TCP Ghost

A drop-in replacement for net.createServer which uses pcap to create ghost connections (also known as tees or clones).

Scope

This modules was written for the following circumstance - if your problem is similar, it may work for you too.

I have an old daemon in production which is accepting TCP connections, where the source IP address is of vital importance.

I want to test a replacement daemon (written in NodeJS) but cannot bind to the TCP port, as it is already in use by the old daemon.

Normally I would insert a tee (npm install duplicator) to do this job. Unfortunately this has the side affect of making all TCP connection appear to orginate at localhost, whichis unacceptable.

Solution

TCP Ghost uses libpcap (like tcpdump and Wireshark) to watch all the packets.

TCP Ghost is used exactly like the net module.

    var ghost = tcpghost.createServer(function(sock) {
      console.log('connected');
      sock.setEncoding('utf8');
      sock.on('data', function(data) {
        console.log('data', data);
      });
    });
    ghost.listen(7777);

See the example and test directories for more details.

The duplication of the net API means that the new daemon can just have it's createServer line modded to test in parallel with an existing server.

Note: There must another process already listening to the port to which you tcpghost binds, otherwise there is no traffic to listen to.

Running the Examples

For this you will need to checkout the git repo.

You will need three terminals.

T1:

$ git clone https://github.com/chrisdew/tcpghost

To be continued...

Warnings

It is currently in early development, but go ahead and give it a try.