Add new module to integration tests.

Add ImageActivity to show image attachment in full-screen

See merge request briar/briar!999

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

@@ -208,6 +208,24 @@ public interface DatabaseComponent {
 	Collection<Message> generateRequestedBatch(Transaction txn, ContactId c,
 			int maxLength, int maxLatency) throws DbException;
 
+	/**
+	 * Returns the number of blocks in the given message.
+	 * <p>
+	 * Read-only.
+	 */
+	int getBlockCount(Transaction txn, MessageId m) throws DbException;
+
+	/**
+	 * Returns the given block of the given message.
+	 * <p>
+	 * Read-only.
+	 *
+	 * @throws NoSuchBlockException if 'blockNumber' is greater than or equal
+	 * to the number of blocks in the message
+	 */
+	byte[] getBlock(Transaction txn, MessageId m, int blockNumber)
+			throws DbException;
+
 	/**
 	 * Returns the contact with the given ID.
 	 * <p/>

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

@@ -0,0 +1,9 @@
+package org.briarproject.bramble.api.db;
+
+/**
+ * Thrown when a database operation is attempted for a block that is not in
+ * the database. This exception may occur due to concurrent updates and does
+ * not indicate a database error.
+ */
+public class NoSuchBlockException extends DbException {
+}

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

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.api.io;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.NoSuchBlockException;
+import org.briarproject.bramble.api.sync.MessageId;
+
+public interface BlockSource {
+
+	/**
+	 * Returns the number of blocks in the given message.
+	 */
+	int getBlockCount(MessageId m) throws DbException;
+
+	/**
+	 * Returns the given block of the given message.
+	 *
+	 * @throws NoSuchBlockException if 'blockNumber' is greater than or equal
+	 * to the number of blocks in the message
+	 */
+	byte[] getBlock(MessageId m, int blockNumber) throws DbException;
+}

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

@@ -0,0 +1,17 @@
+package org.briarproject.bramble.api.io;
+
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.io.IOException;
+import java.io.InputStream;
+
+public interface MessageInputStreamFactory {
+
+	/**
+	 * Returns an {@link InputStream} for reading the given message from the
+	 * database. This method returns immediately. If the message is not in the
+	 * database or cannot be read, reading from the stream will throw an
+	 * {@link IOException};
+	 */
+	InputStream getMessageInputStream(MessageId m);
+}

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

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

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

@@ -9,6 +9,7 @@ import org.briarproject.bramble.db.DatabaseExecutorModule;
 import org.briarproject.bramble.db.DatabaseModule;
 import org.briarproject.bramble.event.EventModule;
 import org.briarproject.bramble.identity.IdentityModule;
+import org.briarproject.bramble.io.IoModule;
 import org.briarproject.bramble.keyagreement.KeyAgreementModule;
 import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.plugin.PluginModule;
@@ -36,6 +37,7 @@ import dagger.Module;
 		DatabaseExecutorModule.class,
 		EventModule.class,
 		IdentityModule.class,
+		IoModule.class,
 		KeyAgreementModule.class,
 		LifecycleModule.class,
 		PluginModule.class,

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

@@ -0,0 +1,29 @@
+package org.briarproject.bramble.db;
+
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.io.BlockSource;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import javax.inject.Inject;
+
+class BlockSourceImpl implements BlockSource {
+
+	private final DatabaseComponent db;
+
+	@Inject
+	BlockSourceImpl(DatabaseComponent db) {
+		this.db = db;
+	}
+
+	@Override
+	public int getBlockCount(MessageId m) throws DbException {
+		return db.transactionWithResult(true, txn -> db.getBlockCount(txn, m));
+	}
+
+	@Override
+	public byte[] getBlock(MessageId m, int blockNumber) throws DbException {
+		return db.transactionWithResult(true, txn ->
+				db.getBlock(txn, m, blockNumber));
+	}
+}

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

@@ -14,6 +14,7 @@ import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.db.DbRunnable;
 import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.MigrationListener;
+import org.briarproject.bramble.api.db.NoSuchBlockException;
 import org.briarproject.bramble.api.db.NoSuchContactException;
 import org.briarproject.bramble.api.db.NoSuchGroupException;
 import org.briarproject.bramble.api.db.NoSuchLocalAuthorException;
@@ -420,6 +421,26 @@ class DatabaseComponentImpl<T> implements DatabaseComponent {
 		return messages;
 	}
 
+	@Override
+	public int getBlockCount(Transaction transaction, MessageId m)
+			throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsMessage(txn, m))
+			throw new NoSuchMessageException();
+		return 1;
+	}
+
+	@Override
+	public byte[] getBlock(Transaction transaction, MessageId m,
+			int blockNumber) throws DbException {
+		T txn = unbox(transaction);
+		if (!db.containsMessage(txn, m))
+			throw new NoSuchMessageException();
+		if (blockNumber != 0)
+			throw new NoSuchBlockException();
+		return db.getMessage(txn, m).getBody();
+	}
+
 	@Override
 	public Contact getContact(Transaction transaction, ContactId c)
 			throws DbException {

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

@@ -3,6 +3,7 @@ package org.briarproject.bramble.db;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseConfig;
 import org.briarproject.bramble.api.event.EventBus;
+import org.briarproject.bramble.api.io.BlockSource;
 import org.briarproject.bramble.api.lifecycle.ShutdownManager;
 import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.system.Clock;
@@ -31,4 +32,9 @@ public class DatabaseModule {
 		return new DatabaseComponentImpl<>(db, Connection.class, eventBus,
 				shutdown);
 	}
+
+	@Provides
+	BlockSource provideBlockSource(BlockSourceImpl blockSource) {
+		return blockSource;
+	}
 }

