;
+
+import org.briarproject.bramble.api.plugin.TransportId;
+
+public interface RemovableDriveConstants {
+
+	TransportId ID = new TransportId("org.briarproject.bramble.drive");
+
+	String PROP_PATH = "path";
+	String PROP_URI = "uri";
+}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/file/RemovableDriveManager.java

@@ -0,0 +1,46 @@
+package org.briarproject.bramble.api.plugin.file;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public interface RemovableDriveManager {
+
+	/**
+	 * Returns the currently running reader task, or null if no reader task
+	 * is running.
+	 */
+	@Nullable
+	RemovableDriveTask getCurrentReaderTask();
+
+	/**
+	 * Returns the currently running writer task,  or null if no writer task
+	 * is running.
+	 */
+	@Nullable
+	RemovableDriveTask getCurrentWriterTask();
+
+	/**
+	 * Starts and returns a reader task, reading from a stream described by
+	 * the given transport properties. If a reader task is already running,
+	 * it will be returned and the argument will be ignored.
+	 */
+	RemovableDriveTask startReaderTask(TransportProperties p);
+
+	/**
+	 * Starts and returns a writer task for the given contact, writing to
+	 * a stream described by the given transport properties. If a writer task
+	 * is already running, it will be returned and the arguments will be
+	 * ignored.
+	 */
+	RemovableDriveTask startWriterTask(ContactId c, TransportProperties p);
+
+	/**
+	 * Returns true if there is anything to send to the given contact.
+	 */
+	boolean isWriterTaskNeeded(ContactId c) throws DbException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/file/RemovableDriveTask.java

@@ -0,0 +1,65 @@
+package org.briarproject.bramble.api.plugin.file;
+
+import org.briarproject.bramble.api.Consumer;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+@NotNullByDefault
+public interface RemovableDriveTask extends Runnable {
+
+	/**
+	 * Returns the {@link TransportProperties} that were used for creating
+	 * this task.
+	 */
+	TransportProperties getTransportProperties();
+
+	/**
+	 * Adds an observer to the task. The observer will be notified of state
+	 * changes on the event thread. If the task has already finished, the
+	 * observer will be notified of its final state.
+	 */
+	void addObserver(Consumer<State> observer);
+
+	/**
+	 * Removes an observer from the task.
+	 */
+	void removeObserver(Consumer<State> observer);
+
+	class State {
+
+		private final long done, total;
+		private final boolean finished, success;
+
+		public State(long done, long total, boolean finished, boolean success) {
+			this.done = done;
+			this.total = total;
+			this.finished = finished;
+			this.success = success;
+		}
+
+		/**
+		 * Returns the total length in bytes of the messages read or written
+		 * so far, or zero if the total is unknown.
+		 */
+		public long getDone() {
+			return done;
+		}
+
+		/**
+		 * Returns the total length in bytes of the messages that will have
+		 * been read or written when the task is complete, or zero if the
+		 * total is unknown.
+		 */
+		public long getTotal() {
+			return total;
+		}
+
+		public boolean isFinished() {
+			return finished;
+		}
+
+		public boolean isSuccess() {
+			return success;
+		}
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/simplex/SimplexPlugin.java

@@ -15,6 +15,12 @@ import javax.annotation.Nullable;
 @NotNullByDefault
 public interface SimplexPlugin extends Plugin {
 
+	/**
+	 * Returns true if the transport is likely to lose streams and the cost of
+	 * transmitting redundant copies of data is cheap.
+	 */
+	boolean isLossyAndCheap();
+
 	/**
 	 * Attempts to create and return a reader for the given transport
 	 * properties. Returns null if a reader cannot be created.

bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncSessionFactory.java

@@ -16,7 +16,7 @@ public interface SyncSessionFactory {
 			PriorityHandler handler);
 
 	SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
-			int maxLatency, StreamWriter streamWriter);
+			int maxLatency, boolean eager, StreamWriter streamWriter);
 
 	SyncSession createDuplexOutgoingSession(ContactId c, TransportId t,
 			int maxLatency, int maxIdleTime, StreamWriter streamWriter,

bramble-api/src/main/java/org/briarproject/bramble/api/sync/event/MessagesSentEvent.java

@@ -18,11 +18,13 @@ public class MessagesSentEvent extends Event {
 
 	private final ContactId contactId;
 	private final Collection<MessageId> messageIds;
+	private final long totalLength;
 
 	public MessagesSentEvent(ContactId contactId,
-			Collection<MessageId> messageIds) {
+			Collection<MessageId> messageIds, long totalLength) {
 		this.contactId = contactId;
 		this.messageIds = messageIds;
+		this.totalLength = totalLength;
 	}
 
 	public ContactId getContactId() {
@@ -32,4 +34,8 @@ public class MessagesSentEvent extends Event {
 	public Collection<MessageId> getMessageIds() {
 		return messageIds;
 	}
+
+	public long getTotalLength() {
+		return totalLength;
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/IncomingMessageHook.java

@@ -10,23 +10,54 @@ public interface IncomingMessageHook {
 
 	/**
 	 * Called once for each incoming message that passes validation.
+	 * <p>
+	 * If an unexpected exception occurs while handling data that is assumed
+	 * to be valid (e.g. locally created metadata), it may be sensible to
+	 * rethrow the unexpected exception as a DbException so that delivery is
+	 * attempted again at next startup. This will allow delivery to succeed if
+	 * the unexpected exception was caused by a bug that has subsequently been
+	 * fixed.
 	 *
 	 * @param txn A read-write transaction
-	 * @return Whether or not this message should be shared
-	 * @throws DbException Should only be used for real database errors.
-	 * If this is thrown, delivery will be attempted again at next startup,
-	 * whereas if an InvalidMessageException is thrown,
-	 * the message will be permanently invalidated.
-	 * @throws InvalidMessageException for any non-database error
-	 * that occurs while handling remotely created data.
-	 * This includes errors that occur while handling locally created data
-	 * in a context controlled by remotely created data
-	 * (for example, parsing the metadata of a dependency
-	 * of an incoming message).
-	 * Throwing this will delete the incoming message and its metadata
-	 * marking it as invalid in the database.
-	 * Never rethrow DbException as InvalidMessageException!
+	 * @throws DbException if a database error occurs while delivering the
+	 * message. Delivery will be attempted again at next startup. Throwing
+	 * this exception has the same effect as returning
+	 * {@link DeliveryAction#DEFER}.
+	 * @throws InvalidMessageException if the message is invalid in the context
+	 * of its dependencies. The message and any dependents will be marked as
+	 * invalid and deleted along with their metadata. Throwing this exception
+	 * has the same effect as returning {@link DeliveryAction#REJECT}.
 	 */
-	boolean incomingMessage(Transaction txn, Message m, Metadata meta)
+	DeliveryAction incomingMessage(Transaction txn, Message m, Metadata meta)
 			throws DbException, InvalidMessageException;
+
+	enum DeliveryAction {
+
+		/**
+		 * The message and any dependent messages will be moved to the
+		 * {@link MessageState#INVALID INVALID state} and deleted, along with
+		 * their metadata.
+		 */
+		REJECT,
+
+		/**
+		 * The message will be moved to the
+		 * {@link MessageState#PENDING PENDING state}. Delivery will be
+		 * attempted again at next startup.
+		 */
+		DEFER,
+
+		/**
+		 * The message will be moved to the
+		 * {@link MessageState#DELIVERED DELIVERED state} and shared.
+		 */
+		ACCEPT_SHARE,
+
+		/**
+		 * The message will be moved to the
+		 * {@link MessageState#DELIVERED DELIVERED state} and will not be
+		 * shared.
+		 */
+		ACCEPT_DO_NOT_SHARE
+	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/sync/validation/MessageState.java

@@ -1,8 +1,33 @@
 package org.briarproject.bramble.api.sync.validation;
 
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction;
+
 public enum MessageState {
 
-	UNKNOWN(0), INVALID(1), PENDING(2), DELIVERED(3);
+	/**
+	 * A remote message that has not yet been validated.
+	 */
+	UNKNOWN(0),
+
+	/**
+	 * A remote message that has failed validation, has been
+	 * {@link DeliveryAction#REJECT rejected} by the local sync client, or
+	 * depends on another message that has failed validation or been rejected.
+	 */
+	INVALID(1),
+
+	/**
+	 * A remote message that has passed validation and is awaiting delivery to
+	 * the local sync client. The message will not be delivered until all its
+	 * dependencies have been validated and delivered.
+	 */
+	PENDING(2),
+
+	/**
+	 * A local message, or a remote message that has passed validation and
+	 * been delivered to the local sync client.
+	 */
+	DELIVERED(3);
 
 	private final int value;
 

bramble-api/src/main/java/org/briarproject/bramble/api/transport/KeyManager.java

@@ -22,8 +22,24 @@ public interface KeyManager {
 
 	/**
 	 * Derives and stores a set of rotation mode transport keys for
-	 * communicating with the given contact over each transport and returns the
-	 * key set IDs.
+	 * communicating with the given contact over the given transport and
+	 * returns the key set ID, or null if the transport is not supported.
+	 * <p/>
+	 * {@link StreamContext StreamContexts} for the contact can be created
+	 * after this method has returned.
+	 *
+	 * @param alice True if the local party is Alice
+	 * @param active Whether the derived keys can be used for outgoing streams
+	 */
+	@Nullable
+	KeySetId addRotationKeys(Transaction txn, ContactId c, TransportId t,
+			SecretKey rootKey, long timestamp, boolean alice,
+			boolean active) throws DbException;
+
+	/**
+	 * Derives and stores a set of rotation mode transport keys for
+	 * communicating with the given contact over each supported transport and
+	 * returns the key set IDs.
 	 * <p/>
 	 * {@link StreamContext StreamContexts} for the contact can be created
 	 * after this method has returned.

bramble-api/src/main/java/org/briarproject/bramble/api/transport/agreement/TransportKeyAgreementManager.java

@@ -0,0 +1,24 @@
+package org.briarproject.bramble.api.transport.agreement;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+
+@NotNullByDefault
+public interface TransportKeyAgreementManager {
+
+	/**
+	 * The unique ID of the transport key agreement client.
+	 */
+	ClientId CLIENT_ID =
+			new ClientId("org.briarproject.bramble.transport.agreement");
+
+	/**
+	 * The current major version of the transport key agreement client.
+	 */
+	int MAJOR_VERSION = 0;
+
+	/**
+	 * The current minor version of the transport key agreement client.
+	 */
+	int MINOR_VERSION = 0;
+}

bramble-api/witness.gradle

@@ -1,27 +1,24 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
-        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
+        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
-        'com.google.dagger:dagger:2.33:dagger-2.33.jar:d8798c5b8cf6b125234e33af5c6293bb9f2208ce29b57924c35b8c0be7b6bdcb',
+        'com.google.dagger:dagger:2.24:dagger-2.24.jar:550a6e46a6dfcdf1d764887b6090cea94f783327e50e5c73754f18facfc70b64',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
-        'junit:junit:4.13.2:junit-4.13.2.jar:8e495b634469d64fb8acfa3495a065cbacc8a0fff55ce1e31007be4c16dc57d3',
-        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
-        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
-        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
+        'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
+        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
+        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
+        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.codehaus.mojo.signature:java16:1.1:java16-1.1.signature:53799223a2c98dba2d0add810bed76315460df285c69e4f397ae6098f87dd619',
         'org.codehaus.mojo:animal-sniffer-ant-tasks:1.16:animal-sniffer-ant-tasks-1.16.jar:890040976fbe2d584619a6a61b1fd2e925b3b5eb342a85eb2762c467c0d64e90',
         'org.codehaus.mojo:animal-sniffer:1.16:animal-sniffer-1.16.jar:72be8bcc226ba43b937c722a08a07852bfa1b11400089265d5df0ee7b38b1d52',
-        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
-        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
-        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
-        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
-        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
-        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
-        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
-        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
-        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
+        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
+        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
+        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
+        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
+        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
+        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
+        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
         'org.ow2.asm:asm-all:5.2:asm-all-5.2.jar:7fbffbc1db3422e2101689fd88df8384b15817b52b9b2b267b9f6d2511dc198d',
-        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
+        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
     ]
 }

bramble-core/build.gradle

@@ -17,16 +17,16 @@ dependencies {
 	implementation 'org.whispersystems:curve25519-java:0.5.0'
 	implementation 'org.briarproject:jtorctl:0.3'
 
-	annotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation 'org.hsqldb:hsqldb:2.3.5' // The last version that supports Java 1.6
-	testImplementation "junit:junit:$junit_version"
-	testImplementation "org.jmock:jmock:$jmock_version"
-	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation 'junit:junit:4.12'
+	testImplementation "org.jmock:jmock:2.8.2"
+	testImplementation "org.jmock:jmock-junit4:2.8.2"
+	testImplementation "org.jmock:jmock-legacy:2.8.2"
 
-	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 
 	signature 'org.codehaus.mojo.signature:java16:1.1@signature'
 }

bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreEagerSingletons.java

@@ -11,6 +11,7 @@ import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.rendezvous.RendezvousModule;
 import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.transport.TransportModule;
+import org.briarproject.bramble.transport.agreement.TransportKeyAgreementModule;
 import org.briarproject.bramble.versioning.VersioningModule;
 
 public interface BrambleCoreEagerSingletons {
@@ -33,6 +34,8 @@ public interface BrambleCoreEagerSingletons {
 
 	void inject(RendezvousModule.EagerSingletons init);
 
+	void inject(TransportKeyAgreementModule.EagerSingletons init);
+
 	void inject(TransportModule.EagerSingletons init);
 
 	void inject(ValidationModule.EagerSingletons init);
@@ -51,6 +54,7 @@ public interface BrambleCoreEagerSingletons {
 			c.inject(new RendezvousModule.EagerSingletons());
 			c.inject(new PluginModule.EagerSingletons());
 			c.inject(new PropertiesModule.EagerSingletons());
+			c.inject(new TransportKeyAgreementModule.EagerSingletons());
 			c.inject(new TransportModule.EagerSingletons());
 			c.inject(new ValidationModule.EagerSingletons());
 			c.inject(new VersioningModule.EagerSingletons());

bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java

@@ -23,6 +23,7 @@ import org.briarproject.bramble.settings.SettingsModule;
 import org.briarproject.bramble.sync.SyncModule;
 import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.transport.TransportModule;
+import org.briarproject.bramble.transport.agreement.TransportKeyAgreementModule;
 import org.briarproject.bramble.versioning.VersioningModule;
 
 import dagger.Module;
@@ -49,6 +50,7 @@ import dagger.Module;
 		RendezvousModule.class,
 		SettingsModule.class,
 		SyncModule.class,
+		TransportKeyAgreementModule.class,
 		TransportModule.class,
 		ValidationModule.class,
 		VersioningModule.class

bramble-core/src/main/java/org/briarproject/bramble/connection/OutgoingSimplexSyncConnection.java

@@ -71,8 +71,10 @@ class OutgoingSimplexSyncConnection extends SyncConnection implements Runnable {
 		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
 				w.getOutputStream(), ctx);
 		ContactId c = requireNonNull(ctx.getContactId());
+		// Use eager retransmission if the transport is lossy and cheap
 		return syncSessionFactory.createSimplexOutgoingSession(c,
-				ctx.getTransportId(), w.getMaxLatency(), streamWriter);
+				ctx.getTransportId(), w.getMaxLatency(), w.isLossyAndCheap(),
+				streamWriter);
 	}
 }
 

bramble-core/src/main/java/org/briarproject/bramble/db/Database.java

@@ -162,6 +162,18 @@ interface Database<T> {
 	KeySetId addTransportKeys(T txn, PendingContactId p, TransportKeys k)
 			throws DbException;
 
+	/**
+	 * Returns true if there are any acks or messages to send to the given
+	 * contact over a transport with the given maximum latency.
+	 * <p/>
+	 * Read-only.
+	 *
+	 * @param eager True if messages that are not yet due for retransmission
+	 * should be included
+	 */
+	boolean containsAnythingToSend(T txn, ContactId c, int maxLatency,
+			boolean eager) throws DbException;
+
 	/**
 	 * Returns true if the database contains the given contact for the given
 	 * local pseudonym.
@@ -215,6 +227,16 @@ interface Database<T> {
 	 */
 	boolean containsTransport(T txn, TransportId t) throws DbException;
 
+	/**
+	 * Returns true if the database contains keys for communicating with the
+	 * given contact over the given transport. Handshake mode and rotation mode
+	 * keys are included, whether activated or not.
+	 * <p/>
+	 * Read-only.
+	 */
+	boolean containsTransportKeys(T txn, ContactId c, TransportId t)
+			throws DbException;
+
 	/**
 	 * Returns true if the database contains the given message, the message is
 	 * shared, and the visibility of the message's group to the given contact
@@ -476,11 +498,37 @@ interface Database<T> {
 	 * Returns the IDs of some messages that are eligible to be sent to the
 	 * given contact, up to the given total length.
 	 * <p/>
+	 * Unlike {@link #getUnackedMessagesToSend(Object, ContactId)} this method
+	 * does not return messages that have already been sent unless they are
+	 * due for retransmission.
+	 * <p/>
 	 * Read-only.
 	 */
 	Collection<MessageId> getMessagesToSend(T txn, ContactId c, int maxLength,
 			int maxLatency) throws DbException;
 
+	/**
+	 * Returns the IDs of all messages that are eligible to be sent to the
+	 * given contact, together with their raw lengths.
+	 * <p/>
+	 * Unlike {@link #getMessagesToSend(Object, ContactId, int, int)} this
+	 * method may return messages that have already been sent and are not yet
+	 * due for retransmission.
+	 * <p/>
+	 * Read-only.
+	 */
+	Map<MessageId, Integer> getUnackedMessagesToSend(T txn, ContactId c)
+			throws DbException;
+
+	/**
+	 * Returns the total length, including headers, of all messages that are
+	 * eligible to be sent to the given contact. This may include messages
+	 * that have already been sent and are not yet due for retransmission.
+	 * <p/>
+	 * Read-only.
+	 */
+	long getUnackedMessageBytesToSend(T txn, ContactId c) throws DbException;
+
 	/**
 	 * Returns the IDs of any messages that need to be validated.
 	 * <p/>
@@ -580,6 +628,16 @@ interface Database<T> {
 	Collection<TransportKeySet> getTransportKeys(T txn, TransportId t)
 			throws DbException;
 
+	/**
+	 * Returns the contact IDs and transport IDs for which the DB contains
+	 * at least one set of transport keys. Handshake mode and rotation mode
+	 * keys are included, whether activated or not.
+	 * <p/>
+	 * Read-only.
+	 */
+	Map<ContactId, Collection<TransportId>> getTransportsWithKeys(T txn)
+			throws DbException;
+
 	/**
 	 * Increments the outgoing stream counter for the given transport keys.
 	 */

bramble-core/src/main/java/org/briarproject/bramble/db/DatabaseComponentImpl.java

@@ -341,6 +341,15 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.addTransportKeys(txn, p, k);
 	}
 
+	@Override
+	public boolean containsAnythingToSend(Transaction transaction, ContactId c,
+			int maxLatency, boolean eager) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		return db.containsAnythingToSend(txn, c, maxLatency, eager);
+	}
+
 	@Override
 	public boolean containsContact(Transaction transaction, AuthorId remote,
 			AuthorId local) throws DbException {
@@ -371,6 +380,13 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.containsPendingContact(txn, p);
 	}
 
+	@Override
+	public boolean containsTransportKeys(Transaction transaction, ContactId c,
+			TransportId t) throws DbException {
+		T txn = unbox(transaction);
+		return db.containsTransportKeys(txn, c, t);
+	}
+
 	@Override
 	public void deleteMessage(Transaction transaction, MessageId m)
 			throws DbException {
@@ -415,14 +431,43 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 			throw new NoSuchContactException();
 		Collection<MessageId> ids =
 				db.getMessagesToSend(txn, c, maxLength, maxLatency);
+		long totalLength = 0;
 		List<Message> messages = new ArrayList<>(ids.size());
 		for (MessageId m : ids) {
-			messages.add(db.getMessage(txn, m));
+			Message message = db.getMessage(txn, m);
+			totalLength += message.getRawLength();
+			messages.add(message);
 			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
 		}
 		if (ids.isEmpty()) return null;
 		db.lowerRequestedFlag(txn, c, ids);
-		transaction.attach(new MessagesSentEvent(c, ids));
+		transaction.attach(new MessagesSentEvent(c, ids, totalLength));
+		return messages;
+	}
+
+	@Override
+	public Collection<Message> generateBatch(Transaction transaction,
+			ContactId c, Collection<MessageId> ids, int maxLatency)
+			throws DbException {
+		if (transaction.isReadOnly()) throw new IllegalArgumentException();
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		long totalLength = 0;
+		List<Message> messages = new ArrayList<>(ids.size());
+		List<MessageId> sentIds = new ArrayList<>(ids.size());
+		for (MessageId m : ids) {
+			if (db.containsVisibleMessage(txn, c, m)) {
+				Message message = db.getMessage(txn, m);
+				totalLength += message.getRawLength();
+				messages.add(message);
+				sentIds.add(m);
+				db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
+			}
+		}
+		if (messages.isEmpty()) return messages;
+		db.lowerRequestedFlag(txn, c, sentIds);
+		transaction.attach(new MessagesSentEvent(c, sentIds, totalLength));
 		return messages;
 	}
 
@@ -467,14 +512,17 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 			throw new NoSuchContactException();
 		Collection<MessageId> ids =
 				db.getRequestedMessagesToSend(txn, c, maxLength, maxLatency);
+		long totalLength = 0;
 		List<Message> messages = new ArrayList<>(ids.size());
 		for (MessageId m : ids) {
-			messages.add(db.getMessage(txn, m));
+			Message message = db.getMessage(txn, m);
+			totalLength += message.getRawLength();
+			messages.add(message);
 			db.updateExpiryTimeAndEta(txn, c, m, maxLatency);
 		}
 		if (ids.isEmpty()) return null;
 		db.lowerRequestedFlag(txn, c, ids);
-		transaction.attach(new MessagesSentEvent(c, ids));
+		transaction.attach(new MessagesSentEvent(c, ids, totalLength));
 		return messages;
 	}
 
@@ -692,6 +740,25 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return status;
 	}
 
+	@Override
+	public Map<MessageId, Integer> getUnackedMessagesToSend(
+			Transaction transaction,
+			ContactId c) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		return db.getUnackedMessagesToSend(txn, c);
+	}
+
+	@Override
+	public long getUnackedMessageBytesToSend(Transaction transaction,
+			ContactId c) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsContact(txn, c))
+			throw new NoSuchContactException();
+		return db.getUnackedMessageBytesToSend(txn, c);
+	}
+
 	@Override
 	public Map<MessageId, MessageState> getMessageDependencies(
 			Transaction transaction, MessageId m) throws DbException {
@@ -765,6 +832,13 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return db.getTransportKeys(txn, t);
 	}
 
+	@Override
+	public Map<ContactId, Collection<TransportId>> getTransportsWithKeys(
+			Transaction transaction) throws DbException {
+		T txn = unbox(transaction);
+		return db.getTransportsWithKeys(txn);
+	}
+
 	@Override
 	public void incrementStreamCounter(Transaction transaction, TransportId t,
 			KeySetId k) throws DbException {

bramble-core/src/main/java/org/briarproject/bramble/db/JdbcDatabase.java

@@ -51,6 +51,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -344,6 +345,11 @@ abstract class JdbcDatabase implements Database<Connection> {
 			"CREATE INDEX IF NOT EXISTS statusesByContactIdTimestamp"
 					+ " ON statuses (contactId, timestamp)";
 
