Add executor with high and low priority queues.

Add a setting to disable Tor when running on battery

Closes #978

See merge request briar/briar!1032

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

@@ -19,9 +19,7 @@ import javax.inject.Inject;
 import static android.content.Intent.ACTION_BATTERY_CHANGED;
 import static android.content.Intent.ACTION_POWER_CONNECTED;
 import static android.content.Intent.ACTION_POWER_DISCONNECTED;
-import static android.os.BatteryManager.BATTERY_STATUS_CHARGING;
+import static android.os.BatteryManager.EXTRA_PLUGGED;
-import static android.os.BatteryManager.BATTERY_STATUS_FULL;
-import static android.os.BatteryManager.EXTRA_STATUS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Logger.getLogger;
 
@@ -48,9 +46,8 @@ class AndroidBatteryManager implements BatteryManager, Service {
 		IntentFilter filter = new IntentFilter(ACTION_BATTERY_CHANGED);
 		Intent i = appContext.registerReceiver(null, filter);
 		if (i == null) return false;
-		int status = i.getIntExtra(EXTRA_STATUS, -1);
+		int status = i.getIntExtra(EXTRA_PLUGGED, 0);
-		return status == BATTERY_STATUS_CHARGING ||
+		return status != 0;
-				status == BATTERY_STATUS_FULL;
 	}
 
 	@Override

bramble-api/src/main/java/org/briarproject/bramble/api/contact/ContactManager.java

@@ -13,6 +13,8 @@ import java.util.Collection;
 
 import javax.annotation.Nullable;
 
+import static org.briarproject.bramble.api.contact.PendingContact.PendingContactState.FAILED;
+
 @NotNullByDefault
 public interface ContactManager {
 
@@ -52,6 +54,35 @@ public interface ContactManager {
 			long timestamp, boolean alice, boolean verified, boolean active)
 			throws DbException;
 
+	/**
+	 * Returns the static link that needs to be sent to the contact to be added.
+	 */
+	String getRemoteContactLink();
+
+	/**
+	 * Returns true if the given link is syntactically valid.
+	 */
+	boolean isValidRemoteContactLink(String link);
+
+	/**
+	 * Requests a new contact to be added via the given {@code link}.
+	 *
+	 * @param link The link received from the contact we want to add.
+	 * @param alias The alias the user has given this contact.
+	 * @return A PendingContact representing the contact to be added.
+	 */
+	PendingContact addRemoteContactRequest(String link, String alias);
+
+	/**
+	 * Returns a list of {@link PendingContact}s.
+	 */
+	Collection<PendingContact> getPendingContacts();
+
+	/**
+	 * Removes a {@link PendingContact} that is in state {@link FAILED}.
+	 */
+	void removePendingContact(PendingContact pendingContact);
+
 	/**
 	 * Returns the contact with the given ID.
 	 */

bramble-api/src/main/java/org/briarproject/bramble/api/contact/PendingContact.java

@@ -0,0 +1,54 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+@Immutable
+@NotNullByDefault
+public class PendingContact {
+
+	public enum PendingContactState {
+		WAITING_FOR_CONNECTION,
+		CONNECTED,
+		ADDING_CONTACT,
+		FAILED
+	}
+
+	private final PendingContactId id;
+	private final String alias;
+	private final PendingContactState state;
+	private final long timestamp;
+
+	public PendingContact(PendingContactId id, String alias,
+			PendingContactState state, long timestamp) {
+		this.id = id;
+		this.alias = alias;
+		this.state = state;
+		this.timestamp = timestamp;
+	}
+
+	public String getAlias() {
+		return alias;
+	}
+
+	public PendingContactState getState() {
+		return state;
+	}
+
+	public long getTimestamp() {
+		return timestamp;
+	}
+
+	@Override
+	public int hashCode() {
+		return id.hashCode();
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof PendingContact &&
+				id.equals(((PendingContact) o).id);
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/PendingContactId.java

@@ -0,0 +1,11 @@
+package org.briarproject.bramble.api.contact;
+
+import org.briarproject.bramble.api.UniqueId;
+
+public class PendingContactId extends UniqueId {
+
+	public PendingContactId(byte[] id) {
+		super(id);
+	}
+
+}

bramble-api/src/main/java/org/briarproject/bramble/api/contact/event/PendingContactStateChangedEvent.java

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.api.contact.event;
+
+import org.briarproject.bramble.api.contact.PendingContact.PendingContactState;
+import org.briarproject.bramble.api.contact.PendingContactId;
+import org.briarproject.bramble.api.event.Event;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * An event that is broadcast when a pending contact's state is changed.
+ */
+@Immutable
+@NotNullByDefault
+public class PendingContactStateChangedEvent extends Event {
+
+	private final PendingContactId id;
+	private final PendingContactState state;
+
+	public PendingContactStateChangedEvent(PendingContactId id,
+			PendingContactState state) {
+		this.id = id;
+		this.state = state;
+	}
+
+	public PendingContactId getId() {
+		return id;
+	}
+
+	public PendingContactState getPendingContactState() {
+		return state;
+	}
+
+}

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

@@ -1,20 +0,0 @@
-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

@@ -1,27 +0,0 @@
-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/plugin/TorConstants.java

@@ -16,6 +16,7 @@ public interface TorConstants {
 	String PREF_TOR_NETWORK = "network2";
 	String PREF_TOR_PORT = "port";
 	String PREF_TOR_MOBILE = "useMobileData";
+	String PREF_TOR_ONLY_WHEN_CHARGING = "onlyWhenCharging";
 
 	int PREF_TOR_NETWORK_AUTOMATIC = 0;
 	int PREF_TOR_NETWORK_WITHOUT_BRIDGES = 1;

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

@@ -1,7 +1,6 @@
 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 {
@@ -11,6 +10,4 @@ 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

@@ -24,12 +24,6 @@ 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

@@ -35,9 +35,4 @@ 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/tree/LeafNode.java

@@ -1,21 +0,0 @@
-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

@@ -1,26 +0,0 @@
-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

@@ -1,21 +0,0 @@
-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

@@ -1,24 +0,0 @@
-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

@@ -1,11 +0,0 @@
-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

@@ -1,38 +0,0 @@
-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/versioning/ClientVersioningManager.java

@@ -38,6 +38,13 @@ public interface ClientVersioningManager {
 	Visibility getClientVisibility(Transaction txn, ContactId contactId,
 			ClientId clientId, int majorVersion) throws DbException;
 
+	/**
+	 * Returns the minor version of the given client that is supported by the
+	 * given contact, or -1 if the contact does not support the client.
+	 */
+	int getClientMinorVersion(Transaction txn, ContactId contactId,
+			ClientId clientId, int majorVersion) throws DbException;
+
 	interface ClientVersioningHook {
 
 		void onClientVisibilityChanging(Transaction txn, Contact c,

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

@@ -0,0 +1,67 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.GuardedBy;
+
+@NotNullByDefault
+public class PriorityExecutor {
+
+	private final Object lock = new Object();
+	private final Executor delegate, high, low;
+	@GuardedBy("lock")
+	private final Queue<Runnable> highQueue = new LinkedList<>();
+	@GuardedBy("lock")
+	private final Queue<Runnable> lowQueue = new LinkedList<>();
+
+	@GuardedBy("lock")
+	private boolean isTaskRunning = false;
+
+	public PriorityExecutor(Executor delegate) {
+		this.delegate = delegate;
+		high = r -> submit(r, true);
+		low = r -> submit(r, false);
+	}
+
+	public Executor getHighPriorityExecutor() {
+		return high;
+	}
+
+	public Executor getLowPriorityExecutor() {
+		return low;
+	}
+
+	private void submit(Runnable r, boolean isHighPriority) {
+		Runnable wrapped = () -> {
+			try {
+				r.run();
+			} finally {
+				scheduleNext();
+			}
+		};
+		synchronized (lock) {
+			if (!isTaskRunning && highQueue.isEmpty() &&
+					(isHighPriority || lowQueue.isEmpty())) {
+				isTaskRunning = true;
+				delegate.execute(wrapped);
+			} else if (isHighPriority) {
+				highQueue.add(wrapped);
+			} else {
+				lowQueue.add(wrapped);
+			}
+		}
+	}
+
+	private void scheduleNext() {
+		synchronized (lock) {
+			Runnable next = highQueue.poll();
+			if (next == null) next = lowQueue.poll();
+			if (next == null) isTaskRunning = false;
+			else delegate.execute(next);
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/contact/ContactManagerImpl.java

@@ -3,6 +3,8 @@ package org.briarproject.bramble.contact;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
+import org.briarproject.bramble.api.contact.PendingContact;
+import org.briarproject.bramble.api.contact.PendingContactId;
 import org.briarproject.bramble.api.crypto.SecretKey;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
@@ -19,12 +21,16 @@ import org.briarproject.bramble.api.transport.KeyManager;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Random;
 import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.regex.Pattern;
 
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static java.util.Collections.emptyList;
+import static org.briarproject.bramble.api.contact.PendingContact.PendingContactState.WAITING_FOR_CONNECTION;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.OURSELVES;
 import static org.briarproject.bramble.api.identity.AuthorInfo.Status.UNKNOWN;
@@ -36,6 +42,12 @@ import static org.briarproject.bramble.util.StringUtils.toUtf8;
 @NotNullByDefault
 class ContactManagerImpl implements ContactManager {
 
+	private static final int LINK_LENGTH = 64;
+	private static final String REMOTE_CONTACT_LINK =
+			"briar://" + getRandomBase32String(LINK_LENGTH);
+	private static final Pattern LINK_REGEX =
+			Pattern.compile("(briar://)?([a-z2-7]{" + LINK_LENGTH + "})");
+
 	private final DatabaseComponent db;
 	private final KeyManager keyManager;
 	private final IdentityManager identityManager;
@@ -84,6 +96,48 @@ class ContactManagerImpl implements ContactManager {
 						verified, active));
 	}
 
+	@Override
+	public String getRemoteContactLink() {
+		// TODO replace with real implementation
+		return REMOTE_CONTACT_LINK;
+	}
+
+	@SuppressWarnings("SameParameterValue")
+	private static String getRandomBase32String(int length) {
+		Random random = new Random();
+		char[] c = new char[length];
+		for (int i = 0; i < length; i++) {
+			int character = random.nextInt(32);
+			if (character < 26) c[i] = (char) ('a' + character);
+			else c[i] = (char) ('2' + (character - 26));
+		}
+		return new String(c);
+	}
+
+	@Override
+	public boolean isValidRemoteContactLink(String link) {
+		return LINK_REGEX.matcher(link).matches();
+	}
+
+	@Override
+	public PendingContact addRemoteContactRequest(String link, String alias) {
+		// TODO replace with real implementation
+		PendingContactId id = new PendingContactId(link.getBytes());
+		return new PendingContact(id, alias, WAITING_FOR_CONNECTION,
+				System.currentTimeMillis());
+	}
+
+	@Override
+	public Collection<PendingContact> getPendingContacts() {
+		// TODO replace with real implementation
+		return emptyList();
+	}
+
+	@Override
+	public void removePendingContact(PendingContact pendingContact) {
+		// TODO replace with real implementation
+	}
+
 	@Override
 	public Contact getContact(ContactId c) throws DbException {
 		return db.transactionWithResult(true, txn -> db.getContact(txn, c));

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

@@ -69,6 +69,7 @@ import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK_AUTOMATIC;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK_NEVER;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_NETWORK_WITH_BRIDGES;
+import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_ONLY_WHEN_CHARGING;
 import static org.briarproject.bramble.api.plugin.TorConstants.PREF_TOR_PORT;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V2;
 import static org.briarproject.bramble.api.plugin.TorConstants.PROP_ONION_V3;
@@ -648,8 +649,10 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			if (s.getNamespace().equals(ID.getString())) {
 				LOG.info("Tor settings updated");
 				settings = s.getSettings();
-				// Works around a bug introduced in Tor 0.3.4.8. Could be
+				// Works around a bug introduced in Tor 0.3.4.8.
-				// replaced with callback.transportDisabled() when fixed.
+				// https://trac.torproject.org/projects/tor/ticket/28027
+				// Could be replaced with callback.transportDisabled()
+				// when fixed.
 				disableNetwork();
 				updateConnectionStatus(networkManager.getNetworkStatus(),
 						batteryManager.isCharging());
@@ -685,6 +688,8 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 			int network = settings.getInt(PREF_TOR_NETWORK,
 					PREF_TOR_NETWORK_AUTOMATIC);
 			boolean useMobile = settings.getBoolean(PREF_TOR_MOBILE, true);
+			boolean onlyWhenCharging =
+					settings.getBoolean(PREF_TOR_ONLY_WHEN_CHARGING, false);
 			boolean bridgesWork = circumventionProvider.doBridgesWork(country);
 			boolean automatic = network == PREF_TOR_NETWORK_AUTOMATIC;
 
@@ -699,9 +704,12 @@ abstract class TorPlugin implements DuplexPlugin, EventHandler, EventListener {
 				if (!online) {
 					LOG.info("Disabling network, device is offline");
 					enableNetwork(false);
+				} else if (!charging && onlyWhenCharging) {
+					LOG.info("Disabling network, device is on battery");
+					enableNetwork(false);
 				} else if (network == PREF_TOR_NETWORK_NEVER ||
 						(!useMobile && !wifi)) {
-					LOG.info("Disabling network due to setting");
+					LOG.info("Disabling network, device is using mobile data");
 					enableNetwork(false);
 				} else if (automatic && blocked && !bridgesWork) {
 					LOG.info("Disabling network, country is blocked");

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

@@ -7,7 +7,6 @@ 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;
@@ -40,19 +39,13 @@ class MessageFactoryImpl implements MessageFactory {
 		if (body.length == 0) throw new IllegalArgumentException();
 		if (body.length > MAX_MESSAGE_BODY_LENGTH)
 			throw new IllegalArgumentException();
-		MessageId id = getMessageIdFromBody(g, timestamp, body);
+		MessageId id = getMessageId(g, timestamp, body);
 		return new Message(id, g, timestamp, body);
 	}
 
-	private MessageId getMessageIdFromBody(GroupId g, long timestamp,
+	private MessageId getMessageId(GroupId g, long timestamp, byte[] body) {
-			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,
@@ -72,7 +65,7 @@ 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 = getMessageIdFromBody(g, timestamp, body);
+		MessageId id = getMessageId(g, timestamp, body);
 		return new Message(id, g, timestamp, body);
 	}
 
@@ -85,10 +78,4 @@ 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/tree/HashTree.java

@@ -1,16 +0,0 @@
-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

@@ -1,46 +0,0 @@
-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

@@ -1,85 +0,0 @@
-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

@@ -1,44 +0,0 @@
-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/versioning/ClientVersioningManagerImpl.java

@@ -89,14 +89,9 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 	public Visibility getClientVisibility(Transaction txn, ContactId contactId,
 			ClientId clientId, int majorVersion) throws DbException {
 		try {
-			Contact contact = db.getContact(txn, contactId);
+			LatestUpdates latest = findLatestUpdates(txn, contactId);
-			Group g = getContactGroup(contact);
+			if (latest == null || latest.remote == null) return INVISIBLE;
-			// Contact may be in the process of being added or removed, so
-			// contact group may not exist
-			if (!db.containsGroup(txn, g.getId())) return INVISIBLE;
-			LatestUpdates latest = findLatestUpdates(txn, g.getId());
 			if (latest.local == null) throw new DbException();
-			if (latest.remote == null) return INVISIBLE;
 			Update localUpdate = loadUpdate(txn, latest.local.messageId);
 			Update remoteUpdate = loadUpdate(txn, latest.remote.messageId);
 			Map<ClientMajorVersion, Visibility> visibilities =
@@ -110,6 +105,24 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 		}
 	}
 
+	@Override
+	public int getClientMinorVersion(Transaction txn, ContactId contactId,
+			ClientId clientId, int majorVersion) throws DbException {
+		try {
+			LatestUpdates latest = findLatestUpdates(txn, contactId);
+			if (latest == null || latest.remote == null) return -1;
+			Update remoteUpdate = loadUpdate(txn, latest.remote.messageId);
+			ClientMajorVersion cv =
+					new ClientMajorVersion(clientId, majorVersion);
+			for (ClientState remote : remoteUpdate.states) {
+				if (remote.majorVersion.equals(cv)) return remote.minorVersion;
+			}
+			return -1;
+		} catch (FormatException e) {
+			throw new DbException(e);
+		}
+	}
+
 	@Override
 	public void createLocalState(Transaction txn) throws DbException {
 		if (db.containsGroup(txn, localGroup.getId())) return;
@@ -336,6 +349,17 @@ class ClientVersioningManagerImpl implements ClientVersioningManager, Client,
 				MAJOR_VERSION, c);
 	}
 
+	@Nullable
+	private LatestUpdates findLatestUpdates(Transaction txn, ContactId c)
+			throws DbException, FormatException {
+		Contact contact = db.getContact(txn, c);
+		Group g = getContactGroup(contact);
+		// Contact may be in the process of being added or removed, so
+		// contact group may not exist
+		if (!db.containsGroup(txn, g.getId())) return null;
+		return findLatestUpdates(txn, g.getId());
+	}
+
 	private LatestUpdates findLatestUpdates(Transaction txn, GroupId g)
 			throws DbException, FormatException {
 		Map<MessageId, BdfDictionary> metadata =

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

@@ -0,0 +1,86 @@
+package org.briarproject.bramble;
+
+import org.briarproject.bramble.test.BrambleTestCase;
+import org.junit.Test;
+
+import java.util.List;
+import java.util.Vector;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.Executor;
+
+import static java.util.Arrays.asList;
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class PriorityExecutorTest extends BrambleTestCase {
+
+	@Test
+	public void testHighPriorityTasksAreDelegatedInOrderOfSubmission()
+			throws Exception {
+		Executor delegate = newSingleThreadExecutor();
+		PriorityExecutor priority = new PriorityExecutor(delegate);
+		Executor high = priority.getHighPriorityExecutor();
+		testTasksAreDelegatedInOrderOfSubmission(high);
+	}
+
+	@Test
+	public void testLowPriorityTasksAreDelegatedInOrderOfSubmission()
+			throws Exception {
+		Executor delegate = newSingleThreadExecutor();
+		PriorityExecutor priority = new PriorityExecutor(delegate);
+		Executor low = priority.getLowPriorityExecutor();
+		testTasksAreDelegatedInOrderOfSubmission(low);
+	}
+
+	@Test
+	public void testHighPriorityTasksAreRunFirst() throws Exception {
+		Executor delegate = newSingleThreadExecutor();
+		PriorityExecutor priority = new PriorityExecutor(delegate);
+		Executor high = priority.getHighPriorityExecutor();
+		Executor low = priority.getLowPriorityExecutor();
+		// Submit a task that will block, causing other tasks to be queued
+		CountDownLatch cork = new CountDownLatch(1);
+		low.execute(() -> {
+			try {
+				cork.await();
+			} catch (InterruptedException e) {
+				fail();
+			}
+		});
+		// Submit alternating tasks to the high and low priority executors
+		List<Integer> results = new Vector<>();
+		CountDownLatch tasksFinished = new CountDownLatch(10);
+		for (int i = 0; i < 10; i++) {
+			int result = i;
+			Runnable task = () -> {
+				results.add(result);
+				tasksFinished.countDown();
+			};
+			if (i % 2 == 0) high.execute(task);
+			else low.execute(task);
+		}
+		// Release the cork and wait for all tasks to finish
+		cork.countDown();
+		tasksFinished.await();
+		// The high-priority tasks should have run before the low-priority tasks
+		assertEquals(asList(0, 2, 4, 6, 8, 1, 3, 5, 7, 9), results);
+	}
+
+	private void testTasksAreDelegatedInOrderOfSubmission(Executor e)
+			throws Exception {
+		List<Integer> results = new Vector<>();
+		CountDownLatch tasksFinished = new CountDownLatch(10);
+		for (int i = 0; i < 10; i++) {
+			int result = i;
+			e.execute(() -> {
+				results.add(result);
+				tasksFinished.countDown();
+			});
+		}
+		// Wait for all the tasks to finish
+		tasksFinished.await();
+		// The tasks should have run in the order they were submitted
+		assertEquals(asList(0, 1, 2, 3, 4, 5, 6, 7, 8, 9), results);
+	}
+}

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

@@ -4,8 +4,6 @@ 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;
 
@@ -29,10 +27,4 @@ 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-core/src/test/java/org/briarproject/bramble/versioning/ClientVersioningManagerImplTest.java

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.data.BdfDictionary;
 import org.briarproject.bramble.api.data.BdfEntry;
 import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.sync.ClientId;
@@ -43,6 +44,7 @@ import static org.briarproject.bramble.util.StringUtils.getRandomString;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.GROUP_KEY_CONTACT_ID;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_LOCAL;
 import static org.briarproject.bramble.versioning.ClientVersioningConstants.MSG_KEY_UPDATE_VERSION;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 
 public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
@@ -657,4 +659,327 @@ public class ClientVersioningManagerImplTest extends BrambleMockTestCase {
 		c.registerClient(clientId, 123, 234, hook);
 		assertFalse(c.incomingMessage(txn, newRemoteUpdate, new Metadata()));
 	}
+
+	@Test
+	public void testReturnsInvisibleIfContactGroupDoesNotExist()
+			throws Exception {
+		expectGetContactGroup(false);
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(INVISIBLE, c.getClientVisibility(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsInvisibleIfNoRemoteUpdateExists() throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(singletonMap(localUpdateId, localUpdateMeta)));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(INVISIBLE, c.getClientVisibility(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test(expected = DbException.class)
+	public void testThrowsExceptionIfNoLocalUpdateExists() throws Exception {
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(singletonMap(remoteUpdateId, remoteUpdateMeta)));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		c.getClientVisibility(txn, contact.getId(), clientId, 123);
+	}
+
+	@Test
+	public void testReturnsInvisibleIfClientNotSupportedLocally()
+			throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is supported remotely but not locally
+		BdfList localUpdateBody = BdfList.of(new BdfList(), 1L);
+		BdfList remoteUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, false)), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, localUpdateId);
+			will(returnValue(localUpdateBody));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(INVISIBLE, c.getClientVisibility(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsInvisibleIfClientNotSupportedRemotely()
+			throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is supported locally but not remotely
+		BdfList localUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, false)), 1L);
+		BdfList remoteUpdateBody = BdfList.of(new BdfList(), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, localUpdateId);
+			will(returnValue(localUpdateBody));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(INVISIBLE, c.getClientVisibility(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsVisibleIfClientNotActiveRemotely() throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is supported locally and remotely but not active
+		BdfList localUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, false)), 1L);
+		BdfList remoteUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, false)), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, localUpdateId);
+			will(returnValue(localUpdateBody));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(VISIBLE, c.getClientVisibility(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsSharedIfClientActiveRemotely() throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is supported locally and remotely and active
+		BdfList localUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, true)), 1L);
+		BdfList remoteUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, true)), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, localUpdateId);
+			will(returnValue(localUpdateBody));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(SHARED, c.getClientVisibility(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsNegativeIfContactGroupDoesNotExist()
+			throws Exception {
+		expectGetContactGroup(false);
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(-1, c.getClientMinorVersion(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsNegativeIfNoRemoteUpdateExists() throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(singletonMap(localUpdateId, localUpdateMeta)));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(-1, c.getClientMinorVersion(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsNegativeIfClientNotSupportedRemotely()
+			throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is not supported remotely
+		BdfList remoteUpdateBody = BdfList.of(new BdfList(), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(-1, c.getClientMinorVersion(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsMinorVersionIfClientNotActiveRemotely()
+			throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is supported remotely but not active
+		BdfList remoteUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, false)), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(234, c.getClientMinorVersion(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	@Test
+	public void testReturnsMinorVersionIfClientActiveRemotely()
+			throws Exception {
+		MessageId localUpdateId = new MessageId(getRandomId());
+		BdfDictionary localUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, true));
+		MessageId remoteUpdateId = new MessageId(getRandomId());
+		BdfDictionary remoteUpdateMeta = BdfDictionary.of(
+				new BdfEntry(MSG_KEY_UPDATE_VERSION, 1L),
+				new BdfEntry(MSG_KEY_LOCAL, false));
+		Map<MessageId, BdfDictionary> messageMetadata = new HashMap<>();
+		messageMetadata.put(localUpdateId, localUpdateMeta);
+		messageMetadata.put(remoteUpdateId, remoteUpdateMeta);
+		// The client is supported remotely and active
+		BdfList remoteUpdateBody = BdfList.of(BdfList.of(
+				BdfList.of(clientId.getString(), 123, 234, true)), 1L);
+
+		expectGetContactGroup(true);
+		context.checking(new Expectations() {{
+			oneOf(clientHelper).getMessageMetadataAsDictionary(txn,
+					contactGroup.getId());
+			will(returnValue(messageMetadata));
+			oneOf(clientHelper).getMessageAsList(txn, remoteUpdateId);
+			will(returnValue(remoteUpdateBody));
+		}});
+
+		ClientVersioningManagerImpl c = createInstance();
+		assertEquals(234, c.getClientMinorVersion(txn, contact.getId(),
+				clientId, 123));
+	}
+
+	private void expectGetContactGroup(boolean exists) throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(db).getContact(txn, contact.getId());
+			will(returnValue(contact));
+			oneOf(contactGroupFactory).createContactGroup(CLIENT_ID,
+					MAJOR_VERSION, contact);
+			will(returnValue(contactGroup));
+			oneOf(db).containsGroup(txn, contactGroup.getId());
+			will(returnValue(exists));
+		}});
+	}
 }

briar-android/build.gradle

@@ -116,7 +116,7 @@ dependencies {
 	implementation 'info.guardianproject.trustedintents:trustedintents:0.2'
 	implementation 'de.hdodenhof:circleimageview:2.2.0'
 	implementation 'com.google.zxing:core:3.3.3'
-	implementation 'uk.co.samuelwall:material-tap-target-prompt:2.12.4'
+	implementation 'uk.co.samuelwall:material-tap-target-prompt:2.14.0'
 	implementation 'com.vanniktech:emoji-google:0.5.1'
 	def glideVersion = '4.8.0'
 	implementation("com.github.bumptech.glide:glide:$glideVersion") {
@@ -134,7 +134,7 @@ dependencies {
 	testImplementation project(path: ':bramble-core', configuration: 'testOutput')
 	testImplementation 'org.robolectric:robolectric:4.0.1'
 	testImplementation 'org.robolectric:shadows-support-v4:3.3.2'
-	testImplementation 'org.mockito:mockito-core:2.13.0'
+	testImplementation 'org.mockito:mockito-core:2.19.0'
 	testImplementation 'junit:junit:4.12'
 	testImplementation "org.jmock:jmock:2.8.2"
 	testImplementation "org.jmock:jmock-junit4:2.8.2"

briar-android/src/androidTestOfficial/java/org/briarproject/briar/android/conversation/AttachmentControllerIntegrationTest.java

