Java puzzle (Single threaded client server)

Without creating additional threads, create a ServerSocket on a random unused port, a client Socket connecting to localhost and a server Socket.

Part 1) Send messages from client to server and back again. (This can be useful in unit tests) [Click for sample solution]

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ServerSocket ss = new ServerSocket(0);
Socket c = new Socket("localhost", ss.getLocalPort());
Socket s= ss.accept();
ss.close();
// sends one byte.
c.getOutputStream().write(1);
int num = s.getInputStream().read();
s.getOutputStream().write(num+1);
int num2 = c.getInputStream().read();

s.close();
c.close();

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Part 2) Do the same with blocking NIO. [Click for sample solution]

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ServerSocketChannel ss = ServerSocketChannel.open();
ss.socket().bind(new InetSocketAddress(0));
SocketChannel c = SocketChannel.open(new InetSocketAddress("localhost", ss.socket().getLocalPort()));
SocketChannel s = ss.accept();
ss.close();
// sends one byte.
ByteBuffer bb1 = ByteBuffer.allocateDirect(1);
c.write(bb1);
// read one byte.
ByteBuffer bb2 = ByteBuffer.allocateDirect(1);
int num = s.read(bb2);

// sends it back.
bb2.flip();
s.write(bb2);

// reads one byte.
bb1.clear();
c.read(bb1);

s.close();
c.close();

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Part 3) Benchmark how many GB/s per second you can transfer this way. [Click for sample solution]

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ServerSocketChannel ss = ServerSocketChannel.open();
ss.socket().bind(new InetSocketAddress(0));
SocketChannel c = SocketChannel.open(new InetSocketAddress("localhost", ss.socket().getLocalPort()));
SocketChannel s = ss.accept();
ss.close();

final int bufferSize = 64 * 1024;
final int runs = 10000;

for (int j = 0; j < 3; j++) {
    ByteBuffer bb1 = ByteBuffer.allocateDirect(bufferSize);
    ByteBuffer bb2 = ByteBuffer.allocateDirect(bufferSize);
    long start = System.nanoTime();
    for (int i = 0; i < runs; i++) {
// sends one buffer.
        bb1.clear();
        c.write(bb1);
// read one buffer.
        bb2.clear();
        int num = s.read(bb2);

// sends it back.
        bb2.flip();
        s.write(bb2);

// reads one byte.
        bb1.clear();
        c.read(bb1);
    }
    long time = System.nanoTime() - start;
    long rate = (long) (1e9 * bufferSize * runs / time / 1e6);
    System.out.println("Transfer rate " + rate + " MB/s");
}

s.close();
c.close();

Prints on my machine

Transfer rate 1963 MB/s
Transfer rate 2330 MB/s
Transfer rate 2365 MB/s

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Part 4) Measure the typical and 99.99% round trip latency, and estimate how much garbage is produced.

For bonus points try the same with Async NIO2 in Java 7.

I will add a solution Nov 29th (after a week)