Satisfies a request for a resource from the cache, if the resource is available; otherwise, sends a request for a resource to the server. If the requested item is available in any cache between the client and the server, the request might be satisfied by the intermediate cache.
A copy of a requested resource is only added to the cache if the response stream for the resource is retrieved and read to the end of the stream. So subsequent requests for the same resource would use a cached copy.