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Re: #535: No 1xx Status Codes

From: Willy Tarreau <w@1wt.eu>
Date: Tue, 15 Jul 2014 11:43:40 +0200
To: Julian Reschke <julian.reschke@gmx.de>
Cc: Mark Nottingham <mnot@mnot.net>, HTTP Working Group <ietf-http-wg@w3.org>
Message-ID: <20140715094340.GC12333@1wt.eu>
Hi Julian,

On Tue, Jul 15, 2014 at 10:35:32AM +0200, Julian Reschke wrote:
> On 2014-07-15 10:13, Mark Nottingham wrote:
> >My .02 -
> >
> >Status codes have semantic "heft" in the protocol, and if an entire class 
> >of them is both poorly supported and has poor interest, it's not 
> >unreasonable to consider deprecating that class of status codes. If 
> >someone tries to use it in the future, they're going to be disappointed, 
> >because it isn't supported in software and APIs; that semantic won't be 
> >useful to express or expect (as was found with 102).
> But we are not deprecating them, we are *removing* them.
> >Persisting 1xx status codes has a real cost; besides the obvious cost of 
> >requiring HTTP/2 implementations to code for them, test them, and support 
> >them, there's also the cost of handling the interoperability problems when 
> >they don't work.
> HTTP/1.1<->2 converters need to code for them anyway: in one case 
> they'll drop them (requires detecting them), in the other case they 
> forward them.

I could be wrong, but the only possible issues I'm seeing with them removed
are :

  - H1->H2 gateways : have to respond 100-continue when getting an Expect
    header field, possibly to later break the connection if the server aborts
    the stream. I don't think it's a huge issue, it's similar to dealing with
    302 on POSTs in my opinion (not easy either but necessary anyway).

  - H2->H1 gateways : may benefit from sending Expect in outgoing POST requests
    or may have to do it over persistent connections, and to strip any 100
    response. This is a difficulty which already has to be dealt with in pure

I'm still seeing use cases for 101. If my H1->H2 gateway receives a WS
Upgrade request, I'm not sure how to pass it to local servers. It can be
worse for explicit proxies which will have to pass this to the rest of the
world. Maybe they'll have to pass them in 1.1, or maybe some will try to
emulate the CONNECT mode in H2, I don't know.

I remember you expressed some desire for 102, I don't know if that cannot
be done with some informational frames later. Or maybe this is the only
thing we'd need : send informational frames in either direction ?

> I agree that Trailers and 1xx are very similar. That being said, I'd 
> rather get Trailer support fixed instead of them going away.

Maybe one day it will be used to transport checksums, but I doubt it given
that I've yet to see a trailer somewhere :-/

> In general, while implementing HTTP/2, tons of code will need to be 
> touched anyway; we should consider that an opportunity to also address 
> 1.1 related bugs.

I agree on this point. I'd formulate it differently though : opportunity
not to reproduce H1 mistakes :-)

Best regards,
Received on Tuesday, 15 July 2014 09:44:06 UTC

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