Hello, World!

2026-07-21 20:58:05 +02:00
commit 8a45d91e8d
6 changed files with 273 additions and 0 deletions
--- a/server/main.go
+++ b/server/main.go
@@ -0,0 +1,144 @@
+package main
+
+import (
+	"encoding/binary"
+	"fmt"
+	"log"
+	"net"
+	"os"
+	"os/exec"
+	"sync"
+
+	"baalvpn/shared"
+
+	"github.com/songgao/packets/ethernet"
+	"github.com/songgao/water"
+)
+
+const IFACE_NAME = "baalvpn"
+
+type Peer struct {
+	RealIP     string
+	InternalIP string
+}
+
+var (
+	peers      = map[string]*Peer{}
+	peersMutex sync.Mutex
+	nextIP     = 3
+)
+
+func main() {
+	if os.Geteuid() != 0 {
+		panic("root permissions needed")
+	}
+
+	config := water.Config{DeviceType: water.TAP}
+	config.Name = IFACE_NAME
+
+	iface, err := water.New(config)
+	if err != nil {
+		panic(err)
+	}
+
+	if err := exec.Command("ip", "addr", "add", "10.1.0.10/24", "dev", IFACE_NAME).Run(); err != nil {
+		panic(err)
+	}
+	if err := exec.Command("ip", "link", "set", "dev", IFACE_NAME, "up").Run(); err != nil {
+		panic(err)
+	}
+
+	log.Println("Listening...")
+
+	go receivePackets()
+	sendPackets(iface)
+}
+
+func sendPackets(iface *water.Interface) {
+	var frame ethernet.Frame
+	for {
+		frame.Resize(1500)
+		n, err := iface.Read([]byte(frame))
+		if err != nil {
+			panic(err)
+		}
+		frame = frame[:n]
+
+		if frame.Destination()[0]&0x01 == 0x01 {
+			log.Println("multicast")
+			continue
+		}
+
+		log.Printf("Dst: %s\n", frame.Destination())
+		log.Printf("Src: %s\n", frame.Source())
+		log.Printf("Ethertype: % x\n", frame.Ethertype())
+		log.Printf("Payload: % x\n", frame.Payload())
+	}
+}
+
+func receivePackets() {
+	listenAddr, err := net.ResolveUDPAddr("udp", ":38000")
+	if err != nil {
+		panic(err)
+	}
+	listener, err := net.ListenUDP("udp", listenAddr)
+	if err != nil {
+		panic(err)
+	}
+	defer listener.Close()
+
+	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:])
+
+	peerIP := addr.IP.String()
+
+	switch pktType {
+	case shared.REQ_REGISTER:
+		peersMutex.Lock()
+		defer peersMutex.Unlock()
+
+		internalIP := fmt.Sprintf("10.1.0.%d", nextIP)
+
+		if peer, ok := peers[addr.IP.String()]; ok {
+			internalIP = peer.InternalIP
+		} else {
+			peers[addr.IP.String()] = &Peer{
+				RealIP:     peerIP,
+				InternalIP: internalIP,
+			}
+			nextIP++
+		}
+
+		resp := shared.BuildPkt(shared.RESP_REGISTER, net.ParseIP(internalIP).To4())
+		if _, err := c.WriteToUDP(resp, addr); err != nil {
+			log.Printf("register WriteToUDP: %v\n", err)
+		}
+	default:
+		log.Println("unknown packet type")
+	}
+}