ngtcp2 + gnutls fails to connect h3: "Resource temporarily unavailable"

[bagder]

It looks like boringssl backed server does not like ClientHello generated by GnuTLS. It is hard for me to debug this because it is TLS internal stuff.

Similar to #6864 but this only happens with GnuTLS builds now.

Originally posted by @tatsuhiro-t in #6864 (comment)

[tatsuhiro-t]

It looks like GnuTLS sends legacy session ID which must be prohibited in QUIC: https://tools.ietf.org/html/draft-ietf-quic-tls-34#section-8.4
Now I have to find how to make GnuTLS stop sending this.
Meanwhile it seems that OpenSSL does not check this thing out, which smells like a bug.

[tatsuhiro-t]

@ueno Is there any way to tell GnuTLS to disable TLSv1.3 compatibility mode?

It looks like #undef TLS13_APPENDIX_D4 disables it, but it is a compile time option.

[ueno]

Not currently, but it should be easy to add. I've filed an issue at:
https://gitlab.com/gnutls/gnutls/-/issues/1208

[bagder]

I'm going to close this issue here since this has been determined to be a GnuTLS bug and it isn't very useful for us to keep it open here as well. This should work with curl once GnuTLS is fixed to do right.