@@ -0,0 +1,279 @@
+package org.briarproject.briar.android.conversation;
+
+import android.content.res.AssetManager;
+import android.support.test.InstrumentationRegistry;
+import android.support.test.runner.AndroidJUnit4;
+
+import org.briarproject.bramble.api.UniqueId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.messaging.Attachment;
+import org.briarproject.briar.api.messaging.AttachmentHeader;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.util.Random;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+@RunWith(AndroidJUnit4.class)
+public class AttachmentControllerIntegrationTest {
+
+	private static final String smallKitten =
+			"https://upload.wikimedia.org/wikipedia/commons/thumb/0/06/Kitten_in_Rizal_Park%2C_Manila.jpg/160px-Kitten_in_Rizal_Park%2C_Manila.jpg";
+	private static final String originalKitten =
+			"https://upload.wikimedia.org/wikipedia/commons/0/06/Kitten_in_Rizal_Park%2C_Manila.jpg";
+	private static final String pngKitten =
+			"https://upload.wikimedia.org/wikipedia/commons/c/c8/Young_cat.png";
+	private static final String uberGif =
+			"https://raw.githubusercontent.com/fuzzdb-project/fuzzdb/master/attack/file-upload/malicious-images/uber.gif";
+	private static final String lottaPixel =
+			"https://raw.githubusercontent.com/fuzzdb-project/fuzzdb/master/attack/file-upload/malicious-images/lottapixel.jpg";
+	private static final String imageIoCrash =
+			"https://www.landaire.net/img/crasher.png";
+	private static final String gimpCrash =
+			"https://gitlab.gnome.org/GNOME/gimp/uploads/75f5b7ed3b09b3f1c13f1f65bffe784f/31153c919d3aa634e8e6cff82219fe7352dd8a37.png";
+	private static final String optiPngAfl =
+			"https://sourceforge.net/p/optipng/bugs/64/attachment/test.gif";
+	private static final String librawError =
+			"https://www.libraw.org/sites/libraw.org/files/P1010671.JPG";
+
+	private final AttachmentDimensions dimensions = new AttachmentDimensions(
+			100, 50, 200, 75, 300
+	);
+	private final MessageId msgId = new MessageId(getRandomId());
+
+	private final AttachmentController controller =
+			new AttachmentController(null, dimensions);
+
+	@Test
+	public void testSmallJpegImage() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(smallKitten);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(msgId, item.getMessageId());
+		assertEquals(160, item.getWidth());
+		assertEquals(240, item.getHeight());
+		assertEquals(160, item.getThumbnailWidth());
+		assertEquals(240, item.getThumbnailHeight());
+		assertEquals("image/jpeg", item.getMimeType());
+		assertEquals("jpg", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testBigJpegImage() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(originalKitten);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(msgId, item.getMessageId());
+		assertEquals(1728, item.getWidth());
+		assertEquals(2592, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.maxHeight, item.getThumbnailHeight());
+		assertEquals("image/jpeg", item.getMimeType());
+		assertEquals("jpg", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testSmallPngImage() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/png");
+		InputStream is = getUrlInputStream(pngKitten);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(msgId, item.getMessageId());
+		assertEquals(737, item.getWidth());
+		assertEquals(510, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(138, item.getThumbnailHeight());
+		assertEquals("image/png", item.getMimeType());
+		assertEquals("png", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testUberGif() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(uberGif);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(1, item.getWidth());
+		assertEquals(1, item.getHeight());
+		assertEquals(dimensions.minHeight, item.getThumbnailWidth());
+		assertEquals(dimensions.minHeight, item.getThumbnailHeight());
+		assertEquals("image/gif", item.getMimeType());
+		assertEquals("gif", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testLottaPixels() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(lottaPixel);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(64250, item.getWidth());
+		assertEquals(64250, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.maxWidth, item.getThumbnailHeight());
+		assertEquals("image/jpeg", item.getMimeType());
+		assertEquals("jpg", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testImageIoCrash() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(imageIoCrash);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(1184, item.getWidth());
+		assertEquals(448, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.minHeight, item.getThumbnailHeight());
+		assertEquals("image/png", item.getMimeType());
+		assertEquals("png", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testGimpCrash() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(gimpCrash);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(1, item.getWidth());
+		assertEquals(1, item.getHeight());
+		assertEquals(dimensions.minHeight, item.getThumbnailWidth());
+		assertEquals(dimensions.minHeight, item.getThumbnailHeight());
+		assertEquals("image/gif", item.getMimeType());
+		assertEquals("gif", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testOptiPngAfl() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(optiPngAfl);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(32, item.getWidth());
+		assertEquals(32, item.getHeight());
+		assertEquals(dimensions.minHeight, item.getThumbnailWidth());
+		assertEquals(dimensions.minHeight, item.getThumbnailHeight());
+		assertEquals("image/gif", item.getMimeType());
+		assertEquals("gif", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testLibrawError() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getUrlInputStream(librawError);
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertTrue(item.hasError());
+	}
+
+	@Test
+	public void testSmallAnimatedGifMaxDimensions() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/gif");
+		InputStream is = getAssetInputStream("animated.gif");
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(65535, item.getWidth());
+		assertEquals(65535, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.maxWidth, item.getThumbnailHeight());
+		assertEquals("image/gif", item.getMimeType());
+		assertEquals("gif", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testSmallAnimatedGifHugeDimensions() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/gif");
+		InputStream is = getAssetInputStream("animated2.gif");
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(10000, item.getWidth());
+		assertEquals(10000, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.maxWidth, item.getThumbnailHeight());
+		assertEquals("image/gif", item.getMimeType());
+		assertEquals("gif", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testSmallGifLargeDimensions() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/gif");
+		InputStream is = getAssetInputStream("error_large.gif");
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(16384, item.getWidth());
+		assertEquals(16384, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.maxWidth, item.getThumbnailHeight());
+		assertEquals("image/gif", item.getMimeType());
+		assertEquals("gif", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testHighError() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getAssetInputStream("error_high.jpg");
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(1, item.getWidth());
+		assertEquals(10000, item.getHeight());
+		assertEquals(dimensions.minWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.maxHeight, item.getThumbnailHeight());
+		assertEquals("image/jpeg", item.getMimeType());
+		assertEquals("jpg", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	@Test
+	public void testWideError() throws Exception {
+		AttachmentHeader h = new AttachmentHeader(msgId, "image/jpeg");
+		InputStream is = getAssetInputStream("error_wide.jpg");
+		Attachment a = new Attachment(is);
+		AttachmentItem item = controller.getAttachmentItem(h, a, true);
+		assertEquals(1920, item.getWidth());
+		assertEquals(1, item.getHeight());
+		assertEquals(dimensions.maxWidth, item.getThumbnailWidth());
+		assertEquals(dimensions.minHeight, item.getThumbnailHeight());
+		assertEquals("image/jpeg", item.getMimeType());
+		assertEquals("jpg", item.getExtension());
+		assertFalse(item.hasError());
+	}
+
+	private InputStream getUrlInputStream(String url) throws IOException {
+		return new URL(url).openStream();
+	}
+
+	private InputStream getAssetInputStream(String name) throws IOException {
+		AssetManager assets = InstrumentationRegistry.getContext().getAssets();
+		return assets.open(name);
+	}
+
+	public static byte[] getRandomBytes(int length) {
+		byte[] b = new byte[length];
+		new Random().nextBytes(b);
+		return b;
+	}
+
+	public static byte[] getRandomId() {
+		return getRandomBytes(UniqueId.LENGTH);
+	}
+
+}

briar-android/src/androidTestOfficial/java/org/briarproject/briar/android/conversation/ConversationActivityNotSignedInTest.java

@@ -0,0 +1,38 @@
+package org.briarproject.briar.android.conversation;
+
+import android.content.Context;
+import android.content.Intent;
+import android.support.test.rule.ActivityTestRule;
+import android.support.test.runner.AndroidJUnit4;
+
+import org.briarproject.briar.R;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static android.support.test.InstrumentationRegistry.getInstrumentation;
+import static android.support.test.espresso.Espresso.onView;
+import static android.support.test.espresso.matcher.ViewMatchers.isDisplayed;
+import static android.support.test.espresso.matcher.ViewMatchers.withText;
+import static org.briarproject.briar.android.ViewActions.waitUntilMatches;
+import static org.briarproject.briar.android.conversation.ConversationActivity.CONTACT_ID;
+
+@RunWith(AndroidJUnit4.class)
+public class ConversationActivityNotSignedInTest {
+
+	@Rule
+	public ActivityTestRule<ConversationActivity> testRule =
+			new ActivityTestRule<>(ConversationActivity.class, false, false);
+
+	@Test
+	public void openWithoutSignedIn() {
+		Context targetContext = getInstrumentation().getTargetContext();
+		Intent intent = new Intent(targetContext, ConversationActivity.class);
+		intent.putExtra(CONTACT_ID, 1);
+		testRule.launchActivity(intent);
+
+		onView(withText(R.string.sign_in_button))
+				.perform(waitUntilMatches(isDisplayed()));
+	}
+
+}

briar-android/src/main/AndroidManifest.xml

@@ -1,6 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest
 	package="org.briarproject.briar"
+	xmlns:tools="http://schemas.android.com/tools"
 	xmlns:android="http://schemas.android.com/apk/res/android">
 
 	<uses-feature android:name="android.hardware.bluetooth" android:required="false"/>
@@ -17,6 +18,7 @@
 	<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 android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
 	<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" />
@@ -28,7 +30,8 @@
 		android:label="@string/app_name"
 		android:logo="@mipmap/ic_launcher_round"
 		android:supportsRtl="true"
-		android:theme="@style/BriarTheme">
+		android:theme="@style/BriarTheme"
+		tools:ignore="GoogleAppIndexingWarning">
 
 		<receiver
 			android:name="org.briarproject.briar.android.login.SignInReminderReceiver"
@@ -116,7 +119,7 @@
 		<activity
 			android:name=".android.conversation.ImageActivity"
 			android:parentActivityName="org.briarproject.briar.android.conversation.ConversationActivity"
-			android:theme="@style/BriarTheme.Transparent.NoActionBar">
+			android:theme="@style/BriarTheme.ActionBarOverlay">
 			<meta-data
 				android:name="android.support.PARENT_ACTIVITY"
 				android:value="org.briarproject.briar.android.conversation.ConversationActivity"/>
@@ -154,7 +157,7 @@
 				android:value="org.briarproject.briar.android.navdrawer.NavDrawerActivity"/>
 		</activity>
 
-			<activity
+		<activity
 			android:name="org.briarproject.briar.android.privategroup.memberlist.GroupMemberListActivity"
 			android:label="@string/groups_member_list"
 			android:parentActivityName="org.briarproject.briar.android.privategroup.conversation.GroupActivity"
@@ -397,7 +400,7 @@
 		<activity
 			android:name="org.briarproject.briar.android.panic.PanicResponderActivity"
 			android:noHistory="true"
-			android:theme="@style/Theme.AppCompat.NoActionBar">
+			android:theme="@style/TranslucentTheme">
 			<!-- this can never have launchMode singleTask or singleInstance! -->
 			<intent-filter>
 				<action android:name="info.guardianproject.panic.action.TRIGGER"/>
@@ -407,12 +410,12 @@
 
 		<activity
 			android:name="org.briarproject.briar.android.logout.ExitActivity"
-			android:theme="@style/Theme.AppCompat.NoActionBar">
+			android:theme="@android:style/Theme.NoDisplay">
 		</activity>
 
 		<activity
 			android:name=".android.logout.HideUiActivity"
-			android:theme="@style/Theme.AppCompat.NoActionBar">
+			android:theme="@android:style/Theme.NoDisplay">
 		</activity>
 
 		<activity

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

@@ -32,7 +32,7 @@ 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;
+import org.briarproject.briar.android.view.EmojiTextInputView;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
 import org.briarproject.briar.api.android.DozeWatchdog;
 import org.briarproject.briar.api.android.LockManager;
@@ -169,7 +169,7 @@ public interface AndroidComponent
 
 	void inject(NotificationCleanupService notificationCleanupService);
 
-	void inject(TextInputView textInputView);
+	void inject(EmojiTextInputView textInputView);
 
 	void inject(BriarModelLoader briarModelLoader);
 

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

@@ -0,0 +1,54 @@
+package org.briarproject.briar.android;
+
+import android.app.Activity;
+import android.app.Application.ActivityLifecycleCallbacks;
+import android.os.Bundle;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.concurrent.atomic.AtomicInteger;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.ThreadSafe;
+
+@ThreadSafe
+@NotNullByDefault
+class BackgroundMonitor implements ActivityLifecycleCallbacks {
+
+	private final AtomicInteger foregroundActivities = new AtomicInteger(0);
+
+	boolean isRunningInBackground() {
+		return foregroundActivities.get() == 0;
+	}
+
+	@Override
+	public void onActivityCreated(Activity a, @Nullable Bundle state) {
+	}
+
+	@Override
+	public void onActivityStarted(Activity a) {
+		foregroundActivities.incrementAndGet();
+	}
+
+	@Override
+	public void onActivityResumed(Activity a) {
+	}
+
+	@Override
+	public void onActivityPaused(Activity a) {
+	}
+
+	@Override
+	public void onActivityStopped(Activity a) {
+		foregroundActivities.decrementAndGet();
+	}
+
+	@Override
+	public void onActivitySaveInstanceState(Activity a,
+			@Nullable Bundle outState) {
+	}
+
+	@Override
+	public void onActivityDestroyed(Activity a) {
+	}
+}

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

@@ -16,4 +16,6 @@ public interface BriarApplication {
 	AndroidComponent getApplicationComponent();
 
 	SharedPreferences getDefaultSharedPreferences();
+
+	boolean isRunningInBackground();
 }

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

@@ -1,5 +1,7 @@
 package org.briarproject.briar.android;
 
+import android.app.ActivityManager;
+import android.app.ActivityManager.RunningAppProcessInfo;
 import android.app.Application;
 import android.content.Context;
 import android.content.SharedPreferences;
@@ -30,6 +32,8 @@ import java.util.logging.Handler;
 import java.util.logging.LogRecord;
 import java.util.logging.Logger;
 
+import static android.app.ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND;
+import static android.os.Build.VERSION.SDK_INT;
 import static java.util.logging.Level.FINE;
 import static java.util.logging.Level.INFO;
 import static org.acra.ReportField.ANDROID_VERSION;
@@ -79,6 +83,7 @@ public class BriarApplicationImpl extends Application
 			Logger.getLogger(BriarApplicationImpl.class.getName());
 
 	private final CachingLogHandler logHandler = new CachingLogHandler();
+	private final BackgroundMonitor backgroundMonitor = new BackgroundMonitor();
 
 	private AndroidComponent applicationComponent;
 	private volatile SharedPreferences prefs;
@@ -115,6 +120,9 @@ public class BriarApplicationImpl extends Application
 
 		applicationComponent = createApplicationComponent();
 		EmojiManager.install(new GoogleEmojiProvider());
+
+		if (SDK_INT < 16)
+			registerActivityLifecycleCallbacks(backgroundMonitor);
 	}
 
 	protected AndroidComponent createApplicationComponent() {
@@ -173,4 +181,15 @@ public class BriarApplicationImpl extends Application
 	public SharedPreferences getDefaultSharedPreferences() {
 		return prefs;
 	}
+
+	@Override
+	public boolean isRunningInBackground() {
+		if (SDK_INT >= 16) {
+			RunningAppProcessInfo info = new RunningAppProcessInfo();
+			ActivityManager.getMyMemoryState(info);
+			return (info.importance != IMPORTANCE_FOREGROUND);
+		} else {
+			return backgroundMonitor.isRunningInBackground();
+		}
+	}
 }

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

@@ -1,7 +1,5 @@
 package org.briarproject.briar.android;
 
-import android.app.ActivityManager;
-import android.app.ActivityManager.RunningAppProcessInfo;
 import android.app.Notification;
 import android.app.NotificationChannel;
 import android.app.NotificationManager;
@@ -35,7 +33,6 @@ import java.util.logging.Logger;
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
-import static android.app.ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND;
 import static android.app.NotificationManager.IMPORTANCE_DEFAULT;
 import static android.app.NotificationManager.IMPORTANCE_NONE;
 import static android.app.PendingIntent.FLAG_UPDATE_CURRENT;
@@ -74,6 +71,7 @@ public class BriarService extends Service {
 
 	@Nullable
 	private BroadcastReceiver receiver = null;
+	private BriarApplication app;
 
 	@Inject
 	AndroidNotificationManager notificationManager;
@@ -93,8 +91,8 @@ public class BriarService extends Service {
 	public void onCreate() {
 		super.onCreate();
 
-		BriarApplication application = (BriarApplication) getApplication();
+		app = (BriarApplication) getApplication();
-		application.getApplicationComponent().inject(this);
+		app.getApplicationComponent().inject(this);
 
 		LOG.info("Created");
 		if (created.getAndSet(true)) {
@@ -220,8 +218,8 @@ public class BriarService extends Service {
 	public void onLowMemory() {
 		super.onLowMemory();
 		LOG.warning("Memory is low");
-		// Clear the UI - this is done in onTrimMemory() if SDK_INT >= 16
+		// If we're not in the foreground, clear the UI to save memory
-		if (SDK_INT < 16) hideUi();
+		if (app.isRunningInBackground()) hideUi();
 	}
 
 	@Override
@@ -235,20 +233,16 @@ public class BriarService extends Service {
 			LOG.info("Trim memory: near middle of LRU list");
 		} else if (level == TRIM_MEMORY_COMPLETE) {
 			LOG.info("Trim memory: near end of LRU list");
-		} else if (SDK_INT >= 16) {
+		} else if (level == TRIM_MEMORY_RUNNING_MODERATE) {
-			if (level == TRIM_MEMORY_RUNNING_MODERATE) {
+			LOG.info("Trim memory: running moderately low");
-				LOG.info("Trim memory: running moderately low");
+		} else if (level == TRIM_MEMORY_RUNNING_LOW) {
-			} else if (level == TRIM_MEMORY_RUNNING_LOW) {
+			LOG.info("Trim memory: running low");
-				LOG.info("Trim memory: running low");
+		} else if (level == TRIM_MEMORY_RUNNING_CRITICAL) {
-			} else if (level == TRIM_MEMORY_RUNNING_CRITICAL) {
+			// This level may be received if SDK_INT < 16, although the
-				LOG.info("Trim memory: running critically low");
+			// constant isn't declared until API level 16
-				// If we're not in the foreground, clear the UI to save memory
+			LOG.warning("Trim memory: running critically low");
-				RunningAppProcessInfo info = new RunningAppProcessInfo();
+			// If we're not in the foreground, clear the UI to save memory
-				ActivityManager.getMyMemoryState(info);
+			if (app.isRunningInBackground()) hideUi();
-				if (info.importance != IMPORTANCE_FOREGROUND) hideUi();
-			} else if (LOG.isLoggable(INFO)) {
-				LOG.info("Trim memory: unknown level " + level);
-			}
 		} else if (LOG.isLoggable(INFO)) {
 			LOG.info("Trim memory: unknown level " + level);
 		}

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

@@ -3,22 +3,29 @@ package org.briarproject.briar.android;
 import android.app.NotificationManager;
 import android.content.Intent;
 import android.os.Bundle;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BaseActivity;
 import org.briarproject.briar.android.fragment.BaseFragment.BaseFragmentListener;
 import org.briarproject.briar.android.fragment.ErrorFragment;
 
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.StartResult;
 import static org.briarproject.briar.android.BriarService.EXTRA_NOTIFICATION_ID;
 import static org.briarproject.briar.android.BriarService.EXTRA_START_RESULT;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class StartupFailureActivity extends BaseActivity implements
 		BaseFragmentListener {
 
 	@Override
-	public void onCreate(Bundle state) {
+	public void onCreate(@Nullable Bundle state) {
 		super.onCreate(state);
 
 		setContentView(R.layout.activity_fragment_container);
@@ -38,7 +45,7 @@ public class StartupFailureActivity extends BaseActivity implements
 		// cancel notification
 		if (notificationId > -1) {
 			Object o = getSystemService(NOTIFICATION_SERVICE);
-			NotificationManager nm = (NotificationManager) o;
+			NotificationManager nm = (NotificationManager) requireNonNull(o);
 			nm.cancel(notificationId);
 		}
 
@@ -66,7 +73,7 @@ public class StartupFailureActivity extends BaseActivity implements
 	}
 
 	@Override
-	public void runOnDbThread(Runnable runnable) {
+	public void runOnDbThread(@NonNull Runnable runnable) {
 		throw new AssertionError("Deprecated and should not be used");
 	}
 

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

@@ -30,4 +30,10 @@ public interface TestingConstants {
 	long EXPIRY_DATE = IS_DEBUG_BUILD || IS_BETA_BUILD ?
 			BuildConfig.BuildTimestamp + 90 * 24 * 60 * 60 * 1000L :
 			Long.MAX_VALUE;
+
+	/**
+	 * Feature flag for enabling image attachments.
+	 */
+	boolean FEATURE_FLAG_IMAGE_ATTACHMENTS = IS_DEBUG_BUILD;
+
 }

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

@@ -20,6 +20,7 @@ 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.conversation.ImageFragment;
 import org.briarproject.briar.android.forum.CreateForumActivity;
 import org.briarproject.briar.android.forum.ForumActivity;
 import org.briarproject.briar.android.forum.ForumListFragment;
@@ -30,7 +31,6 @@ import org.briarproject.briar.android.introduction.IntroductionActivity;
 import org.briarproject.briar.android.introduction.IntroductionMessageFragment;
 import org.briarproject.briar.android.keyagreement.ContactExchangeActivity;
 import org.briarproject.briar.android.keyagreement.ContactExchangeErrorFragment;
-import org.briarproject.briar.android.keyagreement.IntroFragment;
 import org.briarproject.briar.android.keyagreement.KeyAgreementActivity;
 import org.briarproject.briar.android.keyagreement.KeyAgreementFragment;
 import org.briarproject.briar.android.login.AuthorNameFragment;
@@ -48,7 +48,6 @@ import org.briarproject.briar.android.privategroup.conversation.GroupActivity;
 import org.briarproject.briar.android.privategroup.conversation.GroupConversationModule;
 import org.briarproject.briar.android.privategroup.creation.CreateGroupActivity;
 import org.briarproject.briar.android.privategroup.creation.CreateGroupFragment;
-import org.briarproject.briar.android.privategroup.creation.CreateGroupMessageFragment;
 import org.briarproject.briar.android.privategroup.creation.CreateGroupModule;
 import org.briarproject.briar.android.privategroup.creation.GroupInviteActivity;
 import org.briarproject.briar.android.privategroup.creation.GroupInviteFragment;
@@ -69,10 +68,8 @@ import org.briarproject.briar.android.sharing.ForumInvitationActivity;
 import org.briarproject.briar.android.sharing.ForumSharingStatusActivity;
 import org.briarproject.briar.android.sharing.ShareBlogActivity;
 import org.briarproject.briar.android.sharing.ShareBlogFragment;
-import org.briarproject.briar.android.sharing.ShareBlogMessageFragment;
 import org.briarproject.briar.android.sharing.ShareForumActivity;
 import org.briarproject.briar.android.sharing.ShareForumFragment;
-import org.briarproject.briar.android.sharing.ShareForumMessageFragment;
 import org.briarproject.briar.android.sharing.SharingModule;
 import org.briarproject.briar.android.splash.SplashScreenActivity;
 import org.briarproject.briar.android.test.TestDataActivity;
@@ -182,8 +179,6 @@ public interface ActivityComponent {
 
 	void inject(CreateGroupFragment fragment);
 
