Hello, World!

client/main.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"encoding/binary"
+	"log"
+	"net"
+	"os"
+
+	"baalvpn/shared"
+)
+
+const SERVER_IP = "172.20.12.47"
+
+var (
+	internalIP net.IP = nil
+)
+
+func main() {
+	if os.Geteuid() != 0 {
+		panic("root permissions needed")
+	}
+
+	listenAddr, err := net.ResolveUDPAddr("udp", ":38001")
+	if err != nil {
+		panic(err)
+	}
+	listener, err := net.ListenUDP("udp", listenAddr)
+	if err != nil {
+		panic(err)
+	}
+	defer listener.Close()
+
+	go receivePackets(listener)
+	register(listener)
+
+	<-make(chan int) // block forever
+}
+
+func register(c *net.UDPConn) {
+	serverAddr, err := net.ResolveUDPAddr("udp", SERVER_IP+":38000")
+	if err != nil {
+		panic(err)
+	}
+
+	req := shared.BuildPkt(shared.REQ_REGISTER, []byte{})
+	if _, err := c.WriteToUDP(req, serverAddr); err != nil {
+		panic(err)
+	}
+}
+
+func receivePackets(listener *net.UDPConn) {
+	for {
+		buffer := make([]byte, 50000)
+		n, addr, err := listener.ReadFromUDP(buffer)
+		if err != nil {
+			log.Println(err)
+			continue
+		}
+		if n == 0 {
+			continue
+		}
+
+		go receivePacket(listener, buffer[:n], addr)
+	}
+}
+
+func receivePacket(c *net.UDPConn, pkt []byte, addr *net.UDPAddr) {
+	if len(pkt) < 4 {
+		log.Println("packet too short")
+		return
+	}
+	version := binary.LittleEndian.Uint16(pkt[0:])
+	if version != shared.PROTO_VERSION {
+		log.Println("mismatched packet version")
+		return
+	}
+
+	pktType := binary.LittleEndian.Uint16(pkt[2:])
+
+	switch pktType {
+	case shared.RESP_REGISTER:
+		internalIP = net.IP(pkt[4:])
+		log.Println("Received IP from the server:", internalIP.String())
+	default:
+		log.Println("unknown packet type")
+	}
+}