Add versions record to sync protocol.

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

@@ -9,5 +9,5 @@ public interface RecordTypes {
 	byte MESSAGE = 1;
 	byte OFFER = 2;
 	byte REQUEST = 3;
-
+	byte VERSIONS = 4;
 }

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

@@ -35,4 +35,10 @@ 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 number of versions of the sync protocol a peer may support
+	 * simultaneously.
+	 */
+	int MAX_SUPPORTED_VERSIONS = 10;
 }

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

@@ -25,4 +25,7 @@ public interface SyncRecordReader {
 
 	Request readRequest() throws IOException;
 
+	boolean hasVersions() throws IOException;
+
+	Versions readVersions() throws IOException;
 }

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

@@ -15,5 +15,7 @@ public interface SyncRecordWriter {
 
 	void writeRequest(Request r) throws IOException;
 
+	void writeVersions(Versions v) throws IOException;
+
 	void flush() throws IOException;
 }

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

@@ -0,0 +1,26 @@
+package org.briarproject.bramble.api.sync;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.List;
+
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * A record telling the recipient which versions of the sync protocol the
+ * sender supports.
+ */
+@Immutable
+@NotNullByDefault
+public class Versions {
+
+	private final List<Byte> supported;
+
+	public Versions(List<Byte> supported) {
+		this.supported = supported;
+	}
+
+	public List<Byte> getSupportedVersions() {
+		return supported;
+	}
+}

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

@@ -13,6 +13,7 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
+import org.briarproject.bramble.api.sync.Versions;
 import org.briarproject.bramble.util.ByteUtils;
 
 import java.io.IOException;
@@ -26,6 +27,8 @@ import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
+import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
 
@@ -45,7 +48,7 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 
 	private static boolean isKnownRecordType(byte type) {
 		return type == ACK || type == MESSAGE || type == OFFER ||
-				type == REQUEST;
+				type == REQUEST || type == VERSIONS;
 	}
 
 	private final MessageFactory messageFactory;
@@ -148,4 +151,27 @@ class SyncRecordReaderImpl implements SyncRecordReader {
 		if (!hasRequest()) throw new FormatException();
 		return new Request(readMessageIds());
 	}
+
+	@Override
+	public boolean hasVersions() throws IOException {
+		return !eof() && getNextRecordType() == VERSIONS;
+	}
+
+	@Override
+	public Versions readVersions() throws IOException {
+		if (!hasVersions()) throw new FormatException();
+		return new Versions(readSupportedVersions());
+	}
+
+	private List<Byte> readSupportedVersions() throws IOException {
+		if (nextRecord == null) throw new AssertionError();
+		byte[] payload = nextRecord.getPayload();
+		if (payload.length == 0) throw new FormatException();
+		if (payload.length > MAX_SUPPORTED_VERSIONS)
+			throw new FormatException();
+		List<Byte> supported = new ArrayList<>(payload.length);
+		for (byte b : payload) supported.add(b);
+		nextRecord = null;
+		return supported;
+	}
 }

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

@@ -10,6 +10,7 @@ import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
+import org.briarproject.bramble.api.sync.Versions;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
@@ -20,6 +21,7 @@ import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.MESSAGE;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
+import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
 
 @NotThreadSafe
@@ -65,6 +67,12 @@ class SyncRecordWriterImpl implements SyncRecordWriter {
 		writeRecord(REQUEST);
 	}
 
+	@Override
+	public void writeVersions(Versions v) throws IOException {
+		for (byte b : v.getSupportedVersions()) payload.write(b);
+		writeRecord(VERSIONS);
+	}
+
 	@Override
 	public void flush() throws IOException {
 		writer.flush();

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

@@ -10,11 +10,14 @@ import org.briarproject.bramble.api.sync.MessageFactory;
 import org.briarproject.bramble.api.sync.Offer;
 import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
+import org.briarproject.bramble.api.sync.Versions;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.jmock.Expectations;
+import org.junit.Before;
 import org.junit.Test;
 
 import java.io.ByteArrayOutputStream;
+import java.util.List;
 
 import javax.annotation.Nullable;
 
@@ -22,7 +25,9 @@ import static org.briarproject.bramble.api.record.Record.MAX_RECORD_PAYLOAD_BYTE
 import static org.briarproject.bramble.api.sync.RecordTypes.ACK;
 import static org.briarproject.bramble.api.sync.RecordTypes.OFFER;
 import static org.briarproject.bramble.api.sync.RecordTypes.REQUEST;
+import static org.briarproject.bramble.api.sync.RecordTypes.VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
+import static org.briarproject.bramble.api.sync.SyncConstants.MAX_SUPPORTED_VERSIONS;
 import static org.briarproject.bramble.api.sync.SyncConstants.PROTOCOL_VERSION;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
 import static org.junit.Assert.assertEquals;
@@ -35,12 +40,17 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 			context.mock(MessageFactory.class);
 	private final RecordReader recordReader = context.mock(RecordReader.class);
 
