How does a proxy(like squid) knows if the connection is using http?

I'm thinking of make my own protocol tunneling with http. So, in some cases we have user and pass开发者_如何学Goword for proxies like squid.

1-How does it know is really http going on?? does it checks the contents of the TCP connection on port 80?? 2-If so then I really need to use http. If dont I can use any TCP connection on port 80?

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It checks the content decoding and interpreting the HTTP requests and responses, otherwise the proxy wouldn't know where to forward the request.

HTTPS is a different thing (proxy can't read encrypted ssl connections) and just interprets a single CONNECT line sent before the HTTPS traffic.

More Information: http://en.wikipedia.org/wiki/HTTP_tunnel