src/net/sockoptip4_posix_nonlinux.go

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build (unix && !linux) || windows

package net

import (
	"internal/bytealg"
	"runtime"
	"syscall"
)

func joinIPv4Group(fd *netFD, ifi *Interface, ip IP) error {
	mreq := &syscall.IPMreq{Multiaddr: [4]byte{ip[0], ip[1], ip[2], ip[3]}}
	if err := setIPv4MreqToInterface(mreq, ifi); err != nil {
		return err
	}
	err := fd.pfd.SetsockoptIPMreq(syscall.IPPROTO_IP, syscall.IP_ADD_MEMBERSHIP, mreq)
	runtime.KeepAlive(fd)
	return wrapSyscallError("setsockopt", err)
}

func setIPv4MreqToInterface(mreq *syscall.IPMreq, ifi *Interface) error {
	if ifi == nil {
		return nil
	}
	ifat, err := ifi.Addrs()
	if err != nil {
		return err
	}
	for _, ifa := range ifat {
		switch v := ifa.(type) {
		case *IPAddr:
			if a := v.IP.To4(); a != nil {
				copy(mreq.Interface[:], a)
				goto done
			}
		case *IPNet:
			if a := v.IP.To4(); a != nil {
				copy(mreq.Interface[:], a)
				goto done
			}
		}
	}
done:
	if bytealg.Equal(mreq.Interface[:], IPv4zero.To4()) {
		return errNoSuchMulticastInterface
	}
	return nil
}