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From "William A. Rowe Jr." <wr...@rowe-clan.net>
Subject Re: DoS with mod_deflate & range requests
Date Wed, 24 Aug 2011 16:22:20 GMT
On 8/24/2011 10:55 AM, "Plüm, Rüdiger, VF-Group" wrote:
> 
> Hm. If I got it right what Roy says above about the spec sorting and merging is
> not an option as we need to stick to the order and number of ranges the client
> requested. 

No.  Merging -is- recommended.



10.4.17 416 Requested Range Not Satisfiable

   A server SHOULD return a response with this status code if a request
   included a Range request-header field (section 14.35), and none of
   the range-specifier values in this field overlap the current extent
   of the selected resource, and the request did not include an If-Range
   request-header field. (For byte-ranges, this means that the first-
   byte-pos of all of the byte-range-spec values were greater than the
   current length of the selected resource.)

Note; the FIRST byte-pos is invalid.  It doesn't suggest that 416 can be
used for semantically valid ranges longer than the document length, or
to represent that valid byte ranges overlapped.  In fact, if ONE range
can be satisfied, 416 is not appropriate.

So if ONE range can be satisfied, it is to be returned (this is reiterated
in 14.16), which may obviously be out-of-sequence.

I would suggest we simply ignore/extend for all overlapping ranges
rather than rejecting them.

E.g.

  0-, 40-50 becomes 0-
  0-499, 400-599 becomes 0-599
  1000-1075, 200-250, 1051-1100 becomes 1000-1100, 200-250

-Sorting- is to be avoided, although as its a SHOULD, I am happy to break
that recommendation if there is no reasonably efficient solution to the
server side.  As Roy suggests, random access on the server side is very
dubious.  A client issuing rich requests should assemble them and must
respect the individual Content-Range response headers.


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