I made a simple Instant Message Chat Client and Server on TCP, that both run off Adobe AIR. It works great and it was a interesting way to learn basic networking programming.
My Question: Is it possible to change the data in the packet sent from the Chat Server before it arrives at the Client without using the Server or Client to do so? Like perhaps a program?
I am new to Network programming so I apologize if this is a dumb question.
Your question is very broad. So the answer is broad as well. Yes. It's possible.
For that you need to get the packets between the client and server to pass through a third program. There are quite a lot of ways to achieve that. Here's non-exhaustive list:
First, on your own machines (client/server) you could get access to the packet from the operating system using various low-level APIs. For instance iptables+nfqueue in Linux or the Windows Filtering Platform on Windows.
Second, you could get access to the packets by intentionally having them communicate through some proxy program which may or may not reside on the same server as the client or the server.
Third, you could get access to the packets by picking them up from the network itself. For instance, you could set up some Linux machine as a router and have it sit between the client and the server (as long as they're not on the same machine). That Linux machine will now have access to all of the packets that pass through it, and it can pass them to various user-space programs using hooks such as the previously mentioned nfqueue.