Cache Outgoing Data from browser

This might be a very broad question. But this is what i want. I open a website and enter some details in the website like my credentials to login or it may be any data that pass from my browser to the website. Now what i want is that i should cache ( write to a temp file ) 开发者_开发技巧whatever that i send to that website. How can this be done? I tried to extract the data present in the packets that are flowing out of my machine but i find only junk characters in that (may be header). any ideas are welcomed. I am using Ubuntu Linux and would like to achieve this using shell script/C/C++

One option would be to use the Fiddler Web Debugger which is scriptable (C#).

Although it's a Win32 program, it can act as a proxy for any Linux machine. See Debug traffic from another machine (even a Mac or Unix box) for details.

There's also a native Linux app called dsniff which can be used to log all HTTP traffic to a file.