Fix tests.

Add ImageActivity to show image attachment in full-screen

See merge request briar/briar!999

bramble-android/src/main/java/org/briarproject/bramble/BrambleAndroidEagerSingletons.java

@@ -0,0 +1,11 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.battery.AndroidBatteryModule;
+import org.briarproject.bramble.network.AndroidNetworkModule;
+
+public interface BrambleAndroidEagerSingletons {
+
+	void inject(AndroidBatteryModule.EagerSingletons init);
+
+	void inject(AndroidNetworkModule.EagerSingletons init);
+}

bramble-android/src/main/java/org/briarproject/bramble/BrambleAndroidModule.java

@@ -15,4 +15,8 @@ import dagger.Module;
 })
 public class BrambleAndroidModule {
 
+	public static void initEagerSingletons(BrambleAndroidEagerSingletons c) {
+		c.inject(new AndroidBatteryModule.EagerSingletons());
+		c.inject(new AndroidNetworkModule.EagerSingletons());
+	}
 }

bramble-android/src/main/java/org/briarproject/bramble/battery/AndroidBatteryModule.java

@@ -3,6 +3,7 @@ package org.briarproject.bramble.battery;
 import org.briarproject.bramble.api.battery.BatteryManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 
+import javax.inject.Inject;
 import javax.inject.Singleton;
 
 import dagger.Module;
@@ -11,6 +12,11 @@ import dagger.Provides;
 @Module
 public class AndroidBatteryModule {
 
+	public static class EagerSingletons {
+		@Inject
+		BatteryManager batteryManager;
+	}
+
 	@Provides
 	@Singleton
 	BatteryManager provideBatteryManager(LifecycleManager lifecycleManager,

bramble-android/src/main/java/org/briarproject/bramble/network/AndroidNetworkModule.java

@@ -3,6 +3,7 @@ package org.briarproject.bramble.network;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.network.NetworkManager;
 
+import javax.inject.Inject;
 import javax.inject.Singleton;
 
 import dagger.Module;
@@ -11,6 +12,11 @@ import dagger.Provides;
 @Module
 public class AndroidNetworkModule {
 
+	public static class EagerSingletons {
+		@Inject
+		NetworkManager networkManager;
+	}
+
 	@Provides
 	@Singleton
 	NetworkManager provideNetworkManager(LifecycleManager lifecycleManager,

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

@@ -18,8 +18,8 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.util.AndroidUtils;
+import org.briarproject.bramble.util.IoUtils;
 
-import java.io.Closeable;
 import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.ArrayList;
@@ -51,7 +51,6 @@ import static android.bluetooth.BluetoothDevice.EXTRA_DEVICE;
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubMacAddress;
 
 @MethodsNotNullByDefault
@@ -161,11 +160,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	@Override
 	void tryToClose(@Nullable BluetoothServerSocket ss) {
-		try {
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
+		IoUtils.tryToClose(ss, LOG, WARNING);
 	}
 
 	@Override
@@ -195,7 +190,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 			s.connect();
 			return wrapSocket(s);
 		} catch (IOException e) {
-			tryToClose(s);
+			IoUtils.tryToClose(s, LOG, WARNING);
 			throw e;
 		}
 	}
@@ -268,14 +263,6 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 		return addresses;
 	}
 
-	private void tryToClose(@Nullable Closeable c) {
-		try {
-			if (c != null) c.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	private class BluetoothStateReceiver extends BroadcastReceiver {
 
 		@Override

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidSecureRandomProvider.java

@@ -1,5 +1,6 @@
 package org.briarproject.bramble.system;
 
+import android.annotation.SuppressLint;
 import android.app.Application;
 import android.bluetooth.BluetoothAdapter;
 import android.bluetooth.BluetoothDevice;
@@ -26,7 +27,7 @@ import static android.provider.Settings.Secure.ANDROID_ID;
 
 @Immutable
 @NotNullByDefault
-class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
+class AndroidSecureRandomProvider extends UnixSecureRandomProvider {
 
 	private static final int SEED_LENGTH = 32;
 
@@ -37,6 +38,7 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 		appContext = app.getApplicationContext();
 	}
 
+	@SuppressLint("HardwareIds")
 	@Override
 	protected void writeToEntropyPool(DataOutputStream out) throws IOException {
 		super.writeToEntropyPool(out);
@@ -49,12 +51,14 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 		String id = Settings.Secure.getString(contentResolver, ANDROID_ID);
 		if (id != null) out.writeUTF(id);
 		Parcel parcel = Parcel.obtain();
-		WifiManager wm =
-				(WifiManager) appContext.getSystemService(WIFI_SERVICE);
-		List<WifiConfiguration> configs = wm.getConfiguredNetworks();
-		if (configs != null) {
-			for (WifiConfiguration config : configs)
-				parcel.writeParcelable(config, 0);
+		WifiManager wm = (WifiManager) appContext.getApplicationContext()
+				.getSystemService(WIFI_SERVICE);
+		if (wm != null) {
+			List<WifiConfiguration> configs = wm.getConfiguredNetworks();
+			if (configs != null) {
+				for (WifiConfiguration config : configs)
+					parcel.writeParcelable(config, 0);
+			}
 		}
 		BluetoothAdapter bt = BluetoothAdapter.getDefaultAdapter();
 		if (bt != null) {
@@ -77,13 +81,13 @@ class AndroidSecureRandomProvider extends LinuxSecureRandomProvider {
 
 	// Based on https://android-developers.googleblog.com/2013/08/some-securerandom-thoughts.html
 	private void applyOpenSslFix() {
-		byte[] seed = new LinuxSecureRandomSpi().engineGenerateSeed(
+		byte[] seed = new UnixSecureRandomSpi().engineGenerateSeed(
 				SEED_LENGTH);
 		try {
 			// Seed the OpenSSL PRNG
 			Class.forName("org.apache.harmony.xnet.provider.jsse.NativeCrypto")
 					.getMethod("RAND_seed", byte[].class)
-					.invoke(null, seed);
+					.invoke(null, (Object) seed);
 			// Mix the output of the Linux PRNG into the OpenSSL PRNG
 			int bytesRead = (Integer) Class.forName(
 					"org.apache.harmony.xnet.provider.jsse.NativeCrypto")

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

@@ -1,7 +1,6 @@
-package org.briarproject.briar.client;
+package org.briarproject.bramble.api.client;
 
 import org.briarproject.bramble.api.FormatException;
-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.MetadataParser;
@@ -12,7 +11,7 @@ import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
-import org.briarproject.bramble.api.sync.ValidationManager.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -62,5 +61,4 @@ public abstract class BdfIncomingMessageHook implements IncomingMessageHook {
 			throw new InvalidMessageException(e);
 		}
 	}
-
 }

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

@@ -9,7 +9,7 @@ import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
-import org.briarproject.bramble.api.sync.ValidationManager.MessageValidator;
+import org.briarproject.bramble.api.sync.validation.MessageValidator;
 import org.briarproject.bramble.api.system.Clock;
 
 import java.util.logging.Logger;

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

@@ -19,6 +19,7 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySet;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
@@ -28,8 +29,6 @@ import java.util.Map;
 
 import javax.annotation.Nullable;
 
-import static org.briarproject.bramble.api.sync.ValidationManager.State;
-
 /**
  * Encapsulates the database implementation and exposes high-level operations
  * to other components.
@@ -374,12 +373,12 @@ public interface DatabaseComponent {
 	/**
 	 * Returns the IDs and states of all dependencies of the given message.
 	 * For missing dependencies and dependencies in other groups, the state
-	 * {@link State UNKNOWN} is returned.
+	 * {@link MessageState UNKNOWN} is returned.
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependencies(Transaction txn, MessageId m)
-			throws DbException;
+	Map<MessageId, MessageState> getMessageDependencies(Transaction txn,
+			MessageId m) throws DbException;
 
 	/**
 	 * Returns the IDs and states of all dependents of the given message.
@@ -388,15 +387,16 @@ public interface DatabaseComponent {
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependents(Transaction txn, MessageId m)
-			throws DbException;
+	Map<MessageId, MessageState> getMessageDependents(Transaction txn,
+			MessageId m) throws DbException;
 
 	/**
 	 * Gets the validation and delivery state of the given message.
 	 * <p/>
 	 * Read-only.
 	 */
-	State getMessageState(Transaction txn, MessageId m) throws DbException;
+	MessageState getMessageState(Transaction txn, MessageId m)
+			throws DbException;
 
 	/**
 	 * Returns the status of the given delivered message with respect to the
@@ -543,7 +543,7 @@ public interface DatabaseComponent {
 	/**
 	 * Sets the validation and delivery state of the given message.
 	 */
-	void setMessageState(Transaction txn, MessageId m, State state)
+	void setMessageState(Transaction txn, MessageId m, MessageState state)
 			throws DbException;
 
 	/**

bramble-api/src/main/java/org/briarproject/bramble/api/io/BlockSink.java

@@ -0,0 +1,20 @@
+package org.briarproject.bramble.api.io;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.sync.tree.TreeHash;
+
+import java.util.List;
+
+public interface BlockSink {
+
+	/**
+	 * Stores a block of the message with the given temporary ID.
+	 */
+	void putBlock(HashingId h, int blockNumber, byte[] data) throws DbException;
+
+	/**
+	 * Sets the hash tree path of a previously stored block.
+	 */
+	void setPath(HashingId h, int blockNumber, List<TreeHash> path)
+			throws DbException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/io/HashingId.java

@@ -0,0 +1,27 @@
+package org.briarproject.bramble.api.io;
+
+import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Type-safe wrapper for a byte array that uniquely identifies a
+ * {@link Message} while it's being hashed and the {@link MessageId} is not
+ * yet known.
+ */
+@ThreadSafe
+@NotNullByDefault
+public class HashingId extends UniqueId {
+
+	public HashingId(byte[] id) {
+		super(id);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof HashingId && super.equals(o);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/nullsafety/NullSafety.java

@@ -0,0 +1,15 @@
+package org.briarproject.bramble.api.nullsafety;
+
+import javax.annotation.Nullable;
+
+@NotNullByDefault
+public class NullSafety {
+
+	/**
+	 * Stand-in for `Objects.requireNonNull()`.
+	 */
+	public static <T> T requireNonNull(@Nullable T t) {
+		if (t == null) throw new NullPointerException();
+		return t;
+	}
+}

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

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.api.sync;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.tree.TreeHash;
 
 @NotNullByDefault
 public interface MessageFactory {
@@ -10,4 +11,6 @@ public interface MessageFactory {
 	Message createMessage(byte[] raw);
 
 	byte[] getRawMessage(Message m);
+
+	MessageId getMessageId(GroupId g, long timestamp, TreeHash rootHash);
 }

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

@@ -24,6 +24,12 @@ public class MessageId extends UniqueId {
 	public static final String BLOCK_LABEL =
 			"org.briarproject.bramble/MESSAGE_BLOCK";
 
+	/**
+	 * Label for hashing two tree hashes to produce a parent.
+	 */
+	public static final String TREE_LABEL =
+			"org.briarproject.bramble/MESSAGE_TREE";
+
 	public MessageId(byte[] id) {
 		super(id);
 	}

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

@@ -35,4 +35,9 @@ public interface SyncConstants {
 	 * The maximum number of message IDs in an ack, offer or request record.
 	 */
 	int MAX_MESSAGE_IDS = MAX_RECORD_PAYLOAD_BYTES / UniqueId.LENGTH;
+
+	/**
+	 * The maximum length of a message block in bytes.
+	 */
+	int MAX_BLOCK_LENGTH = 32 * 2014; // 32 KiB
 }

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

@@ -1,87 +0,0 @@
-package org.briarproject.bramble.api.sync;
-
-import org.briarproject.bramble.api.crypto.SecretKey;
-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.lifecycle.LifecycleManager;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-/**
- * Responsible for managing message validators and passing them messages to
- * validate.
- */
-@NotNullByDefault
-public interface ValidationManager {
-
-	enum State {
-
-		UNKNOWN(0), INVALID(1), PENDING(2), DELIVERED(3);
-
-		private final int value;
-
-		State(int value) {
-			this.value = value;
-		}
-
-		public int getValue() {
-			return value;
-		}
-
-		public static State fromValue(int value) {
-			for (State s : values()) if (s.value == value) return s;
-			throw new IllegalArgumentException();
-		}
-	}
-
-	/**
-	 * Registers the message validator for the given client. This method
-	 * should be called before
-	 * {@link LifecycleManager#startServices(SecretKey)}.
-	 */
-	void registerMessageValidator(ClientId c, int majorVersion,
-			MessageValidator v);
-
-	/**
-	 * Registers the incoming message hook for the given client. The hook will
-	 * be called once for each incoming message that passes validation. This
-	 * method should be called before
-	 * {@link LifecycleManager#startServices(SecretKey)}.
-	 */
-	void registerIncomingMessageHook(ClientId c, int majorVersion,
-			IncomingMessageHook hook);
-
-	interface MessageValidator {
-
-		/**
-		 * Validates the given message and returns its metadata and
-		 * dependencies.
-		 */
-		MessageContext validateMessage(Message m, Group g)
-				throws InvalidMessageException;
-	}
-
-	interface IncomingMessageHook {
-
-		/**
-		 * Called once for each incoming message that passes validation.
-		 *
-		 * @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!
-		 */
-		boolean incomingMessage(Transaction txn, Message m, Metadata meta)
-				throws DbException, InvalidMessageException;
-	}
-}

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

@@ -3,11 +3,10 @@ package org.briarproject.bramble.api.sync.event;
 import org.briarproject.bramble.api.event.Event;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 
 import javax.annotation.concurrent.Immutable;
 
-import static org.briarproject.bramble.api.sync.ValidationManager.State;
-
 /**
  * An event that is broadcast when a message state changed.
  */
@@ -17,10 +16,10 @@ public class MessageStateChangedEvent extends Event {
 
 	private final MessageId messageId;
 	private final boolean local;
-	private final State state;
+	private final MessageState state;
 
 	public MessageStateChangedEvent(MessageId messageId, boolean local,
-			State state) {
+			MessageState state) {
 		this.messageId = messageId;
 		this.local = local;
 		this.state = state;
@@ -34,7 +33,7 @@ public class MessageStateChangedEvent extends Event {
 		return local;
 	}
 
-	public State getState() {
+	public MessageState getState() {
 		return state;
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/api/sync/tree/LeafNode.java

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.api.sync.tree;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public class LeafNode extends TreeNode {
+
+	public LeafNode(TreeHash hash, int blockNumber) {
+		super(hash, 0, blockNumber, blockNumber);
+	}
+
+	@Override
+	public TreeNode getLeftChild() {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public TreeNode getRightChild() {
+		throw new UnsupportedOperationException();
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/tree/ParentNode.java

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.sync.tree;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public class ParentNode extends TreeNode {
+
+	private final TreeNode left, right;
+
+	public ParentNode(TreeHash hash, TreeNode left, TreeNode right) {
+		super(hash, Math.max(left.getHeight(), right.getHeight()) + 1,
+				left.getFirstBlockNumber(), right.getLastBlockNumber());
+		this.left = left;
+		this.right = right;
+	}
+
+	@Override
+	public TreeNode getLeftChild() {
+		return left;
+	}
+
+	@Override
+	public TreeNode getRightChild() {
+		return right;
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/tree/StreamHasher.java

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.api.sync.tree;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.io.BlockSink;
+import org.briarproject.bramble.api.io.HashingId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+@NotNullByDefault
+public interface StreamHasher {
+
+	/**
+	 * Reads the given input stream, divides the data into blocks, stores
+	 * the blocks and the resulting hash tree using the given block sink and
+	 * temporary ID, and returns the hash tree.
+	 */
+	TreeNode hash(InputStream in, BlockSink sink, HashingId h)
+			throws IOException, DbException;
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/tree/TreeHash.java

@@ -0,0 +1,24 @@
+package org.briarproject.bramble.api.sync.tree;
+
+import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Type-safe wrapper for a byte array that uniquely identifies a sequence of
+ * one or more message blocks.
+ */
+@ThreadSafe
+@NotNullByDefault
+public class TreeHash extends UniqueId {
+
+	public TreeHash(byte[] id) {
+		super(id);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof TreeHash && super.equals(o);
+	}
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/tree/TreeHasher.java

@@ -0,0 +1,11 @@
+package org.briarproject.bramble.api.sync.tree;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public interface TreeHasher {
+
+	LeafNode hashBlock(int blockNumber, byte[] data);
+
+	ParentNode mergeTrees(TreeNode left, TreeNode right);
+}

bramble-api/src/main/java/org/briarproject/bramble/api/sync/tree/TreeNode.java

@@ -0,0 +1,38 @@
+package org.briarproject.bramble.api.sync.tree;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public abstract class TreeNode {
+
+	private final TreeHash hash;
+	private final int height, firstBlockNumber, lastBlockNumber;
+
+	TreeNode(TreeHash hash, int height, int firstBlockNumber,
+			int lastBlockNumber) {
+		this.hash = hash;
+		this.height = height;
+		this.firstBlockNumber = firstBlockNumber;
+		this.lastBlockNumber = lastBlockNumber;
+	}
+
+	public TreeHash getHash() {
+		return hash;
+	}
+
+	public int getHeight() {
+		return height;
+	}
+
+	public int getFirstBlockNumber() {
+		return firstBlockNumber;
+	}
+
+	public int getLastBlockNumber() {
+		return lastBlockNumber;
+	}
+
+	public abstract TreeNode getLeftChild();
+
+	public abstract TreeNode getRightChild();
+}

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

@@ -0,0 +1,31 @@
+package org.briarproject.bramble.api.sync.validation;
+
+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.sync.InvalidMessageException;
+import org.briarproject.bramble.api.sync.Message;
+
+public interface IncomingMessageHook {
+
+	/**
+	 * Called once for each incoming message that passes validation.
+	 *
+	 * @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!
+	 */
+	boolean incomingMessage(Transaction txn, Message m, Metadata meta)
+			throws DbException, InvalidMessageException;
+}

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

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.api.sync.validation;
+
+public enum MessageState {
+
+	UNKNOWN(0), INVALID(1), PENDING(2), DELIVERED(3);
+
+	private final int value;
+
+	MessageState(int value) {
+		this.value = value;
+	}
+
+	public int getValue() {
+		return value;
+	}
+
+	public static MessageState fromValue(int value) {
+		for (MessageState s : values()) if (s.value == value) return s;
+		throw new IllegalArgumentException();
+	}
+}

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

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.api.sync.validation;
+
+import org.briarproject.bramble.api.sync.Group;
+import org.briarproject.bramble.api.sync.InvalidMessageException;
+import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageContext;
+
+public interface MessageValidator {
+
+	/**
+	 * Validates the given message and returns its metadata and
+	 * dependencies.
+	 */
+	MessageContext validateMessage(Message m, Group g)
+			throws InvalidMessageException;
+}

