diff --git a/bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncConstants.java b/bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncConstants.java
index a6e3474f3..4a4200872 100644
--- a/bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncConstants.java
+++ b/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
 }
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java b/bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java
index 44535a50a..6dee021a8 100644
--- a/bramble-core/src/main/java/org/briarproject/bramble/BrambleCoreModule.java
+++ b/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,
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/io/IoModule.java b/bramble-core/src/main/java/org/briarproject/bramble/io/IoModule.java
new file mode 100644
index 000000000..8e996766d
--- /dev/null
+++ b/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;
+	}
+}
diff --git a/bramble-core/src/main/java/org/briarproject/bramble/io/MessageInputStreamFactoryImpl.java b/bramble-core/src/main/java/org/briarproject/bramble/io/MessageInputStreamFactoryImpl.java
new file mode 100644
index 000000000..16d420d5d
--- /dev/null
+++ b/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);
+	}
+}
diff --git a/bramble-core/src/test/java/org/briarproject/bramble/io/BlockSourceInputStreamTest.java b/bramble-core/src/test/java/org/briarproject/bramble/io/BlockSourceInputStreamTest.java
index 5f3c7539a..8675cf15b 100644
--- a/bramble-core/src/test/java/org/briarproject/bramble/io/BlockSourceInputStreamTest.java
+++ b/bramble-core/src/test/java/org/briarproject/bramble/io/BlockSourceInputStreamTest.java
@@ -15,6 +15,7 @@ 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;
@@ -25,8 +26,6 @@ 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 static final int BLOCK_BYTES = 32 * 1024;
-	private static final int MIN_BUFFER_BYTES = 32 * 1024;
 
 	private final BlockSource blockSource;
 
@@ -42,8 +41,8 @@ public class BlockSourceInputStreamTest extends BrambleMockTestCase {
 	@Test
 	public void testReadSingleBytes() throws IOException {
 		byte[] data = createRandomData();
-		BlockSource source = new ByteArrayBlockSource(data, BLOCK_BYTES);
-		InputStream in = new BlockSourceInputStream(MIN_BUFFER_BYTES, executor,
+		BlockSource source = new ByteArrayBlockSource(data, MAX_BLOCK_LENGTH);
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
 				source, messageId);
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
 		//noinspection ForLoopReplaceableByForEach
@@ -62,8 +61,8 @@ public class BlockSourceInputStreamTest extends BrambleMockTestCase {
 	@Test
 	public void testReadByteArrays() throws IOException {
 		byte[] data = createRandomData();
-		BlockSource source = new ByteArrayBlockSource(data, BLOCK_BYTES);
-		InputStream in = new BlockSourceInputStream(MIN_BUFFER_BYTES, executor,
+		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];
@@ -93,7 +92,7 @@ public class BlockSourceInputStreamTest extends BrambleMockTestCase {
 			will(throwException(new DbException()));
 		}});
 
-		InputStream in = new BlockSourceInputStream(MIN_BUFFER_BYTES, executor,
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
 				blockSource, messageId);
 		//noinspection ResultOfMethodCallIgnored
 		in.read();
@@ -108,7 +107,7 @@ public class BlockSourceInputStreamTest extends BrambleMockTestCase {
 			will(throwException(new DbException()));
 		}});
 
-		InputStream in = new BlockSourceInputStream(MIN_BUFFER_BYTES, executor,
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
 				blockSource, messageId);
 		//noinspection ResultOfMethodCallIgnored
 		in.read();
@@ -116,12 +115,12 @@ public class BlockSourceInputStreamTest extends BrambleMockTestCase {
 
 	@Test
 	public void testReadFullBlockAtEndOfMessage() throws Exception {
-		testReadBlockAtEndOfMessage(BLOCK_BYTES);
+		testReadBlockAtEndOfMessage(MAX_BLOCK_LENGTH);
 	}
 
 	@Test
 	public void testReadPartialBlockAtEndOfMessage() throws Exception {
-		testReadBlockAtEndOfMessage(BLOCK_BYTES - 1);
+		testReadBlockAtEndOfMessage(MAX_BLOCK_LENGTH - 1);
 	}
 
 	private void testReadBlockAtEndOfMessage(int blockLength) throws Exception {
@@ -135,9 +134,9 @@ public class BlockSourceInputStreamTest extends BrambleMockTestCase {
 			will(returnValue(block));
 		}});
 
-		InputStream in = new BlockSourceInputStream(MIN_BUFFER_BYTES, executor,
+		InputStream in = new BlockSourceInputStream(MAX_BLOCK_LENGTH, executor,
 				blockSource, messageId);
-		byte[] buf = new byte[BLOCK_BYTES * 2];
+		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));