-	void inject(CreateGroupMessageFragment fragment);
-
 	void inject(GroupListFragment fragment);
 
 	void inject(GroupInviteFragment fragment);
@@ -194,20 +189,14 @@ public interface ActivityComponent {
 
 	void inject(FeedFragment fragment);
 
-	void inject(IntroFragment fragment);
-
 	void inject(KeyAgreementFragment fragment);
 
 	void inject(ContactChooserFragment fragment);
 
 	void inject(ShareForumFragment fragment);
 
-	void inject(ShareForumMessageFragment fragment);
-
 	void inject(ShareBlogFragment fragment);
 
-	void inject(ShareBlogMessageFragment fragment);
-
 	void inject(IntroductionMessageFragment fragment);
 
 	void inject(SettingsFragment fragment);
@@ -218,4 +207,6 @@ public interface ActivityComponent {
 
 	void inject(AliasDialogFragment aliasDialogFragment);
 
+	void inject(ImageFragment imageFragment);
+
 }

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

@@ -15,6 +15,8 @@ import android.view.ViewGroup.LayoutParams;
 import android.view.inputmethod.InputMethodManager;
 
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.AndroidComponent;
 import org.briarproject.briar.android.BriarApplication;
@@ -51,6 +53,8 @@ import static org.briarproject.briar.android.TestingConstants.PREVENT_SCREENSHOT
  * Warning: Some activities don't extend {@link BaseActivity}.
  *          E.g. {@link DevReportActivity}
  */
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public abstract class BaseActivity extends AppCompatActivity
 		implements DestroyableContext, OnTapFilteredListener {
 
@@ -77,6 +81,17 @@ public abstract class BaseActivity extends AppCompatActivity
 
 	@Override
 	public void onCreate(@Nullable Bundle state) {
+		// create the ActivityComponent *before* calling super.onCreate()
+		// because it already attaches fragments which need access
+		// to the component for their own injection
+		AndroidComponent applicationComponent =
+				((BriarApplication) getApplication()).getApplicationComponent();
+		activityComponent = DaggerActivityComponent.builder()
+				.androidComponent(applicationComponent)
+				.activityModule(getActivityModule())
+				.forumModule(getForumModule())
+				.build();
+		injectActivity(activityComponent);
 		super.onCreate(state);
 
 		// WARNING: When removing this or making it possible to turn it off,
@@ -86,17 +101,6 @@ public abstract class BaseActivity extends AppCompatActivity
 		//          unlock screen is shown.
 		if (PREVENT_SCREENSHOTS) getWindow().addFlags(FLAG_SECURE);
 
-		AndroidComponent applicationComponent =
-				((BriarApplication) getApplication()).getApplicationComponent();
-
-		activityComponent = DaggerActivityComponent.builder()
-				.androidComponent(applicationComponent)
-				.activityModule(getActivityModule())
-				.forumModule(getForumModule())
-				.build();
-
-		injectActivity(activityComponent);
-
 		for (ActivityLifecycleController alc : lifecycleControllers) {
 			alc.onActivityCreate(this);
 		}

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

@@ -1,6 +1,5 @@
 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;
@@ -10,6 +9,8 @@ import android.transition.Transition;
 import android.view.Window;
 import android.widget.CheckBox;
 
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.controller.BriarController;
 import org.briarproject.briar.android.controller.DbController;
@@ -36,7 +37,8 @@ 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;
 
-@SuppressLint("Registered")
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public abstract class BriarActivity extends BaseActivity {
 
 	public static final String GROUP_ID = "briar.GROUP_ID";
@@ -60,7 +62,8 @@ public abstract class BriarActivity extends BaseActivity {
 	}
 
 	@Override
-	protected void onActivityResult(int request, int result, Intent data) {
+	protected void onActivityResult(int request, int result,
+			@Nullable Intent data) {
 		super.onActivityResult(request, result, data);
 		if (request == REQUEST_PASSWORD) {
 			// The result can be RESULT_CANCELED if there's no account
@@ -89,7 +92,7 @@ public abstract class BriarActivity extends BaseActivity {
 		} else if (lockManager.isLocked() && !isFinishing()) {
 			// Also check that the activity isn't finishing already.
 			// This is possible if we finished in onActivityResult().
-			// Lauching another UnlockActivity would cause a loop.
+			// Launching another UnlockActivity would cause a loop.
 			Intent i = new Intent(this, UnlockActivity.class);
 			startActivityForResult(i, REQUEST_UNLOCK);
 		} else if (SDK_INT >= 23) {
@@ -111,6 +114,10 @@ public abstract class BriarActivity extends BaseActivity {
 		lockManager.onActivityStop();
 	}
 
+	protected boolean signedIn() {
+		return briarController.accountSignedIn();
+	}
+
 	/**
 	 * Sets the transition animations.
 	 * @param enterTransition used to move views into initial positions

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

@@ -14,5 +14,7 @@ public interface RequestCodes {
 	int REQUEST_BLUETOOTH_DISCOVERABLE = 10;
 	int REQUEST_UNLOCK = 11;
 	int REQUEST_KEYGUARD_UNLOCK = 12;
+	int REQUEST_ATTACH_IMAGE = 13;
+	int REQUEST_SAVE_ATTACHMENT = 14;
 
 }

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

@@ -24,6 +24,8 @@ import javax.annotation.Nullable;
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
+import static java.util.Objects.requireNonNull;
+import static java.util.logging.Logger.getLogger;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
 import static org.briarproject.briar.android.util.UiUtils.MIN_DATE_RESOLUTION;
 
@@ -35,7 +37,7 @@ abstract class BasePostFragment extends BaseFragment {
 	static final String POST_ID = "briar.POST_ID";
 
 	private static final Logger LOG =
-			Logger.getLogger(BasePostFragment.class.getName());
+			getLogger(BasePostFragment.class.getName());
 
 	private final Handler handler = new Handler(Looper.getMainLooper());
 
@@ -52,7 +54,7 @@ abstract class BasePostFragment extends BaseFragment {
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
 		// retrieve MessageId of blog post from arguments
-		byte[] p = getArguments().getByteArray(POST_ID);
+		byte[] p = requireNonNull(getArguments()).getByteArray(POST_ID);
 		if (p == null) throw new IllegalStateException("No post ID in args");
 		postId = new MessageId(p);
 
@@ -68,6 +70,7 @@ abstract class BasePostFragment extends BaseFragment {
 
 			@Override
 			public void onAuthorClick(BlogPostItem post) {
+				if (getContext() == null) return;
 				Intent i = new Intent(getContext(), BlogActivity.class);
 				i.putExtra(GROUP_ID, post.getGroupId().getBytes());
 				i.setFlags(FLAG_ACTIVITY_CLEAR_TOP);

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

@@ -43,6 +43,7 @@ import javax.inject.Inject;
 import static android.app.Activity.RESULT_OK;
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
 import static android.widget.Toast.LENGTH_SHORT;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_SHARE_BLOG;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_WRITE_BLOG_POST;
@@ -69,7 +70,6 @@ public class BlogFragment extends BaseFragment
 	private boolean isMyBlog = false, canDeleteBlog = false;
 
 	static BlogFragment newInstance(GroupId groupId) {
-
 		BlogFragment f = new BlogFragment();
 
 		Bundle bundle = new Bundle();
@@ -79,20 +79,27 @@ public class BlogFragment extends BaseFragment
 		return f;
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		blogController.setBlogSharingListener(this);
+		sharingController.setSharingListener(this);
+	}
+
 	@Nullable
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-		Bundle args = getArguments();
+		Bundle args = requireNonNull(getArguments());
 		byte[] b = args.getByteArray(GROUP_ID);
 		if (b == null) throw new IllegalStateException("No group ID in args");
 		groupId = new GroupId(b);
 
 		View v = inflater.inflate(R.layout.fragment_blog, container, false);
 
-		adapter =
+		adapter = new BlogPostAdapter(requireNonNull(getActivity()), this,
-				new BlogPostAdapter(getActivity(), this, getFragmentManager());
+				getFragmentManager());
 		list = v.findViewById(R.id.postList);
 		list.setLayoutManager(new LinearLayoutManager(getActivity()));
 		list.setAdapter(adapter);
@@ -102,13 +109,6 @@ public class BlogFragment extends BaseFragment
 		return v;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-		blogController.setBlogSharingListener(this);
-		sharingController.setSharingListener(this);
-	}
-
 	@Override
 	public void onStart() {
 		super.onStart();
@@ -218,7 +218,10 @@ public class BlogFragment extends BaseFragment
 
 	@Override
 	public void onAuthorClick(BlogPostItem post) {
-		if (post.getGroupId().equals(groupId)) return; // We're already there
+		if (post.getGroupId().equals(groupId) || getContext() == null) {
+			// We're already there
+			return;
+		}
 		Intent i = new Intent(getContext(), BlogActivity.class);
 		i.putExtra(GROUP_ID, post.getGroupId().getBytes());
 		i.setFlags(FLAG_ACTIVITY_CLEAR_TOP);

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

@@ -35,6 +35,7 @@ import javax.inject.Inject;
 import static android.app.Activity.RESULT_OK;
 import static android.content.Intent.FLAG_ACTIVITY_CLEAR_TOP;
 import static android.support.design.widget.Snackbar.LENGTH_LONG;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_WRITE_BLOG_POST;
 
@@ -64,13 +65,18 @@ public class FeedFragment extends BaseFragment implements
 		return f;
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+		feedController.setFeedListener(this);
+	}
+
 	@Nullable
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-
+		requireNonNull(getActivity()).setTitle(R.string.blogs_button);
-		getActivity().setTitle(R.string.blogs_button);
 
 		View v = inflater.inflate(R.layout.fragment_blog, container, false);
 
@@ -88,12 +94,6 @@ public class FeedFragment extends BaseFragment implements
 		return v;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-		feedController.setFeedListener(this);
-	}
-
 	@Override
 	public void onActivityResult(int requestCode, int resultCode, Intent data) {
 		super.onActivityResult(requestCode, resultCode, data);

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

@@ -17,6 +17,7 @@ import org.briarproject.briar.android.controller.handler.UiResultExceptionHandle
 import javax.annotation.Nullable;
 import javax.inject.Inject;
 
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
 
 @UiThread
@@ -42,13 +43,17 @@ public class FeedPostFragment extends BasePostFragment {
 		return f;
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
 	@Nullable
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-
+		Bundle args = requireNonNull(getArguments());
-		Bundle args = getArguments();
 		byte[] b = args.getByteArray(GROUP_ID);
 		if (b == null) throw new IllegalStateException("No group ID in args");
 		blogId = new GroupId(b);
@@ -61,11 +66,6 @@ public class FeedPostFragment extends BasePostFragment {
 		return TAG;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	@Override
 	public void onStart() {
 		super.onStart();

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

@@ -1,5 +1,6 @@
 package org.briarproject.briar.android.blog;
 
+import android.net.Uri;
 import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -18,7 +19,10 @@ import org.briarproject.briar.android.controller.handler.UiExceptionHandler;
 import org.briarproject.briar.android.controller.handler.UiResultExceptionHandler;
 import org.briarproject.briar.android.fragment.BaseFragment;
 import org.briarproject.briar.android.view.TextInputView;
-import org.briarproject.briar.android.view.TextInputView.TextInputListener;
+import org.briarproject.briar.android.view.TextSendController;
+import org.briarproject.briar.android.view.TextSendController.SendListener;
+
+import java.util.List;
 
 import javax.annotation.Nullable;
 import javax.inject.Inject;
@@ -27,18 +31,18 @@ import static android.view.View.FOCUS_DOWN;
 import static android.view.View.GONE;
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
 import static org.briarproject.briar.android.blog.BasePostFragment.POST_ID;
+import static org.briarproject.briar.api.blog.BlogConstants.MAX_BLOG_POST_TEXT_LENGTH;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
-public class ReblogFragment extends BaseFragment implements TextInputListener {
+public class ReblogFragment extends BaseFragment implements SendListener {
 
 	public static final String TAG = ReblogFragment.class.getName();
 
 	private ViewHolder ui;
-	private GroupId blogId;
-	private MessageId postId;
 	private BlogPostItem item;
 
 	@Inject
@@ -70,24 +74,22 @@ public class ReblogFragment extends BaseFragment implements TextInputListener {
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
 
-		Bundle args = getArguments();
+		Bundle args = requireNonNull(getArguments());
-		blogId = new GroupId(args.getByteArray(GROUP_ID));
+		GroupId blogId =
-		postId = new MessageId(args.getByteArray(POST_ID));
+				new GroupId(requireNonNull(args.getByteArray(GROUP_ID)));
+		MessageId postId =
+				new MessageId(requireNonNull(args.getByteArray(POST_ID)));
 
 		View v = inflater.inflate(R.layout.fragment_reblog, container, false);
 		ui = new ViewHolder(v);
 		ui.post.setTransitionName(postId);
-		ui.input.setSendButtonEnabled(false);
+		TextSendController sendController =
+				new TextSendController(ui.input, this, true);
+		ui.input.setSendController(sendController);
+		ui.input.setEnabled(false);
+		ui.input.setMaxTextLength(MAX_BLOG_POST_TEXT_LENGTH);
 		showProgressBar();
 
-		return v;
-	}
-
-	@Override
-	public void onStart() {
-		super.onStart();
-
-		// TODO: Load blog post when fragment is created. #631
 		feedController.loadBlogPost(blogId, postId,
 				new UiResultExceptionHandler<BlogPostItem, DbException>(
 						this) {
@@ -102,6 +104,8 @@ public class ReblogFragment extends BaseFragment implements TextInputListener {
 						handleDbException(exception);
 					}
 				});
+
+		return v;
 	}
 
 	private void bindViewHolder() {
@@ -112,16 +116,14 @@ public class ReblogFragment extends BaseFragment implements TextInputListener {
 		ui.post.bindItem(item);
 		ui.post.hideReblogButton();
 
-		ui.input.setListener(this);
+		ui.input.setEnabled(true);
-		ui.input.setSendButtonEnabled(true);
 		ui.scrollView.post(() -> ui.scrollView.fullScroll(FOCUS_DOWN));
 	}
 
 	@Override
-	public void onSendClick(String text) {
+	public void onSendClick(@Nullable String text, List<Uri> imageUris) {
 		ui.input.hideSoftKeyboard();
-		String comment = getComment();
+		feedController.repeatPost(item, text,
-		feedController.repeatPost(item, comment,
 				new UiExceptionHandler<DbException>(this) {
 					@Override
 					public void onExceptionUi(DbException exception) {
@@ -131,12 +133,6 @@ public class ReblogFragment extends BaseFragment implements TextInputListener {
 		finish();
 	}
 
-	@Nullable
-	private String getComment() {
-		if (ui.input.getText().length() == 0) return null;
-		return ui.input.getText().toString();
-	}
-
 	private void showProgressBar() {
 		ui.progressBar.setVisibility(VISIBLE);
 		ui.input.setVisibility(GONE);

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

@@ -1,9 +1,9 @@
 package org.briarproject.briar.android.blog;
 
 import android.content.Intent;
+import android.net.Uri;
 import android.os.Bundle;
-import android.text.Editable;
+import android.support.annotation.Nullable;
-import android.text.TextWatcher;
 import android.view.KeyEvent;
 import android.view.MenuItem;
 import android.widget.ProgressBar;
@@ -14,19 +14,22 @@ import org.briarproject.bramble.api.FormatException;
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.identity.LocalAuthor;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.sync.GroupId;
-import org.briarproject.bramble.util.StringUtils;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
 import org.briarproject.briar.android.view.TextInputView;
-import org.briarproject.briar.android.view.TextInputView.TextInputListener;
+import org.briarproject.briar.android.view.TextSendController;
+import org.briarproject.briar.android.view.TextSendController.SendListener;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
 import org.briarproject.briar.api.blog.BlogManager;
 import org.briarproject.briar.api.blog.BlogPost;
 import org.briarproject.briar.api.blog.BlogPostFactory;
 
 import java.security.GeneralSecurityException;
+import java.util.List;
 import java.util.logging.Logger;
 
 import javax.inject.Inject;
@@ -35,10 +38,13 @@ import static android.view.View.GONE;
 import static android.view.View.VISIBLE;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
+import static org.briarproject.bramble.util.StringUtils.isNullOrEmpty;
 import static org.briarproject.briar.api.blog.BlogConstants.MAX_BLOG_POST_TEXT_LENGTH;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class WriteBlogPostActivity extends BriarActivity
-		implements OnEditorActionListener, TextInputListener {
+		implements OnEditorActionListener, SendListener {
 
 	private static final Logger LOG =
 			Logger.getLogger(WriteBlogPostActivity.class.getName());
@@ -58,9 +64,8 @@ public class WriteBlogPostActivity extends BriarActivity
 	@Inject
 	volatile BlogManager blogManager;
 
-	@SuppressWarnings("ConstantConditions")
 	@Override
-	public void onCreate(Bundle state) {
+	public void onCreate(@Nullable Bundle state) {
 		super.onCreate(state);
 
 		Intent i = getIntent();
@@ -71,24 +76,10 @@ public class WriteBlogPostActivity extends BriarActivity
 		setContentView(R.layout.activity_write_blog_post);
 
 		input = findViewById(R.id.textInput);
-		input.setSendButtonEnabled(false);
+		TextSendController sendController =
-		input.addTextChangedListener(new TextWatcher() {
+				new TextSendController(input, this, false);
-			@Override
+		input.setSendController(sendController);
-			public void beforeTextChanged(CharSequence s, int start, int count,
+		input.setMaxTextLength(MAX_BLOG_POST_TEXT_LENGTH);
-					int after) {
-			}
-
-			@Override
-			public void onTextChanged(CharSequence s, int start, int before,
-					int count) {
-			}
-
-			@Override
-			public void afterTextChanged(Editable s) {
-				enableOrDisablePublishButton();
-			}
-		});
-		input.setListener(this);
 
 		progressBar = findViewById(R.id.progressBar);
 	}
@@ -127,18 +118,15 @@ public class WriteBlogPostActivity extends BriarActivity
 		return true;
 	}
 
-	private void enableOrDisablePublishButton() {
-		input.setSendButtonEnabled(input.getText().length() > 0);
-	}
-
 	@Override
-	public void onSendClick(String text) {
+	public void onSendClick(@Nullable String text, List<Uri> imageUris) {
+		if (isNullOrEmpty(text)) throw new AssertionError();
+
 		// hide publish button, show progress bar
 		input.hideSoftKeyboard();
 		input.setVisibility(GONE);
 		progressBar.setVisibility(VISIBLE);
 
-		text = StringUtils.truncateUtf8(text, MAX_BLOG_POST_TEXT_LENGTH);
 		storePost(text);
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/contact/ContactListFragment.java

@@ -51,11 +51,13 @@ import javax.inject.Inject;
 import static android.os.Build.VERSION.SDK_INT;
 import static android.support.v4.app.ActivityOptionsCompat.makeSceneTransitionAnimation;
 import static android.support.v4.view.ViewCompat.getTransitionName;
+import static java.util.Objects.requireNonNull;
 import static java.util.logging.Level.WARNING;
 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.conversation.ConversationActivity.CONTACT_ID;
+import static org.briarproject.briar.android.util.UiUtils.isSamsung7;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
@@ -102,8 +104,7 @@ public class ContactListFragment extends BaseFragment implements EventListener {
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-
+		requireNonNull(getActivity()).setTitle(R.string.contact_list_button);
-		getActivity().setTitle(R.string.contact_list_button);
 
 		View contentView = inflater.inflate(R.layout.list, container, false);
 
@@ -114,7 +115,7 @@ public class ContactListFragment extends BaseFragment implements EventListener {
 					ContactId contactId = item.getContact().getId();
 					i.putExtra(CONTACT_ID, contactId.getInt());
 
-					if (SDK_INT >= 23) {
+					if (SDK_INT >= 23 && !isSamsung7()) {
 						ContactListItemViewHolder holder =
 								(ContactListItemViewHolder) list
 										.getRecyclerView()

briar-android/src/main/java/org/briarproject/briar/android/contactselection/BaseContactSelectorFragment.java

@@ -25,6 +25,7 @@ import java.util.Collection;
 
 import javax.annotation.Nullable;
 
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.activity.BriarActivity.GROUP_ID;
 import static org.briarproject.briar.android.contactselection.ContactSelectorActivity.CONTACTS;
 import static org.briarproject.briar.android.contactselection.ContactSelectorActivity.getContactsFromIds;
@@ -50,10 +51,10 @@ public abstract class BaseContactSelectorFragment<I extends SelectableContactIte
 	}
 
 	@Override
-	public void onCreate(Bundle savedInstanceState) {
+	public void onCreate(@Nullable Bundle savedInstanceState) {
 		super.onCreate(savedInstanceState);
 
-		Bundle args = getArguments();
+		Bundle args = requireNonNull(getArguments());
 		byte[] b = args.getByteArray(GROUP_ID);
 		if (b == null) throw new IllegalStateException("No GroupId");
 		groupId = new GroupId(b);
@@ -72,7 +73,7 @@ public abstract class BaseContactSelectorFragment<I extends SelectableContactIte
 		list.setEmptyImage(R.drawable.ic_empty_state_contact_list);
 		list.setEmptyText(getString(R.string.no_contacts_selector));
 		list.setEmptyAction(getString(R.string.no_contacts_selector_action));
-		adapter = getAdapter(getContext(), this);
+		adapter = getAdapter(requireNonNull(getContext()), this);
 		list.setAdapter(adapter);
 
 		// restore selected contacts if available

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

@@ -39,8 +39,8 @@ public class AliasDialogFragment extends AppCompatDialogFragment {
 
 		setStyle(STYLE_NO_TITLE, R.style.BriarDialogTheme);
 
-		if (getActivity() == null) return;
+		BriarActivity a = (BriarActivity) requireNonNull(getActivity());
-		((BriarActivity) getActivity()).getActivityComponent().inject(this);
+		a.getActivityComponent().inject(this);
 		viewModel = ViewModelProviders.of(getActivity(), viewModelFactory)
 				.get(ConversationViewModel.class);
 	}
@@ -48,7 +48,6 @@ public class AliasDialogFragment extends AppCompatDialogFragment {
 	@Override
 	public View onCreateView(@NonNull LayoutInflater inflater,
 			ViewGroup container, Bundle savedInstanceState) {
-
 		View v = inflater.inflate(R.layout.fragment_alias_dialog, container,
 				false);
 
@@ -69,4 +68,5 @@ public class AliasDialogFragment extends AppCompatDialogFragment {
 
 		return v;
 	}
+
 }

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

@@ -1,20 +1,24 @@
 package org.briarproject.briar.android.conversation;
 
-import android.content.res.Resources;
 import android.graphics.BitmapFactory;
+import android.graphics.BitmapFactory.Options;
 import android.support.annotation.Nullable;
 import android.support.media.ExifInterface;
+import android.webkit.MimeTypeMap;
+
+import com.bumptech.glide.util.MarkEnforcingInputStream;
 
 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.android.conversation.ImageHelper.DecodeResult;
 import org.briarproject.briar.api.messaging.Attachment;
 import org.briarproject.briar.api.messaging.AttachmentHeader;
 import org.briarproject.briar.api.messaging.MessagingManager;
 
+import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.ArrayList;
@@ -42,8 +46,10 @@ class AttachmentController {
 
 	private static final Logger LOG =
 			getLogger(AttachmentController.class.getName());
+	private static final int READ_LIMIT = 1024 * 8192;
 
 	private final MessagingManager messagingManager;
+	private final ImageHelper imageHelper;
 	private final int defaultSize;
 	private final int minWidth, maxWidth;
 	private final int minHeight, maxHeight;
@@ -51,18 +57,38 @@ class AttachmentController {
 	private final Map<MessageId, List<AttachmentItem>> attachmentCache =
 			new ConcurrentHashMap<>();
 
