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Weird MAX_CONCURRENT_STREAMS value with empty HTTP/2 SETTINGS frame

From: Alexandre Pion via curl-users <curl-users_at_cool.haxx.se>
Date: Fri, 5 Jun 2020 17:38:47 +0200 (CEST)

Hi all,

I was looking for MAX_CONCURRENT_STREAMS SETTINGS value with curl and it appears that when receiving an empty SETTINGS frame curl says the server announced 4294967295 MAX_CONCURRENT_STREAMS. Is this a normal behavior ?

The commands I used :

% curl -v --http2 https://odvr.nic.cz/
...
* Using Stream ID: 1 (easy handle 0x562af48fb040)
> GET / HTTP/2
> Host: odvr.nic.cz
> user-agent: curl/7.68.0
> accept: */*
>
* Connection state changed (MAX_CONCURRENT_STREAMS == 4294967295)!
< HTTP/2 404
...

% nghttp -nv https://odvr.nic.cz/
...
[ 0.106] send HEADERS frame <length=36, flags=0x25, stream_id=13>
          ; END_STREAM | END_HEADERS | PRIORITY
          (padlen=0, dep_stream_id=11, weight=16, exclusive=0)
          ; Open new stream
          :method: GET
          :path: /
          :scheme: https
          :authority: odvr.nic.czp
          accept: */*
          accept-encoding: gzip, deflate
          user-agent: nghttp2/1.36.0
[ 0.132] recv SETTINGS frame <length=0, flags=0x01, stream_id=0>
          ; ACK
          (niv=0)
[ 0.175] recv (stream_id=13) :status: 404
[ 0.176] recv HEADERS frame <length=1, flags=0x04, stream_id=13>
          ; END_HEADERS
          (padlen=0)
          ; First response header
[ 0.176] recv DATA frame <length=0, flags=0x01, stream_id=13>
          ; END_STREAM
[ 0.176] send GOAWAY frame <length=8, flags=0x00, stream_id=0>
          (last_stream_id=0, error_code=NO_ERROR(0x00), opaque_data(0)=[])

% curl -V
curl 7.68.0 (x86_64-pc-linux-gnu) libcurl/7.68.0 OpenSSL/1.1.1d libidn2/2.0.5 nghttp2/1.36.0
Release-Date: 2020-01-08
Protocols: dict file ftp ftps gopher http https imap imaps pop3 pop3s rtsp smb smbs smtp smtps telnet tftp
Features: AsynchDNS HTTP2 HTTPS-proxy IDN IPv6 Largefile NTLM NTLM_WB SSL TLS-SRP UnixSockets

Thanks

Alex
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Received on 2020-06-05