bramble-core/src/main/java/org/briarproject/bramble/io/BlockInputStream.java

@@ -0,0 +1,155 @@
+package org.briarproject.bramble.io;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InterruptedIOException;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+import static java.lang.System.arraycopy;
+import static java.lang.Thread.currentThread;
+
+/**
+ * An {@link InputStream} that asynchronously fetches blocks of data on demand.
+ */
+@ThreadSafe
+@NotNullByDefault
+abstract class BlockInputStream extends InputStream {
+
+	private final int minBufferBytes;
+	private final BlockingQueue<Buffer> queue = new ArrayBlockingQueue<>(1);
+	private final Object lock = new Object();
+
+	@GuardedBy("lock")
+	@Nullable
+	private Buffer buffer = null;
+
+	@GuardedBy("lock")
+	private int offset = 0;
+
+	@GuardedBy("lock")
+	private boolean fetchingBlock = false;
+
+	abstract void fetchBlockAsync(int blockNumber);
+
+	BlockInputStream(int minBufferBytes) {
+		this.minBufferBytes = minBufferBytes;
+	}
+
+	@Override
+	public int read() throws IOException {
+		synchronized (lock) {
+			if (!prepareRead()) return -1;
+			if (buffer == null) throw new AssertionError();
+			return buffer.data[offset++] & 0xFF;
+		}
+	}
+
+	@Override
+	public int read(byte[] b) throws IOException {
+		return read(b, 0, b.length);
+	}
+
+	@Override
+	public int read(byte[] b, int off, int len) throws IOException {
+		if (off < 0 || len < 0 || off + len > b.length)
+			throw new IllegalArgumentException();
+		synchronized (lock) {
+			if (!prepareRead()) return -1;
+			if (buffer == null) throw new AssertionError();
+			len = Math.min(len, buffer.length - offset);
+			if (len < 0) throw new AssertionError();
+			arraycopy(buffer.data, offset, b, off, len);
+			offset += len;
+			return len;
+		}
+	}
+
+	private boolean prepareRead() throws IOException {
+		throwExceptionIfNecessary();
+		if (isEndOfStream()) return false;
+		if (shouldFetchBlock()) fetchBlockAsync();
+		waitForBlock();
+		if (buffer == null) throw new AssertionError();
+		return offset < buffer.length;
+	}
+
+	@GuardedBy("lock")
+	private void throwExceptionIfNecessary() throws IOException {
+		if (buffer != null && buffer.exception != null)
+			throw new IOException(buffer.exception);
+	}
+
+	@GuardedBy("lock")
+	private boolean isEndOfStream() {
+		return buffer != null && offset == buffer.length && !fetchingBlock;
+	}
+
+	@GuardedBy("lock")
+	private boolean shouldFetchBlock() {
+		if (fetchingBlock) return false;
+		if (buffer == null) return true;
+		if (buffer.length == 0) return false;
+		return buffer.length - offset < minBufferBytes;
+	}
+
+	@GuardedBy("lock")
+	private void fetchBlockAsync() {
+		if (buffer == null) fetchBlockAsync(0);
+		else fetchBlockAsync(buffer.blockNumber + 1);
+		fetchingBlock = true;
+	}
+
+	@GuardedBy("lock")
+	private void waitForBlock() throws IOException {
+		if (buffer != null && offset < buffer.length) return;
+		try {
+			buffer = queue.take();
+		} catch (InterruptedException e) {
+			currentThread().interrupt();
+			throw new InterruptedIOException();
+		}
+		fetchingBlock = false;
+		offset = 0;
+		throwExceptionIfNecessary();
+	}
+
+	void fetchSucceeded(int blockNumber, byte[] data, int length) {
+		queue.add(new Buffer(blockNumber, data, length));
+	}
+
+	void fetchFailed(int blockNumber, Exception exception) {
+		queue.add(new Buffer(blockNumber, exception));
+	}
+
+	private static class Buffer {
+
+		private final int blockNumber;
+		private final byte[] data;
+		private final int length;
+		@Nullable
+		private final Exception exception;
+
+		private Buffer(int blockNumber, byte[] data, int length) {
+			if (length < 0 || length > data.length)
+				throw new IllegalArgumentException();
+			this.blockNumber = blockNumber;
+			this.data = data;
+			this.length = length;
+			exception = null;
+		}
+
+		private Buffer(int blockNumber, Exception exception) {
+			this.blockNumber = blockNumber;
+			this.exception = exception;
+			data = new byte[0];
+			length = 0;
+		}
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/io/BlockSourceInputStream.java

@@ -0,0 +1,53 @@
+package org.briarproject.bramble.io;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.io.BlockSource;
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.util.concurrent.Executor;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * A {@link BlockInputStream} that fetches data from a {@link BlockSource}.
+ */
+@ThreadSafe
+@NotNullByDefault
+class BlockSourceInputStream extends BlockInputStream {
+
+	private final Executor executor;
+	private final BlockSource blockSource;
+	private final MessageId messageId;
+
+	private volatile int blockCount = -1;
+
+	BlockSourceInputStream(int minBufferBytes, Executor executor,
+			BlockSource blockSource, MessageId messageId) {
+		super(minBufferBytes);
+		this.executor = executor;
+		this.blockSource = blockSource;
+		this.messageId = messageId;
+	}
+
+	@Override
+	void fetchBlockAsync(int blockNumber) {
+		executor.execute(() -> {
+			try {
+				if (blockCount == -1) {
+					blockCount = blockSource.getBlockCount(messageId);
+				}
+				if (blockNumber > blockCount) {
+					fetchFailed(blockNumber, new IllegalArgumentException());
+				} else if (blockNumber == blockCount) {
+					fetchSucceeded(blockNumber, new byte[0], 0); // EOF
+				} else {
+					byte[] block = blockSource.getBlock(messageId, blockNumber);
+					fetchSucceeded(blockNumber, block, block.length);
+				}
+			} catch (DbException e) {
+				fetchFailed(blockNumber, e);
+			}
+		});
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/io/IoModule.java

@@ -0,0 +1,16 @@
+package org.briarproject.bramble.io;
+
+import org.briarproject.bramble.api.io.MessageInputStreamFactory;
+
+import dagger.Module;
+import dagger.Provides;
+
+@Module
+public class IoModule {
+
+	@Provides
+	MessageInputStreamFactory provideMessageInputStreamFactory(
+			MessageInputStreamFactoryImpl messageInputStreamFactory) {
+		return messageInputStreamFactory;
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/io/MessageInputStreamFactoryImpl.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.io;
+
+import org.briarproject.bramble.api.db.DatabaseExecutor;
+import org.briarproject.bramble.api.io.BlockSource;
+import org.briarproject.bramble.api.io.MessageInputStreamFactory;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import java.io.InputStream;
+import java.util.concurrent.Executor;
+
+import javax.inject.Inject;
+
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_BLOCK_LENGTH;
+
+class MessageInputStreamFactoryImpl implements MessageInputStreamFactory {
+
+	private final Executor dbExecutor;
+	private final BlockSource blockSource;
+
+	@Inject
+	MessageInputStreamFactoryImpl(@DatabaseExecutor Executor dbExecutor,
+			BlockSource blockSource) {
+		this.dbExecutor = dbExecutor;
+		this.blockSource = blockSource;
+	}
+
+	@Override
+	public InputStream getMessageInputStream(MessageId m) {
+		return new BlockSourceInputStream(MAX_BLOCK_LENGTH, dbExecutor,
+				blockSource, m);
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/io/BlockSourceInputStreamTest.java

