webui4frpc/internal/cluster/lo_addr.go

// LocalAddr helpers: resolve this node's routable LAN address used when a
// forward targets a loopback (127.0.0.1/0.0.0.0/localhost) and is NOT marked
// local-only — the task is distributed to the cluster, so the backend address
// must be reachable from whichever node claims it.
package cluster

import (
	"net"
)

// LanAddr returns this host's first non-loopback IPv4 address ("" if none can
// be determined, e.g. offline/no interface).
func LanAddr() string {
	addrs, err := net.InterfaceAddrs()
	if err != nil {
		return ""
	}
	for _, a := range addrs {
		if ipn, ok := a.(*net.IPNet); ok {
			ip := ipn.IP
			if ip.IsLoopback() || ip.To4() == nil {
				continue
			}
			return ip.String()
		}
	}
	return ""
}

// IsLoopbackIP reports whether addr is a loopback/unspecified/localhost value
// that must be rewritten to a routable address before cluster distribution.
func IsLoopbackIP(addr string) bool {
	switch addr {
	case "", "127.0.0.1", "0.0.0.0", "::1", "::", "localhost":
		return true
	}
	return false
}

// RewriteForCluster returns addr if it is routable, or the LAN address when it
// is loopback. Returns original when no LAN address is known (keeps ip as-is).
func RewriteForCluster(addr string) string {
	if !IsLoopbackIP(addr) {
		return addr
	}
	if lan := LanAddr(); lan != "" {
		return lan
	}
	return addr
}