-	AttachmentController(MessagingManager messagingManager, Resources res) {
+	AttachmentController(MessagingManager messagingManager,
+			AttachmentDimensions dimensions, ImageHelper imageHelper) {
 		this.messagingManager = messagingManager;
-		defaultSize =
+		this.imageHelper = imageHelper;
-				res.getDimensionPixelSize(R.dimen.message_bubble_image_default);
+		defaultSize = dimensions.defaultSize;
-		minWidth = res.getDimensionPixelSize(
+		minWidth = dimensions.minWidth;
-				R.dimen.message_bubble_image_min_width);
+		maxWidth = dimensions.maxWidth;
-		maxWidth = res.getDimensionPixelSize(
+		minHeight = dimensions.minHeight;
-				R.dimen.message_bubble_image_max_width);
+		maxHeight = dimensions.maxHeight;
-		minHeight = res.getDimensionPixelSize(
+	}
-				R.dimen.message_bubble_image_min_height);
+
-		maxHeight = res.getDimensionPixelSize(
+	AttachmentController(MessagingManager messagingManager,
-				R.dimen.message_bubble_image_max_height);
+			AttachmentDimensions dimensions) {
+		this(messagingManager, dimensions, new ImageHelper() {
+			@Override
+			public DecodeResult decodeStream(InputStream is) {
+				Options options = new Options();
+				options.inJustDecodeBounds = true;
+				BitmapFactory.decodeStream(is, null, options);
+				String mimeType = options.outMimeType;
+				if (mimeType == null) mimeType = "";
+				return new DecodeResult(options.outWidth, options.outHeight,
+						mimeType);
+			}
+
+			@Nullable
+			@Override
+			public String getExtensionFromMimeType(String mimeType) {
+				MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
+				return mimeTypeMap.getExtensionFromMimeType(mimeType);
+			}
+		});
 	}
 
 	void put(MessageId messageId, List<AttachmentItem> attachments) {
@@ -81,31 +107,53 @@ class AttachmentController {
 		List<Pair<AttachmentHeader, Attachment>> attachments =
 				new ArrayList<>(headers.size());
 		for (AttachmentHeader h : headers) {
-			Attachment a =
+			Attachment a = messagingManager.getAttachment(h.getMessageId());
-					messagingManager.getAttachment(h.getMessageId());
 			attachments.add(new Pair<>(h, a));
 		}
 		logDuration(LOG, "Loading attachment", start);
 		return attachments;
 	}
 
+	/**
+	 * Creates {@link AttachmentItem}s from the passed headers and Attachments.
+	 * <p>
+	 * Note: This closes the {@link Attachment}'s {@link InputStream}.
+	 */
 	List<AttachmentItem> getAttachmentItems(
 			List<Pair<AttachmentHeader, Attachment>> attachments) {
+		boolean needsSize = attachments.size() == 1;
 		List<AttachmentItem> items = new ArrayList<>(attachments.size());
 		for (Pair<AttachmentHeader, Attachment> a : attachments) {
 			AttachmentItem item =
-					getAttachmentItem(a.getFirst(), a.getSecond());
+					getAttachmentItem(a.getFirst(), a.getSecond(), needsSize);
 			items.add(item);
 		}
 		return items;
 	}
 
-	private AttachmentItem getAttachmentItem(AttachmentHeader h, Attachment a) {
+	/**
+	 * Creates an {@link AttachmentItem} from the {@link Attachment}'s
+	 * {@link InputStream} which will be closed when this method returns.
+	 */
+	AttachmentItem getAttachmentItem(AttachmentHeader h, Attachment a,
+			boolean needsSize) {
 		MessageId messageId = h.getMessageId();
-		Size size = new Size();
+		if (!needsSize) {
+			String mimeType = h.getContentType();
+			String extension = imageHelper.getExtensionFromMimeType(mimeType);
+			boolean hasError = false;
+			if (extension == null) {
+				extension = "";
+				hasError = true;
+			}
+			return new AttachmentItem(messageId, 0, 0, mimeType, extension, 0,
+					0, hasError);
+		}
 
-		InputStream is = a.getStream();
+		Size size = new Size();
-		is.mark(Integer.MAX_VALUE);
+		InputStream is = new MarkEnforcingInputStream(
+				new BufferedInputStream(a.getStream()));
+		is.mark(READ_LIMIT);
 		try {
 			// use exif to get size
 			if (h.getContentType().equals("image/jpeg")) {
@@ -118,6 +166,8 @@ class AttachmentController {
 			// use BitmapFactory to get size
 			if (size.error) {
 				is.reset();
+				// need to mark again to re-add read limit
+				is.mark(READ_LIMIT);
 				size = getSizeFromBitmap(is);
 			}
 		} catch (IOException e) {
@@ -127,19 +177,24 @@ class AttachmentController {
 		}
 
 		// calculate thumbnail size
-		Size thumbnailSize = new Size(defaultSize, defaultSize);
+		Size thumbnailSize = new Size(defaultSize, defaultSize, size.mimeType);
 		if (!size.error) {
-			thumbnailSize = getThumbnailSize(size.width, size.height);
+			thumbnailSize =
+					getThumbnailSize(size.width, size.height, size.mimeType);
 		}
+		// get file extension
+		String extension = imageHelper.getExtensionFromMimeType(size.mimeType);
+		boolean hasError = extension == null || size.error;
+		if (extension == null) extension = "";
 		return new AttachmentItem(messageId, size.width, size.height,
-				thumbnailSize.width, thumbnailSize.height, size.error);
+				size.mimeType, extension, thumbnailSize.width,
+				thumbnailSize.height, hasError);
 	}
 
 	/**
 	 * Gets the size of a JPEG {@link InputStream} if EXIF info is available.
 	 */
-	private static Size getSizeFromExif(InputStream is)
+	private Size getSizeFromExif(InputStream is) throws IOException {
-			throws IOException {
 		ExifInterface exif = new ExifInterface(is);
 		// these can return 0 independent of default value
 		int width = exif.getAttributeInt(TAG_IMAGE_WIDTH, 0);
@@ -151,24 +206,21 @@ class AttachmentController {
 				orientation == ORIENTATION_TRANSVERSE ||
 				orientation == ORIENTATION_TRANSPOSE) {
 			//noinspection SuspiciousNameCombination
-			return new Size(height, width);
+			return new Size(height, width, "image/jpeg");
 		}
-		return new Size(width, height);
+		return new Size(width, height, "image/jpeg");
 	}
 
 	/**
 	 * Gets the size of any image {@link InputStream}.
 	 */
-	private static Size getSizeFromBitmap(InputStream is) {
+	private Size getSizeFromBitmap(InputStream is) {
-		BitmapFactory.Options options = new BitmapFactory.Options();
+		DecodeResult result = imageHelper.decodeStream(is);
-		options.inJustDecodeBounds = true;
+		if (result.width < 1 || result.height < 1) return new Size();
-		BitmapFactory.decodeStream(is, null, options);
+		return new Size(result.width, result.height, result.mimeType);
-		if (options.outWidth < 1 || options.outHeight < 1)
-			return new Size();
-		return new Size(options.outWidth, options.outHeight);
 	}
 
-	private Size getThumbnailSize(int width, int height) {
+	private Size getThumbnailSize(int width, int height, String mimeType) {
 		float widthPercentage = maxWidth / (float) width;
 		float heightPercentage = maxHeight / (float) height;
 		float scaleFactor = Math.min(widthPercentage, heightPercentage);
@@ -184,24 +236,27 @@ class AttachmentController {
 			if (thumbnailWidth > maxWidth) thumbnailWidth = maxWidth;
 			if (thumbnailHeight > maxHeight) thumbnailHeight = maxHeight;
 		}
-		return new Size(thumbnailWidth, thumbnailHeight);
+		return new Size(thumbnailWidth, thumbnailHeight, mimeType);
 	}
 
 	private static class Size {
 
 		private final int width;
 		private final int height;
+		private final String mimeType;
 		private final boolean error;
 
-		private Size(int width, int height) {
+		private Size(int width, int height, String mimeType) {
 			this.width = width;
 			this.height = height;
+			this.mimeType = mimeType;
 			this.error = false;
 		}
 
 		private Size() {
 			this.width = 0;
 			this.height = 0;
+			this.mimeType = "";
 			this.error = true;
 		}
 	}

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

@@ -0,0 +1,39 @@
+package org.briarproject.briar.android.conversation;
+
+import android.content.res.Resources;
+import android.support.annotation.VisibleForTesting;
+
+import org.briarproject.briar.R;
+
+class AttachmentDimensions {
+
+	final int defaultSize;
+	final int minWidth, maxWidth;
+	final int minHeight, maxHeight;
+
+	@VisibleForTesting
+	AttachmentDimensions(int defaultSize, int minWidth, int maxWidth,
+			int minHeight, int maxHeight) {
+		this.defaultSize = defaultSize;
+		this.minWidth = minWidth;
+		this.maxWidth = maxWidth;
+		this.minHeight = minHeight;
+		this.maxHeight = maxHeight;
+	}
+
+	static AttachmentDimensions getAttachmentDimensions(Resources res) {
+		int defaultSize =
+				res.getDimensionPixelSize(R.dimen.message_bubble_image_default);
+		int minWidth = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_min_width);
+		int maxWidth = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_max_width);
+		int minHeight = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_min_height);
+		int maxHeight = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_max_height);
+		return new AttachmentDimensions(defaultSize, minWidth, maxWidth,
+				minHeight, minHeight);
+	}
+
+}

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

@@ -2,10 +2,13 @@ package org.briarproject.briar.android.conversation;
 
 import android.os.Parcel;
 import android.os.Parcelable;
+import android.support.annotation.Nullable;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageId;
 
+import java.util.concurrent.atomic.AtomicLong;
+
 import javax.annotation.concurrent.Immutable;
 
 @Immutable
@@ -14,8 +17,10 @@ public class AttachmentItem implements Parcelable {
 
 	private final MessageId messageId;
 	private final int width, height;
+	private final String mimeType, extension;
 	private final int thumbnailWidth, thumbnailHeight;
 	private final boolean hasError;
+	private final long instanceId;
 
 	public static final Creator<AttachmentItem> CREATOR =
 			new Creator<AttachmentItem>() {
@@ -30,14 +35,20 @@ public class AttachmentItem implements Parcelable {
 				}
 			};
 
-	AttachmentItem(MessageId messageId, int width, int height,
+	private static final AtomicLong NEXT_INSTANCE_ID = new AtomicLong(0);
-			int thumbnailWidth, int thumbnailHeight, boolean hasError) {
+
+	AttachmentItem(MessageId messageId, int width, int height, String mimeType,
+			String extension, int thumbnailWidth, int thumbnailHeight,
+			boolean hasError) {
 		this.messageId = messageId;
 		this.width = width;
 		this.height = height;
+		this.mimeType = mimeType;
+		this.extension = extension;
 		this.thumbnailWidth = thumbnailWidth;
 		this.thumbnailHeight = thumbnailHeight;
 		this.hasError = hasError;
+		instanceId = NEXT_INSTANCE_ID.getAndIncrement();
 	}
 
 	protected AttachmentItem(Parcel in) {
@@ -46,9 +57,12 @@ public class AttachmentItem implements Parcelable {
 		messageId = new MessageId(messageIdByte);
 		width = in.readInt();
 		height = in.readInt();
+		mimeType = in.readString();
+		extension = in.readString();
 		thumbnailWidth = in.readInt();
 		thumbnailHeight = in.readInt();
 		hasError = in.readByte() != 0;
+		instanceId = in.readLong();
 	}
 
 	public MessageId getMessageId() {
@@ -63,6 +77,14 @@ public class AttachmentItem implements Parcelable {
 		return height;
 	}
 
+	String getMimeType() {
+		return mimeType;
+	}
+
+	String getExtension() {
+		return extension;
+	}
+
 	int getThumbnailWidth() {
 		return thumbnailWidth;
 	}
@@ -75,9 +97,8 @@ public class AttachmentItem implements Parcelable {
 		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());
+		return String.valueOf(instanceId);
 	}
 
 	@Override
@@ -90,9 +111,18 @@ public class AttachmentItem implements Parcelable {
 		dest.writeByteArray(messageId.getBytes());
 		dest.writeInt(width);
 		dest.writeInt(height);
+		dest.writeString(mimeType);
+		dest.writeString(extension);
 		dest.writeInt(thumbnailWidth);
 		dest.writeInt(thumbnailHeight);
 		dest.writeByte((byte) (hasError ? 1 : 0));
+		dest.writeLong(instanceId);
+	}
+
+	@Override
+	public boolean equals(@Nullable Object o) {
+		return o instanceof AttachmentItem &&
+				instanceId == ((AttachmentItem) o).instanceId;
 	}
 
 }

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

@@ -1,11 +1,14 @@
 package org.briarproject.briar.android.conversation;
 
+import android.annotation.SuppressLint;
 import android.arch.lifecycle.Observer;
 import android.arch.lifecycle.ViewModelProvider;
 import android.arch.lifecycle.ViewModelProviders;
 import android.content.DialogInterface;
 import android.content.Intent;
+import android.net.Uri;
 import android.os.Bundle;
+import android.os.Parcelable;
 import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
 import android.support.design.widget.Snackbar;
@@ -27,7 +30,6 @@ import android.widget.ImageView;
 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;
@@ -44,14 +46,11 @@ import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.bramble.api.plugin.event.ContactConnectedEvent;
 import org.briarproject.bramble.api.plugin.event.ContactDisconnectedEvent;
-import org.briarproject.bramble.api.settings.Settings;
 import org.briarproject.bramble.api.settings.SettingsManager;
 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.event.MessagesAckedEvent;
 import org.briarproject.bramble.api.sync.event.MessagesSentEvent;
-import org.briarproject.bramble.util.StringUtils;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.activity.BriarActivity;
@@ -62,8 +61,12 @@ import org.briarproject.briar.android.forum.ForumActivity;
 import org.briarproject.briar.android.introduction.IntroductionActivity;
 import org.briarproject.briar.android.privategroup.conversation.GroupActivity;
 import org.briarproject.briar.android.view.BriarRecyclerView;
+import org.briarproject.briar.android.view.ImagePreview;
+import org.briarproject.briar.android.view.TextAttachmentController;
+import org.briarproject.briar.android.view.TextAttachmentController.AttachImageListener;
 import org.briarproject.briar.android.view.TextInputView;
-import org.briarproject.briar.android.view.TextInputView.TextInputListener;
+import org.briarproject.briar.android.view.TextSendController;
+import org.briarproject.briar.android.view.TextSendController.SendListener;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
 import org.briarproject.briar.api.blog.BlogSharingManager;
 import org.briarproject.briar.api.client.ProtocolStateException;
@@ -78,7 +81,6 @@ 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;
 import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 import org.briarproject.briar.api.privategroup.invitation.GroupInvitationManager;
@@ -100,11 +102,12 @@ import im.delight.android.identicons.IdenticonDrawable;
 import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt;
 import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt.PromptStateChangeListener;
 
+import static android.arch.lifecycle.Lifecycle.State.STARTED;
 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.view.Gravity.RIGHT;
 import static android.widget.Toast.LENGTH_SHORT;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.sort;
@@ -114,11 +117,14 @@ import static java.util.logging.Level.WARNING;
 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.bramble.util.StringUtils.isNullOrEmpty;
+import static org.briarproject.briar.android.TestingConstants.FEATURE_FLAG_IMAGE_ATTACHMENTS;
+import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_ATTACH_IMAGE;
 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.ATTACHMENTS;
+import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENT_POSITION;
 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;
 import static org.briarproject.briar.android.util.UiUtils.observeOnce;
@@ -129,15 +135,16 @@ import static uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt.S
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
 public class ConversationActivity extends BriarActivity
-		implements EventListener, ConversationListener, TextInputListener,
+		implements EventListener, ConversationListener, SendListener,
-		TextCache, AttachmentCache {
+		TextCache, AttachmentCache, AttachImageListener {
 
 	public static final String CONTACT_ID = "briar.CONTACT_ID";
 
 	private static final Logger LOG =
 			Logger.getLogger(ConversationActivity.class.getName());
-	private static final String SHOW_ONBOARDING_INTRODUCTION =
+
-			"showOnboardingIntroduction";
+	private static final int TRANSITION_DURATION_MS = 500;
+	private static final int ONBOARDING_DELAY_MS = 250;
 
 	@Inject
 	AndroidNotificationManager notificationManager;
@@ -146,20 +153,8 @@ public class ConversationActivity extends BriarActivity
 	@Inject
 	@CryptoExecutor
 	Executor cryptoExecutor;
-
+	@Inject
-	private final Map<MessageId, String> textCache = new ConcurrentHashMap<>();
+	ViewModelProvider.Factory viewModelFactory;
-	private AttachmentController attachmentController;
-
-	private ConversationViewModel viewModel;
-	private ConversationVisitor visitor;
-	private ConversationAdapter adapter;
-	private Toolbar toolbar;
-	private CircleImageView toolbarAvatar;
-	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
 	@Inject
@@ -182,22 +177,37 @@ public class ConversationActivity extends BriarActivity
 	volatile BlogSharingManager blogSharingManager;
 	@Inject
 	volatile GroupInvitationManager groupInvitationManager;
-	@Inject
-	ViewModelProvider.Factory viewModelFactory;
-
-	private volatile ContactId contactId;
-	@Nullable
-	private volatile GroupId messagingGroupId;
 
+	private final Map<MessageId, String> textCache = new ConcurrentHashMap<>();
 	private final Observer<String> contactNameObserver = name -> {
 		requireNonNull(name);
 		loadMessages();
 	};
 
+	private AttachmentController attachmentController;
+	private ConversationViewModel viewModel;
+	private ConversationVisitor visitor;
+	private ConversationAdapter adapter;
+	private Toolbar toolbar;
+	private CircleImageView toolbarAvatar;
+	private ImageView toolbarStatus;
+	private TextView toolbarTitle;
+	private BriarRecyclerView list;
+	private LinearLayoutManager layoutManager;
+	private TextInputView textInputView;
+	private TextSendController sendController;
+	@Nullable
+	private Parcelable layoutManagerState;
+
+	private volatile ContactId contactId;
+
 	@Override
 	public void onCreate(@Nullable Bundle state) {
 		if (SDK_INT >= 21) {
-			Transition slide = new Slide(END);
+			// Spurious lint warning - using END causes a crash
+			@SuppressLint("RtlHardcoded")
+			Transition slide = new Slide(RIGHT);
+			slide.setDuration(TRANSITION_DURATION_MS);
 			setSceneTransitionAnimation(slide, null, slide);
 		}
 		super.onCreate(state);
@@ -209,7 +219,6 @@ public class ConversationActivity extends BriarActivity
 
 		viewModel = ViewModelProviders.of(this, viewModelFactory)
 				.get(ConversationViewModel.class);
-		viewModel.setContactId(contactId);
 		attachmentController = viewModel.getAttachmentController();
 
 		setContentView(R.layout.activity_conversation);
@@ -233,6 +242,8 @@ public class ConversationActivity extends BriarActivity
 			requireNonNull(deleted);
 			if (deleted) finish();
 		});
+		viewModel.getAddedPrivateMessage().observe(this,
+				this::onAddedPrivateMessage);
 
 		setTransitionName(toolbarAvatar, getAvatarTransitionName(contactId));
 		setTransitionName(toolbarStatus, getBulbTransitionName(contactId));
@@ -247,7 +258,29 @@ public class ConversationActivity extends BriarActivity
 		list.setEmptyText(getString(R.string.no_private_messages));
 
 		textInputView = findViewById(R.id.text_input_container);
-		textInputView.setListener(this);
+		if (FEATURE_FLAG_IMAGE_ATTACHMENTS) {
+			ImagePreview imagePreview = findViewById(R.id.imagePreview);
+			sendController = new TextAttachmentController(textInputView,
+					imagePreview, this, this);
+			observeOnce(viewModel.hasImageSupport(), this, hasSupport -> {
+				if (hasSupport != null && hasSupport) {
+					// remove cast when removing FEATURE_FLAG_IMAGE_ATTACHMENTS
+					((TextAttachmentController) sendController)
+							.setImagesSupported();
+				}
+			});
+		} else {
+			sendController = new TextSendController(textInputView, this, false);
+		}
+		textInputView.setSendController(sendController);
+		textInputView.setMaxTextLength(MAX_PRIVATE_MESSAGE_TEXT_LENGTH);
+		textInputView.setEnabled(false);
+		textInputView.addOnKeyboardShownListener(this::scrollToBottom);
+	}
+
+	private void scrollToBottom() {
+		int items = adapter.getItemCount();
+		if (items > 0) list.scrollToPosition(items - 1);
 	}
 
 	@Override
@@ -256,7 +289,8 @@ public class ConversationActivity extends BriarActivity
 	}
 
 	@Override
-	protected void onActivityResult(int request, int result, Intent data) {
+	protected void onActivityResult(int request, int result,
+			@Nullable Intent data) {
 		super.onActivityResult(request, result, data);
 
 		if (request == REQUEST_INTRODUCTION && result == RESULT_OK) {
@@ -264,6 +298,9 @@ public class ConversationActivity extends BriarActivity
 					Snackbar.LENGTH_SHORT);
 			snackbar.getView().setBackgroundResource(R.color.briar_primary);
 			snackbar.show();
+		} else if (request == REQUEST_ATTACH_IMAGE && result == RESULT_OK) {
+			// remove cast when removing FEATURE_FLAG_IMAGE_ATTACHMENTS
+			((TextAttachmentController) sendController).onImageReceived(data);
 		}
 	}
 
@@ -278,6 +315,16 @@ public class ConversationActivity extends BriarActivity
 		list.startPeriodicUpdate();
 	}
 
+	@Override
+	public void onResume() {
+		super.onResume();
+		// Trigger loading of contact data, noop if data was loaded already.
+		//
+		// We can only start loading data *after* we are sure
+		// the user has signed in. After sign-in, onCreate() isn't run again.
+		if (signedIn()) viewModel.setContactId(contactId);
+	}
+
 	@Override
 	public void onStop() {
 		super.onStop();
@@ -287,16 +334,39 @@ public class ConversationActivity extends BriarActivity
 		list.stopPeriodicUpdate();
 	}
 
+	@Override
+	protected void onSaveInstanceState(Bundle outState) {
+		super.onSaveInstanceState(outState);
+		if (layoutManager != null) {
+			layoutManagerState = layoutManager.onSaveInstanceState();
+			outState.putParcelable("layoutManager", layoutManagerState);
+		}
+	}
+
+	@Override
+	protected void onRestoreInstanceState(Bundle savedInstanceState) {
+		super.onRestoreInstanceState(savedInstanceState);
+		layoutManagerState = savedInstanceState.getParcelable("layoutManager");
+	}
+
 	@Override
 	public boolean onCreateOptionsMenu(Menu menu) {
 		// Inflate the menu items for use in the action bar
 		MenuInflater inflater = getMenuInflater();
 		inflater.inflate(R.menu.conversation_actions, menu);
 
-		enableIntroductionActionIfAvailable(
+		// enable introduction action if available
-				menu.findItem(R.id.action_introduction));
+		observeOnce(viewModel.showIntroductionAction(), this, enable -> {
-		enableAliasActionIfAvailable(
+			if (enable != null && enable) {
-				menu.findItem(R.id.action_set_alias));
+				menu.findItem(R.id.action_introduction).setEnabled(true);
+				// show introduction onboarding, if needed
+				observeOnce(viewModel.showIntroductionOnboarding(), this,
+						this::showIntroductionOnboarding);
+			}
+		});
+		// enable alias action if available
+		observeOnce(viewModel.getContact(), this, contact ->
+				menu.findItem(R.id.action_set_alias).setEnabled(true));
 
 		return super.onCreateOptionsMenu(menu);
 	}
@@ -359,33 +429,10 @@ public class ConversationActivity extends BriarActivity
 						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
+					// its size so we can set the scroll position correctly
 					ConversationMessageHeader latest = sorted.get(0);
 					if (latest instanceof PrivateMessageHeader) {
-						MessageId id = latest.getId();
+						eagerlyLoadMessageSize((PrivateMessageHeader) latest);
-						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);
@@ -397,17 +444,51 @@ public class ConversationActivity extends BriarActivity
 		});
 	}
 
+	private void eagerlyLoadMessageSize(PrivateMessageHeader h)
+			throws DbException {
+		MessageId id = h.getId();
+		// If the message has text, load it
+		if (h.hasText()) {
+			String text = textCache.get(id);
+			if (text == null) {
+				LOG.info("Eagerly loading text for latest message");
+				text = messagingManager.getMessageText(id);
+				textCache.put(id, text);
+			}
+		}
+		// If the message has a single image, load its size - for multiple
+		// images we use a grid so the size is fixed
+		if (h.getAttachmentHeaders().size() == 1) {
+			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);
+			}
+		}
+	}
+
 	private void displayMessages(int revision,
 			Collection<ConversationMessageHeader> headers) {
 		runOnUiThreadUnlessDestroyed(() -> {
 			if (revision == adapter.getRevision()) {
 				adapter.incrementRevision();
-				textInputView.setSendButtonEnabled(true);
+				textInputView.setEnabled(true);
+				// start observing onboarding after enabling (only once, because
+				// we only update this when an onboarding should be shown)
+				observeOnce(viewModel.showImageOnboarding(), this,
+						this::showImageOnboarding);
 				List<ConversationItem> items = createItems(headers);
 				adapter.addAll(items);
 				list.showData();
-				// Scroll to the bottom
+				if (layoutManagerState == null) {
-				list.scrollToPosition(adapter.getItemCount() - 1);
+					scrollToBottom();
+				} else {
+					// Restore the previous scroll position
+					layoutManager.onRestoreInstanceState(layoutManagerState);
+				}
 			} else {
 				LOG.info("Concurrent update, reloading");
 				loadMessages();
@@ -448,21 +529,28 @@ public class ConversationActivity extends BriarActivity
 			Pair<Integer, ConversationMessageItem> pair =
 					adapter.getMessageItem(m);
 			if (pair != null) {
+				boolean scroll = shouldScrollWhenUpdatingMessage();
 				pair.getSecond().setText(text);
-				boolean bottom = adapter.isScrolledToBottom(layoutManager);
 				adapter.notifyItemChanged(pair.getFirst());
-				if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
+				if (scroll) scrollToBottom();
 			}
 		});
 	}
 
