Issue #14061 - Fix Alt-Svc header to use HTTP/3 connector port

[afarber]

Fixes #14061

• Add AltSvcCustomizer to HTTP2ServerConnectionFactory that automatically adds the Alt-Svc header to HTTP/2 responses, advertising HTTP/3 availability with the correct port and configurable ma (max-age) attribute per RFC 7838.
• AltSvcCustomizer.setMaxAge(Duration) allows configuring the ma attribute (default: 24 hours, set to null to omit)
• Remove the old AltSvcCustomizer from HTTP3ServerConnectionFactory which incorrectly used the HTTP/2 port
• Add tests for Alt-Svc header generation and maxAge configuration
• Update documentation with ma attribute explanation

[sbordet]

@afarber, I think it's slightly more complicated.

1. HTTP2ServerConnectionFactory and HTTP3ServerConnectionFactory share the same HttpConfiguration.
   In this case, HTTP/2 requests will be customized by AltSvcCustomizer, and your fix to look up the HTTP/3 port is good.
2. However, it may really be the case that the 2 HttpConfigurations are different (because e.g. HTTP/3 has different buffer requirements than HTTP/2).
   In this case, HTTP/2 requests will never be customized.
3. The Alt-Svc header is minimal and cannot be customized, for example with the ma attribute.

In light of this, I think it is perhaps best to make AltSvcCustomizer a public class with more configuration for the header as specified by RFC 7838.

We can have a http3-alt-svc.mod; module http3 depends on http3-alt-svc, and http3-alt-svc is after http2.

@afarber let me know if you want to continue to work on this given the instructions above, otherwise we'll take over.

Thanks!

[sbordet]

@lorban thoughts on the above?

[lorban]

@sbordet an alternative could be to move the alt-svc logic to the H2 connection factory: move the AltSvcCustomizer to HTTP2ServerConnectionFactory, add it on construction like we currently do for H3 and make it scan through the server's connectors in search for one that has the h3 protocol and is a network connector to read its port and generate the alt-svc header.

[afarber]

Hi @sbordet and @lorban, is this what you mean? Moved AltSvcCustomizer to HTTP2ServerConnectionFactory where it scans server.getConnectors() for one with h3 protocol to read the port.

[lorban]

There are a few small things to change here and there, but overall this is the idea I had in mind.

@sbordet what do you think of this?

[lorban]

Besides a few small improvements to the doc, this LGTM.

BTW, did you sign the Eclipse Contributor Agreement?

[lorban]

@sbordet is there anything you want to add to this?