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

@@ -0,0 +1,31 @@
+package org.briarproject.bramble.api.sync.validation;
+
+import org.briarproject.bramble.api.crypto.SecretKey;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.ClientId;
+
+/**
+ * Responsible for managing message validators and passing them messages to
+ * validate.
+ */
+@NotNullByDefault
+public interface ValidationManager {
+
+	/**
+	 * Registers the {@link MessageValidator} for the given client. This method
+	 * should be called before
+	 * {@link LifecycleManager#startServices(SecretKey)}.
+	 */
+	void registerMessageValidator(ClientId c, int majorVersion,
+			MessageValidator v);
+
+	/**
+	 * Registers the {@link IncomingMessageHook} for the given client. The hook
+	 * will be called once for each incoming message that passes validation.
+	 * This method should be called before
+	 * {@link LifecycleManager#startServices(SecretKey)}.
+	 */
+	void registerIncomingMessageHook(ClientId c, int majorVersion,
+			IncomingMessageHook hook);
+}

bramble-api/src/main/java/org/briarproject/bramble/util/IoUtils.java

@@ -8,12 +8,15 @@ import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.net.ServerSocket;
 import java.net.Socket;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 
 import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
 public class IoUtils {
@@ -54,16 +57,35 @@ public class IoUtils {
 			out.flush();
 			out.close();
 		} catch (IOException e) {
-			tryToClose(in);
-			tryToClose(out);
+			tryToClose(in, LOG, WARNING);
+			tryToClose(out, LOG, WARNING);
 		}
 	}
 
-	private static void tryToClose(@Nullable Closeable c) {
+	public static void tryToClose(@Nullable Closeable c, Logger logger,
+			Level level) {
 		try {
 			if (c != null) c.close();
 		} catch (IOException e) {
-			// We did our best
+			logException(logger, level, e);
+		}
+	}
+
+	public static void tryToClose(@Nullable Socket s, Logger logger,
+			Level level) {
+		try {
+			if (s != null) s.close();
+		} catch (IOException e) {
+			logException(logger, level, e);
+		}
+	}
+
+	public static void tryToClose(@Nullable ServerSocket ss, Logger logger,
+			Level level) {
+		try {
+			if (ss != null) ss.close();
+		} catch (IOException e) {
+			logException(logger, level, e);
 		}
 	}
 

bramble-api/src/main/java/org/briarproject/bramble/util/OsUtils.java

@@ -10,8 +10,6 @@ public class OsUtils {
 	@Nullable
 	private static final String os = System.getProperty("os.name");
 	@Nullable
-	private static final String version = System.getProperty("os.version");
-	@Nullable
 	private static final String vendor = System.getProperty("java.vendor");
 
 	public static boolean isWindows() {

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

@@ -8,7 +8,7 @@ import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.plugin.PluginModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.reporting.ReportingModule;
-import org.briarproject.bramble.sync.SyncModule;
+import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.transport.TransportModule;
 import org.briarproject.bramble.versioning.VersioningModule;
@@ -31,11 +31,11 @@ public interface BrambleCoreEagerSingletons {
 
 	void inject(ReportingModule.EagerSingletons init);
 
-	void inject(SyncModule.EagerSingletons init);
-
 	void inject(SystemModule.EagerSingletons init);
 
 	void inject(TransportModule.EagerSingletons init);
 
+	void inject(ValidationModule.EagerSingletons init);
+
 	void inject(VersioningModule.EagerSingletons init);
 }

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

@@ -19,6 +19,7 @@ import org.briarproject.bramble.reporting.ReportingModule;
 import org.briarproject.bramble.settings.SettingsModule;
 import org.briarproject.bramble.socks.SocksModule;
 import org.briarproject.bramble.sync.SyncModule;
+import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.transport.TransportModule;
 import org.briarproject.bramble.versioning.VersioningModule;
@@ -47,6 +48,7 @@ import dagger.Module;
 		SyncModule.class,
 		SystemModule.class,
 		TransportModule.class,
+		ValidationModule.class,
 		VersioningModule.class
 })
 public class BrambleCoreModule {
@@ -60,9 +62,9 @@ public class BrambleCoreModule {
 		c.inject(new PluginModule.EagerSingletons());
 		c.inject(new PropertiesModule.EagerSingletons());
 		c.inject(new ReportingModule.EagerSingletons());
-		c.inject(new SyncModule.EagerSingletons());
 		c.inject(new SystemModule.EagerSingletons());
 		c.inject(new TransportModule.EagerSingletons());
+		c.inject(new ValidationModule.EagerSingletons());
 		c.inject(new VersioningModule.EagerSingletons());
 	}
 }

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

@@ -22,7 +22,7 @@ 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.sync.MessageStatus;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySet;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
@@ -106,7 +106,7 @@ interface Database<T> {
 	 * @param sender the contact from whom the message was received, or null
 	 * if the message was created locally.
 	 */
-	void addMessage(T txn, Message m, State state, boolean shared,
+	void addMessage(T txn, Message m, MessageState state, boolean shared,
 			@Nullable ContactId sender) throws DbException;
 
 	/**
@@ -114,7 +114,7 @@ interface Database<T> {
 	 * in the given state.
 	 */
 	void addMessageDependency(T txn, Message dependent, MessageId dependency,
-			State dependentState) throws DbException;
+			MessageState dependentState) throws DbException;
 
 	/**
 	 * Records that a message has been offered by the given contact.
@@ -310,11 +310,11 @@ interface Database<T> {
 	/**
 	 * Returns the IDs and states of all dependencies of the given message.
 	 * For missing dependencies and dependencies in other groups, the state
-	 * {@link State UNKNOWN} is returned.
+	 * {@link MessageState UNKNOWN} is returned.
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependencies(T txn, MessageId m)
+	Map<MessageId, MessageState> getMessageDependencies(T txn, MessageId m)
 			throws DbException;
 
 	/**
@@ -324,7 +324,7 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	Map<MessageId, State> getMessageDependents(T txn, MessageId m)
+	Map<MessageId, MessageState> getMessageDependents(T txn, MessageId m)
 			throws DbException;
 
 	/**
@@ -383,7 +383,7 @@ interface Database<T> {
 	 * <p/>
 	 * Read-only.
 	 */
-	State getMessageState(T txn, MessageId m) throws DbException;
+	MessageState getMessageState(T txn, MessageId m) throws DbException;
 
 	/**
 	 * Returns the status of all delivered messages in the given group with
@@ -637,7 +637,8 @@ interface Database<T> {
 	/**
 	 * Sets the validation and delivery state of the given message.
 	 */
-	void setMessageState(T txn, MessageId m, State state) throws DbException;
+	void setMessageState(T txn, MessageId m, MessageState state)
+			throws DbException;
 
 	/**
 	 * Sets the reordering window for the given key set and transport in the

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

@@ -43,7 +43,6 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
 import org.briarproject.bramble.api.sync.event.GroupAddedEvent;
 import org.briarproject.bramble.api.sync.event.GroupRemovedEvent;
 import org.briarproject.bramble.api.sync.event.GroupVisibilityUpdatedEvent;
@@ -55,6 +54,7 @@ import org.briarproject.bramble.api.sync.event.MessageToAckEvent;
 import org.briarproject.bramble.api.sync.event.MessageToRequestEvent;
 import org.briarproject.bramble.api.sync.event.MessagesAckedEvent;
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.transport.KeySet;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.TransportKeys;
@@ -75,8 +75,8 @@ import javax.inject.Inject;
 import static java.util.logging.Level.WARNING;
 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.ValidationManager.State.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_OFFERED_MESSAGES;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -579,7 +579,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public State getMessageState(Transaction transaction, MessageId m)
+	public MessageState getMessageState(Transaction transaction, MessageId m)
 			throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
@@ -619,8 +619,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependencies(Transaction transaction,
-			MessageId m) throws DbException {
+	public Map<MessageId, MessageState> getMessageDependencies(
+			Transaction transaction, MessageId m) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
@@ -628,8 +628,8 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependents(Transaction transaction,
-			MessageId m) throws DbException {
+	public Map<MessageId, MessageState> getMessageDependents(
+			Transaction transaction, MessageId m) throws DbException {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
 			throw new NoSuchMessageException();
@@ -918,7 +918,7 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 
 	@Override
 	public void setMessageState(Transaction transaction, MessageId m,
-			State state) throws DbException {
+			MessageState state) throws DbException {
 		if (transaction.isReadOnly()) throw new IllegalArgumentException();
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, m))
@@ -935,10 +935,10 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		T txn = unbox(transaction);
 		if (!db.containsMessage(txn, dependent.getId()))
 			throw new NoSuchMessageException();
-		State dependentState = db.getMessageState(txn, dependent.getId());
+		MessageState dependentState =
+				db.getMessageState(txn, dependent.getId());
 		for (MessageId dependency : dependencies) {
-			db.addMessageDependency(txn, dependent, dependency,
-					dependentState);
+			db.addMessageDependency(txn, dependent, dependency, dependentState);
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/db/H2Database.java

@@ -15,16 +15,23 @@ import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Properties;
+import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
 /**
  * Contains all the H2-specific code for the database.
  */
 @NotNullByDefault
 class H2Database extends JdbcDatabase {
 
+	private static final Logger LOG = getLogger(H2Database.class.getName());
+
 	private static final String HASH_TYPE = "BINARY(32)";
 	private static final String SECRET_TYPE = "BINARY(32)";
 	private static final String BINARY_TYPE = "BINARY";
@@ -121,8 +128,8 @@ class H2Database extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
-			tryToClose(c);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -14,16 +14,24 @@ import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.SQLException;
 import java.sql.Statement;
+import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
+
 /**
  * Contains all the HSQLDB-specific code for the database.
  */
 @NotNullByDefault
 class HyperSqlDatabase extends JdbcDatabase {
 
+	private static final Logger LOG =
+			getLogger(HyperSqlDatabase.class.getName());
+
 	private static final String HASH_TYPE = "BINARY(32)";
 	private static final String SECRET_TYPE = "BINARY(32)";
 	private static final String BINARY_TYPE = "BINARY";
@@ -72,8 +80,8 @@ class HyperSqlDatabase extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
-			tryToClose(c);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -122,8 +130,8 @@ class HyperSqlDatabase extends JdbcDatabase {
 			s.close();
 			c.close();
 		} catch (SQLException e) {
-			tryToClose(s);
-			tryToClose(c);
+			tryToClose(s, LOG, WARNING);
+			tryToClose(c, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -24,7 +24,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.KeySet;
@@ -64,14 +64,15 @@ 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.SyncConstants.MESSAGE_HEADER_LENGTH;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.PENDING;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.DB_SETTINGS_NAMESPACE;
 import static org.briarproject.bramble.db.DatabaseConstants.LAST_COMPACTED_KEY;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_COMPACTION_INTERVAL_MS;
 import static org.briarproject.bramble.db.DatabaseConstants.SCHEMA_VERSION_KEY;
 import static org.briarproject.bramble.db.ExponentialBackoff.calculateExpiry;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
@@ -458,30 +459,6 @@ abstract class JdbcDatabase implements Database<Connection> {
 		mergeSettings(txn, s, DB_SETTINGS_NAMESPACE);
 	}
 
-	private void tryToClose(@Nullable ResultSet rs) {
-		try {
-			if (rs != null) rs.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	protected void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	protected void tryToClose(@Nullable Connection c) {
-		try {
-			if (c != null) c.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	private void createTables(Connection txn) throws DbException {
 		Statement s = null;
 		try {
@@ -502,7 +479,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(dbTypes.replaceTypes(CREATE_INCOMING_KEYS));
 			s.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -519,7 +496,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			s.executeUpdate(INDEX_STATUSES_BY_CONTACT_ID_TIMESTAMP);
 			s.close();
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -566,11 +543,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 		} catch (SQLException e) {
 			// Try to close the connection
 			logException(LOG, WARNING, e);
-			try {
-				txn.close();
-			} catch (SQLException e1) {
-				logException(LOG, WARNING, e1);
-			}
+			tryToClose(txn, LOG, WARNING);
 			// Whatever happens, allow the database to close
 			connectionsLock.lock();
 			try {
@@ -659,8 +632,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return c;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -681,7 +654,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -704,7 +677,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			// Create a status row for each message in the group
 			addStatus(txn, c, g, groupShared);
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -724,7 +697,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			while (rs.next()) {
 				MessageId id = new MessageId(rs.getBytes(1));
 				long timestamp = rs.getLong(2);
-				State state = State.fromValue(rs.getInt(3));
+				MessageState state = MessageState.fromValue(rs.getInt(3));
 				boolean messageShared = rs.getBoolean(4);
 				int length = rs.getInt(5);
 				boolean deleted = rs.getBoolean(6);
@@ -735,8 +708,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs.close();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -761,13 +734,13 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public void addMessage(Connection txn, Message m, State state,
+	public void addMessage(Connection txn, Message m, MessageState state,
 			boolean messageShared, @Nullable ContactId sender)
 			throws DbException {
 		PreparedStatement ps = null;
@@ -810,7 +783,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -840,14 +813,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	private void addStatus(Connection txn, MessageId m, ContactId c, GroupId g,
-			long timestamp, int length, State state, boolean groupShared,
+			long timestamp, int length, MessageState state, boolean groupShared,
 			boolean messageShared, boolean deleted, boolean seen)
 			throws DbException {
 		PreparedStatement ps = null;
@@ -873,14 +846,15 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
 	public void addMessageDependency(Connection txn, Message dependent,
-			MessageId dependency, State dependentState) throws DbException {
+			MessageId dependency, MessageState dependentState)
+			throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -891,9 +865,9 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.setBytes(1, dependency.getBytes());
 			ps.setBytes(2, dependent.getGroupId().getBytes());
 			rs = ps.executeQuery();
-			State dependencyState = null;
+			MessageState dependencyState = null;
 			if (rs.next()) {
-				dependencyState = State.fromValue(rs.getInt(1));
+				dependencyState = MessageState.fromValue(rs.getInt(1));
 				if (rs.next()) throw new DbStateException();
 			}
 			rs.close();
@@ -914,8 +888,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -934,7 +908,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1014,8 +988,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return keySetId;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1038,8 +1012,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1060,8 +1034,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1082,8 +1056,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1104,8 +1078,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1126,8 +1100,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1148,8 +1122,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1173,8 +1147,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return found;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1197,8 +1171,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return count;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1222,7 +1196,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1239,7 +1213,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1272,8 +1246,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			return new Contact(c, author, localAuthorId, alias, verified,
 					active);
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1309,8 +1283,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return contacts;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1332,8 +1306,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1370,8 +1344,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return contacts;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1394,8 +1368,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return new Group(g, clientId, majorVersion, descriptor);
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1422,8 +1396,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return groups;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1448,8 +1422,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return v;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1472,8 +1446,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return visible;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1504,8 +1478,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return localAuthor;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1536,8 +1510,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return authors;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1565,8 +1539,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			System.arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
 			return new Message(m, g, timestamp, body);
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1589,8 +1563,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1627,8 +1601,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (intersection == null) throw new AssertionError();
 			return intersection;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1660,8 +1634,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return all;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1695,8 +1669,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return metadata;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1719,8 +1693,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return metadata;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1745,8 +1719,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return metadata;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1775,8 +1749,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return statuses;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1806,14 +1780,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return status;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependencies(Connection txn,
+	public Map<MessageId, MessageState> getMessageDependencies(Connection txn,
 			MessageId m) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1824,10 +1798,10 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
 			rs = ps.executeQuery();
-			Map<MessageId, State> dependencies = new HashMap<>();
+			Map<MessageId, MessageState> dependencies = new HashMap<>();
 			while (rs.next()) {
 				MessageId dependency = new MessageId(rs.getBytes(1));
-				State state = State.fromValue(rs.getInt(2));
+				MessageState state = MessageState.fromValue(rs.getInt(2));
 				if (rs.wasNull())
 					state = UNKNOWN; // Missing or in a different group
 				dependencies.put(dependency, state);
@@ -1836,14 +1810,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return dependencies;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public Map<MessageId, State> getMessageDependents(Connection txn,
+	public Map<MessageId, MessageState> getMessageDependents(Connection txn,
 			MessageId m) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1857,24 +1831,24 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, m.getBytes());
 			rs = ps.executeQuery();
-			Map<MessageId, State> dependents = new HashMap<>();
+			Map<MessageId, MessageState> dependents = new HashMap<>();
 			while (rs.next()) {
 				MessageId dependent = new MessageId(rs.getBytes(1));
-				State state = State.fromValue(rs.getInt(2));
+				MessageState state = MessageState.fromValue(rs.getInt(2));
 				dependents.put(dependent, state);
 			}
 			rs.close();
 			ps.close();
 			return dependents;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public State getMessageState(Connection txn, MessageId m)
+	public MessageState getMessageState(Connection txn, MessageId m)
 			throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
@@ -1884,14 +1858,14 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.setBytes(1, m.getBytes());
 			rs = ps.executeQuery();
 			if (!rs.next()) throw new DbStateException();
-			State state = State.fromValue(rs.getInt(1));
+			MessageState state = MessageState.fromValue(rs.getInt(1));
 			if (rs.next()) throw new DbStateException();
 			rs.close();
 			ps.close();
 			return state;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1915,8 +1889,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1949,8 +1923,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -1974,8 +1948,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2013,8 +1987,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2032,7 +2006,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 	}
 
 	private Collection<MessageId> getMessagesInState(Connection txn,
-			State state) throws DbException {
+			MessageState state) throws DbException {
 		PreparedStatement ps = null;
 		ResultSet rs = null;
 		try {
@@ -2047,8 +2021,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2075,8 +2049,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2105,8 +2079,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return nextSendTime;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2144,8 +2118,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return ids;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2167,8 +2141,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return s;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2233,8 +2207,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return keys;
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2253,7 +2227,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2280,7 +2254,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			}
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2307,7 +2281,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			}
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2337,7 +2311,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2359,7 +2333,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			rs = ps.executeQuery();
 			if (!rs.next()) throw new DbStateException();
 			GroupId g = new GroupId(rs.getBytes(1));
-			State state = State.fromValue(rs.getInt(2));
+			MessageState state = MessageState.fromValue(rs.getInt(2));
 			rs.close();
 			ps.close();
 			// Insert any keys that don't already exist
@@ -2382,8 +2356,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2449,7 +2423,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			}
 			return added;
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2496,7 +2470,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2515,7 +2489,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2534,7 +2508,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2553,7 +2527,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2570,7 +2544,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2586,7 +2560,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2614,7 +2588,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2631,7 +2605,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2647,7 +2621,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2666,7 +2640,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			ps.close();
 			return affected == 1;
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2691,7 +2665,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2708,7 +2682,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2729,7 +2703,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2748,7 +2722,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2766,7 +2740,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2784,7 +2758,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2803,7 +2777,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2833,7 +2807,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2859,13 +2833,13 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
 
