HTTP if-none-match and if-modified-since and 304 clarification in PHP

[Storndooxoppy]

My question is about how to reply a HTTP 304 "Not Modified" when I receive both if-none-match and if-modified-since from a proxy/client request.From RFC 2616 secttion 14.26 ( http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26 ):\[quote\] If none of the entity tags match, then the server MAY perform the requested method as if the If-None-Match header field did not exist, but MUST also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server MUST NOT return a 304 (Not Modified) response.\[/quote\]I am not sure to understand this statement...[*]"If none of the entity tags match" in PHP do they speak of $_SERVER['HTTP_IF_NONE_MATCH'] vs. my ETags that I sent earlier?[*]If I understand correctly this statement, as soon as none of the ETags listed in $_SERVER['HTTP_IF_NONE_MATCH'] match my ETags, I stop all verifications and serve the page normally. Anyone can translate this RFC part in pseudo-code (or PHP code) and/or answer my 2 points above?EDIT 1:Thank you St.Woland for your answer. Can you (or anyone else) tell me if I'm correct on these 6 points:[*]The format of $_SERVER['HTTP_IF_NONE_MATCH'] can be either:a)If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"b) If-None-Match: "xyzzy"and NOT:c) If-None-Match: "xyzzy, r2d2xxxx, c3piozzzz"[*]If !array_key_exists('HTTP_IF_NONE_MATCH', $_SERVER), anyTagMatched() returns NULL.[*]As soon as an ETag in $_SERVER['HTTP_IF_NONE_MATCH'] match my document ETag, anyTagMatched() returns TRUE.[*]If none of the Etags in $_SERVER['HTTP_IF_NONE_MATCH'] are matching my document ETag, anyTagMatched() returns FALSE.[*]If $_SERVER['HTTP_IF_MODIFIED_SINCE'] is set and matches my document "last modified" date isExpired() returns FALSE, otherwise return TRUE.[*]As soon as anyTagMatched() returns TRUE, I issue a 304. If anyTagMatched() returned NULL and isExpired() returned FALSE I can issue a 304. In any other situation I serve my page as normal (I also issue the up-to-date Last-Modified and ETag headers).