[Libwebsockets] empty settings frame from remote client

Marek 'MMx' Ludha mludha at gmail.com
Wed Aug 26 11:50:58 CEST 2020


Hi.

I believe there's a bug here:
https://libwebsockets.org/git/libwebsockets/tree/lib/roles/h2/http2.c?h=v4.0-stable#n1109
(also in master:
https://libwebsockets.org/git/libwebsockets/tree/lib/roles/h2/http2.c#n1119)
This line disallows remote clients to send a Settings frame with length 0
without ACK flag set. I didn't find any mention in the RFC that this should
be an error. On the contrary, it explicitly allows for empty Settings frame
after client preface: "This sequence ["PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"]
MUST be followed by a SETTINGS frame (Section 6.5), which MAY be empty." (
https://tools.ietf.org/html/rfc7540#section-3.5).

Is there any intention behind this check or do you consider it a bug?

Regards,
Marek Ludha
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