@@ -0,0 +1,151 @@
+package org.briarproject.bramble.io;
+
+import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.io.BlockSource;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.bramble.test.BrambleMockTestCase;
+import org.jmock.Expectations;
+import org.jmock.lib.concurrent.Synchroniser;
+import org.junit.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.util.Random;
+import java.util.concurrent.Executor;
+
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_BLOCK_LENGTH;
+import static org.briarproject.bramble.test.TestUtils.getRandomId;
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.spongycastle.util.Arrays.copyOfRange;
+
+public class BlockSourceInputStreamTest extends BrambleMockTestCase {
+
+	private static final int MAX_DATA_BYTES = 1_000_000;
+	private static final int READ_BUFFER_BYTES = 4 * 1024;
+
+	private final BlockSource blockSource;
+
+	private final Random random = new Random();
+	private final Executor executor = newSingleThreadExecutor();
+	private final MessageId messageId = new MessageId(getRandomId());
+
+	public BlockSourceInputStreamTest() {
+		context.setThreadingPolicy(new Synchroniser());
+		blockSource = context.mock(BlockSource.class);
+	}
+
+	@Test
+	public void testReadSingleBytes() throws IOException {
+		byte[] data = createRandomData();
+		BlockSource source = new ByteArrayBlockSource(data, MAX_BLOCK_LENGTH);
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
+				source, messageId);
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		//noinspection ForLoopReplaceableByForEach
+		for (int i = 0; i < data.length; i++) {
+			int read = in.read();
+			assertNotEquals(-1, read);
+			out.write(read);
+		}
+		assertEquals(-1, in.read());
+		in.close();
+		out.flush();
+		out.close();
+		assertArrayEquals(data, out.toByteArray());
+	}
+
+	@Test
+	public void testReadByteArrays() throws IOException {
+		byte[] data = createRandomData();
+		BlockSource source = new ByteArrayBlockSource(data, MAX_BLOCK_LENGTH);
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
+				source, messageId);
+		ByteArrayOutputStream out = new ByteArrayOutputStream();
+		byte[] buf = new byte[READ_BUFFER_BYTES];
+		int dataOffset = 0;
+		while (dataOffset < data.length) {
+			int length = Math.min(random.nextInt(buf.length) + 1,
+					data.length - dataOffset);
+			int bufOffset = 0;
+			if (length < buf.length)
+				bufOffset = random.nextInt(buf.length - length);
+			int read = in.read(buf, bufOffset, length);
+			assertNotEquals(-1, read);
+			out.write(buf, bufOffset, read);
+			dataOffset += read;
+		}
+		assertEquals(-1, in.read(buf, 0, 0));
+		in.close();
+		out.flush();
+		out.close();
+		assertArrayEquals(data, out.toByteArray());
+	}
+
+	@Test(expected = IOException.class)
+	public void testDbExceptionFromGetBlockCountIsRethrown() throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(blockSource).getBlockCount(messageId);
+			will(throwException(new DbException()));
+		}});
+
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
+				blockSource, messageId);
+		//noinspection ResultOfMethodCallIgnored
+		in.read();
+	}
+
+	@Test(expected = IOException.class)
+	public void testDbExceptionFromGetBlockIsRethrown() throws Exception {
+		context.checking(new Expectations() {{
+			oneOf(blockSource).getBlockCount(messageId);
+			will(returnValue(1));
+			oneOf(blockSource).getBlock(messageId, 0);
+			will(throwException(new DbException()));
+		}});
+
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
+				blockSource, messageId);
+		//noinspection ResultOfMethodCallIgnored
+		in.read();
+	}
+
+	@Test
+	public void testReadFullBlockAtEndOfMessage() throws Exception {
+		testReadBlockAtEndOfMessage(MAX_BLOCK_LENGTH);
+	}
+
+	@Test
+	public void testReadPartialBlockAtEndOfMessage() throws Exception {
+		testReadBlockAtEndOfMessage(MAX_BLOCK_LENGTH - 1);
+	}
+
+	private void testReadBlockAtEndOfMessage(int blockLength) throws Exception {
+		byte[] block = new byte[blockLength];
+		random.nextBytes(block);
+
+		context.checking(new Expectations() {{
+			oneOf(blockSource).getBlockCount(messageId);
+			will(returnValue(1));
+			oneOf(blockSource).getBlock(messageId, 0);
+			will(returnValue(block));
+		}});
+
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
+				blockSource, messageId);
+		byte[] buf = new byte[MAX_BLOCK_LENGTH * 2];
+		assertEquals(block.length, in.read(buf, 0, buf.length));
+		assertArrayEquals(block, copyOfRange(buf, 0, block.length));
+		assertEquals(-1, in.read(buf, 0, buf.length));
+	}
+
+	private byte[] createRandomData() {
+		int length = random.nextInt(MAX_DATA_BYTES) + 1;
+		byte[] data = new byte[length];
+		random.nextBytes(data);
+		return data;
+	}
+}

bramble-core/src/test/java/org/briarproject/bramble/io/ByteArrayBlockSource.java

@@ -0,0 +1,32 @@
+package org.briarproject.bramble.io;
+
+import org.briarproject.bramble.api.io.BlockSource;
+import org.briarproject.bramble.api.sync.MessageId;
+
+import static java.lang.System.arraycopy;
+
+class ByteArrayBlockSource implements BlockSource {
+
+	private final byte[] data;
+	private final int blockBytes;
+
+	ByteArrayBlockSource(byte[] data, int blockBytes) {
+		this.data = data;
+		this.blockBytes = blockBytes;
+	}
+
+	@Override
+	public int getBlockCount(MessageId m) {
+		return (data.length + blockBytes - 1) / blockBytes;
+	}
+
+	@Override
+	public byte[] getBlock(MessageId m, int blockNumber) {
+		int offset = blockNumber * blockBytes;
+		if (offset >= data.length) throw new IllegalArgumentException();
+		int length = Math.min(blockBytes, data.length - offset);
+		byte[] block = new byte[length];
+		arraycopy(data, offset, block, 0, length);
+		return block;
+	}
+}

