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From "William A. Rowe, Jr." <wr...@rowe-clan.net>
Subject Re: mod_deflate DoS using HEAD
Date Wed, 15 Jul 2009 08:53:38 GMT
Joe Orton wrote:
> 
> I'm confused.  Why do this check so late, and why does r->bytes_sent 
> matter?  Why does it "screw up the protocol" if the DEFLATE filter does 
> nothing for a HEAD request?  Because of the concern that a HEAD will 
> return a different C-L & C-E to a GET on the same resource with the same 
> Accept-Encoding header?  Does 2616 mandate that a resource must always 
> exactly the same set of content-codings across methods and time?  
> (AFAICT there is no MUST on that front; it's a SHOULD if anything)

Read through to the end, it breaks all proxied content;

9.4 HEAD

   The HEAD method is identical to GET except that the server MUST NOT
   return a message-body in the response. The metainformation contained
   in the HTTP headers in response to a HEAD request SHOULD be identical
   to the information sent in response to a GET request. This method can
   be used for obtaining metainformation about the entity implied by the
   request without transferring the entity-body itself. This method is
   often used for testing hypertext links for validity, accessibility,
   and recent modification.

   The response to a HEAD request MAY be cacheable in the sense that the
   information contained in the response MAY be used to update a
   previously cached entity from that resource. If the new field values
   indicate that the cached entity differs from the current entity (as
   would be indicated by a change in Content-Length, Content-MD5, ETag
   or Last-Modified), then the cache MUST treat the cache entry as
   stale.


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