Jetty 12.1.4 demo HTTP/3 wrong port in alt-svc response header

[michal-niklas]

Jetty version(s)
Jetty 12.1.4

Jetty Environment
Jetty demo

HTTP version
HTTP/3

Java version/vendor (use: java -version)

openjdk version "25.0.1" 2025-10-21
OpenJDK Runtime Environment (Red_Hat-25.0.1.0.8-1) (build 25.0.1+8)
OpenJDK 64-Bit Server VM (Red_Hat-25.0.1.0.8-1) (build 25.0.1+8, mixed mode, sharing)

OS type/version
Fedora release 43 (Forty Three)

Description
I think Jetty demo has wrong default configuration for HTTP/3. After running demo on default settings my netstat output looks like:

  mn:~$ netstat -anp | grep 38203
  tcp6  0  0 :::8443   :::*       LISTEN      38203/java
  tcp6  0  0 :::8080   :::*       LISTEN      38203/java
  udp6  0  0 :::8444   :::*                   38203/java

In browser debug (F12) I see header:
alt-svc: h3=":8443"

HTTP/3 specification for this header:
https://datatracker.ietf.org/doc/html/rfc9114#name-http-alternative-services
says about UDP port, so I think it should be header alt-svc: h3=":8444", or default config should use 8443 as as a default UDP port.

How to reproduce?

1. run demo as described in documentation and add http3 module
2. look at netstat output and alt-svc response headers

[sbordet]

When using HTTP3ServerConnectionFactory, AltSvcCustomizer is added to the Server instance so it now customizes requests from all connectors, not only the H3 connector.

There is an assumption that the H2 connector is the same as the H3 connector, and hence the H2 port is used in the Alt-Svc header.

We should make this configurable in HTTP3ServerConnectionFactory, so it would be possible to use different ports for H2 and H3.