Hello, it's been some time since my forum posts below:

https://caddy.community/t/experimental-http3-behind-firewall-port-forwarding/14746/8

But very much hoping to continue this conversation and get a config server option implemented to enable a http3 custom port header.

This is for a (maybe common?) use case where caddy is behind another udp/tcp load balancer (eg. AWS ELB) and listening on an address other than the default 443.

Given this basic Caddyfile:

{
	http_port 8080
	https_port 8443
	debug
}

https://localhost:8443 {
	tls internal
	respond "hello there"
}

I currently get the following output (note the alt-svc header values 8443 matches the https_port value):

$ curl -I https://localhost:8443
HTTP/2 200
alt-svc: h3=":8443"; ma=2592000,h3-29=":8443"; ma=2592000
server: Caddy
content-length: 11
date: Wed, 31 Aug 2022 01:09:32 GMT

Right now, i could hard code the following (since upstream supports this):

	s.h3server.Port = 443

into this line here: https://github.com/caddyserver/caddy/blob/master/modules/caddyhttp/server.go#L488

If i recompile using xcaddy, i get the desired behavour (given the same Caddyfile):

curl -I https://localhost:8443
HTTP/2 200
alt-svc: h3=":443"; ma=2592000,h3-29=":443"; ma=2592000
server: Caddy
content-length: 11
date: Wed, 31 Aug 2022 01:10:21 GMT

It seems to me a better option though not to hardcode this value, and instead expose config to control what port is advertised.

eg.

s.h3server.Port = <value taken from json or caddyfile option TBC>

Before attempting a PR, it would be good to understand what the approach should be and/or where the config should sit. (I noticed the protocol option is deprecated for example in the code).

Keen for any thoughts - is this potentially low hanging fruit? Or more likely to be difficult to implement?

Thanks! 😄