briar-android/build.gradle

@@ -123,6 +123,7 @@ dependencies {
 		exclude group: 'com.android.support'
 		exclude module: 'disklrucache' // when there's no disk cache, we can't accidentally use it
 	}
+	implementation 'com.github.chrisbanes:PhotoView:2.1.4' // later versions already use androidx
 
 	annotationProcessor 'com.google.dagger:dagger-compiler:2.19'
 	annotationProcessor "com.github.bumptech.glide:compiler:$glideVersion"

briar-android/src/main/AndroidManifest.xml

@@ -113,6 +113,15 @@
 				/>
 		</activity>
 
+		<activity
+			android:name=".android.conversation.ImageActivity"
+			android:parentActivityName="org.briarproject.briar.android.conversation.ConversationActivity"
+			android:theme="@style/BriarTheme.Transparent.NoActionBar">
+			<meta-data
+				android:name="android.support.PARENT_ACTIVITY"
+				android:value="org.briarproject.briar.android.conversation.ConversationActivity"/>
+		</activity>
+
 		<activity
 			android:name="org.briarproject.briar.android.privategroup.creation.CreateGroupActivity"
 			android:label="@string/groups_create_group_title"

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

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

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

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

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

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

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

@@ -1,5 +1,8 @@
 package org.briarproject.briar.android.conversation;
 
+import android.os.Parcel;
+import android.os.Parcelable;
+
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.MessageId;
 
@@ -7,13 +10,26 @@ import javax.annotation.concurrent.Immutable;
 
 @Immutable
 @NotNullByDefault
-public class AttachmentItem {
+public class AttachmentItem implements Parcelable {
 
 	private final MessageId messageId;
 	private final int width, height;
 	private final int thumbnailWidth, thumbnailHeight;
 	private final boolean hasError;
 
+	public static final Creator<AttachmentItem> CREATOR =
+			new Creator<AttachmentItem>() {
+				@Override
+				public AttachmentItem createFromParcel(Parcel in) {
+					return new AttachmentItem(in);
+				}
+
+				@Override
+				public AttachmentItem[] newArray(int size) {
+					return new AttachmentItem[size];
+				}
+			};
+
 	AttachmentItem(MessageId messageId, int width, int height,
 			int thumbnailWidth, int thumbnailHeight, boolean hasError) {
 		this.messageId = messageId;
@@ -24,6 +40,17 @@ public class AttachmentItem {
 		this.hasError = hasError;
 	}
 
+	protected AttachmentItem(Parcel in) {
+		byte[] messageIdByte = new byte[MessageId.LENGTH];
+		in.readByteArray(messageIdByte);
+		messageId = new MessageId(messageIdByte);
+		width = in.readInt();
+		height = in.readInt();
+		thumbnailWidth = in.readInt();
+		thumbnailHeight = in.readInt();
+		hasError = in.readByte() != 0;
+	}
+
 	public MessageId getMessageId() {
 		return messageId;
 	}
@@ -48,4 +75,24 @@ public class AttachmentItem {
 		return hasError;
 	}
 
+	// TODO use counter instead, because in theory one attachment can appear in more than one messages
+	String getTransitionName() {
+		return String.valueOf(messageId.hashCode());
+	}
+
+	@Override
+	public int describeContents() {
+		return 0;
+	}
+
+	@Override
+	public void writeToParcel(Parcel dest, int flags) {
+		dest.writeByteArray(messageId.getBytes());
+		dest.writeInt(width);
+		dest.writeInt(height);
+		dest.writeInt(thumbnailWidth);
+		dest.writeInt(thumbnailHeight);
+		dest.writeByte((byte) (hasError ? 1 : 0));
+	}
+
 }

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

@@ -9,11 +9,15 @@ import android.os.Bundle;
 import android.support.annotation.Nullable;
 import android.support.annotation.UiThread;
 import android.support.design.widget.Snackbar;
+import android.support.v4.app.ActivityCompat;
+import android.support.v4.app.ActivityOptionsCompat;
 import android.support.v4.content.ContextCompat;
 import android.support.v7.app.AlertDialog;
 import android.support.v7.widget.ActionMenuView;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.Toolbar;
+import android.transition.Slide;
+import android.transition.Transition;
 import android.util.SparseArray;
 import android.view.Menu;
 import android.view.MenuInflater;
@@ -96,8 +100,11 @@ import im.delight.android.identicons.IdenticonDrawable;
 import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt;
 import uk.co.samuelwall.materialtaptargetprompt.MaterialTapTargetPrompt.PromptStateChangeListener;
 
+import static android.os.Build.VERSION.SDK_INT;
+import static android.support.v4.app.ActivityOptionsCompat.makeSceneTransitionAnimation;
 import static android.support.v4.view.ViewCompat.setTransitionName;
 import static android.support.v7.util.SortedList.INVALID_POSITION;
+import static android.view.Gravity.END;
 import static android.widget.Toast.LENGTH_SHORT;
 import static java.util.Collections.emptyList;
 import static java.util.Collections.sort;
@@ -108,6 +115,9 @@ import static org.briarproject.bramble.util.LogUtils.logDuration;
 import static org.briarproject.bramble.util.LogUtils.logException;
 import static org.briarproject.bramble.util.LogUtils.now;
 import static org.briarproject.briar.android.activity.RequestCodes.REQUEST_INTRODUCTION;
+import static org.briarproject.briar.android.conversation.ImageActivity.ATTACHMENT;
+import static org.briarproject.briar.android.conversation.ImageActivity.DATE;
+import static org.briarproject.briar.android.conversation.ImageActivity.NAME;
 import static org.briarproject.briar.android.settings.SettingsFragment.SETTINGS_NAMESPACE;
 import static org.briarproject.briar.android.util.UiUtils.getAvatarTransitionName;
 import static org.briarproject.briar.android.util.UiUtils.getBulbTransitionName;
@@ -186,7 +196,10 @@ public class ConversationActivity extends BriarActivity
 
 	@Override
 	public void onCreate(@Nullable Bundle state) {
-		setSceneTransitionAnimation();
+		if (SDK_INT >= 21) {
+			Transition slide = new Slide(END);
+			setSceneTransitionAnimation(slide, null, slide);
+		}
 		super.onCreate(state);
 
