// 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.

package net

import (
	"os"
	"syscall"
)

// interfaceMulticastAddrTable returns addresses for a specific
// interface.
func interfaceMulticastAddrTable(ifi *Interface) ([]Addr, error) {
	tab, err := syscall.RouteRIB(syscall.NET_RT_IFLIST2, ifi.Index)
	if err != nil {
		return nil, os.NewSyscallError("routerib", err)
	}
	msgs, err := syscall.ParseRoutingMessage(tab)
	if err != nil {
		return nil, os.NewSyscallError("parseroutingmessage", err)
	}
	var ifmat []Addr
	for _, m := range msgs {
		switch m := m.(type) {
		case *syscall.InterfaceMulticastAddrMessage:
			if ifi.Index == int(m.Header.Index) {
				ifma, err := newMulticastAddr(ifi, m)
				if err != nil {
					return nil, err
				}
				if ifma != nil {
					ifmat = append(ifmat, ifma)
				}
			}
		}
	}
	return ifmat, nil
}

func newMulticastAddr(ifi *Interface, m *syscall.InterfaceMulticastAddrMessage) (*IPAddr, error) {
	sas, err := syscall.ParseRoutingSockaddr(m)
	if err != nil {
		return nil, os.NewSyscallError("parseroutingsockaddr", err)
	}
	switch sa := sas[syscall.RTAX_IFA].(type) {
	case *syscall.SockaddrInet4:
		return &IPAddr{IP: IPv4(sa.Addr[0], sa.Addr[1], sa.Addr[2], sa.Addr[3])}, nil
	case *syscall.SockaddrInet6:
		ifma := IPAddr{IP: make(IP, IPv6len)}
		copy(ifma.IP, sa.Addr[:])
		// NOTE: KAME based IPv6 protocol stack usually embeds
		// the interface index in the interface-local or
		// link-local address as the kernel-internal form.
		if ifma.IP.IsInterfaceLocalMulticast() || ifma.IP.IsLinkLocalMulticast() {
			ifma.IP[2], ifma.IP[3] = 0, 0
		}
		return &ifma, nil
	default:
		return nil, nil
	}
}