+	private static final String
+			INDEX_STATUSES_BY_CONTACT_ID_TX_COUNT_TIMESTAMP =
+			"CREATE INDEX IF NOT EXISTS statusesByContactIdTxCountTimestamp"
+					+ " ON statuses (contactId, txCount, timestamp)";
+
 	private static final String INDEX_MESSAGES_BY_CLEANUP_DEADLINE =
 			"CREATE INDEX IF NOT EXISTS messagesByCleanupDeadline"
 					+ " ON messages (cleanupDeadline)";
@@ -570,6 +576,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(INDEX_MESSAGE_DEPENDENCIES_BY_DEPENDENCY_ID);
 			s.executeUpdate(INDEX_STATUSES_BY_CONTACT_ID_GROUP_ID);
 			s.executeUpdate(INDEX_STATUSES_BY_CONTACT_ID_TIMESTAMP);
+			s.executeUpdate(INDEX_STATUSES_BY_CONTACT_ID_TX_COUNT_TIMESTAMP);
 			s.executeUpdate(INDEX_MESSAGES_BY_CLEANUP_DEADLINE);
 			s.close();
 		} catch (SQLException e) {
@@ -1120,6 +1127,55 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public boolean containsAnythingToSend(Connection txn, ContactId c,
+			int maxLatency, boolean eager) throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT NULL FROM statuses"
+					+ " WHERE contactId = ? AND ack = TRUE";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			rs = ps.executeQuery();
+			boolean acksToSend = rs.next();
+			rs.close();
+			ps.close();
+			if (acksToSend) return true;
+			if (eager) {
+				sql = "SELECT NULL from statuses"
+						+ " WHERE contactId = ? AND state = ?"
+						+ " AND groupShared = TRUE AND messageShared = TRUE"
+						+ " AND deleted = FALSE AND seen = FALSE";
+				ps = txn.prepareStatement(sql);
+				ps.setInt(1, c.getInt());
+				ps.setInt(2, DELIVERED.getValue());
+			} else {
+				long now = clock.currentTimeMillis();
+				long eta = now + maxLatency;
+				sql = "SELECT NULL FROM statuses"
+						+ " WHERE contactId = ? AND state = ?"
+						+ " AND groupShared = TRUE AND messageShared = TRUE"
+						+ " AND deleted = FALSE AND seen = FALSE"
+						+ " AND (expiry <= ? OR eta > ?)";
+				ps = txn.prepareStatement(sql);
+				ps.setInt(1, c.getInt());
+				ps.setInt(2, DELIVERED.getValue());
+				ps.setLong(3, now);
+				ps.setLong(4, eta);
+			}
+			rs = ps.executeQuery();
+			boolean messagesToSend = rs.next();
+			rs.close();
+			ps.close();
+			return messagesToSend;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public boolean containsContact(Connection txn, AuthorId remote,
 			AuthorId local) throws DbException {
@@ -1277,6 +1333,29 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public boolean containsTransportKeys(Connection txn, ContactId c,
+			TransportId t) throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT NULL FROM outgoingKeys"
+					+ " WHERE contactId = ? AND transportId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setString(2, t.getString());
+			rs = ps.executeQuery();
+			boolean found = rs.next();
+			rs.close();
+			ps.close();
+			return found;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public boolean containsVisibleMessage(Connection txn, ContactId c,
 			MessageId m) throws DbException {
@@ -2205,6 +2284,63 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public Map<MessageId, Integer> getUnackedMessagesToSend(Connection txn,
+			ContactId c) throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT length, messageId FROM statuses"
+					+ " WHERE contactId = ? AND state = ?"
+					+ " AND groupShared = TRUE AND messageShared = TRUE"
+					+ " AND deleted = FALSE AND seen = FALSE"
+					+ " ORDER BY txCount, timestamp";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, DELIVERED.getValue());
+			rs = ps.executeQuery();
+			Map<MessageId, Integer> results = new LinkedHashMap<>();
+			while (rs.next()) {
+				int length = rs.getInt(1);
+				MessageId id = new MessageId(rs.getBytes(2));
+				results.put(id, length);
+			}
+			rs.close();
+			ps.close();
+			return results;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
+	@Override
+	public long getUnackedMessageBytesToSend(Connection txn, ContactId c)
+			throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT SUM(length) FROM statuses"
+					+ " WHERE contactId = ? AND state = ?"
+					+ " AND groupShared = TRUE AND messageShared = TRUE"
+					+ " AND deleted = FALSE AND seen = FALSE";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, DELIVERED.getValue());
+			rs = ps.executeQuery();
+			rs.next();
+			long total = rs.getInt(1);
+			rs.close();
+			ps.close();
+			return total;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public Collection<MessageId> getMessagesToValidate(Connection txn)
 			throws DbException {
@@ -2574,6 +2710,38 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	@Override
+	public Map<ContactId, Collection<TransportId>> getTransportsWithKeys(
+			Connection txn) throws DbException {
+		Statement s = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT DISTINCT contactId, transportId"
+					+ " FROM outgoingKeys";
+			s = txn.createStatement();
+			rs = s.executeQuery(sql);
+			Map<ContactId, Collection<TransportId>> ids = new HashMap<>();
+			while (rs.next()) {
+				ContactId c = new ContactId(rs.getInt(1));
+				TransportId t = new TransportId(rs.getString(2));
+				Collection<TransportId> transportIds = ids.get(c);
+				if (transportIds == null) {
+					transportIds = new ArrayList<>();
+					ids.put(c, transportIds);
+				}
+				transportIds.add(t);
+			}
+			rs.close();
+			s.close();
+			return ids;
+		} catch (SQLException e) {
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(s, LOG, WARNING);
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public void incrementStreamCounter(Connection txn, TransportId t,
 			KeySetId k) throws DbException {

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/AbstractBluetoothPlugin.java

@@ -473,16 +473,6 @@ abstract class AbstractBluetoothPlugin<S, SS> implements BluetoothPlugin,
 		return discoverSemaphore.availablePermits() == 0;
 	}
 
-	@Override
-	public void disablePolling() {
-		connectionLimiter.startLimiting();
-	}
-
-	@Override
-	public void enablePolling() {
-		connectionLimiter.endLimiting();
-	}
-
 	@Override
 	public DuplexTransportConnection discoverAndConnectForSetup(String uuid) {
 		DuplexTransportConnection conn = discoverAndConnect(uuid);
@@ -511,9 +501,9 @@ abstract class AbstractBluetoothPlugin<S, SS> implements BluetoothPlugin,
 			if (s.getNamespace().equals(ID.getString()))
 				ioExecutor.execute(() -> onSettingsUpdated(s.getSettings()));
 		} else if (e instanceof KeyAgreementListeningEvent) {
-			connectionLimiter.startLimiting();
+			ioExecutor.execute(connectionLimiter::keyAgreementStarted);
 		} else if (e instanceof KeyAgreementStoppedListeningEvent) {
-			connectionLimiter.endLimiting();
+			ioExecutor.execute(connectionLimiter::keyAgreementEnded);
 		} else if (e instanceof RemoteTransportPropertiesUpdatedEvent) {
 			RemoteTransportPropertiesUpdatedEvent r =
 					(RemoteTransportPropertiesUpdatedEvent) e;

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothConnectionLimiter.java

@@ -7,15 +7,14 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 interface BluetoothConnectionLimiter {
 
 	/**
-	 * Tells the limiter to not allow regular polling connections (because we
-	 * are about to do key agreement, or connect via BT for setup).
+	 * Informs the limiter that key agreement has started.
 	 */
-	void startLimiting();
+	void keyAgreementStarted();
 
 	/**
-	 * Tells the limiter to no longer limit regular polling connections.
+	 * Informs the limiter that key agreement has ended.
 	 */
-	void endLimiting();
+	void keyAgreementEnded();
 
 	/**
 	 * Returns true if a contact connection can be opened. This method does not

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothConnectionLimiterImpl.java

@@ -30,37 +30,34 @@ class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 	private final List<DuplexTransportConnection> connections =
 			new LinkedList<>();
 	@GuardedBy("lock")
-	private int limitingInProgress = 0;
+	private boolean keyAgreementInProgress = false;
 
 	BluetoothConnectionLimiterImpl(EventBus eventBus) {
 		this.eventBus = eventBus;
 	}
 
 	@Override
-	public void startLimiting() {
+	public void keyAgreementStarted() {
 		synchronized (lock) {
-			limitingInProgress++;
+			keyAgreementInProgress = true;
 		}
-		LOG.info("Limiting started");
+		LOG.info("Key agreement started");
 		eventBus.broadcast(new CloseSyncConnectionsEvent(ID));
 	}
 
 	@Override
-	public void endLimiting() {
+	public void keyAgreementEnded() {
 		synchronized (lock) {
-			limitingInProgress--;
-			if (limitingInProgress < 0) {
-				throw new IllegalStateException();
-			}
+			keyAgreementInProgress = false;
 		}
-		LOG.info("Limiting ended");
+		LOG.info("Key agreement ended");
 	}
 
 	@Override
 	public boolean canOpenContactConnection() {
 		synchronized (lock) {
-			if (limitingInProgress > 0) {
-				LOG.info("Can't open contact connection while limiting");
+			if (keyAgreementInProgress) {
+				LOG.info("Can't open contact connection during key agreement");
 				return false;
 			} else {
 				LOG.info("Can open contact connection");

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothPlugin.java

@@ -11,10 +11,6 @@ public interface BluetoothPlugin extends DuplexPlugin {
 
 	boolean isDiscovering();
 
-	void disablePolling();
-
-	void enablePolling();
-
 	@Nullable
 	DuplexTransportConnection discoverAndConnectForSetup(String uuid);
 

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/AbstractRemovableDrivePlugin.java

@@ -0,0 +1,119 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.ConnectionHandler;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.util.Collection;
+import java.util.logging.Logger;
+
+import javax.annotation.concurrent.Immutable;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.ID;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@Immutable
+@NotNullByDefault
+abstract class AbstractRemovableDrivePlugin implements SimplexPlugin {
+
+	private static final Logger LOG =
+			getLogger(AbstractRemovableDrivePlugin.class.getName());
+
+	private final int maxLatency;
+
+	abstract InputStream openInputStream(TransportProperties p)
+			throws IOException;
+
+	abstract OutputStream openOutputStream(TransportProperties p)
+			throws IOException;
+
+	AbstractRemovableDrivePlugin(int maxLatency) {
+		this.maxLatency = maxLatency;
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public int getMaxLatency() {
+		return maxLatency;
+	}
+
+	@Override
+	public int getMaxIdleTime() {
+		// Unused for simplex transports
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public void start() {
+	}
+
+	@Override
+	public void stop() {
+	}
+
+	@Override
+	public State getState() {
+		return ACTIVE;
+	}
+
+	@Override
+	public int getReasonsDisabled() {
+		return 0;
+	}
+
+	@Override
+	public boolean shouldPoll() {
+		return false;
+	}
+
+	@Override
+	public int getPollingInterval() {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public void poll(
+			Collection<Pair<TransportProperties, ConnectionHandler>> properties) {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public boolean isLossyAndCheap() {
+		return true;
+	}
+
+	@Override
+	public TransportConnectionReader createReader(TransportProperties p) {
+		try {
+			return new TransportInputStreamReader(openInputStream(p));
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+
+	@Override
+	public TransportConnectionWriter createWriter(TransportProperties p) {
+		try {
+			return new TransportOutputStreamWriter(this, openOutputStream(p));
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/FilePlugin.java

@@ -15,8 +15,8 @@ import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
-import static org.briarproject.bramble.api.plugin.FileConstants.PROP_PATH;
 import static org.briarproject.bramble.api.plugin.Plugin.State.ACTIVE;
+import static org.briarproject.bramble.api.plugin.file.FileConstants.PROP_PATH;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/FileTransportWriter.java

@@ -36,6 +36,11 @@ class FileTransportWriter implements TransportConnectionWriter {
 		return plugin.getMaxIdleTime();
 	}
 
+	@Override
+	public boolean isLossyAndCheap() {
+		return plugin.isLossyAndCheap();
+	}
+
 	@Override
 	public OutputStream getOutputStream() {
 		return out;

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveManagerImpl.java

@@ -0,0 +1,102 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveManager;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.util.concurrent.Executor;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.plugin.file.RemovableDrivePluginFactory.MAX_LATENCY;
+
+@ThreadSafe
+@NotNullByDefault
+class RemovableDriveManagerImpl
+		implements RemovableDriveManager, RemovableDriveTaskRegistry {
+
+	private final Executor ioExecutor;
+	private final DatabaseComponent db;
+	private final RemovableDriveTaskFactory taskFactory;
+	private final Object lock = new Object();
+
+	@GuardedBy("lock")
+	private RemovableDriveTask reader = null;
+	@GuardedBy("lock")
+	private RemovableDriveTask writer = null;
+
+	@Inject
+	RemovableDriveManagerImpl(@IoExecutor Executor ioExecutor,
+			DatabaseComponent db, RemovableDriveTaskFactory taskFactory) {
+		this.ioExecutor = ioExecutor;
+		this.db = db;
+		this.taskFactory = taskFactory;
+	}
+
+	@Nullable
+	@Override
+	public RemovableDriveTask getCurrentReaderTask() {
+		synchronized (lock) {
+			return reader;
+		}
+	}
+
+	@Nullable
+	@Override
+	public RemovableDriveTask getCurrentWriterTask() {
+		synchronized (lock) {
+			return writer;
+		}
+	}
+
+	@Override
+	public RemovableDriveTask startReaderTask(TransportProperties p) {
+		RemovableDriveTask created;
+		synchronized (lock) {
+			if (reader != null) return reader;
+			reader = created = taskFactory.createReader(this, p);
+		}
+		ioExecutor.execute(created);
+		return created;
+	}
+
+	@Override
+	public RemovableDriveTask startWriterTask(ContactId c,
+			TransportProperties p) {
+		RemovableDriveTask created;
+		synchronized (lock) {
+			if (writer != null) return writer;
+			writer = created = taskFactory.createWriter(this, c, p);
+		}
+		ioExecutor.execute(created);
+		return created;
+	}
+
+	@Override
+	public boolean isWriterTaskNeeded(ContactId c) throws DbException {
+		return db.transactionWithResult(true, txn ->
+				db.containsAnythingToSend(txn, c, MAX_LATENCY, true));
+	}
+
+	@Override
+	public void removeReader(RemovableDriveTask task) {
+		synchronized (lock) {
+			if (reader == task) reader = null;
+		}
+	}
+
+	@Override
+	public void removeWriter(RemovableDriveTask task) {
+		synchronized (lock) {
+			if (writer == task) writer = null;
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveModule.java

@@ -0,0 +1,25 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.plugin.file.RemovableDriveManager;
+
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class RemovableDriveModule {
+
+	@Provides
+	@Singleton
+	RemovableDriveManager provideRemovableDriveManager(
+			RemovableDriveManagerImpl removableDriveManager) {
+		return removableDriveManager;
+	}
+
+	@Provides
+	RemovableDriveTaskFactory provideTaskFactory(
+			RemovableDriveTaskFactoryImpl taskFactory) {
+		return taskFactory;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDrivePlugin.java

@@ -0,0 +1,38 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import javax.annotation.concurrent.Immutable;
+
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.PROP_PATH;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
+
+@Immutable
+@NotNullByDefault
+class RemovableDrivePlugin extends AbstractRemovableDrivePlugin {
+
+	RemovableDrivePlugin(int maxLatency) {
+		super(maxLatency);
+	}
+
+	@Override
+	InputStream openInputStream(TransportProperties p) throws IOException {
+		String path = p.get(PROP_PATH);
+		if (isNullOrEmpty(path)) throw new IllegalArgumentException();
+		return new FileInputStream(path);
+	}
+
+	@Override
+	OutputStream openOutputStream(TransportProperties p) throws IOException {
+		String path = p.get(PROP_PATH);
+		if (isNullOrEmpty(path)) throw new IllegalArgumentException();
+		return new FileOutputStream(path);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDrivePluginFactory.java

@@ -0,0 +1,41 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginCallback;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static java.util.concurrent.TimeUnit.DAYS;
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.ID;
+
+@Immutable
+@NotNullByDefault
+public class RemovableDrivePluginFactory implements SimplexPluginFactory {
+
+	static final int MAX_LATENCY = (int) DAYS.toMillis(14);
+
+	@Inject
+	RemovableDrivePluginFactory() {
+	}
+
+	@Override
+	public TransportId getId() {
+		return ID;
+	}
+
+	@Override
+	public int getMaxLatency() {
+		return MAX_LATENCY;
+	}
+
+	@Nullable
+	@Override
+	public SimplexPlugin createPlugin(PluginCallback callback) {
+		return new RemovableDrivePlugin(MAX_LATENCY);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveReaderTask.java

@@ -0,0 +1,69 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.ID;
+
+@NotNullByDefault
+class RemovableDriveReaderTask extends RemovableDriveTaskImpl {
+
+	private final static Logger LOG =
+			getLogger(RemovableDriveReaderTask.class.getName());
+
+	RemovableDriveReaderTask(
+			Executor eventExecutor,
+			PluginManager pluginManager,
+			ConnectionManager connectionManager,
+			EventBus eventBus,
+			RemovableDriveTaskRegistry registry,
+			TransportProperties transportProperties) {
+		super(eventExecutor, pluginManager, connectionManager, eventBus,
+				registry, transportProperties);
+	}
+
+	@Override
+	public void run() {
+		TransportConnectionReader r =
+				getPlugin().createReader(transportProperties);
+		if (r == null) {
+			LOG.warning("Failed to create reader");
+			registry.removeReader(this);
+			setSuccess(false);
+			return;
+		}
+		connectionManager.manageIncomingConnection(ID, new DecoratedReader(r));
+	}
+
+	private class DecoratedReader implements TransportConnectionReader {
+
+		private final TransportConnectionReader delegate;
+
+		private DecoratedReader(TransportConnectionReader delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public InputStream getInputStream() throws IOException {
+			return delegate.getInputStream();
+		}
+
+		@Override
+		public void dispose(boolean exception, boolean recognised)
+				throws IOException {
+			delegate.dispose(exception, recognised);
+			registry.removeReader(RemovableDriveReaderTask.this);
+			setSuccess(!exception && recognised);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveTaskFactory.java

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+@NotNullByDefault
+interface RemovableDriveTaskFactory {
+
+	RemovableDriveTask createReader(RemovableDriveTaskRegistry registry,
+			TransportProperties p);
+
+	RemovableDriveTask createWriter(RemovableDriveTaskRegistry registry,
+			ContactId c, TransportProperties p);
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveTaskFactoryImpl.java

@@ -0,0 +1,55 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+@Immutable
+@NotNullByDefault
+class RemovableDriveTaskFactoryImpl implements RemovableDriveTaskFactory {
+
+	private final DatabaseComponent db;
+	private final Executor eventExecutor;
+	private final PluginManager pluginManager;
+	private final ConnectionManager connectionManager;
+	private final EventBus eventBus;
+
+	@Inject
+	RemovableDriveTaskFactoryImpl(
+			DatabaseComponent db,
+			@EventExecutor Executor eventExecutor,
+			PluginManager pluginManager,
+			ConnectionManager connectionManager,
+			EventBus eventBus) {
+		this.db = db;
+		this.eventExecutor = eventExecutor;
+		this.pluginManager = pluginManager;
+		this.connectionManager = connectionManager;
+		this.eventBus = eventBus;
+	}
+
+	@Override
+	public RemovableDriveTask createReader(RemovableDriveTaskRegistry registry,
+			TransportProperties p) {
+		return new RemovableDriveReaderTask(eventExecutor, pluginManager,
+				connectionManager, eventBus, registry, p);
+	}
+
+	@Override
+	public RemovableDriveTask createWriter(RemovableDriveTaskRegistry registry,
+			ContactId c, TransportProperties p) {
+		return new RemovableDriveWriterTask(db, eventExecutor, pluginManager,
+				connectionManager, eventBus, registry, c, p);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveTaskImpl.java

@@ -0,0 +1,116 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.Consumer;
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.properties.TransportProperties;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.lang.Math.min;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.ID;
+
+@ThreadSafe
+@NotNullByDefault
+abstract class RemovableDriveTaskImpl implements RemovableDriveTask {
+
+	private final Executor eventExecutor;
+	private final PluginManager pluginManager;
+	final ConnectionManager connectionManager;
+	final EventBus eventBus;
+	final RemovableDriveTaskRegistry registry;
+	final TransportProperties transportProperties;
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private final List<Consumer<State>> observers = new ArrayList<>();
+	@GuardedBy("lock")
+	private State state = new State(0, 0, false, false);
+
+	RemovableDriveTaskImpl(
+			Executor eventExecutor,
+			PluginManager pluginManager,
+			ConnectionManager connectionManager,
+			EventBus eventBus,
+			RemovableDriveTaskRegistry registry,
+			TransportProperties transportProperties) {
+		this.eventExecutor = eventExecutor;
+		this.pluginManager = pluginManager;
+		this.connectionManager = connectionManager;
+		this.eventBus = eventBus;
+		this.registry = registry;
+		this.transportProperties = transportProperties;
+	}
+
+	@Override
+	public TransportProperties getTransportProperties() {
+		return transportProperties;
+	}
+
+	@Override
+	public void addObserver(Consumer<State> o) {
+		State state;
+		synchronized (lock) {
+			observers.add(o);
+			state = this.state;
+		}
+		if (state.isFinished()) {
+			eventExecutor.execute(() -> o.accept(state));
+		}
+	}
+
+	@Override
+	public void removeObserver(Consumer<State> o) {
+		synchronized (lock) {
+			observers.remove(o);
+		}
+	}
+
+	SimplexPlugin getPlugin() {
+		return (SimplexPlugin) requireNonNull(pluginManager.getPlugin(ID));
+	}
+
+	void setTotal(long total) {
+		synchronized (lock) {
+			state = new State(state.getDone(), total, state.isFinished(),
+					state.isSuccess());
+			notifyObservers();
+		}
+	}
+
+	void addDone(long done) {
+		synchronized (lock) {
+			// Done and total come from different sources; make them consistent
+			done = min(state.getDone() + done, state.getTotal());
+			state = new State(done, state.getTotal(), state.isFinished(),
+					state.isSuccess());
+			notifyObservers();
+		}
+	}
+
+	void setSuccess(boolean success) {
+		synchronized (lock) {
+			state = new State(state.getDone(), state.getTotal(), true, success);
+			notifyObservers();
+		}
+	}
+
+	@GuardedBy("lock")
+	private void notifyObservers() {
+		List<Consumer<State>> observers = new ArrayList<>(this.observers);
+		State state = this.state;
+		eventExecutor.execute(() -> {
+			for (Consumer<State> o : observers) o.accept(state);
+		});
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveTaskRegistry.java

@@ -0,0 +1,12 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+
+@NotNullByDefault
+interface RemovableDriveTaskRegistry {
+
+	void removeReader(RemovableDriveTask task);
+
+	void removeWriter(RemovableDriveTask task);
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveWriterTask.java

@@ -0,0 +1,126 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.connection.ConnectionManager;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.event.EventListener;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginManager;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.ID;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class RemovableDriveWriterTask extends RemovableDriveTaskImpl
+		implements EventListener {
+
+	private static final Logger LOG =
+			getLogger(RemovableDriveWriterTask.class.getName());
+
+	private final DatabaseComponent db;
+	private final ContactId contactId;
+
+	RemovableDriveWriterTask(
+			DatabaseComponent db,
+			Executor eventExecutor,
+			PluginManager pluginManager,
+			ConnectionManager connectionManager,
+			EventBus eventBus,
+			RemovableDriveTaskRegistry registry,
+			ContactId contactId,
+			TransportProperties transportProperties) {
+		super(eventExecutor, pluginManager, connectionManager, eventBus,
+				registry, transportProperties);
+		this.db = db;
+		this.contactId = contactId;
+	}
+
+	@Override
+	public void run() {
+		SimplexPlugin plugin = getPlugin();
+		TransportConnectionWriter w = plugin.createWriter(transportProperties);
+		if (w == null) {
+			LOG.warning("Failed to create writer");
+			registry.removeWriter(this);
+			setSuccess(false);
+			return;
+		}
+		try {
+			setTotal(db.transactionWithResult(true, txn ->
+					db.getUnackedMessageBytesToSend(txn, contactId)));
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			registry.removeWriter(this);
+			setSuccess(false);
+			return;
+		}
+		eventBus.addListener(this);
+		connectionManager.manageOutgoingConnection(contactId, ID,
+				new DecoratedWriter(w));
+	}
+
+	@Override
+	public void eventOccurred(Event e) {
+		if (e instanceof MessagesSentEvent) {
+			MessagesSentEvent m = (MessagesSentEvent) e;
+			if (contactId.equals(m.getContactId())) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info(m.getMessageIds().size() + " messages sent");
+				}
+				addDone(m.getTotalLength());
+			}
+		}
+	}
+
+	private class DecoratedWriter implements TransportConnectionWriter {
+
+		private final TransportConnectionWriter delegate;
+
+		private DecoratedWriter(TransportConnectionWriter delegate) {
+			this.delegate = delegate;
+		}
+
+		@Override
+		public int getMaxLatency() {
+			return delegate.getMaxLatency();
+		}
+
+		@Override
+		public int getMaxIdleTime() {
+			return delegate.getMaxIdleTime();
+		}
+
+		@Override
+		public boolean isLossyAndCheap() {
+			return delegate.isLossyAndCheap();
+		}
+
+		@Override
+		public OutputStream getOutputStream() throws IOException {
+			return delegate.getOutputStream();
+		}
+
+		@Override
+		public void dispose(boolean exception) throws IOException {
+			delegate.dispose(exception);
+			registry.removeWriter(RemovableDriveWriterTask.this);
+			eventBus.removeListener(RemovableDriveWriterTask.this);
+			setSuccess(!exception);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/TransportInputStreamReader.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionReader;
+
+import java.io.InputStream;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
+
+@NotNullByDefault
+class TransportInputStreamReader implements TransportConnectionReader {
+
+	private static final Logger LOG =
+			getLogger(TransportInputStreamReader.class.getName());
+
+	private final InputStream in;
+
+	TransportInputStreamReader(InputStream in) {
+		this.in = in;
+	}
+
+	@Override
+	public InputStream getInputStream() {
+		return in;
+	}
+
+	@Override
+	public void dispose(boolean exception, boolean recognised) {
+		tryToClose(in, LOG, WARNING);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/TransportOutputStreamWriter.java

@@ -0,0 +1,52 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
+
+import java.io.OutputStream;
+import java.util.logging.Logger;
+
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
+
+@NotNullByDefault
+class TransportOutputStreamWriter implements TransportConnectionWriter {
+
+	private static final Logger LOG =
+			getLogger(TransportOutputStreamWriter.class.getName());
+
+	private final SimplexPlugin plugin;
+	private final OutputStream out;
+
+	TransportOutputStreamWriter(SimplexPlugin plugin, OutputStream out) {
+		this.plugin = plugin;
+		this.out = out;
+	}
+
+	@Override
+	public int getMaxLatency() {
+		return plugin.getMaxLatency();
+	}
+
+	@Override
+	public int getMaxIdleTime() {
+		return plugin.getMaxIdleTime();
+	}
+
+	@Override
+	public boolean isLossyAndCheap() {
+		return plugin.isLossyAndCheap();
+	}
+
+	@Override
+	public OutputStream getOutputStream() {
+		return out;
+	}
+
+	@Override
+	public void dispose(boolean exception) {
+		tryToClose(out, LOG, WARNING);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/properties/TransportPropertyManagerImpl.java

