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Re: Last Call: <draft-ietf-httpbis-early-hints-03.txt> (An HTTP Status Code for Indicating Hints) to Experimental RFC

Julian Reschke <julian.reschke@gmx.de> Sun, 25 June 2017 10:51 UTC

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Subject: Re: Last Call: <draft-ietf-httpbis-early-hints-03.txt> (An HTTP Status Code for Indicating Hints) to Experimental RFC
To: Willy Tarreau <w@1wt.eu>
Cc: ietf@ietf.org, httpbis-chairs@ietf.org, Mark Nottingham <mnot@mnot.net>, draft-ietf-httpbis-early-hints@ietf.org, ietf-http-wg@w3.org, alexey.melnikov@isode.com
References: <149806437201.15854.12299810594896460001.idtracker@ietfa.amsl.com> <dcdff226-e12d-bb83-982f-8253f46ae935@gmx.de> <20170625104629.GA29021@1wt.eu>
From: Julian Reschke <julian.reschke@gmx.de>
Message-ID: <602955e2-cfd0-e4c8-7afa-e8f3ea78ab3a@gmx.de>
Date: Sun, 25 Jun 2017 12:50:30 +0200
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On 2017-06-25 12:46, Willy Tarreau wrote:
> Hi Julian,
> 
> On Sun, Jun 25, 2017 at 12:11:29PM +0200, Julian Reschke wrote:
>>     An intermediary MAY drop the informational response. (...)
>>
>> That seems to contradict a MUST-level requirement in RFC 7231
>> (https://www.greenbytes.de/tech/webdav/rfc7231.html#rfc.section.6.2.p.3)
> 
> Not completely. An intermediary not aware of 103 may map it to 100. If

It may do so, but it's not allowed to (IMHO).

> the intermediary inserted an "Expect: 100 continue" header field, we
> can reasonably imagine that such an intermediary might also drop the
> returning 103. This wording in 7231 may even encourage some implementations
> to do so : "A proxy MUST forward 1xx responses unless the proxy itself
> requested the generation of the 1xx response". Speaking about 1xx here
> may be read as "I asked for 100, I'm receiving 1xx so that matches".

But that sounds like a bug in the proxy to me. A 103 is not a 100.

>>     Server response:
>>
>>       HTTP/1.1 103 Early Hints
>>       Link: </style.css>; rel=preload; as=style
>>       Link: </script.js>; rel=preload; as=script
>>
>>       HTTP/1.1 200 OK
>>       Date: Fri, 26 May 2017 10:02:11 GMT
>>       Content-Length: 1234
>>       Content-Type: text/html; charset=utf-8
>>       Link: </style.css>; rel=preload; as=style
>>       Link: </script.js>; rel=preload; as=script
>>
>>       <!doctype html>
>>       [... rest of the response body is ommitted from the example ...]
>>
>> The example suggests that early hints are repeated in the final response. Do
>> they have to, actually?
> 
> If we imagine that clients ignore 103 or that intermediaries occasionally
> drop it, I think it's desirable to send them. Said differently, the 103
> response prepends a copy of the Link header fields that the final response
> is supposed to present to help the client fetch them earlier.
> ...

Understood. But is this a requirement or just a suggestion? Does a 
client need to forget the information from the 103 when it's not 
repeated in the final response?

Best regards, Julian

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