What is the difference when connecting through a proxy?

Question

I know what a proxy is, and the basics of how they work.

What I was wondering is, what is different in a request that goes through a proxy?

I know when I configure Firefox I simply configure the proxy in a dialog. When I program in python I can use an environment variable.

If I am programming in an environment that doesn't already have support for a proxy, how do I connect through a proxy? Is there an extra header added to requests? Is the protocol slightly different?

Answer 1

The protocol is slightly different. Where a direct connection to example.com would say:

GET /index.html HTTP/1.1

a connection through a proxy would say:

GET http://example.com/index.html HTTP/1.1