@@ -44,6 +44,7 @@ import static org.briarproject.bramble.api.properties.TransportPropertyConstants
 import static org.briarproject.bramble.api.properties.TransportPropertyConstants.MSG_KEY_TRANSPORT_ID;
 import static org.briarproject.bramble.api.properties.TransportPropertyConstants.MSG_KEY_VERSION;
 import static org.briarproject.bramble.api.properties.TransportPropertyConstants.REFLECTED_PROPERTY_PREFIX;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
 import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 
 @Immutable
@@ -115,8 +116,8 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 	}
 
 	@Override
-	public boolean incomingMessage(Transaction txn, Message m, Metadata meta)
-			throws DbException, InvalidMessageException {
+	public DeliveryAction incomingMessage(Transaction txn, Message m,
+			Metadata meta) throws DbException, InvalidMessageException {
 		try {
 			// Find the latest update for this transport, if any
 			BdfDictionary d = metadataParser.parse(meta);
@@ -131,14 +132,14 @@ class TransportPropertyManagerImpl implements TransportPropertyManager,
 					// We've already received a newer update - delete this one
 					db.deleteMessage(txn, m.getId());
 					db.deleteMessageMetadata(txn, m.getId());
-					return false;
+					return ACCEPT_DO_NOT_SHARE;
 				}
 			}
 			txn.attach(new RemoteTransportPropertiesUpdatedEvent(t));
 		} catch (FormatException e) {
 			throw new InvalidMessageException(e);
 		}
-		return false;
+		return ACCEPT_DO_NOT_SHARE;
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/sync/SimplexOutgoingSession.java

@@ -15,6 +15,7 @@ import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
@@ -22,7 +23,11 @@ import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Map.Entry;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.Executor;
 import java.util.concurrent.LinkedBlockingQueue;
@@ -61,6 +66,7 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private final ContactId contactId;
 	private final TransportId transportId;
 	private final int maxLatency;
+	private final boolean eager;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
 	private final AtomicInteger outstandingQueries;
@@ -70,7 +76,7 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 
 	SimplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
 			EventBus eventBus, ContactId contactId, TransportId transportId,
-			int maxLatency, StreamWriter streamWriter,
+			int maxLatency, boolean eager, StreamWriter streamWriter,
 			SyncRecordWriter recordWriter) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
@@ -78,6 +84,7 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		this.contactId = contactId;
 		this.transportId = transportId;
 		this.maxLatency = maxLatency;
+		this.eager = eager;
 		this.streamWriter = streamWriter;
 		this.recordWriter = recordWriter;
 		outstandingQueries = new AtomicInteger(2); // One per type of record
@@ -92,8 +99,9 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 			// Send our supported protocol versions
 			recordWriter.writeVersions(new Versions(SUPPORTED_VERSIONS));
 			// Start a query for each type of record
-			dbExecutor.execute(new GenerateAck());
-			dbExecutor.execute(new GenerateBatch());
+			dbExecutor.execute(this::generateAck);
+			if (eager) dbExecutor.execute(this::loadUnackedMessageIds);
+			else dbExecutor.execute(this::generateBatch);
 			// Write records until interrupted or no more records to write
 			try {
 				while (!interrupted) {
@@ -138,81 +146,110 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		}
 	}
 
-	private class GenerateAck implements Runnable {
-
-		@DatabaseExecutor
-		@Override
-		public void run() {
-			if (interrupted) return;
-			try {
-				Ack a = db.transactionWithNullableResult(false, txn ->
-						db.generateAck(txn, contactId, MAX_MESSAGE_IDS));
-				if (LOG.isLoggable(INFO))
-					LOG.info("Generated ack: " + (a != null));
-				if (a == null) decrementOutstandingQueries();
-				else writerTasks.add(new WriteAck(a));
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				interrupt();
+	@DatabaseExecutor
+	private void loadUnackedMessageIds() {
+		if (interrupted) return;
+		try {
+			Map<MessageId, Integer> ids = db.transactionWithResult(true, txn ->
+					db.getUnackedMessagesToSend(txn, contactId));
+			if (LOG.isLoggable(INFO)) {
+				LOG.info(ids.size() + " unacked messages to send");
 			}
+			if (ids.isEmpty()) decrementOutstandingQueries();
+			else dbExecutor.execute(() -> generateEagerBatch(ids));
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			interrupt();
 		}
 	}
 
-	private class WriteAck implements ThrowingRunnable<IOException> {
-
-		private final Ack ack;
-
-		private WriteAck(Ack ack) {
-			this.ack = ack;
+	@DatabaseExecutor
+	private void generateEagerBatch(Map<MessageId, Integer> ids) {
+		if (interrupted) return;
+		// Take some message IDs from `ids` to form a batch
+		Collection<MessageId> batchIds = new ArrayList<>();
+		long totalLength = 0;
+		Iterator<Entry<MessageId, Integer>> it = ids.entrySet().iterator();
+		while (it.hasNext()) {
+			// Check whether the next message will fit in the batch
+			Entry<MessageId, Integer> e = it.next();
+			int length = e.getValue();
+			if (totalLength + length > MAX_RECORD_PAYLOAD_BYTES) break;
+			// Add the message to the batch
+			it.remove();
+			batchIds.add(e.getKey());
+			totalLength += length;
 		}
-
-		@IoExecutor
-		@Override
-		public void run() throws IOException {
-			if (interrupted) return;
-			recordWriter.writeAck(ack);
-			LOG.info("Sent ack");
-			dbExecutor.execute(new GenerateAck());
+		if (batchIds.isEmpty()) throw new AssertionError();
+		try {
+			Collection<Message> batch =
+					db.transactionWithResult(false, txn ->
+							db.generateBatch(txn, contactId, batchIds,
+									maxLatency));
+			writerTasks.add(() -> writeEagerBatch(batch, ids));
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			interrupt();
 		}
 	}
 
-	private class GenerateBatch implements Runnable {
+	@IoExecutor
+	private void writeEagerBatch(Collection<Message> batch,
+			Map<MessageId, Integer> ids) throws IOException {
+		if (interrupted) return;
+		for (Message m : batch) recordWriter.writeMessage(m);
+		LOG.info("Sent eager batch");
+		if (ids.isEmpty()) decrementOutstandingQueries();
+		else dbExecutor.execute(() -> generateEagerBatch(ids));
+	}
 
-		@DatabaseExecutor
-		@Override
-		public void run() {
-			if (interrupted) return;
-			try {
-				Collection<Message> b =
-						db.transactionWithNullableResult(false, txn ->
-								db.generateBatch(txn, contactId,
-										MAX_RECORD_PAYLOAD_BYTES, maxLatency));
-				if (LOG.isLoggable(INFO))
-					LOG.info("Generated batch: " + (b != null));
-				if (b == null) decrementOutstandingQueries();
-				else writerTasks.add(new WriteBatch(b));
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-				interrupt();
-			}
+	@DatabaseExecutor
+	private void generateAck() {
+		if (interrupted) return;
+		try {
+			Ack a = db.transactionWithNullableResult(false, txn ->
+					db.generateAck(txn, contactId, MAX_MESSAGE_IDS));
+			if (LOG.isLoggable(INFO))
+				LOG.info("Generated ack: " + (a != null));
+			if (a == null) decrementOutstandingQueries();
+			else writerTasks.add(() -> writeAck(a));
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			interrupt();
 		}
 	}
 
-	private class WriteBatch implements ThrowingRunnable<IOException> {
+	@IoExecutor
+	private void writeAck(Ack ack) throws IOException {
+		if (interrupted) return;
+		recordWriter.writeAck(ack);
+		LOG.info("Sent ack");
+		dbExecutor.execute(this::generateAck);
+	}
 
-		private final Collection<Message> batch;
-
-		private WriteBatch(Collection<Message> batch) {
-			this.batch = batch;
+	@DatabaseExecutor
+	private void generateBatch() {
+		if (interrupted) return;
+		try {
+			Collection<Message> b =
+					db.transactionWithNullableResult(false, txn ->
+							db.generateBatch(txn, contactId,
+									MAX_RECORD_PAYLOAD_BYTES, maxLatency));
+			if (LOG.isLoggable(INFO))
+				LOG.info("Generated batch: " + (b != null));
+			if (b == null) decrementOutstandingQueries();
+			else writerTasks.add(() -> writeBatch(b));
+		} catch (DbException e) {
+			logException(LOG, WARNING, e);
+			interrupt();
 		}
+	}
 
-		@IoExecutor
-		@Override
-		public void run() throws IOException {
-			if (interrupted) return;
-			for (Message m : batch) recordWriter.writeMessage(m);
-			LOG.info("Sent batch");
-			dbExecutor.execute(new GenerateBatch());
-		}
+	@IoExecutor
+	private void writeBatch(Collection<Message> batch) throws IOException {
+		if (interrupted) return;
+		for (Message m : batch) recordWriter.writeMessage(m);
+		LOG.info("Sent batch");
+		dbExecutor.execute(this::generateBatch);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/sync/SyncSessionFactoryImpl.java

@@ -60,12 +60,12 @@ class SyncSessionFactoryImpl implements SyncSessionFactory {
 
 	@Override
 	public SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
-			int maxLatency, StreamWriter streamWriter) {
+			int maxLatency, boolean eager, StreamWriter streamWriter) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
 		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c, t,
-				maxLatency, streamWriter, recordWriter);
+				maxLatency, eager, streamWriter, recordWriter);
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/sync/validation/ValidationManagerImpl.java

@@ -20,6 +20,7 @@ import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.event.MessageAddedEvent;
 import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction;
 import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.sync.validation.MessageValidator;
 import org.briarproject.bramble.api.sync.validation.ValidationManager;
@@ -40,6 +41,10 @@ import javax.inject.Inject;
 
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_SHARE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.DEFER;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.REJECT;
 import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
 import static org.briarproject.bramble.api.sync.validation.MessageState.INVALID;
 import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
@@ -185,16 +190,19 @@ class ValidationManagerImpl implements ValidationManager, Service,
 						int majorVersion = g.getMajorVersion();
 						Metadata meta =
 								db.getMessageMetadataForValidator(txn, id);
-						DeliveryResult result =
+						DeliveryAction action =
 								deliverMessage(txn, m, c, majorVersion, meta);
-						if (result.valid) {
-							addPendingDependents(txn, id, pending);
-							if (result.share) {
-								db.setMessageShared(txn, id);
-								toShare.addAll(states.keySet());
-							}
-						} else {
+						if (action == REJECT) {
+							invalidateMessage(txn, id);
 							addDependentsToInvalidate(txn, id, invalidate);
+						} else if (action == ACCEPT_SHARE) {
+							db.setMessageState(txn, m.getId(), DELIVERED);
+							addPendingDependents(txn, id, pending);
+							db.setMessageShared(txn, id);
+							toShare.addAll(states.keySet());
+						} else if (action == ACCEPT_DO_NOT_SHARE) {
+							db.setMessageState(txn, m.getId(), DELIVERED);
+							addPendingDependents(txn, id, pending);
 						}
 					}
 				}
@@ -275,16 +283,21 @@ class ValidationManagerImpl implements ValidationManager, Service,
 					Metadata meta = context.getMetadata();
 					db.mergeMessageMetadata(txn, id, meta);
 					if (allDelivered) {
-						DeliveryResult result =
+						DeliveryAction action =
 								deliverMessage(txn, m, c, majorVersion, meta);
-						if (result.valid) {
-							addPendingDependents(txn, id, pending);
-							if (result.share) {
-								db.setMessageShared(txn, id);
-								toShare.addAll(dependencies);
-							}
-						} else {
+						if (action == REJECT) {
+							invalidateMessage(txn, id);
 							addDependentsToInvalidate(txn, id, invalidate);
+						} else if (action == DEFER) {
+							db.setMessageState(txn, id, PENDING);
+						} else if (action == ACCEPT_SHARE) {
+							db.setMessageState(txn, id, DELIVERED);
+							addPendingDependents(txn, id, pending);
+							db.setMessageShared(txn, id);
+							toShare.addAll(dependencies);
+						} else if (action == ACCEPT_DO_NOT_SHARE) {
+							db.setMessageState(txn, id, DELIVERED);
+							addPendingDependents(txn, id, pending);
 						}
 					} else {
 						db.setMessageState(txn, id, PENDING);
@@ -304,23 +317,21 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	}
 
 	@DatabaseExecutor
-	private DeliveryResult deliverMessage(Transaction txn, Message m,
-			ClientId c, int majorVersion, Metadata meta) throws DbException {
-		// Deliver the message to the client if it's registered a hook
-		boolean shareMsg = false;
+	private DeliveryAction deliverMessage(Transaction txn, Message m,
+			ClientId c, int majorVersion, Metadata meta) {
+		// Deliver the message to the client if it has registered a hook
 		ClientMajorVersion cv = new ClientMajorVersion(c, majorVersion);
 		IncomingMessageHook hook = hooks.get(cv);
-		if (hook != null) {
-			try {
-				shareMsg = hook.incomingMessage(txn, m, meta);
-			} catch (InvalidMessageException e) {
-				logException(LOG, INFO, e);
-				invalidateMessage(txn, m.getId());
-				return new DeliveryResult(false, false);
-			}
+		if (hook == null) return ACCEPT_DO_NOT_SHARE;
+		try {
+			return hook.incomingMessage(txn, m, meta);
+		} catch (DbException e) {
+			logException(LOG, INFO, e);
+			return DEFER;
+		} catch (InvalidMessageException e) {
+			logException(LOG, INFO, e);
+			return REJECT;
 		}
-		db.setMessageState(txn, m.getId(), DELIVERED);
-		return new DeliveryResult(true, shareMsg);
 	}
 
 	@DatabaseExecutor
@@ -447,14 +458,4 @@ class ValidationManagerImpl implements ValidationManager, Service,
 			logException(LOG, WARNING, e);
 		}
 	}
-
-	private static class DeliveryResult {
-
-		private final boolean valid, share;
-
-		private DeliveryResult(boolean valid, boolean share) {
-			this.valid = valid;
-			this.share = share;
-		}
-	}
 }

bramble-core/src/main/java/org/briarproject/bramble/transport/KeyManagerImpl.java

@@ -51,7 +51,6 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 	private final DatabaseComponent db;
 	private final Executor dbExecutor;
 	private final PluginConfig pluginConfig;
-	private final TransportKeyManagerFactory transportKeyManagerFactory;
 	private final TransportCrypto transportCrypto;
 
 	private final ConcurrentHashMap<TransportId, TransportKeyManager> managers;
@@ -61,34 +60,39 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 	KeyManagerImpl(DatabaseComponent db,
 			@DatabaseExecutor Executor dbExecutor,
 			PluginConfig pluginConfig,
-			TransportKeyManagerFactory transportKeyManagerFactory,
-			TransportCrypto transportCrypto) {
+			TransportCrypto transportCrypto,
+			TransportKeyManagerFactory transportKeyManagerFactory) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.pluginConfig = pluginConfig;
-		this.transportKeyManagerFactory = transportKeyManagerFactory;
 		this.transportCrypto = transportCrypto;
 		managers = new ConcurrentHashMap<>();
+		for (SimplexPluginFactory f : pluginConfig.getSimplexFactories()) {
+			TransportKeyManager m = transportKeyManagerFactory.
+					createTransportKeyManager(f.getId(), f.getMaxLatency());
+			managers.put(f.getId(), m);
+		}
+		for (DuplexPluginFactory f : pluginConfig.getDuplexFactories()) {
+			TransportKeyManager m = transportKeyManagerFactory.
+					createTransportKeyManager(f.getId(), f.getMaxLatency());
+			managers.put(f.getId(), m);
+		}
 	}
 
 	@Override
 	public void startService() throws ServiceException {
 		if (used.getAndSet(true)) throw new IllegalStateException();
-		Map<TransportId, Integer> transports = new HashMap<>();
-		for (SimplexPluginFactory f : pluginConfig.getSimplexFactories())
-			transports.put(f.getId(), f.getMaxLatency());
-		for (DuplexPluginFactory f : pluginConfig.getDuplexFactories())
-			transports.put(f.getId(), f.getMaxLatency());
 		try {
 			db.transaction(false, txn -> {
-				for (Entry<TransportId, Integer> e : transports.entrySet())
-					db.addTransport(txn, e.getKey(), e.getValue());
-				for (Entry<TransportId, Integer> e : transports.entrySet()) {
-					TransportKeyManager m = transportKeyManagerFactory
-							.createTransportKeyManager(e.getKey(),
-									e.getValue());
-					managers.put(e.getKey(), m);
-					m.start(txn);
+				for (SimplexPluginFactory f :
+						pluginConfig.getSimplexFactories()) {
+					db.addTransport(txn, f.getId(), f.getMaxLatency());
+					managers.get(f.getId()).start(txn);
+				}
+				for (DuplexPluginFactory f :
+						pluginConfig.getDuplexFactories()) {
+					db.addTransport(txn, f.getId(), f.getMaxLatency());
+					managers.get(f.getId()).start(txn);
 				}
 			});
 		} catch (DbException e) {
@@ -101,9 +105,17 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 	}
 
 	@Override
-	public Map<TransportId, KeySetId> addRotationKeys(
-			Transaction txn, ContactId c, SecretKey rootKey, long timestamp,
-			boolean alice, boolean active) throws DbException {
+	public KeySetId addRotationKeys(Transaction txn, ContactId c,
+			TransportId t, SecretKey rootKey, long timestamp, boolean alice,
+			boolean active) throws DbException {
+		return withManager(t, m ->
+				m.addRotationKeys(txn, c, rootKey, timestamp, alice, active));
+	}
+
+	@Override
+	public Map<TransportId, KeySetId> addRotationKeys(Transaction txn,
+			ContactId c, SecretKey rootKey, long timestamp, boolean alice,
+			boolean active) throws DbException {
 		Map<TransportId, KeySetId> ids = new HashMap<>();
 		for (Entry<TransportId, TransportKeyManager> e : managers.entrySet()) {
 			TransportId t = e.getKey();
@@ -137,7 +149,7 @@ class KeyManagerImpl implements KeyManager, Service, EventListener {
 			PendingContactId p, PublicKey theirPublicKey, KeyPair ourKeyPair)
 			throws DbException, GeneralSecurityException {
 		SecretKey staticMasterKey = transportCrypto
-					.deriveStaticMasterKey(theirPublicKey, ourKeyPair);
+				.deriveStaticMasterKey(theirPublicKey, ourKeyPair);
 		SecretKey rootKey =
 				transportCrypto.deriveHandshakeRootKey(staticMasterKey, true);
 		boolean alice = transportCrypto.isAlice(theirPublicKey, ourKeyPair);

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/MessageEncoder.java

@@ -0,0 +1,22 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+
+@NotNullByDefault
+interface MessageEncoder {
+
+	Message encodeKeyMessage(GroupId contactGroupId,
+			TransportId transportId, PublicKey publicKey);
+
+	Message encodeActivateMessage(GroupId contactGroupId,
+			TransportId transportId, MessageId previousMessageId);
+
+	BdfDictionary encodeMessageMetadata(TransportId transportId,
+			MessageType type, boolean local);
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/MessageEncoderImpl.java

@@ -0,0 +1,77 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.system.Clock;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.transport.agreement.MessageType.ACTIVATE;
+import static org.briarproject.bramble.transport.agreement.MessageType.KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_IS_SESSION;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_LOCAL;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_MESSAGE_TYPE;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_TRANSPORT_ID;
+
+@Immutable
+@NotNullByDefault
+class MessageEncoderImpl implements MessageEncoder {
+
+	private final ClientHelper clientHelper;
+	private final Clock clock;
+
+	@Inject
+	MessageEncoderImpl(ClientHelper clientHelper, Clock clock) {
+		this.clientHelper = clientHelper;
+		this.clock = clock;
+	}
+
+	@Override
+	public Message encodeKeyMessage(GroupId contactGroupId,
+			TransportId transportId, PublicKey publicKey) {
+		BdfList body = BdfList.of(
+				KEY.getValue(),
+				transportId.getString(),
+				publicKey.getEncoded());
+		return encodeMessage(contactGroupId, body);
+	}
+
+	@Override
+	public Message encodeActivateMessage(GroupId contactGroupId,
+			TransportId transportId, MessageId previousMessageId) {
+		BdfList body = BdfList.of(
+				ACTIVATE.getValue(),
+				transportId.getString(),
+				previousMessageId);
+		return encodeMessage(contactGroupId, body);
+	}
+
+	@Override
+	public BdfDictionary encodeMessageMetadata(TransportId transportId,
+			MessageType type, boolean local) {
+		return BdfDictionary.of(
+				new BdfEntry(MSG_KEY_IS_SESSION, false),
+				new BdfEntry(MSG_KEY_TRANSPORT_ID, transportId.getString()),
+				new BdfEntry(MSG_KEY_MESSAGE_TYPE, type.getValue()),
+				new BdfEntry(MSG_KEY_LOCAL, local));
+	}
+
+	private Message encodeMessage(GroupId contactGroupId, BdfList body) {
+		try {
+			return clientHelper.createMessage(contactGroupId,
+					clock.currentTimeMillis(), clientHelper.toByteArray(body));
+		} catch (FormatException e) {
+			throw new AssertionError();
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/MessageType.java

@@ -0,0 +1,29 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+enum MessageType {
+
+	KEY(0),
+	ACTIVATE(1);
+
+	private final int value;
+
+	MessageType(int value) {
+		this.value = value;
+	}
+
+	int getValue() {
+		return value;
+	}
+
+	static MessageType fromValue(int value) throws FormatException {
+		for (MessageType t : values()) if (t.value == value) return t;
+		throw new FormatException();
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/Session.java

@@ -0,0 +1,58 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.transport.KeySetId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+class Session {
+
+	private final State state;
+	@Nullable
+	private final MessageId lastLocalMessageId;
+	@Nullable
+	private final KeyPair localKeyPair;
+	@Nullable
+	private final Long localTimestamp;
+	@Nullable
+	private final KeySetId keySetId;
+
+	Session(State state, @Nullable MessageId lastLocalMessageId,
+			@Nullable KeyPair localKeyPair, @Nullable Long localTimestamp,
+			@Nullable KeySetId keySetId) {
+		this.state = state;
+		this.lastLocalMessageId = lastLocalMessageId;
+		this.localKeyPair = localKeyPair;
+		this.localTimestamp = localTimestamp;
+		this.keySetId = keySetId;
+	}
+
+	State getState() {
+		return state;
+	}
+
+	@Nullable
+	MessageId getLastLocalMessageId() {
+		return lastLocalMessageId;
+	}
+
+	@Nullable
+	KeyPair getLocalKeyPair() {
+		return localKeyPair;
+	}
+
+	@Nullable
+	Long getLocalTimestamp() {
+		return localTimestamp;
+	}
+
+	@Nullable
+	KeySetId getKeySetId() {
+		return keySetId;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/SessionEncoder.java

@@ -0,0 +1,13 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+
+@NotNullByDefault
+interface SessionEncoder {
+
+	BdfDictionary encodeSession(Session s, TransportId transportId);
+
+	BdfDictionary getSessionQuery(TransportId transportId);
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/SessionEncoderImpl.java

@@ -0,0 +1,68 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.transport.KeySetId;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.api.data.BdfDictionary.NULL_VALUE;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_IS_SESSION;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_TRANSPORT_ID;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_KEY_SET_ID;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LAST_LOCAL_MESSAGE_ID;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LOCAL_PRIVATE_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LOCAL_PUBLIC_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LOCAL_TIMESTAMP;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_STATE;
+
+@Immutable
+@NotNullByDefault
+class SessionEncoderImpl implements SessionEncoder {
+
+	@Inject
+	SessionEncoderImpl() {
+	}
+
+	@Override
+	public BdfDictionary encodeSession(Session s, TransportId transportId) {
+		BdfDictionary meta = new BdfDictionary();
+		meta.put(MSG_KEY_IS_SESSION, true);
+		meta.put(MSG_KEY_TRANSPORT_ID, transportId.getString());
+		meta.put(SESSION_KEY_STATE, s.getState().getValue());
+		putNullable(meta, SESSION_KEY_LAST_LOCAL_MESSAGE_ID,
+				s.getLastLocalMessageId());
+		KeyPair localKeyPair = s.getLocalKeyPair();
+		if (localKeyPair == null) {
+			meta.put(SESSION_KEY_LOCAL_PUBLIC_KEY, NULL_VALUE);
+			meta.put(SESSION_KEY_LOCAL_PRIVATE_KEY, NULL_VALUE);
+		} else {
+			meta.put(SESSION_KEY_LOCAL_PUBLIC_KEY,
+					localKeyPair.getPublic().getEncoded());
+			meta.put(SESSION_KEY_LOCAL_PRIVATE_KEY,
+					localKeyPair.getPrivate().getEncoded());
+		}
+		putNullable(meta, SESSION_KEY_LOCAL_TIMESTAMP, s.getLocalTimestamp());
+		KeySetId keySetId = s.getKeySetId();
+		if (keySetId == null) meta.put(SESSION_KEY_KEY_SET_ID, NULL_VALUE);
+		else meta.put(SESSION_KEY_KEY_SET_ID, keySetId.getInt());
+		return meta;
+	}
+
+	@Override
+	public BdfDictionary getSessionQuery(TransportId transportId) {
+		return BdfDictionary.of(
+				new BdfEntry(MSG_KEY_IS_SESSION, true),
+				new BdfEntry(MSG_KEY_TRANSPORT_ID, transportId.getString()));
+	}
+
+	private void putNullable(BdfDictionary meta, String key,
+			@Nullable Object o) {
+		meta.put(key, o == null ? NULL_VALUE : o);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/SessionParser.java