+	// When a message's text or attachments are loaded, scroll to the bottom
+	// if the conversation is visible and we were previously at the bottom
+	private boolean shouldScrollWhenUpdatingMessage() {
+		return getLifecycle().getCurrentState().isAtLeast(STARTED)
+				&& adapter.isScrolledToBottom(layoutManager);
+	}
+
 	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
+				// TODO move getting the items off to IoExecutor, if size == 1
 				List<AttachmentItem> items =
 						attachmentController.getAttachmentItems(attachments);
 				displayMessageAttachments(messageId, items);
@@ -479,10 +567,10 @@ public class ConversationActivity extends BriarActivity
 			Pair<Integer, ConversationMessageItem> pair =
 					adapter.getMessageItem(m);
 			if (pair != null) {
+				boolean scroll = shouldScrollWhenUpdatingMessage();
 				pair.getSecond().setAttachments(items);
-				boolean bottom = adapter.isScrolledToBottom(layoutManager);
 				adapter.notifyItemChanged(pair.getFirst());
-				if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
+				if (scroll) scrollToBottom();
 			}
 		});
 	}
@@ -531,10 +619,13 @@ public class ConversationActivity extends BriarActivity
 
 	private void addConversationItem(ConversationItem item) {
 		runOnUiThreadUnlessDestroyed(() -> {
-			boolean bottom = adapter.isScrolledToBottom(layoutManager);
 			adapter.incrementRevision();
 			adapter.add(item);
-			if (bottom) list.scrollToPosition(adapter.getItemCount() - 1);
+			// When adding a new message, scroll to the bottom if the
+			// conversation is visible, even if we're not currently at
+			// the bottom
+			if (getLifecycle().getCurrentState().isAtLeast(STARTED))
+				scrollToBottom();
 		});
 	}
 
@@ -570,14 +661,18 @@ public class ConversationActivity extends BriarActivity
 	}
 
 	@Override
-	public void onSendClick(String text) {
+	public void onAttachImage(Intent intent) {
-		if (text.isEmpty()) return;
+		startActivityForResult(intent, REQUEST_ATTACH_IMAGE);
-		text = StringUtils.truncateUtf8(text, MAX_PRIVATE_MESSAGE_TEXT_LENGTH);
+	}
+
+	@Override
+	public void onSendClick(@Nullable String text, List<Uri> imageUris) {
+		if (isNullOrEmpty(text) && imageUris.isEmpty())
+			throw new AssertionError();
 		long timestamp = System.currentTimeMillis();
 		timestamp = Math.max(timestamp, getMinTimestampForNewMessage());
-		if (messagingGroupId == null) loadGroupId(text, timestamp);
+		viewModel.sendMessage(text, imageUris, timestamp);
-		else createMessage(text, timestamp);
+		textInputView.clearText();
-		textInputView.setText("");
 	}
 
 	private long getMinTimestampForNewMessage() {
@@ -586,48 +681,10 @@ public class ConversationActivity extends BriarActivity
 		return item == null ? 0 : item.getTime() + 1;
 	}
 
-	private void loadGroupId(String text, long timestamp) {
+	private void onAddedPrivateMessage(@Nullable PrivateMessageHeader h) {
-		runOnDbThread(() -> {
+		if (h == null) return;
-			try {
+		addConversationItem(h.accept(visitor));
-				messagingGroupId =
+		viewModel.onAddedPrivateMessageSeen();
-						messagingManager.getConversationId(contactId);
-				createMessage(text, timestamp);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-			}
-
-		});
-	}
-
-	private void createMessage(String text, long timestamp) {
-		cryptoExecutor.execute(() -> {
-			try {
-				//noinspection ConstantConditions init in loadGroupId()
-				storeMessage(privateMessageFactory.createPrivateMessage(
-						messagingGroupId, timestamp, text, emptyList()), text);
-			} catch (FormatException e) {
-				throw new RuntimeException(e);
-			}
-		});
-	}
-
-	private void storeMessage(PrivateMessage m, String text) {
-		runOnDbThread(() -> {
-			try {
-				long start = now();
-				messagingManager.addLocalMessage(m);
-				logDuration(LOG, "Storing message", start);
-				Message message = m.getMessage();
-				PrivateMessageHeader h = new PrivateMessageHeader(
-						message.getId(), message.getGroupId(),
-						message.getTimestamp(), true, false, false, false,
-						true, emptyList());
-				textCache.put(message.getId(), text);
-				addConversationItem(h.accept(visitor));
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-			}
-		});
 	}
 
 	private void askToRemoveContact() {
@@ -664,74 +721,70 @@ public class ConversationActivity extends BriarActivity
 		});
 	}
 
-	private void enableIntroductionActionIfAvailable(MenuItem item) {
+	private void showImageOnboarding(@Nullable Boolean show) {
-		runOnDbThread(() -> {
+		if (show == null || !show) return;
-			try {
+		if (SDK_INT >= 21) {
-				if (contactManager.getActiveContacts().size() > 1) {
+			// show onboarding only after the enter transition has ended
-					enableIntroductionAction(item);
+			// otherwise the tap target animation won't play
-					Settings settings =
+			textInputView.postDelayed(this::showImageOnboarding,
-							settingsManager.getSettings(SETTINGS_NAMESPACE);
+					TRANSITION_DURATION_MS + ONBOARDING_DELAY_MS);
-					if (settings.getBoolean(SHOW_ONBOARDING_INTRODUCTION,
+		} else {
-							true)) {
+			showImageOnboarding();
-						showIntroductionOnboarding();
+		}
-					}
-				}
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
-			}
-		});
 	}
 
-	private void enableAliasActionIfAvailable(MenuItem item) {
+	private void showImageOnboarding() {
-		observeOnce(viewModel.getContact(), this, c -> item.setEnabled(true));
+		// remove cast when removing FEATURE_FLAG_IMAGE_ATTACHMENTS
+		((TextAttachmentController) sendController)
+				.showImageOnboarding(this, () ->
+						viewModel.onImageOnboardingSeen());
 	}
 
-	private void enableIntroductionAction(MenuItem item) {
+	private void showIntroductionOnboarding(@Nullable Boolean show) {
-		runOnUiThreadUnlessDestroyed(() -> item.setEnabled(true));
+		if (show == null || !show) return;
+		if (SDK_INT >= 21) {
+			// show onboarding only after the enter transition has ended
+			// otherwise the tap target animation won't play
+			textInputView.postDelayed(this::showIntroductionOnboarding,
+					TRANSITION_DURATION_MS + ONBOARDING_DELAY_MS);
+		} else {
+			showIntroductionOnboarding();
+		}
 	}
 
 	private void showIntroductionOnboarding() {
-		runOnUiThreadUnlessDestroyed(() -> {
+		// find view of overflow icon
-			// find view of overflow icon
+		View target = null;
-			View target = null;
+		for (int i = 0; i < toolbar.getChildCount(); i++) {
-			for (int i = 0; i < toolbar.getChildCount(); i++) {
+			if (toolbar.getChildAt(i) instanceof ActionMenuView) {
-				if (toolbar.getChildAt(i) instanceof ActionMenuView) {
+				ActionMenuView menu = (ActionMenuView) toolbar.getChildAt(i);
-					ActionMenuView menu =
+				// The overflow icon should be the last child of the menu
-							(ActionMenuView) toolbar.getChildAt(i);
+				target = menu.getChildAt(menu.getChildCount() - 1);
-					target = menu.getChildAt(menu.getChildCount() - 1);
+				// If the menu hasn't been populated yet, use the menu itself
-					break;
+				// as the target
-				}
+				if (target == null) target = menu;
-			}
+				break;
-			if (target == null) {
-				LOG.warning("No Overflow Icon found!");
-				return;
 			}
+		}
+		if (target == null) {
+			LOG.warning("No Overflow Icon found!");
+			return;
+		}
 
-			PromptStateChangeListener listener = (prompt, state) -> {
+		PromptStateChangeListener listener = (prompt, state) -> {
-				if (state == STATE_DISMISSED || state == STATE_FINISHED) {
+			if (state == STATE_DISMISSED || state == STATE_FINISHED) {
-					introductionOnboardingSeen();
+				viewModel.onIntroductionOnboardingSeen();
-				}
-			};
-			new MaterialTapTargetPrompt.Builder(ConversationActivity.this,
-					R.style.OnboardingDialogTheme).setTarget(target)
-					.setPrimaryText(R.string.introduction_onboarding_title)
-					.setSecondaryText(R.string.introduction_onboarding_text)
-					.setIcon(R.drawable.ic_more_vert_accent)
-					.setPromptStateChangeListener(listener)
-					.show();
-		});
-	}
-
-	private void introductionOnboardingSeen() {
-		runOnDbThread(() -> {
-			try {
-				Settings settings = new Settings();
-				settings.putBoolean(SHOW_ONBOARDING_INTRODUCTION, false);
-				settingsManager.mergeSettings(settings, SETTINGS_NAMESPACE);
-			} catch (DbException e) {
-				logException(LOG, WARNING, e);
 			}
-		});
+		};
+		new MaterialTapTargetPrompt.Builder(ConversationActivity.this,
+				R.style.OnboardingDialogTheme).setTarget(target)
+				.setPrimaryText(R.string.introduction_onboarding_title)
+				.setSecondaryText(R.string.introduction_onboarding_text)
+				.setIcon(R.drawable.ic_more_vert_accent)
+				.setBackgroundColour(
+						ContextCompat.getColor(this, R.color.briar_primary))
+				.setPromptStateChangeListener(listener)
+				.show();
 	}
 
 	@Override
@@ -825,19 +878,18 @@ public class ConversationActivity extends BriarActivity
 		} else {
 			name = getString(R.string.you);
 		}
+		ArrayList<AttachmentItem> attachments =
+				new ArrayList<>(messageItem.getAttachments());
 		Intent i = new Intent(this, ImageActivity.class);
-		i.putExtra(ATTACHMENT, item);
+		i.putParcelableArrayListExtra(ATTACHMENTS, attachments);
+		i.putExtra(ATTACHMENT_POSITION, attachments.indexOf(item));
 		i.putExtra(NAME, name);
 		i.putExtra(DATE, messageItem.getTime());
-		if (SDK_INT >= 23) {
+		// restoring list position should not trigger android bug #224270
-			String transitionName = item.getTransitionName();
+		String transitionName = item.getTransitionName();
-			ActivityOptionsCompat options =
+		ActivityOptionsCompat options =
-					makeSceneTransitionAnimation(this, view, transitionName);
+				makeSceneTransitionAnimation(this, view, transitionName);
-			ActivityCompat.startActivity(this, i, options.toBundle());
+		ActivityCompat.startActivity(this, i, options.toBundle());
-		} else {
-			// work-around for android bug #224270
-			startActivity(i);
-		}
 	}
 
 	@DatabaseExecutor

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

@@ -3,6 +3,7 @@ package org.briarproject.briar.android.conversation;
 import android.content.Context;
 import android.support.annotation.LayoutRes;
 import android.support.v7.widget.LinearLayoutManager;
+import android.support.v7.widget.RecyclerView.RecycledViewPool;
 import android.util.SparseArray;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -21,11 +22,17 @@ class ConversationAdapter
 		extends BriarAdapter<ConversationItem, ConversationItemViewHolder> {
 
 	private ConversationListener listener;
+	private final RecycledViewPool imageViewPool;
+	private final ImageItemDecoration imageItemDecoration;
 
 	ConversationAdapter(Context ctx,
 			ConversationListener conversationListener) {
 		super(ctx, ConversationItem.class);
 		listener = conversationListener;
+		// This shares the same pool for view recycling between all image lists
+		imageViewPool = new RecycledViewPool();
+		// Share the item decoration as well
+		imageItemDecoration = new ImageItemDecoration(ctx);
 	}
 
 	@LayoutRes
@@ -42,15 +49,17 @@ class ConversationAdapter
 				type, viewGroup, false);
 		switch (type) {
 			case R.layout.list_item_conversation_msg_in:
-				return new ConversationMessageViewHolder(v, true);
+				return new ConversationMessageViewHolder(v, listener, true,
+						imageViewPool, imageItemDecoration);
 			case R.layout.list_item_conversation_msg_out:
-				return new ConversationMessageViewHolder(v, false);
+				return new ConversationMessageViewHolder(v, listener, false,
+						imageViewPool, imageItemDecoration);
 			case R.layout.list_item_conversation_notice_in:
-				return new ConversationNoticeViewHolder(v, true);
+				return new ConversationNoticeViewHolder(v, listener, true);
 			case R.layout.list_item_conversation_notice_out:
-				return new ConversationNoticeViewHolder(v, false);
+				return new ConversationNoticeViewHolder(v, listener, false);
 			case R.layout.list_item_conversation_request:
-				return new ConversationRequestViewHolder(v, true);
+				return new ConversationRequestViewHolder(v, listener, true);
 			default:
 				throw new IllegalArgumentException("Unknown ConversationItem");
 		}
@@ -59,7 +68,7 @@ class ConversationAdapter
 	@Override
 	public void onBindViewHolder(ConversationItemViewHolder ui, int position) {
 		ConversationItem item = items.get(position);
-		ui.bind(item, listener);
+		ui.bind(item);
 		listener.onItemVisible(item);
 	}
 

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

@@ -18,14 +18,17 @@ import static org.briarproject.briar.android.util.UiUtils.formatDate;
 @NotNullByDefault
 abstract class ConversationItemViewHolder extends ViewHolder {
 
+	protected final ConversationListener listener;
 	protected final ConstraintLayout layout;
 	@Nullable
 	private final OutItemViewHolder outViewHolder;
 	private final TextView text;
 	protected final TextView time;
 
-	ConversationItemViewHolder(View v, boolean isIncoming) {
+	ConversationItemViewHolder(View v, ConversationListener listener,
+			boolean isIncoming) {
 		super(v);
+		this.listener = listener;
 		this.outViewHolder = isIncoming ? null : new OutItemViewHolder(v);
 		layout = v.findViewById(R.id.layout);
 		text = v.findViewById(R.id.text);
@@ -33,7 +36,7 @@ abstract class ConversationItemViewHolder extends ViewHolder {
 	}
 
 	@CallSuper
-	void bind(ConversationItem item, ConversationListener listener) {
+	void bind(ConversationItem item) {
 		if (item.getText() != null) {
 			text.setText(trim(item.getText()));
 		}

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

@@ -1,63 +1,45 @@
 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.support.v7.widget.RecyclerView;
+import android.support.v7.widget.RecyclerView.RecycledViewPool;
 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.constraint.ConstraintSet.WRAP_CONTENT;
-import static android.support.v4.view.ViewCompat.LAYOUT_DIRECTION_RTL;
+import static android.support.v4.content.ContextCompat.getColor;
-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 {
 
-	@DrawableRes
+	private final ImageAdapter adapter;
-	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) {
+	ConversationMessageViewHolder(View v, ConversationListener listener,
-		super(v, isIncoming);
+			boolean isIncoming, RecycledViewPool imageViewPool,
-		imageView = v.findViewById(R.id.imageView);
+			ImageItemDecoration imageItemDecoration) {
+		super(v, listener, isIncoming);
 		statusLayout = v.findViewById(R.id.statusLayout);
-		radiusBig = v.getContext().getResources()
+
-				.getDimensionPixelSize(R.dimen.message_bubble_radius_big);
+		// image list
-		radiusSmall = v.getContext().getResources()
+		RecyclerView list = v.findViewById(R.id.imageList);
-				.getDimensionPixelSize(R.dimen.message_bubble_radius_small);
+		list.setRecycledViewPool(imageViewPool);
+		adapter = new ImageAdapter(v.getContext(), listener);
+		list.setAdapter(adapter);
+		list.addItemDecoration(imageItemDecoration);
 
 		// remember original status text color
 		timeColor = time.getCurrentTextColor();
-		timeColorBubble =
+		timeColorBubble = getColor(v.getContext(), R.color.briar_white);
-				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
@@ -77,85 +59,55 @@ class ConversationMessageViewHolder extends ConversationItemViewHolder {
 	}
 
 	@Override
-	void bind(ConversationItem conversationItem,
+	void bind(ConversationItem conversationItem) {
-			ConversationListener listener) {
+		super.bind(conversationItem);
-		super.bind(conversationItem, listener);
 		ConversationMessageItem item =
 				(ConversationMessageItem) conversationItem;
 		if (item.getAttachments().isEmpty()) {
 			bindTextItem();
 		} else {
-			bindImageItem(item, listener);
+			bindImageItem(item);
 		}
 	}
 
 	private void bindTextItem() {
-		clearImage();
+		resetStatusLayoutForText();
+		textConstraints.applyTo(layout);
+		adapter.clear();
+	}
+
+	private void bindImageItem(ConversationMessageItem item) {
+		ConstraintSet constraintSet;
+		if (item.getText() == null) {
+			statusLayout.setBackgroundResource(R.drawable.msg_status_bubble);
+			time.setTextColor(timeColorBubble);
+			constraintSet = imageConstraints;
+		} else {
+			resetStatusLayoutForText();
+			constraintSet = imageTextConstraints;
+		}
+
+		if (item.getAttachments().size() == 1) {
+			// apply image size constraints for a single image
+			AttachmentItem attachment = item.getAttachments().get(0);
+			int width = attachment.getThumbnailWidth();
+			int height = attachment.getThumbnailHeight();
+			constraintSet.constrainWidth(R.id.imageList, width);
+			constraintSet.constrainHeight(R.id.imageList, height);
+		} else {
+			// bubble adapts to size of image list
+			constraintSet.constrainWidth(R.id.imageList, WRAP_CONTENT);
+			constraintSet.constrainHeight(R.id.imageList, WRAP_CONTENT);
+		}
+		constraintSet.applyTo(layout);
+		adapter.setConversationItem(item);
+	}
+
+	private void resetStatusLayoutForText() {
 		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/ConversationNoticeViewHolder.java

@@ -19,16 +19,17 @@ class ConversationNoticeViewHolder extends ConversationItemViewHolder {
 
 	private final TextView msgText;
 
-	ConversationNoticeViewHolder(View v, boolean isIncoming) {
+	ConversationNoticeViewHolder(View v, ConversationListener listener,
-		super(v, isIncoming);
+			boolean isIncoming) {
+		super(v, listener, isIncoming);
 		msgText = v.findViewById(R.id.msgText);
 	}
 
 	@Override
 	@CallSuper
-	void bind(ConversationItem item, ConversationListener listener) {
+	void bind(ConversationItem item) {
 		ConversationNoticeItem notice = (ConversationNoticeItem) item;
-		super.bind(notice, listener);
+		super.bind(notice);
 
 		String text = notice.getMsgText();
 		if (isNullOrEmpty(text)) {

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

@@ -17,16 +17,17 @@ class ConversationRequestViewHolder extends ConversationNoticeViewHolder {
 	private final Button acceptButton;
 	private final Button declineButton;
 
-	ConversationRequestViewHolder(View v, boolean isIncoming) {
+	ConversationRequestViewHolder(View v, ConversationListener listener,
-		super(v, isIncoming);
+			boolean isIncoming) {
+		super(v, listener, isIncoming);
 		acceptButton = v.findViewById(R.id.acceptButton);
 		declineButton = v.findViewById(R.id.declineButton);
 	}
 
 	@Override
-	void bind(ConversationItem item, ConversationListener listener) {
+	void bind(ConversationItem item) {
 		ConversationRequestItem request = (ConversationRequestItem) item;
-		super.bind(request, listener);
+		super.bind(request);
 
 		if (request.wasAnswered() && request.canBeOpened()) {
 			acceptButton.setVisibility(VISIBLE);

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

@@ -5,19 +5,40 @@ import android.arch.lifecycle.AndroidViewModel;
 import android.arch.lifecycle.LiveData;
 import android.arch.lifecycle.MutableLiveData;
 import android.arch.lifecycle.Transformations;
+import android.content.ContentResolver;
+import android.net.Uri;
 import android.support.annotation.Nullable;
+import android.support.annotation.UiThread;
 
+import org.briarproject.bramble.api.FormatException;
+import org.briarproject.bramble.api.Pair;
 import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
+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.db.DbException;
 import org.briarproject.bramble.api.db.NoSuchContactException;
 import org.briarproject.bramble.api.identity.AuthorId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.settings.Settings;
+import org.briarproject.bramble.api.settings.SettingsManager;
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.briar.android.util.UiUtils;
+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;
+import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
 import java.util.concurrent.Executor;
 import java.util.logging.Logger;
 
@@ -26,19 +47,34 @@ import javax.inject.Inject;
 import static java.util.Objects.requireNonNull;
 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;
+import static org.briarproject.briar.android.conversation.AttachmentDimensions.getAttachmentDimensions;
+import static org.briarproject.briar.android.settings.SettingsFragment.SETTINGS_NAMESPACE;
+import static org.briarproject.briar.android.util.UiUtils.observeForeverOnce;
 
 @NotNullByDefault
 public class ConversationViewModel extends AndroidViewModel {
 
 	private static Logger LOG =
 			getLogger(ConversationViewModel.class.getName());
+	private static final String SHOW_ONBOARDING_IMAGE =
+			"showOnboardingImage";
+	private static final String SHOW_ONBOARDING_INTRODUCTION =
+			"showOnboardingIntroduction";
 
 	@DatabaseExecutor
 	private final Executor dbExecutor;
+	@CryptoExecutor
+	private final Executor cryptoExecutor;
+	// TODO replace with TransactionManager once it exists
+	private final DatabaseComponent db;
+	private final MessagingManager messagingManager;
 	private final ContactManager contactManager;
+	private final SettingsManager settingsManager;
+	private final PrivateMessageFactory privateMessageFactory;
 	private final AttachmentController attachmentController;
 
 	@Nullable
@@ -48,38 +84,64 @@ public class ConversationViewModel extends AndroidViewModel {
 			Transformations.map(contact, c -> c.getAuthor().getId());
 	private final LiveData<String> contactName =
 			Transformations.map(contact, UiUtils::getContactDisplayName);
+	private final MutableLiveData<Boolean> imageSupport =
+			new MutableLiveData<>();
+	private final MutableLiveData<Boolean> showImageOnboarding =
+			new MutableLiveData<>();
+	private final MutableLiveData<Boolean> showIntroductionOnboarding =
+			new MutableLiveData<>();
+	private final MutableLiveData<Boolean> showIntroductionAction =
+			new MutableLiveData<>();
 	private final MutableLiveData<Boolean> contactDeleted =
 			new MutableLiveData<>();
+	private final MutableLiveData<GroupId> messagingGroupId =
+			new MutableLiveData<>();
+	private final MutableLiveData<PrivateMessageHeader> addedHeader =
+			new MutableLiveData<>();
 
 	@Inject
 	ConversationViewModel(Application application,
 			@DatabaseExecutor Executor dbExecutor,
-			ContactManager contactManager, MessagingManager messagingManager) {
+			@CryptoExecutor Executor cryptoExecutor, DatabaseComponent db,
+			MessagingManager messagingManager, ContactManager contactManager,
+			SettingsManager settingsManager,
+			PrivateMessageFactory privateMessageFactory) {
 		super(application);
 		this.dbExecutor = dbExecutor;
+		this.cryptoExecutor = cryptoExecutor;
+		this.db = db;
+		this.messagingManager = messagingManager;
 		this.contactManager = contactManager;
+		this.settingsManager = settingsManager;
+		this.privateMessageFactory = privateMessageFactory;
 		this.attachmentController = new AttachmentController(messagingManager,
-				application.getResources());
+				getAttachmentDimensions(application.getResources()));
 		contactDeleted.setValue(false);
 	}
 
+	/**
+	 * Setting the {@link ContactId} automatically triggers loading of other
+	 * data.
+	 */
 	void setContactId(ContactId contactId) {
 		if (this.contactId == null) {
 			this.contactId = contactId;
-			loadContact();
+			loadContact(contactId);
 		} else if (!contactId.equals(this.contactId)) {
 			throw new IllegalStateException();
 		}
 	}
 
