Monitor socket with ngrep or perl for activity, then issue command

Question

I'd like to use ngrep and/or perl to monitor the incoming data stream on a socket, then, when the appropriate characters arrive, like in this case, the string "192.168.1.101:8080", input to the data stream a redirect to another ipaddress, such as "192.168.1.102"

Is this even possible?

Answer 1

Sure, thats possible.

Algorithm/application would require:

• MiM listenning server (creating sockets session sockets)
• hand-shake on MiM:
• (best thing would be if there would be a text stream not binary protocol used)

• recv from client, parse message then:

• if IP comes in, open or use already opened socket to the target server/port

• send message or rest of the message to target server
• provide communication beteween client and target sever (operate as gateway)
• recv() client or server and send() back to appropriate side

General advice: operate on select() or epoll(), approach more advanced but better.

Answer 2

This can done easily in Perl.

Take a look at perldoc perlipc, IO::Socket and IO::Select for examples.

You might find Beej's Guide to Network Programming helpful, too. The examples are all in C, but Perl's networking API is pretty close to the C flavor.