 	@Override
-	public void setMessageState(Connection txn, MessageId m, State state)
+	public void setMessageState(Connection txn, MessageId m, MessageState state)
 			throws DbException {
 		PreparedStatement ps = null;
 		try {
@@ -2912,7 +2886,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2935,7 +2909,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2954,7 +2928,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected < 0 || affected > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -2990,8 +2964,8 @@ abstract class JdbcDatabase implements Database<Connection> {
 			if (affected != 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(rs);
-			tryToClose(ps);
+			tryToClose(rs, LOG, WARNING);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
@@ -3058,7 +3032,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 				if (rows < 0 || rows > 1) throw new DbStateException();
 			ps.close();
 		} catch (SQLException e) {
-			tryToClose(ps);
+			tryToClose(ps, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}

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

@@ -0,0 +1,42 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+import javax.annotation.Nullable;
+
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+class JdbcUtils {
+
+	static void tryToClose(@Nullable ResultSet rs, Logger logger, Level level) {
+		try {
+			if (rs != null) rs.close();
+		} catch (SQLException e) {
+			logException(logger, level, e);
+		}
+	}
+
+	static void tryToClose(@Nullable Statement s, Logger logger, Level level) {
+		try {
+			if (s != null) s.close();
+		} catch (SQLException e) {
+			logException(logger, level, e);
+		}
+	}
+
+	static void tryToClose(@Nullable Connection c, Logger logger, Level level) {
+		try {
+			if (c != null) c.close();
+		} catch (SQLException e) {
+			logException(logger, level, e);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/db/Migration38_39.java

@@ -7,10 +7,8 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
-
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration38_39 implements Migration<Connection> {
 
@@ -40,16 +38,8 @@ class Migration38_39 implements Migration<Connection> {
 					+ " ALTER COLUMN contactId"
 					+ " SET NOT NULL");
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
-
-	private void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

bramble-core/src/main/java/org/briarproject/bramble/db/Migration39_40.java

@@ -7,10 +7,8 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
-
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration39_40 implements Migration<Connection> {
 
@@ -39,16 +37,8 @@ class Migration39_40 implements Migration<Connection> {
 					+ " ALTER COLUMN eta"
 					+ " SET NOT NULL");
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
-
-	private void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

bramble-core/src/main/java/org/briarproject/bramble/db/Migration40_41.java

@@ -7,11 +7,9 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
-
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.db.JdbcUtils.tryToClose;
 
 class Migration40_41 implements Migration<Connection> {
 
@@ -41,16 +39,8 @@ class Migration40_41 implements Migration<Connection> {
 			s.execute("ALTER TABLE contacts"
 					+ dbTypes.replaceTypes(" ADD alias _STRING"));
 		} catch (SQLException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw new DbException(e);
 		}
 	}
-
-	private void tryToClose(@Nullable Statement s) {
-		try {
-			if (s != null) s.close();
-		} catch (SQLException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

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

@@ -4,12 +4,11 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportConnectionReader;
 
 import java.io.File;
-import java.io.IOException;
 import java.io.InputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @NotNullByDefault
 class FileTransportReader implements TransportConnectionReader {
@@ -34,11 +33,7 @@ class FileTransportReader implements TransportConnectionReader {
 
 	@Override
 	public void dispose(boolean exception, boolean recognised) {
-		try {
-			in.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
+		tryToClose(in, LOG, WARNING);
 		plugin.readerFinished(file, exception, recognised);
 	}
 }

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

@@ -4,12 +4,11 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportConnectionWriter;
 
 import java.io.File;
-import java.io.IOException;
 import java.io.OutputStream;
 import java.util.logging.Logger;
 
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @NotNullByDefault
 class FileTransportWriter implements TransportConnectionWriter {
@@ -44,11 +43,7 @@ class FileTransportWriter implements TransportConnectionWriter {
 
 	@Override
 	public void dispose(boolean exception) {
-		try {
-			out.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
+		tryToClose(out, LOG, WARNING);
 		plugin.writerFinished(file, exception);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/LanTcpPlugin.java

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.util.IoUtils;
 import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
@@ -35,7 +36,6 @@ import static org.briarproject.bramble.api.plugin.LanTcpConstants.ID;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PREF_LAN_IP_PORTS;
 import static org.briarproject.bramble.api.plugin.LanTcpConstants.PROP_IP_PORTS;
 import static org.briarproject.bramble.util.ByteUtils.MAX_16_BIT_UNSIGNED;
-import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.PrivacyUtils.scrubSocketAddress;
 
 @NotNullByDefault
@@ -293,11 +293,7 @@ class LanTcpPlugin extends TcpPlugin {
 
 		@Override
 		public void close() {
-			try {
-				ss.close();
-			} catch (IOException e) {
-				logException(LOG, WARNING, e);
-			}
+			IoUtils.tryToClose(ss, LOG, WARNING);
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/plugin/tcp/TcpPlugin.java

@@ -11,6 +11,7 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.properties.TransportProperties;
+import org.briarproject.bramble.util.IoUtils;
 import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
@@ -153,13 +154,8 @@ abstract class TcpPlugin implements DuplexPlugin {
 	}
 
 	protected void tryToClose(@Nullable ServerSocket ss) {
-		try {
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		} finally {
-			callback.transportDisabled();
-		}
+		IoUtils.tryToClose(ss, LOG, WARNING);
+		callback.transportDisabled();
 	}
 
 	String getIpPortString(InetSocketAddress a) {

bramble-core/src/main/java/org/briarproject/bramble/plugin/tor/TorPlugin.java

@@ -31,7 +31,6 @@ import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
 import org.briarproject.bramble.util.IoUtils;
 
-import java.io.Closeable;
 import java.io.EOFException;
 import java.io.File;
 import java.io.FileInputStream;
@@ -303,8 +302,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			IoUtils.copyAndClose(in, out);
 			doneFile.createNewFile();
 		} catch (IOException e) {
-			tryToClose(in);
-			tryToClose(out);
+			IoUtils.tryToClose(in, LOG, WARNING);
+			IoUtils.tryToClose(out, LOG, WARNING);
 			throw new PluginException(e);
 		}
 	}
@@ -341,22 +340,6 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 		return getClass().getClassLoader().getResourceAsStream("torrc");
 	}
 
-	private void tryToClose(@Nullable Closeable c) {
-		try {
-			if (c != null) c.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private void tryToClose(@Nullable Socket s) {
-		try {
-			if (s != null) s.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	private void listFiles(File f) {
 		if (f.isDirectory()) {
 			File[] children = f.listFiles();
@@ -378,7 +361,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			}
 			return b;
 		} finally {
-			tryToClose(in);
+			IoUtils.tryToClose(in, LOG, WARNING);
 		}
 	}
 
@@ -418,13 +401,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 	}
 
 	private void tryToClose(@Nullable ServerSocket ss) {
-		try {
-			if (ss != null) ss.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		} finally {
-			callback.transportDisabled();
-		}
+		IoUtils.tryToClose(ss, LOG, WARNING);
+		callback.transportDisabled();
 	}
 
 	private void publishHiddenService(String port) {
@@ -593,7 +571,7 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				LOG.info("Could not connect to " + scrubOnion(bestOnion)
 						+ ": " + e.toString());
 			}
-			tryToClose(s);
+			IoUtils.tryToClose(s, LOG, WARNING);
 			return null;
 		}
 	}

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

@@ -5,7 +5,7 @@ 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.properties.TransportPropertyManager;
-import org.briarproject.bramble.api.sync.ValidationManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 

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

@@ -24,7 +24,7 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager.ClientVersioningHook;

bramble-core/src/main/java/org/briarproject/bramble/reporting/DevReporterImpl.java

@@ -12,7 +12,6 @@ import org.briarproject.bramble.api.reporting.DevReporter;
 import org.briarproject.bramble.util.IoUtils;
 import org.briarproject.bramble.util.StringUtils;
 
-import java.io.Closeable;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
@@ -26,13 +25,12 @@ import java.net.Socket;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
-import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 import javax.net.SocketFactory;
 
 import static java.util.logging.Level.WARNING;
-import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
 
 @Immutable
 @NotNullByDefault
@@ -66,7 +64,7 @@ class DevReporterImpl implements DevReporter, EventListener {
 			s.setSoTimeout(SOCKET_TIMEOUT);
 			return s;
 		} catch (IOException e) {
-			tryToClose(s);
+			tryToClose(s, LOG, WARNING);
 			throw e;
 		}
 	}
@@ -88,8 +86,7 @@ class DevReporterImpl implements DevReporter, EventListener {
 			writer.append(armoured);
 			writer.flush();
 		} finally {
-			if (writer != null)
-				writer.close();
+			tryToClose(writer, LOG, WARNING);
 		}
 	}
 
@@ -121,27 +118,11 @@ class DevReporterImpl implements DevReporter, EventListener {
 				f.delete();
 			} catch (IOException e) {
 				LOG.log(WARNING, "Failed to send reports", e);
-				tryToClose(out);
-				tryToClose(in);
+				tryToClose(out, LOG, WARNING);
+				tryToClose(in, LOG, WARNING);
 				return;
 			}
 		}
 		LOG.info("Reports sent");
 	}
-
-	private void tryToClose(@Nullable Closeable c) {
-		try {
-			if (c != null) c.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
-	private void tryToClose(@Nullable Socket s) {
-		try {
-			if (s != null) s.close();
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
 }

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

@@ -7,6 +7,7 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.sync.tree.TreeHash;
 import org.briarproject.bramble.util.ByteUtils;
 
 import javax.annotation.concurrent.Immutable;
@@ -39,13 +40,19 @@ class MessageFactoryImpl implements MessageFactory {
 		if (body.length == 0) throw new IllegalArgumentException();
 		if (body.length > MAX_MESSAGE_BODY_LENGTH)
 			throw new IllegalArgumentException();
-		MessageId id = getMessageId(g, timestamp, body);
+		MessageId id = getMessageIdFromBody(g, timestamp, body);
 		return new Message(id, g, timestamp, body);
 	}
 
-	private MessageId getMessageId(GroupId g, long timestamp, byte[] body) {
+	private MessageId getMessageIdFromBody(GroupId g, long timestamp,
+			byte[] body) {
 		// There's only one block, so the root hash is the hash of the block
 		byte[] rootHash = crypto.hash(BLOCK_LABEL, FORMAT_VERSION_BYTES, body);
+		return getMessageIdFromRootHash(g, timestamp, rootHash);
+	}
+
+	private MessageId getMessageIdFromRootHash(GroupId g, long timestamp,
+			byte[] rootHash) {
 		byte[] timeBytes = new byte[INT_64_BYTES];
 		ByteUtils.writeUint64(timestamp, timeBytes, 0);
 		byte[] idHash = crypto.hash(ID_LABEL, FORMAT_VERSION_BYTES,
@@ -65,7 +72,7 @@ class MessageFactoryImpl implements MessageFactory {
 		long timestamp = ByteUtils.readUint64(raw, UniqueId.LENGTH);
 		byte[] body = new byte[raw.length - MESSAGE_HEADER_LENGTH];
 		System.arraycopy(raw, MESSAGE_HEADER_LENGTH, body, 0, body.length);
-		MessageId id = getMessageId(g, timestamp, body);
+		MessageId id = getMessageIdFromBody(g, timestamp, body);
 		return new Message(id, g, timestamp, body);
 	}
 
@@ -78,4 +85,10 @@ class MessageFactoryImpl implements MessageFactory {
 		System.arraycopy(body, 0, raw, MESSAGE_HEADER_LENGTH, body.length);
 		return raw;
 	}
+
+	@Override
+	public MessageId getMessageId(GroupId g, long timestamp,
+			TreeHash rootHash) {
+		return getMessageIdFromRootHash(g, timestamp, rootHash.getBytes());
+	}
 }

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

@@ -1,23 +1,11 @@
 package org.briarproject.bramble.sync;
 
-import org.briarproject.bramble.PoliteExecutor;
-import org.briarproject.bramble.api.crypto.CryptoComponent;
-import org.briarproject.bramble.api.crypto.CryptoExecutor;
-import org.briarproject.bramble.api.db.DatabaseComponent;
-import org.briarproject.bramble.api.db.DatabaseExecutor;
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.sync.GroupFactory;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.SyncRecordReaderFactory;
 import org.briarproject.bramble.api.sync.SyncRecordWriterFactory;
 import org.briarproject.bramble.api.sync.SyncSessionFactory;
-import org.briarproject.bramble.api.sync.ValidationManager;
-import org.briarproject.bramble.api.system.Clock;
 
-import java.util.concurrent.Executor;
-
-import javax.inject.Inject;
 import javax.inject.Singleton;
 
 import dagger.Module;
@@ -26,29 +14,14 @@ import dagger.Provides;
 @Module
 public class SyncModule {
 
-	public static class EagerSingletons {
-		@Inject
-		ValidationManager validationManager;
-	}
-
-	/**
-	 * The maximum number of validation tasks to delegate to the crypto
-	 * executor concurrently.
-	 * <p>
-	 * The number of available processors can change during the lifetime of the
-	 * JVM, so this is just a reasonable guess.
-	 */
-	private static final int MAX_CONCURRENT_VALIDATION_TASKS =
-			Math.max(1, Runtime.getRuntime().availableProcessors() - 1);
-
 	@Provides
-	GroupFactory provideGroupFactory(CryptoComponent crypto) {
-		return new GroupFactoryImpl(crypto);
+	GroupFactory provideGroupFactory(GroupFactoryImpl groupFactory) {
+		return groupFactory;
 	}
 
 	@Provides
-	MessageFactory provideMessageFactory(CryptoComponent crypto) {
-		return new MessageFactoryImpl(crypto);
+	MessageFactory provideMessageFactory(MessageFactoryImpl messageFactory) {
+		return messageFactory;
 	}
 
 	@Provides
@@ -65,30 +38,8 @@ public class SyncModule {
 
 	@Provides
 	@Singleton
-	SyncSessionFactory provideSyncSessionFactory(DatabaseComponent db,
-			@DatabaseExecutor Executor dbExecutor, EventBus eventBus,
-			Clock clock, SyncRecordReaderFactory recordReaderFactory,
-			SyncRecordWriterFactory recordWriterFactory) {
-		return new SyncSessionFactoryImpl(db, dbExecutor, eventBus, clock,
-				recordReaderFactory, recordWriterFactory);
-	}
-
-	@Provides
-	@Singleton
-	ValidationManager provideValidationManager(
-			LifecycleManager lifecycleManager, EventBus eventBus,
-			ValidationManagerImpl validationManager) {
-		lifecycleManager.registerService(validationManager);
-		eventBus.addListener(validationManager);
-		return validationManager;
-	}
-
-	@Provides
-	@Singleton
-	@ValidationExecutor
-	Executor provideValidationExecutor(
-			@CryptoExecutor Executor cryptoExecutor) {
-		return new PoliteExecutor("ValidationExecutor", cryptoExecutor,
-				MAX_CONCURRENT_VALIDATION_TASKS);
+	SyncSessionFactory provideSyncSessionFactory(
+			SyncSessionFactoryImpl syncSessionFactory) {
+		return syncSessionFactory;
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/sync/tree/HashTree.java

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.sync.tree;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.tree.LeafNode;
+import org.briarproject.bramble.api.sync.tree.TreeNode;
+
+import javax.annotation.concurrent.NotThreadSafe;
+
+@NotThreadSafe
+@NotNullByDefault
+interface HashTree {
+
+	void addLeaf(LeafNode leaf);
+
+	TreeNode getRoot();
+}

bramble-core/src/main/java/org/briarproject/bramble/sync/tree/HashTreeImpl.java

@@ -0,0 +1,46 @@
+package org.briarproject.bramble.sync.tree;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.tree.LeafNode;
+import org.briarproject.bramble.api.sync.tree.TreeHasher;
+import org.briarproject.bramble.api.sync.tree.TreeNode;
+
+import java.util.Deque;
+import java.util.LinkedList;
+
+import javax.inject.Inject;
+
+@NotNullByDefault
+class HashTreeImpl implements HashTree {
+
+	private final TreeHasher treeHasher;
+	private final Deque<TreeNode> nodes = new LinkedList<>();
+
+	@Inject
+	HashTreeImpl(TreeHasher treeHasher) {
+		this.treeHasher = treeHasher;
+	}
+
+	@Override
+	public void addLeaf(LeafNode leaf) {
+		TreeNode add = leaf;
+		int height = leaf.getHeight();
+		TreeNode last = nodes.peekLast();
+		while (last != null && last.getHeight() == height) {
+			add = treeHasher.mergeTrees(last, add);
+			height = add.getHeight();
+			nodes.removeLast();
+			last = nodes.peekLast();
+		}
+		nodes.addLast(add);
+	}
+
+	@Override
+	public TreeNode getRoot() {
+		TreeNode root = nodes.removeLast();
+		while (!nodes.isEmpty()) {
+			root = treeHasher.mergeTrees(nodes.removeLast(), root);
+		}
+		return root;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/sync/tree/StreamHasherImpl.java

@@ -0,0 +1,85 @@
+package org.briarproject.bramble.sync.tree;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.io.BlockSink;
+import org.briarproject.bramble.api.io.HashingId;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.tree.StreamHasher;
+import org.briarproject.bramble.api.sync.tree.TreeHash;
+import org.briarproject.bramble.api.sync.tree.TreeHasher;
+import org.briarproject.bramble.api.sync.tree.TreeNode;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.LinkedList;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+import javax.inject.Provider;
+
+import static java.util.Arrays.copyOfRange;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_BLOCK_LENGTH;
+
+@Immutable
+@NotNullByDefault
+class StreamHasherImpl implements StreamHasher {
+
+	private final TreeHasher treeHasher;
+	private final Provider<HashTree> hashTreeProvider;
+
+	@Inject
+	StreamHasherImpl(TreeHasher treeHasher,
+			Provider<HashTree> hashTreeProvider) {
+		this.treeHasher = treeHasher;
+		this.hashTreeProvider = hashTreeProvider;
+	}
+
+	@Override
+	public TreeNode hash(InputStream in, BlockSink sink, HashingId h)
+			throws IOException, DbException {
+		HashTree tree = hashTreeProvider.get();
+		byte[] block = new byte[MAX_BLOCK_LENGTH];
+		int read;
+		for (int blockNumber = 0; (read = read(in, block)) > 0; blockNumber++) {
+			byte[] data;
+			if (read == block.length) data = block;
+			else data = copyOfRange(block, 0, read);
+			sink.putBlock(h, blockNumber, data);
+			tree.addLeaf(treeHasher.hashBlock(blockNumber, data));
+		}
+		TreeNode root = tree.getRoot();
+		setPaths(sink, h, root, new LinkedList<>());
+		return root;
+	}
+
+	/**
+	 * Reads a block from the given input stream and returns the number of
+	 * bytes read, or 0 if no bytes were read before reaching the end of the
+	 * stream.
+	 */
+	private int read(InputStream in, byte[] block) throws IOException {
+		int offset = 0;
+		while (offset < block.length) {
+			int read = in.read(block, offset, block.length - offset);
+			if (read == -1) return offset;
+			offset += read;
+		}
+		return offset;
+	}
+
+	private void setPaths(BlockSink sink, HashingId h, TreeNode node,
+			LinkedList<TreeHash> path) throws DbException {
+		if (node.getHeight() == 0) {
+			// We've reached a leaf - store the path
+			sink.setPath(h, node.getFirstBlockNumber(), path);
+		} else {
+			// Add the right child's hash to the path and traverse the left
+			path.addFirst(node.getRightChild().getHash());
+			setPaths(sink, h, node.getLeftChild(), path);
+			// Add the left child's hash to the path and traverse the right
+			path.removeFirst();
+			path.addFirst(node.getLeftChild().getHash());
+			setPaths(sink, h, node.getRightChild(), path);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/sync/tree/TreeHasherImpl.java

