bind interfaces subdirective

[MayCXC]

Assistance Disclosure

No AI was used.

Adds an interfaces subdirective to bind to implement #7256 without changing how addresses are parsed:

example.com {
    bind 10.0.0.1 tcp4/127.0.0.1 tcp6/[::1] {
        interfaces eth0 tcp4/eth1 tcp6/eth2
        protocols h1 h2
    }
}

in the example above, the site is bound to at least six addresses and served with two protocols. This way the tcp6/ udp6/ and ip6: networks can be used instead of a new version mode syntax, and the port is read from the site block again instead of the directive arguments.

Only one address is bound per prefix for interfaces assigned a cidr. This is preferable to composing or selecting multiple addresses to emulate a bind to device syscall; a socket manager can do that natively without the overhead of opening 2^n listeners at once, or the unreliability of trying to open the first one available iteratively. e.g. for linux, the user could apply #7342 with systemd.socket and BindToDevice/FreeBind.

Tests are todo, ideally we will mock the value of net.InterfaceByName and parse a caddyfile.

[MayCXC]

converted to draft because it shares some diffs with #7342