-	private void loadContact() {
+	private void loadContact(ContactId contactId) {
 		dbExecutor.execute(() -> {
 			try {
 				long start = now();
-				Contact c =
+				Contact c = contactManager.getContact(contactId);
-						contactManager.getContact(requireNonNull(contactId));
 				contact.postValue(c);
 				logDuration(LOG, "Loading contact", start);
+				start = now();
+				checkFeaturesAndOnboarding(contactId);
+				logDuration(LOG, "Checking for image support", start);
 			} catch (NoSuchContactException e) {
 				contactDeleted.postValue(true);
 			} catch (DbException e) {
@@ -93,13 +155,179 @@ public class ConversationViewModel extends AndroidViewModel {
 			try {
 				contactManager.setContactAlias(requireNonNull(contactId),
 						alias.isEmpty() ? null : alias);
-				loadContact();
+				loadContact(contactId);
 			} catch (DbException e) {
 				logException(LOG, WARNING, e);
 			}
 		});
 	}
 
+	void sendMessage(@Nullable String text, List<Uri> uris, long timestamp) {
+		if (messagingGroupId.getValue() == null) loadGroupId();
+		observeForeverOnce(messagingGroupId, groupId -> {
+			if (groupId == null) return;
+			// calls through to creating and storing the message
+			storeAttachments(groupId, text, uris, timestamp);
+		});
+	}
+
+	private void loadGroupId() {
+		if (contactId == null) throw new IllegalStateException();
+		dbExecutor.execute(() -> {
+			try {
+				messagingGroupId.postValue(
+						messagingManager.getConversationId(contactId));
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
+
+	@DatabaseExecutor
+	private void checkFeaturesAndOnboarding(ContactId c) throws DbException {
+		// check if images are supported
+		boolean imagesSupported = db.transactionWithResult(true, txn ->
+				messagingManager.contactSupportsImages(txn, c));
+		imageSupport.postValue(imagesSupported);
+
+		// check if introductions are supported
+		Collection<Contact> contacts = contactManager.getActiveContacts();
+		boolean introductionSupported = contacts.size() > 1;
+		showIntroductionAction.postValue(introductionSupported);
+
+		Settings settings = settingsManager.getSettings(SETTINGS_NAMESPACE);
+		if (imagesSupported &&
+				settings.getBoolean(SHOW_ONBOARDING_IMAGE, true)) {
+			// check if we should show onboarding, only if images are supported
+			showImageOnboarding.postValue(true);
+			// allow observer to stop listening for changes
+			showIntroductionOnboarding.postValue(false);
+		} else {
+			// allow observer to stop listening for changes
+			showImageOnboarding.postValue(false);
+			// we only show one onboarding dialog at a time
+			if (introductionSupported &&
+					settings.getBoolean(SHOW_ONBOARDING_INTRODUCTION, true)) {
+				showIntroductionOnboarding.postValue(true);
+			} else {
+				// allow observer to stop listening for changes
+				showIntroductionOnboarding.postValue(false);
+			}
+		}
+	}
+
+	void onImageOnboardingSeen() {
+		onOnboardingSeen(SHOW_ONBOARDING_IMAGE);
+	}
+
+	void onIntroductionOnboardingSeen() {
+		onOnboardingSeen(SHOW_ONBOARDING_INTRODUCTION);
+	}
+
+	private void onOnboardingSeen(String key) {
+		dbExecutor.execute(() -> {
+			try {
+				Settings settings = new Settings();
+				settings.putBoolean(key, false);
+				settingsManager.mergeSettings(settings, SETTINGS_NAMESPACE);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
+
+	private void storeAttachments(GroupId groupId, @Nullable String text,
+			List<Uri> uris, long timestamp) {
+		dbExecutor.execute(() -> {
+			long start = now();
+			List<AttachmentHeader> attachments = new ArrayList<>();
+			List<AttachmentItem> items = new ArrayList<>();
+			boolean needsSize = uris.size() == 1;
+			for (Uri uri : uris) {
+				Pair<AttachmentHeader, AttachmentItem> pair =
+						createAttachmentHeader(groupId, uri, timestamp,
+								needsSize);
+				if (pair == null) continue;
+				attachments.add(pair.getFirst());
+				items.add(pair.getSecond());
+			}
+			logDuration(LOG, "Storing attachments", start);
+			createMessage(groupId, text, attachments, items, timestamp);
+		});
+	}
+
+	@Nullable
+	@DatabaseExecutor
+	private Pair<AttachmentHeader, AttachmentItem> createAttachmentHeader(
+			GroupId groupId, Uri uri, long timestamp, boolean needsSize) {
+		InputStream is = null;
+		try {
+			ContentResolver contentResolver =
+					getApplication().getContentResolver();
+			is = contentResolver.openInputStream(uri);
+			if (is == null) throw new IOException();
+			String contentType = contentResolver.getType(uri);
+			if (contentType == null) throw new IOException("null content type");
+			AttachmentHeader h = messagingManager
+					.addLocalAttachment(groupId, timestamp, contentType, is);
+			is.close();
+			// re-open stream to get AttachmentItem
+			is = contentResolver.openInputStream(uri);
+			if (is == null) throw new IOException();
+			AttachmentItem item = attachmentController
+					.getAttachmentItem(h, new Attachment(is), needsSize);
+			return new Pair<>(h, item);
+		} catch (DbException | IOException e) {
+			logException(LOG, WARNING, e);
+			return null;
+		} finally {
+			if (is != null) tryToClose(is, LOG, WARNING);
+		}
+	}
+
+	private void createMessage(GroupId groupId, @Nullable String text,
+			List<AttachmentHeader> attachments, List<AttachmentItem> aItems,
+			long timestamp) {
+		cryptoExecutor.execute(() -> {
+			try {
+				// TODO remove when text can be null in the backend
+				String msgText = text == null ? "null" : text;
+				PrivateMessage pm = privateMessageFactory
+						.createPrivateMessage(groupId, timestamp, msgText,
+								attachments);
+				attachmentController.put(pm.getMessage().getId(), aItems);
+				storeMessage(pm, msgText, attachments);
+			} catch (FormatException e) {
+				throw new RuntimeException(e);
+			}
+		});
+	}
+
+	private void storeMessage(PrivateMessage m, @Nullable String text,
+			List<AttachmentHeader> attachments) {
+		dbExecutor.execute(() -> {
+			try {
+				long start = now();
+				messagingManager.addLocalMessage(m);
+				logDuration(LOG, "Storing message", start);
+				Message message = m.getMessage();
+				PrivateMessageHeader h = new PrivateMessageHeader(
+						message.getId(), message.getGroupId(),
+						message.getTimestamp(), true, true, false, false,
+						text != null, attachments);
+				// TODO add text to cache when available here
+				addedHeader.postValue(h);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+			}
+		});
+	}
+
+	@UiThread
+	void onAddedPrivateMessageSeen() {
+		addedHeader.setValue(null);
+	}
+
 	AttachmentController getAttachmentController() {
 		return attachmentController;
 	}
@@ -116,8 +344,28 @@ public class ConversationViewModel extends AndroidViewModel {
 		return contactName;
 	}
 
+	LiveData<Boolean> hasImageSupport() {
+		return imageSupport;
+	}
+
+	LiveData<Boolean> showImageOnboarding() {
+		return showImageOnboarding;
+	}
+
+	LiveData<Boolean> showIntroductionOnboarding() {
+		return showIntroductionOnboarding;
+	}
+
+	LiveData<Boolean> showIntroductionAction() {
+		return showIntroductionAction;
+	}
+
 	LiveData<Boolean> isContactDeleted() {
 		return contactDeleted;
 	}
 
+	LiveData<PrivateMessageHeader> getAddedPrivateMessage() {
+		return addedHeader;
+	}
+
 }

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

@@ -1,54 +1,80 @@
 package org.briarproject.briar.android.conversation;
 
-import android.graphics.drawable.Animatable;
+import android.arch.lifecycle.ViewModelProvider;
+import android.arch.lifecycle.ViewModelProviders;
+import android.content.DialogInterface.OnClickListener;
+import android.content.Intent;
 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.design.widget.Snackbar;
+import android.support.v4.app.Fragment;
+import android.support.v4.app.FragmentManager;
+import android.support.v4.app.FragmentStatePagerAdapter;
+import android.support.v4.content.ContextCompat;
+import android.support.v4.graphics.drawable.DrawableCompat;
+import android.support.v4.view.ViewPager;
+import android.support.v7.app.AlertDialog.Builder;
 import android.support.v7.widget.Toolbar;
 import android.transition.Fade;
 import android.transition.Transition;
+import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
+import android.view.ViewTreeObserver.OnGlobalLayoutListener;
 import android.view.Window;
 import android.widget.TextView;
 
-import com.bumptech.glide.load.DataSource;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
-import com.bumptech.glide.load.engine.GlideException;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-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 java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.List;
+import java.util.Locale;
+
+import javax.inject.Inject;
+
+import static android.content.Intent.ACTION_CREATE_DOCUMENT;
+import static android.content.Intent.CATEGORY_OPENABLE;
+import static android.content.Intent.EXTRA_TITLE;
 import static android.graphics.Color.TRANSPARENT;
 import static android.os.Build.VERSION.SDK_INT;
+import static android.support.design.widget.Snackbar.LENGTH_LONG;
 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.activity.RequestCodes.REQUEST_SAVE_ATTACHMENT;
 import static org.briarproject.briar.android.util.UiUtils.formatDateAbsolute;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class ImageActivity extends BriarActivity
-		implements PullDownLayout.Callback {
+		implements PullDownLayout.Callback, OnGlobalLayoutListener {
 
-	final static String ATTACHMENT = "attachment";
+	final static String ATTACHMENTS = "attachments";
+	final static String ATTACHMENT_POSITION = "position";
 	final static String NAME = "name";
 	final static String DATE = "date";
 
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private ImageViewModel viewModel;
 	private PullDownLayout layout;
 	private AppBarLayout appBarLayout;
-	private PhotoView photoView;
+	private ViewPager viewPager;
+	private List<AttachmentItem> attachments;
 
 	@Override
 	public void injectActivity(ActivityComponent component) {
@@ -60,18 +86,23 @@ public class ImageActivity extends BriarActivity
 		super.onCreate(state);
 
 		// Transitions
-		supportPostponeEnterTransition();
+		if (state == null) supportPostponeEnterTransition();
 		Window window = getWindow();
 		if (SDK_INT >= 21) {
 			Transition transition = new Fade();
 			setSceneTransitionAnimation(transition, null, transition);
 		}
 
+		// get View Model
+		viewModel = ViewModelProviders.of(this, viewModelFactory)
+				.get(ImageViewModel.class);
+		viewModel.getSaveState().observe(this, this::onImageSaveStateChanged);
+
 		// inflate layout
 		setContentView(R.layout.activity_image);
 		layout = findViewById(R.id.layout);
-		layout.getBackground().setAlpha(255);
 		layout.setCallback(this);
+		layout.getViewTreeObserver().addOnGlobalLayoutListener(this);
 
 		// Status Bar
 		if (SDK_INT >= 21) {
@@ -88,59 +119,35 @@ public class ImageActivity extends BriarActivity
 		TextView dateView = toolbar.findViewById(R.id.dateView);
 
 		// Intent Extras
-		AttachmentItem attachment = getIntent().getParcelableExtra(ATTACHMENT);
+		Intent i = getIntent();
-		String name = getIntent().getStringExtra(NAME);
+		attachments = i.getParcelableArrayListExtra(ATTACHMENTS);
-		long time = getIntent().getLongExtra(DATE, 0);
+		int position = i.getIntExtra(ATTACHMENT_POSITION, -1);
+		if (position == -1) throw new IllegalStateException();
+		String name = i.getStringExtra(NAME);
+		long time = i.getLongExtra(DATE, 0);
 		String date = formatDateAbsolute(this, time);
 		contactName.setText(name);
 		dateView.setText(date);
 
-		// Image View
+		// Set up image ViewPager
-		photoView = findViewById(R.id.photoView);
+		viewPager = findViewById(R.id.viewPager);
+		ImagePagerAdapter pagerAdapter =
+				new ImagePagerAdapter(getSupportFragmentManager());
+		viewPager.setAdapter(pagerAdapter);
+		viewPager.setCurrentItem(position);
+
 		if (SDK_INT >= 16) {
-			photoView.setOnClickListener(view -> toggleSystemUi());
+			viewModel.getOnImageClicked().observe(this, this::onImageClicked);
 			window.getDecorView().setSystemUiVisibility(
 					SYSTEM_UI_FLAG_LAYOUT_STABLE |
 							SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
 		}
+	}
 
-		// Request Listener
+	@Override
-		RequestListener<Drawable> listener = new RequestListener<Drawable>() {
+	public boolean onCreateOptionsMenu(Menu menu) {
-			@Override
+		getMenuInflater().inflate(R.menu.image_actions, menu);
-			public boolean onLoadFailed(@Nullable GlideException e,
+		return super.onCreateOptionsMenu(menu);
-					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
@@ -149,11 +156,36 @@ public class ImageActivity extends BriarActivity
 			case android.R.id.home:
 				onBackPressed();
 				return true;
+			case R.id.action_save_image:
+				showSaveImageDialog();
+				return true;
 			default:
 				return super.onOptionsItemSelected(item);
 		}
 	}
 
+	@Override
+	public void onGlobalLayout() {
+		viewModel.setToolbarPosition(
+				appBarLayout.getTop(), appBarLayout.getBottom()
+		);
+		if (SDK_INT >= 16) {
+			layout.getViewTreeObserver().removeOnGlobalLayoutListener(this);
+		} else {
+			layout.getViewTreeObserver().removeGlobalOnLayoutListener(this);
+		}
+	}
+
+	@Override
+	protected void onActivityResult(int request, int result,
+			@Nullable Intent data) {
+		super.onActivityResult(request, result, data);
+		if (request == REQUEST_SAVE_ATTACHMENT && result == RESULT_OK &&
+				data != null) {
+			viewModel.saveImage(getVisibleAttachment(), data.getData());
+		}
+	}
+
 	@Override
 	public void onPullStart() {
 		appBarLayout.animate()
@@ -163,7 +195,6 @@ public class ImageActivity extends BriarActivity
 
 	@Override
 	public void onPull(float progress) {
-		layout.getBackground().setAlpha(Math.round((1 - progress) * 255));
 	}
 
 	@Override
@@ -178,6 +209,14 @@ public class ImageActivity extends BriarActivity
 		supportFinishAfterTransition();
 	}
 
+	@RequiresApi(api = 16)
+	private void onImageClicked(@Nullable Boolean clicked) {
+		if (clicked != null && clicked) {
+			toggleSystemUi();
+			viewModel.onOnImageClickSeen();
+		}
+	}
+
 	@RequiresApi(api = 16)
 	private void toggleSystemUi() {
 		View decorView = getWindow().getDecorView();
@@ -190,9 +229,8 @@ public class ImageActivity extends BriarActivity
 
 	@RequiresApi(api = 16)
 	private void hideSystemUi(View decorView) {
-		decorView.setSystemUiVisibility(SYSTEM_UI_FLAG_LAYOUT_STABLE
+		decorView.setSystemUiVisibility(SYSTEM_UI_FLAG_FULLSCREEN |
-				| SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
+				SYSTEM_UI_FLAG_LAYOUT_STABLE | SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
-				| SYSTEM_UI_FLAG_FULLSCREEN
 		);
 		appBarLayout.animate()
 				.translationYBy(-1 * appBarLayout.getHeight())
@@ -204,8 +242,7 @@ public class ImageActivity extends BriarActivity
 	@RequiresApi(api = 16)
 	private void showSystemUi(View decorView) {
 		decorView.setSystemUiVisibility(
-				SYSTEM_UI_FLAG_LAYOUT_STABLE
+				SYSTEM_UI_FLAG_LAYOUT_STABLE | SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
-						| SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN
 		);
 		appBarLayout.animate()
 				.translationYBy(appBarLayout.getHeight())
@@ -214,20 +251,76 @@ public class ImageActivity extends BriarActivity
 				.start();
 	}
 
-	private boolean isOverlappingToolbar(Drawable drawable) {
+	private void showSaveImageDialog() {
-		int width = drawable.getIntrinsicWidth();
+		OnClickListener okListener = (dialog, which) -> {
-		int height = drawable.getIntrinsicHeight();
+			if (SDK_INT >= 19) {
-		float widthPercentage = photoView.getWidth() / (float) width;
+				Intent intent = getCreationIntent();
-		float heightPercentage = photoView.getHeight() / (float) height;
+				startActivityForResult(intent, REQUEST_SAVE_ATTACHMENT);
-		float scaleFactor = Math.min(widthPercentage, heightPercentage);
+			} else {
-		int realWidth = (int) (width * scaleFactor);
+				viewModel.saveImage(getVisibleAttachment());
-		int realHeight = (int) (height * scaleFactor);
+			}
-		// return if photo doesn't use the full width,
+		};
-		// because it will be moved to the right otherwise
+		Builder builder = new Builder(this, R.style.BriarDialogTheme);
-		if (realWidth < photoView.getWidth()) return false;
+		builder.setTitle(getString(R.string.dialog_title_save_image));
-		int drawableTop = (photoView.getHeight() - realHeight) / 2;
+		builder.setMessage(getString(R.string.dialog_message_save_image));
-		return drawableTop < appBarLayout.getBottom() &&
+		Drawable icon = ContextCompat.getDrawable(this, R.drawable.ic_security);
-				drawableTop != appBarLayout.getTop();
+		DrawableCompat.setTint(requireNonNull(icon),
+				ContextCompat.getColor(this, R.color.color_primary));
+		builder.setIcon(icon);
+		builder.setPositiveButton(R.string.save_image, okListener);
+		builder.setNegativeButton(R.string.cancel, null);
+		builder.show();
+	}
+
+	@RequiresApi(api = 19)
+	private Intent getCreationIntent() {
+		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss",
+				Locale.getDefault());
+		String fileName = sdf.format(new Date());
+		Intent intent = new Intent(ACTION_CREATE_DOCUMENT);
+		intent.addCategory(CATEGORY_OPENABLE);
+		intent.setType(getVisibleAttachment().getMimeType());
+		intent.putExtra(EXTRA_TITLE, fileName);
+		return intent;
+	}
+
+	private void onImageSaveStateChanged(@Nullable Boolean error) {
+		if (error == null) return;
+		int stringRes = error ?
+				R.string.save_image_error : R.string.save_image_success;
+		int colorRes = error ?
+				R.color.briar_red : R.color.briar_primary;
+		Snackbar s = Snackbar.make(layout, stringRes, LENGTH_LONG);
+		s.getView().setBackgroundResource(colorRes);
+		s.show();
+		viewModel.onSaveStateSeen();
+	}
+
+	AttachmentItem getVisibleAttachment() {
+		return attachments.get(viewPager.getCurrentItem());
+	}
+
+	private class ImagePagerAdapter extends FragmentStatePagerAdapter {
+
+		private boolean isFirst = true;
+
+		private ImagePagerAdapter(FragmentManager fm) {
+			super(fm);
+		}
+
+		@Override
+		public Fragment getItem(int position) {
+			Fragment f = ImageFragment
+					.newInstance(attachments.get(position), isFirst);
+			isFirst = false;
+			return f;
+		}
+
+		@Override
+		public int getCount() {
+			return attachments.size();
+		}
+
 	}
 
 }

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

@@ -0,0 +1,155 @@
+package org.briarproject.briar.android.conversation;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.support.annotation.Nullable;
+import android.support.v7.widget.RecyclerView.Adapter;
+import android.util.DisplayMetrics;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.WindowManager;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.conversation.glide.Radii;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static android.content.Context.WINDOW_SERVICE;
+import static java.util.Objects.requireNonNull;
+import static org.briarproject.briar.android.util.UiUtils.isRtl;
+
+@NotNullByDefault
+class ImageAdapter extends Adapter<ImageViewHolder> {
+
+	private final List<AttachmentItem> items = new ArrayList<>();
+	private final ConversationListener listener;
+	private final int imageSize;
+	private final int radiusBig, radiusSmall;
+	private final boolean isRtl;
+	@Nullable
+	private ConversationMessageItem conversationItem;
+
+	ImageAdapter(Context ctx, ConversationListener listener) {
+		this.listener = listener;
+		imageSize = getImageSize(ctx);
+		Resources res = ctx.getResources();
+		radiusBig =
+				res.getDimensionPixelSize(R.dimen.message_bubble_radius_big);
+		radiusSmall =
+				res.getDimensionPixelSize(R.dimen.message_bubble_radius_small);
+		isRtl = isRtl(ctx);
+	}
+
+	@Override
+	public ImageViewHolder onCreateViewHolder(ViewGroup viewGroup, int type) {
+		View v = LayoutInflater.from(viewGroup.getContext()).inflate(
+				R.layout.list_item_image, viewGroup, false);
+		return new ImageViewHolder(v, imageSize);
+	}
+
+	@Override
+	public void onBindViewHolder(ImageViewHolder imageViewHolder,
+			int position) {
+		// get item
+		requireNonNull(conversationItem);
+		AttachmentItem item = items.get(position);
+		// set onClick listener
+		imageViewHolder.itemView.setOnClickListener(v ->
+				listener.onAttachmentClicked(v, conversationItem, item)
+		);
+		// bind view holder
+		int size = items.size();
+		boolean isIncoming = conversationItem.isIncoming();
+		boolean hasText = conversationItem.getText() != null;
+		Radii r = getRadii(position, size, isIncoming, hasText);
+		imageViewHolder.bind(item, r, size == 1, singleInRow(position, size));
+	}
+
+	@Override
+	public int getItemCount() {
+		return items.size();
+	}
+
+	void setConversationItem(ConversationMessageItem item) {
+		this.conversationItem = item;
+		this.items.clear();
+		this.items.addAll(item.getAttachments());
+		notifyDataSetChanged();
+	}
+
+	private int getImageSize(Context ctx) {
+		Resources res = ctx.getResources();
+		WindowManager windowManager =
+				(WindowManager) ctx.getSystemService(WINDOW_SERVICE);
+		DisplayMetrics displayMetrics = new DisplayMetrics();
+		if (windowManager == null) {
+			return res.getDimensionPixelSize(
+					R.dimen.message_bubble_image_default);
+		}
+		windowManager.getDefaultDisplay().getMetrics(displayMetrics);
+		int imageSize = displayMetrics.widthPixels / 3;
+		int maxSize = res.getDimensionPixelSize(
+				R.dimen.message_bubble_image_max_width);
+		return Math.min(imageSize, maxSize);
+	}
+
+	private Radii getRadii(int pos, int num, boolean isIncoming,
+			boolean hasText) {
+		boolean left = isLeft(pos);
+		boolean single = num == 1;
+		// Top Row
+		int topLeft;
+		int topRight;
+		if (single) {
+			topLeft = isIncoming ? radiusSmall : radiusBig;
+			topRight = !isIncoming ? radiusSmall : radiusBig;
+		} else if (isTopRow(pos)) {
+			topLeft = left ? (isIncoming ? radiusSmall : radiusBig) : 0;
+			topRight = !left ? (!isIncoming ? radiusSmall : radiusBig) : 0;
+		} else {
+			topLeft = 0;
+			topRight = 0;
+		}
+		// Bottom Row
+		boolean singleInRow = singleInRow(pos, num);
+		int bottomLeft;
+		int bottomRight;
+		if (!hasText && isBottomRow(pos, num)) {
+			bottomLeft = singleInRow || left ? radiusBig : 0;
+			bottomRight = singleInRow || !left ? radiusBig : 0;
+		} else {
+			bottomLeft = 0;
+			bottomRight = 0;
+		}
+		if (isRtl) return new Radii(topRight, topLeft, bottomRight, bottomLeft);
+		return new Radii(topLeft, topRight, bottomLeft, bottomRight);
+	}
+
+	void clear() {
+		items.clear();
+		notifyDataSetChanged();
+	}
+
+	static boolean isTopRow(int pos) {
+		return pos < 2;
+	}
+
+	static boolean isLeft(int pos) {
+		return pos % 2 == 0;
+	}
+
+	static boolean isBottomRow(int pos, int num) {
+		return num % 2 == 0 ?
+				pos >= num - 2 : // last two, if even
+				pos > num - 2;   // last one, if odd
+	}
+
+	static boolean singleInRow(int pos, int num) {
+		// last item of an odd number
+		return num % 2 != 0 && pos == num -1;
+	}
+
+}