@@ -0,0 +1,44 @@
+package org.briarproject.bramble.sync.tree;
+
+import org.briarproject.bramble.api.crypto.CryptoComponent;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.tree.LeafNode;
+import org.briarproject.bramble.api.sync.tree.ParentNode;
+import org.briarproject.bramble.api.sync.tree.TreeHash;
+import org.briarproject.bramble.api.sync.tree.TreeHasher;
+import org.briarproject.bramble.api.sync.tree.TreeNode;
+
+import javax.annotation.concurrent.Immutable;
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.api.sync.Message.FORMAT_VERSION;
+import static org.briarproject.bramble.api.sync.MessageId.BLOCK_LABEL;
+import static org.briarproject.bramble.api.sync.MessageId.TREE_LABEL;
+
+@Immutable
+@NotNullByDefault
+class TreeHasherImpl implements TreeHasher {
+
+	private static final byte[] FORMAT_VERSION_BYTES =
+			new byte[] {FORMAT_VERSION};
+
+	private final CryptoComponent crypto;
+
+	@Inject
+	TreeHasherImpl(CryptoComponent crypto) {
+		this.crypto = crypto;
+	}
+
+	@Override
+	public LeafNode hashBlock(int blockNumber, byte[] data) {
+		byte[] hash = crypto.hash(BLOCK_LABEL, FORMAT_VERSION_BYTES, data);
+		return new LeafNode(new TreeHash(hash), blockNumber);
+	}
+
+	@Override
+	public ParentNode mergeTrees(TreeNode left, TreeNode right) {
+		byte[] hash = crypto.hash(TREE_LABEL, FORMAT_VERSION_BYTES,
+				left.getHash().getBytes(), right.getHash().getBytes());
+		return new ParentNode(new TreeHash(hash), left, right);
+	}
+}

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

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.sync;
+package org.briarproject.bramble.sync.validation;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.Target;

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

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.sync;
+package org.briarproject.bramble.sync.validation;
 
 import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.db.DatabaseComponent;
@@ -18,8 +18,11 @@ import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager;
 import org.briarproject.bramble.api.sync.event.MessageAddedEvent;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.MessageState;
+import org.briarproject.bramble.api.sync.validation.MessageValidator;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
 import org.briarproject.bramble.api.versioning.ClientMajorVersion;
 
 import java.util.Collection;
@@ -37,9 +40,9 @@ 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.ValidationManager.State.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
+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;
 import static org.briarproject.bramble.util.LogUtils.logException;
 
 @ThreadSafe
@@ -166,9 +169,9 @@ class ValidationManagerImpl implements ValidationManager, Service,
 				// Check if message is still pending
 				if (db.getMessageState(txn, id) == PENDING) {
 					// Check if dependencies are valid and delivered
-					Map<MessageId, State> states =
+					Map<MessageId, MessageState> states =
 							db.getMessageDependencies(txn, id);
-					for (Entry<MessageId, State> e : states.entrySet()) {
+					for (Entry<MessageId, MessageState> e : states.entrySet()) {
 						if (e.getValue() == INVALID) anyInvalid = true;
 						if (e.getValue() != DELIVERED) allDelivered = false;
 					}
@@ -256,9 +259,9 @@ class ValidationManagerImpl implements ValidationManager, Service,
 				if (!dependencies.isEmpty()) {
 					db.addMessageDependencies(txn, m, dependencies);
 					// Check if dependencies are valid and delivered
-					Map<MessageId, State> states =
+					Map<MessageId, MessageState> states =
 							db.getMessageDependencies(txn, id);
-					for (Entry<MessageId, State> e : states.entrySet()) {
+					for (Entry<MessageId, MessageState> e : states.entrySet()) {
 						if (e.getValue() == INVALID) anyInvalid = true;
 						if (e.getValue() != DELIVERED) allDelivered = false;
 					}
@@ -322,8 +325,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void addPendingDependents(Transaction txn, MessageId m,
 			Queue<MessageId> pending) throws DbException {
-		Map<MessageId, State> states = db.getMessageDependents(txn, m);
-		for (Entry<MessageId, State> e : states.entrySet()) {
+		Map<MessageId, MessageState> states = db.getMessageDependents(txn, m);
+		for (Entry<MessageId, MessageState> e : states.entrySet()) {
 			if (e.getValue() == PENDING) pending.add(e.getKey());
 		}
 	}
@@ -411,8 +414,8 @@ class ValidationManagerImpl implements ValidationManager, Service,
 	@DatabaseExecutor
 	private void addDependentsToInvalidate(Transaction txn,
 			MessageId m, Queue<MessageId> invalidate) throws DbException {
-		Map<MessageId, State> states = db.getMessageDependents(txn, m);
-		for (Entry<MessageId, State> e : states.entrySet()) {
+		Map<MessageId, MessageState> states = db.getMessageDependents(txn, m);
+		for (Entry<MessageId, MessageState> e : states.entrySet()) {
 			if (e.getValue() != INVALID) invalidate.add(e.getKey());
 		}
 	}

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

@@ -0,0 +1,53 @@
+package org.briarproject.bramble.sync.validation;
+
+import org.briarproject.bramble.PoliteExecutor;
+import org.briarproject.bramble.api.crypto.CryptoExecutor;
+import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
+
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+import javax.inject.Singleton;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class ValidationModule {
+
+	public static class EagerSingletons {
+		@Inject
+		ValidationManager validationManager;
+	}
+
+	/**
+	 * The maximum number of validation tasks to delegate to the crypto
+	 * executor concurrently.
+	 * <p>
+	 * The number of available processors can change during the lifetime of the
+	 * JVM, so this is just a reasonable guess.
+	 */
+	private static final int MAX_CONCURRENT_VALIDATION_TASKS =
+			Math.max(1, Runtime.getRuntime().availableProcessors() - 1);
+
+	@Provides
+	@Singleton
+	ValidationManager provideValidationManager(
+			LifecycleManager lifecycleManager, EventBus eventBus,
+			ValidationManagerImpl validationManager) {
+		lifecycleManager.registerService(validationManager);
+		eventBus.addListener(validationManager);
+		return validationManager;
+	}
+
+	@Provides
+	@Singleton
+	@ValidationExecutor
+	Executor provideValidationExecutor(
+			@CryptoExecutor Executor cryptoExecutor) {
+		return new PoliteExecutor("ValidationExecutor", cryptoExecutor,
+				MAX_CONCURRENT_VALIDATION_TASKS);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/system/UnixSecureRandomProvider.java

@@ -13,32 +13,33 @@ 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.util.LogUtils.logException;
 
 @Immutable
 @NotNullByDefault
-class LinuxSecureRandomProvider extends AbstractSecureRandomProvider {
+class UnixSecureRandomProvider extends AbstractSecureRandomProvider {
 
 	private static final Logger LOG =
-			Logger.getLogger(LinuxSecureRandomProvider.class.getName());
+			getLogger(UnixSecureRandomProvider.class.getName());
 
 	private static final File RANDOM_DEVICE = new File("/dev/urandom");
 
 	private final AtomicBoolean seeded = new AtomicBoolean(false);
 	private final File outputDevice;
 
-	LinuxSecureRandomProvider() {
+	UnixSecureRandomProvider() {
 		this(RANDOM_DEVICE);
 	}
 
-	LinuxSecureRandomProvider(File outputDevice) {
+	UnixSecureRandomProvider(File outputDevice) {
 		this.outputDevice = outputDevice;
 	}
 
 	@Override
 	public Provider getProvider() {
 		if (!seeded.getAndSet(true)) writeSeed();
-		return new LinuxProvider();
+		return new UnixProvider();
 	}
 
 	protected void writeSeed() {
@@ -55,15 +56,15 @@ class LinuxSecureRandomProvider extends AbstractSecureRandomProvider {
 	}
 
 	// Based on https://android-developers.googleblog.com/2013/08/some-securerandom-thoughts.html
-	private static class LinuxProvider extends Provider {
+	private static class UnixProvider extends Provider {
 
-		private LinuxProvider() {
-			super("LinuxPRNG", 1.1, "A Linux-specific PRNG using /dev/urandom");
+		private UnixProvider() {
+			super("UnixPRNG", 1.0, "A Unix-specific PRNG using /dev/urandom");
 			// Although /dev/urandom is not a SHA-1 PRNG, some callers
 			// explicitly request a SHA1PRNG SecureRandom and we need to
 			// prevent them from getting the default implementation whose
 			// output may have low entropy.
-			put("SecureRandom.SHA1PRNG", LinuxSecureRandomSpi.class.getName());
+			put("SecureRandom.SHA1PRNG", UnixSecureRandomSpi.class.getName());
 			put("SecureRandom.SHA1PRNG ImplementedIn", "Software");
 		}
 	}

bramble-core/src/main/java/org/briarproject/bramble/system/UnixSecureRandomSpi.java

@@ -10,22 +10,24 @@ import java.security.SecureRandomSpi;
 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.LogUtils.logException;
 
-public class LinuxSecureRandomSpi extends SecureRandomSpi {
+public class UnixSecureRandomSpi extends SecureRandomSpi {
 
 	private static final Logger LOG =
-			Logger.getLogger(LinuxSecureRandomSpi.class.getName());
+			getLogger(UnixSecureRandomSpi.class.getName());
 
 	private static final File RANDOM_DEVICE = new File("/dev/urandom");
 
 	private final File inputDevice, outputDevice;
 
-	public LinuxSecureRandomSpi() {
+	@SuppressWarnings("WeakerAccess")
+	public UnixSecureRandomSpi() {
 		this(RANDOM_DEVICE, RANDOM_DEVICE);
 	}
 
-	LinuxSecureRandomSpi(File inputDevice, File outputDevice) {
+	UnixSecureRandomSpi(File inputDevice, File outputDevice) {
 		this.inputDevice = inputDevice;
 		this.outputDevice = outputDevice;
 	}

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

@@ -23,7 +23,7 @@ import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientMajorVersion;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;

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

@@ -4,7 +4,7 @@ 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.ValidationManager;
+import org.briarproject.bramble.api.sync.validation.ValidationManager;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
 

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

@@ -64,8 +64,8 @@ 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.SyncConstants.MAX_MESSAGE_LENGTH;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+import static org.briarproject.bramble.api.sync.validation.MessageState.DELIVERED;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.api.transport.TransportConstants.REORDERING_WINDOW_SIZE;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_OFFERED_MESSAGES;
 import static org.briarproject.bramble.test.TestUtils.getAuthor;

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

@@ -11,7 +11,7 @@ import org.briarproject.bramble.api.sync.Group;
 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.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.test.UTest;
 import org.junit.After;
@@ -33,7 +33,7 @@ import java.util.logging.Logger;
 
 import static java.util.logging.Level.OFF;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
+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.getAuthor;
 import static org.briarproject.bramble.test.TestUtils.getGroup;
@@ -565,7 +565,8 @@ public abstract class DatabasePerformanceTest extends BrambleTestCase {
 				for (int k = 0; k < MESSAGES_PER_GROUP; k++) {
 					Message m = getMessage(g.getId());
 					messages.add(m);
-					State state = State.fromValue(random.nextInt(4));
+					MessageState state =
+							MessageState.fromValue(random.nextInt(4));
 					boolean shared = random.nextBoolean();
 					ContactId sender = random.nextBoolean() ? c : null;
 					db.addMessage(txn, m, state, shared, sender);

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

@@ -18,7 +18,7 @@ import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
+import org.briarproject.bramble.api.sync.validation.MessageState;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.KeySet;
@@ -58,10 +58,10 @@ 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.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+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;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.db.DatabaseConstants.DB_SETTINGS_NAMESPACE;
 import static org.briarproject.bramble.db.DatabaseConstants.LAST_COMPACTED_KEY;
 import static org.briarproject.bramble.db.DatabaseConstants.MAX_COMPACTION_INTERVAL_MS;
@@ -1309,7 +1309,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessageDependency(txn, message1, messageId3, PENDING);
 		db.addMessageDependency(txn, message2, messageId4, INVALID);
 
-		Map<MessageId, State> dependencies;
+		Map<MessageId, MessageState> dependencies;
 
 		// Retrieve dependencies for root
 		dependencies = db.getMessageDependencies(txn, messageId);
@@ -1333,7 +1333,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		dependencies = db.getMessageDependencies(txn, messageId4);
 		assertEquals(0, dependencies.size());
 
-		Map<MessageId, State> dependents;
+		Map<MessageId, MessageState> dependents;
 
 		// Root message does not have dependents
 		dependents = db.getMessageDependents(txn, messageId);
@@ -1408,7 +1408,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		db.addMessageDependency(txn, message, messageId3, PENDING);
 
 		// Retrieve the dependencies for the root
-		Map<MessageId, State> dependencies;
+		Map<MessageId, MessageState> dependencies;
 		dependencies = db.getMessageDependencies(txn, messageId);
 
 		// The cross-group dependency should have state UNKNOWN
@@ -1421,7 +1421,7 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 		assertEquals(DELIVERED, dependencies.get(messageId3));
 
 		// Retrieve the dependents for the message in the second group
-		Map<MessageId, State> dependents;
+		Map<MessageId, MessageState> dependents;
 		dependents = db.getMessageDependents(txn, messageId1);
 
 		// The cross-group dependent should be excluded

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

@@ -2,6 +2,7 @@ package org.briarproject.bramble.sync;
 
 import org.briarproject.bramble.crypto.CryptoModule;
 import org.briarproject.bramble.record.RecordModule;
+import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
 import org.briarproject.bramble.test.TestSecureRandomModule;
 import org.briarproject.bramble.transport.TransportModule;
@@ -17,6 +18,7 @@ import dagger.Component;
 		RecordModule.class,
 		SyncModule.class,
 		SystemModule.class,
+		ValidationModule.class,
 		TransportModule.class
 })
 interface SyncIntegrationTestComponent {

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

@@ -1,4 +1,4 @@
-package org.briarproject.bramble.sync;
+package org.briarproject.bramble.sync.validation;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DatabaseComponent;
@@ -13,10 +13,10 @@ import org.briarproject.bramble.api.sync.InvalidMessageException;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageContext;
 import org.briarproject.bramble.api.sync.MessageId;
-import org.briarproject.bramble.api.sync.ValidationManager.IncomingMessageHook;
-import org.briarproject.bramble.api.sync.ValidationManager.MessageValidator;
-import org.briarproject.bramble.api.sync.ValidationManager.State;
 import org.briarproject.bramble.api.sync.event.MessageAddedEvent;
+import org.briarproject.bramble.api.sync.validation.IncomingMessageHook;
+import org.briarproject.bramble.api.sync.validation.MessageState;
+import org.briarproject.bramble.api.sync.validation.MessageValidator;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.DbExpectations;
 import org.briarproject.bramble.test.ImmediateExecutor;
@@ -32,10 +32,10 @@ import static java.util.Collections.emptyList;
 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.ValidationManager.State.DELIVERED;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.INVALID;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.PENDING;
-import static org.briarproject.bramble.api.sync.ValidationManager.State.UNKNOWN;
+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;
+import static org.briarproject.bramble.api.sync.validation.MessageState.UNKNOWN;
 import static org.briarproject.bramble.test.TestUtils.getClientId;
 import static org.briarproject.bramble.test.TestUtils.getGroup;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
@@ -559,7 +559,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 	public void testRecursiveInvalidation() throws Exception {
 		MessageId messageId3 = new MessageId(getRandomId());
 		MessageId messageId4 = new MessageId(getRandomId());
-		Map<MessageId, State> twoDependents = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependents = new LinkedHashMap<>();
 		twoDependents.put(messageId1, PENDING);
 		twoDependents.put(messageId2, PENDING);
 		Transaction txn = new Transaction(null, true);
@@ -643,10 +643,10 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 		Message message4 = getMessage(groupId);
 		MessageId messageId3 = message3.getId();
 		MessageId messageId4 = message4.getId();
-		Map<MessageId, State> twoDependents = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependents = new LinkedHashMap<>();
 		twoDependents.put(messageId1, PENDING);
 		twoDependents.put(messageId2, PENDING);
-		Map<MessageId, State> twoDependencies = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependencies = new LinkedHashMap<>();
 		twoDependencies.put(messageId1, DELIVERED);
 		twoDependencies.put(messageId2, DELIVERED);
 		Transaction txn = new Transaction(null, true);
@@ -765,7 +765,7 @@ public class ValidationManagerImplTest extends BrambleMockTestCase {
 
 	@Test
 	public void testOnlyReadyPendingDependentsGetDelivered() throws Exception {
-		Map<MessageId, State> twoDependencies = new LinkedHashMap<>();
+		Map<MessageId, MessageState> twoDependencies = new LinkedHashMap<>();
 		twoDependencies.put(messageId, DELIVERED);
 		twoDependencies.put(messageId2, UNKNOWN);
 		Transaction txn = new Transaction(null, true);

bramble-core/src/test/java/org/briarproject/bramble/system/UnixSecureRandomProviderTest.java

@@ -1,8 +1,6 @@
 package org.briarproject.bramble.system;
 
 import org.briarproject.bramble.test.BrambleTestCase;
-import org.briarproject.bramble.test.TestUtils;
-import org.briarproject.bramble.util.OsUtils;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -10,48 +8,50 @@ import org.junit.Test;
 import java.io.File;
 import java.security.Provider;
 
+import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
+import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.briarproject.bramble.util.OsUtils.isLinux;
+import static org.briarproject.bramble.util.OsUtils.isMac;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assume.assumeTrue;
 
-public class LinuxSecureRandomProviderTest extends BrambleTestCase {
+public class UnixSecureRandomProviderTest extends BrambleTestCase {
 
-	private final File testDir = TestUtils.getTestDirectory();
+	private final File testDir = getTestDirectory();
 
 	@Before
 	public void setUp() {
-		testDir.mkdirs();
+		assumeTrue(isLinux() || isMac());
+		assertTrue(testDir.mkdirs());
 	}
 