@@ -0,0 +1,11 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+interface SessionParser {
+
+	Session parseSession(BdfDictionary meta) throws FormatException;
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/SessionParserImpl.java

@@ -0,0 +1,67 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.crypto.PrivateKey;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.transport.KeySetId;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_KEY_SET_ID;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LAST_LOCAL_MESSAGE_ID;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LOCAL_PRIVATE_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LOCAL_PUBLIC_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_LOCAL_TIMESTAMP;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.SESSION_KEY_STATE;
+
+@Immutable
+@NotNullByDefault
+class SessionParserImpl implements SessionParser {
+
+	private final TransportKeyAgreementCrypto crypto;
+
+	@Inject
+	SessionParserImpl(TransportKeyAgreementCrypto crypto) {
+		this.crypto = crypto;
+	}
+
+	@Override
+	public Session parseSession(BdfDictionary meta) throws FormatException {
+		State state =
+				State.fromValue(meta.getLong(SESSION_KEY_STATE).intValue());
+
+		MessageId lastLocalMessageId = null;
+		byte[] lastLocalMessageIdBytes =
+				meta.getOptionalRaw(SESSION_KEY_LAST_LOCAL_MESSAGE_ID);
+		if (lastLocalMessageIdBytes != null) {
+			lastLocalMessageId = new MessageId(lastLocalMessageIdBytes);
+		}
+
+		KeyPair localKeyPair = null;
+		byte[] localPublicKeyBytes =
+				meta.getOptionalRaw(SESSION_KEY_LOCAL_PUBLIC_KEY);
+		byte[] localPrivateKeyBytes =
+				meta.getOptionalRaw(SESSION_KEY_LOCAL_PRIVATE_KEY);
+		if (localPublicKeyBytes != null && localPrivateKeyBytes != null) {
+			PublicKey pub = crypto.parsePublicKey(localPublicKeyBytes);
+			PrivateKey priv = crypto.parsePrivateKey(localPrivateKeyBytes);
+			localKeyPair = new KeyPair(pub, priv);
+		}
+
+		Long localTimestamp = meta.getOptionalLong(SESSION_KEY_LOCAL_TIMESTAMP);
+
+		KeySetId keySetId = null;
+		Long keySetIdLong = meta.getOptionalLong(SESSION_KEY_KEY_SET_ID);
+		if (keySetIdLong != null) {
+			keySetId = new KeySetId(keySetIdLong.intValue());
+		}
+
+		return new Session(state, lastLocalMessageId, localKeyPair,
+				localTimestamp, keySetId);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/State.java

@@ -0,0 +1,43 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+enum State {
+
+	/**
+	 * We've sent a key message and are awaiting the contact's key message.
+	 */
+	AWAIT_KEY(0),
+
+	/**
+	 * We've exchanged key messages, derived the transport keys and sent an
+	 * activate message, and now we're awaiting the contact's activate message.
+	 */
+	AWAIT_ACTIVATE(1),
+
+	/**
+	 * We've exchanged key messages and activate messages, and have derived and
+	 * activated the transport keys. This is the end state.
+	 */
+	ACTIVATED(2);
+
+	private final int value;
+
+	State(int value) {
+		this.value = value;
+	}
+
+	int getValue() {
+		return value;
+	}
+
+	static State fromValue(int value) throws FormatException {
+		for (State s : values()) if (s.value == value) return s;
+		throw new FormatException();
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementConstants.java

@@ -0,0 +1,27 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+interface TransportKeyAgreementConstants {
+
+	String MSG_KEY_IS_SESSION = "isSession";
+	String MSG_KEY_MESSAGE_TYPE = "messageType";
+	String MSG_KEY_TRANSPORT_ID = "transportId";
+	String MSG_KEY_PUBLIC_KEY = "publicKey";
+	String MSG_KEY_LOCAL = "local";
+
+	String SESSION_KEY_STATE = "state";
+	String SESSION_KEY_LAST_LOCAL_MESSAGE_ID = "lastLocalMessageId";
+	String SESSION_KEY_LOCAL_PUBLIC_KEY = "localPublicKey";
+	String SESSION_KEY_LOCAL_PRIVATE_KEY = "localPrivateKey";
+	String SESSION_KEY_LOCAL_TIMESTAMP = "localTimestamp";
+	String SESSION_KEY_KEY_SET_ID = "keySetId";
+
+	/**
+	 * Label for deriving the root key from key pairs.
+	 */
+	String ROOT_KEY_LABEL =
+			"org.briarproject.bramble.transport.agreement/ROOT_KEY";
+
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementCrypto.java

@@ -0,0 +1,23 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.crypto.PrivateKey;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.security.GeneralSecurityException;
+
+@NotNullByDefault
+interface TransportKeyAgreementCrypto {
+
+	KeyPair generateKeyPair();
+
+	SecretKey deriveRootKey(KeyPair localKeyPair, PublicKey remotePublicKey)
+			throws GeneralSecurityException;
+
+	PublicKey parsePublicKey(byte[] encoded) throws FormatException;
+
+	PrivateKey parsePrivateKey(byte[] encoded) throws FormatException;
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementCryptoImpl.java

@@ -0,0 +1,66 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.crypto.PrivateKey;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.security.GeneralSecurityException;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.api.Bytes.compare;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.ROOT_KEY_LABEL;
+
+@Immutable
+@NotNullByDefault
+class TransportKeyAgreementCryptoImpl implements TransportKeyAgreementCrypto {
+
+	private final CryptoComponent crypto;
+
+	@Inject
+	TransportKeyAgreementCryptoImpl(CryptoComponent crypto) {
+		this.crypto = crypto;
+	}
+
+	@Override
+	public KeyPair generateKeyPair() {
+		return crypto.generateAgreementKeyPair();
+	}
+
+	@Override
+	public SecretKey deriveRootKey(KeyPair localKeyPair,
+			PublicKey remotePublicKey) throws GeneralSecurityException {
+		byte[] theirPublic = remotePublicKey.getEncoded();
+		byte[] ourPublic = localKeyPair.getPublic().getEncoded();
+		boolean alice = compare(ourPublic, theirPublic) < 0;
+		byte[][] inputs = {
+				alice ? ourPublic : theirPublic,
+				alice ? theirPublic : ourPublic
+		};
+		return crypto.deriveSharedSecret(ROOT_KEY_LABEL, remotePublicKey,
+				localKeyPair, inputs);
+	}
+
+	@Override
+	public PublicKey parsePublicKey(byte[] encoded) throws FormatException {
+		try {
+			return crypto.getAgreementKeyParser().parsePublicKey(encoded);
+		} catch (GeneralSecurityException e) {
+			throw new FormatException();
+		}
+	}
+
+	@Override
+	public PrivateKey parsePrivateKey(byte[] encoded) throws FormatException {
+		try {
+			return crypto.getAgreementKeyParser().parsePrivateKey(encoded);
+		} catch (GeneralSecurityException e) {
+			throw new FormatException();
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementManagerImpl.java

@@ -0,0 +1,409 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.BdfIncomingMessageHook;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.client.ContactGroupFactory;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.ContactManager.ContactHook;
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataParser;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Metadata;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager.OpenDatabaseHook;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Group.Visibility;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.KeySetId;
+import org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager.ClientVersioningHook;
+
+import java.security.GeneralSecurityException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static java.lang.Math.min;
+import static java.util.Collections.singletonMap;
+import static java.util.logging.Level.INFO;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.Bytes.compare;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.DEFER;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.REJECT;
+import static org.briarproject.bramble.transport.agreement.MessageType.ACTIVATE;
+import static org.briarproject.bramble.transport.agreement.MessageType.KEY;
+import static org.briarproject.bramble.transport.agreement.State.ACTIVATED;
+import static org.briarproject.bramble.transport.agreement.State.AWAIT_ACTIVATE;
+import static org.briarproject.bramble.transport.agreement.State.AWAIT_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_MESSAGE_TYPE;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_PUBLIC_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_TRANSPORT_ID;
+
+@Immutable
+@NotNullByDefault
+class TransportKeyAgreementManagerImpl extends BdfIncomingMessageHook
+		implements TransportKeyAgreementManager, OpenDatabaseHook, ContactHook,
+		ClientVersioningHook {
+
+	private static final Logger LOG =
+			getLogger(TransportKeyAgreementManagerImpl.class.getName());
+
+	private final ContactGroupFactory contactGroupFactory;
+	private final ClientVersioningManager clientVersioningManager;
+	private final IdentityManager identityManager;
+	private final KeyManager keyManager;
+	private final MessageEncoder messageEncoder;
+	private final SessionEncoder sessionEncoder;
+	private final SessionParser sessionParser;
+	private final TransportKeyAgreementCrypto crypto;
+
+	private final List<TransportId> transports;
+	private final Group localGroup;
+
+	@Inject
+	TransportKeyAgreementManagerImpl(
+			DatabaseComponent db,
+			ClientHelper clientHelper,
+			MetadataParser metadataParser,
+			ContactGroupFactory contactGroupFactory,
+			ClientVersioningManager clientVersioningManager,
+			IdentityManager identityManager,
+			KeyManager keyManager,
+			MessageEncoder messageEncoder,
+			SessionEncoder sessionEncoder,
+			SessionParser sessionParser,
+			TransportKeyAgreementCrypto crypto,
+			PluginConfig config) {
+		super(db, clientHelper, metadataParser);
+		this.contactGroupFactory = contactGroupFactory;
+		this.clientVersioningManager = clientVersioningManager;
+		this.identityManager = identityManager;
+		this.keyManager = keyManager;
+		this.messageEncoder = messageEncoder;
+		this.sessionEncoder = sessionEncoder;
+		this.sessionParser = sessionParser;
+		this.crypto = crypto;
+		transports = new ArrayList<>();
+		for (DuplexPluginFactory duplex : config.getDuplexFactories()) {
+			transports.add(duplex.getId());
+		}
+		for (SimplexPluginFactory simplex : config.getSimplexFactories()) {
+			transports.add(simplex.getId());
+		}
+		localGroup = contactGroupFactory.createLocalGroup(CLIENT_ID,
+				MAJOR_VERSION);
+	}
+
+	@Override
+	public void onDatabaseOpened(Transaction txn) throws DbException {
+		Collection<Contact> contacts = db.getContacts(txn);
+		if (!db.containsGroup(txn, localGroup.getId())) {
+			db.addGroup(txn, localGroup);
+			// Set things up for any pre-existing contacts
+			for (Contact c : contacts) addingContact(txn, c);
+		}
+		// Find any contacts and transports that need keys
+		Map<ContactId, Collection<TransportId>> transportsWithKeys =
+				db.getTransportsWithKeys(txn);
+		for (Contact c : contacts) {
+			Collection<TransportId> withKeys =
+					transportsWithKeys.get(c.getId());
+			for (TransportId t : transports) {
+				if (withKeys == null || !withKeys.contains(t)) {
+					// We need keys for this contact and transport
+					GroupId contactGroupId = getContactGroup(c).getId();
+					SavedSession ss = loadSession(txn, contactGroupId, t);
+					if (ss == null) {
+						// Start a session by sending our key message
+						startSession(txn, contactGroupId, t);
+					}
+				}
+			}
+		}
+	}
+
+	@Override
+	public void addingContact(Transaction txn, Contact c) throws DbException {
+		// Create a group to share with the contact
+		Group g = getContactGroup(c);
+		db.addGroup(txn, g);
+		// Attach the contact ID to the group
+		clientHelper.setContactId(txn, g.getId(), c.getId());
+		// Apply the client's visibility to the contact group
+		Visibility client = clientVersioningManager.getClientVisibility(txn,
+				c.getId(), CLIENT_ID, MAJOR_VERSION);
+		db.setGroupVisibility(txn, c.getId(), g.getId(), client);
+	}
+
+	@Override
+	public void removingContact(Transaction txn, Contact c) throws DbException {
+		db.removeGroup(txn, getContactGroup(c));
+	}
+
+	@Override
+	public void onClientVisibilityChanging(Transaction txn, Contact c,
+			Visibility v) throws DbException {
+		// Apply the client's visibility to the contact group
+		Group g = getContactGroup(c);
+		db.setGroupVisibility(txn, c.getId(), g.getId(), v);
+	}
+
+	@Override
+	protected DeliveryAction incomingMessage(Transaction txn, Message m,
+			BdfList body, BdfDictionary meta)
+			throws DbException, FormatException {
+		MessageType type = MessageType.fromValue(
+				meta.getLong(MSG_KEY_MESSAGE_TYPE).intValue());
+		TransportId t = new TransportId(meta.getString(MSG_KEY_TRANSPORT_ID));
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Received " + type + " message for " + t);
+		}
+		if (!transports.contains(t)) {
+			// Defer handling the message until we support the transport
+			return DEFER;
+		}
+		SavedSession ss = loadSession(txn, m.getGroupId(), t);
+		if (type == KEY) return handleKeyMessage(txn, t, m, meta, ss);
+		else if (type == ACTIVATE) return handleActivateMessage(txn, t, ss);
+		else throw new AssertionError();
+	}
+
+	private DeliveryAction handleKeyMessage(Transaction txn, TransportId t,
+			Message m, BdfDictionary meta, @Nullable SavedSession ss)
+			throws DbException, FormatException {
+		ContactId c = clientHelper.getContactId(txn, m.getGroupId());
+		boolean haveKeys = db.containsTransportKeys(txn, c, t);
+		if (ss == null) {
+			if (haveKeys) {
+				// We have keys but no session, so we must have derived keys
+				// when adding the contact. If the contact didn't support
+				// the transport when they added us, they wouldn't have
+				// derived keys at that time. If they later added support for
+				// the transport then they would have started a session, so a
+				// key message is valid in this case
+				return handleKeyMessageForNewSession(txn, c, t, m, meta);
+			} else {
+				// We don't have keys, so we should have created a session at
+				// startup
+				throw new IllegalStateException();
+			}
+		} else if (ss.session.getState() == AWAIT_KEY) {
+			if (haveKeys) {
+				// We have keys, so we shouldn't be in the AWAIT_KEY state,
+				// even if the contact didn't derive keys when adding us and
+				// later started a session
+				throw new IllegalStateException();
+			} else {
+				// This is the key message we're waiting for
+				return handleKeyMessageForExistingSession(txn, c, t, m, meta,
+						ss);
+			}
+		} else {
+			return REJECT; // Not valid in this state
+		}
+	}
+
+	private DeliveryAction handleActivateMessage(Transaction txn,
+			TransportId t, @Nullable SavedSession ss) throws DbException {
+		if (ss != null && ss.session.getState() == AWAIT_ACTIVATE) {
+			// Activate the keys and finish the session
+			KeySetId keySetId = requireNonNull(ss.session.getKeySetId());
+			keyManager.activateKeys(txn, singletonMap(t, keySetId));
+			Session session = new Session(ACTIVATED,
+					ss.session.getLastLocalMessageId(), null, null, null);
+			saveSession(txn, t, ss.storageId, session);
+			return ACCEPT_DO_NOT_SHARE;
+		} else {
+			return REJECT; // Not valid in this state
+		}
+	}
+
+	private DeliveryAction handleKeyMessageForNewSession(Transaction txn,
+			ContactId c, TransportId t, Message m, BdfDictionary meta)
+			throws DbException, FormatException {
+		KeyPair localKeyPair = crypto.generateKeyPair();
+		PublicKey remotePublicKey =
+				crypto.parsePublicKey(meta.getRaw(MSG_KEY_PUBLIC_KEY));
+		Message keyMessage = sendKeyMessage(txn, m.getGroupId(), t,
+				localKeyPair.getPublic());
+		long minTimestamp = min(keyMessage.getTimestamp(), m.getTimestamp());
+		SecretKey rootKey;
+		try {
+			rootKey = crypto.deriveRootKey(localKeyPair, remotePublicKey);
+		} catch (GeneralSecurityException e) {
+			return REJECT; // Invalid public key
+		}
+		boolean alice = isLocalPartyAlice(txn, db.getContact(txn, c));
+		KeySetId keySetId = keyManager.addRotationKeys(txn, c, t, rootKey,
+				minTimestamp, alice, false);
+		Message activateMessage =
+				sendActivateMessage(txn, m.getGroupId(), t, keyMessage.getId());
+		Session session = new Session(AWAIT_ACTIVATE, activateMessage.getId(),
+				null, null, keySetId);
+		saveNewSession(txn, m.getGroupId(), t, session);
+		return ACCEPT_DO_NOT_SHARE;
+	}
+
+	private DeliveryAction handleKeyMessageForExistingSession(Transaction txn,
+			ContactId c, TransportId t, Message m, BdfDictionary meta,
+			SavedSession ss) throws DbException, FormatException {
+		KeyPair localKeyPair = requireNonNull(ss.session.getLocalKeyPair());
+		PublicKey remotePublicKey =
+				crypto.parsePublicKey(meta.getRaw(MSG_KEY_PUBLIC_KEY));
+		long localTimestamp = requireNonNull(ss.session.getLocalTimestamp());
+		long minTimestamp = min(localTimestamp, m.getTimestamp());
+		SecretKey rootKey;
+		try {
+			rootKey = crypto.deriveRootKey(localKeyPair, remotePublicKey);
+		} catch (GeneralSecurityException e) {
+			return REJECT; // Invalid public key
+		}
+		boolean alice = isLocalPartyAlice(txn, db.getContact(txn, c));
+		KeySetId keySetId = keyManager.addRotationKeys(txn, c, t, rootKey,
+				minTimestamp, alice, false);
+		MessageId previousMessageId =
+				requireNonNull(ss.session.getLastLocalMessageId());
+		Message activateMessage =
+				sendActivateMessage(txn, m.getGroupId(), t, previousMessageId);
+		Session session = new Session(AWAIT_ACTIVATE, activateMessage.getId(),
+				null, null, keySetId);
+		saveSession(txn, t, ss.storageId, session);
+		return ACCEPT_DO_NOT_SHARE;
+	}
+
+	private void startSession(Transaction txn, GroupId contactGroupId,
+			TransportId t) throws DbException {
+		KeyPair localKeyPair = crypto.generateKeyPair();
+		Message keyMessage = sendKeyMessage(txn, contactGroupId, t,
+				localKeyPair.getPublic());
+		Session session = new Session(AWAIT_KEY, keyMessage.getId(),
+				localKeyPair, keyMessage.getTimestamp(), null);
+		saveNewSession(txn, contactGroupId, t, session);
+	}
+
+	@Nullable
+	private SavedSession loadSession(Transaction txn, GroupId contactGroupId,
+			TransportId t) throws DbException {
+		try {
+			BdfDictionary query = sessionEncoder.getSessionQuery(t);
+			Collection<MessageId> ids =
+					clientHelper.getMessageIds(txn, contactGroupId, query);
+			if (ids.size() > 1) throw new DbException();
+			if (ids.isEmpty()) {
+				if (LOG.isLoggable(INFO)) LOG.info("No session for " + t);
+				return null;
+			}
+			MessageId storageId = ids.iterator().next();
+			BdfDictionary bdfSession =
+					clientHelper.getMessageMetadataAsDictionary(txn, storageId);
+			Session session = sessionParser.parseSession(bdfSession);
+			if (LOG.isLoggable(INFO)) {
+				LOG.info("Loaded session in state " + session.getState()
+						+ " for " + t);
+			}
+			return new SavedSession(session, storageId);
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
+	private void saveNewSession(Transaction txn, GroupId contactGroupId,
+			TransportId t, Session session) throws DbException {
+		Message m =
+				clientHelper.createMessageForStoringMetadata(contactGroupId);
+		db.addLocalMessage(txn, m, new Metadata(), false, false);
+		MessageId storageId = m.getId();
+		saveSession(txn, t, storageId, session);
+	}
+
+	private void saveSession(Transaction txn, TransportId t,
+			MessageId storageId, Session session) throws DbException {
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Saving session in state " + session.getState()
+					+ " for " + t);
+		}
+		BdfDictionary meta = sessionEncoder.encodeSession(session, t);
+		try {
+			clientHelper.mergeMessageMetadata(txn, storageId, meta);
+		} catch (FormatException e) {
+			throw new AssertionError();
+		}
+	}
+
+	private Message sendKeyMessage(Transaction txn, GroupId contactGroupId,
+			TransportId t, PublicKey publicKey) throws DbException {
+		Message m = messageEncoder.encodeKeyMessage(contactGroupId, t,
+				publicKey);
+		sendMessage(txn, t, m, KEY);
+		return m;
+	}
+
+	private Message sendActivateMessage(Transaction txn,
+			GroupId contactGroupId, TransportId t, MessageId previousMessageId)
+			throws DbException {
+		Message m = messageEncoder.encodeActivateMessage(contactGroupId, t,
+				previousMessageId);
+		sendMessage(txn, t, m, ACTIVATE);
+		return m;
+	}
+
+	private void sendMessage(Transaction txn, TransportId t, Message m,
+			MessageType type) throws DbException {
+		BdfDictionary meta =
+				messageEncoder.encodeMessageMetadata(t, type, true);
+		try {
+			clientHelper.addLocalMessage(txn, m, meta, true, false);
+		} catch (FormatException e) {
+			throw new AssertionError();
+		}
+	}
+
+	private Group getContactGroup(Contact c) {
+		return contactGroupFactory.createContactGroup(CLIENT_ID,
+				MAJOR_VERSION, c);
+	}
+
+	private boolean isLocalPartyAlice(Transaction txn, Contact c)
+			throws DbException {
+		Author local = identityManager.getLocalAuthor(txn);
+		Author remote = c.getAuthor();
+		return compare(local.getId().getBytes(), remote.getId().getBytes()) < 0;
+	}
+
+	private static class SavedSession {
+
+		private final Session session;
+		private final MessageId storageId;
+
+		private SavedSession(Session session, MessageId storageId) {
+			this.session = session;
+			this.storageId = storageId;
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementModule.java

@@ -0,0 +1,83 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+import static org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager.CLIENT_ID;
+import static org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager.MAJOR_VERSION;
+import static org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager.MINOR_VERSION;
+
+@Module
+public class TransportKeyAgreementModule {
+
+	public static class EagerSingletons {
+		@Inject
+		TransportKeyAgreementManager transportKeyAgreementManager;
+		@Inject
+		TransportKeyAgreementValidator transportKeyAgreementValidator;
+	}
+
+	@Provides
+	@Singleton
+	TransportKeyAgreementManager provideTransportKeyAgreementManager(
+			LifecycleManager lifecycleManager,
+			ValidationManager validationManager,
+			ContactManager contactManager,
+			ClientVersioningManager clientVersioningManager,
+			TransportKeyAgreementManagerImpl transportKeyAgreementManager) {
+		lifecycleManager.registerOpenDatabaseHook(transportKeyAgreementManager);
+		validationManager.registerIncomingMessageHook(CLIENT_ID,
+				MAJOR_VERSION, transportKeyAgreementManager);
+		contactManager.registerContactHook(transportKeyAgreementManager);
+		clientVersioningManager.registerClient(CLIENT_ID, MAJOR_VERSION,
+				MINOR_VERSION, transportKeyAgreementManager);
+		return transportKeyAgreementManager;
+	}
+
+	@Provides
+	@Singleton
+	TransportKeyAgreementValidator provideTransportKeyAgreementValidator(
+			ClientHelper clientHelper, MetadataEncoder metadataEncoder,
+			Clock clock, MessageEncoder messageEncoder,
+			ValidationManager validationManager) {
+		TransportKeyAgreementValidator validator =
+				new TransportKeyAgreementValidator(clientHelper,
+						metadataEncoder, clock, messageEncoder);
+		validationManager.registerMessageValidator(CLIENT_ID, MAJOR_VERSION,
+				validator);
+		return validator;
+	}
+
+	@Provides
+	MessageEncoder provideMessageEncoder(MessageEncoderImpl messageEncoder) {
+		return messageEncoder;
+	}
+
+	@Provides
+	SessionEncoder provideSessionEncoder(SessionEncoderImpl sessionEncoder) {
+		return sessionEncoder;
+	}
+
+	@Provides
+	SessionParser provideSessionParser(SessionParserImpl sessionParser) {
+		return sessionParser;
+	}
+
+	@Provides
+	TransportKeyAgreementCrypto provideTransportKeyAgreementCrypto(
+			TransportKeyAgreementCryptoImpl transportKeyAgreementCrypto) {
+		return transportKeyAgreementCrypto;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementValidator.java