 		Intent i = getIntent();
@@ -802,6 +815,31 @@ public class ConversationActivity extends BriarActivity
 		startActivity(i);
 	}
 
+	@Override
+	public void onAttachmentClicked(View view,
+			ConversationMessageItem messageItem, AttachmentItem item) {
+		String name;
+		if (messageItem.isIncoming()) {
+			// must be available when items are being displayed
+			name = viewModel.getContactDisplayName().getValue();
+		} else {
+			name = getString(R.string.you);
+		}
+		Intent i = new Intent(this, ImageActivity.class);
+		i.putExtra(ATTACHMENT, item);
+		i.putExtra(NAME, name);
+		i.putExtra(DATE, messageItem.getTime());
+		if (SDK_INT >= 23) {
+			String transitionName = item.getTransitionName();
+			ActivityOptionsCompat options =
+					makeSceneTransitionAnimation(this, view, transitionName);
+			ActivityCompat.startActivity(this, i, options.toBundle());
+		} else {
+			// work-around for android bug #224270
+			startActivity(i);
+		}
+	}
+
 	@DatabaseExecutor
 	private void respondToIntroductionRequest(SessionId sessionId,
 			boolean accept, long time) throws DbException {
@@ -845,4 +883,5 @@ public class ConversationActivity extends BriarActivity
 		}
 		return attachments;
 	}
+
 }

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

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

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

@@ -85,7 +85,7 @@ class ConversationMessageViewHolder extends ConversationItemViewHolder {
 		if (item.getAttachments().isEmpty()) {
 			bindTextItem();
 		} else {
-			bindImageItem(item);
+			bindImageItem(item, listener);
 		}
 	}
 
@@ -98,7 +98,8 @@ class ConversationMessageViewHolder extends ConversationItemViewHolder {
 		textConstraints.applyTo(layout);
 	}
 
-	private void bindImageItem(ConversationMessageItem item) {
+	private void bindImageItem(ConversationMessageItem item,
+			ConversationListener listener) {
 		// TODO show more than just the first image
 		AttachmentItem attachment = item.getAttachments().get(0);
 
@@ -127,17 +128,18 @@ class ConversationMessageViewHolder extends ConversationItemViewHolder {
 			clearImage();
 			imageView.setImageResource(ERROR_RES);
 		} else {
-			loadImage(item, attachment);
+			loadImage(item, attachment, listener);
 		}
 	}
 
 	private void clearImage() {
 		GlideApp.with(imageView)
 				.clear(imageView);
+		imageView.setOnClickListener(null);
 	}
 
 	private void loadImage(ConversationMessageItem item,
-			AttachmentItem attachment) {
+			AttachmentItem attachment, ConversationListener listener) {
 		boolean leftCornerSmall =
 				(isIncoming() && !isRtl) || (!isIncoming() && isRtl);
 		boolean bottomRound = item.getText() == null;
@@ -152,6 +154,8 @@ class ConversationMessageViewHolder extends ConversationItemViewHolder {
 				.transition(withCrossFade())
 				.into(imageView)
 				.waitForLayout();
+		imageView.setOnClickListener(
+				view -> listener.onAttachmentClicked(view, item, attachment));
 	}
 
 }

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

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

briar-android/src/main/java/org/briarproject/briar/android/util/UiUtils.java

@@ -16,6 +16,7 @@ import android.support.annotation.ColorInt;
 import android.support.annotation.ColorRes;
 import android.support.annotation.MainThread;
 import android.support.annotation.Nullable;
+import android.support.annotation.RequiresApi;
 import android.support.design.widget.TextInputLayout;
 import android.support.v4.app.FragmentManager;
 import android.support.v4.content.ContextCompat;
@@ -31,6 +32,7 @@ import android.text.method.LinkMovementMethod;
 import android.text.style.ClickableSpan;
 import android.text.style.ForegroundColorSpan;
 import android.text.style.URLSpan;
+import android.transition.Transition;
 import android.util.TypedValue;
 import android.view.KeyEvent;
 import android.view.View;
@@ -60,12 +62,16 @@ import static android.support.v7.app.AppCompatDelegate.MODE_NIGHT_NO;
 import static android.support.v7.app.AppCompatDelegate.MODE_NIGHT_YES;
 import static android.support.v7.app.AppCompatDelegate.setDefaultNightMode;
 import static android.text.format.DateUtils.DAY_IN_MILLIS;
+import static android.text.format.DateUtils.FORMAT_ABBREV_ALL;
 import static android.text.format.DateUtils.FORMAT_ABBREV_MONTH;
 import static android.text.format.DateUtils.FORMAT_ABBREV_RELATIVE;
 import static android.text.format.DateUtils.FORMAT_ABBREV_TIME;
 import static android.text.format.DateUtils.FORMAT_SHOW_DATE;
+import static android.text.format.DateUtils.FORMAT_SHOW_TIME;
+import static android.text.format.DateUtils.FORMAT_SHOW_YEAR;
 import static android.text.format.DateUtils.MINUTE_IN_MILLIS;
 import static android.text.format.DateUtils.WEEK_IN_MILLIS;
+import static android.text.format.DateUtils.YEAR_IN_MILLIS;
 import static android.view.KeyEvent.ACTION_DOWN;
 import static android.view.KeyEvent.KEYCODE_ENTER;
 import static android.view.inputmethod.EditorInfo.IME_NULL;
@@ -117,6 +123,13 @@ public class UiUtils {
 				MIN_DATE_RESOLUTION, flags).toString();
 	}
 
+	public static String formatDateAbsolute(Context ctx, long time) {
+		int flags = FORMAT_SHOW_TIME | FORMAT_SHOW_DATE | FORMAT_ABBREV_ALL;
+		long diff = System.currentTimeMillis() - time;
+		if (diff >= YEAR_IN_MILLIS) flags |= FORMAT_SHOW_YEAR;
+		return DateUtils.formatDateTime(ctx, time, flags);
+	}
+
 	public static int getDaysUntilExpiry() {
 		long now = System.currentTimeMillis();
 		long daysBeforeExpiry = (EXPIRY_DATE - now) / 1000 / 60 / 60 / 24;
@@ -318,6 +331,12 @@ public class UiUtils {
 				keyEvent.getKeyCode() == KEYCODE_ENTER;
 	}
 