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

@@ -0,0 +1,133 @@
+package org.briarproject.briar.android.conversation;
+
+import android.arch.lifecycle.ViewModelProvider;
+import android.arch.lifecycle.ViewModelProviders;
+import android.graphics.drawable.Animatable;
+import android.graphics.drawable.Drawable;
+import android.os.Bundle;
+import android.support.annotation.Nullable;
+import android.support.v4.app.Fragment;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+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.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.briar.R;
+import org.briarproject.briar.android.activity.BaseActivity;
+import org.briarproject.briar.android.conversation.glide.GlideApp;
+
+import javax.annotation.ParametersAreNonnullByDefault;
+import javax.inject.Inject;
+
+import static android.os.Build.VERSION.SDK_INT;
+import static android.widget.ImageView.ScaleType.FIT_START;
+import static com.bumptech.glide.load.engine.DiskCacheStrategy.NONE;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
+import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENT_POSITION;
+
+@MethodsNotNullByDefault
+@ParametersAreNonnullByDefault
+public class ImageFragment extends Fragment {
+
+	private final static String IS_FIRST = "isFirst";
+
+	@Inject
+	ViewModelProvider.Factory viewModelFactory;
+
+	private AttachmentItem attachment;
+	private boolean isFirst;
+	private ImageViewModel viewModel;
+	private PhotoView photoView;
+
+	static ImageFragment newInstance(AttachmentItem a, boolean isFirst) {
+		ImageFragment f = new ImageFragment();
+		Bundle args = new Bundle();
+		args.putParcelable(ATTACHMENT_POSITION, a);
+		args.putBoolean(IS_FIRST, isFirst);
+		f.setArguments(args);
+		return f;
+	}
+
+	@Override
+	public void onActivityCreated(@Nullable Bundle savedInstanceState) {
+		super.onActivityCreated(savedInstanceState);
+		BaseActivity a = (BaseActivity) requireNonNull(getActivity());
+		a.getActivityComponent().inject(this);
+	}
+
+	@Override
+	public void onCreate(@Nullable Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+
+		Bundle args = requireNonNull(getArguments());
+		attachment = requireNonNull(args.getParcelable(ATTACHMENT_POSITION));
+		isFirst = args.getBoolean(IS_FIRST);
+	}
+
+	@Nullable
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
+		View v = inflater.inflate(R.layout.fragment_image, container,
+				false);
+
+		viewModel = ViewModelProviders.of(requireNonNull(getActivity()),
+				viewModelFactory).get(ImageViewModel.class);
+
+		photoView = v.findViewById(R.id.photoView);
+		photoView.setScaleLevels(1, 2, 4);
+		photoView.setOnClickListener(view -> viewModel.clickImage());
+
+		// Request Listener
+		RequestListener<Drawable> listener = new RequestListener<Drawable>() {
+			@Override
+			public boolean onLoadFailed(@Nullable GlideException e,
+					Object model, Target<Drawable> target,
+					boolean isFirstResource) {
+				if (getActivity() != null && isFirst)
+					getActivity().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 (viewModel.isOverlappingToolbar(photoView, resource)) {
+					photoView.setScaleType(FIT_START);
+				}
+				if (getActivity() != null && isFirst) {
+					getActivity().supportStartPostponedEnterTransition();
+				}
+				return false;
+			}
+		};
+
+		// Load Image
+		GlideApp.with(this)
+				.load(attachment)
+				// TODO allow if size < maxTextureSize ?
+//				.override(SIZE_ORIGINAL)
+				.diskCacheStrategy(NONE)
+				.error(R.drawable.ic_image_broken)
+				.addListener(listener)
+				.into(photoView);
+
+		return v;
+	}
+
+}

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

@@ -0,0 +1,29 @@
+package org.briarproject.briar.android.conversation;
+
+import android.support.annotation.Nullable;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.io.InputStream;
+
+@NotNullByDefault
+interface ImageHelper {
+
+	DecodeResult decodeStream(InputStream is);
+
+	@Nullable
+	String getExtensionFromMimeType(String mimeType);
+
+	class DecodeResult {
+
+		final int width;
+		final int height;
+		final String mimeType;
+
+		DecodeResult(int width, int height, String mimeType) {
+			this.width = width;
+			this.height = height;
+			this.mimeType = mimeType;
+		}
+	}
+}

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

@@ -0,0 +1,54 @@
+package org.briarproject.briar.android.conversation;
+
+import android.content.Context;
+import android.content.res.Resources;
+import android.graphics.Rect;
+import android.support.v7.widget.RecyclerView;
+import android.support.v7.widget.RecyclerView.ItemDecoration;
+import android.support.v7.widget.RecyclerView.State;
+import android.view.View;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.briar.R;
+
+import static org.briarproject.briar.android.conversation.ImageAdapter.isBottomRow;
+import static org.briarproject.briar.android.conversation.ImageAdapter.isLeft;
+import static org.briarproject.briar.android.conversation.ImageAdapter.isTopRow;
+import static org.briarproject.briar.android.conversation.ImageAdapter.singleInRow;
+import static org.briarproject.briar.android.util.UiUtils.isRtl;
+
+@NotNullByDefault
+class ImageItemDecoration extends ItemDecoration {
+
+	private final int border;
+	private final boolean isRtl;
+
+	ImageItemDecoration(Context ctx) {
+		Resources res = ctx.getResources();
+
+		// for pixel perfection, add a pixel to the border if it has an odd size
+		int b = res.getDimensionPixelSize(R.dimen.message_bubble_border);
+		int realBorderSize = b % 2 == 0 ? b : b + 1;
+
+		// we are applying half the border around the insides of each image
+		// to prevent differently sized images looking slightly broken
+		border = realBorderSize / 2;
+
+		// find out if we are showing a RTL language
+		isRtl = isRtl(ctx);
+	}
+
+	@Override
+	public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
+			State state) {
+		if (state.getItemCount() == 1) return;
+		int pos = parent.getChildAdapterPosition(view);
+		int num = state.getItemCount();
+		boolean start = isLeft(pos) ^ isRtl;
+		outRect.top = isTopRow(pos) ? 0 : border;
+		outRect.left = start ? 0 : border;
+		outRect.right = start && !singleInRow(pos, num) ? border : 0;
+		outRect.bottom = isBottomRow(pos, num) ? 0 : border;
+	}
+
+}

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

@@ -0,0 +1,74 @@
+package org.briarproject.briar.android.conversation;
+
+import android.graphics.Bitmap;
+import android.support.annotation.DrawableRes;
+import android.support.v7.widget.RecyclerView.ViewHolder;
+import android.support.v7.widget.StaggeredGridLayoutManager.LayoutParams;
+import android.view.View;
+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 org.briarproject.briar.android.conversation.glide.Radii;
+
+import static android.os.Build.VERSION.SDK_INT;
+import static com.bumptech.glide.load.engine.DiskCacheStrategy.NONE;
+import static com.bumptech.glide.load.resource.drawable.DrawableTransitionOptions.withCrossFade;
+
+@NotNullByDefault
+class ImageViewHolder extends ViewHolder {
+
+	@DrawableRes
+	private static final int ERROR_RES = R.drawable.ic_image_broken;
+
+	protected final ImageView imageView;
+	private final int imageSize;
+
+	ImageViewHolder(View v, int imageSize) {
+		super(v);
+		imageView = v.findViewById(R.id.imageView);
+		this.imageSize = imageSize;
+	}
+
+	void bind(AttachmentItem attachment, Radii r, boolean single,
+			boolean needsStretch) {
+		if (attachment.hasError()) {
+			GlideApp.with(imageView)
+					.clear(imageView);
+			imageView.setImageResource(ERROR_RES);
+		} else {
+			setImageViewDimensions(attachment, single, needsStretch);
+			loadImage(attachment, r);
+			if (SDK_INT >= 21) {
+				imageView.setTransitionName(attachment.getTransitionName());
+			}
+		}
+	}
+
+	private void setImageViewDimensions(AttachmentItem a, boolean single,
+			boolean needsStretch) {
+		LayoutParams params = (LayoutParams) imageView.getLayoutParams();
+		int width = needsStretch ? imageSize * 2 : imageSize;
+		params.width = single ? a.getThumbnailWidth() : width;
+		params.height = single ? a.getThumbnailHeight() : imageSize;
+		params.setFullSpan(!single && needsStretch);
+		imageView.setLayoutParams(params);
+	}
+
+	private void loadImage(AttachmentItem a, Radii r) {
+		Transformation<Bitmap> transformation = new BriarImageTransformation(r);
+		GlideApp.with(imageView)
+				.load(a)
+				.diskCacheStrategy(NONE)
+				.error(ERROR_RES)
+				.transform(transformation)
+				.transition(withCrossFade())
+				.into(imageView)
+				.waitForLayout();
+	}
+
+}

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

@@ -0,0 +1,214 @@
+package org.briarproject.briar.android.conversation;
+
+import android.app.Application;
+import android.arch.lifecycle.AndroidViewModel;
+import android.arch.lifecycle.LiveData;
+import android.arch.lifecycle.MutableLiveData;
+import android.graphics.drawable.Drawable;
+import android.net.Uri;
+import android.support.annotation.Nullable;
+import android.support.annotation.UiThread;
+import android.view.View;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.messaging.Attachment;
+import org.briarproject.briar.api.messaging.MessagingManager;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+import java.util.concurrent.Executor;
+import java.util.logging.Logger;
+
+import javax.inject.Inject;
+
+import static android.media.MediaScannerConnection.scanFile;
+import static android.os.Environment.DIRECTORY_PICTURES;
+import static android.os.Environment.getExternalStoragePublicDirectory;
+import static java.util.logging.Level.WARNING;
+import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.util.IoUtils.copyAndClose;
+import static org.briarproject.bramble.util.LogUtils.logException;
+
+@NotNullByDefault
+public class ImageViewModel extends AndroidViewModel {
+
+	private static Logger LOG = getLogger(ImageViewModel.class.getName());
+
+	private final MessagingManager messagingManager;
+	@DatabaseExecutor
+	private final Executor dbExecutor;
+	@IoExecutor
+	private final Executor ioExecutor;
+
+	/**
+	 * true means there was an error saving the image, false if image was saved.
+	 */
+	private final MutableLiveData<Boolean> saveState = new MutableLiveData<>();
+	private final MutableLiveData<Boolean> imageClicked =
+			new MutableLiveData<>();
+	private int toolbarTop, toolbarBottom;
+
+	@Inject
+	ImageViewModel(Application application,
+			MessagingManager messagingManager,
+			@DatabaseExecutor Executor dbExecutor,
+			@IoExecutor Executor ioExecutor) {
+		super(application);
+		this.messagingManager = messagingManager;
+		this.dbExecutor = dbExecutor;
+		this.ioExecutor = ioExecutor;
+	}
+
+	void clickImage() {
+		imageClicked.setValue(true);
+	}
+
+	/**
+	 * A LiveData that is true if the image was clicked,
+	 * false if it wasn't.
+	 *
+	 * Call {@link #onOnImageClickSeen()} after consuming an update.
+	 */
+	LiveData<Boolean> getOnImageClicked() {
+		return imageClicked;
+	}
+
+	@UiThread
+	void onOnImageClickSeen() {
+		imageClicked.setValue(false);
+	}
+
+	void setToolbarPosition(int top, int bottom) {
+		toolbarTop = top;
+		toolbarBottom = bottom;
+	}
+
+	boolean isOverlappingToolbar(View screenView, Drawable drawable) {
+		int width = drawable.getIntrinsicWidth();
+		int height = drawable.getIntrinsicHeight();
+		float widthPercentage = screenView.getWidth() / (float) width;
+		float heightPercentage = screenView.getHeight() / (float) height;
+		float scaleFactor = Math.min(widthPercentage, heightPercentage);
+		int realWidth = (int) (width * scaleFactor);
+		int realHeight = (int) (height * scaleFactor);
+		// return if image doesn't use the full width,
+		// because it will be moved to the right otherwise
+		if (realWidth < screenView.getWidth()) return false;
+		int drawableTop = (screenView.getHeight() - realHeight) / 2;
+		return drawableTop < toolbarBottom && drawableTop != toolbarTop;
+	}
+
+	/**
+	 * A LiveData that is true if there was an error
+	 * and false if the image was saved.
+	 * It can be null otherwise, if no image was saved recently.
+	 *
+	 * Call {@link #onSaveStateSeen()} after consuming an update.
+	 */
+	LiveData<Boolean> getSaveState() {
+		return saveState;
+	}
+
+	@UiThread
+	void onSaveStateSeen() {
+		saveState.setValue(null);
+	}
+
+	/**
+	 * Saves the attachment to a writeable {@link Uri}.
+	 */
+	@UiThread
+	void saveImage(AttachmentItem attachment, @Nullable Uri uri) {
+		if (uri == null) {
+			saveState.setValue(true);
+		} else {
+			saveImage(attachment, () -> getOutputStream(uri), null);
+		}
+	}
+
+	/**
+	 * Saves the attachment on external storage,
+	 * assuming the permission was granted during install time.
+	 */
+	void saveImage(AttachmentItem attachment) {
+		File file = getImageFile(attachment);
+		saveImage(attachment, () -> getOutputStream(file), () -> scanFile(
+				getApplication(), new String[] {file.toString()}, null, null));
+	}
+
+	private void saveImage(AttachmentItem attachment, OutputStreamProvider osp,
+			@Nullable Runnable afterCopy) {
+		MessageId messageId = attachment.getMessageId();
+		dbExecutor.execute(() -> {
+			try {
+				Attachment a = messagingManager.getAttachment(messageId);
+				copyImageFromDb(a, osp, afterCopy);
+			} catch (DbException e) {
+				logException(LOG, WARNING, e);
+				saveState.postValue(true);
+			}
+		});
+	}
+
+	private void copyImageFromDb(Attachment a, OutputStreamProvider osp,
+			@Nullable Runnable afterCopy) {
+		ioExecutor.execute(() -> {
+			try {
+				InputStream is = a.getStream();
+				OutputStream os = osp.getOutputStream();
+				copyAndClose(is, os);
+				if (afterCopy != null) afterCopy.run();
+				saveState.postValue(false);
+			} catch (IOException e) {
+				logException(LOG, WARNING, e);
+				saveState.postValue(true);
+			}
+		});
+	}
+
+	private String getFileName() {
+		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss",
+				Locale.getDefault());
+		return sdf.format(new Date());
+	}
+
+	private File getImageFile(AttachmentItem attachment) {
+		File path = getExternalStoragePublicDirectory(DIRECTORY_PICTURES);
+		//noinspection ResultOfMethodCallIgnored
+		path.mkdirs();
+		String fileName = getFileName();
+		String ext = "." + attachment.getExtension();
+		File file = new File(path, fileName + ext);
+		int i = 1;
+		while (file.exists()) {
+			file = new File(path, fileName + " (" + i + ")" + ext);
+		}
+		return file;
+	}
+
+	private OutputStream getOutputStream(File file) throws IOException {
+		return new FileOutputStream(file);
+	}
+
+	private OutputStream getOutputStream(Uri uri) throws IOException {
+		OutputStream os =
+				getApplication().getContentResolver().openOutputStream(uri);
+		if (os == null) throw new IOException();
+		return os;
+	}
+
+	private interface OutputStreamProvider {
+		OutputStream getOutputStream() throws IOException;
+	}
+
+}

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

@@ -40,7 +40,7 @@ class BriarDataFetcher implements DataFetcher<InputStream> {
 	private volatile boolean cancel = false;
 
 	@Inject
-	public BriarDataFetcher(MessagingManager messagingManager,
+	BriarDataFetcher(MessagingManager messagingManager,
 			@DatabaseExecutor Executor dbExecutor, AttachmentItem attachment) {
 		this.messagingManager = messagingManager;
 		this.dbExecutor = dbExecutor;

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

@@ -7,10 +7,8 @@ import com.bumptech.glide.load.resource.bitmap.CenterCrop;
 
 public class BriarImageTransformation extends MultiTransformation<Bitmap> {
 
-	public BriarImageTransformation(int smallRadius, int radius,
+	public BriarImageTransformation(Radii r) {
-			boolean leftCornerSmall, boolean bottomRound) {
+		super(new CenterCrop(), new CustomCornersTransformation(r));
-		super(new CenterCrop(), new ImageCornerTransformation(
-				smallRadius, radius, leftCornerSmall, bottomRound));
 	}
 
 }

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

@@ -22,7 +22,7 @@ public final class BriarModelLoader
 	@Inject
 	BriarDataFetcherFactory dataFetcherFactory;
 
-	public BriarModelLoader(BriarApplication app) {
+	BriarModelLoader(BriarApplication app) {
 		app.getApplicationComponent().inject(this);
 	}
 

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

@@ -16,7 +16,7 @@ class BriarModelLoaderFactory
 
 	private final BriarApplication app;
 
-	public BriarModelLoaderFactory(BriarApplication app) {
+	BriarModelLoaderFactory(BriarApplication app) {
 		this.app = app;
 	}
 

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

@@ -0,0 +1,129 @@
+package org.briarproject.briar.android.conversation.glide;
+
+import android.graphics.Bitmap;
+import android.graphics.BitmapShader;
+import android.graphics.Canvas;
+import android.graphics.Paint;
+import android.graphics.RectF;
+import android.support.annotation.NonNull;
+
+import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
+import com.bumptech.glide.load.resource.bitmap.BitmapTransformation;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.security.MessageDigest;
+
+import javax.annotation.concurrent.Immutable;
+
+import static android.graphics.Bitmap.Config.ARGB_8888;
+import static android.graphics.Shader.TileMode.CLAMP;
+
+@Immutable
+@NotNullByDefault
+class CustomCornersTransformation extends BitmapTransformation {
+
+	private static final String ID =
+			CustomCornersTransformation.class.getName();
+
+	private final Radii radii;
+
+	CustomCornersTransformation(Radii radii) {
+		this.radii = radii;
+	}
+
+	@Override
+	protected Bitmap transform(BitmapPool pool, Bitmap toTransform,
+			int outWidth, int outHeight) {
+		int width = toTransform.getWidth();
+		int height = toTransform.getHeight();
+
+		Bitmap bitmap = pool.get(width, height, ARGB_8888);
+		bitmap.setHasAlpha(true);
+
+		Canvas canvas = new Canvas(bitmap);
+		Paint paint = new Paint();
+		paint.setAntiAlias(true);
+		paint.setShader(new BitmapShader(toTransform, CLAMP, CLAMP));
+		drawRect(canvas, paint, width, height);
+		return bitmap;
+	}
+
+	private void drawRect(Canvas canvas, Paint paint, float width,
+			float height) {
+		drawTopLeft(canvas, paint, radii.topLeft, width, height);
+		drawTopRight(canvas, paint, radii.topRight, width, height);
+		drawBottomLeft(canvas, paint, radii.bottomLeft, width, height);
+		drawBottomRight(canvas, paint, radii.bottomRight, width, height);
+	}
+
+	private void drawTopLeft(Canvas canvas, Paint paint, int radius,
+			float width, float height) {
+		RectF rect = new RectF(
+				0,
+				0,
+				width / 2 + radius + 1,
+				height / 2 + radius + 1
+		);
+		if (radius == 0) canvas.drawRect(rect, paint);
+		else canvas.drawRoundRect(rect, radius, radius, paint);
+	}
+
+	private void drawTopRight(Canvas canvas, Paint paint, int radius,
+			float width, float height) {
+		RectF rect = new RectF(
+				width / 2 - radius,
+				0,
+				width,
+				height / 2 + radius + 1
+		);
+		if (radius == 0) canvas.drawRect(rect, paint);
+		else canvas.drawRoundRect(rect, radius, radius, paint);
+	}
+
+	private void drawBottomLeft(Canvas canvas, Paint paint, int radius,
+			float width, float height) {
+		RectF rect = new RectF(
+				0,
+				height / 2 - radius,
+				width / 2 + radius + 1,
+				height
+		);
+		if (radius == 0) canvas.drawRect(rect, paint);
+		else canvas.drawRoundRect(rect, radius, radius, paint);
+	}
+
+	private void drawBottomRight(Canvas canvas, Paint paint, int radius,
+			float width, float height) {
+		RectF rect = new RectF(
+				width / 2 - radius,
+				height / 2 - radius,
+				width,
+				height
+		);
+		if (radius == 0) canvas.drawRect(rect, paint);
+		else canvas.drawRoundRect(rect, radius, radius, paint);
+	}
+
+	@Override
+	public String toString() {
+		return "ImageCornerTransformation(" + radii + ")";
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		return o instanceof CustomCornersTransformation &&
+				radii.equals(((CustomCornersTransformation) o).radii);
+	}
+
+	@Override
+	public int hashCode() {
+		return ID.hashCode() + radii.hashCode();
+	}
+
+	@Override
+	public void updateDiskCacheKey(@NonNull MessageDigest messageDigest) {
+		messageDigest.update((ID + radii).getBytes(CHARSET));
+	}
+
+}

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

@@ -1,111 +0,0 @@
-package org.briarproject.briar.android.conversation.glide;
-
-import android.graphics.Bitmap;
-import android.graphics.BitmapShader;
-import android.graphics.Canvas;
-import android.graphics.Paint;
-import android.graphics.RectF;
-import android.support.annotation.NonNull;
-
-import com.bumptech.glide.load.engine.bitmap_recycle.BitmapPool;
-import com.bumptech.glide.load.resource.bitmap.BitmapTransformation;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-import java.security.MessageDigest;
-
-import javax.annotation.concurrent.Immutable;
-
-import static android.graphics.Bitmap.Config.ARGB_8888;
-import static android.graphics.Shader.TileMode.CLAMP;
-
-@Immutable
-@NotNullByDefault
-class ImageCornerTransformation extends BitmapTransformation {
-
-	private static final String ID = ImageCornerTransformation.class.getName();
-
-	private final int smallRadius, radius;
-	private final boolean leftCornerSmall, bottomRound;
-
-	ImageCornerTransformation(int smallRadius, int radius,
-			boolean leftCornerSmall, boolean bottomRound) {
-		this.smallRadius = smallRadius;
-		this.radius = radius;
-		this.leftCornerSmall = leftCornerSmall;
-		this.bottomRound = bottomRound;
-	}
-
-	@Override
-	protected Bitmap transform(BitmapPool pool, Bitmap toTransform,
-			int outWidth, int outHeight) {
-		int width = toTransform.getWidth();
-		int height = toTransform.getHeight();
-
-		Bitmap bitmap = pool.get(width, height, ARGB_8888);
-		bitmap.setHasAlpha(true);
-
-		Canvas canvas = new Canvas(bitmap);
-		Paint paint = new Paint();
-		paint.setAntiAlias(true);
-		paint.setShader(new BitmapShader(toTransform, CLAMP, CLAMP));
-		drawRect(canvas, paint, width, height);
-		return bitmap;
-	}
-
-	private void drawRect(Canvas canvas, Paint paint, float width,
-			float height) {
-		drawSmallCorner(canvas, paint, width);
-		drawBigCorners(canvas, paint, width, height);
-	}
-
-	private void drawSmallCorner(Canvas canvas, Paint paint, float width) {
-		float left = leftCornerSmall ? 0 : width - radius;
-		float right = leftCornerSmall ? radius : width;
-		canvas.drawRoundRect(new RectF(left, 0, right, radius),
-				smallRadius, smallRadius, paint);
-	}
-
-	private void drawBigCorners(Canvas canvas, Paint paint, float width,
-			float height) {
-		float top = bottomRound ? 0 : radius;
-		RectF rect = new RectF(0, top, width, height);
-		if (bottomRound) {
-			canvas.drawRoundRect(rect, radius, radius, paint);
-		} else {
-			canvas.drawRect(rect, paint);
-			canvas.drawRoundRect(new RectF(0, 0, width, radius * 2),
-					radius, radius, paint);
-		}
-	}
-
-	@Override
-	public String toString() {
-		return "ImageCornerTransformation(smallRadius=" + smallRadius +
-				", radius=" + radius + ", leftCornerSmall=" + leftCornerSmall +
-				", bottomRound=" + bottomRound + ")";
-	}
-
-	@Override
-	public boolean equals(Object o) {
-		return o instanceof ImageCornerTransformation &&
-				((ImageCornerTransformation) o).smallRadius == smallRadius &&
-				((ImageCornerTransformation) o).radius == radius &&
-				((ImageCornerTransformation) o).leftCornerSmall ==
-						leftCornerSmall &&
-				((ImageCornerTransformation) o).bottomRound == bottomRound;
-	}
-
-	@Override
-	public int hashCode() {
-		return ID.hashCode() + (smallRadius << 16) ^ (radius << 2) ^
-				(leftCornerSmall ? 2 : 0) ^ (bottomRound ? 1 : 0);
-	}
-
-	@Override
-	public void updateDiskCacheKey(@NonNull MessageDigest messageDigest) {
-		messageDigest.update((ID + '|' + smallRadius + '|' + radius + '|' +
-				leftCornerSmall + '|' + bottomRound).getBytes(CHARSET));
-	}
-
-}

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

@@ -0,0 +1,41 @@
+package org.briarproject.briar.android.conversation.glide;
+
+import android.support.annotation.Nullable;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public class Radii {
+
+	public final int topLeft, topRight, bottomLeft, bottomRight;
+
+	public Radii(int topLeft, int topRight, int bottomLeft, int bottomRight) {
+		this.topLeft = topLeft;
+		this.topRight = topRight;
+		this.bottomLeft = bottomLeft;
+		this.bottomRight = bottomRight;
+	}
+
+	@Override
+	public boolean equals(@Nullable Object o) {
+		return o instanceof Radii &&
+				topLeft == ((Radii) o).topLeft &&
+				topRight == ((Radii) o).topRight &&
+				bottomLeft == ((Radii) o).bottomLeft &&
+				bottomRight == ((Radii) o).bottomRight;
+	}
+
+	@Override
+	public int hashCode() {
+		return topLeft << 24 ^ topRight << 16 ^ bottomLeft << 8 ^ bottomRight;
+	}
+
+	@Override
+	public String toString() {
+		return "Radii(topLeft=" + topLeft +
+				",topRight=" + topRight +
+				",bottomLeft=" + bottomLeft +
+				",bottomRight=" + bottomRight;
+	}
+
+}

briar-android/src/main/java/org/briarproject/briar/android/forum/ForumListFragment.java

