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Re: estimated Content-Length with chunked encoding

From: William A. Rowe, Jr. <wrowe@rowe-clan.net>
Date: Mon, 20 Oct 2008 19:36:49 -0500
Message-ID: <48FD2421.6080502@rowe-clan.net>
To: Jamie Lokier <jamie@shareable.org>
CC: Henrik Nordstrom <henrik@henriknordstrom.net>, Greg Dean <dean.greg@gmail.com>, ietf-http-wg@w3.org

Jamie Lokier wrote:
> Henrik Nordstrom wrote:
>> On mån, 2008-10-20 at 13:52 -0700, Greg Dean wrote:
>>> Transfer-Encoding: chunked
>>> Estimated-Content-Length: 300000
>>> This would allow for the recipient of such a message to prepare for a
>>> message of a certain size.
>> Looks useful to me, for the reasons you outlined and a bunch more. See
>> for example the NTLM auth chunked discussion a year ago or so..
>>
>> For responses it's meaningful even without chunked.
>>
>> I don't see anything wrong with it, especially not with the length being
>> an estiamte and not the exact expected lenght.
> 
> In some circumstances you may be able to refine the estimate as the
> message is being transmitted.
> 
> Chunk extensions ("chunk-extension") would suit that:
> 
>     1000;estimated-remaining=299000
>     (1000 bytes)
>     1000;estimated-remaining=298000
>     (1000 bytes)
> 
> I don't know if chunk extensions break in the real world, though.

Or, permit

     1000;completed=25%
     (1000 bytes)
     1000;completed=25%
     (1000 bytes)

My only concern about implementing an 'estimated' extension is what is
your pain tolerance in terms of deviation?  Would a min or max be a better
fit to the problem set?

Given that precomputing the result size is often suboptimal for todays'
assembled responses, but there is a desire to have something to share with
the user, the % notation might work well.  I'm concerned that the estimate
will become an expectation, also costly to precompute, but rarely useful
in practice.
Received on Tuesday, 21 October 2008 00:37:38 GMT

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