 	@Test
 	public void testGetProviderWritesToRandomDeviceOnFirstCall()
 			throws Exception {
-		if (!(OsUtils.isLinux())) {
-			System.err.println("WARNING: Skipping test, can't run on this OS");
-			return;
-		}
 		// Redirect the provider's output to a file
 		File urandom = new File(testDir, "urandom");
-		urandom.delete();
+		if (urandom.exists()) assertTrue(urandom.delete());
 		assertTrue(urandom.createNewFile());
 		assertEquals(0, urandom.length());
-		LinuxSecureRandomProvider p = new LinuxSecureRandomProvider(urandom);
+		UnixSecureRandomProvider p = new UnixSecureRandomProvider(urandom);
 		// Getting a provider should write entropy to the file
 		Provider provider = p.getProvider();
 		assertNotNull(provider);
-		assertEquals("LinuxPRNG", provider.getName());
+		assertEquals("UnixPRNG", provider.getName());
 		// There should be at least 16 bytes from the clock, 8 from the runtime
 		long length = urandom.length();
 		assertTrue(length >= 24);
 		// Getting another provider should not write to the file again
 		provider = p.getProvider();
 		assertNotNull(provider);
-		assertEquals("LinuxPRNG", provider.getName());
+		assertEquals("UnixPRNG", provider.getName());
 		assertEquals(length, urandom.length());
 	}
 
 	@After
 	public void tearDown() {
-		TestUtils.deleteTestDirectory(testDir);
+		deleteTestDirectory(testDir);
 	}
 }

bramble-core/src/test/java/org/briarproject/bramble/system/UnixSecureRandomSpiTest.java

@@ -4,7 +4,6 @@ import org.briarproject.bramble.api.Bytes;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.test.TestUtils;
 import org.briarproject.bramble.util.IoUtils;
-import org.briarproject.bramble.util.OsUtils;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -15,31 +14,33 @@ import java.io.FileOutputStream;
 import java.util.HashSet;
 import java.util.Set;
 
+import static org.briarproject.bramble.test.TestUtils.deleteTestDirectory;
+import static org.briarproject.bramble.test.TestUtils.getTestDirectory;
+import static org.briarproject.bramble.util.OsUtils.isLinux;
+import static org.briarproject.bramble.util.OsUtils.isMac;
 import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assume.assumeTrue;
 
 
-public class LinuxSecureRandomSpiTest extends BrambleTestCase {
+public class UnixSecureRandomSpiTest extends BrambleTestCase {
 
 	private static final File RANDOM_DEVICE = new File("/dev/urandom");
 	private static final int SEED_BYTES = 32;
 
-	private final File testDir = TestUtils.getTestDirectory();
+	private final File testDir = getTestDirectory();
 
 	@Before
 	public void setUp() {
-		testDir.mkdirs();
+		assumeTrue(isLinux() || isMac());
+		assertTrue(testDir.mkdirs());
 	}
 
 	@Test
 	public void testSeedsAreDistinct() {
-		if (!(OsUtils.isLinux())) {
-			System.err.println("WARNING: Skipping test, can't run on this OS");
-			return;
-		}
 		Set<Bytes> seeds = new HashSet<>();
-		LinuxSecureRandomSpi engine = new LinuxSecureRandomSpi();
+		UnixSecureRandomSpi engine = new UnixSecureRandomSpi();
 		for (int i = 0; i < 1000; i++) {
 			byte[] seed = engine.engineGenerateSeed(SEED_BYTES);
 			assertEquals(SEED_BYTES, seed.length);
@@ -49,19 +50,15 @@ public class LinuxSecureRandomSpiTest extends BrambleTestCase {
 
 	@Test
 	public void testEngineSetSeedWritesToRandomDevice() throws Exception {
-		if (!(OsUtils.isLinux())) {
-			System.err.println("WARNING: Skipping test, can't run on this OS");
-			return;
-		}
 		// Redirect the engine's output to a file
 		File urandom = new File(testDir, "urandom");
-		urandom.delete();
+		if (urandom.exists()) assertTrue(urandom.delete());
 		assertTrue(urandom.createNewFile());
 		assertEquals(0, urandom.length());
 		// Generate a seed
 		byte[] seed = TestUtils.getRandomBytes(SEED_BYTES);
 		// Check that the engine writes the seed to the file
-		LinuxSecureRandomSpi engine = new LinuxSecureRandomSpi(RANDOM_DEVICE,
+		UnixSecureRandomSpi engine = new UnixSecureRandomSpi(RANDOM_DEVICE,
 				urandom);
 		engine.engineSetSeed(seed);
 		assertEquals(SEED_BYTES, urandom.length());
@@ -74,15 +71,11 @@ public class LinuxSecureRandomSpiTest extends BrambleTestCase {
 
 	@Test
 	public void testEngineNextBytesReadsFromRandomDevice() throws Exception {
-		if (!(OsUtils.isLinux())) {
-			System.err.println("WARNING: Skipping test, can't run on this OS");
-			return;
-		}
 		// Generate some entropy
 		byte[] entropy = TestUtils.getRandomBytes(SEED_BYTES);
 		// Write the entropy to a file
 		File urandom = new File(testDir, "urandom");
-		urandom.delete();
+		if (urandom.exists()) assertTrue(urandom.delete());
 		FileOutputStream out = new FileOutputStream(urandom);
 		out.write(entropy);
 		out.flush();
@@ -90,7 +83,7 @@ public class LinuxSecureRandomSpiTest extends BrambleTestCase {
 		assertTrue(urandom.exists());
 		assertEquals(SEED_BYTES, urandom.length());
 		// Check that the engine reads from the file
-		LinuxSecureRandomSpi engine = new LinuxSecureRandomSpi(urandom,
+		UnixSecureRandomSpi engine = new UnixSecureRandomSpi(urandom,
 				RANDOM_DEVICE);
 		byte[] b = new byte[SEED_BYTES];
 		engine.engineNextBytes(b);
@@ -99,15 +92,11 @@ public class LinuxSecureRandomSpiTest extends BrambleTestCase {
 
 	@Test
 	public void testEngineGenerateSeedReadsFromRandomDevice() throws Exception {
-		if (!(OsUtils.isLinux())) {
-			System.err.println("WARNING: Skipping test, can't run on this OS");
-			return;
-		}
 		// Generate some entropy
 		byte[] entropy = TestUtils.getRandomBytes(SEED_BYTES);
 		// Write the entropy to a file
 		File urandom = new File(testDir, "urandom");
-		urandom.delete();
+		if (urandom.exists()) assertTrue(urandom.delete());
 		FileOutputStream out = new FileOutputStream(urandom);
 		out.write(entropy);
 		out.flush();
@@ -115,7 +104,7 @@ public class LinuxSecureRandomSpiTest extends BrambleTestCase {
 		assertTrue(urandom.exists());
 		assertEquals(SEED_BYTES, urandom.length());
 		// Check that the engine reads from the file
-		LinuxSecureRandomSpi engine = new LinuxSecureRandomSpi(urandom,
+		UnixSecureRandomSpi engine = new UnixSecureRandomSpi(urandom,
 				RANDOM_DEVICE);
 		byte[] b = engine.engineGenerateSeed(SEED_BYTES);
 		assertArrayEquals(entropy, b);
@@ -123,6 +112,6 @@ public class LinuxSecureRandomSpiTest extends BrambleTestCase {
 
 	@After
 	public void tearDown() {
-		TestUtils.deleteTestDirectory(testDir);
+		deleteTestDirectory(testDir);
 	}
 }

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

@@ -4,6 +4,8 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.MessageFactory;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.api.sync.tree.TreeHash;
 
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
 
@@ -27,4 +29,10 @@ public class TestMessageFactory implements MessageFactory {
 		System.arraycopy(body, 0, raw, MESSAGE_HEADER_LENGTH, body.length);
 		return raw;
 	}
+
+	@Override
+	public MessageId getMessageId(GroupId g, long timestamp,
+			TreeHash rootHash) {
+		throw new UnsupportedOperationException();
+	}
 }

bramble-java/src/main/java/org/briarproject/bramble/lifecycle/DesktopLifecycleModule.java

@@ -1,20 +1,21 @@
 package org.briarproject.bramble.lifecycle;
 
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
-import org.briarproject.bramble.util.OsUtils;
 
 import javax.inject.Singleton;
 
 import dagger.Module;
 import dagger.Provides;
 
+import static org.briarproject.bramble.util.OsUtils.isWindows;
+
 @Module
 public class DesktopLifecycleModule extends LifecycleModule {
 
 	@Provides
 	@Singleton
 	ShutdownManager provideDesktopShutdownManager() {
-		if (OsUtils.isWindows()) return new WindowsShutdownManagerImpl();
+		if (isWindows()) return new WindowsShutdownManagerImpl();
 		else return new ShutdownManagerImpl();
 	}
 }

bramble-java/src/main/java/org/briarproject/bramble/lifecycle/WindowsShutdownManagerImpl.java

@@ -15,7 +15,6 @@ import com.sun.jna.win32.W32APIFunctionMapper;
 import com.sun.jna.win32.W32APITypeMapper;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.util.OsUtils;
 
 import java.util.Collections;
 import java.util.HashMap;
@@ -29,6 +28,7 @@ import static com.sun.jna.Library.OPTION_FUNCTION_MAPPER;
 import static com.sun.jna.Library.OPTION_TYPE_MAPPER;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.OsUtils.isWindows;
 
 @ThreadSafe
 @NotNullByDefault
@@ -71,7 +71,7 @@ class WindowsShutdownManagerImpl extends ShutdownManagerImpl {
 
 	// Locking: lock
 	private void initialise() {
-		if (OsUtils.isWindows()) {
+		if (isWindows()) {
 			new EventLoop().start();
 		} else {
 			LOG.warning("Windows shutdown manager used on non-Windows OS");
@@ -111,7 +111,7 @@ class WindowsShutdownManagerImpl extends ShutdownManagerImpl {
 		public void run() {
 			try {
 				// Load user32.dll
-				User32 user32 = (User32) Native.loadLibrary("user32",
+				User32 user32 = Native.loadLibrary("user32",
 						User32.class, options);
 				// Create a callback to handle the WM_QUERYENDSESSION message
 				WindowProc proc = (hwnd, msg, wp, lp) -> {

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

@@ -10,7 +10,6 @@ import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
 
 import java.io.File;
-import java.io.IOException;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.security.CodeSource;
@@ -19,9 +18,9 @@ import java.util.concurrent.Executor;
 import javax.net.SocketFactory;
 
 @NotNullByDefault
-class LinuxTorPlugin extends TorPlugin {
+abstract class JavaTorPlugin extends TorPlugin {
 
-	LinuxTorPlugin(Executor ioExecutor, NetworkManager networkManager,
+	JavaTorPlugin(Executor ioExecutor, NetworkManager networkManager,
 			LocationUtils locationUtils, SocketFactory torSocketFactory,
 			Clock clock, ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
@@ -34,17 +33,6 @@ class LinuxTorPlugin extends TorPlugin {
 				torDirectory);
 	}
 
-	@Override
-	protected int getProcessId() {
-		try {
-			// Java 9: ProcessHandle.current().pid()
-			return Integer.parseInt(
-					new File("/proc/self").getCanonicalFile().getName());
-		} catch (IOException e) {
-			throw new AssertionError(e);
-		}
-	}
-
 	@Override
 	protected long getLastUpdateTime() {
 		CodeSource codeSource =
@@ -58,5 +46,4 @@ class LinuxTorPlugin extends TorPlugin {
 			throw new AssertionError(e);
 		}
 	}
-
 }

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

@@ -0,0 +1,47 @@
+package org.briarproject.bramble.plugin.tor;
+
+import com.sun.jna.Library;
+import com.sun.jna.Native;
+
+import org.briarproject.bramble.api.battery.BatteryManager;
+import org.briarproject.bramble.api.network.NetworkManager;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.plugin.Backoff;
+import org.briarproject.bramble.api.plugin.duplex.DuplexPluginCallback;
+import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.LocationUtils;
+import org.briarproject.bramble.api.system.ResourceProvider;
+
+import java.io.File;
+import java.util.concurrent.Executor;
+
+import javax.net.SocketFactory;
+
+@NotNullByDefault
+class UnixTorPlugin extends JavaTorPlugin {
+
+	UnixTorPlugin(Executor ioExecutor, NetworkManager networkManager,
+			LocationUtils locationUtils, SocketFactory torSocketFactory,
+			Clock clock, ResourceProvider resourceProvider,
+			CircumventionProvider circumventionProvider,
+			BatteryManager batteryManager, Backoff backoff,
+			DuplexPluginCallback callback, String architecture, int maxLatency,
+			int maxIdleTime, File torDirectory) {
+		super(ioExecutor, networkManager, locationUtils, torSocketFactory,
+				clock, resourceProvider, circumventionProvider, batteryManager,
+				backoff, callback, architecture, maxLatency, maxIdleTime,
+				torDirectory);
+	}
+
+	@Override
+	protected int getProcessId() {
+		return CLibrary.INSTANCE.getpid();
+	}
+
+	private interface CLibrary extends Library {
+
+		CLibrary INSTANCE = (CLibrary) Native.loadLibrary("c", CLibrary.class);
+
+		int getpid();
+	}
+}

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

@@ -22,14 +22,15 @@ import java.util.logging.Logger;
 import javax.annotation.concurrent.Immutable;
 import javax.net.SocketFactory;
 
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.bramble.util.OsUtils.isLinux;
 
 @Immutable
 @NotNullByDefault
-public class LinuxTorPluginFactory implements DuplexPluginFactory {
+public class UnixTorPluginFactory implements DuplexPluginFactory {
 
 	private static final Logger LOG =
-			Logger.getLogger(LinuxTorPluginFactory.class.getName());
+			getLogger(UnixTorPluginFactory.class.getName());
 
 	private static final int MAX_LATENCY = 30 * 1000; // 30 seconds
 	private static final int MAX_IDLE_TIME = 30 * 1000; // 30 seconds
@@ -49,7 +50,7 @@ public class LinuxTorPluginFactory implements DuplexPluginFactory {
 	private final Clock clock;
 	private final File torDirectory;
 
-	public LinuxTorPluginFactory(Executor ioExecutor,
+	public UnixTorPluginFactory(Executor ioExecutor,
 			NetworkManager networkManager, LocationUtils locationUtils,
 			EventBus eventBus, SocketFactory torSocketFactory,
 			BackoffFactory backoffFactory, ResourceProvider resourceProvider,
@@ -95,7 +96,7 @@ public class LinuxTorPluginFactory implements DuplexPluginFactory {
 
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
-		LinuxTorPlugin plugin = new LinuxTorPlugin(ioExecutor, networkManager,
+		UnixTorPlugin plugin = new UnixTorPlugin(ioExecutor, networkManager,
 				locationUtils, torSocketFactory, clock, resourceProvider,
 				circumventionProvider, batteryManager, backoff, callback,
 				architecture, MAX_LATENCY, MAX_IDLE_TIME, torDirectory);

bramble-java/src/main/java/org/briarproject/bramble/system/DesktopSecureRandomModule.java

@@ -1,19 +1,24 @@
 package org.briarproject.bramble.system;
 
 import org.briarproject.bramble.api.system.SecureRandomProvider;
-import org.briarproject.bramble.util.OsUtils;
 
 import javax.inject.Singleton;
 
 import dagger.Module;
 import dagger.Provides;
 
+import static org.briarproject.bramble.util.OsUtils.isLinux;
+import static org.briarproject.bramble.util.OsUtils.isMac;
+
 @Module
 public class DesktopSecureRandomModule {
 
 	@Provides
 	@Singleton
 	SecureRandomProvider provideSecureRandomProvider() {
-		return OsUtils.isLinux() ? new LinuxSecureRandomProvider() : null;
+		if (isLinux() || isMac())
+			return new UnixSecureRandomProvider();
+		// TODO: Create a secure random provider for Windows
+		throw new UnsupportedOperationException();
 	}
 }

bramble-java/src/test/java/org/briarproject/bramble/plugin/tor/BridgeTest.java

@@ -70,7 +70,7 @@ public class BridgeTest extends BrambleTestCase {
 	private final File torDir = getTestDirectory();
 	private final String bridge;
 
-	private LinuxTorPluginFactory factory;
+	private UnixTorPluginFactory factory;
 
 	public BridgeTest(String bridge) {
 		this.bridge = bridge;
@@ -108,7 +108,7 @@ public class BridgeTest extends BrambleTestCase {
 				return singletonList(bridge);
 			}
 		};
-		factory = new LinuxTorPluginFactory(ioExecutor, networkManager,
+		factory = new UnixTorPluginFactory(ioExecutor, networkManager,
 				locationUtils, eventBus, torSocketFactory, backoffFactory,
 				resourceProvider, bridgeProvider, batteryManager, clock,
 				torDir);
@@ -124,7 +124,7 @@ public class BridgeTest extends BrambleTestCase {
 		DuplexPlugin duplexPlugin =
 				factory.createPlugin(new TorPluginCallBack());
 		assertNotNull(duplexPlugin);
-		LinuxTorPlugin plugin = (LinuxTorPlugin) duplexPlugin;
+		UnixTorPlugin plugin = (UnixTorPlugin) duplexPlugin;
 
 		LOG.warning("Testing " + bridge);
 		try {

briar-android/build.gradle

@@ -104,6 +104,7 @@ dependencies {
 	}
 	implementation "com.android.support:cardview-v7:$supportVersion"
 	implementation "com.android.support:support-annotations:$supportVersion"
+	implementation "com.android.support:exifinterface:$supportVersion"
 	implementation 'com.android.support.constraint:constraint-layout:1.1.3'
 	implementation "android.arch.lifecycle:extensions:1.1.1"
 
@@ -117,8 +118,15 @@ dependencies {
 	implementation 'com.google.zxing:core:3.3.3'
 	implementation 'uk.co.samuelwall:material-tap-target-prompt:2.12.4'
 	implementation 'com.vanniktech:emoji-google:0.5.1'
+	def glideVersion = '4.8.0'
+	implementation("com.github.bumptech.glide:glide:$glideVersion") {
+		exclude group: 'com.android.support'
+		exclude module: 'disklrucache' // when there's no disk cache, we can't accidentally use it
+	}
+	implementation 'com.github.chrisbanes:PhotoView:2.1.4' // later versions already use androidx
 
 	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
+	annotationProcessor "com.github.bumptech.glide:compiler:$glideVersion"
 
 	compileOnly 'javax.annotation:jsr250-api:1.0'
 

briar-android/proguard-rules.txt

@@ -30,3 +30,6 @@
 
 # Emoji
 -keep class com.vanniktech.emoji.**
+
+# Glide
+-dontwarn com.bumptech.glide.load.engine.cache.DiskLruCacheWrapper

briar-android/src/androidTest/java/org/briarproject/briar/android/BriarTestComponentApplication.java

@@ -1,5 +1,6 @@
 package org.briarproject.briar.android;
 
+import org.briarproject.bramble.BrambleAndroidModule;
 import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.briar.BriarCoreModule;
 
@@ -12,6 +13,7 @@ public class BriarTestComponentApplication extends BriarApplicationImpl {
 		// We need to load the eager singletons directly after making the
 		// dependency graphs
 		BrambleCoreModule.initEagerSingletons(component);
+		BrambleAndroidModule.initEagerSingletons(component);
 		BriarCoreModule.initEagerSingletons(component);
 		AndroidEagerSingletons.initEagerSingletons(component);
 		return component;

briar-android/src/main/AndroidManifest.xml

@@ -7,7 +7,6 @@
 	<uses-feature android:name="android.hardware.camera" android:required="false"/>
 	<uses-feature android:name="android.hardware.touchscreen" android:required="false" />
 