@@ -0,0 +1,77 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.client.BdfMessageContext;
+import org.briarproject.bramble.api.client.BdfMessageValidator;
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataEncoder;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.system.Clock;
+
+import javax.annotation.concurrent.Immutable;
+
+import static java.util.Collections.singletonList;
+import static org.briarproject.bramble.api.crypto.CryptoConstants.MAX_AGREEMENT_PUBLIC_KEY_BYTES;
+import static org.briarproject.bramble.api.plugin.TransportId.MAX_TRANSPORT_ID_LENGTH;
+import static org.briarproject.bramble.transport.agreement.MessageType.ACTIVATE;
+import static org.briarproject.bramble.transport.agreement.MessageType.KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_PUBLIC_KEY;
+import static org.briarproject.bramble.util.ValidationUtils.checkLength;
+import static org.briarproject.bramble.util.ValidationUtils.checkSize;
+
+@Immutable
+@NotNullByDefault
+class TransportKeyAgreementValidator extends BdfMessageValidator {
+
+	private final MessageEncoder messageEncoder;
+
+	TransportKeyAgreementValidator(ClientHelper clientHelper,
+			MetadataEncoder metadataEncoder, Clock clock,
+			MessageEncoder messageEncoder) {
+		super(clientHelper, metadataEncoder, clock);
+		this.messageEncoder = messageEncoder;
+	}
+
+	@Override
+	protected BdfMessageContext validateMessage(Message m, Group g,
+			BdfList body) throws FormatException {
+		MessageType type = MessageType.fromValue(body.getLong(0).intValue());
+		if (type == KEY) return validateKeyMessage(body);
+		else if (type == ACTIVATE) return validateActivateMessage(body);
+		else throw new AssertionError();
+	}
+
+	private BdfMessageContext validateKeyMessage(BdfList body)
+			throws FormatException {
+		// Message type, transport ID, public key
+		checkSize(body, 3);
+		String transportId = body.getString(1);
+		checkLength(transportId, 1, MAX_TRANSPORT_ID_LENGTH);
+		byte[] publicKey = body.getRaw(2);
+		checkLength(publicKey, 1, MAX_AGREEMENT_PUBLIC_KEY_BYTES);
+		BdfDictionary meta = messageEncoder.encodeMessageMetadata(
+				new TransportId(transportId), KEY, false);
+		meta.put(MSG_KEY_PUBLIC_KEY, publicKey);
+		return new BdfMessageContext(meta);
+	}
+
+	private BdfMessageContext validateActivateMessage(BdfList body)
+			throws FormatException {
+		// Message type, transport ID, previous message ID
+		checkSize(body, 3);
+		String transportId = body.getString(1);
+		checkLength(transportId, 1, MAX_TRANSPORT_ID_LENGTH);
+		byte[] previousMessageId = body.getRaw(2);
+		checkLength(previousMessageId, MessageId.LENGTH);
+		BdfDictionary meta = messageEncoder.encodeMessageMetadata(
+				new TransportId(transportId), ACTIVATE, false);
+		MessageId dependency = new MessageId(previousMessageId);
+		return new BdfMessageContext(meta, singletonList(dependency));
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/versioning/ClientVersioningManagerImpl.java

@@ -50,6 +50,7 @@ import static java.util.Collections.emptyList;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_LOCAL;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_UPDATE_VERSION;
 
@@ -173,8 +174,8 @@ class ClientVersioningManagerImpl implements ClientVersioningManager,
 	}
 
 	@Override
-	public boolean incomingMessage(Transaction txn, Message m, Metadata meta)
-			throws DbException, InvalidMessageException {
+	public DeliveryAction incomingMessage(Transaction txn, Message m,
+			Metadata meta) throws DbException, InvalidMessageException {
 		try {
 			// Parse the new remote update
 			Update newRemoteUpdate = parseUpdate(clientHelper.toList(m));
@@ -187,7 +188,7 @@ class ClientVersioningManagerImpl implements ClientVersioningManager,
 					&& latest.remote.updateVersion > newRemoteUpdateVersion) {
 				db.deleteMessage(txn, m.getId());
 				db.deleteMessageMetadata(txn, m.getId());
-				return false;
+				return ACCEPT_DO_NOT_SHARE;
 			}
 			// Load and parse the latest local update
 			if (latest.local == null) throw new DbException();
@@ -241,7 +242,7 @@ class ClientVersioningManagerImpl implements ClientVersioningManager,
 		} catch (FormatException e) {
 			throw new InvalidMessageException(e);
 		}
-		return false;
+		return ACCEPT_DO_NOT_SHARE;
 	}
 
 	private void storeClientVersions(Transaction txn,

bramble-core/src/main/resources/bridges

@@ -1,3 +1,6 @@
+Bridge obfs4 192.95.36.142:443 CDF2E852BF539B82BD10E27E9115A31734E378C2 cert=qUVQ0srL1JI/vO6V6m/24anYXiJD3QP2HgzUKQtQ7GRqqUvs7P+tG43RtAqdhLOALP7DJQ iat-mode=1
+Bridge obfs4 38.229.1.78:80 C8CBDB2464FC9804A69531437BCF2BE31FDD2EE4 cert=Hmyfd2ev46gGY7NoVxA9ngrPF2zCZtzskRTzoWXbxNkzeVnGFPWmrTtILRyqCTjHR+s9dg iat-mode=1
+Bridge obfs4 38.229.33.83:80 0BAC39417268B96B9F514E7F63FA6FBA1A788955 cert=VwEFpk9F/UN9JED7XpG1XOjm/O8ZCXK80oPecgWnNDZDv5pdkhq1OpbAH0wNqOT6H6BmRQ iat-mode=1
 Bridge obfs4 37.218.245.14:38224 D9A82D2F9C2F65A18407B1D2B764F130847F8B5D cert=bjRaMrr1BRiAW8IE9U5z27fQaYgOhX1UCmOpg2pFpoMvo6ZgQMzLsaTzzQNTlm7hNcb+Sg iat-mode=0
 Bridge obfs4 85.31.186.26:443 91A6354697E6B02A386312F68D82CF86824D3606 cert=PBwr+S8JTVZo6MPdHnkTwXJPILWADLqfMGoVvhZClMq/Urndyd42BwX9YFJHZnBB3H0XCw iat-mode=0
 Bridge obfs4 193.11.166.194:27015 2D82C2E354D531A68469ADF7F878FA6060C6BACA cert=4TLQPJrTSaDffMK7Nbao6LC7G9OW/NHkUwIdjLSS3KYf0Nv4/nQiiI8dY2TcsQx01NniOg iat-mode=0

bramble-core/src/test/java/org/briarproject/bramble/db/DatabaseComponentImplTest.java

@@ -298,11 +298,11 @@ public class DatabaseComponentImplTest extends BrambleMockTestCase {
 			throws Exception {
 		context.checking(new Expectations() {{
 			// Check whether the contact is in the DB (which it's not)
-			exactly(18).of(database).startTransaction();
+			exactly(19).of(database).startTransaction();
 			will(returnValue(txn));
-			exactly(18).of(database).containsContact(txn, contactId);
+			exactly(19).of(database).containsContact(txn, contactId);
 			will(returnValue(false));
-			exactly(18).of(database).abortTransaction(txn);
+			exactly(19).of(database).abortTransaction(txn);
 		}});
 		DatabaseComponent db = createDatabaseComponent(database, eventBus,
 				eventExecutor, shutdownManager);
@@ -349,7 +349,7 @@ public class DatabaseComponentImplTest extends BrambleMockTestCase {
 		}
 
 		try {
-			db.transaction(false, transaction ->
+			db.transaction(true, transaction ->
 					db.getContact(transaction, contactId));
 			fail();
 		} catch (NoSuchContactException expected) {
@@ -357,7 +357,15 @@ public class DatabaseComponentImplTest extends BrambleMockTestCase {
 		}
 
 		try {
-			db.transaction(false, transaction ->
+			db.transaction(true, transaction ->
+					db.getUnackedMessageBytesToSend(transaction, contactId));
+			fail();
+		} catch (NoSuchContactException expected) {
+			// Expected
+		}
+
+		try {
+			db.transaction(true, transaction ->
 					db.getMessageStatus(transaction, contactId, groupId));
 			fail();
 		} catch (NoSuchContactException expected) {
@@ -365,7 +373,7 @@ public class DatabaseComponentImplTest extends BrambleMockTestCase {
 		}
 
 		try {
-			db.transaction(false, transaction ->
+			db.transaction(true, transaction ->
 					db.getMessageStatus(transaction, contactId, messageId));
 			fail();
 		} catch (NoSuchContactException expected) {
@@ -373,7 +381,7 @@ public class DatabaseComponentImplTest extends BrambleMockTestCase {
 		}
 
 		try {
-			db.transaction(false, transaction ->
+			db.transaction(true, transaction ->
 					db.getGroupVisibility(transaction, contactId, groupId));
 			fail();
 		} catch (NoSuchContactException expected) {
@@ -381,7 +389,7 @@ public class DatabaseComponentImplTest extends BrambleMockTestCase {
 		}
 
 		try {
-			db.transaction(false, transaction ->
+			db.transaction(true, transaction ->
 					db.getSyncVersions(transaction, contactId));
 			fail();
 		} catch (NoSuchContactException expected) {

bramble-core/src/test/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

@@ -57,6 +57,7 @@ import java.util.concurrent.atomic.AtomicLong;
 
 import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.singleton;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
 import static java.util.concurrent.TimeUnit.SECONDS;
@@ -222,18 +223,13 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessage(txn, message, DELIVERED, true, false, null);
 
 		// The contact has not seen the message, so it should be sendable
-		Collection<MessageId> ids =
-				db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
+		assertOneMessageToSendEagerly(db, txn);
+		assertOneMessageToSendLazily(db, txn);
 
 		// Changing the status to seen = true should make the message unsendable
 		db.raiseSeenFlag(txn, contactId, messageId);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendEagerly(db, txn);
+		assertNothingToSendLazily(db, txn);
 
 		db.commitTransaction(txn);
 		db.close();
@@ -253,32 +249,23 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessage(txn, message, UNKNOWN, true, false, null);
 
 		// The message has not been validated, so it should not be sendable
-		Collection<MessageId> ids = db.getMessagesToSend(txn, contactId,
-				ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Marking the message delivered should make it sendable
 		db.setMessageState(txn, messageId, DELIVERED);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
+		assertOneMessageToSendLazily(db, txn);
+		assertOneMessageToSendEagerly(db, txn);
 
 		// Marking the message invalid should make it unsendable
 		db.setMessageState(txn, messageId, INVALID);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Marking the message pending should make it unsendable
 		db.setMessageState(txn, messageId, PENDING);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		db.commitTransaction(txn);
 		db.close();
@@ -297,39 +284,28 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessage(txn, message, DELIVERED, true, false, null);
 
 		// The group is invisible, so the message should not be sendable
-		Collection<MessageId> ids = db.getMessagesToSend(txn, contactId,
-				ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Making the group visible should not make the message sendable
 		db.addGroupVisibility(txn, contactId, groupId, false);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Sharing the group should make the message sendable
 		db.setGroupVisibility(txn, contactId, groupId, true);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
+		assertOneMessageToSendEagerly(db, txn);
+		assertOneMessageToSendLazily(db, txn);
 
 		// Unsharing the group should make the message unsendable
 		db.setGroupVisibility(txn, contactId, groupId, false);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Making the group invisible should make the message unsendable
 		db.removeGroupVisibility(txn, contactId, groupId);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		db.commitTransaction(txn);
 		db.close();
@@ -349,18 +325,13 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessage(txn, message, DELIVERED, false, false, null);
 
 		// The message is not shared, so it should not be sendable
-		Collection<MessageId> ids = db.getMessagesToSend(txn, contactId,
-				ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Sharing the message should make it sendable
 		db.setMessageShared(txn, messageId, true);
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
+		assertOneMessageToSendLazily(db, txn);
+		assertOneMessageToSendEagerly(db, txn);
 
 		db.commitTransaction(txn);
 		db.close();
@@ -380,10 +351,13 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessage(txn, message, DELIVERED, true, false, null);
 
 		// The message is sendable, but too large to send
+		assertOneMessageToSendLazily(db, txn);
+		assertOneMessageToSendEagerly(db, txn);
 		Collection<MessageId> ids =
 				db.getMessagesToSend(txn, contactId, message.getRawLength() - 1,
 						MAX_LATENCY);
 		assertTrue(ids.isEmpty());
+
 		// The message is just the right size to send
 		ids = db.getMessagesToSend(txn, contactId, message.getRawLength(),
 				MAX_LATENCY);
@@ -405,6 +379,12 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addGroup(txn, group);
 		db.addGroupVisibility(txn, contactId, groupId, false);
 
+		// Initially there should be nothing to send
+		assertFalse(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, false));
+		assertFalse(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, true));
+
 		// Add some messages to ack
 		Message message1 = getMessage(groupId);
 		MessageId messageId1 = message1.getId();
@@ -412,6 +392,10 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessage(txn, message1, DELIVERED, true, false, contactId);
 
 		// Both message IDs should be returned
+		assertTrue(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, false));
+		assertTrue(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, true));
 		Collection<MessageId> ids = db.getMessagesToAck(txn, contactId, 1234);
 		assertEquals(asList(messageId, messageId1), ids);
 
@@ -419,6 +403,10 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.lowerAckFlag(txn, contactId, asList(messageId, messageId1));
 
 		// Both message IDs should have been removed
+		assertFalse(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, false));
+		assertFalse(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, true));
 		assertEquals(emptyList(), db.getMessagesToAck(txn,
 				contactId, 1234));
 
@@ -427,6 +415,10 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.raiseAckFlag(txn, contactId, messageId1);
 
 		// Both message IDs should be returned
+		assertTrue(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, false));
+		assertTrue(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, true));
 		ids = db.getMessagesToAck(txn, contactId, 1234);
 		assertEquals(asList(messageId, messageId1), ids);
 
@@ -447,22 +439,25 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addGroupVisibility(txn, contactId, groupId, true);
 		db.addMessage(txn, message, DELIVERED, true, false, null);
 
-		// Retrieve the message from the database and mark it as sent
-		Collection<MessageId> ids = db.getMessagesToSend(txn, contactId,
-				ONE_MEGABYTE, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
+		// The message should be sendable via lazy or eager retransmission
+		assertOneMessageToSendLazily(db, txn);
+		assertOneMessageToSendEagerly(db, txn);
+
+		// Mark the message as sent
 		db.updateExpiryTimeAndEta(txn, contactId, messageId, MAX_LATENCY);
 
-		// The message should no longer be sendable
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		// The message should no longer be sendable via lazy retransmission,
+		// but it should still be sendable via eager retransmission
+		assertNothingToSendLazily(db, txn);
+		assertOneMessageToSendEagerly(db, txn);
 
-		// Pretend that the message was acked
+		// Mark the message as acked
 		db.raiseSeenFlag(txn, contactId, messageId);
 
-		// The message still should not be sendable
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		// The message still should not be sendable via lazy or eager
+		// retransmission
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		db.commitTransaction(txn);
 		db.close();
@@ -676,7 +671,9 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		Connection txn = db.startTransaction();
 
 		// Initially there should be no transport keys in the database
+		assertFalse(db.containsTransportKeys(txn, contactId, transportId));
 		assertEquals(emptyList(), db.getTransportKeys(txn, transportId));
+		assertTrue(db.getTransportsWithKeys(txn).isEmpty());
 
 		// Add the contact, the transport and the transport keys
 		db.addIdentity(txn, identity);
@@ -687,6 +684,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		assertEquals(keySetId1, db.addTransportKeys(txn, contactId, keys1));
 
 		// Retrieve the transport keys
+		assertTrue(db.containsTransportKeys(txn, contactId, transportId));
 		Collection<TransportKeySet> allKeys =
 				db.getTransportKeys(txn, transportId);
 		assertEquals(2, allKeys.size());
@@ -699,6 +697,8 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 				assertKeysEquals(keys1, ks.getKeys());
 			}
 		}
+		assertEquals(singletonMap(contactId, singletonList(transportId)),
+				db.getTransportsWithKeys(txn));
 
 		// Update the transport keys
 		TransportKeys updated = createTransportKeys(timePeriod + 1, active);
@@ -710,6 +710,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 				null, updated1));
 
 		// Retrieve the transport keys again
+		assertTrue(db.containsTransportKeys(txn, contactId, transportId));
 		allKeys = db.getTransportKeys(txn, transportId);
 		assertEquals(2, allKeys.size());
 		for (TransportKeySet ks : allKeys) {
@@ -721,10 +722,14 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 				assertKeysEquals(updated1, ks.getKeys());
 			}
 		}
+		assertEquals(singletonMap(contactId, singletonList(transportId)),
+				db.getTransportsWithKeys(txn));
 
 		// Removing the contact should remove the transport keys
 		db.removeContact(txn, contactId);
+		assertFalse(db.containsTransportKeys(txn, contactId, transportId));
 		assertEquals(emptyList(), db.getTransportKeys(txn, transportId));
+		assertTrue(db.getTransportsWithKeys(txn).isEmpty());
 
 		db.commitTransaction(txn);
 		db.close();
@@ -1925,11 +1930,8 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		assertTrue(db.containsVisibleMessage(txn, contactId, messageId));
 
 		// The message should be sendable
-		Collection<MessageId> ids = db.getMessagesToSend(txn, contactId,
-				ONE_MEGABYTE, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertEquals(singletonList(messageId), ids);
+		assertOneMessageToSendLazily(db, txn);
+		assertOneMessageToSendEagerly(db, txn);
 
 		// The message should be available
 		Message m = db.getMessage(txn, messageId);
@@ -1945,10 +1947,8 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		assertTrue(db.containsVisibleMessage(txn, contactId, messageId));
 
 		// The message should not be sendable
-		ids = db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
-		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
-		assertTrue(ids.isEmpty());
+		assertNothingToSendLazily(db, txn);
+		assertNothingToSendEagerly(db, txn);
 
 		// Requesting the message should throw an exception
 		try {
@@ -2577,6 +2577,50 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		deleteTestDirectory(testDir);
 	}
 
+	private void assertNothingToSendLazily(Database<Connection> db,
+			Connection txn) throws Exception {
+		assertFalse(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, false));
+		Collection<MessageId> ids =
+				db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
+		assertTrue(ids.isEmpty());
+		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
+		assertTrue(ids.isEmpty());
+	}
+
+	private void assertOneMessageToSendLazily(Database<Connection> db,
+			Connection txn) throws Exception {
+		assertTrue(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, false));
+		Collection<MessageId> ids =
+				db.getMessagesToSend(txn, contactId, ONE_MEGABYTE, MAX_LATENCY);
+		assertEquals(singletonList(messageId), ids);
+		ids = db.getMessagesToOffer(txn, contactId, 100, MAX_LATENCY);
+		assertEquals(singletonList(messageId), ids);
+	}
+
+	private void assertNothingToSendEagerly(Database<Connection> db,
+			Connection txn) throws Exception {
+		assertFalse(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, true));
+		Map<MessageId, Integer> unacked =
+				db.getUnackedMessagesToSend(txn, contactId);
+		assertTrue(unacked.isEmpty());
+		assertEquals(0, db.getUnackedMessageBytesToSend(txn, contactId));
+	}
+
+	private void assertOneMessageToSendEagerly(Database<Connection> db,
+			Connection txn) throws Exception {
+		assertTrue(
+				db.containsAnythingToSend(txn, contactId, MAX_LATENCY, true));
+		Map<MessageId, Integer> unacked =
+				db.getUnackedMessagesToSend(txn, contactId);
+		assertEquals(singleton(messageId), unacked.keySet());
+		assertEquals(message.getRawLength(), unacked.get(messageId).intValue());
+		assertEquals(message.getRawLength(),
+				db.getUnackedMessageBytesToSend(txn, contactId));
+	}
+
 	private static class StoppedClock implements Clock {
 
 		private final long time;

bramble-core/src/test/java/org/briarproject/bramble/plugin/file/RemovableDriveIntegrationTest.java

@@ -0,0 +1,168 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.event.EventListener;
+import org.briarproject.bramble.api.identity.Author;
+import org.briarproject.bramble.api.identity.Identity;
+import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
+import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.api.sync.event.MessageStateChangedEvent;
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.briarproject.bramble.test.TestDatabaseConfigModule;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.File;
+import java.util.concurrent.CountDownLatch;
+
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static org.briarproject.bramble.api.plugin.file.FileConstants.PROP_PATH;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
+import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
+import static org.briarproject.bramble.test.TestUtils.getSecretKey;
+import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.junit.Assert.assertTrue;
+
+public class RemovableDriveIntegrationTest extends BrambleTestCase {
+
+	private static final int TIMEOUT_MS = 5_000;
+
+	private final File testDir = getTestDirectory();
+	private final File aliceDir = new File(testDir, "alice");
+	private final File bobDir = new File(testDir, "bob");
+
+	private final SecretKey rootKey = getSecretKey();
+	private final long timestamp = System.currentTimeMillis();
+
+	private RemovableDriveIntegrationTestComponent alice, bob;
+
+	@Before
+	public void setUp() {
+		assertTrue(testDir.mkdirs());
+		alice = DaggerRemovableDriveIntegrationTestComponent.builder()
+				.testDatabaseConfigModule(
+						new TestDatabaseConfigModule(aliceDir)).build();
+		RemovableDriveIntegrationTestComponent.Helper
+				.injectEagerSingletons(alice);
+		bob = DaggerRemovableDriveIntegrationTestComponent.builder()
+				.testDatabaseConfigModule(
+						new TestDatabaseConfigModule(bobDir)).build();
+		RemovableDriveIntegrationTestComponent.Helper
+				.injectEagerSingletons(bob);
+	}
+
+	@Test
+	public void testWriteAndRead() throws Exception {
+		// Create the identities
+		Identity aliceIdentity =
+				alice.getIdentityManager().createIdentity("Alice");
+		Identity bobIdentity = bob.getIdentityManager().createIdentity("Bob");
+		// Set up the devices and get the contact IDs
+		ContactId bobId = setUp(alice, aliceIdentity,
+				bobIdentity.getLocalAuthor(), true);
+		ContactId aliceId = setUp(bob, bobIdentity,
+				aliceIdentity.getLocalAuthor(), false);
+		// Sync Alice's client versions and transport properties
+		read(bob, write(alice, bobId), 2);
+		// Sync Bob's client versions and transport properties
+		read(alice, write(bob, aliceId), 2);
+	}
+
+	private ContactId setUp(RemovableDriveIntegrationTestComponent device,
+			Identity local, Author remote, boolean alice) throws Exception {
+		// Add an identity for the user
+		IdentityManager identityManager = device.getIdentityManager();
+		identityManager.registerIdentity(local);
+		// Start the lifecycle manager
+		LifecycleManager lifecycleManager = device.getLifecycleManager();
+		lifecycleManager.startServices(getSecretKey());
+		lifecycleManager.waitForStartup();
+		// Add the other user as a contact
+		ContactManager contactManager = device.getContactManager();
+		return contactManager.addContact(remote, local.getId(), rootKey,
+				timestamp, alice, true, true);
+	}
+
+	@SuppressWarnings("SameParameterValue")
+	private void read(RemovableDriveIntegrationTestComponent device,
+			File file, int deliveries) throws Exception {
+		// Listen for message deliveries
+		MessageDeliveryListener listener =
+				new MessageDeliveryListener(deliveries);
+		device.getEventBus().addListener(listener);
+		// Read the incoming stream
+		TransportProperties p = new TransportProperties();
+		p.put(PROP_PATH, file.getAbsolutePath());
+		RemovableDriveTask reader =
+				device.getRemovableDriveManager().startReaderTask(p);
+		CountDownLatch disposedLatch = new CountDownLatch(1);
+		reader.addObserver(state -> {
+			if (state.isFinished()) disposedLatch.countDown();
+		});
+		// Wait for the messages to be delivered
+		assertTrue(listener.delivered.await(TIMEOUT_MS, MILLISECONDS));
+		// Clean up the listener
+		device.getEventBus().removeListener(listener);
+		// Wait for the reader to be disposed
+		disposedLatch.await(TIMEOUT_MS, MILLISECONDS);
+	}
+
+	private File write(RemovableDriveIntegrationTestComponent device,
+			ContactId contactId) throws Exception {
+		// Write the outgoing stream to a file
+		File file = File.createTempFile("sync", ".tmp", testDir);
+		TransportProperties p = new TransportProperties();
+		p.put(PROP_PATH, file.getAbsolutePath());
+		RemovableDriveTask writer = device.getRemovableDriveManager()
+				.startWriterTask(contactId, p);
+		CountDownLatch disposedLatch = new CountDownLatch(1);
+		writer.addObserver(state -> {
+			if (state.isFinished()) disposedLatch.countDown();
+		});
+		// Wait for the writer to be disposed
+		disposedLatch.await(TIMEOUT_MS, MILLISECONDS);
+		// Return the file containing the stream
+		return file;
+	}
+
+	private void tearDown(RemovableDriveIntegrationTestComponent device)
+			throws Exception {
+		// Stop the lifecycle manager
+		LifecycleManager lifecycleManager = device.getLifecycleManager();
+		lifecycleManager.stopServices();
+		lifecycleManager.waitForShutdown();
+	}
+
+	@After
+	public void tearDown() throws Exception {
+		// Tear down the devices
+		tearDown(alice);
+		tearDown(bob);
+		deleteTestDirectory(testDir);
+	}
+
+	@NotNullByDefault
+	private static class MessageDeliveryListener implements EventListener {
+
+		private final CountDownLatch delivered;
+
+		private MessageDeliveryListener(int deliveries) {
+			delivered = new CountDownLatch(deliveries);
+		}
+
+		@Override
+		public void eventOccurred(Event e) {
+			if (e instanceof MessageStateChangedEvent) {
+				MessageStateChangedEvent m = (MessageStateChangedEvent) e;
+				if (m.getState().equals(DELIVERED)) delivered.countDown();
+			}
+		}
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/plugin/file/RemovableDriveIntegrationTestComponent.java

