add all files from Hong

server/sendEthernet.go

@@ -0,0 +1,96 @@
+// Copyright 2018-present the CoreDHCP Authors. All rights reserved
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
+
+// +build linux
+
+package server
+
+import (
+	"fmt"
+	"net"
+	"syscall"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"github.com/insomniacslk/dhcp/dhcpv4"
+)
+
+//this function sends an unicast to the hardware address defined in resp.ClientHWAddr,
+//the layer3 destination address is still the broadcast address;
+//iface: the interface where the DHCP message should be sent;
+//resp: DHCPv4 struct, which should be sent;
+func sendEthernet(iface net.Interface, resp *dhcpv4.DHCPv4) error {
+
+	eth := layers.Ethernet{
+		EthernetType: layers.EthernetTypeIPv4,
+		SrcMAC:       iface.HardwareAddr,
+		DstMAC:       resp.ClientHWAddr,
+	}
+	ip := layers.IPv4{
+		Version:  4,
+		TTL:      64,
+		SrcIP:    resp.ServerIPAddr,
+		DstIP:    resp.YourIPAddr,
+		Protocol: layers.IPProtocolUDP,
+		Flags:    layers.IPv4DontFragment,
+	}
+	udp := layers.UDP{
+		SrcPort: dhcpv4.ServerPort,
+		DstPort: dhcpv4.ClientPort,
+	}
+
+	err := udp.SetNetworkLayerForChecksum(&ip)
+	if err != nil {
+		return fmt.Errorf("Send Ethernet: Couldn't set network layer: %v", err)
+	}
+
+	buf := gopacket.NewSerializeBuffer()
+	opts := gopacket.SerializeOptions{
+		ComputeChecksums: true,
+		FixLengths:       true,
+	}
+
+	// Decode a packet
+	packet := gopacket.NewPacket(resp.ToBytes(), layers.LayerTypeDHCPv4, gopacket.NoCopy)
+	dhcpLayer := packet.Layer(layers.LayerTypeDHCPv4)
+	dhcp, ok := dhcpLayer.(gopacket.SerializableLayer)
+	if !ok {
+		return fmt.Errorf("Layer %s is not serializable", dhcpLayer.LayerType().String())
+	}
+	err = gopacket.SerializeLayers(buf, opts, &eth, &ip, &udp, dhcp)
+	if err != nil {
+		return fmt.Errorf("Cannot serialize layer: %v", err)
+	}
+	data := buf.Bytes()
+
+	fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, 0)
+	if err != nil {
+		return fmt.Errorf("Send Ethernet: Cannot open socket: %v", err)
+	}
+	defer func() {
+		err = syscall.Close(fd)
+		if err != nil {
+			log.Errorf("Send Ethernet: Cannot close socket: %v", err)
+		}
+	}()
+
+	err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
+	if err != nil {
+		log.Errorf("Send Ethernet: Cannot set option for socket: %v", err)
+	}
+
+	var hwAddr [8]byte
+	copy(hwAddr[0:6], resp.ClientHWAddr[0:6])
+	ethAddr := syscall.SockaddrLinklayer{
+		Protocol: 0,
+		Ifindex:  iface.Index,
+		Halen:    6,
+		Addr:     hwAddr, //not used
+	}
+	err = syscall.Sendto(fd, data, 0, &ethAddr)
+	if err != nil {
+		return fmt.Errorf("Cannot send frame via socket: %v", err)
+	}
+	return nil
+}