relay packets

server/main.go

@@ -2,21 +2,15 @@ package main
 
 import (
 	"encoding/binary"
-	"encoding/hex"
 	"fmt"
 	"log"
 	"net"
 	"os"
-	"os/exec"
 	"sync"
 
 	"baalvpn/shared"
-
-	"github.com/songgao/water"
 )
 
-const IFACE_NAME = "baalvpn"
-
 type Peer struct {
 	RealIP     string
 	InternalIP string
@@ -26,7 +20,7 @@ var (
 	peers      = map[string]*Peer{}
 	peersMutex sync.Mutex
 	nextIP     = 3
-	iface      *water.Interface
+	conn       *net.UDPConn
 )
 
 func main() {
@@ -34,22 +28,6 @@ func main() {
 		panic("root permissions needed")
 	}
 
-	config := water.Config{DeviceType: water.TAP}
-	config.Name = IFACE_NAME
-
-	var err error
-	iface, err = water.New(config)
-	if err != nil {
-		panic(err)
-	}
-
-	if err := exec.Command("ip", "addr", "add", "10.1.0.2/24", "dev", IFACE_NAME).Run(); err != nil {
-		panic(err)
-	}
-	if err := exec.Command("ip", "link", "set", "dev", IFACE_NAME, "up").Run(); err != nil {
-		panic(err)
-	}
-
 	receivePackets()
 }
 
@@ -60,15 +38,15 @@ func receivePackets() {
 	if err != nil {
 		panic(err)
 	}
-	listener, err := net.ListenUDP("udp", listenAddr)
+	conn, err = net.ListenUDP("udp", listenAddr)
 	if err != nil {
 		panic(err)
 	}
-	defer listener.Close()
+	defer conn.Close()
 
 	for {
 		buffer := make([]byte, 50000)
-		n, addr, err := listener.ReadFromUDP(buffer)
+		n, addr, err := conn.ReadFromUDP(buffer)
 		if err != nil {
 			log.Println(err)
 			continue
@@ -77,11 +55,11 @@ func receivePackets() {
 			continue
 		}
 
-		go receivePacket(listener, buffer[:n], addr)
+		go receivePacket(buffer[:n], addr)
 	}
 }
 
-func receivePacket(conn *net.UDPConn, pkt []byte, addr *net.UDPAddr) {
+func receivePacket(pkt []byte, addr *net.UDPAddr) {
 	if len(pkt) < 4 {
 		log.Println("packet too short")
 		return
@@ -101,6 +79,7 @@ func receivePacket(conn *net.UDPConn, pkt []byte, addr *net.UDPAddr) {
 		peersMutex.Lock()
 		defer peersMutex.Unlock()
 
+		// TODO
 		internalIP := fmt.Sprintf("10.1.0.%d", nextIP)
 
 		if peer, ok := peers[addr.IP.String()]; ok {
@@ -118,9 +97,65 @@ func receivePacket(conn *net.UDPConn, pkt []byte, addr *net.UDPAddr) {
 			log.Println(err)
 		}
 	case shared.REQ_DATA:
-		fmt.Println("received packet from " + peerIP + ":")
-		fmt.Println(hex.EncodeToString(pkt[4:]))
+		log.Println("received packet from " + peerIP + ":")
+
+		frame := pkt[4:]
+		etherType := binary.BigEndian.Uint16(frame[12:14])
+		payload := frame[14:]
+
+		switch etherType {
+		case 0x0800: // IPv4
+			destIP := net.IP(payload[16:20]).String()
+			if peer := getPeerByInternalIP(destIP); peer != nil {
+				log.Println("relaying to", peer.RealIP)
+				resp := shared.BuildPkt(shared.RESP_DATA, frame)
+				sendTo(peer.RealIP, resp)
+			} else {
+				log.Println("unknown dest IP: " + destIP)
+			}
+		case 0x0806: // ARP
+			log.Println("broadcasting ARP")
+			resp := shared.BuildPkt(shared.RESP_DATA, frame)
+			broadcast(resp, peerIP)
+		case 0x86dd: // IPv6
+			log.Println("IPv6") // TODO
+		default:
+			log.Printf("unhandled EtherType: 0x%x\n", etherType)
+		}
 	default:
 		log.Println("unknown packet type")
 	}
 }
+
+func broadcast(pkt []byte, except string) {
+	peersMutex.Lock()
+	defer peersMutex.Unlock()
+	for _, p := range peers {
+		if p.RealIP == except {
+			continue
+		}
+		sendTo(p.RealIP, pkt)
+	}
+}
+
+func sendTo(ip string, pkt []byte) {
+	addr, err := net.ResolveUDPAddr("udp", ip+":38001")
+	if err != nil {
+		log.Println(err)
+		return
+	}
+	if _, err := conn.WriteToUDP(pkt, addr); err != nil {
+		log.Println(err)
+	}
+}
+
+func getPeerByInternalIP(internalIP string) *Peer {
+	peersMutex.Lock()
+	defer peersMutex.Unlock()
+	for _, p := range peers {
+		if p.InternalIP == internalIP {
+			return p
+		}
+	}
+	return nil
+}