A basic TCP proxy written in node.js

tcpproxy.js

var net = require("net");

process.on("uncaughtException", function(error) {
  console.error(error);
});

if (process.argv.length != 5) {
  console.log("usage: %s <localport> <remotehost> <remoteport>", process.argv[1]);
  process.exit();
}

var localport = process.argv[2];
var remotehost = process.argv[3];
var remoteport = process.argv[4];

var server = net.createServer(function (localsocket) {
  var remotesocket = new net.Socket();

  remotesocket.connect(remoteport, remotehost);

  localsocket.on('connect', function (data) {
    console.log(">>> connection #%d from %s:%d",
      server.connections,
      localsocket.remoteAddress,
      localsocket.remotePort
    );
  });

  localsocket.on('data', function (data) {
    console.log("%s:%d - writing data to remote",
      localsocket.remoteAddress,
      localsocket.remotePort
    );
    var flushed = remotesocket.write(data);
    if (!flushed) {
      console.log("  remote not flushed; pausing local");
      localsocket.pause();
    }
  });

  remotesocket.on('data', function(data) {
    console.log("%s:%d - writing data to local",
      localsocket.remoteAddress,
      localsocket.remotePort
    );
    var flushed = localsocket.write(data);
    if (!flushed) {
      console.log("  local not flushed; pausing remote");
      remotesocket.pause();
    }
  });

  localsocket.on('drain', function() {
    console.log("%s:%d - resuming remote",
      localsocket.remoteAddress,
      localsocket.remotePort
    );
    remotesocket.resume();
  });

  remotesocket.on('drain', function() {
    console.log("%s:%d - resuming local",
      localsocket.remoteAddress,
      localsocket.remotePort
    );
    localsocket.resume();
  });

  localsocket.on('close', function(had_error) {
    console.log("%s:%d - closing remote",
      localsocket.remoteAddress,
      localsocket.remotePort
    );
    remotesocket.end();
  });

  remotesocket.on('close', function(had_error) {
    console.log("%s:%d - closing local",
      localsocket.remoteAddress,
      localsocket.remotePort
    );
    localsocket.end();
  });

});

server.listen(localport);

console.log("redirecting connections from 127.0.0.1:%d to %s:%d", localport, remotehost, remoteport);