fix: disable h3 for unix domain socket

[Geun-Oh]

Related Issue: #6760

Disable HTTP/3 for unix domain socket

Caddyfile

example.com {
  bind unix/@test
  respond 200
}

Preview

2025/01/05 05:28:28.361	INFO	using adjacent Caddyfile
2025/01/05 05:28:28.361	INFO	adapted config to JSON	{"adapter": "caddyfile"}
2025/01/05 05:28:28.361	WARN	Caddyfile input is not formatted; run 'caddy fmt --overwrite' to fix inconsistencies	{"adapter": "caddyfile", "file": "Caddyfile", "line": 2}
2025/01/05 05:28:28.363	INFO	admin	admin endpoint started	{"address": "localhost:2019", "enforce_origin": false, "origins": ["//localhost:2019", "//[::1]:2019", "//127.0.0.1:2019"]}
2025/01/05 05:28:28.363	INFO	http.auto_https	enabling automatic HTTP->HTTPS redirects	{"server_name": "srv0"}
2025/01/05 05:28:28.363	WARN	http	HTTP/3 disabled because Unix can't multiplex STREAM and DGRAM on same socket	{"file": "@test"}
2025/01/05 05:28:28.363	INFO	tls.cache.maintenance	started background certificate maintenance	{"cache": "0x14000625400"}
2025/01/05 05:28:28.364	INFO	http.log	server running	{"name": "srv0", "protocols": ["h1", "h2"]}
2025/01/05 05:28:28.364	INFO	http	enabling automatic TLS certificate management	{"domains": ["example.com"]}
2025/01/05 05:28:28.365	INFO	autosaved config (load with --resume flag)	{"file": "/Users/user/.config/caddy/autosave.json"}
2025/01/05 05:28:28.365	INFO	serving initial configuration
2025/01/05 05:28:28.370	INFO	tls	storage cleaning happened too recently; skipping for now	{"storage": "FileStorage:/Users/user/.local/share/caddy", "instance": "534925d6-3750-47c4-9f3b-703fce2d2263", "try_again": "2025/01/06 05:28:28.370", "try_again_in": 86399.99999975}
2025/01/05 05:28:28.371	INFO	tls	finished cleaning storage units
2025/01/05 05:28:28.373	INFO	tls.obtain	acquiring lock	{"identifier": "example.com"}

It's the same behavior with version 2.8.4

Please tell me if there is another points that I have to care about.

---

BTW, do you mind if caddy to provide HTTP/3 uds connection (with only SOCK_DGRAM)?
Maybe it'll be good if caddy provides optional uds connection with configuration in Caddyfile.
Like below...

example.com {
  bind_http3 unix/@test
  respond 200
}

If you have mind with it, I'll make a new issue.

Thanks.

[CLAassistant]

All committers have signed the CLA.

[mholt]

Thanks for the patch. LGTM at a glance. Do you have any other critiques, @WeidiDeng ?