+	@RequiresApi(api = 21)
+	public static void excludeSystemUi(Transition transition) {
+		transition.excludeTarget(android.R.id.statusBarBackground, true);
+		transition.excludeTarget(android.R.id.navigationBarBackground, true);
+	}
+
 	/**
 	 * Observes the given {@link LiveData} until the first change.
 	 * If the LiveData's value is available, the {@link Observer} will be

briar-android/src/main/java/org/briarproject/briar/android/view/PullDownLayout.java

@@ -0,0 +1,161 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2015 XiNGRZ <xxx@oxo.ooo>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.briarproject.briar.android.view;
+
+import android.content.Context;
+import android.support.annotation.Nullable;
+import android.support.v4.view.ViewCompat;
+import android.support.v4.widget.ViewDragHelper;
+import android.util.AttributeSet;
+import android.view.MotionEvent;
+import android.view.View;
+import android.view.ViewConfiguration;
+import android.widget.FrameLayout;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+@NotNullByDefault
+public class PullDownLayout extends FrameLayout {
+
+	private final ViewDragHelper dragger;
+
+	private final int minimumFlingVelocity;
+
+	@Nullable
+	private Callback callback;
+
+	public PullDownLayout(Context context) {
+		this(context, null);
+	}
+
+	public PullDownLayout(Context context, @Nullable AttributeSet attrs) {
+		this(context, attrs, 0);
+	}
+
+	public PullDownLayout(Context context, @Nullable AttributeSet attrs,
+			int defStyleAttr) {
+		super(context, attrs, defStyleAttr);
+		dragger = ViewDragHelper.create(this, 1f / 8f, new ViewDragCallback());
+		minimumFlingVelocity =
+				ViewConfiguration.get(context).getScaledMinimumFlingVelocity();
+	}
+
+	public void setCallback(@Nullable Callback callback) {
+		this.callback = callback;
+	}
+
+	@Override
+	public boolean onInterceptTouchEvent(MotionEvent ev) {
+		return dragger.shouldInterceptTouchEvent(ev);
+	}
+
+	@Override
+	public boolean onTouchEvent(MotionEvent event) {
+		dragger.processTouchEvent(event);
+		return true;
+	}
+
+	@Override
+	public void computeScroll() {
+		if (dragger.continueSettling(true)) {
+			ViewCompat.postInvalidateOnAnimation(this);
+		}
+	}
+
+	public interface Callback {
+
+		void onPullStart();
+
+		void onPull(float progress);
+
+		void onPullCancel();
+
+		void onPullComplete();
+
+	}
+
+	private class ViewDragCallback extends ViewDragHelper.Callback {
+
+		@Override
+		public boolean tryCaptureView(View child, int pointerId) {
+			return true;
+		}
+
+		@Override
+		public int clampViewPositionHorizontal(View child, int left, int dx) {
+			return 0;
+		}
+
+		@Override
+		public int clampViewPositionVertical(View child, int top, int dy) {
+			return Math.max(0, top);
+		}
+
+		@Override
+		public int getViewHorizontalDragRange(View child) {
+			return 0;
+		}
+
+		@Override
+		public int getViewVerticalDragRange(View child) {
+			return getHeight();
+		}
+
+		@Override
+		public void onViewCaptured(View capturedChild, int activePointerId) {
+			if (callback != null) {
+				callback.onPullStart();
+			}
+		}
+
+		@Override
+		public void onViewPositionChanged(View changedView, int left, int top,
+				int dx, int dy) {
+			if (callback != null) {
+				callback.onPull((float) top / (float) getHeight());
+			}
+		}
+
+		@Override
+		public void onViewReleased(View releasedChild, float xvel, float yvel) {
+			int slop = yvel > minimumFlingVelocity ? getHeight() / 6 :
+					getHeight() / 3;
+			if (releasedChild.getTop() > slop) {
+				if (callback != null) {
+					callback.onPullComplete();
+				}
+			} else {
+				if (callback != null) {
+					callback.onPullCancel();
+				}
+
+				dragger.settleCapturedViewAt(0, 0);
+				invalidate();
+			}
+		}
+
+	}
+
+}

briar-android/src/main/res/layout/activity_image.xml

@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="utf-8"?>
+<org.briarproject.briar.android.view.PullDownLayout
+	android:id="@+id/layout"
+	xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent"
+	android:background="@color/briar_black"
+	tools:context=".android.conversation.ImageActivity">
+
+	<com.github.chrisbanes.photoview.PhotoView
+		android:id="@+id/photoView"
+		android:layout_width="match_parent"
+		android:layout_height="match_parent"
+		tools:ignore="ContentDescription"
+		tools:srcCompat="@tools:sample/backgrounds/scenic"/>
+
+	<android.support.design.widget.AppBarLayout
+		android:id="@+id/appBarLayout"
+		android:layout_width="match_parent"
+		android:layout_height="wrap_content"
+		android:background="@color/msg_status_bubble_background">
+
+		<android.support.v7.widget.Toolbar
+			android:id="@+id/toolbar"
+			style="@style/BriarToolbar"
+			android:layout_width="match_parent"
+			android:layout_height="wrap_content"
+			android:background="@color/msg_status_bubble_background"
+			android:fitsSystemWindows="true">
+
+			<LinearLayout
+				android:layout_width="wrap_content"
+				android:layout_height="match_parent"
+				android:orientation="vertical">
+
+				<com.vanniktech.emoji.EmojiTextView
+					android:id="@+id/contactName"
+					style="@style/TextAppearance.AppCompat.Widget.ActionBar.Title.Inverse"
+					android:layout_width="wrap_content"
+					android:layout_height="match_parent"
+					android:ellipsize="end"
+					android:maxLines="1"
+					android:textColor="@color/action_bar_text"
+					tools:text="Contact Name of someone who chose a long name"/>
+
+				<TextView
+					android:id="@+id/dateView"
+					android:layout_width="wrap_content"
+					android:layout_height="wrap_content"
+					android:textColor="@color/action_bar_text"
+					tools:text="date"/>
+
+			</LinearLayout>
+
+		</android.support.v7.widget.Toolbar>
+
+	</android.support.design.widget.AppBarLayout>
+
+</org.briarproject.briar.android.view.PullDownLayout>

briar-android/src/main/res/values/strings.xml

@@ -134,6 +134,8 @@
 	<string name="dialog_title_delete_contact">Confirm Contact Deletion</string>
 	<string name="dialog_message_delete_contact">Are you sure that you want to remove this contact and all messages exchanged with this contact?</string>
 	<string name="contact_deleted_toast">Contact deleted</string>
+	<!-- This is shown in the action bar when opening an image in fullscreen that the user sent -->
+	<string name="you">You</string>
 