+	private SyncRecordReader reader;
+
+	@Before
+	public void setUp() {
+		reader = new SyncRecordReaderImpl(messageFactory, recordReader);
+	}
+
 	@Test
 	public void testNoFormatExceptionIfAckIsMaximumSize() throws Exception {
 		expectReadRecord(createAck());
 
-		SyncRecordReader reader =
-				new SyncRecordReaderImpl(messageFactory, recordReader);
 		Ack ack = reader.readAck();
 		assertEquals(MAX_MESSAGE_IDS, ack.getMessageIds().size());
 	}
@@ -49,8 +59,6 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 	public void testFormatExceptionIfAckIsEmpty() throws Exception {
 		expectReadRecord(createEmptyAck());
 
-		SyncRecordReader reader =
-				new SyncRecordReaderImpl(messageFactory, recordReader);
 		reader.readAck();
 	}
 
@@ -58,8 +66,6 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 	public void testNoFormatExceptionIfOfferIsMaximumSize() throws Exception {
 		expectReadRecord(createOffer());
 
-		SyncRecordReader reader =
-				new SyncRecordReaderImpl(messageFactory, recordReader);
 		Offer offer = reader.readOffer();
 		assertEquals(MAX_MESSAGE_IDS, offer.getMessageIds().size());
 	}
@@ -68,8 +74,6 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 	public void testFormatExceptionIfOfferIsEmpty() throws Exception {
 		expectReadRecord(createEmptyOffer());
 
-		SyncRecordReader reader =
-				new SyncRecordReaderImpl(messageFactory, recordReader);
 		reader.readOffer();
 	}
 
@@ -77,8 +81,6 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 	public void testNoFormatExceptionIfRequestIsMaximumSize() throws Exception {
 		expectReadRecord(createRequest());
 
-		SyncRecordReader reader =
-				new SyncRecordReaderImpl(messageFactory, recordReader);
 		Request request = reader.readRequest();
 		assertEquals(MAX_MESSAGE_IDS, request.getMessageIds().size());
 	}
@@ -87,11 +89,36 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 	public void testFormatExceptionIfRequestIsEmpty() throws Exception {
 		expectReadRecord(createEmptyRequest());
 
-		SyncRecordReader reader =
-				new SyncRecordReaderImpl(messageFactory, recordReader);
 		reader.readRequest();
 	}
 
+	@Test
+	public void testNoFormatExceptionIfVersionsIsMaximumSize()
+			throws Exception {
+		expectReadRecord(createVersions(MAX_SUPPORTED_VERSIONS));
+
+		Versions versions = reader.readVersions();
+		List<Byte> supported = versions.getSupportedVersions();
+		assertEquals(MAX_SUPPORTED_VERSIONS, supported.size());
+		for (int i = 0; i < supported.size(); i++) {
+			assertEquals(i, (int) supported.get(i));
+		}
+	}
+
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfVersionsIsEmpty() throws Exception {
+		expectReadRecord(createVersions(0));
+
+		reader.readVersions();
+	}
+
+	@Test(expected = FormatException.class)
+	public void testFormatExceptionIfVersionsIsTooLarge() throws Exception {
+		expectReadRecord(createVersions(MAX_SUPPORTED_VERSIONS + 1));
+
+		reader.readVersions();
+	}
+
 	@Test
 	public void testEofReturnsTrueWhenAtEndOfStream() throws Exception {
 		expectReadRecord(createAck());
@@ -140,6 +167,12 @@ public class SyncRecordReaderImplTest extends BrambleMockTestCase {
 		return new Record(PROTOCOL_VERSION, REQUEST, new byte[0]);
 	}
 
+	private Record createVersions(int numVersions) {
+		byte[] payload = new byte[numVersions];
+		for (int i = 0; i < payload.length; i++) payload[i] = (byte) i;
+		return new Record(PROTOCOL_VERSION, VERSIONS, payload);
+	}
+
 	private byte[] createPayload() throws Exception {
 		ByteArrayOutputStream payload = new ByteArrayOutputStream();
 		while (payload.size() + UniqueId.LENGTH <= MAX_RECORD_PAYLOAD_BYTES) {