RE: #445: Transfer-Codings

On Thursday,24 April 2014 23:13, MORGAN, Keith Shearl wrote:
>

>... Although it might be odd for an implementation to mix compressed and uncompressed frames within a segment,

> I can think of examples where it might be convenient.



Sorry to reply to my own-email, but I wanted to mention a few examples where it might be convenient to allow compressed and uncompressed frames within a segment.  These examples may or may not be pathological.  Perhaps others with more experience have other examples??



1) A server under heavy load might want to dynamically switch off gzip frame compression to conserve cpu resources.  Allowing a mix of compressed and uncompressed frames within a segment would allow a server to immediately switch from compressed frames to uncompressed frames.



2) Amos mentioned here [1] that intermediaries may want to extract a range from a resource they already have cached.  I could imagine a scenario where the intermediary might want to cache the resource with the frames compressed (i.e. as received) to avoid re-compressing for clients which support gzip.  To accomplish that the intermediary could index the offsets of the underlying data contained in each compressed frame.  When later servicing a range request the intermediary would first find the frame which contains the beginning offset of the range.  That frame would likely need to be decompressed to discard the data < the beginning offset.  The data from that frame >= the beginning offset could be re-compressed or sent uncompressed.  All of the frames in-between the beginning and end offsets would be sent as-is (i.e. compressed).  The frame containing the end offset of the range would be processed in the same manner as the frame containing the beginning offset.





[1] http://lists.w3.org/Archives/Public/ietf-http-wg/2014AprJun/0115.html



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