-	<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
 	<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
 	<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
 	<uses-permission android:name="android.permission.BLUETOOTH" />
@@ -18,6 +17,7 @@
 	<uses-permission android:name="android.permission.USE_FINGERPRINT"/>
 	<uses-permission android:name="android.permission.VIBRATE" />
 	<uses-permission android:name="android.permission.WAKE_LOCK" />
+	<uses-permission-sdk-23 android:name="android.permission.ACCESS_COARSE_LOCATION" />
 	<uses-permission-sdk-23 android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS"/>
 	<uses-permission-sdk-23 android:name="android.permission.USE_BIOMETRIC" />
 
@@ -113,6 +113,15 @@
 				/>
 		</activity>
 
+		<activity
+			android:name=".android.conversation.ImageActivity"
+			android:parentActivityName="org.briarproject.briar.android.conversation.ConversationActivity"
+			android:theme="@style/BriarTheme.Transparent.NoActionBar">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.conversation.ConversationActivity"/>
+		</activity>
+
 		<activity
 			android:name="org.briarproject.briar.android.privategroup.creation.CreateGroupActivity"
 			android:label="@string/groups_create_group_title"

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

@@ -2,6 +2,7 @@ package org.briarproject.briar.android;
 
 import android.arch.lifecycle.ViewModelProvider;
 
+import org.briarproject.bramble.BrambleAndroidEagerSingletons;
 import org.briarproject.bramble.BrambleAndroidModule;
 import org.briarproject.bramble.BrambleCoreEagerSingletons;
 import org.briarproject.bramble.BrambleCoreModule;
@@ -28,6 +29,7 @@ import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.plugin.tor.CircumventionProvider;
 import org.briarproject.briar.BriarCoreEagerSingletons;
 import org.briarproject.briar.BriarCoreModule;
+import org.briarproject.briar.android.conversation.glide.BriarModelLoader;
 import org.briarproject.briar.android.login.SignInReminderReceiver;
 import org.briarproject.briar.android.reporting.BriarReportSender;
 import org.briarproject.briar.android.view.TextInputView;
@@ -39,11 +41,11 @@ import org.briarproject.briar.api.blog.BlogManager;
 import org.briarproject.briar.api.blog.BlogPostFactory;
 import org.briarproject.briar.api.blog.BlogSharingManager;
 import org.briarproject.briar.api.client.MessageTracker;
+import org.briarproject.briar.api.conversation.ConversationManager;
 import org.briarproject.briar.api.feed.FeedManager;
 import org.briarproject.briar.api.forum.ForumManager;
 import org.briarproject.briar.api.forum.ForumSharingManager;
 import org.briarproject.briar.api.introduction.IntroductionManager;
-import org.briarproject.briar.api.conversation.ConversationManager;
 import org.briarproject.briar.api.messaging.MessagingManager;
 import org.briarproject.briar.api.messaging.PrivateMessageFactory;
 import org.briarproject.briar.api.privategroup.GroupMessageFactory;
@@ -68,7 +70,8 @@ import dagger.Component;
 		AppModule.class
 })
 public interface AndroidComponent
-		extends BrambleCoreEagerSingletons, BriarCoreEagerSingletons {
+		extends BrambleCoreEagerSingletons, BrambleAndroidEagerSingletons,
+		BriarCoreEagerSingletons {
 
 	// Exposed objects
 	@CryptoExecutor
@@ -168,6 +171,8 @@ public interface AndroidComponent
 
 	void inject(TextInputView textInputView);
 
+	void inject(BriarModelLoader briarModelLoader);
+
 	// Eager singleton load
 	void inject(AppModule.EagerSingletons init);
 }

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

@@ -66,10 +66,14 @@ public class AppModule {
 		@Inject
 		AndroidNotificationManager androidNotificationManager;
 		@Inject
+		ScreenFilterMonitor screenFilterMonitor;
+		@Inject
 		NetworkUsageLogger networkUsageLogger;
 		@Inject
 		DozeWatchdog dozeWatchdog;
 		@Inject
+		LockManager lockManager;
+		@Inject
 		RecentEmoji recentEmoji;
 	}
 

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

@@ -15,6 +15,7 @@ import com.vanniktech.emoji.google.GoogleEmojiProvider;
 import org.acra.ACRA;
 import org.acra.ReportingInteractionMode;
 import org.acra.annotation.ReportsCrashes;
+import org.briarproject.bramble.BrambleAndroidModule;
 import org.briarproject.bramble.BrambleCoreModule;
 import org.briarproject.briar.BriarCoreModule;
 import org.briarproject.briar.R;
@@ -124,6 +125,7 @@ public class BriarApplicationImpl extends Application
 		// We need to load the eager singletons directly after making the
 		// dependency graphs
 		BrambleCoreModule.initEagerSingletons(androidComponent);
+		BrambleAndroidModule.initEagerSingletons(androidComponent);
 		BriarCoreModule.initEagerSingletons(androidComponent);
 		AndroidEagerSingletons.initEagerSingletons(androidComponent);
 		return androidComponent;

briar-android/src/main/java/org/briarproject/briar/android/activity/ActivityComponent.java

@@ -15,10 +15,11 @@ import org.briarproject.briar.android.blog.ReblogFragment;
 import org.briarproject.briar.android.blog.RssFeedImportActivity;
 import org.briarproject.briar.android.blog.RssFeedManageActivity;
 import org.briarproject.briar.android.blog.WriteBlogPostActivity;
-import org.briarproject.briar.android.conversation.AliasDialogFragment;
 import org.briarproject.briar.android.contact.ContactListFragment;
 import org.briarproject.briar.android.contact.ContactModule;
+import org.briarproject.briar.android.conversation.AliasDialogFragment;
 import org.briarproject.briar.android.conversation.ConversationActivity;
+import org.briarproject.briar.android.conversation.ImageActivity;
 import org.briarproject.briar.android.forum.CreateForumActivity;
 import org.briarproject.briar.android.forum.ForumActivity;
 import org.briarproject.briar.android.forum.ForumListFragment;
@@ -110,6 +111,8 @@ public interface ActivityComponent {
 
 	void inject(ConversationActivity activity);
 
+	void inject(ImageActivity activity);
+
 	void inject(ForumInvitationActivity activity);
 
 	void inject(BlogInvitationActivity activity);

briar-android/src/main/java/org/briarproject/briar/android/activity/BriarActivity.java

@@ -2,12 +2,11 @@ package org.briarproject.briar.android.activity;
 
 import android.annotation.SuppressLint;
 import android.content.Intent;
+import android.support.annotation.RequiresApi;
 import android.support.v7.app.ActionBar;
 import android.support.v7.app.AlertDialog;
 import android.support.v7.widget.Toolbar;
-import android.transition.Slide;
 import android.transition.Transition;
-import android.view.Gravity;
 import android.view.Window;
 import android.widget.CheckBox;
 
@@ -33,6 +32,7 @@ import static android.os.Build.VERSION.SDK_INT;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_DOZE_WHITELISTING;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_PASSWORD;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_UNLOCK;
+import static org.briarproject.briar.android.util.UiUtils.excludeSystemUi;
 import static org.briarproject.briar.android.util.UiUtils.getDozeWhitelistingIntent;
 import static org.briarproject.briar.android.util.UiUtils.isSamsung7;
 
@@ -111,21 +111,28 @@ public abstract class BriarActivity extends BaseActivity {
 		lockManager.onActivityStop();
 	}
 
-	public void setSceneTransitionAnimation() {
-		if (SDK_INT < 21) return;
+	/**
+	 * Sets the transition animations.
+	 * @param enterTransition used to move views into initial positions
+	 * @param exitTransition used to move views out when starting a <b>new</b> activity.
+	 * @param returnTransition used when window is closing, because the activity is finishing.
+	 */
+	@RequiresApi(api = 21)
+	public void setSceneTransitionAnimation(
+			@Nullable Transition enterTransition,
+			@Nullable Transition exitTransition,
+			@Nullable Transition returnTransition) {
 		// workaround for #1007
 		if (isSamsung7()) {
 			return;
 		}
-		Transition slide = new Slide(Gravity.RIGHT);
-		slide.excludeTarget(android.R.id.statusBarBackground, true);
-		slide.excludeTarget(android.R.id.navigationBarBackground, true);
+		if (enterTransition != null) excludeSystemUi(enterTransition);
+		if (exitTransition != null) excludeSystemUi(exitTransition);
+		if (returnTransition != null) excludeSystemUi(returnTransition);
 		Window window = getWindow();
-		window.requestFeature(Window.FEATURE_CONTENT_TRANSITIONS);
-		window.setExitTransition(slide);
-		window.setEnterTransition(slide);
-		window.setTransitionBackgroundFadeDuration(getResources()
-				.getInteger(android.R.integer.config_longAnimTime));
+		window.setEnterTransition(enterTransition);
+		window.setExitTransition(exitTransition);
+		window.setReturnTransition(returnTransition);
 	}
 
 	/**

briar-android/src/main/java/org/briarproject/briar/android/blog/ReblogActivity.java

@@ -18,7 +18,6 @@ public class ReblogActivity extends BriarActivity implements
 
 	@Override
 	public void onCreate(Bundle savedInstanceState) {
-		setSceneTransitionAnimation();
 		super.onCreate(savedInstanceState);
 
 		Intent intent = getIntent();

briar-android/src/main/java/org/briarproject/briar/android/conversation/AttachmentController.java

@@ -0,0 +1,209 @@
+package org.briarproject.briar.android.conversation;
+
+import android.content.res.Resources;
+import android.graphics.BitmapFactory;
+import android.support.annotation.Nullable;
+import android.support.media.ExifInterface;
+
+import org.briarproject.bramble.api.Pair;
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.R;
+import org.briarproject.briar.api.messaging.Attachment;
+import org.briarproject.briar.api.messaging.AttachmentHeader;
+import org.briarproject.briar.api.messaging.MessagingManager;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.Logger;
+
+import static android.support.media.ExifInterface.ORIENTATION_ROTATE_270;
+import static android.support.media.ExifInterface.ORIENTATION_ROTATE_90;
+import static android.support.media.ExifInterface.ORIENTATION_TRANSPOSE;
+import static android.support.media.ExifInterface.ORIENTATION_TRANSVERSE;
+import static android.support.media.ExifInterface.TAG_IMAGE_LENGTH;
+import static android.support.media.ExifInterface.TAG_IMAGE_WIDTH;
+import static android.support.media.ExifInterface.TAG_ORIENTATION;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
+import static org.briarproject.bramble.util.LogUtils.logDuration;
+import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.LogUtils.now;
+
+@NotNullByDefault
+class AttachmentController {
+
+	private static final Logger LOG =
+			getLogger(AttachmentController.class.getName());
+
+	private final MessagingManager messagingManager;
+	private final int defaultSize;
+	private final int minWidth, maxWidth;
+	private final int minHeight, maxHeight;
+
+	private final Map<MessageId, List<AttachmentItem>> attachmentCache =
+			new ConcurrentHashMap<>();
+
+	AttachmentController(MessagingManager messagingManager, Resources res) {
+		this.messagingManager = messagingManager;
+		defaultSize =
+				res.getDimensionPixelSize(R.dimen.message_bubble_image_default);
+		minWidth = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_min_width);
+		maxWidth = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_max_width);
+		minHeight = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_min_height);
+		maxHeight = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_max_height);
+	}
+
+	void put(MessageId messageId, List<AttachmentItem> attachments) {
+		attachmentCache.put(messageId, attachments);
+	}
+
+	@Nullable
+	List<AttachmentItem> get(MessageId messageId) {
+		return attachmentCache.get(messageId);
+	}
+
+	@DatabaseExecutor
+	List<Pair<AttachmentHeader, Attachment>> getMessageAttachments(
+			List<AttachmentHeader> headers) throws DbException {
+		long start = now();
+		List<Pair<AttachmentHeader, Attachment>> attachments =
+				new ArrayList<>(headers.size());
+		for (AttachmentHeader h : headers) {
+			Attachment a =
+					messagingManager.getAttachment(h.getMessageId());
+			attachments.add(new Pair<>(h, a));
+		}
+		logDuration(LOG, "Loading attachment", start);
+		return attachments;
+	}
+
+	List<AttachmentItem> getAttachmentItems(
+			List<Pair<AttachmentHeader, Attachment>> attachments) {
+		List<AttachmentItem> items = new ArrayList<>(attachments.size());
+		for (Pair<AttachmentHeader, Attachment> a : attachments) {
+			AttachmentItem item =
+					getAttachmentItem(a.getFirst(), a.getSecond());
+			items.add(item);
+		}
+		return items;
+	}
+
+	private AttachmentItem getAttachmentItem(AttachmentHeader h, Attachment a) {
+		MessageId messageId = h.getMessageId();
+		Size size = new Size();
+
+		InputStream is = a.getStream();
+		is.mark(Integer.MAX_VALUE);
+		try {
+			// use exif to get size
+			if (h.getContentType().equals("image/jpeg")) {
+				size = getSizeFromExif(is);
+			}
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		}
+		try {
+			// use BitmapFactory to get size
+			if (size.error) {
+				is.reset();
+				size = getSizeFromBitmap(is);
+			}
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
+		} finally {
+			tryToClose(is, LOG, WARNING);
+		}
+
+		// calculate thumbnail size
+		Size thumbnailSize = new Size(defaultSize, defaultSize);
+		if (!size.error) {
+			thumbnailSize = getThumbnailSize(size.width, size.height);
+		}
+		return new AttachmentItem(messageId, size.width, size.height,
+				thumbnailSize.width, thumbnailSize.height, size.error);
+	}
+
+	/**
+	 * Gets the size of a JPEG {@link InputStream} if EXIF info is available.
+	 */
+	private static Size getSizeFromExif(InputStream is)
+			throws IOException {
+		ExifInterface exif = new ExifInterface(is);
+		// these can return 0 independent of default value
+		int width = exif.getAttributeInt(TAG_IMAGE_WIDTH, 0);
+		int height = exif.getAttributeInt(TAG_IMAGE_LENGTH, 0);
+		if (width == 0 || height == 0) return new Size();
+		int orientation = exif.getAttributeInt(TAG_ORIENTATION, 0);
+		if (orientation == ORIENTATION_ROTATE_90 ||
+				orientation == ORIENTATION_ROTATE_270 ||
+				orientation == ORIENTATION_TRANSVERSE ||
+				orientation == ORIENTATION_TRANSPOSE) {
+			//noinspection SuspiciousNameCombination
+			return new Size(height, width);
+		}
+		return new Size(width, height);
+	}
+
+	/**
+	 * Gets the size of any image {@link InputStream}.
+	 */
+	private static Size getSizeFromBitmap(InputStream is) {
+		BitmapFactory.Options options = new BitmapFactory.Options();
+		options.inJustDecodeBounds = true;
+		BitmapFactory.decodeStream(is, null, options);
+		if (options.outWidth < 1 || options.outHeight < 1)
+			return new Size();
+		return new Size(options.outWidth, options.outHeight);
+	}
+
+	private Size getThumbnailSize(int width, int height) {
+		float widthPercentage = maxWidth / (float) width;
+		float heightPercentage = maxHeight / (float) height;
+		float scaleFactor = Math.min(widthPercentage, heightPercentage);
+		if (scaleFactor > 1) scaleFactor = 1f;
+		int thumbnailWidth = (int) (width * scaleFactor);
+		int thumbnailHeight = (int) (height * scaleFactor);
+		if (thumbnailWidth < minWidth || thumbnailHeight < minHeight) {
+			widthPercentage = minWidth / (float) width;
+			heightPercentage = minHeight / (float) height;
+			scaleFactor = Math.max(widthPercentage, heightPercentage);
+			thumbnailWidth = (int) (width * scaleFactor);
+			thumbnailHeight = (int) (height * scaleFactor);
+			if (thumbnailWidth > maxWidth) thumbnailWidth = maxWidth;
+			if (thumbnailHeight > maxHeight) thumbnailHeight = maxHeight;
+		}
+		return new Size(thumbnailWidth, thumbnailHeight);
+	}
+
+	private static class Size {
+
+		private final int width;
+		private final int height;
+		private final boolean error;
+
+		private Size(int width, int height) {
+			this.width = width;
+			this.height = height;
+			this.error = false;
+		}
+
+		private Size() {
+			this.width = 0;
+			this.height = 0;
+			this.error = true;
+		}
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/AttachmentItem.java

@@ -0,0 +1,98 @@
+package org.briarproject.briar.android.conversation;
+
+import android.os.Parcel;
+import android.os.Parcelable;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class AttachmentItem implements Parcelable {
+
+	private final MessageId messageId;
+	private final int width, height;
+	private final int thumbnailWidth, thumbnailHeight;
+	private final boolean hasError;
+
+	public static final Creator<AttachmentItem> CREATOR =
+			new Creator<AttachmentItem>() {
+				@Override
+				public AttachmentItem createFromParcel(Parcel in) {
+					return new AttachmentItem(in);
+				}
+
+				@Override
+				public AttachmentItem[] newArray(int size) {
+					return new AttachmentItem[size];
+				}
+			};
+
+	AttachmentItem(MessageId messageId, int width, int height,
+			int thumbnailWidth, int thumbnailHeight, boolean hasError) {
+		this.messageId = messageId;
+		this.width = width;
+		this.height = height;
+		this.thumbnailWidth = thumbnailWidth;
+		this.thumbnailHeight = thumbnailHeight;
+		this.hasError = hasError;
+	}
+
+	protected AttachmentItem(Parcel in) {
+		byte[] messageIdByte = new byte[MessageId.LENGTH];
+		in.readByteArray(messageIdByte);
+		messageId = new MessageId(messageIdByte);
+		width = in.readInt();
+		height = in.readInt();
+		thumbnailWidth = in.readInt();
+		thumbnailHeight = in.readInt();
+		hasError = in.readByte() != 0;
+	}
+
+	public MessageId getMessageId() {
+		return messageId;
+	}
+
+	int getWidth() {
+		return width;
+	}
+
+	int getHeight() {
+		return height;
+	}
+
+	int getThumbnailWidth() {
+		return thumbnailWidth;
+	}
+
+	int getThumbnailHeight() {
+		return thumbnailHeight;
+	}
+
+	boolean hasError() {
+		return hasError;
+	}
+
+	// TODO use counter instead, because in theory one attachment can appear in more than one messages
+	String getTransitionName() {
+		return String.valueOf(messageId.hashCode());
+	}
+
+	@Override
+	public int describeContents() {
+		return 0;
+	}
+
+	@Override
+	public void writeToParcel(Parcel dest, int flags) {
+		dest.writeByteArray(messageId.getBytes());
+		dest.writeInt(width);
+		dest.writeInt(height);
+		dest.writeInt(thumbnailWidth);
+		dest.writeInt(thumbnailHeight);
+		dest.writeByte((byte) (hasError ? 1 : 0));
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationActivity.java

