Re: Last Call: <draft-ietf-httpbis-header-structure-18.txt> (Structured Field Values for HTTP) to Proposed Standard

Mark Nottingham <> Mon, 18 May 2020 06:09 UTC

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From: Mark Nottingham <>
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Date: Mon, 18 May 2020 16:06:08 +1000
Cc:,, HTTP Working Group <>, Barry Leiba <>,
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To: "Julian F. Reschke" <>
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Subject: Re: Last Call: <draft-ietf-httpbis-header-structure-18.txt> (Structured Field Values for HTTP) to Proposed Standard
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> On 15 May 2020, at 6:20 pm, Julian Reschke <> wrote:
>>> What bugs me is that we have an invalid message to start with, but the
>>> spec apparently *requires* receivers to accept it, albeit with
>>> potentially unpredictable results.
>>> IMHO it would be better to allow those recipients that *can* detect the
>>> brokenness to reject these fields.
>> The problem is that many recipients won't be able to. This includes not only when an intermediary combines multiple field lines into one, but also when a server or library does so (which is more common IME).
> Yes.
>> We already have potential inconsistency in whitespace caused by such combination. I'm reluctant to add another dimension of inconsistency (whether or not the SH^HF implementation can recognise this situation and reject early).
> Understood, but I would see it this way: having *some* implementations
> able to detect broken input is better than nobody detecting it, because
> this way the problem might be fixed.
> I'd really like to hear some more feedback on this. Note that this is
> related to what we can say in draft-ietf-httpbis-semantics - is a
> recipient allowed *not* to combine field lines when they are clearly in
> error, such as with:
>  Location:
>  Location: bar

I think this means adding something like this near the bottom of 4.2. Parsing Structured Fields:

Parsers MAY fail when processing a field value spread across multiple field lines, when one of those lines does not parse as that field. For example, a parsing handling an Example-String field that's defined as a sf-string is allowed to fail when processing this field section:

Example-String: "foo
Example-String: bar"

Does that do it?


Mark Nottingham