Server.java

// Naive proxy server to route data from 12345 to postgres as 5432
// 
// javac Server.java
// java -server Server

import java.io.IOException;
import java.nio.channels.*;
import java.nio.ByteBuffer;
import java.net.*;

public class Server {

  private ServerSocketChannel server;

  public Server() throws IOException {
    this.server = ServerSocketChannel.open();
    this.server.socket().bind(new InetSocketAddress(12345));  
  }

  private void run() throws IOException {
    for ( ;; ) {
      SocketChannel socket = this.server.accept();
      socket.configureBlocking(false);
      new Thread(new ProxyExecutor(socket)).start();
    }
  }

  public static void main(String[] args) {
    try {
      new Server().run();
    }
    catch(IOException e) {
      e.printStackTrace();
      System.exit(-1);
    }
  }
  
}

class ProxyExecutor implements Runnable {
  private SocketChannel socket;

  public ProxyExecutor(SocketChannel socket) {
    this.socket = socket;
  }

  public void run() {
    try {
      SocketChannel postgres = SocketChannel.open(new InetSocketAddress(5432));
      postgres.configureBlocking(false);

      ByteBuffer buffer = ByteBuffer.allocate(1024);

      for ( ;; ) {
        if ( this.socket.read(buffer) == -1 ) {
          break;
        }

        buffer.flip();
        postgres.write(buffer);
        buffer.clear();
        postgres.read(buffer);
        buffer.flip();
        this.socket.write(buffer);
        buffer.clear();
      }

      postgres.close();
      this.socket.close();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }
}

server.rb

# Naive proxy to route data from 12345 to postgres on 5432
# jruby --server server.rb

require 'socket'

server = TCPServer.new('0.0.0.0', 12345)

loop do
  begin
    socket = server.accept_nonblock
  rescue Errno::EAGAIN, Errno::ECONNABORTED, Errno::EPROTO, Errno::EINTR
    IO.select([server])
    retry
  end

  Thread.new do
    begin
      postgres = TCPSocket.new('0.0.0.0', 5432)

      loop do
        while (data = socket.read_nonblock(1024)) != ""
          postgres.write data
        end

        while (data = postgres.read_nonblock(1024)) != ""
          socket.write data
        end
      end
    rescue EOFError
      postgres.close
      socket.close
    end
  end
end