Writes to the reliability layer should be asynchronous.

The flow control window will limit the amount of buffered data.

src/net/sf/briar/plugins/modem/ReliabilityLayer.java

 package net.sf.briar.plugins.modem;
 
+import static java.util.logging.Level.WARNING;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.logging.Logger;
 
 class ReliabilityLayer implements ReadHandler, WriteHandler {
 
+	private static final Logger LOG =
+			Logger.getLogger(ReliabilityLayer.class.getName());
+
 	private final WriteHandler writeHandler;
 	private final Receiver receiver;
 	private final SlipDecoder decoder;
 	private final ReceiverInputStream inputStream;
 	private final SenderOutputStream outputStream;
+	private final BlockingQueue<byte[]> writes;
 
 	private volatile boolean valid = true;
 
@@ -22,6 +31,31 @@ class ReliabilityLayer implements ReadHandler, WriteHandler {
 		decoder = new SlipDecoder(receiver);
 		inputStream = new ReceiverInputStream(receiver);
 		outputStream = new SenderOutputStream(sender);
+		writes = new LinkedBlockingQueue<byte[]>();
+	}
+
+	void init() {
+		new Thread("ReliabilityLayer") {
+			@Override
+			public void run() {
+				try {
+					while(valid) {
+						byte[] b = writes.take();
+						if(b.length == 0) return; // Poison pill
+						writeHandler.handleWrite(b, b.length);
+					}
+				} catch(InterruptedException e) {
+					if(LOG.isLoggable(WARNING))
+						LOG.warning("Interrupted while writing");
+					valid = false;
+					Thread.currentThread().interrupt();
+				} catch(IOException e) {
+					if(LOG.isLoggable(WARNING))
+						LOG.warning("Interrupted while writing");
+					valid = false;
+				}
+			}
+		}.start();
 	}
 
 	InputStream getInputStream() {
@@ -35,6 +69,7 @@ class ReliabilityLayer implements ReadHandler, WriteHandler {
 	void invalidate() {
 		valid = false;
 		receiver.invalidate();
+		writes.add(new byte[0]); // Poison pill
 	}
 
 	// The modem calls this method to pass data up to the SLIP decoder
@@ -46,6 +81,12 @@ class ReliabilityLayer implements ReadHandler, WriteHandler {
 	// The SLIP encoder calls this method to pass data down to the modem
 	public void handleWrite(byte[] b, int length) throws IOException {
 		if(!valid) throw new IOException("Connection closed");
-		writeHandler.handleWrite(b, length);
+		if(length == 0) return;
+		if(length < b.length) {
+			byte[] copy = new byte[length];
+			System.arraycopy(b, 0, copy, 0, length);
+			b = copy;
+		}
+		writes.add(b);
 	}
 }