Re: [HTTP/3]Sending reserved frame before SETTINGS

[Ian Swett <[e-mail]>]

Thanks for bringing this up Renjie.  I agree the subsequent text seems to
clarify the answer.

However, is that the behavior we want, given it does limit extensibility in
some small ways?

On Sat, Feb 1, 2020 at 11:25 AM Ryan Hamilton <[e-mail]> wrote:

> Wow, interesting question!
>
> 6.2.1 requires the SETTINGS frame to be first on the control frame:
>
>    If the first frame of the control stream is any other frame
>    type, this MUST be treated as a connection error of type
>    H3_MISSING_SETTINGS.
>
>
> Whereas 7.2.9 says reserved frames have no semantic meaning:
>
>    Frame types of the format "0x1f * N + 0x21" for integer values of N
>    are reserved to exercise the requirement that unknown types be
>    ignored (Section 9 <https://tools.ietf.org/html/draft-ietf-quic-http-25#section-9>).  These frames have no semantics, and can be sent
>    on any open stream when application-layer padding is desired.
>
>
> This sounds like a conflict since something that has no semantics seems
> like it should not cause errors! However, looking Section 9 I think we find
> the resolution:
>
>    Implementations MUST ignore unknown or unsupported values in all
>    extensible protocol elements.  Implementations MUST discard frames
>    and unidirectional streams that have unknown or unsupported types.
>    This means that any of these extension points can be safely used by
>    extensions without prior arrangement or negotiation.  However, where
>    a known frame type is required to be in a specific location, such as
>    the SETTINGS frame as the first frame of the control stream (see
>    Section 6.2.1 <https://tools.ietf.org/html/draft-ietf-quic-http-25#section-6..2.1>), an unknown frame type does not satisfy that
>    requirement and SHOULD be treated as an error.
>
>
> So it seems that it's illegal to send a GREASED frame before the SETTINGS frame. Does that sound right to you?
>
>
> Cheers,
>
>
> Ryan
>
>
> On Fri, Jan 31, 2020 at 11:10 PM Renjie Tang <renjietang=
> [e-mail]> wrote:
>
>> Hi all,
>>
>> When I was implementing greasing for HTTP/3 frames, I came across a
>> potential confusion.
>>
>> Presumably, if a non-reserved unknown frame is received before SETTINGS
>> on a control stream, the connection should be closed.
>>
>> But if a reserved frame is received before SETTINGS frame on a control
>> stream, does it count as an error and close the connection? Or should
>> it simply be ignored because it has no semantic meaning?
>>
>> Thanks!
>> Renjie
>>
>