Re: [quicwg/base-drafts] Incorrect values for Required Insert Count (#3305)

Bence Béky <> Fri, 28 February 2020 14:58 UTC

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Date: Fri, 28 Feb 2020 06:58:29 -0800
From: Bence Béky <>
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Subject: Re: [quicwg/base-drafts] Incorrect values for Required Insert Count (#3305)
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This is not only a performance problem or a potential deadlock.

If the encoder sends an unnecessarily large Required Insert Count but does not consider the stream blocked if the Known Insert Count is at least as large as the actual Required Insert Count, and the decoder does not start decoding until the Known Insert Count reaches the Required Insert Count received in the header block prefix (therefore it does not realize that the stream is in fact not blocked), then the encoder and the decoder might have a different idea about the number of blocked streams.  This might result in the decoder closing the connection due to SETTINGS_QPACK_BLOCKED_STREAMS violation.

Of course is the encoder uses the same incorrect value for sending as Required Insert Count and for bookkeeping of blocked streams then this problem does not arise.

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