@@ -9,11 +9,15 @@ import android.os.Bundle;
 import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
 import android.support.design.widget.Snackbar;
+import android.support.v4.app.ActivityCompat;
+import android.support.v4.app.ActivityOptionsCompat;
 import android.support.v4.content.ContextCompat;
 import android.support.v7.app.AlertDialog;
 import android.support.v7.widget.ActionMenuView;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.Toolbar;
+import android.transition.Slide;
+import android.transition.Transition;
 import android.util.SparseArray;
 import android.view.Menu;
 import android.view.MenuInflater;
@@ -24,6 +28,7 @@ import android.widget.TextView;
 import android.widget.Toast;
 
 import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.contact.event.ContactRemovedEvent;
@@ -51,6 +56,7 @@ import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
 import org.briarproject.briar.android.blog.BlogActivity;
+import org.briarproject.briar.android.conversation.ConversationVisitor.AttachmentCache;
 import org.briarproject.briar.android.conversation.ConversationVisitor.TextCache;
 import org.briarproject.briar.android.forum.ForumActivity;
 import org.briarproject.briar.android.introduction.IntroductionActivity;
@@ -69,6 +75,8 @@ import org.briarproject.briar.api.conversation.ConversationResponse;
 import org.briarproject.briar.api.conversation.event.ConversationMessageReceivedEvent;
 import org.briarproject.briar.api.forum.ForumSharingManager;
 import org.briarproject.briar.api.introduction.IntroductionManager;
+import org.briarproject.briar.api.messaging.Attachment;
+import org.briarproject.briar.api.messaging.AttachmentHeader;
 import org.briarproject.briar.api.messaging.MessagingManager;
 import org.briarproject.briar.api.messaging.PrivateMessage;
 import org.briarproject.briar.api.messaging.PrivateMessageFactory;
@@ -92,10 +100,14 @@ import im.delight.android.identicons.IdenticonDrawable;
 import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt;
 import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt.PromptStateChangeListener;
 
+import static android.os.Build.VERSION.SDK_INT;
+import static android.support.v4.app.ActivityOptionsCompat.makeSceneTransitionAnimation;
 import static android.support.v4.view.ViewCompat.setTransitionName;
 import static android.support.v7.util.SortedList.INVALID_POSITION;
+import static android.view.Gravity.END;
 import static android.widget.Toast.LENGTH_SHORT;
 import static java.util.Collections.emptyList;
+import static java.util.Collections.sort;
 import static java.util.Objects.requireNonNull;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
@@ -103,6 +115,9 @@ import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_INTRODUCTION;
+import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENT;
+import static org.briarproject.briar.android.conversation.ImageActivity.DATE;
+import static org.briarproject.briar.android.conversation.ImageActivity.NAME;
 import static org.briarproject.briar.android.settings.SettingsFragment.SETTINGS_NAMESPACE;
 import static org.briarproject.briar.android.util.UiUtils.getAvatarTransitionName;
 import static org.briarproject.briar.android.util.UiUtils.getBulbTransitionName;
@@ -115,7 +130,7 @@ import static uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt.S
 @ParametersNotNullByDefault
 public class ConversationActivity extends BriarActivity
 		implements EventListener, ConversationListener, TextInputListener,
-		TextCache {
+		TextCache, AttachmentCache {
 
 	public static final String CONTACT_ID = "briar.CONTACT_ID";
 
@@ -133,6 +148,7 @@ public class ConversationActivity extends BriarActivity
 	Executor cryptoExecutor;
 
 	private final Map<MessageId, String> textCache = new ConcurrentHashMap<>();
+	private AttachmentController attachmentController;
 
 	private ConversationViewModel viewModel;
 	private ConversationVisitor visitor;
@@ -142,6 +158,7 @@ public class ConversationActivity extends BriarActivity
 	private ImageView toolbarStatus;
 	private TextView toolbarTitle;
 	private BriarRecyclerView list;
+	private LinearLayoutManager layoutManager;
 	private TextInputView textInputView;
 
 	// Fields that are accessed from background threads must be volatile
@@ -179,7 +196,10 @@ public class ConversationActivity extends BriarActivity
 
 	@Override
 	public void onCreate(@Nullable Bundle state) {
-		setSceneTransitionAnimation();
+		if (SDK_INT >= 21) {
+			Transition slide = new Slide(END);
+			setSceneTransitionAnimation(slide, null, slide);
+		}
 		super.onCreate(state);
 
 		Intent i = getIntent();
@@ -190,6 +210,7 @@ public class ConversationActivity extends BriarActivity
 		viewModel = ViewModelProviders.of(this, viewModelFactory)
 				.get(ConversationViewModel.class);
 		viewModel.setContactId(contactId);
+		attachmentController = viewModel.getAttachmentController();
 
 		setContentView(R.layout.activity_conversation);
 
@@ -216,11 +237,12 @@ public class ConversationActivity extends BriarActivity
 		setTransitionName(toolbarAvatar, getAvatarTransitionName(contactId));
 		setTransitionName(toolbarStatus, getBulbTransitionName(contactId));
 
-		visitor = new ConversationVisitor(this, this,
+		visitor = new ConversationVisitor(this, this, this,
 				viewModel.getContactDisplayName());
 		adapter = new ConversationAdapter(this, this);
 		list = findViewById(R.id.conversationView);
-		list.setLayoutManager(new LinearLayoutManager(this));
+		layoutManager = new LinearLayoutManager(this);
+		list.setLayoutManager(layoutManager);
 		list.setAdapter(adapter);
 		list.setEmptyText(getString(R.string.no_private_messages));
 
@@ -330,7 +352,43 @@ public class ConversationActivity extends BriarActivity
 				Collection<ConversationMessageHeader> headers =
 						conversationManager.getMessageHeaders(contactId);
 				logDuration(LOG, "Loading messages", start);
-				displayMessages(revision, headers);
+				// Sort headers by timestamp in *descending* order
+				List<ConversationMessageHeader> sorted =
+						new ArrayList<>(headers);
+				sort(sorted, (a, b) ->
+						Long.compare(b.getTimestamp(), a.getTimestamp()));
+				if (!sorted.isEmpty()) {
+					// If the latest header is a private message, eagerly load
+					// its text so we can set the scroll position correctly
+					ConversationMessageHeader latest = sorted.get(0);
+					if (latest instanceof PrivateMessageHeader) {
+						MessageId id = latest.getId();
+						PrivateMessageHeader h = (PrivateMessageHeader) latest;
+						if (h.hasText()) {
+							String text = textCache.get(id);
+							if (text == null) {
+								LOG.info(
+										"Eagerly loading text of latest message");
+								text = messagingManager.getMessageText(id);
+								textCache.put(id, text);
+							}
+						}
+						if (!h.getAttachmentHeaders().isEmpty()) {
+							List<AttachmentItem> items =
+									attachmentController.get(id);
+							if (items == null) {
+								LOG.info(
+										"Eagerly loading image size for latest message");
+								items = attachmentController.getAttachmentItems(
+										attachmentController
+												.getMessageAttachments(
+														h.getAttachmentHeaders()));
+								attachmentController.put(id, items);
+							}
+						}
+					}
+				}
+				displayMessages(revision, sorted);
 			} catch (NoSuchContactException e) {
 				finishOnUiThread();
 			} catch (DbException e) {
@@ -387,16 +445,44 @@ public class ConversationActivity extends BriarActivity
 	private void displayMessageText(MessageId m, String text) {
 		runOnUiThreadUnlessDestroyed(() -> {
 			textCache.put(m, text);
-			SparseArray<ConversationMessageItem> messages =
-					adapter.getMessageItems();
-			for (int i = 0; i < messages.size(); i++) {
-				ConversationItem item = messages.valueAt(i);
-				if (item.getId().equals(m)) {
-					item.setText(text);
-					adapter.notifyItemChanged(messages.keyAt(i));
-					list.scrollToPosition(adapter.getItemCount() - 1);
-					return;
-				}
+			Pair<Integer, ConversationMessageItem> pair =
+					adapter.getMessageItem(m);
+			if (pair != null) {
+				pair.getSecond().setText(text);
+				boolean bottom = adapter.isScrolledToBottom(layoutManager);
+				adapter.notifyItemChanged(pair.getFirst());
+				if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
+			}
+		});
+	}
+
+	private void loadMessageAttachments(MessageId messageId,
+			List<AttachmentHeader> headers) {
+		runOnDbThread(() -> {
+			try {
+				List<Pair<AttachmentHeader, Attachment>> attachments =
+						attachmentController.getMessageAttachments(headers);
+				// TODO move getting the items off to the IoExecutor
+				List<AttachmentItem> items =
+						attachmentController.getAttachmentItems(attachments);
+				displayMessageAttachments(messageId, items);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
+
+	private void displayMessageAttachments(MessageId m,
+			List<AttachmentItem> items) {
+		runOnUiThreadUnlessDestroyed(() -> {
+			attachmentController.put(m, items);
+			Pair<Integer, ConversationMessageItem> pair =
+					adapter.getMessageItem(m);
+			if (pair != null) {
+				pair.getSecond().setAttachments(items);
+				boolean bottom = adapter.isScrolledToBottom(layoutManager);
+				adapter.notifyItemChanged(pair.getFirst());
+				if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
 			}
 		});
 	}
@@ -445,10 +531,10 @@ public class ConversationActivity extends BriarActivity
 
 	private void addConversationItem(ConversationItem item) {
 		runOnUiThreadUnlessDestroyed(() -> {
+			boolean bottom = adapter.isScrolledToBottom(layoutManager);
 			adapter.incrementRevision();
 			adapter.add(item);
-			// Scroll to the bottom
-			list.scrollToPosition(adapter.getItemCount() - 1);
+			if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
 		});
 	}
 
@@ -729,6 +815,31 @@ public class ConversationActivity extends BriarActivity
 		startActivity(i);
 	}
 
+	@Override
+	public void onAttachmentClicked(View view,
+			ConversationMessageItem messageItem, AttachmentItem item) {
+		String name;
+		if (messageItem.isIncoming()) {
+			// must be available when items are being displayed
+			name = viewModel.getContactDisplayName().getValue();
+		} else {
+			name = getString(R.string.you);
+		}
+		Intent i = new Intent(this, ImageActivity.class);
+		i.putExtra(ATTACHMENT, item);
+		i.putExtra(NAME, name);
+		i.putExtra(DATE, messageItem.getTime());
+		if (SDK_INT >= 23) {
+			String transitionName = item.getTransitionName();
+			ActivityOptionsCompat options =
+					makeSceneTransitionAnimation(this, view, transitionName);
+			ActivityCompat.startActivity(this, i, options.toBundle());
+		} else {
+			// work-around for android bug #224270
+			startActivity(i);
+		}
+	}
+
 	@DatabaseExecutor
 	private void respondToIntroductionRequest(SessionId sessionId,
 			boolean accept, long time) throws DbException {
@@ -761,4 +872,16 @@ public class ConversationActivity extends BriarActivity
 		if (text == null) loadMessageText(m);
 		return text;
 	}
+
+	@Override
+	public List<AttachmentItem> getAttachmentItems(MessageId m,
+			List<AttachmentHeader> headers) {
+		List<AttachmentItem> attachments = attachmentController.get(m);
+		if (attachments == null) {
+			loadMessageAttachments(m, headers);
+			return emptyList();
+		}
+		return attachments;
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationAdapter.java

@@ -2,12 +2,15 @@ package org.briarproject.briar.android.conversation;
 
 import android.content.Context;
 import android.support.annotation.LayoutRes;
+import android.support.v7.widget.LinearLayoutManager;
 import android.util.SparseArray;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.util.BriarAdapter;
 
@@ -98,16 +101,20 @@ class ConversationAdapter
 		return messages;
 	}
 
-	SparseArray<ConversationMessageItem> getMessageItems() {
-		SparseArray<ConversationMessageItem> messages = new SparseArray<>();
-
+	@Nullable
+	Pair<Integer, ConversationMessageItem> getMessageItem(MessageId messageId) {
 		for (int i = 0; i < items.size(); i++) {
 			ConversationItem item = items.get(i);
-			if (item instanceof ConversationMessageItem) {
-				messages.put(i, (ConversationMessageItem) item);
+			if (item instanceof ConversationMessageItem &&
+					item.getId().equals(messageId)) {
+				return new Pair<>(i, (ConversationMessageItem) item);
 			}
 		}
-		return messages;
+		return null;
+	}
+
+	boolean isScrolledToBottom(LinearLayoutManager layoutManager) {
+		return layoutManager.findLastVisibleItemPosition() == items.size() - 1;
 	}
 
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationItemViewHolder.java

@@ -3,9 +3,9 @@ package org.briarproject.briar.android.conversation;
 import android.support.annotation.CallSuper;
 import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
+import android.support.constraint.ConstraintLayout;
 import android.support.v7.widget.RecyclerView.ViewHolder;
 import android.view.View;
-import android.view.ViewGroup;
 import android.widget.TextView;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
@@ -18,11 +18,11 @@ import static org.briarproject.briar.android.util.UiUtils.formatDate;
 @NotNullByDefault
 abstract class ConversationItemViewHolder extends ViewHolder {
 
-	protected final ViewGroup layout;
+	protected final ConstraintLayout layout;
 	@Nullable
 	private final OutItemViewHolder outViewHolder;
 	private final TextView text;
-	private final TextView time;
+	protected final TextView time;
 
 	ConversationItemViewHolder(View v, boolean isIncoming) {
 		super(v);

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationListener.java

@@ -1,6 +1,7 @@
 package org.briarproject.briar.android.conversation;
 
 import android.support.annotation.UiThread;
+import android.view.View;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
@@ -14,4 +15,7 @@ interface ConversationListener {
 
 	void openRequestedShareable(ConversationRequestItem item);
 
+	void onAttachmentClicked(View view, ConversationMessageItem messageItem,
+			AttachmentItem attachmentItem);
+
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationMessageItem.java

@@ -3,7 +3,6 @@ package org.briarproject.briar.android.conversation;
 import android.support.annotation.LayoutRes;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.briar.api.messaging.AttachmentHeader;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 
 import java.util.List;
@@ -14,15 +13,20 @@ import javax.annotation.concurrent.NotThreadSafe;
 @NotNullByDefault
 class ConversationMessageItem extends ConversationItem {
 
-	private final List<AttachmentHeader> attachments;
+	private List<AttachmentItem> attachments;
 
-	ConversationMessageItem(@LayoutRes int layoutRes, PrivateMessageHeader h) {
+	ConversationMessageItem(@LayoutRes int layoutRes, PrivateMessageHeader h,
+			List<AttachmentItem> attachments) {
 		super(layoutRes, h);
-		this.attachments = h.getAttachmentHeaders();
+		this.attachments = attachments;
 	}
 
-	List<AttachmentHeader> getAttachments() {
+	List<AttachmentItem> getAttachments() {
 		return attachments;
 	}
 
+	void setAttachments(List<AttachmentItem> attachments) {
+		this.attachments = attachments;
+	}
+
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationMessageViewHolder.java

@@ -1,18 +1,161 @@
 package org.briarproject.briar.android.conversation;
 
+import android.content.res.Configuration;
+import android.graphics.Bitmap;
+import android.support.annotation.DrawableRes;
 import android.support.annotation.UiThread;
+import android.support.constraint.ConstraintSet;
+import android.support.v4.content.ContextCompat;
 import android.view.View;
+import android.view.ViewGroup;
+import android.widget.ImageView;
+
+import com.bumptech.glide.load.Transformation;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.conversation.glide.BriarImageTransformation;
+import org.briarproject.briar.android.conversation.glide.GlideApp;
+
+import static android.os.Build.VERSION.SDK_INT;
+import static android.support.v4.view.ViewCompat.LAYOUT_DIRECTION_RTL;
+import static com.bumptech.glide.load.engine.DiskCacheStrategy.NONE;
+import static com.bumptech.glide.load.resource.drawable.DrawableTransitionOptions.withCrossFade;
 
 @UiThread
 @NotNullByDefault
 class ConversationMessageViewHolder extends ConversationItemViewHolder {
 
-	// image support will be added here (#1242)
+	@DrawableRes
+	private static final int ERROR_RES = R.drawable.ic_image_broken;
+
+	private final ImageView imageView;
+	private final ViewGroup statusLayout;
+	private final int timeColor, timeColorBubble;
+	private final int radiusBig, radiusSmall;
+	private final boolean isRtl;
+	private final ConstraintSet textConstraints = new ConstraintSet();
+	private final ConstraintSet imageConstraints = new ConstraintSet();
+	private final ConstraintSet imageTextConstraints = new ConstraintSet();
 
