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It's my understanding that caching is one of the main utilities of a proxy server. I'm currently trying to develop a simple one and I would like to know exactly how caching works.

Intuitively I think that it's basically an association between a request and a response. For example: for the following request: "GET google.com" you have the following response: "HTTP/1.0 200 OK..."

That way, whenever the proxy server receives a request for that URL he can reply with the cached response (I'm not really worried right now about when to serve the cached response and when to actually send the request to the real destination).

What I don't understand is how to establish the association between a request and a response since the HTTP response doesn't have any field saying "hey this is the response you get when you request the X URL" (or does it?).

Should I get this information by analyzing the underlying protocols? If so, how?

André Lourenço
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Your cache proxy server is already putted into play when a request arrives. Therefore you have the requested resource URL. Then you look in your cache and try to find the cached resource for the requested resource URL, if you cannot find the resource in your cache (or the cache is outdated), you fetch the data from the source. Keep in Mind, that you have to invalidate the cached resource if you receive a PUT, POST or DELETE request.

Frank Olschewski
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