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2.2.1.2.8 Cache-Control

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This header is used to request that any intermediate caching server such as a proxy, not cache the content of the HTTP Response, as specified in [RFC2068], section 14.9. 

 Cache-Control = 2(«Cache-Control:» cache-directive CRLF)
 cache-directive = "no-cache"; (see [RFC2068], section 14.9.1)
     / "max-age=" delta-seconds; (see [RFC2068], section 14.9.3)
 delta-seconds = 1*DIGIT

If the "no-cache" directive is specified for Cache-Control, the server MUST NOT use its cache to respond to any request from the client. The "max-age" directive can be set to 0 to force the intermediate caching server to re-validate the cache entry before responding to any request.

Some proxies honor one cache directive while other proxies honor the other. The client MUST send both of the cache directives as part of the request to be compatible with the widest variety of proxies. This header is repeated for the two values of Cache-directive.

Example: Cache-Control: max-age=0 CRLF Cache-Control: no-cache CRLF<3>