Added message queue manager.

briar-api/src/org/briarproject/api/clients/MessageQueueManager.java

@@ -0,0 +1,38 @@
+package org.briarproject.api.clients;
+
+import org.briarproject.api.db.DbException;
+import org.briarproject.api.db.Metadata;
+import org.briarproject.api.db.Transaction;
+import org.briarproject.api.sync.ClientId;
+import org.briarproject.api.sync.Group;
+
+public interface MessageQueueManager {
+
+	/**
+	 * The key used for storing the queue's state in the group metadata.
+	 */
+	String QUEUE_STATE_KEY = "queueState";
+
+	/**
+	 * Sends a message using the given queue.
+	 */
+	QueueMessage sendMessage(Transaction txn, Group queue, long timestamp,
+			byte[] body, Metadata meta) throws DbException;
+
+	/**
+	 * Sets the message validator for the given client.
+	 */
+	void registerMessageValidator(ClientId c, QueueMessageValidator v);
+
+	/**
+	 * Sets the incoming message hook for the given client. The hook will be
+	 * called once for each incoming message that passes validation. Messages
+	 * are passed to the hook in order.
+	 */
+	void registerIncomingMessageHook(ClientId c, IncomingQueueMessageHook hook);
+
+	interface IncomingQueueMessageHook {
+		void incomingMessage(Transaction txn, QueueMessage q, Metadata meta)
+				throws DbException;
+	}
+}

briar-api/src/org/briarproject/api/clients/QueueMessage.java

@@ -0,0 +1,28 @@
+package org.briarproject.api.clients;
+
+import org.briarproject.api.sync.GroupId;
+import org.briarproject.api.sync.Message;
+import org.briarproject.api.sync.MessageId;
+
+import static org.briarproject.api.sync.SyncConstants.MAX_MESSAGE_BODY_LENGTH;
+import static org.briarproject.api.sync.SyncConstants.MESSAGE_HEADER_LENGTH;
+
+public class QueueMessage extends Message {
+
+	public static final int QUEUE_MESSAGE_HEADER_LENGTH =
+			MESSAGE_HEADER_LENGTH + 8;
+	public static final int MAX_QUEUE_MESSAGE_BODY_LENGTH =
+			MAX_MESSAGE_BODY_LENGTH - 8;
+
+	private final long queuePosition;
+
+	public QueueMessage(MessageId id, GroupId groupId, long timestamp,
+			long queuePosition, byte[] raw) {
+		super(id, groupId, timestamp, raw);
+		this.queuePosition = queuePosition;
+	}
+
+	public long getQueuePosition() {
+		return queuePosition;
+	}
+}

briar-api/src/org/briarproject/api/clients/QueueMessageFactory.java

@@ -0,0 +1,12 @@
+package org.briarproject.api.clients;
+
+import org.briarproject.api.sync.GroupId;
+import org.briarproject.api.sync.MessageId;
+
+public interface QueueMessageFactory {
+
+	QueueMessage createMessage(GroupId groupId, long timestamp,
+			long queuePosition, byte[] body);
+
+	QueueMessage createMessage(MessageId id, byte[] raw);
+}

briar-api/src/org/briarproject/api/clients/QueueMessageValidator.java

@@ -0,0 +1,13 @@
+package org.briarproject.api.clients;
+
+import org.briarproject.api.db.Metadata;
+import org.briarproject.api.sync.Group;
+
+public interface QueueMessageValidator {
+
+	/**
+	 * Validates the given message and returns its metadata if the message
+	 * is valid, or null if the message is invalid.
+	 */
+	Metadata validateMessage(QueueMessage q, Group g);
+}