@@ -0,0 +1,53 @@
+package org.briarproject.bramble.plugin.file;
+
+import org.briarproject.bramble.BrambleCoreEagerSingletons;
+import org.briarproject.bramble.BrambleCoreModule;
+import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.plugin.file.RemovableDriveManager;
+import org.briarproject.bramble.battery.DefaultBatteryManagerModule;
+import org.briarproject.bramble.event.DefaultEventExecutorModule;
+import org.briarproject.bramble.system.DefaultWakefulIoExecutorModule;
+import org.briarproject.bramble.system.TimeTravelModule;
+import org.briarproject.bramble.test.TestDatabaseConfigModule;
+import org.briarproject.bramble.test.TestSecureRandomModule;
+
+import javax.inject.Singleton;
+
+import dagger.Component;
+
+@Singleton
+@Component(modules = {
+		BrambleCoreModule.class,
+		DefaultBatteryManagerModule.class,
+		DefaultEventExecutorModule.class,
+		DefaultWakefulIoExecutorModule.class,
+		TestDatabaseConfigModule.class,
+		RemovableDriveIntegrationTestModule.class,
+		RemovableDriveModule.class,
+		TestSecureRandomModule.class,
+		TimeTravelModule.class
+})
+interface RemovableDriveIntegrationTestComponent
+		extends BrambleCoreEagerSingletons {
+
+	ContactManager getContactManager();
+
+	EventBus getEventBus();
+
+	IdentityManager getIdentityManager();
+
+	LifecycleManager getLifecycleManager();
+
+	RemovableDriveManager getRemovableDriveManager();
+
+	class Helper {
+
+		public static void injectEagerSingletons(
+				RemovableDriveIntegrationTestComponent c) {
+			BrambleCoreEagerSingletons.Helper.injectEagerSingletons(c);
+		}
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/plugin/file/RemovableDriveIntegrationTestModule.java

@@ -1,61 +1,81 @@
-package org.briarproject.bramble.plugin;
+package org.briarproject.bramble.plugin.file;
 
+import org.briarproject.bramble.api.FeatureFlags;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.BluetoothConstants;
-import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
-import org.briarproject.bramble.plugin.bluetooth.JavaBluetoothPluginFactory;
-import org.briarproject.bramble.plugin.modem.ModemPluginFactory;
-import org.briarproject.bramble.plugin.tcp.LanTcpPluginFactory;
-import org.briarproject.bramble.plugin.tcp.WanTcpPluginFactory;
 
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
+import javax.inject.Singleton;
+
 import dagger.Module;
 import dagger.Provides;
 
-import static java.util.Arrays.asList;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
-import static java.util.Collections.singletonMap;
 
 @Module
-public class DesktopPluginModule extends PluginModule {
+class RemovableDriveIntegrationTestModule {
 
 	@Provides
-	PluginConfig getPluginConfig(JavaBluetoothPluginFactory bluetooth,
-			ModemPluginFactory modem, LanTcpPluginFactory lan,
-			WanTcpPluginFactory wan) {
+	@Singleton
+	PluginConfig providePluginConfig(RemovableDrivePluginFactory drive) {
 		@NotNullByDefault
 		PluginConfig pluginConfig = new PluginConfig() {
 
 			@Override
 			public Collection<DuplexPluginFactory> getDuplexFactories() {
-				return asList(bluetooth, modem, lan, wan);
-			}
-
-			@Override
-			public Collection<SimplexPluginFactory> getSimplexFactories() {
 				return emptyList();
 			}
 
+			@Override
+			public Collection<SimplexPluginFactory> getSimplexFactories() {
+				return singletonList(drive);
+			}
+
 			@Override
 			public boolean shouldPoll() {
-				return true;
+				return false;
 			}
 
 			@Override
 			public Map<TransportId, List<TransportId>> getTransportPreferences() {
-				// Prefer LAN to Bluetooth
-				return singletonMap(BluetoothConstants.ID,
-						singletonList(LanTcpConstants.ID));
+				return emptyMap();
 			}
+
 		};
 		return pluginConfig;
 	}
+
+	@Provides
+	FeatureFlags provideFeatureFlags() {
+		return new FeatureFlags() {
+
+			@Override
+			public boolean shouldEnableImageAttachments() {
+				return true;
+			}
+
+			@Override
+			public boolean shouldEnableProfilePictures() {
+				return true;
+			}
+
+			@Override
+			public boolean shouldEnableDisappearingMessages() {
+				return true;
+			}
+
+			@Override
+			public boolean shouldEnableConnectViaBluetooth() {
+				return true;
+			}
+		};
+	}
 }

bramble-core/src/test/java/org/briarproject/bramble/properties/TransportPropertyManagerImplTest.java

@@ -43,6 +43,7 @@ import static org.briarproject.bramble.api.properties.TransportPropertyConstants
 import static org.briarproject.bramble.api.properties.TransportPropertyManager.CLIENT_ID;
 import static org.briarproject.bramble.api.properties.TransportPropertyManager.MAJOR_VERSION;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
 import static org.briarproject.bramble.test.TestUtils.getContact;
 import static org.briarproject.bramble.test.TestUtils.getGroup;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
@@ -230,7 +231,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
-		assertFalse(t.incomingMessage(txn, message, meta));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				t.incomingMessage(txn, message, meta));
 		assertTrue(hasEvent(txn, RemoteTransportPropertiesUpdatedEvent.class));
 	}
 
@@ -269,7 +271,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
-		assertFalse(t.incomingMessage(txn, message, meta));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				t.incomingMessage(txn, message, meta));
 		assertTrue(hasEvent(txn, RemoteTransportPropertiesUpdatedEvent.class));
 	}
 
@@ -308,7 +311,8 @@ public class TransportPropertyManagerImplTest extends BrambleMockTestCase {
 		}});
 
 		TransportPropertyManagerImpl t = createInstance();
-		assertFalse(t.incomingMessage(txn, message, meta));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				t.incomingMessage(txn, message, meta));
 		assertFalse(hasEvent(txn, RemoteTransportPropertiesUpdatedEvent.class));
 	}
 

bramble-core/src/test/java/org/briarproject/bramble/sync/SimplexOutgoingSessionTest.java

@@ -17,9 +17,14 @@ import org.briarproject.bramble.test.DbExpectations;
 import org.briarproject.bramble.test.ImmediateExecutor;
 import org.junit.Test;
 
+import java.util.LinkedHashMap;
+import java.util.Map;
 import java.util.concurrent.Executor;
 
+import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
+import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTES;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.test.TestUtils.getContactId;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
@@ -39,14 +44,19 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 	private final Executor dbExecutor = new ImmediateExecutor();
 	private final ContactId contactId = getContactId();
 	private final TransportId transportId = getTransportId();
-	private final Message message = getMessage(new GroupId(getRandomId()));
-	private final MessageId messageId = message.getId();
+	private final Ack ack =
+			new Ack(singletonList(new MessageId(getRandomId())));
+	private final Message message = getMessage(new GroupId(getRandomId()),
+			MAX_MESSAGE_BODY_LENGTH);
+	private final Message message1 = getMessage(new GroupId(getRandomId()),
+			MAX_MESSAGE_BODY_LENGTH);
 
 	@Test
 	public void testNothingToSend() throws Exception {
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
 				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
-				streamWriter, recordWriter);
+				false, streamWriter, recordWriter);
+
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction noMsgTxn = new Transaction(null, false);
 
@@ -63,8 +73,8 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 			// No messages to send
 			oneOf(db).transactionWithNullableResult(with(false),
 					withNullableDbCallable(noMsgTxn));
-			oneOf(db).generateBatch(with(noMsgTxn), with(contactId),
-					with(any(int.class)), with(MAX_LATENCY));
+			oneOf(db).generateBatch(noMsgTxn, contactId,
+					MAX_RECORD_PAYLOAD_BYTES, MAX_LATENCY);
 			will(returnValue(null));
 			// Send the end of stream marker
 			oneOf(streamWriter).sendEndOfStream();
@@ -76,11 +86,44 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 	}
 
 	@Test
-	public void testSomethingToSend() throws Exception {
-		Ack ack = new Ack(singletonList(messageId));
+	public void testNothingToSendEagerly() throws Exception {
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
 				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
-				streamWriter, recordWriter);
+				true, streamWriter, recordWriter);
+
+		Transaction noAckTxn = new Transaction(null, false);
+		Transaction noIdsTxn = new Transaction(null, true);
+
+		context.checking(new DbExpectations() {{
+			// Add listener
+			oneOf(eventBus).addListener(session);
+			// Send the protocol versions
+			oneOf(recordWriter).writeVersions(with(any(Versions.class)));
+			// No acks to send
+			oneOf(db).transactionWithNullableResult(with(false),
+					withNullableDbCallable(noAckTxn));
+			oneOf(db).generateAck(noAckTxn, contactId, MAX_MESSAGE_IDS);
+			will(returnValue(null));
+			// No messages to send
+			oneOf(db).transactionWithResult(with(true),
+					withDbCallable(noIdsTxn));
+			oneOf(db).getUnackedMessagesToSend(noIdsTxn, contactId);
+			will(returnValue(emptyMap()));
+			// Send the end of stream marker
+			oneOf(streamWriter).sendEndOfStream();
+			// Remove listener
+			oneOf(eventBus).removeListener(session);
+		}});
+
+		session.run();
+	}
+
+	@Test
+	public void testSomethingToSend() throws Exception {
+		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
+				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
+				false, streamWriter, recordWriter);
+
 		Transaction ackTxn = new Transaction(null, false);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction msgTxn = new Transaction(null, false);
@@ -100,8 +143,8 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 			// One message to send
 			oneOf(db).transactionWithNullableResult(with(false),
 					withNullableDbCallable(msgTxn));
-			oneOf(db).generateBatch(with(msgTxn), with(contactId),
-					with(any(int.class)), with(MAX_LATENCY));
+			oneOf(db).generateBatch(msgTxn, contactId,
+					MAX_RECORD_PAYLOAD_BYTES, MAX_LATENCY);
 			will(returnValue(singletonList(message)));
 			oneOf(recordWriter).writeMessage(message);
 			// No more acks
@@ -112,8 +155,8 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 			// No more messages
 			oneOf(db).transactionWithNullableResult(with(false),
 					withNullableDbCallable(noMsgTxn));
-			oneOf(db).generateBatch(with(noMsgTxn), with(contactId),
-					with(any(int.class)), with(MAX_LATENCY));
+			oneOf(db).generateBatch(noMsgTxn, contactId,
+					MAX_RECORD_PAYLOAD_BYTES, MAX_LATENCY);
 			will(returnValue(null));
 			// Send the end of stream marker
 			oneOf(streamWriter).sendEndOfStream();
@@ -123,4 +166,63 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
 		session.run();
 	}
+
+	@Test
+	public void testSomethingToSendEagerly() throws Exception {
+		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
+				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
+				true, streamWriter, recordWriter);
+
+		Map<MessageId, Integer> unacked = new LinkedHashMap<>();
+		unacked.put(message.getId(), message.getRawLength());
+		unacked.put(message1.getId(), message1.getRawLength());
+
+		Transaction ackTxn = new Transaction(null, false);
+		Transaction noAckTxn = new Transaction(null, false);
+		Transaction idsTxn = new Transaction(null, true);
+		Transaction msgTxn = new Transaction(null, false);
+		Transaction msgTxn1 = new Transaction(null, false);
+
+		context.checking(new DbExpectations() {{
+			// Add listener
+			oneOf(eventBus).addListener(session);
+			// Send the protocol versions
+			oneOf(recordWriter).writeVersions(with(any(Versions.class)));
+			// One ack to send
+			oneOf(db).transactionWithNullableResult(with(false),
+					withNullableDbCallable(ackTxn));
+			oneOf(db).generateAck(ackTxn, contactId, MAX_MESSAGE_IDS);
+			will(returnValue(ack));
+			oneOf(recordWriter).writeAck(ack);
+			// No more acks
+			oneOf(db).transactionWithNullableResult(with(false),
+					withNullableDbCallable(noAckTxn));
+			oneOf(db).generateAck(noAckTxn, contactId, MAX_MESSAGE_IDS);
+			will(returnValue(null));
+			// Two messages to send
+			oneOf(db).transactionWithResult(with(true), withDbCallable(idsTxn));
+			oneOf(db).getUnackedMessagesToSend(idsTxn, contactId);
+			will(returnValue(unacked));
+			// Send the first message
+			oneOf(db).transactionWithResult(with(false),
+					withDbCallable(msgTxn));
+			oneOf(db).generateBatch(msgTxn, contactId,
+					singletonList(message.getId()), MAX_LATENCY);
+			will(returnValue(singletonList(message)));
+			oneOf(recordWriter).writeMessage(message);
+			// Send the second message
+			oneOf(db).transactionWithResult(with(false),
+					withDbCallable(msgTxn1));
+			oneOf(db).generateBatch(msgTxn1, contactId,
+					singletonList(message1.getId()), MAX_LATENCY);
+			will(returnValue(singletonList(message1)));
+			oneOf(recordWriter).writeMessage(message1);
+			// Send the end of stream marker
+			oneOf(streamWriter).sendEndOfStream();
+			// Remove listener
+			oneOf(eventBus).removeListener(session);
+		}});
+
+		session.run();
+	}
 }

bramble-core/src/test/java/org/briarproject/bramble/sync/validation/ValidationManagerImplTest.java

@@ -31,6 +31,8 @@ import static java.util.Arrays.asList;
 import static java.util.Collections.emptyMap;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_SHARE;
 import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
 import static org.briarproject.bramble.api.sync.validation.MessageState.INVALID;
 import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
@@ -111,7 +113,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the first message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
@@ -167,7 +169,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(new Metadata()));
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn, message, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn, messageId, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn, messageId);
@@ -187,7 +189,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(metadata));
 			// Deliver the dependent
 			oneOf(hook).incomingMessage(txn1, message2, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId2, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId2);
@@ -247,7 +249,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
-			will(returnValue(true));
+			will(returnValue(ACCEPT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
@@ -367,7 +369,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
@@ -432,7 +434,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);
@@ -602,7 +604,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId, DELIVERED);
 			// The message has two pending dependents: 1 and 2
 			oneOf(db).getMessageDependents(txn1, messageId);
@@ -622,7 +624,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(metadata));
 			// Deliver message 1
 			oneOf(hook).incomingMessage(txn2, message1, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn2, messageId1, DELIVERED);
 			// Message 1 has one pending dependent: 3
 			oneOf(db).getMessageDependents(txn2, messageId1);
@@ -642,7 +644,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(metadata));
 			// Deliver message 2
 			oneOf(hook).incomingMessage(txn3, message2, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn3, messageId2, DELIVERED);
 			// Message 2 has one pending dependent: 3 (same dependent as 1)
 			oneOf(db).getMessageDependents(txn3, messageId2);
@@ -662,6 +664,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(metadata));
 			// Deliver message 3
 			oneOf(hook).incomingMessage(txn4, message3, metadata);
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn4, messageId3, DELIVERED);
 			// Message 3 has one pending dependent: 4
 			oneOf(db).getMessageDependents(txn4, messageId3);
@@ -685,7 +688,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			will(returnValue(metadata));
 			// Deliver message 4
 			oneOf(hook).incomingMessage(txn6, message4, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn6, messageId4, DELIVERED);
 			// Message 4 has no pending dependents
 			oneOf(db).getMessageDependents(txn6, messageId4);
@@ -717,7 +720,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 			oneOf(db).mergeMessageMetadata(txn1, messageId, metadata);
 			// Deliver the message
 			oneOf(hook).incomingMessage(txn1, message, metadata);
-			will(returnValue(false));
+			will(returnValue(ACCEPT_DO_NOT_SHARE));
 			oneOf(db).setMessageState(txn1, messageId, DELIVERED);
 			// Get any pending dependents
 			oneOf(db).getMessageDependents(txn1, messageId);

bramble-core/src/test/java/org/briarproject/bramble/test/TestDuplexTransportConnection.java

@@ -25,7 +25,7 @@ public class TestDuplexTransportConnection
 	@SuppressWarnings("WeakerAccess")
 	public TestDuplexTransportConnection(InputStream in, OutputStream out) {
 		reader = new TestTransportConnectionReader(in);
-		writer = new TestTransportConnectionWriter(out);
+		writer = new TestTransportConnectionWriter(out, false);
 	}
 
 	@Override

bramble-core/src/test/java/org/briarproject/bramble/test/TestTransportConnectionWriter.java

@@ -15,10 +15,13 @@ public class TestTransportConnectionWriter
 		implements TransportConnectionWriter {
 
 	private final OutputStream out;
+	private final boolean lossyAndCheap;
 	private final CountDownLatch disposed = new CountDownLatch(1);
 
-	public TestTransportConnectionWriter(OutputStream out) {
+	public TestTransportConnectionWriter(OutputStream out,
+			boolean lossyAndCheap) {
 		this.out = out;
+		this.lossyAndCheap = lossyAndCheap;
 	}
 
 	public CountDownLatch getDisposedLatch() {
@@ -35,6 +38,11 @@ public class TestTransportConnectionWriter
 		return 60_000;
 	}
 
+	@Override
+	public boolean isLossyAndCheap() {
+		return lossyAndCheap;
+	}
+
 	@Override
 	public OutputStream getOutputStream() {
 		return out;

bramble-core/src/test/java/org/briarproject/bramble/transport/KeyManagerImplTest.java

@@ -25,6 +25,7 @@ import java.util.Collection;
 import java.util.Map;
 import java.util.Random;
 
+import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.transport.TransportConstants.TAG_LENGTH;
@@ -71,8 +72,7 @@ public class KeyManagerImplTest extends BrambleMockTestCase {
 	private final SecretKey rootKey = getSecretKey();
 	private final Random random = new Random();
 
-	private final KeyManagerImpl keyManager = new KeyManagerImpl(db, executor,
-			pluginConfig, transportKeyManagerFactory, transportCrypto);
+	private KeyManagerImpl keyManager;
 
 	@Before
 	public void testStartService() throws Exception {
@@ -83,18 +83,25 @@ public class KeyManagerImplTest extends BrambleMockTestCase {
 				singletonList(pluginFactory);
 		int maxLatency = 1337;
 
-		context.checking(new DbExpectations() {{
-			oneOf(pluginConfig).getSimplexFactories();
+		context.checking(new Expectations() {{
+			allowing(pluginConfig).getSimplexFactories();
 			will(returnValue(factories));
-			oneOf(pluginFactory).getId();
+			allowing(pluginFactory).getId();
 			will(returnValue(transportId));
-			oneOf(pluginFactory).getMaxLatency();
+			allowing(pluginFactory).getMaxLatency();
 			will(returnValue(maxLatency));
-			oneOf(db).addTransport(txn, transportId, maxLatency);
+			allowing(pluginConfig).getDuplexFactories();
+			will(returnValue(emptyList()));
 			oneOf(transportKeyManagerFactory)
 					.createTransportKeyManager(transportId, maxLatency);
 			will(returnValue(transportKeyManager));
-			oneOf(pluginConfig).getDuplexFactories();
+		}});
+
+		keyManager = new KeyManagerImpl(db, executor,
+				pluginConfig, transportCrypto, transportKeyManagerFactory);
+
+		context.checking(new DbExpectations() {{
+			oneOf(db).addTransport(txn, transportId, maxLatency);
 			oneOf(db).transaction(with(false), withDbRunnable(txn));
 			oneOf(transportKeyManager).start(txn);
 		}});
@@ -235,4 +242,37 @@ public class KeyManagerImplTest extends BrambleMockTestCase {
 		keyManager.eventOccurred(event);
 		executor.runUntilIdle();
 	}
+
+	@Test
+	public void testAddMultipleRotationKeySets() throws Exception {
+		long timestamp = System.currentTimeMillis();
+		boolean alice = random.nextBoolean();
+		boolean active = random.nextBoolean();
+
+		context.checking(new Expectations() {{
+			oneOf(transportKeyManager).addRotationKeys(txn, contactId,
+					rootKey, timestamp, alice, active);
+			will(returnValue(keySetId));
+		}});
+
+		assertEquals(singletonMap(transportId, keySetId),
+				keyManager.addRotationKeys(txn, contactId, rootKey, timestamp,
+						alice, active));
+	}
+
+	@Test
+	public void testAddSingleRotationKeySet() throws Exception {
+		long timestamp = System.currentTimeMillis();
+		boolean alice = random.nextBoolean();
+		boolean active = random.nextBoolean();
+
+		context.checking(new Expectations() {{
+			oneOf(transportKeyManager).addRotationKeys(txn, contactId,
+					rootKey, timestamp, alice, active);
+			will(returnValue(keySetId));
+		}});
+
+		assertEquals(keySetId, keyManager.addRotationKeys(txn, contactId,
+				transportId, rootKey, timestamp, alice, active));
+	}
 }

bramble-core/src/test/java/org/briarproject/bramble/transport/agreement/TransportKeyAgreementManagerImplTest.java

