Clash.Meta/component/dialer/bind_darwin.go

package dialer

import (
	"net"
	"syscall"
)

func bindIfaceToDialer(dialer *net.Dialer, ifaceName string) error {
	iface, err := net.InterfaceByName(ifaceName)
	if err != nil {
		return err
	}

	dialer.Control = func(network, address string, c syscall.RawConn) error {
		return c.Control(func(fd uintptr) {
			switch network {
			case "tcp4", "udp4":
				syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_BOUND_IF, iface.Index)
			case "tcp6", "udp6":
				syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_BOUND_IF, iface.Index)
			}
		})
	}

	return nil
}

func bindIfaceToListenConfig(lc *net.ListenConfig, ifaceName string) error {
	iface, err := net.InterfaceByName(ifaceName)
	if err != nil {
		return err
	}

	lc.Control = func(network, address string, c syscall.RawConn) error {
		return c.Control(func(fd uintptr) {
			switch network {
			case "tcp4", "udp4":
				syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IP, syscall.IP_BOUND_IF, iface.Index)
			case "tcp6", "udp6":
				syscall.SetsockoptInt(int(fd), syscall.IPPROTO_IPV6, syscall.IPV6_BOUND_IF, iface.Index)
			}
		})
	}

	return nil
}