Editing TCP packets "on the fly"

Is there a tool / source code example to stop incoming and outgoing packets, let them be edited and send the modded packets out or let them in? (for linux)

Like the Tamper Data addon for Firefox, just for TCP packets.

I believe you can do that with ettercap. You just have to set up a MITM attack. If it can't, just look up MITM tools or even just how to do MITM attacks so you can write your own code.

P.S. MITM = man in the middle

Thx :) But ettercap isn't really what I was looking for. I'll try other MITM tools.

Actualy from the description of your problem ettercap is exactly what you are looking for. You can implememnt arp poisoning and have all packets routed through you. Then you can write your filter. So say just use the replace code in the manual for ec and it will tell you how to. Easy as stuff. Unless your looking for GUI then you should stfu.

lol im gunna go and try typing with oven mites on cause im cool like that : ]