@@ -0,0 +1,554 @@
+package org.briarproject.bramble.transport.agreement;
+
+import org.briarproject.bramble.api.client.ClientHelper;
+import org.briarproject.bramble.api.client.ContactGroupFactory;
+import org.briarproject.bramble.api.contact.Contact;
+import org.briarproject.bramble.api.crypto.KeyPair;
+import org.briarproject.bramble.api.crypto.PublicKey;
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.data.BdfDictionary;
+import org.briarproject.bramble.api.data.BdfEntry;
+import org.briarproject.bramble.api.data.BdfList;
+import org.briarproject.bramble.api.data.MetadataParser;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.Metadata;
+import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.identity.IdentityManager;
+import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.plugin.PluginConfig;
+import org.briarproject.bramble.api.plugin.TransportId;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
+import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.transport.KeyManager;
+import org.briarproject.bramble.api.transport.KeySetId;
+import org.briarproject.bramble.api.versioning.ClientVersioningManager;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.briarproject.bramble.test.CaptureArgumentAction;
+import org.jmock.Expectations;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.concurrent.atomic.AtomicReference;
+
+import static java.lang.Math.min;
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
+import static java.util.Collections.singletonMap;
+import static org.briarproject.bramble.api.Bytes.compare;
+import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.DEFER;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.REJECT;
+import static org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager.CLIENT_ID;
+import static org.briarproject.bramble.api.transport.agreement.TransportKeyAgreementManager.MAJOR_VERSION;
+import static org.briarproject.bramble.test.TestUtils.getAgreementPrivateKey;
+import static org.briarproject.bramble.test.TestUtils.getAgreementPublicKey;
+import static org.briarproject.bramble.test.TestUtils.getContact;
+import static org.briarproject.bramble.test.TestUtils.getGroup;
+import static org.briarproject.bramble.test.TestUtils.getLocalAuthor;
+import static org.briarproject.bramble.test.TestUtils.getMessage;
+import static org.briarproject.bramble.test.TestUtils.getSecretKey;
+import static org.briarproject.bramble.test.TestUtils.getTransportId;
+import static org.briarproject.bramble.transport.agreement.MessageType.ACTIVATE;
+import static org.briarproject.bramble.transport.agreement.MessageType.KEY;
+import static org.briarproject.bramble.transport.agreement.State.ACTIVATED;
+import static org.briarproject.bramble.transport.agreement.State.AWAIT_ACTIVATE;
+import static org.briarproject.bramble.transport.agreement.State.AWAIT_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_MESSAGE_TYPE;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_PUBLIC_KEY;
+import static org.briarproject.bramble.transport.agreement.TransportKeyAgreementConstants.MSG_KEY_TRANSPORT_ID;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+public class TransportKeyAgreementManagerImplTest extends BrambleMockTestCase {
+
+	private final DatabaseComponent db = context.mock(DatabaseComponent.class);
+	private final ClientHelper clientHelper = context.mock(ClientHelper.class);
+	private final MetadataParser metadataParser =
+			context.mock(MetadataParser.class);
+	private final ContactGroupFactory contactGroupFactory =
+			context.mock(ContactGroupFactory.class);
+	private final ClientVersioningManager clientVersioningManager =
+			context.mock(ClientVersioningManager.class);
+	private final IdentityManager identityManager =
+			context.mock(IdentityManager.class);
+	private final KeyManager keyManager = context.mock(KeyManager.class);
+	private final MessageEncoder messageEncoder =
+			context.mock(MessageEncoder.class);
+	private final SessionEncoder sessionEncoder =
+			context.mock(SessionEncoder.class);
+	private final SessionParser sessionParser =
+			context.mock(SessionParser.class);
+	private final TransportKeyAgreementCrypto crypto =
+			context.mock(TransportKeyAgreementCrypto.class);
+	private final PluginConfig pluginConfig = context.mock(PluginConfig.class);
+	private final SimplexPluginFactory simplexFactory =
+			context.mock(SimplexPluginFactory.class);
+	private final DuplexPluginFactory duplexFactory =
+			context.mock(DuplexPluginFactory.class);
+
+	private final TransportId simplexTransportId = getTransportId();
+	private final TransportId duplexTransportId = getTransportId();
+	private final Group localGroup = getGroup(CLIENT_ID, MAJOR_VERSION);
+	private final Group contactGroup = getGroup(CLIENT_ID, MAJOR_VERSION);
+	private final Contact contact = getContact();
+	private final LocalAuthor localAuthor = getLocalAuthor();
+	private final boolean alice = compare(localAuthor.getId().getBytes(),
+			contact.getAuthor().getId().getBytes()) < 0;
+	private final KeyPair localKeyPair =
+			new KeyPair(getAgreementPublicKey(), getAgreementPrivateKey());
+	private final PublicKey remotePublicKey = getAgreementPublicKey();
+	private final SecretKey rootKey = getSecretKey();
+	private final KeySetId keySetId = new KeySetId(123);
+
+	private final Message storageMessage = getMessage(contactGroup.getId());
+	private final Message localKeyMessage = getMessage(contactGroup.getId());
+	private final Message localActivateMessage =
+			getMessage(contactGroup.getId());
+	private final Message remoteKeyMessage = getMessage(contactGroup.getId());
+	private final Message remoteActivateMessage =
+			getMessage(contactGroup.getId());
+	private final long localTimestamp = localKeyMessage.getTimestamp();
+	private final long remoteTimestamp = remoteKeyMessage.getTimestamp();
+
+	// These query and metadata dictionaries are handled by the manager without
+	// inspecting their contents, so we can use empty dictionaries for testing
+	private final BdfDictionary sessionQuery = new BdfDictionary();
+	private final BdfDictionary sessionMeta = new BdfDictionary();
+	private final BdfDictionary localKeyMeta = new BdfDictionary();
+	private final BdfDictionary localActivateMeta = new BdfDictionary();
+
+	// The manager doesn't use the incoming message body, so it can be empty
+	private final BdfList remoteMessageBody = new BdfList();
+
+	private final BdfDictionary remoteKeyMeta = BdfDictionary.of(
+			new BdfEntry(MSG_KEY_MESSAGE_TYPE, KEY.getValue()),
+			new BdfEntry(MSG_KEY_TRANSPORT_ID,
+					simplexTransportId.getString()),
+			new BdfEntry(MSG_KEY_PUBLIC_KEY, remotePublicKey.getEncoded()));
+
+	private final BdfDictionary remoteActivateMeta = BdfDictionary.of(
+			new BdfEntry(MSG_KEY_MESSAGE_TYPE, ACTIVATE.getValue()),
+			new BdfEntry(MSG_KEY_TRANSPORT_ID,
+					simplexTransportId.getString()));
+
+	private TransportKeyAgreementManagerImpl manager;
+
+	@Before
+	public void setUp() {
+		context.checking(new Expectations() {{
+			oneOf(pluginConfig).getSimplexFactories();
+			will(returnValue(singletonList(simplexFactory)));
+			oneOf(simplexFactory).getId();
+			will(returnValue(simplexTransportId));
+			oneOf(pluginConfig).getDuplexFactories();
+			will(returnValue(singletonList(duplexFactory)));
+			oneOf(duplexFactory).getId();
+			will(returnValue(duplexTransportId));
+			oneOf(contactGroupFactory)
+					.createLocalGroup(CLIENT_ID, MAJOR_VERSION);
+			will(returnValue(localGroup));
+		}});
+
+		manager = new TransportKeyAgreementManagerImpl(db, clientHelper,
+				metadataParser, contactGroupFactory, clientVersioningManager,
+				identityManager, keyManager, messageEncoder, sessionEncoder,
+				sessionParser, crypto, pluginConfig);
+	}
+
+	@Test
+	public void testCreatesContactGroupAtStartupIfLocalGroupDoesNotExist()
+			throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		context.checking(new Expectations() {{
+			oneOf(db).getContacts(txn);
+			will(returnValue(singletonList(contact)));
+			// The local group doesn't exist so we need to create contact groups
+			oneOf(db).containsGroup(txn, localGroup.getId());
+			will(returnValue(false));
+			oneOf(db).addGroup(txn, localGroup);
+			// Create the contact group and set it up
+			oneOf(contactGroupFactory).createContactGroup(CLIENT_ID,
+					MAJOR_VERSION, contact);
+			will(returnValue(contactGroup));
+			oneOf(db).addGroup(txn, contactGroup);
+			oneOf(clientHelper)
+					.setContactId(txn, contactGroup.getId(), contact.getId());
+			oneOf(clientVersioningManager).getClientVisibility(txn,
+					contact.getId(), CLIENT_ID, MAJOR_VERSION);
+			will(returnValue(VISIBLE));
+			oneOf(db).setGroupVisibility(txn, contact.getId(),
+					contactGroup.getId(), VISIBLE);
+			// We already have keys for both transports
+			oneOf(db).getTransportsWithKeys(txn);
+			will(returnValue(singletonMap(contact.getId(),
+					asList(simplexTransportId, duplexTransportId))));
+		}});
+
+		manager.onDatabaseOpened(txn);
+	}
+
+	@Test
+	public void testDoesNotCreateContactGroupAtStartupIfLocalGroupExists()
+			throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		context.checking(new Expectations() {{
+			oneOf(db).getContacts(txn);
+			will(returnValue(singletonList(contact)));
+			// The local group exists so we don't need to create contact groups
+			oneOf(db).containsGroup(txn, localGroup.getId());
+			will(returnValue(true));
+			// We already have keys for both transports
+			oneOf(db).getTransportsWithKeys(txn);
+			will(returnValue(singletonMap(contact.getId(),
+					asList(simplexTransportId, duplexTransportId))));
+		}});
+
+		manager.onDatabaseOpened(txn);
+	}
+
+	@Test
+	public void testStartsSessionAtStartup() throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		context.checking(new Expectations() {{
+			oneOf(db).getContacts(txn);
+			will(returnValue(singletonList(contact)));
+			// The local group exists so we don't need to create contact groups
+			oneOf(db).containsGroup(txn, localGroup.getId());
+			will(returnValue(true));
+			// We need keys for the simplex transport
+			oneOf(db).getTransportsWithKeys(txn);
+			will(returnValue(singletonMap(contact.getId(),
+					singletonList(duplexTransportId))));
+			// Get the contact group ID
+			oneOf(contactGroupFactory)
+					.createContactGroup(CLIENT_ID, MAJOR_VERSION, contact);
+			will(returnValue(contactGroup));
+		}});
+
+		// Check whether a session exists - it doesn't
+		expectSessionDoesNotExist(txn);
+		// Generate the local key pair
+		expectGenerateLocalKeyPair();
+		// Send a key message
+		expectSendKeyMessage(txn);
+		// Save the session
+		expectCreateStorageMessage(txn);
+		AtomicReference<Session> savedSession = expectSaveSession(txn);
+
+		manager.onDatabaseOpened(txn);
+
+		assertEquals(AWAIT_KEY, savedSession.get().getState());
+		assertEquals(localKeyMessage.getId(),
+				savedSession.get().getLastLocalMessageId());
+		assertEquals(localKeyPair, savedSession.get().getLocalKeyPair());
+		assertEquals(Long.valueOf(localTimestamp),
+				savedSession.get().getLocalTimestamp());
+		assertNull(savedSession.get().getKeySetId());
+	}
+
+	@Test
+	public void testDefersMessageIfTransportIsNotSupported() throws Exception {
+		Transaction txn = new Transaction(null, false);
+		TransportId unknownTransportId = getTransportId();
+		BdfDictionary meta = new BdfDictionary(remoteKeyMeta);
+		meta.put(MSG_KEY_TRANSPORT_ID, unknownTransportId.getString());
+
+		assertEquals(DEFER, manager.incomingMessage(txn, remoteKeyMessage,
+				remoteMessageBody, meta));
+	}
+
+	@Test
+	public void testAcceptsKeyMessageInAwaitKeyState() throws Exception {
+		Transaction txn = new Transaction(null, false);
+		Session loadedSession = new Session(AWAIT_KEY,
+				localKeyMessage.getId(), localKeyPair, localTimestamp, null);
+
+		// Check whether a session exists - it does
+		expectLoadSession(txn, loadedSession);
+		// Load the contact ID
+		expectLoadContactId(txn);
+		// Check whether we already have keys - we don't
+		expectKeysExist(txn, false);
+		// Parse the remote public key
+		expectParseRemotePublicKey();
+		// Derive and store the transport keys
+		expectDeriveAndStoreTransportKeys(txn);
+		// Send an activate message
+		expectSendActivateMessage(txn);
+		// Save the session
+		AtomicReference<Session> savedSession = expectSaveSession(txn);
+
+		assertEquals(ACCEPT_DO_NOT_SHARE, manager.incomingMessage(txn,
+				remoteKeyMessage, remoteMessageBody, remoteKeyMeta));
+
+		assertEquals(AWAIT_ACTIVATE, savedSession.get().getState());
+		assertEquals(localActivateMessage.getId(),
+				savedSession.get().getLastLocalMessageId());
+		assertNull(savedSession.get().getLocalKeyPair());
+		assertNull(savedSession.get().getLocalTimestamp());
+		assertEquals(keySetId, savedSession.get().getKeySetId());
+	}
+
+	@Test
+	public void testAcceptsKeyMessageIfWeHaveTransportKeysButNoSession()
+			throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		// Check whether a session exists - it doesn't
+		expectSessionDoesNotExist(txn);
+		// Load the contact ID
+		expectLoadContactId(txn);
+		// Check whether we already have keys - we do
+		expectKeysExist(txn, true);
+		// Generate the local key pair
+		expectGenerateLocalKeyPair();
+		// Parse the remote public key
+		expectParseRemotePublicKey();
+		// Send a key message
+		expectSendKeyMessage(txn);
+		// Derive and store the transport keys
+		expectDeriveAndStoreTransportKeys(txn);
+		// Send an activate message
+		expectSendActivateMessage(txn);
+		// Save the session
+		expectCreateStorageMessage(txn);
+		AtomicReference<Session> savedSession = expectSaveSession(txn);
+
+		assertEquals(ACCEPT_DO_NOT_SHARE, manager.incomingMessage(txn,
+				remoteKeyMessage, remoteMessageBody, remoteKeyMeta));
+
+		assertEquals(AWAIT_ACTIVATE, savedSession.get().getState());
+		assertEquals(localActivateMessage.getId(),
+				savedSession.get().getLastLocalMessageId());
+		assertNull(savedSession.get().getLocalKeyPair());
+		assertNull(savedSession.get().getLocalTimestamp());
+		assertEquals(keySetId, savedSession.get().getKeySetId());
+	}
+
+	@Test
+	public void testRejectsKeyMessageInAwaitActivateState() throws Exception {
+		Session loadedSession = new Session(AWAIT_ACTIVATE,
+				localActivateMessage.getId(), null, null, keySetId);
+		testRejectsKeyMessageWithExistingSession(loadedSession);
+	}
+
+	@Test
+	public void testRejectsKeyMessageInActivatedState() throws Exception {
+		Session loadedSession = new Session(ACTIVATED,
+				localActivateMessage.getId(), null, null, null);
+		testRejectsKeyMessageWithExistingSession(loadedSession);
+	}
+
+	private void testRejectsKeyMessageWithExistingSession(Session loadedSession)
+			throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		// Check whether a session exists - it does
+		expectLoadSession(txn, loadedSession);
+		// Load the contact ID
+		expectLoadContactId(txn);
+		// Check whether we already have keys - we don't
+		expectKeysExist(txn, false);
+
+		assertEquals(REJECT, manager.incomingMessage(txn,
+				remoteKeyMessage, remoteMessageBody, remoteKeyMeta));
+	}
+
+	@Test
+	public void testAcceptsActivateMessageInAwaitActivateState()
+			throws Exception {
+		Transaction txn = new Transaction(null, false);
+		Session loadedSession = new Session(AWAIT_ACTIVATE,
+				localActivateMessage.getId(), null, null, keySetId);
+
+		// Check whether a session exists - it does
+		expectLoadSession(txn, loadedSession);
+
+		// Activate the transport keys
+		context.checking(new Expectations() {{
+			oneOf(keyManager).activateKeys(txn,
+					singletonMap(simplexTransportId, keySetId));
+		}});
+
+		// Save the session
+		AtomicReference<Session> savedSession = expectSaveSession(txn);
+
+		assertEquals(ACCEPT_DO_NOT_SHARE, manager.incomingMessage(txn,
+				remoteActivateMessage, remoteMessageBody, remoteActivateMeta));
+
+		assertEquals(ACTIVATED, savedSession.get().getState());
+		assertEquals(localActivateMessage.getId(),
+				savedSession.get().getLastLocalMessageId());
+		assertNull(savedSession.get().getLocalKeyPair());
+		assertNull(savedSession.get().getLocalTimestamp());
+		assertNull(savedSession.get().getKeySetId());
+	}
+
+	@Test
+	public void testRejectsActivateMessageWithNoSession() throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		// Check whether a session exists - it doesn't
+		expectSessionDoesNotExist(txn);
+
+		assertEquals(REJECT, manager.incomingMessage(txn,
+				remoteActivateMessage, remoteMessageBody, remoteActivateMeta));
+	}
+
+	@Test
+	public void testRejectsActivateMessageInAwaitKeyState() throws Exception {
+		Session loadedSession = new Session(AWAIT_KEY,
+				localKeyMessage.getId(), localKeyPair, localTimestamp, null);
+		testRejectsActivateMessageWithExistingSession(loadedSession);
+	}
+
+	@Test
+	public void testRejectsActivateMessageInActivatedState() throws Exception {
+		Session loadedSession = new Session(ACTIVATED,
+				localActivateMessage.getId(), null, null, null);
+		testRejectsActivateMessageWithExistingSession(loadedSession);
+	}
+
+	private void testRejectsActivateMessageWithExistingSession(
+			Session loadedSession) throws Exception {
+		Transaction txn = new Transaction(null, false);
+
+		// Check whether a session exists - it does
+		expectLoadSession(txn, loadedSession);
+
+		assertEquals(REJECT, manager.incomingMessage(txn,
+				remoteActivateMessage, remoteMessageBody, remoteActivateMeta));
+	}
+
+	private void expectSessionDoesNotExist(Transaction txn) throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(sessionEncoder).getSessionQuery(simplexTransportId);
+			will(returnValue(sessionQuery));
+			oneOf(clientHelper)
+					.getMessageIds(txn, contactGroup.getId(), sessionQuery);
+			will(returnValue(emptyList()));
+		}});
+	}
+
+	private void expectLoadSession(Transaction txn, Session loadedSession)
+			throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(sessionEncoder).getSessionQuery(simplexTransportId);
+			will(returnValue(sessionQuery));
+			oneOf(clientHelper)
+					.getMessageIds(txn, contactGroup.getId(), sessionQuery);
+			will(returnValue(singletonList(storageMessage.getId())));
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					storageMessage.getId());
+			will(returnValue(sessionMeta));
+			oneOf(sessionParser).parseSession(sessionMeta);
+			will(returnValue(loadedSession));
+		}});
+	}
+
+	private void expectSendKeyMessage(Transaction txn) throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(messageEncoder).encodeKeyMessage(contactGroup.getId(),
+					simplexTransportId, localKeyPair.getPublic());
+			will(returnValue(localKeyMessage));
+			oneOf(messageEncoder)
+					.encodeMessageMetadata(simplexTransportId, KEY, true);
+			will(returnValue(localKeyMeta));
+			oneOf(clientHelper).addLocalMessage(txn, localKeyMessage,
+					localKeyMeta, true, false);
+		}});
+	}
+
+	private void expectSendActivateMessage(Transaction txn) throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(messageEncoder).encodeActivateMessage(contactGroup.getId(),
+					simplexTransportId, localKeyMessage.getId());
+			will(returnValue(localActivateMessage));
+			oneOf(messageEncoder)
+					.encodeMessageMetadata(simplexTransportId, ACTIVATE, true);
+			will(returnValue(localActivateMeta));
+			oneOf(clientHelper).addLocalMessage(txn, localActivateMessage,
+					localActivateMeta, true, false);
+		}});
+	}
+
+	private void expectCreateStorageMessage(Transaction txn) throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(clientHelper)
+					.createMessageForStoringMetadata(contactGroup.getId());
+			will(returnValue(storageMessage));
+			oneOf(db).addLocalMessage(txn, storageMessage, new Metadata(),
+					false, false);
+		}});
+	}
+
+	private AtomicReference<Session> expectSaveSession(Transaction txn)
+			throws Exception {
+		AtomicReference<Session> savedSession = new AtomicReference<>();
+
+		context.checking(new Expectations() {{
+			oneOf(sessionEncoder).encodeSession(with(any(Session.class)),
+					with(simplexTransportId));
+			will(doAll(
+					new CaptureArgumentAction<>(savedSession, Session.class, 0),
+					returnValue(sessionMeta)));
+			oneOf(clientHelper).mergeMessageMetadata(txn,
+					storageMessage.getId(), sessionMeta);
+		}});
+
+		return savedSession;
+	}
+
+	private void expectLoadContactId(Transaction txn) throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getContactId(txn, contactGroup.getId());
+			will(returnValue(contact.getId()));
+		}});
+	}
+
+	private void expectGenerateLocalKeyPair() {
+		context.checking(new Expectations() {{
+			oneOf(crypto).generateKeyPair();
+			will(returnValue(localKeyPair));
+		}});
+	}
+
+	private void expectParseRemotePublicKey() throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(crypto).parsePublicKey(remotePublicKey.getEncoded());
+			will(returnValue(remotePublicKey));
+		}});
+	}
+
+	private void expectDeriveAndStoreTransportKeys(Transaction txn)
+			throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(crypto).deriveRootKey(localKeyPair, remotePublicKey);
+			will(returnValue(rootKey));
+			oneOf(db).getContact(txn, contact.getId());
+			will(returnValue(contact));
+			oneOf(identityManager).getLocalAuthor(txn);
+			will(returnValue(localAuthor));
+			oneOf(keyManager).addRotationKeys(txn, contact.getId(),
+					simplexTransportId, rootKey,
+					min(localTimestamp, remoteTimestamp), alice, false);
+			will(returnValue(keySetId));
+		}});
+	}
+
+	private void expectKeysExist(Transaction txn, boolean exist)
+			throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(db).containsTransportKeys(txn, contact.getId(),
+					simplexTransportId);
+			will(returnValue(exist));
+		}});
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/versioning/ClientVersioningManagerImplTest.java

@@ -31,6 +31,7 @@ import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.sync.Group.Visibility.INVISIBLE;
 import static org.briarproject.bramble.api.sync.Group.Visibility.SHARED;
 import static org.briarproject.bramble.api.sync.Group.Visibility.VISIBLE;
+import static org.briarproject.bramble.api.sync.validation.IncomingMessageHook.DeliveryAction.ACCEPT_DO_NOT_SHARE;
 import static org.briarproject.bramble.api.versioning.ClientVersioningManager.CLIENT_ID;
 import static org.briarproject.bramble.api.versioning.ClientVersioningManager.MAJOR_VERSION;
 import static org.briarproject.bramble.test.TestUtils.getClientId;
@@ -41,7 +42,6 @@ import static org.briarproject.bramble.test.TestUtils.getRandomId;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_LOCAL;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_UPDATE_VERSION;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
 
 public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 
@@ -419,7 +419,8 @@ public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 
 		ClientVersioningManagerImpl c = createInstance();
 		c.registerClient(clientId, 123, 234, hook);
-		assertFalse(c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
 	}
 
 	@Test
@@ -464,7 +465,8 @@ public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 
 		ClientVersioningManagerImpl c = createInstance();
 		c.registerClient(clientId, 123, 234, hook);
-		assertFalse(c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
 	}
 
 	@Test
@@ -496,7 +498,8 @@ public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 
 		ClientVersioningManagerImpl c = createInstance();
 		c.registerClient(clientId, 123, 234, hook);
-		assertFalse(c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
 	}
 
 	@Test
@@ -579,7 +582,8 @@ public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 
 		ClientVersioningManagerImpl c = createInstance();
 		c.registerClient(clientId, 123, 234, hook);
-		assertFalse(c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
 	}
 
 	@Test
@@ -649,7 +653,8 @@ public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 
 		ClientVersioningManagerImpl c = createInstance();
 		c.registerClient(clientId, 123, 234, hook);
-		assertFalse(c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
+		assertEquals(ACCEPT_DO_NOT_SHARE,
+				c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
 	}
 
 	@Test

bramble-core/witness.gradle

@@ -1,12 +1,11 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
-        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
+        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
-        'com.google.dagger:dagger-compiler:2.33:dagger-compiler-2.33.jar:aa8a0d8370c578fd6999802d0d90b9829377a46d2c1141e11b8f737970e7155e',
-        'com.google.dagger:dagger-producers:2.33:dagger-producers-2.33.jar:5897f0b6eef799c2adfe3ccacc58c0fb374d58acb063c3ebe5366c38a8bce5c8',
-        'com.google.dagger:dagger-spi:2.33:dagger-spi-2.33.jar:e2dcab2221b8afb9556ef0a1c83b0bd5f42552e254322a257330f754cdbbb9d4',
-        'com.google.dagger:dagger:2.33:dagger-2.33.jar:d8798c5b8cf6b125234e33af5c6293bb9f2208ce29b57924c35b8c0be7b6bdcb',
+        'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
+        'com.google.dagger:dagger-producers:2.24:dagger-producers-2.24.jar:f10f45b95191954d5d6b043fca9e62fb621d21bf70634b8f8476c7988b504c3a',
+        'com.google.dagger:dagger-spi:2.24:dagger-spi-2.24.jar:c038445d14dbcb4054e61bf49e05009edf26fce4fdc7ec1a9db544784f68e718',
+        'com.google.dagger:dagger:2.24:dagger-2.24.jar:550a6e46a6dfcdf1d764887b6090cea94f783327e50e5c73754f18facfc70b64',
         'com.google.errorprone:error_prone_annotations:2.2.0:error_prone_annotations-2.2.0.jar:6ebd22ca1b9d8ec06d41de8d64e0596981d9607b42035f9ed374f9de271a481a',
         'com.google.errorprone:javac-shaded:9-dev-r4023-3:javac-shaded-9-dev-r4023-3.jar:65bfccf60986c47fbc17c9ebab0be626afc41741e0a6ec7109e0768817a36f30',
         'com.google.googlejavaformat:google-java-format:1.5:google-java-format-1.5.jar:aa19ad7850fb85178aa22f2fddb163b84d6ce4d0035872f30d4408195ca1144e',
@@ -16,15 +15,15 @@ dependencyVerification {
         'com.google.j2objc:j2objc-annotations:1.1:j2objc-annotations-1.1.jar:2994a7eb78f2710bd3d3bfb639b2c94e219cedac0d4d084d516e78c16dddecf6',
         'com.h2database:h2:1.4.192:h2-1.4.192.jar:225b22e9857235c46c93861410b60b8c81c10dc8985f4faf188985ba5445126c',
         'com.madgag.spongycastle:core:1.58.0.0:core-1.58.0.0.jar:199617dd5698c5a9312b898c0a4cec7ce9dd8649d07f65d91629f58229d72728',
-        'com.squareup:javapoet:1.13.0:javapoet-1.13.0.jar:4c7517e848a71b36d069d12bb3bf46a70fd4cda3105d822b0ed2e19c00b69291',
+        'com.squareup:javapoet:1.11.1:javapoet-1.11.1.jar:9cbf2107be499ec6e95afd36b58e3ca122a24166cdd375732e51267d64058e90',
         'javax.annotation:jsr250-api:1.0:jsr250-api-1.0.jar:a1a922d0d9b6d183ed3800dfac01d1e1eb159f0e8c6f94736931c1def54a941f',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
-        'junit:junit:4.13.2:junit-4.13.2.jar:8e495b634469d64fb8acfa3495a065cbacc8a0fff55ce1e31007be4c16dc57d3',
-        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
+        'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
         'net.i2p.crypto:eddsa:0.2.0:eddsa-0.2.0.jar:a7cb1b85c16e2f0730b9204106929a1d9aaae1df728adc7041a8b8b605692140',
-        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
-        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
+        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
+        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
+        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.bitlet:weupnp:0.1.4:weupnp-0.1.4.jar:88df7e6504929d00bdb832863761385c68ab92af945b04f0770b126270a444fb',
         'org.briarproject:jtorctl:0.3:jtorctl-0.3.jar:f2939238a097898998432effe93b0334d97a787972ab3a91a8973a1d309fc864',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
@@ -33,22 +32,16 @@ dependencyVerification {
         'org.codehaus.mojo:animal-sniffer-annotations:1.17:animal-sniffer-annotations-1.17.jar:92654f493ecfec52082e76354f0ebf87648dc3d5cec2e3c3cdb947c016747a53',
         'org.codehaus.mojo:animal-sniffer-ant-tasks:1.16:animal-sniffer-ant-tasks-1.16.jar:890040976fbe2d584619a6a61b1fd2e925b3b5eb342a85eb2762c467c0d64e90',
         'org.codehaus.mojo:animal-sniffer:1.16:animal-sniffer-1.16.jar:72be8bcc226ba43b937c722a08a07852bfa1b11400089265d5df0ee7b38b1d52',
-        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
-        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
-        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
+        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
+        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
         'org.hsqldb:hsqldb:2.3.5:hsqldb-2.3.5.jar:6676a6977ac98997a80f827ddbd3fe8ca1e0853dad1492512135fd1a222ccfad',
-        'org.jetbrains.kotlin:kotlin-stdlib-common:1.4.20:kotlin-stdlib-common-1.4.20.jar:a7112c9b3cefee418286c9c9372f7af992bd1e6e030691d52f60cb36dbec8320',
-        'org.jetbrains.kotlin:kotlin-stdlib:1.4.20:kotlin-stdlib-1.4.20.jar:b8ab1da5cdc89cb084d41e1f28f20a42bd431538642a5741c52bbfae3fa3e656',
-        'org.jetbrains.kotlinx:kotlinx-metadata-jvm:0.1.0:kotlinx-metadata-jvm-0.1.0.jar:9753bb39efef35957c5c15df9a3cb769aabf2cdfa74b47afcb7760e5146be3b5',
-        'org.jetbrains:annotations:13.0:annotations-13.0.jar:ace2a10dc8e2d5fd34925ecac03e4988b2c0f851650c94b8cef49ba1bd111478',
-        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
-        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
-        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
-        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
-        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
-        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
+        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
+        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
+        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
+        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
+        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
         'org.ow2.asm:asm-all:5.2:asm-all-5.2.jar:7fbffbc1db3422e2101689fd88df8384b15817b52b9b2b267b9f6d2511dc198d',
-        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
+        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
         'org.whispersystems:curve25519-java:0.5.0:curve25519-java-0.5.0.jar:0aadd43cf01d11e9b58f867b3c4f25c3194e8b0623d1953d32dfbfbee009e38d',
     ]
 }

bramble-java/build.gradle

@@ -14,22 +14,21 @@ configurations {
 dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
 	implementation fileTree(dir: 'libs', include: '*.jar')
-	def jna_version = '4.5.2'
-	implementation "net.java.dev.jna:jna:$jna_version"
-	implementation "net.java.dev.jna:jna-platform:$jna_version"
-	tor 'org.briarproject:tor:0.3.5.15'
+	implementation 'net.java.dev.jna:jna:4.5.2'
+	implementation 'net.java.dev.jna:jna-platform:4.5.2'
+	tor 'org.briarproject:tor:0.3.5.13-1@zip'
 	tor 'org.briarproject:obfs4proxy:0.0.12-dev-40245c4a@zip'
 
