vendor: add github.com/d2g

vendor/github.com/d2g/dhcp4client/pktsock_linux.go

@@ -0,0 +1,147 @@
+package dhcp4client
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+	"net"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+const (
+	minIPHdrLen = 20
+	maxIPHdrLen = 60
+	udpHdrLen   = 8
+	ip4Ver      = 0x40
+	ttl         = 16
+	srcPort     = 68
+	dstPort     = 67
+)
+
+var (
+	bcastMAC = []byte{255, 255, 255, 255, 255, 255}
+)
+
+// abstracts AF_PACKET
+type packetSock struct {
+	fd      int
+	ifindex int
+}
+
+func NewPacketSock(ifindex int) (*packetSock, error) {
+	fd, err := unix.Socket(unix.AF_PACKET, unix.SOCK_DGRAM, int(swap16(unix.ETH_P_IP)))
+	if err != nil {
+		return nil, err
+	}
+
+	addr := unix.SockaddrLinklayer{
+		Ifindex:  ifindex,
+		Protocol: swap16(unix.ETH_P_IP),
+	}
+
+	if err = unix.Bind(fd, &addr); err != nil {
+		return nil, err
+	}
+
+	return &packetSock{
+		fd:      fd,
+		ifindex: ifindex,
+	}, nil
+}
+
+func (pc *packetSock) Close() error {
+	return unix.Close(pc.fd)
+}
+
+func (pc *packetSock) Write(packet []byte) error {
+	lladdr := unix.SockaddrLinklayer{
+		Ifindex:  pc.ifindex,
+		Protocol: swap16(unix.ETH_P_IP),
+		Halen:    uint8(len(bcastMAC)),
+	}
+	copy(lladdr.Addr[:], bcastMAC)
+
+	pkt := make([]byte, minIPHdrLen+udpHdrLen+len(packet))
+
+	fillIPHdr(pkt[0:minIPHdrLen], udpHdrLen+uint16(len(packet)))
+	fillUDPHdr(pkt[minIPHdrLen:minIPHdrLen+udpHdrLen], uint16(len(packet)))
+
+	// payload
+	copy(pkt[minIPHdrLen+udpHdrLen:len(pkt)], packet)
+
+	return unix.Sendto(pc.fd, pkt, 0, &lladdr)
+}
+
+func (pc *packetSock) ReadFrom() ([]byte, net.IP, error) {
+	pkt := make([]byte, maxIPHdrLen+udpHdrLen+MaxDHCPLen)
+	n, _, err := unix.Recvfrom(pc.fd, pkt, 0)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	// IP hdr len
+	ihl := int(pkt[0]&0x0F) * 4
+	// Source IP address
+	src := net.IP(pkt[12:16])
+
+	return pkt[ihl+udpHdrLen : n], src, nil
+}
+
+func (pc *packetSock) SetReadTimeout(t time.Duration) error {
+
+	tv := unix.NsecToTimeval(t.Nanoseconds())
+	return unix.SetsockoptTimeval(pc.fd, unix.SOL_SOCKET, unix.SO_RCVTIMEO, &tv)
+}
+
+// compute's 1's complement checksum
+func chksum(p []byte, csum []byte) {
+	cklen := len(p)
+	s := uint32(0)
+	for i := 0; i < (cklen - 1); i += 2 {
+		s += uint32(p[i+1])<<8 | uint32(p[i])
+	}
+	if cklen&1 == 1 {
+		s += uint32(p[cklen-1])
+	}
+	s = (s >> 16) + (s & 0xffff)
+	s = s + (s >> 16)
+	s = ^s
+
+	csum[0] = uint8(s & 0xff)
+	csum[1] = uint8(s >> 8)
+}
+
+func fillIPHdr(hdr []byte, payloadLen uint16) {
+	// version + IHL
+	hdr[0] = ip4Ver | (minIPHdrLen / 4)
+	// total length
+	binary.BigEndian.PutUint16(hdr[2:4], uint16(len(hdr))+payloadLen)
+	// identification
+	if _, err := rand.Read(hdr[4:5]); err != nil {
+		panic(err)
+	}
+	// TTL
+	hdr[8] = 16
+	// Protocol
+	hdr[9] = unix.IPPROTO_UDP
+	// dst IP
+	copy(hdr[16:20], net.IPv4bcast.To4())
+	// compute IP hdr checksum
+	chksum(hdr[0:len(hdr)], hdr[10:12])
+}
+
+func fillUDPHdr(hdr []byte, payloadLen uint16) {
+	// src port
+	binary.BigEndian.PutUint16(hdr[0:2], srcPort)
+	// dest port
+	binary.BigEndian.PutUint16(hdr[2:4], dstPort)
+	// length
+	binary.BigEndian.PutUint16(hdr[4:6], udpHdrLen+payloadLen)
+}
+
+func swap16(x uint16) uint16 {
+	var b [2]byte
+	binary.BigEndian.PutUint16(b[:], x)
+	return binary.LittleEndian.Uint16(b[:])
+}