@@ -44,6 +44,7 @@ import javax.annotation.Nullable;
 import javax.inject.Inject;
 
 import static android.support.design.widget.Snackbar.LENGTH_INDEFINITE;
+import static java.util.Objects.requireNonNull;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -80,13 +81,18 @@ public class ForumListFragment extends BaseEventFragment implements
 		return fragment;
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
 	@Nullable
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
 
-		getActivity().setTitle(R.string.forums_button);
+		requireNonNull(getActivity()).setTitle(R.string.forums_button);
 
 		View contentView =
 				inflater.inflate(R.layout.fragment_forum_list, container,
@@ -102,7 +108,7 @@ public class ForumListFragment extends BaseEventFragment implements
 		snackbar.getView().setBackgroundResource(R.color.briar_primary);
 		snackbar.setAction(R.string.show, this);
 		snackbar.setActionTextColor(ContextCompat
-				.getColor(getContext(), R.color.briar_button_text_positive));
+				.getColor(getActivity(), R.color.briar_button_text_positive));
 
 		return contentView;
 	}
@@ -112,11 +118,6 @@ public class ForumListFragment extends BaseEventFragment implements
 		return TAG;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	@Override
 	public void onStart() {
 		super.onStart();

briar-android/src/main/java/org/briarproject/briar/android/fragment/BaseFragment.java

@@ -10,11 +10,15 @@ import android.support.v4.app.FragmentActivity;
 import android.view.MenuItem;
 
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.android.DestroyableContext;
 import org.briarproject.briar.android.activity.ActivityComponent;
 
 import javax.annotation.Nullable;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public abstract class BaseFragment extends Fragment
 		implements DestroyableContext {
 
@@ -22,12 +26,15 @@ public abstract class BaseFragment extends Fragment
 
 	public abstract String getUniqueTag();
 
-	public abstract void injectFragment(ActivityComponent component);
-
 	@Override
 	public void onAttach(Context context) {
 		super.onAttach(context);
 		listener = (BaseFragmentListener) context;
+		injectFragment(listener.getActivityComponent());
+	}
+
+	public void injectFragment(ActivityComponent component) {
+		// fragments that need to inject, can override this method
 	}
 
 	@Override
@@ -38,12 +45,6 @@ public abstract class BaseFragment extends Fragment
 		setHasOptionsMenu(true);
 	}
 
-	@Override
-	public void onActivityCreated(@Nullable Bundle savedInstanceState) {
-		super.onActivityCreated(savedInstanceState);
-		injectFragment(listener.getActivityComponent());
-	}
-
 	@Override
 	public boolean onOptionsItemSelected(MenuItem item) {
 		switch (item.getItemId()) {

briar-android/src/main/java/org/briarproject/briar/android/fragment/ErrorFragment.java

@@ -10,7 +10,6 @@ import android.widget.TextView;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
-import org.briarproject.briar.android.activity.ActivityComponent;
 
 
 @MethodsNotNullByDefault
@@ -57,9 +56,4 @@ public class ErrorFragment extends BaseFragment {
 		return v;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		// not necessary
-	}
-
 }

briar-android/src/main/java/org/briarproject/briar/android/introduction/ContactChooserFragment.java

@@ -1,7 +1,8 @@
 package org.briarproject.briar.android.introduction;
 
-import android.content.Context;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
+import android.support.annotation.UiThread;
 import android.support.v7.widget.LinearLayoutManager;
 import android.view.LayoutInflater;
 import android.view.View;
@@ -11,6 +12,8 @@ import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.ConnectionRegistry;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
@@ -28,10 +31,14 @@ import java.util.logging.Logger;
 
 import javax.inject.Inject;
 
+import static java.util.Objects.requireNonNull;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.briar.android.conversation.ConversationActivity.CONTACT_ID;
 
+@UiThread
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class ContactChooserFragment extends BaseFragment {
 
 	public static final String TAG = ContactChooserFragment.class.getName();
@@ -51,7 +58,6 @@ public class ContactChooserFragment extends BaseFragment {
 	volatile ConnectionRegistry connectionRegistry;
 
 	public static ContactChooserFragment newInstance(ContactId id) {
-
 		Bundle args = new Bundle();
 
 		ContactChooserFragment fragment = new ContactChooserFragment();
@@ -61,13 +67,13 @@ public class ContactChooserFragment extends BaseFragment {
 	}
 
 	@Override
-	public void onAttach(Context context) {
+	public void injectFragment(ActivityComponent component) {
-		super.onAttach(context);
+		component.inject(this);
 	}
 
 	@Override
-	public View onCreateView(LayoutInflater inflater, ViewGroup container,
+	public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container,
-			Bundle savedInstanceState) {
+			@Nullable Bundle savedInstanceState) {
 
 		View contentView = inflater.inflate(R.layout.list, container, false);
 
@@ -77,14 +83,16 @@ public class ContactChooserFragment extends BaseFragment {
 					Contact c2 = item.getContact();
 					showMessageScreen(c1, c2);
 				};
-		adapter = new ContactListAdapter(getActivity(), onContactClickListener);
+		adapter = new ContactListAdapter(requireNonNull(getActivity()),
+				onContactClickListener);
 
 		list = contentView.findViewById(R.id.list);
 		list.setLayoutManager(new LinearLayoutManager(getActivity()));
 		list.setAdapter(adapter);
 		list.setEmptyText(R.string.no_contacts);
 
-		contactId = new ContactId(getArguments().getInt(CONTACT_ID));
+		contactId = new ContactId(
+				requireNonNull(getArguments()).getInt(CONTACT_ID));
 
 		return contentView;
 	}
@@ -107,11 +115,6 @@ public class ContactChooserFragment extends BaseFragment {
 		return TAG;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	private void loadContacts() {
 		listener.runOnDbThread(() -> {
 			try {

briar-android/src/main/java/org/briarproject/briar/android/introduction/IntroductionMessageFragment.java

@@ -1,8 +1,8 @@
 package org.briarproject.briar.android.introduction;
 
 import android.content.Context;
+import android.net.Uri;
 import android.os.Bundle;
-import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.v7.app.ActionBar;
 import android.view.LayoutInflater;
@@ -17,14 +17,17 @@ import org.briarproject.bramble.api.contact.Contact;
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.contact.ContactManager;
 import org.briarproject.bramble.api.db.DbException;
-import org.briarproject.bramble.util.StringUtils;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.fragment.BaseFragment;
 import org.briarproject.briar.android.view.TextInputView;
-import org.briarproject.briar.android.view.TextInputView.TextInputListener;
+import org.briarproject.briar.android.view.TextSendController;
+import org.briarproject.briar.android.view.TextSendController.SendListener;
 import org.briarproject.briar.api.introduction.IntroductionManager;
 
+import java.util.List;
 import java.util.logging.Logger;
 
 import javax.inject.Inject;
@@ -36,13 +39,16 @@ import static android.app.Activity.RESULT_OK;
 import static android.view.View.GONE;
 import static android.view.View.VISIBLE;
 import static android.widget.Toast.LENGTH_SHORT;
+import static java.util.Objects.requireNonNull;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.briar.android.util.UiUtils.getContactDisplayName;
 import static org.briarproject.briar.api.introduction.IntroductionConstants.MAX_INTRODUCTION_TEXT_LENGTH;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class IntroductionMessageFragment extends BaseFragment
-		implements TextInputListener {
+		implements SendListener {
 
 	public static final String TAG =
 			IntroductionMessageFragment.class.getName();
@@ -72,11 +78,6 @@ public class IntroductionMessageFragment extends BaseFragment
 		return fragment;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	@Override
 	public void onAttach(Context context) {
 		super.onAttach(context);
@@ -84,8 +85,14 @@ public class IntroductionMessageFragment extends BaseFragment
 	}
 
 	@Override
-	public View onCreateView(@NonNull LayoutInflater inflater,
+	public void injectFragment(ActivityComponent component) {
-			ViewGroup container, Bundle savedInstanceState) {
+		component.inject(this);
+	}
+
+	@Override
+	public View onCreateView(LayoutInflater inflater,
+			@Nullable ViewGroup container,
+			@Nullable Bundle savedInstanceState) {
 
 		// change toolbar text
 		ActionBar actionBar = introductionActivity.getSupportActionBar();
@@ -93,11 +100,26 @@ public class IntroductionMessageFragment extends BaseFragment
 			actionBar.setTitle(R.string.introduction_message_title);
 		}
 
+		// get contact IDs from fragment arguments
+		Bundle args = requireNonNull(getArguments());
+		int contactId1 = args.getInt(CONTACT_ID_1, -1);
+		int contactId2 = args.getInt(CONTACT_ID_2, -1);
+		if (contactId1 == -1 || contactId2 == -1) {
+			throw new AssertionError("Use newInstance() to instantiate");
+		}
+
 		// inflate view
 		View v = inflater.inflate(R.layout.introduction_message, container,
 				false);
 		ui = new ViewHolder(v);
-		ui.message.setSendButtonEnabled(false);
+		TextSendController sendController =
+				new TextSendController(ui.message, this, true);
+		ui.message.setSendController(sendController);
+		ui.message.setMaxTextLength(MAX_INTRODUCTION_TEXT_LENGTH);
+		ui.message.setEnabled(false);
+
+		// get contacts and then show view
+		prepareToSetUpViews(contactId1, contactId2);
 
 		return v;
 	}
@@ -105,16 +127,6 @@ public class IntroductionMessageFragment extends BaseFragment
 	@Override
 	public void onStart() {
 		super.onStart();
-
-		// get contact IDs from fragment arguments
-		int contactId1 = getArguments().getInt(CONTACT_ID_1, -1);
-		int contactId2 = getArguments().getInt(CONTACT_ID_2, -1);
-		if (contactId1 == -1 || contactId2 == -1) {
-			throw new java.lang.InstantiationError(
-					"You need to use newInstance() to instantiate");
-		}
-		// get contacts and then show view
-		prepareToSetUpViews(contactId1, contactId2);
 	}
 
 	@Override
@@ -156,13 +168,10 @@ public class IntroductionMessageFragment extends BaseFragment
 			ui.progressBar.setVisibility(GONE);
 
 			if (possible) {
-				// set button action
-				ui.message.setListener(IntroductionMessageFragment.this);
-
 				// show views
 				ui.notPossible.setVisibility(GONE);
 				ui.message.setVisibility(VISIBLE);
-				ui.message.setSendButtonEnabled(true);
+				ui.message.setEnabled(true);
 				ui.message.showSoftKeyboard();
 			} else {
 				ui.notPossible.setVisibility(VISIBLE);
@@ -184,14 +193,11 @@ public class IntroductionMessageFragment extends BaseFragment
 	}
 
 	@Override
-	public void onSendClick(@NonNull String text) {
+	public void onSendClick(@Nullable String text, List<Uri> imageUris) {
 		// disable button to prevent accidental double invitations
-		ui.message.setSendButtonEnabled(false);
+		ui.message.setEnabled(false);
 
-		String txt = ui.message.getText().toString();
+		makeIntroduction(contact1, contact2, text);
-		if (txt.isEmpty()) txt = null;
-		else txt = StringUtils.truncateUtf8(txt, MAX_INTRODUCTION_TEXT_LENGTH);
-		makeIntroduction(contact1, contact2, txt);
 
 		// don't wait for the introduction to be made before finishing activity
 		introductionActivity.hideSoftKeyboard(ui.message);

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/ContactExchangeErrorFragment.java

@@ -44,6 +44,11 @@ public class ContactExchangeErrorFragment extends BaseFragment {
 		return TAG;
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
 	@Nullable
 	@Override
 	public View onCreateView(LayoutInflater inflater,
@@ -74,11 +79,6 @@ public class ContactExchangeErrorFragment extends BaseFragment {
 		return v;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	private void triggerFeedback() {
 		finish();
 		UiUtils.triggerFeedback(androidExecutor);

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/IntroFragment.java

@@ -10,7 +10,6 @@ import android.widget.ScrollView;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
-import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.fragment.BaseFragment;
 
 import javax.annotation.Nullable;
@@ -39,11 +38,6 @@ public class IntroFragment extends BaseFragment {
 		return fragment;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	@Override
 	public void onAttach(Context context) {
 		super.onAttach(context);

briar-android/src/main/java/org/briarproject/briar/android/keyagreement/KeyAgreementFragment.java

@@ -53,6 +53,7 @@ import static android.view.View.VISIBLE;
 import static android.view.ViewGroup.LayoutParams.MATCH_PARENT;
 import static android.widget.LinearLayout.HORIZONTAL;
 import static android.widget.Toast.LENGTH_LONG;
+import static java.util.Objects.requireNonNull;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static org.briarproject.bramble.util.LogUtils.logException;
@@ -136,7 +137,8 @@ public class KeyAgreementFragment extends BaseEventFragment
 	@Override
 	public void onActivityCreated(@Nullable Bundle savedInstanceState) {
 		super.onActivityCreated(savedInstanceState);
-		getActivity().setRequestedOrientation(SCREEN_ORIENTATION_NOSENSOR);
+		requireNonNull(getActivity())
+				.setRequestedOrientation(SCREEN_ORIENTATION_NOSENSOR);
 		cameraView.setPreviewConsumer(new QrCodeDecoder(this));
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/login/AuthorNameFragment.java

@@ -18,6 +18,7 @@ import javax.annotation.Nullable;
 
 import static android.view.inputmethod.EditorInfo.IME_ACTION_NEXT;
 import static android.view.inputmethod.EditorInfo.IME_ACTION_NONE;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.bramble.api.identity.AuthorConstants.MAX_AUTHOR_NAME_LENGTH;
 import static org.briarproject.briar.android.util.UiUtils.setError;
 
@@ -35,11 +36,16 @@ public class AuthorNameFragment extends SetupFragment {
 		return new AuthorNameFragment();
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-		getActivity().setTitle(getString(R.string.setup_title));
+		requireNonNull(getActivity()).setTitle(getString(R.string.setup_title));
 		View v = inflater.inflate(R.layout.fragment_setup_author_name,
 				container, false);
 		authorNameWrapper = v.findViewById(R.id.nickname_entry_wrapper);
@@ -57,11 +63,6 @@ public class AuthorNameFragment extends SetupFragment {
 		return TAG;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	@Override
 	protected String getHelpText() {
 		return getString(R.string.setup_name_explanation);

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

@@ -19,6 +19,7 @@ import org.briarproject.briar.android.util.UiUtils;
 
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_DOZE_WHITELISTING;
 import static org.briarproject.briar.android.util.UiUtils.showOnboardingDialog;
 
@@ -39,11 +40,16 @@ public class DozeFragment extends SetupFragment
 		return new DozeFragment();
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-		getActivity().setTitle(getString(R.string.setup_doze_title));
+		requireNonNull(getActivity()).setTitle(getString(R.string.setup_doze_title));
 		setHasOptionsMenu(false);
 		View v = inflater.inflate(R.layout.fragment_setup_doze, container,
 						false);
@@ -65,11 +71,6 @@ public class DozeFragment extends SetupFragment
 		return TAG;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-	}
-
 	@Override
 	protected String getHelpText() {
 		return getString(R.string.setup_doze_explanation);

briar-android/src/main/java/org/briarproject/briar/android/login/PasswordFragment.java

@@ -23,6 +23,7 @@ import static android.content.Context.INPUT_METHOD_SERVICE;
 import static android.view.View.INVISIBLE;
 import static android.view.View.VISIBLE;
 import static android.view.inputmethod.EditorInfo.IME_ACTION_DONE;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.bramble.api.crypto.PasswordStrengthEstimator.QUITE_WEAK;
 
 @MethodsNotNullByDefault
@@ -43,11 +44,16 @@ public class PasswordFragment extends SetupFragment {
 		return new PasswordFragment();
 	}
 
+	@Override
+	public void injectFragment(ActivityComponent component) {
+		component.inject(this);
+	}
+
 	@Override
 	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
-		getActivity().setTitle(getString(R.string.setup_password_intro));
+		requireNonNull(getActivity()).setTitle(getString(R.string.setup_password_intro));
 		View v = inflater.inflate(R.layout.fragment_setup_password, container,
 						false);
 
@@ -64,6 +70,11 @@ public class PasswordFragment extends SetupFragment {
 		passwordConfirmation.addTextChangedListener(this);
 		nextButton.setOnClickListener(this);
 
+		if (!setupController.needToShowDozeFragment()) {
+			nextButton.setText(R.string.create_account_button);
+			passwordConfirmation.setImeOptions(IME_ACTION_DONE);
+		}
+
 		return v;
 	}
 
@@ -72,17 +83,6 @@ public class PasswordFragment extends SetupFragment {
 		return TAG;
 	}
 
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		component.inject(this);
-
-		// the controller is not yet available in onCreateView()
-		if (!setupController.needToShowDozeFragment()) {
-			nextButton.setText(R.string.create_account_button);
-			passwordConfirmation.setImeOptions(IME_ACTION_DONE);
-		}
-	}
-
 	@Override
 	protected String getHelpText() {
 		return getString(R.string.setup_password_explanation);

briar-android/src/main/java/org/briarproject/briar/android/login/SetupFragment.java

@@ -11,7 +11,8 @@ import android.view.View.OnClickListener;
 import android.widget.TextView;
 import android.widget.TextView.OnEditorActionListener;
 
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
 import org.briarproject.briar.android.fragment.BaseFragment;
 
@@ -22,7 +23,8 @@ import static android.view.inputmethod.EditorInfo.IME_ACTION_NEXT;
 import static org.briarproject.briar.android.util.UiUtils.enterPressed;
 import static org.briarproject.briar.android.util.UiUtils.showOnboardingDialog;
 
-@NotNullByDefault
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 abstract class SetupFragment extends BaseFragment implements TextWatcher,
 		OnEditorActionListener, OnClickListener {
 

briar-android/src/main/java/org/briarproject/briar/android/logout/ExitActivity.java

@@ -1,14 +1,13 @@
 package org.briarproject.briar.android.logout;
 
-import android.os.Build;
+import android.app.Activity;
 import android.os.Bundle;
 
-import org.briarproject.briar.android.activity.ActivityComponent;
-import org.briarproject.briar.android.activity.BaseActivity;
-
 import java.util.logging.Logger;
 
-public class ExitActivity extends BaseActivity {
+import static android.os.Build.VERSION.SDK_INT;
+
+public class ExitActivity extends Activity {
 
 	private static final Logger LOG =
 			Logger.getLogger(ExitActivity.class.getName());
@@ -16,14 +15,9 @@ public class ExitActivity extends BaseActivity {
 	@Override
 	public void onCreate(Bundle state) {
 		super.onCreate(state);
-		if (Build.VERSION.SDK_INT >= 21) finishAndRemoveTask();
+		if (SDK_INT >= 21) finishAndRemoveTask();
 		else finish();
 		LOG.info("Exiting");
 		System.exit(0);
 	}
-
-	@Override
-	public void injectActivity(ActivityComponent component) {
-
-	}
 }

briar-android/src/main/java/org/briarproject/briar/android/logout/HideUiActivity.java

@@ -1,20 +1,13 @@
 package org.briarproject.briar.android.logout;
 
+import android.app.Activity;
 import android.os.Bundle;
 
-import org.briarproject.briar.android.activity.ActivityComponent;
+public class HideUiActivity extends Activity {
-import org.briarproject.briar.android.activity.BaseActivity;
-
-public class HideUiActivity extends BaseActivity {
 
 	@Override
 	public void onCreate(Bundle state) {
 		super.onCreate(state);
 		finish();
 	}
-
-	@Override
-	public void injectActivity(ActivityComponent component) {
-
-	}
 }

briar-android/src/main/java/org/briarproject/briar/android/logout/SignOutFragment.java

@@ -5,19 +5,21 @@ import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.briar.R;
-import org.briarproject.briar.android.activity.ActivityComponent;
 import org.briarproject.briar.android.fragment.BaseFragment;
 
-import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class SignOutFragment extends BaseFragment {
 
 	public static final String TAG = SignOutFragment.class.getName();
 
 	@Override
-	public View onCreateView(@Nonnull LayoutInflater inflater,
+	public View onCreateView(LayoutInflater inflater,
 			@Nullable ViewGroup container,
 			@Nullable Bundle savedInstanceState) {
 		return inflater.inflate(R.layout.fragment_sign_out, container, false);
@@ -27,9 +29,4 @@ public class SignOutFragment extends BaseFragment {
 	public String getUniqueTag() {
 		return TAG;
 	}
-
-	@Override
-	public void injectFragment(ActivityComponent component) {
-		// no need to inject
-	}
 }

briar-android/src/main/java/org/briarproject/briar/android/navdrawer/NavDrawerActivity.java

@@ -5,6 +5,7 @@ import android.content.Intent;
 import android.content.res.Configuration;
 import android.os.Bundle;
 import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.NavigationView;
 import android.support.design.widget.NavigationView.OnNavigationItemSelectedListener;
 import android.support.v4.app.ActivityCompat;
@@ -12,6 +13,7 @@ import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentTransaction;
 import android.support.v4.content.ContextCompat;
 import android.support.v4.widget.DrawerLayout;
+import android.support.v7.app.ActionBar;
 import android.support.v7.app.ActionBarDrawerToggle;
 import android.support.v7.widget.Toolbar;
 import android.view.LayoutInflater;
@@ -25,6 +27,8 @@ import android.widget.TextView;
 
 import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
+import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
+import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
 import org.briarproject.bramble.api.plugin.BluetoothConstants;
 import org.briarproject.bramble.api.plugin.LanTcpConstants;
 import org.briarproject.bramble.api.plugin.TorConstants;
@@ -54,6 +58,7 @@ import static android.support.v4.view.GravityCompat.START;
 import static android.support.v4.widget.DrawerLayout.LOCK_MODE_LOCKED_CLOSED;
 import static android.view.View.GONE;
 import static android.view.View.VISIBLE;
+import static java.util.Objects.requireNonNull;
 import static org.briarproject.bramble.api.lifecycle.LifecycleManager.LifecycleState.RUNNING;
 import static org.briarproject.briar.android.BriarService.EXTRA_STARTUP_FAILED;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_PASSWORD;
@@ -61,6 +66,8 @@ import static org.briarproject.briar.android.navdrawer.NavDrawerController.Expir
 import static org.briarproject.briar.android.navdrawer.NavDrawerController.ExpiryWarning.UPDATE;
 import static org.briarproject.briar.android.util.UiUtils.getDaysUntilExpiry;
 
+@MethodsNotNullByDefault
+@ParametersNotNullByDefault
 public class NavDrawerActivity extends BriarActivity implements
 		BaseFragmentListener, TransportStateListener,
 		OnNavigationItemSelectedListener {
@@ -112,9 +119,8 @@ public class NavDrawerActivity extends BriarActivity implements
 		component.inject(this);
 	}
 
-	@SuppressWarnings("ConstantConditions")
 	@Override
-	public void onCreate(Bundle state) {
+	public void onCreate(@Nullable Bundle state) {
 		super.onCreate(state);
 		exitIfStartupFailed(getIntent());
 		setContentView(R.layout.activity_nav_drawer);
@@ -125,8 +131,9 @@ public class NavDrawerActivity extends BriarActivity implements
 		GridView transportsView = findViewById(R.id.transportsView);
 
 		setSupportActionBar(toolbar);
-		getSupportActionBar().setDisplayHomeAsUpEnabled(true);
+		ActionBar actionBar = requireNonNull(getSupportActionBar());
-		getSupportActionBar().setHomeButtonEnabled(true);
+		actionBar.setDisplayHomeAsUpEnabled(true);
+		actionBar.setHomeButtonEnabled(true);
 
 		drawerToggle = new ActionBarDrawerToggle(this, drawerLayout, toolbar,
 				R.string.nav_drawer_open_description,
@@ -165,7 +172,8 @@ public class NavDrawerActivity extends BriarActivity implements
 	}
 
 	@Override
-	protected void onActivityResult(int request, int result, Intent data) {
+	protected void onActivityResult(int request, int result,
+			@Nullable Intent data) {
 		super.onActivityResult(request, result, data);
 		if (request == REQUEST_PASSWORD && result == RESULT_OK) {
 			controller.shouldAskForDozeWhitelisting(this,
@@ -253,7 +261,7 @@ public class NavDrawerActivity extends BriarActivity implements
 	}
 
 	@Override
-	public void onPostCreate(Bundle savedInstanceState) {
+	public void onPostCreate(@Nullable Bundle savedInstanceState) {
 		super.onPostCreate(savedInstanceState);
 		drawerToggle.syncState();
 	}