-	annotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation project(path: ':bramble-core', configuration: 'testOutput')
-	testImplementation "junit:junit:$junit_version"
-	testImplementation "org.jmock:jmock:$jmock_version"
-	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
+	testImplementation 'junit:junit:4.12'
+	testImplementation "org.jmock:jmock:2.8.2"
+	testImplementation "org.jmock:jmock-junit4:2.8.2"
+	testImplementation "org.jmock:jmock-legacy:2.8.2"
 
-	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	testAnnotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 }
 
 def torBinariesDir = 'src/main/resources'

bramble-java/src/main/java/org/briarproject/bramble/plugin/tor/UnixTorPluginFactory.java

@@ -16,7 +16,6 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
-import org.briarproject.bramble.api.system.WakefulIoExecutor;
 
 import java.io.File;
 import java.util.concurrent.Executor;
@@ -56,8 +55,8 @@ public class UnixTorPluginFactory implements DuplexPluginFactory {
 	private final File torDirectory;
 
 	@Inject
-	public UnixTorPluginFactory(@IoExecutor Executor ioExecutor,
-			@WakefulIoExecutor Executor wakefulIoExecutor,
+	UnixTorPluginFactory(@IoExecutor Executor ioExecutor,
+			@IoExecutor Executor wakefulIoExecutor,
 			NetworkManager networkManager,
 			LocationUtils locationUtils,
 			EventBus eventBus,

bramble-java/witness.gradle

@@ -1,12 +1,11 @@
 dependencyVerification {
     verify = [
-        'cglib:cglib:3.2.8:cglib-3.2.8.jar:3f64de999ecc5595dc84ca8ff0879d8a34c8623f9ef3c517a53ed59023fcb9db',
-        'com.google.code.findbugs:annotations:3.0.1:annotations-3.0.1.jar:6b47ff0a6de0ce17cbedc3abb0828ca5bce3009d53ea47b3723ff023c4742f79',
+        'cglib:cglib:3.2.0:cglib-3.2.0.jar:adb13bab79712ad6bdf1bd59f2a3918018a8016e722e8a357065afb9e6690861',
         'com.google.code.findbugs:jsr305:3.0.2:jsr305-3.0.2.jar:766ad2a0783f2687962c8ad74ceecc38a28b9f72a2d085ee438b7813e928d0c7',
-        'com.google.dagger:dagger-compiler:2.33:dagger-compiler-2.33.jar:aa8a0d8370c578fd6999802d0d90b9829377a46d2c1141e11b8f737970e7155e',
-        'com.google.dagger:dagger-producers:2.33:dagger-producers-2.33.jar:5897f0b6eef799c2adfe3ccacc58c0fb374d58acb063c3ebe5366c38a8bce5c8',
-        'com.google.dagger:dagger-spi:2.33:dagger-spi-2.33.jar:e2dcab2221b8afb9556ef0a1c83b0bd5f42552e254322a257330f754cdbbb9d4',
-        'com.google.dagger:dagger:2.33:dagger-2.33.jar:d8798c5b8cf6b125234e33af5c6293bb9f2208ce29b57924c35b8c0be7b6bdcb',
+        'com.google.dagger:dagger-compiler:2.24:dagger-compiler-2.24.jar:3c5afb955fb188da485cb2c048eff37dce0e1530b9780a0f2f7187d16d1ccc1f',
+        'com.google.dagger:dagger-producers:2.24:dagger-producers-2.24.jar:f10f45b95191954d5d6b043fca9e62fb621d21bf70634b8f8476c7988b504c3a',
+        'com.google.dagger:dagger-spi:2.24:dagger-spi-2.24.jar:c038445d14dbcb4054e61bf49e05009edf26fce4fdc7ec1a9db544784f68e718',
+        'com.google.dagger:dagger:2.24:dagger-2.24.jar:550a6e46a6dfcdf1d764887b6090cea94f783327e50e5c73754f18facfc70b64',
         'com.google.errorprone:error_prone_annotations:2.2.0:error_prone_annotations-2.2.0.jar:6ebd22ca1b9d8ec06d41de8d64e0596981d9607b42035f9ed374f9de271a481a',
         'com.google.errorprone:javac-shaded:9-dev-r4023-3:javac-shaded-9-dev-r4023-3.jar:65bfccf60986c47fbc17c9ebab0be626afc41741e0a6ec7109e0768817a36f30',
         'com.google.googlejavaformat:google-java-format:1.5:google-java-format-1.5.jar:aa19ad7850fb85178aa22f2fddb163b84d6ce4d0035872f30d4408195ca1144e',
@@ -14,34 +13,28 @@ dependencyVerification {
         'com.google.guava:guava:27.1-jre:guava-27.1-jre.jar:4a5aa70cc968a4d137e599ad37553e5cfeed2265e8c193476d7119036c536fe7',
         'com.google.guava:listenablefuture:9999.0-empty-to-avoid-conflict-with-guava:listenablefuture-9999.0-empty-to-avoid-conflict-with-guava.jar:b372a037d4230aa57fbeffdef30fd6123f9c0c2db85d0aced00c91b974f33f99',
         'com.google.j2objc:j2objc-annotations:1.1:j2objc-annotations-1.1.jar:2994a7eb78f2710bd3d3bfb639b2c94e219cedac0d4d084d516e78c16dddecf6',
-        'com.squareup:javapoet:1.13.0:javapoet-1.13.0.jar:4c7517e848a71b36d069d12bb3bf46a70fd4cda3105d822b0ed2e19c00b69291',
+        'com.squareup:javapoet:1.11.1:javapoet-1.11.1.jar:9cbf2107be499ec6e95afd36b58e3ca122a24166cdd375732e51267d64058e90',
         'javax.annotation:jsr250-api:1.0:jsr250-api-1.0.jar:a1a922d0d9b6d183ed3800dfac01d1e1eb159f0e8c6f94736931c1def54a941f',
         'javax.inject:javax.inject:1:javax.inject-1.jar:91c77044a50c481636c32d916fd89c9118a72195390452c81065080f957de7ff',
-        'junit:junit:4.13.2:junit-4.13.2.jar:8e495b634469d64fb8acfa3495a065cbacc8a0fff55ce1e31007be4c16dc57d3',
-        'net.bytebuddy:byte-buddy:1.9.12:byte-buddy-1.9.12.jar:3688c3d434bebc3edc5516296a2ed0f47b65e451071b4afecad84f902f0efc11',
+        'junit:junit:4.12:junit-4.12.jar:59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a',
         'net.java.dev.jna:jna-platform:4.5.2:jna-platform-4.5.2.jar:f1d00c167d8921c6e23c626ef9f1c3ae0be473c95c68ffa012bc7ae55a87e2d6',
         'net.java.dev.jna:jna:4.5.2:jna-4.5.2.jar:0c8eb7acf67261656d79005191debaba3b6bf5dd60a43735a245429381dbecff',
-        'net.jcip:jcip-annotations:1.0:jcip-annotations-1.0.jar:be5805392060c71474bf6c9a67a099471274d30b83eef84bfc4e0889a4f1dcc0',
         'net.ltgt.gradle.incap:incap:0.2:incap-0.2.jar:b625b9806b0f1e4bc7a2e3457119488de3cd57ea20feedd513db070a573a4ffd',
-        'org.apache-extras.beanshell:bsh:2.0b6:bsh-2.0b6.jar:a17955976070c0573235ee662f2794a78082758b61accffce8d3f8aedcd91047',
+        'org.apache.ant:ant-launcher:1.9.4:ant-launcher-1.9.4.jar:7bccea20b41801ca17bcbc909a78c835d0f443f12d639c77bd6ae3d05861608d',
+        'org.apache.ant:ant:1.9.4:ant-1.9.4.jar:649ae0730251de07b8913f49286d46bba7b92d47c5f332610aa426c4f02161d8',
+        'org.beanshell:bsh:1.3.0:bsh-1.3.0.jar:9b04edc75d19db54f1b4e8b5355e9364384c6cf71eb0a1b9724c159d779879f8',
         'org.briarproject:obfs4proxy:0.0.12-dev-40245c4a:obfs4proxy-0.0.12-dev-40245c4a.zip:172029e7058b3a83ac93ac4991a44bf76e16ce8d46f558f5836d57da3cb3a766',
-        'org.briarproject:tor:0.3.5.15:tor-0.3.5.15.jar:2ff5b5a3b5eaa97d699629ad24ba9584b3199d0ffdb1ea7d8a02de3016b80e7a',
+        'org.briarproject:tor:0.3.5.13-1:tor-0.3.5.13-1.zip:ef35c16bf8dc1f4c75ed71d9f55e4514f383d124ec96b859aca647c990927c99',
         'org.checkerframework:checker-compat-qual:2.5.3:checker-compat-qual-2.5.3.jar:d76b9afea61c7c082908023f0cbc1427fab9abd2df915c8b8a3e7a509bccbc6d',
         'org.checkerframework:checker-qual:2.5.2:checker-qual-2.5.2.jar:64b02691c8b9d4e7700f8ee2e742dce7ea2c6e81e662b7522c9ee3bf568c040a',
         'org.codehaus.mojo:animal-sniffer-annotations:1.17:animal-sniffer-annotations-1.17.jar:92654f493ecfec52082e76354f0ebf87648dc3d5cec2e3c3cdb947c016747a53',
-        'org.hamcrest:hamcrest-core:2.1:hamcrest-core-2.1.jar:e09109e54a289d88506b9bfec987ddd199f4217c9464132668351b9a4f00bee9',
-        'org.hamcrest:hamcrest-library:2.1:hamcrest-library-2.1.jar:b7e2b6895b3b679f0e47b6380fda391b225e9b78505db9d8bdde8d3cc8d52a21',
-        'org.hamcrest:hamcrest:2.1:hamcrest-2.1.jar:ba93b2e3a562322ba432f0a1b53addcc55cb188253319a020ed77f824e692050',
-        'org.jetbrains.kotlin:kotlin-stdlib-common:1.4.20:kotlin-stdlib-common-1.4.20.jar:a7112c9b3cefee418286c9c9372f7af992bd1e6e030691d52f60cb36dbec8320',
-        'org.jetbrains.kotlin:kotlin-stdlib:1.4.20:kotlin-stdlib-1.4.20.jar:b8ab1da5cdc89cb084d41e1f28f20a42bd431538642a5741c52bbfae3fa3e656',
-        'org.jetbrains.kotlinx:kotlinx-metadata-jvm:0.1.0:kotlinx-metadata-jvm-0.1.0.jar:9753bb39efef35957c5c15df9a3cb769aabf2cdfa74b47afcb7760e5146be3b5',
-        'org.jetbrains:annotations:13.0:annotations-13.0.jar:ace2a10dc8e2d5fd34925ecac03e4988b2c0f851650c94b8cef49ba1bd111478',
-        'org.jmock:jmock-imposters:2.12.0:jmock-imposters-2.12.0.jar:3b836269745a137c9b2347e8d7c2104845b126ef04f012d6bfd94f1a7dea7b09',
-        'org.jmock:jmock-junit4:2.12.0:jmock-junit4-2.12.0.jar:3233062fc889637c151a24f1ee086bad04321ab7d8264fef279daff0fa27205b',
-        'org.jmock:jmock-legacy:2.12.0:jmock-legacy-2.12.0.jar:dea3a9cca653d082e2fe7e40232e982fe03a9984c7d67ceff24f3e03fe580dcd',
-        'org.jmock:jmock-testjar:2.12.0:jmock-testjar-2.12.0.jar:efefbcf6cd294d0e29f0c46eb2a3380d4ca4e1763ff719c69e2f2ac62f564a04',
-        'org.jmock:jmock:2.12.0:jmock-2.12.0.jar:266d07314c0cd343c46ff8a55601272de8cf406807caf55e6f313295f83d10be',
-        'org.objenesis:objenesis:3.0.1:objenesis-3.0.1.jar:7a8ff780b9ff48415d7c705f60030b0acaa616e7f823c98eede3b63508d4e984',
-        'org.ow2.asm:asm:7.1:asm-7.1.jar:4ab2fa2b6d2cc9ccb1eaa05ea329c407b47b13ed2915f62f8c4b8cc96258d4de',
+        'org.hamcrest:hamcrest-core:1.3:hamcrest-core-1.3.jar:66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9',
+        'org.hamcrest:hamcrest-library:1.3:hamcrest-library-1.3.jar:711d64522f9ec410983bd310934296da134be4254a125080a0416ec178dfad1c',
+        'org.jmock:jmock-junit4:2.8.2:jmock-junit4-2.8.2.jar:f7ee4df4f7bd7b7f1cafad3b99eb74d579f109d5992ff625347352edb55e674c',
+        'org.jmock:jmock-legacy:2.8.2:jmock-legacy-2.8.2.jar:f2b985a5c08a9edb7f37612330c058809da3f6a6d63ce792426ebf8ff0d6d31b',
+        'org.jmock:jmock-testjar:2.8.2:jmock-testjar-2.8.2.jar:8900860f72c474e027cf97fe78dcbf154a1aa7fc62b6845c5fb4e4f3c7bc8760',
+        'org.jmock:jmock:2.8.2:jmock-2.8.2.jar:6c73cb4a2e6dbfb61fd99c9a768539c170ab6568e57846bd60dbf19596b65b16',
+        'org.objenesis:objenesis:2.1:objenesis-2.1.jar:c74330cc6b806c804fd37e74487b4fe5d7c2750c5e15fbc6efa13bdee1bdef80',
+        'org.ow2.asm:asm:5.0.4:asm-5.0.4.jar:896618ed8ae62702521a78bc7be42b7c491a08e6920a15f89a3ecdec31e9a220',
     ]
 }

briar-android/build.gradle

@@ -26,8 +26,8 @@ android {
 	defaultConfig {
 		minSdkVersion 16
 		targetSdkVersion 30
-		versionCode 10305
-		versionName "1.3.5"
+		versionCode 10303
+		versionName "1.3.3"
 		applicationId "org.briarproject.briar.android"
 
 		vectorDrawables.useSupportLibrary = true
@@ -100,13 +100,13 @@ dependencies {
 	implementation project(path: ':bramble-core', configuration: 'default')
 	implementation project(':bramble-android')
 
-	implementation 'androidx.fragment:fragment:1.3.4'
+	implementation 'androidx.fragment:fragment:1.3.0'
 	implementation 'androidx.preference:preference:1.1.1'
-	implementation 'androidx.exifinterface:exifinterface:1.3.2'
+	implementation 'androidx.exifinterface:exifinterface:1.3.1'
 	implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'
 	implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
-	implementation 'com.google.android.material:material:1.3.0'
-	implementation 'androidx.recyclerview:recyclerview-selection:1.1.0'
+	implementation 'com.google.android.material:material:1.2.1'
+	implementation 'androidx.recyclerview:recyclerview-selection:1.1.0-rc03'
 
 	implementation 'info.guardianproject.panic:panic:1.0'
 	implementation 'info.guardianproject.trustedintents:trustedintents:0.2'
@@ -122,26 +122,27 @@ dependencies {
 		exclude module: 'disklrucache' // when there's no disk cache, we can't accidentally use it
 	}
 
-	annotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	annotationProcessor 'com.google.dagger:dagger-compiler:2.24'
 	annotationProcessor "com.github.bumptech.glide:compiler:$glideVersion"
 
 	compileOnly 'javax.annotation:jsr250-api:1.0'
 
 	def espressoVersion = '3.3.0'
+	def jmockVersion = '2.8.2'
 	testImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	testImplementation project(path: ':bramble-core', configuration: 'testOutput')
 	testImplementation 'androidx.test:runner:1.3.0'
 	testImplementation 'androidx.test.ext:junit:1.1.2'
-	testImplementation 'androidx.fragment:fragment-testing:1.3.4'
+	testImplementation 'androidx.fragment:fragment-testing:1.2.5'
 	testImplementation "androidx.arch.core:core-testing:2.1.0"
 	testImplementation "androidx.test.espresso:espresso-core:$espressoVersion"
 	testImplementation 'org.robolectric:robolectric:4.3.1'
-	testImplementation 'org.mockito:mockito-core:3.9.0'
-	testImplementation "junit:junit:$junit_version"
-	testImplementation "org.jmock:jmock:$jmock_version"
-	testImplementation "org.jmock:jmock-junit4:$jmock_version"
-	testImplementation "org.jmock:jmock-legacy:$jmock_version"
-	testAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	testImplementation 'org.mockito:mockito-core:3.1.0'
+	testImplementation 'junit:junit:4.13.1'
+	testImplementation "org.jmock:jmock:$jmockVersion"
+	testImplementation "org.jmock:jmock-junit4:$jmockVersion"
+	testImplementation "org.jmock:jmock-legacy:$jmockVersion"
+	testAnnotationProcessor "com.google.dagger:dagger-compiler:2.24"
 
 	androidTestImplementation project(path: ':bramble-api', configuration: 'testOutput')
 	androidTestImplementation 'androidx.test.ext:junit:1.1.2'
@@ -150,9 +151,9 @@ dependencies {
 	androidTestImplementation "androidx.test.espresso:espresso-intents:$espressoVersion"
 	androidTestImplementation 'androidx.test:runner:1.3.0'
 	androidTestUtil 'androidx.test:orchestrator:1.3.0'
-	androidTestAnnotationProcessor "com.google.dagger:dagger-compiler:$dagger_version"
+	androidTestAnnotationProcessor "com.google.dagger:dagger-compiler:2.24"
 	androidTestCompileOnly 'javax.annotation:jsr250-api:1.0'
-	androidTestImplementation "junit:junit:$junit_version"
+	androidTestImplementation 'junit:junit:4.13.1'
 	androidTestScreenshotImplementation 'tools.fastlane:screengrab:2.0.0'
 	androidTestScreenshotImplementation 'com.jraska:falcon:2.1.1'
 	androidTestScreenshotImplementation 'androidx.test.uiautomator:uiautomator:2.2.0'

briar-android/src/main/AndroidManifest.xml

@@ -104,7 +104,8 @@
 
 		<activity
 			android:name="org.briarproject.briar.android.account.SetupActivity"
-			android:label="@string/setup_title" />
+			android:label="@string/setup_title"
+			android:windowSoftInputMode="adjustResize|stateAlwaysVisible" />
 
 		<activity
 			android:name="org.briarproject.briar.android.splash.SplashScreenActivity"

briar-android/src/main/java/org/briarproject/briar/android/AndroidComponent.java

@@ -28,6 +28,7 @@ import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.AndroidWakeLockManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
+import org.briarproject.bramble.plugin.file.RemovableDriveModule;
 import org.briarproject.bramble.plugin.tor.CircumventionProvider;
 import org.briarproject.bramble.system.ClockModule;
 import org.briarproject.briar.BriarCoreEagerSingletons;
@@ -83,7 +84,8 @@ import dagger.Component;
 		AppModule.class,
 		AttachmentModule.class,
 		ClockModule.class,
-		MediaModule.class
+		MediaModule.class,
+		RemovableDriveModule.class
 })
 public interface AndroidComponent
 		extends BrambleCoreEagerSingletons, BrambleAndroidEagerSingletons,

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -24,6 +24,8 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reporting.DevConfig;
 import org.briarproject.bramble.plugin.bluetooth.AndroidBluetoothPluginFactory;
+import org.briarproject.bramble.plugin.file.AndroidRemovableDrivePluginFactory;
+import org.briarproject.bramble.plugin.file.RemovableDriveModule;
 import org.briarproject.bramble.plugin.tcp.AndroidLanTcpPluginFactory;
 import org.briarproject.bramble.plugin.tor.AndroidTorPluginFactory;
 import org.briarproject.bramble.util.AndroidUtils;
@@ -67,7 +69,6 @@ import dagger.Provides;
 import static android.content.Context.MODE_PRIVATE;
 import static android.os.Build.VERSION.SDK_INT;
 import static java.util.Arrays.asList;
-import static java.util.Collections.emptyList;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
 import static org.briarproject.bramble.api.reporting.ReportingConstants.DEV_ONION_ADDRESS;
@@ -92,6 +93,7 @@ import static org.briarproject.briar.android.TestingConstants.IS_DEBUG_BUILD;
 		GroupListModule.class,
 		GroupConversationModule.class,
 		SharingModule.class,
+		RemovableDriveModule.class
 })
 public class AppModule {
 
@@ -149,8 +151,10 @@ public class AppModule {
 	}
 
 	@Provides
+	@Singleton
 	PluginConfig providePluginConfig(AndroidBluetoothPluginFactory bluetooth,
-			AndroidTorPluginFactory tor, AndroidLanTcpPluginFactory lan) {
+			AndroidTorPluginFactory tor, AndroidLanTcpPluginFactory lan,
+			AndroidRemovableDrivePluginFactory drive) {
 		@NotNullByDefault
 		PluginConfig pluginConfig = new PluginConfig() {
 
@@ -161,7 +165,7 @@ public class AppModule {
 
 			@Override
 			public Collection<SimplexPluginFactory> getSimplexFactories() {
-				return emptyList();
+				return singletonList(drive);
 			}
 
 			@Override

briar-android/src/main/java/org/briarproject/briar/android/account/DozeFragment.java

@@ -32,7 +32,6 @@ public class DozeFragment extends SetupFragment
 	private DozeView dozeView;
 	private HuaweiProtectedAppsView huaweiProtectedAppsView;
 	private HuaweiAppLaunchView huaweiAppLaunchView;
-	private XiaomiView xiaomiView;
 	private Button next;
 	private boolean secondAttempt = false;
 
@@ -54,8 +53,6 @@ public class DozeFragment extends SetupFragment
 		huaweiProtectedAppsView.setOnCheckedChangedListener(this);
 		huaweiAppLaunchView = v.findViewById(R.id.huaweiAppLaunchView);
 		huaweiAppLaunchView.setOnCheckedChangedListener(this);
-		xiaomiView = v.findViewById(R.id.xiaomiView);
-		xiaomiView.setOnCheckedChangedListener(this);
 		next = v.findViewById(R.id.next);
 		ProgressBar progressBar = v.findViewById(R.id.progress);
 
@@ -101,8 +98,7 @@ public class DozeFragment extends SetupFragment
 	public void onCheckedChanged() {
 		next.setEnabled(dozeView.isChecked() &&
 				huaweiProtectedAppsView.isChecked() &&
-				huaweiAppLaunchView.isChecked() &&
-				xiaomiView.isChecked());
+				huaweiAppLaunchView.isChecked());
 	}
 
 	@SuppressLint("BatteryLife")

briar-android/src/main/java/org/briarproject/briar/android/account/DozeHelperImpl.java

@@ -10,7 +10,6 @@ class DozeHelperImpl implements DozeHelper {
 		Context appContext = context.getApplicationContext();
 		return needsDozeWhitelisting(appContext) ||
 				HuaweiProtectedAppsView.needsToBeShown(appContext) ||
-				HuaweiAppLaunchView.needsToBeShown(appContext) ||
-				XiaomiView.isXiaomiOrRedmiDevice();
+				HuaweiAppLaunchView.needsToBeShown(appContext);
 	}
 }

briar-android/src/main/java/org/briarproject/briar/android/account/SetPasswordFragment.java

@@ -118,7 +118,7 @@ public class SetPasswordFragment extends SetupFragment {
 	@Override
 	public void onClick(View view) {
 		IBinder token = passwordEntry.getWindowToken();
-		Object o = requireContext().getSystemService(INPUT_METHOD_SERVICE);
+		Object o = getContext().getSystemService(INPUT_METHOD_SERVICE);
 		((InputMethodManager) o).hideSoftInputFromWindow(token, 0);
 		viewModel.setPassword(passwordEntry.getText().toString());
 	}

briar-android/src/main/java/org/briarproject/briar/android/account/SetupActivity.java

@@ -26,8 +26,6 @@ import static org.briarproject.briar.android.account.SetupViewModel.State.CREATE
 import static org.briarproject.briar.android.account.SetupViewModel.State.DOZE;
 import static org.briarproject.briar.android.account.SetupViewModel.State.FAILED;
 import static org.briarproject.briar.android.account.SetupViewModel.State.SET_PASSWORD;
-import static org.briarproject.briar.android.util.UiUtils.setInputStateAlwaysVisible;
-import static org.briarproject.briar.android.util.UiUtils.setInputStateHidden;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
@@ -57,13 +55,10 @@ public class SetupActivity extends BaseActivity
 
 	private void onStateChanged(SetupViewModel.State state) {
 		if (state == AUTHOR_NAME) {
-			setInputStateAlwaysVisible(this);
 			showInitialFragment(AuthorNameFragment.newInstance());
 		} else if (state == SET_PASSWORD) {
-			setInputStateAlwaysVisible(this);
 			showPasswordFragment();
 		} else if (state == DOZE) {
-			setInputStateHidden(this);
 			showDozeFragment();
 		} else if (state == CREATED || state == FAILED) {
 			// TODO: Show an error if failed