 	<!-- Adding Contacts -->
 	<string name="add_contact_title">Add a Contact</string>

briar-android/src/main/res/values/themes.xml

@@ -18,6 +18,12 @@
 		<item name="toolbarStyle">@style/BriarToolbar</item>
 	</style>
 
+	<style name="BriarTheme.Transparent.NoActionBar" parent="BriarTheme.NoActionBar">
+		<item name="android:windowBackground">@android:color/transparent</item>
+		<item name="android:windowIsTranslucent">true</item>
+		<item name="android:windowActionBarOverlay">true</item>
+	</style>
+
 	<style name="ActivityAnimation" parent="@android:style/Animation.Activity">
 		<item name="android:activityOpenEnterAnimation">@anim/screen_new_in</item>
 		<item name="android:activityOpenExitAnimation">@anim/screen_old_out</item>

briar-android/witness.gradle

@@ -89,6 +89,7 @@ dependencyVerification {
         'com.github.bumptech.glide:compiler:4.8.0:compiler-4.8.0.jar:1fa93dd0cf7ef0b8b98a59a67a1ee84915416c2d677d83a771ea3e32ad15e6bf',
         'com.github.bumptech.glide:gifdecoder:4.8.0:gifdecoder-4.8.0.aar:b00c5454a023a9488ea49603930d9c25e09192e5ceaadf64977aa52946b3c1b4',
         'com.github.bumptech.glide:glide:4.8.0:glide-4.8.0.aar:5ddf08b12cc43332e812988f16c2c39e7fce49d1c4d94b7948dcde7f00bf49d6',
+        'com.github.chrisbanes:PhotoView:2.1.4:PhotoView-2.1.4.aar:04cb397fcb3df0757c8aed6927ebdd247930b5c78ee9acc59cd07dccdaaf3460',
         'com.google.android.apps.common.testing.accessibility.framework:accessibility-test-framework:2.0:accessibility-test-framework-2.0.jar:cdf16ef8f5b8023d003ce3cc1b0d51bda737762e2dab2fedf43d1c4292353f7f',
         'com.google.android.apps.common.testing.accessibility.framework:accessibility-test-framework:2.1:accessibility-test-framework-2.1.jar:7b0aa6ed7553597ce0610684a9f7eca8021eee218f2e2f427c04a7fbf5f920bd',
         'com.google.code.findbugs:jsr305:1.3.9:jsr305-1.3.9.jar:905721a0eea90a81534abb7ee6ef4ea2e5e645fa1def0a5cd88402df1b46c9ed',

briar-api/src/main/java/org/briarproject/briar/api/client/ThreadedMessage.java

@@ -9,6 +9,8 @@ import org.briarproject.briar.api.messaging.PrivateMessage;
 import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
+import static java.util.Collections.emptyList;
+
 @Immutable
 @NotNullByDefault
 public abstract class ThreadedMessage extends PrivateMessage {
@@ -19,7 +21,7 @@ public abstract class ThreadedMessage extends PrivateMessage {
 
 	public ThreadedMessage(Message message, @Nullable MessageId parent,
 			Author author) {
-		super(message);
+		super(message, emptyList());
 		this.parent = parent;
 		this.author = author;
 	}

briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateMessage.java

@@ -3,6 +3,8 @@ package org.briarproject.briar.api.messaging;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.Message;
 
+import java.util.List;
+
 import javax.annotation.concurrent.Immutable;
 
 @Immutable
@@ -10,13 +12,18 @@ import javax.annotation.concurrent.Immutable;
 public class PrivateMessage {
 
 	private final Message message;
+	private final List<AttachmentHeader> attachments;
 
-	public PrivateMessage(Message message) {
+	public PrivateMessage(Message message, List<AttachmentHeader> attachments) {
 		this.message = message;
+		this.attachments = attachments;
 	}
 
 	public Message getMessage() {
 		return message;
 	}
 
+	public List<AttachmentHeader> getAttachmentHeaders() {
+		return attachments;
+	}
 }

briar-core/src/main/java/org/briarproject/briar/messaging/MessagingManagerImpl.java

@@ -11,13 +11,16 @@ import org.briarproject.bramble.api.data.BdfList;
 import org.briarproject.bramble.api.data.MetadataParser;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DbException;
+import org.briarproject.bramble.api.db.Metadata;
 import org.briarproject.bramble.api.db.Transaction;
+import org.briarproject.bramble.api.io.MessageInputStreamFactory;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.Client;
 import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.Group.Visibility;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
+import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.MessageStatus;
 import org.briarproject.bramble.api.versioning.ClientVersioningManager;
@@ -32,16 +35,17 @@ import org.briarproject.briar.api.messaging.PrivateMessageHeader;
 import org.briarproject.briar.api.messaging.event.PrivateMessageReceivedEvent;
 import org.briarproject.briar.client.ConversationClientImpl;
 
+import java.io.InputStream;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Map;
-import java.util.Random;
 
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static java.util.Collections.emptyList;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_LENGTH;
 import static org.briarproject.briar.client.MessageTrackerConstants.MSG_KEY_READ;
 
 @Immutable
@@ -51,15 +55,21 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	private final ClientVersioningManager clientVersioningManager;
 	private final ContactGroupFactory contactGroupFactory;
+	private final MessageFactory messageFactory;
+	private final MessageInputStreamFactory messageInputStreamFactory;
 
 	@Inject
 	MessagingManagerImpl(DatabaseComponent db, ClientHelper clientHelper,
 			ClientVersioningManager clientVersioningManager,
 			MetadataParser metadataParser, MessageTracker messageTracker,
-			ContactGroupFactory contactGroupFactory) {
+			ContactGroupFactory contactGroupFactory,
+			MessageFactory messageFactory,
+			MessageInputStreamFactory messageInputStreamFactory) {
 		super(db, clientHelper, metadataParser, messageTracker);
 		this.clientVersioningManager = clientVersioningManager;
 		this.contactGroupFactory = contactGroupFactory;
+		this.messageFactory = messageFactory;
+		this.messageInputStreamFactory = messageInputStreamFactory;
 	}
 
