37 

    38 // PktInfo4 encodes Inet4Pktinfo into a socket control message of type IP_PKTINFO.

    39 func PktInfo4(info *Inet4Pktinfo) []byte {

    40 	b := make([]byte, CmsgSpace(SizeofInet4Pktinfo))

    41 	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))

    42 	h.Level = SOL_IP

    43 	h.Type = IP_PKTINFO

    44 	h.SetLen(CmsgLen(SizeofInet4Pktinfo))

    45 	*(*Inet4Pktinfo)(h.data(0)) = *info

    46 	return b

    47 }

    48 

    49 // PktInfo6 encodes Inet6Pktinfo into a socket control message of type IPV6_PKTINFO.

    50 func PktInfo6(info *Inet6Pktinfo) []byte {

    51 	b := make([]byte, CmsgSpace(SizeofInet6Pktinfo))

    52 	h := (*Cmsghdr)(unsafe.Pointer(&b[0]))

    53 	h.Level = SOL_IPV6

    54 	h.Type = IPV6_PKTINFO

    55 	h.SetLen(CmsgLen(SizeofInet6Pktinfo))

    56 	*(*Inet6Pktinfo)(h.data(0)) = *info

    57 	return b

    58 }

    59 

    60 // ParseOrigDstAddr decodes a socket control message containing the original

    61 // destination address. To receive such a message the IP_RECVORIGDSTADDR or

    62 // IPV6_RECVORIGDSTADDR option must be enabled on the socket.

    63 func ParseOrigDstAddr(m *SocketControlMessage) (Sockaddr, error) {

    64 	switch {

    65 	case m.Header.Level == SOL_IP && m.Header.Type == IP_ORIGDSTADDR:

    66 		pp := (*RawSockaddrInet4)(unsafe.Pointer(&m.Data[0]))

    67 		sa := new(SockaddrInet4)

    68 		p := (*[2]byte)(unsafe.Pointer(&pp.Port))

    69 		sa.Port = int(p[0])<<8 + int(p[1])

    70 		sa.Addr = pp.Addr

    71 		return sa, nil

    72 

    73 	case m.Header.Level == SOL_IPV6 && m.Header.Type == IPV6_ORIGDSTADDR:

    74 		pp := (*RawSockaddrInet6)(unsafe.Pointer(&m.Data[0]))

    75 		sa := new(SockaddrInet6)

    76 		p := (*[2]byte)(unsafe.Pointer(&pp.Port))

    77 		sa.Port = int(p[0])<<8 + int(p[1])

    78 		sa.ZoneId = pp.Scope_id

    79 		sa.Addr = pp.Addr

    80 		return sa, nil

    81 

    82 	default:

    83 		return nil, EINVAL

    84 	}

    85 }