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Re: [Technical Errata Reported] RFC7540 (5249)

"Roy T. Fielding" <fielding@gbiv.com> Fri, 02 February 2018 17:12 UTC

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From: "Roy T. Fielding" <fielding@gbiv.com>
In-Reply-To: <3e511c0e-15fa-094e-2132-e9d0b40ac7e3@ninenines.eu>
Date: Fri, 02 Feb 2018 09:09:39 -0800
Cc: Willy Tarreau <w@1wt.eu>, Martin Thomson <martin.thomson@gmail.com>, HTTP Working Group <ietf-http-wg@w3.org>, Vasiliy Faronov <vfaronov@gmail.com>
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References: <20180201011901.E0600B80DAC@rfc-editor.org> <CABkgnnWJzG2YJ3UDsA5hfFT=1sKuEqGsBLFxWmsN1_XqFOROSg@mail.gmail.com> <20180201063200.GB1387@1wt.eu> <3e511c0e-15fa-094e-2132-e9d0b40ac7e3@ninenines.eu>
To: Loïc Hoguin <essen@ninenines.eu>
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Subject: Re: [Technical Errata Reported] RFC7540 (5249)
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> On Feb 2, 2018, at 1:43 AM, Loïc Hoguin <essen@ninenines.eu> wrote:
> On 02/01/2018 07:32 AM, Willy Tarreau wrote:
>> On Thu, Feb 01, 2018 at 12:43:53PM +1100, Martin Thomson wrote:
>>> The observation is correct.  However, I'm not sure that this is the
>>> solution I would choose.  I'm not sure, but I think that an empty
>>> header field would cause problems.
>> Some intermediaries risk to drop it, considering that empty is equivalent
>> to absent.
> 
> I'm curious about this as I don't recall reading this in the RFCs. [...]

FTR, an empty HTTP/1 field value is definitely not equivalent to absent.  In some cases
it is an error; in other cases it has a distinct meaning (like in Accept). An intermediary
that absent-mindedly removed empty fields is just broken, but that doesn't apply to
CGI (which is not HTTP) nor HTTP2-Settings (which should be listed in Connection to
prevent it from being forwarded).

Cheers,

....Roy

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