Connection reuse not working for HTTP3 connections

[mackenzie-remote]

I did this

When I use a version of curl that supports HTTP3, and uses the alt-svc cache file, domains that do have h3 enabled don't seem to do connection reuse, where-as if I connect to h2 the connection is reused.

Example curl.config file:

url = "https://www.youtube.com/feeds/videos.xml?channel_id=UCC8VtutLDSrreNEZj8CU01A"
output = /dev/null
next
url = "https://www.youtube.com/feeds/videos.xml?channel_id=UC7_VGkwCoKfqh1eZEkzey3A"
output = /dev/null

curl --alt-svc alt-svc.txt -v -K curl.config

The first time (with verbose) and an empty alt-svc, I can see this log message between the first and second transfer:

* Re-using existing connection with host www.youtube.com

When running curl a second time with a populated alt-svc cache it connects using hhttp3 and it does not say 'Re-using existing connection' but

* Connected to www.youtube.com () port 443

(and I verified that it wasn't just a logging issue - when I ran tcpdump I could see that it was opening a new udp connection with a different source port).

I expected the following

For subsequent connections are reused to the same host when using http3.

curl/libcurl version

curl 8.10.0 (aarch64-apple-darwin) libcurl/8.10.0 OpenSSL/3.3.2 zlib/1.3.1 brotli/1.1.0 zstd/1.5.6 c-ares/1.33.1 libidn2/2.3.7 libpsl/0.21.5 libssh2/1.11.0 nghttp2/1.63.0 nghttp3/1.5.0
Release-Date: 2024-09-11
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns mqtt pop3 pop3s scp sftp smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS brotli HSTS HTTP2 HTTP3 HTTPS-proxy IDN IPv6 Largefile libz NTLM PSL SSL threadsafe TLS-SRP TrackMemory UnixSockets zstd

operating system

Darwin xx 23.6.0 Darwin Kernel Version 23.6.0: Mon Jul 29 21:14:21 PDT 2024; root:xnu-10063.141.2~1/RELEASE_ARM64_T8103 arm64

[icing]

@mackenzie-remote can you provide us a curl trace of such a situation? Please invoke curl with curl -v --trace-config=ids,time,http/3. That should give us an idea what is going on. Thanks!

[mackenzie-remote]

OK that's annoying. I can't replicate the issue on Darwin, but I can replicate it on Linux.

Binaries built by this project https://github.com/stunnel/static-curl at
https://github.com/stunnel/static-curl/releases/download/8.10.1/curl-linux-aarch64-8.10.1.tar.xz

curl version:
curl 8.10.1 (aarch64-pc-linux-gnu) libcurl/8.10.1 OpenSSL/3.3.2 zlib/1.3.1 brotli/1.1.0 zstd/1.5.6 c-ares/1.33.1 libidn2/2.3.7 libpsl/0.21.5 libssh2/1.11.0 nghttp2/1.63.0 nghttp3/1.5.0
Release-Date: 2024-09-18
Protocols: dict file ftp ftps gopher gophers http https imap imaps ipfs ipns mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp ws wss
Features: alt-svc AsynchDNS brotli HSTS HTTP2 HTTP3 HTTPS-proxy IDN IPv6 Largefile libz NTLM PSL SSL threadsafe TLS-SRP TrackMemory UnixSockets zstd

OS version:
Linux xx 6.5.0-1021-oracle #21~22.04.1-Ubuntu SMP Fri Apr 5 20:30:17 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

Logs attached as requested with -v --trace-config ids,time,http/3

File 1 is first run with no alt-svc.txt
File 2 is the second run with alt-svc.txt as follows:

# Your alt-svc cache. https://curl.se/docs/alt-svc.html
# This file was generated by libcurl! Edit at your own risk.
h2 www.youtube.com 443 h3 www.youtube.com 443 "20241018 21:52:04" 0 0
h3 www.youtube.com 443 h3 www.youtube.com 443 "20241018 21:52:10" 0 0

issue14890-8.10.1-trace-1.log
issue14890-8.10.1-trace-2.log

[icing]

Thanks. I have reproduced in a local test case that the first url's connection is indeed not reused, but should have been. Investigating...

[icing]

Found the problem. HTTP/3 connections were not reused when the transfer had no specific requirements. This led to your second request to open a new connection.

Should be fixed in #14966.

[mackenzie-remote]

Thanks, am trying to build that locally to test the fixed branch.. Will report back.

[mackenzie-remote]

That fixed the issue, thank you again @icing!

Happy log expert from the second run showing it re-using the existing HTTP/3 connection:

12:29:42.607193 [0-0] * [HTTP/3] [0] easy handle is done
12:29:42.607222 [0-0] * Connection #0 to host www.youtube.com left intact
12:29:42.607807 [1-0] * [HTTP/3] negotiated idle timeout: 120000ms
12:29:42.607842 [1-0] * Re-using existing connection with host www.youtube.com