Initial commit

1 files changed, 146 insertions, 0 deletions

diff --git a/dhcpv4/client.go b/dhcpv4/client.go
new file mode 100644
index 0000000..34724e4
--- /dev/null
+++ b/dhcpv4/client.go
@@ -0,0 +1,146 @@
+package dhcpv4
+
+import (
+	"encoding/binary"
+	"golang.org/x/net/ipv4"
+	"net"
+	"syscall"
+	"time"
+)
+
+const (
+	maxUDPReceivedPacketSize = 8192 // arbitrary size. Theoretically could be up to 65kb
+)
+
+type Client struct {
+	Network string
+	Dialer  *net.Dialer
+	Timeout time.Duration
+}
+
+func makeRawBroadcastPacket(payload []byte) ([]byte, error) {
+	udp := make([]byte, 8)
+	binary.BigEndian.PutUint16(udp[:2], ClientPort)
+	binary.BigEndian.PutUint16(udp[2:4], ServerPort)
+	binary.BigEndian.PutUint16(udp[4:6], uint16(8+len(payload)))
+	binary.BigEndian.PutUint16(udp[6:8], 0) // try to offload the checksum
+
+	h := ipv4.Header{
+		Version:  4,
+		Len:      20,
+		TotalLen: 20 + len(udp) + len(payload),
+		TTL:      64,
+		Protocol: 17, // UDP
+		Dst:      net.IPv4bcast,
+		Src:      net.IPv4zero,
+	}
+	ret, err := h.Marshal()
+	if err != nil {
+		return nil, err
+	}
+	ret = append(ret, udp...)
+	ret = append(ret, payload...)
+	return ret, nil
+}
+
+// Run a full DORA transaction: Discovery, Offer, Request, Acknowledge, over
+// UDP. Does not retry in case of failures.
+// Returns a list of DHCPv4 structures representing the exchange. It can contain
+// up to four elements, ordered as Discovery, Offer, Request and Acknowledge.
+// In case of errors, an error is returned, and the list of DHCPv4 objects will
+// be shorted than 4, containing all the sent and received DHCPv4 messages.
+func (c *Client) Exchange(d *DHCPv4, ifname string) ([]DHCPv4, error) {
+	conversation := make([]DHCPv4, 1)
+	var err error
+
+	// Discovery
+	if d == nil {
+		d, err = NewDiscovery()
+		if err != nil {
+			return conversation, err
+		}
+		iface, err := net.InterfaceByName(ifname)
+		if err != nil {
+			return conversation, err
+		}
+		d.SetClientHwAddr(iface.HardwareAddr)
+	}
+	conversation[0] = *d
+
+	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_RAW, syscall.IPPROTO_RAW)
+	if err != nil {
+		return conversation, err
+	}
+	err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+	if err != nil {
+		return conversation, err
+	}
+	err = syscall.SetsockoptInt(fd, syscall.IPPROTO_IP, syscall.IP_HDRINCL, 1)
+	if err != nil {
+		return conversation, err
+	}
+	err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_BROADCAST, 1)
+	if err != nil {
+		return conversation, err
+	}
+	err = syscall.BindToDevice(fd, ifname)
+	if err != nil {
+		return conversation, err
+	}
+
+	daddr := syscall.SockaddrInet4{Port: ClientPort, Addr: [4]byte{255, 255, 255, 255}}
+	packet, err := makeRawBroadcastPacket(d.ToBytes())
+	if err != nil {
+		return conversation, err
+	}
+	err = syscall.Sendto(fd, packet, 0, &daddr)
+	if err != nil {
+		return conversation, err
+	}
+
+	// Offer
+	conn, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IPv4(0, 0, 0, 0), Port: ClientPort})
+	if err != nil {
+		return conversation, err
+	}
+	defer conn.Close()
+
+	buf := make([]byte, maxUDPReceivedPacketSize)
+	oobdata := []byte{} // ignoring oob data
+	n, _, _, _, err := conn.ReadMsgUDP(buf, oobdata)
+	offer, err := FromBytes(buf[:n])
+	if err != nil {
+		return conversation, err
+	}
+	// TODO match the packet content
+	// TODO check that the peer address matches the declared server IP and port
+	conversation = append(conversation, *offer)
+
+	// Request
+	request, err := RequestFromOffer(*offer)
+	if err != nil {
+		return conversation, err
+	}
+	conversation = append(conversation, *request)
+	packet, err = makeRawBroadcastPacket(request.ToBytes())
+	if err != nil {
+		return conversation, err
+	}
+	err = syscall.Sendto(fd, packet, 0, &daddr)
+	if err != nil {
+		return conversation, err
+	}
+
+	// Acknowledge
+	buf = make([]byte, maxUDPReceivedPacketSize)
+	n, _, _, _, err = conn.ReadMsgUDP(buf, oobdata)
+	acknowledge, err := FromBytes(buf[:n])
+	if err != nil {
+		return conversation, err
+	}
+	// TODO match the packet content
+	// TODO check that the peer address matches the declared server IP and port
+	conversation = append(conversation, *acknowledge)
+
+	return conversation, nil
+}