 	@Override
@@ -142,9 +152,11 @@ class MessagingManagerImpl extends ConversationClientImpl
 			meta.put("read", true);
 			clientHelper.addLocalMessage(txn, m.getMessage(), meta, true);
 			messageTracker.trackOutgoingMessage(txn, m.getMessage());
+			for (AttachmentHeader h : m.getAttachmentHeaders())
+				db.setMessageShared(txn, h.getMessageId());
 			db.commitTransaction(txn);
 		} catch (FormatException e) {
-			throw new RuntimeException(e);
+			throw new AssertionError(e);
 		} finally {
 			db.endTransaction(txn);
 		}
@@ -152,11 +164,16 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	@Override
 	public AttachmentHeader addLocalAttachment(GroupId groupId, long timestamp,
-			String contentType, ByteBuffer data) {
-		// TODO add real implementation
-		byte[] b = new byte[MessageId.LENGTH];
-		new Random().nextBytes(b);
-		return new AttachmentHeader(new MessageId(b), "image/png");
+			String contentType, ByteBuffer data) throws DbException {
+		// TODO: Remove this restriction when large messages are supported
+		byte[] body = data.array();
+		if (body.length > MAX_MESSAGE_LENGTH) throw new DbException();
+		// TODO: Store message type and content type
+		Message m = messageFactory.createMessage(groupId, timestamp, body);
+		Metadata meta = new Metadata();
+		// Attachment will be shared when private message is added
+		db.transaction(false, txn -> db.addLocalMessage(txn, m, meta, false));
+		return new AttachmentHeader(m.getId(), contentType);
 	}
 
 	private ContactId getContactId(Transaction txn, GroupId g)
@@ -236,8 +253,9 @@ class MessagingManagerImpl extends ConversationClientImpl
 
 	@Override
 	public Attachment getAttachment(MessageId m) {
-		// TODO add real implementation
-		throw new IllegalStateException("Not yet implemented");
+		InputStream in = messageInputStreamFactory.getMessageInputStream(m);
+		// TODO: Read message type and content type
+		return new Attachment(in);
 	}
 
 }

briar-core/src/main/java/org/briarproject/briar/messaging/PrivateMessageFactoryImpl.java

@@ -39,6 +39,6 @@ class PrivateMessageFactoryImpl implements PrivateMessageFactory {
 		// Serialise the message
 		BdfList message = BdfList.of(text);
 		Message m = clientHelper.createMessage(groupId, timestamp, message);
-		return new PrivateMessage(m);
+		return new PrivateMessage(m, attachments);
 	}
 }

briar-core/src/test/java/org/briarproject/briar/introduction/IntroductionIntegrationTestComponent.java

@@ -8,6 +8,7 @@ import org.briarproject.bramble.data.DataModule;
 import org.briarproject.bramble.db.DatabaseModule;
 import org.briarproject.bramble.event.EventModule;
 import org.briarproject.bramble.identity.IdentityModule;
+import org.briarproject.bramble.io.IoModule;
 import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.record.RecordModule;
@@ -50,6 +51,7 @@ import dagger.Component;
 		GroupInvitationModule.class,
 		IdentityModule.class,
 		IntroductionModule.class,
+		IoModule.class,
 		LifecycleModule.class,
 		MessagingModule.class,
 		PrivateGroupModule.class,

briar-core/src/test/java/org/briarproject/briar/messaging/MessageSizeIntegrationTestComponent.java

@@ -8,6 +8,7 @@ import org.briarproject.bramble.data.DataModule;
 import org.briarproject.bramble.db.DatabaseModule;
 import org.briarproject.bramble.event.EventModule;
 import org.briarproject.bramble.identity.IdentityModule;
+import org.briarproject.bramble.io.IoModule;
 import org.briarproject.bramble.sync.SyncModule;
 import org.briarproject.bramble.sync.validation.ValidationModule;
 import org.briarproject.bramble.system.SystemModule;
@@ -40,6 +41,7 @@ import dagger.Component;
 		EventModule.class,
 		ForumModule.class,
 		IdentityModule.class,
+		IoModule.class,
 		MessagingModule.class,
 		SyncModule.class,
 		SystemModule.class,

briar-core/src/test/java/org/briarproject/briar/messaging/SimplexMessagingIntegrationTestComponent.java

@@ -15,6 +15,7 @@ import org.briarproject.bramble.data.DataModule;
 import org.briarproject.bramble.db.DatabaseModule;
 import org.briarproject.bramble.event.EventModule;
 import org.briarproject.bramble.identity.IdentityModule;
+import org.briarproject.bramble.io.IoModule;
 import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.record.RecordModule;
 import org.briarproject.bramble.sync.SyncModule;
@@ -48,6 +49,7 @@ import dagger.Component;
 		DatabaseModule.class,
 		EventModule.class,
 		IdentityModule.class,
+		IoModule.class,
 		LifecycleModule.class,
 		MessagingModule.class,
 		RecordModule.class,

briar-core/src/test/java/org/briarproject/briar/test/BriarIntegrationTestComponent.java

@@ -17,6 +17,7 @@ import org.briarproject.bramble.data.DataModule;
 import org.briarproject.bramble.db.DatabaseModule;
 import org.briarproject.bramble.event.EventModule;
 import org.briarproject.bramble.identity.IdentityModule;
+import org.briarproject.bramble.io.IoModule;
 import org.briarproject.bramble.lifecycle.LifecycleModule;
 import org.briarproject.bramble.properties.PropertiesModule;
 import org.briarproject.bramble.record.RecordModule;
@@ -68,6 +69,7 @@ import dagger.Component;
 		GroupInvitationModule.class,
 		IdentityModule.class,
 		IntroductionModule.class,
+		IoModule.class,
 		LifecycleModule.class,
 		MessagingModule.class,
 		PrivateGroupModule.class,

briar-headless/src/test/java/org/briarproject/briar/headless/messaging/MessagingControllerImplTest.kt

@@ -62,7 +62,7 @@ internal class MessagingControllerImplTest : ControllerTest() {
             emptyList()
         )
     private val sessionId = SessionId(getRandomId())
-    private val privateMessage = PrivateMessage(message)
+    private val privateMessage = PrivateMessage(message, emptyList())
 
     @Test
     fun list() {

build.gradle

@@ -5,6 +5,7 @@ allprojects {
 		jcenter()
 		mavenLocal()
 		google()
+		maven { url "https://jitpack.io" }
 	}
 	afterEvaluate {
 		tasks.withType(Test) {