 	ConversationMessageViewHolder(View v, boolean isIncoming) {
 		super(v, isIncoming);
+		imageView = v.findViewById(R.id.imageView);
+		statusLayout = v.findViewById(R.id.statusLayout);
+		radiusBig = v.getContext().getResources()
+				.getDimensionPixelSize(R.dimen.message_bubble_radius_big);
+		radiusSmall = v.getContext().getResources()
+				.getDimensionPixelSize(R.dimen.message_bubble_radius_small);
+
+		// remember original status text color
+		timeColor = time.getCurrentTextColor();
+		timeColorBubble =
+				ContextCompat.getColor(v.getContext(), R.color.briar_white);
+
+		// find out if we are showing a RTL language, Use the configuration,
+		// because getting the layout direction of views is not reliable
+		Configuration config =
+				imageView.getContext().getResources().getConfiguration();
+		isRtl = SDK_INT >= 17 &&
+				config.getLayoutDirection() == LAYOUT_DIRECTION_RTL;
+
+		// clone constraint sets from layout files
+		textConstraints
+				.clone(v.getContext(), R.layout.list_item_conversation_msg_in);
+		imageConstraints.clone(v.getContext(),
+				R.layout.list_item_conversation_msg_image);
+		imageTextConstraints.clone(v.getContext(),
+				R.layout.list_item_conversation_msg_image_text);
+
+		// in/out are different layouts, so we need to do this only once
+		textConstraints
+				.setHorizontalBias(R.id.statusLayout, isIncoming() ? 1 : 0);
+		imageConstraints
+				.setHorizontalBias(R.id.statusLayout, isIncoming() ? 1 : 0);
+		imageTextConstraints
+				.setHorizontalBias(R.id.statusLayout, isIncoming() ? 1 : 0);
+	}
+
+	@Override
+	void bind(ConversationItem conversationItem,
+			ConversationListener listener) {
+		super.bind(conversationItem, listener);
+		ConversationMessageItem item =
+				(ConversationMessageItem) conversationItem;
+		if (item.getAttachments().isEmpty()) {
+			bindTextItem();
+		} else {
+			bindImageItem(item, listener);
+		}
+	}
+
+	private void bindTextItem() {
+		clearImage();
+		statusLayout.setBackgroundResource(0);
+		// also reset padding (the background drawable defines some)
+		statusLayout.setPadding(0, 0, 0, 0);
+		time.setTextColor(timeColor);
+		textConstraints.applyTo(layout);
+	}
+
+	private void bindImageItem(ConversationMessageItem item,
+			ConversationListener listener) {
+		// TODO show more than just the first image
+		AttachmentItem attachment = item.getAttachments().get(0);
+
+		ConstraintSet constraintSet;
+		if (item.getText() == null) {
+			statusLayout
+					.setBackgroundResource(R.drawable.msg_status_bubble);
+			time.setTextColor(timeColorBubble);
+			constraintSet = imageConstraints;
+		} else {
+			statusLayout.setBackgroundResource(0);
+			// also reset padding (the background drawable defines some)
+			statusLayout.setPadding(0, 0, 0, 0);
+			time.setTextColor(timeColor);
+			constraintSet = imageTextConstraints;
+		}
+
+		// apply image size constraints, so glides picks them up for scaling
+		int width = attachment.getThumbnailWidth();
+		int height = attachment.getThumbnailHeight();
+		constraintSet.constrainWidth(R.id.imageView, width);
+		constraintSet.constrainHeight(R.id.imageView, height);
+		constraintSet.applyTo(layout);
+
+		if (attachment.hasError()) {
+			clearImage();
+			imageView.setImageResource(ERROR_RES);
+		} else {
+			loadImage(item, attachment, listener);
+		}
+	}
+
+	private void clearImage() {
+		GlideApp.with(imageView)
+				.clear(imageView);
+		imageView.setOnClickListener(null);
+	}
+
+	private void loadImage(ConversationMessageItem item,
+			AttachmentItem attachment, ConversationListener listener) {
+		boolean leftCornerSmall =
+				(isIncoming() && !isRtl) || (!isIncoming() && isRtl);
+		boolean bottomRound = item.getText() == null;
+		Transformation<Bitmap> transformation = new BriarImageTransformation(
+				radiusSmall, radiusBig, leftCornerSmall, bottomRound);
+
+		GlideApp.with(imageView)
+				.load(attachment)
+				.diskCacheStrategy(NONE)
+				.error(ERROR_RES)
+				.transform(transformation)
+				.transition(withCrossFade())
+				.into(imageView)
+				.waitForLayout();
+		imageView.setOnClickListener(
+				view -> listener.onAttachmentClicked(view, item, attachment));
 	}
 
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationModule.java

@@ -0,0 +1,19 @@
+package org.briarproject.briar.android.conversation;
+
+import org.briarproject.briar.android.activity.ActivityScope;
+import org.briarproject.briar.android.conversation.glide.BriarDataFetcherFactory;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class ConversationModule {
+
+	@ActivityScope
+	@Provides
+	BriarDataFetcherFactory provideBriarDataFetcherFactory(
+			BriarDataFetcherFactory dataFetcherFactory) {
+		return dataFetcherFactory;
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationViewModel.java

@@ -16,6 +16,7 @@ import org.briarproject.bramble.api.db.NoSuchContactException;
 import org.briarproject.bramble.api.identity.AuthorId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.briar.android.util.UiUtils;
+import org.briarproject.briar.api.messaging.MessagingManager;
 
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
@@ -38,6 +39,7 @@ public class ConversationViewModel extends AndroidViewModel {
 	@DatabaseExecutor
 	private final Executor dbExecutor;
 	private final ContactManager contactManager;
+	private final AttachmentController attachmentController;
 
 	@Nullable
 	private ContactId contactId = null;
@@ -52,10 +54,12 @@ public class ConversationViewModel extends AndroidViewModel {
 	@Inject
 	ConversationViewModel(Application application,
 			@DatabaseExecutor Executor dbExecutor,
-			ContactManager contactManager) {
+			ContactManager contactManager, MessagingManager messagingManager) {
 		super(application);
 		this.dbExecutor = dbExecutor;
 		this.contactManager = contactManager;
+		this.attachmentController = new AttachmentController(messagingManager,
+				application.getResources());
 		contactDeleted.setValue(false);
 	}
 
@@ -96,6 +100,10 @@ public class ConversationViewModel extends AndroidViewModel {
 		});
 	}
 
+	AttachmentController getAttachmentController() {
+		return attachmentController;
+	}
+
 	LiveData<Contact> getContact() {
 		return contact;
 	}

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationVisitor.java

@@ -9,17 +9,21 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.R;
 import org.briarproject.briar.api.blog.BlogInvitationRequest;
 import org.briarproject.briar.api.blog.BlogInvitationResponse;
+import org.briarproject.briar.api.conversation.ConversationMessageVisitor;
 import org.briarproject.briar.api.forum.ForumInvitationRequest;
 import org.briarproject.briar.api.forum.ForumInvitationResponse;
 import org.briarproject.briar.api.introduction.IntroductionRequest;
 import org.briarproject.briar.api.introduction.IntroductionResponse;
+import org.briarproject.briar.api.messaging.AttachmentHeader;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
-import org.briarproject.briar.api.conversation.ConversationMessageVisitor;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationRequest;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationResponse;
 
+import java.util.List;
+
 import javax.annotation.Nullable;
 
+import static java.util.Collections.emptyList;
 import static org.briarproject.briar.android.conversation.ConversationRequestItem.RequestType.BLOG;
 import static org.briarproject.briar.android.conversation.ConversationRequestItem.RequestType.FORUM;
 import static org.briarproject.briar.android.conversation.ConversationRequestItem.RequestType.GROUP;
@@ -33,24 +37,33 @@ class ConversationVisitor implements
 
 	private final Context ctx;
 	private final TextCache textCache;
+	private final AttachmentCache attachmentCache;
 	private final LiveData<String> contactName;
 
 	ConversationVisitor(Context ctx, TextCache textCache,
-			LiveData<String> contactName) {
+			AttachmentCache attachmentCache, LiveData<String> contactName) {
 		this.ctx = ctx;
 		this.textCache = textCache;
+		this.attachmentCache = attachmentCache;
 		this.contactName = contactName;
 	}
 
 	@Override
 	public ConversationItem visitPrivateMessageHeader(PrivateMessageHeader h) {
 		ConversationItem item;
+		List<AttachmentItem> attachments;
+		if (h.getAttachmentHeaders().isEmpty()) {
+			attachments = emptyList();
+		} else {
+			attachments = attachmentCache
+					.getAttachmentItems(h.getId(), h.getAttachmentHeaders());
+		}
 		if (h.isLocal()) {
 			item = new ConversationMessageItem(
-					R.layout.list_item_conversation_msg_out, h);
+					R.layout.list_item_conversation_msg_out, h, attachments);
 		} else {
 			item = new ConversationMessageItem(
-					R.layout.list_item_conversation_msg_in, h);
+					R.layout.list_item_conversation_msg_in, h, attachments);
 		}
 		if (h.hasText()) {
 			String text = textCache.getText(h.getId());
@@ -216,11 +229,18 @@ class ConversationVisitor implements
 			return new ConversationNoticeItem(
 					R.layout.list_item_conversation_notice_out, text, r);
 		} else {
-			String text = ctx.getString(R.string.introduction_request_received,
-					contactName.getValue(), name);
+			String text;
+			if (r.isContact()) {
+				text = ctx.getString(
+						R.string.introduction_request_exists_received,
+						contactName.getValue(), name);
+			} else {
+				text = ctx.getString(R.string.introduction_request_received,
+						contactName.getValue(), name);
+			}
 			return new ConversationRequestItem(
-					R.layout.list_item_conversation_request, text, INTRODUCTION,
-					r);
+					R.layout.list_item_conversation_request, text,
+					INTRODUCTION, r);
 		}
 	}
 
@@ -272,4 +292,9 @@ class ConversationVisitor implements
 		@Nullable
 		String getText(MessageId m);
 	}
+
+	interface AttachmentCache {
+		List<AttachmentItem> getAttachmentItems(MessageId m,
+				List<AttachmentHeader> headers);
+	}
 }

briar-android/src/main/java/org/briarproject/briar/android/conversation/ImageActivity.java

@@ -0,0 +1,233 @@
+package org.briarproject.briar.android.conversation;
+
+import android.graphics.drawable.Animatable;
+import android.graphics.drawable.Drawable;
+import android.os.Bundle;
+import android.support.annotation.Nullable;
+import android.support.annotation.RequiresApi;
+import android.support.design.widget.AppBarLayout;
+import android.support.v7.widget.Toolbar;
+import android.transition.Fade;
+import android.transition.Transition;
+import android.view.MenuItem;
+import android.view.View;
+import android.view.Window;
+import android.widget.TextView;
+
+import com.bumptech.glide.load.DataSource;
+import com.bumptech.glide.load.engine.GlideException;
+import com.bumptech.glide.request.RequestListener;
+import com.bumptech.glide.request.target.Target;
+import com.github.chrisbanes.photoview.PhotoView;
+
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.ActivityComponent;
+import org.briarproject.briar.android.activity.BriarActivity;
+import org.briarproject.briar.android.conversation.glide.GlideApp;
+import org.briarproject.briar.android.view.PullDownLayout;
+
+import static android.graphics.Color.TRANSPARENT;
+import static android.os.Build.VERSION.SDK_INT;
+import static android.view.View.GONE;
+import static android.view.View.SYSTEM_UI_FLAG_FULLSCREEN;
+import static android.view.View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN;
+import static android.view.View.SYSTEM_UI_FLAG_LAYOUT_STABLE;
+import static android.view.View.VISIBLE;
+import static android.view.WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS;
+import static android.widget.ImageView.ScaleType.FIT_START;
+import static com.bumptech.glide.load.engine.DiskCacheStrategy.NONE;
+import static java.util.Objects.requireNonNull;
+import static org.briarproject.briar.android.util.UiUtils.formatDateAbsolute;
+
+public class ImageActivity extends BriarActivity
+		implements PullDownLayout.Callback {
+
+	final static String ATTACHMENT = "attachment";
+	final static String NAME = "name";
+	final static String DATE = "date";
+
+	private PullDownLayout layout;
+	private AppBarLayout appBarLayout;
+	private PhotoView photoView;
+
+	@Override
+	public void injectActivity(ActivityComponent component) {
+		component.inject(this);
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle state) {
+		super.onCreate(state);
+
+		// Transitions
+		supportPostponeEnterTransition();
+		Window window = getWindow();
+		if (SDK_INT >= 21) {
+			Transition transition = new Fade();
+			setSceneTransitionAnimation(transition, null, transition);
+		}
+
+		// inflate layout
+		setContentView(R.layout.activity_image);
+		layout = findViewById(R.id.layout);
+		layout.getBackground().setAlpha(255);
+		layout.setCallback(this);
+
+		// Status Bar
+		if (SDK_INT >= 21) {
+			window.setStatusBarColor(TRANSPARENT);
+		} else if (SDK_INT >= 19) {
+			// we can't make the status bar transparent, but translucent
+			window.addFlags(FLAG_TRANSLUCENT_STATUS);
+		}
+
+		// Toolbar
+		appBarLayout = findViewById(R.id.appBarLayout);
+		Toolbar toolbar = requireNonNull(setUpCustomToolbar(true));
+		TextView contactName = toolbar.findViewById(R.id.contactName);
+		TextView dateView = toolbar.findViewById(R.id.dateView);
+
+		// Intent Extras
+		AttachmentItem attachment = getIntent().getParcelableExtra(ATTACHMENT);
+		String name = getIntent().getStringExtra(NAME);
+		long time = getIntent().getLongExtra(DATE, 0);
+		String date = formatDateAbsolute(this, time);
+		contactName.setText(name);
+		dateView.setText(date);
+
+		// Image View
+		photoView = findViewById(R.id.photoView);
+		if (SDK_INT >= 16) {
+			photoView.setOnClickListener(view -> toggleSystemUi());
+			window.getDecorView().setSystemUiVisibility(
+					SYSTEM_UI_FLAG_LAYOUT_STABLE |
+							SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
+		}
+
+		// Request Listener
+		RequestListener<Drawable> listener = new RequestListener<Drawable>() {
+			@Override
+			public boolean onLoadFailed(@Nullable GlideException e,
+					Object model, Target<Drawable> target,
+					boolean isFirstResource) {
+				supportStartPostponedEnterTransition();
+				return false;
+			}
+
+			@Override
+			public boolean onResourceReady(Drawable resource, Object model,
+					Target<Drawable> target, DataSource dataSource,
+					boolean isFirstResource) {
+				if (SDK_INT >= 21 && !(resource instanceof Animatable)) {
+					// set transition name only when not animatable,
+					// because the animation won't start otherwise
+					photoView.setTransitionName(
+							attachment.getTransitionName());
+				}
+				// Move image to the top if overlapping toolbar
+				if (isOverlappingToolbar(resource)) {
+					photoView.setScaleType(FIT_START);
+				}
+				supportStartPostponedEnterTransition();
+				return false;
+			}
+		};
+
+		// Load Image
+		GlideApp.with(this)
+				.load(attachment)
+				.diskCacheStrategy(NONE)
+				.error(R.drawable.ic_image_broken)
+				.dontTransform()
+				.addListener(listener)
+				.into(photoView);
+	}
+
+	@Override
+	public boolean onOptionsItemSelected(MenuItem item) {
+		switch (item.getItemId()) {
+			case android.R.id.home:
+				onBackPressed();
+				return true;
+			default:
+				return super.onOptionsItemSelected(item);
+		}
+	}
+
+	@Override
+	public void onPullStart() {
+		appBarLayout.animate()
+				.alpha(0f)
+				.start();
+	}
+
+	@Override
+	public void onPull(float progress) {
+		layout.getBackground().setAlpha(Math.round((1 - progress) * 255));
+	}
+
+	@Override
+	public void onPullCancel() {
+		appBarLayout.animate()
+				.alpha(1f)
+				.start();
+	}
+
+	@Override
+	public void onPullComplete() {
+		supportFinishAfterTransition();
+	}
+
+	@RequiresApi(api = 16)
+	private void toggleSystemUi() {
+		View decorView = getWindow().getDecorView();
+		if (appBarLayout.getVisibility() == VISIBLE) {
+			hideSystemUi(decorView);
+		} else {
+			showSystemUi(decorView);
+		}
+	}
+
+	@RequiresApi(api = 16)
+	private void hideSystemUi(View decorView) {
+		decorView.setSystemUiVisibility(SYSTEM_UI_FLAG_LAYOUT_STABLE
+				| SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
+				| SYSTEM_UI_FLAG_FULLSCREEN
+		);
+		appBarLayout.animate()
+				.translationYBy(-1 * appBarLayout.getHeight())
+				.alpha(0f)
+				.withEndAction(() -> appBarLayout.setVisibility(GONE))
+				.start();
+	}
+
+	@RequiresApi(api = 16)
+	private void showSystemUi(View decorView) {
+		decorView.setSystemUiVisibility(
+				SYSTEM_UI_FLAG_LAYOUT_STABLE
+						| SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
+		);
+		appBarLayout.animate()
+				.translationYBy(appBarLayout.getHeight())
+				.alpha(1f)
+				.withStartAction(() -> appBarLayout.setVisibility(VISIBLE))
+				.start();
+	}
+
+	private boolean isOverlappingToolbar(Drawable drawable) {
+		int width = drawable.getIntrinsicWidth();
+		int height = drawable.getIntrinsicHeight();
+		float widthPercentage = photoView.getWidth() / (float) width;
+		float heightPercentage = photoView.getHeight() / (float) height;
+		float scaleFactor = Math.min(widthPercentage, heightPercentage);
+		int realWidth = (int) (width * scaleFactor);
+		int realHeight = (int) (height * scaleFactor);
+		// return if photo doesn't use the full width,
+		// because it will be moved to the right otherwise
+		if (realWidth < photoView.getWidth()) return false;
+		int drawableTop = (photoView.getHeight() - realHeight) / 2;
+		return drawableTop < appBarLayout.getBottom() &&
+				drawableTop != appBarLayout.getTop();
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/glide/BriarDataFetcher.java

@@ -0,0 +1,85 @@
+package org.briarproject.briar.android.conversation.glide;
+
+import android.support.annotation.Nullable;
+
+import com.bumptech.glide.Priority;
+import com.bumptech.glide.load.DataSource;
+import com.bumptech.glide.load.data.DataFetcher;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.android.conversation.AttachmentItem;
+import org.briarproject.briar.api.messaging.MessagingManager;
+
+import java.io.InputStream;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import static com.bumptech.glide.load.DataSource.LOCAL;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.tryToClose;
+
+@NotNullByDefault
+class BriarDataFetcher implements DataFetcher<InputStream> {
+
+	private final static Logger LOG =
+			getLogger(BriarDataFetcher.class.getName());
+
+	private final MessagingManager messagingManager;
+	@DatabaseExecutor
+	private final Executor dbExecutor;
+	private final AttachmentItem attachment;
+
+	@Nullable
+	private volatile InputStream inputStream;
+	private volatile boolean cancel = false;
+
+	@Inject
+	public BriarDataFetcher(MessagingManager messagingManager,
+			@DatabaseExecutor Executor dbExecutor, AttachmentItem attachment) {
+		this.messagingManager = messagingManager;
+		this.dbExecutor = dbExecutor;
+		this.attachment = attachment;
+	}
+
+	@Override
+	public void loadData(Priority priority,
+			DataCallback<? super InputStream> callback) {
+		MessageId id = attachment.getMessageId();
+		dbExecutor.execute(() -> {
+			if (cancel) return;
+			try {
+				inputStream = messagingManager.getAttachment(id).getStream();
+				callback.onDataReady(inputStream);
+			} catch (DbException e) {
+				callback.onLoadFailed(e);
+			}
+		});
+	}
+
+	@Override
+	public void cleanup() {
+		tryToClose(inputStream, LOG, WARNING);
+	}
+
+	@Override
+	public void cancel() {
+		cancel = true;
+	}
+
+	@Override
+	public Class<InputStream> getDataClass() {
+		return InputStream.class;
+	}
+
+	@Override
+	public DataSource getDataSource() {
+		return LOCAL;
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/conversation/glide/BriarDataFetcherFactory.java

@@ -0,0 +1,30 @@
+package org.briarproject.briar.android.conversation.glide;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.android.conversation.AttachmentItem;
+import org.briarproject.briar.api.messaging.MessagingManager;
+
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+
+@NotNullByDefault
+public class BriarDataFetcherFactory {
+
+	private final MessagingManager messagingManager;
+	@DatabaseExecutor
+	private final Executor dbExecutor;
+
+	@Inject
+	public BriarDataFetcherFactory(MessagingManager messagingManager,
+			@DatabaseExecutor Executor dbExecutor) {
+		this.messagingManager = messagingManager;
+		this.dbExecutor = dbExecutor;
+	}
+
+	BriarDataFetcher createBriarDataFetcher(AttachmentItem model) {
+		return new BriarDataFetcher(messagingManager, dbExecutor, model);
+	}
+
+}