vtun/server/server.go

package server

import (
	"log"
	"net"
	"sync"

	"github.com/net-byte/vtun/common/cipher"
	"github.com/net-byte/vtun/common/config"
	"github.com/net-byte/vtun/tun"
	"github.com/songgao/water"
)

type Forwarder struct {
	localConn  *net.UDPConn
	cliConnMap sync.Map
}

type ForwardData struct {
	localConn *net.UDPConn
	data      []byte
}

// Start server
func Start(config config.Config) {
	iface := tun.CreateTun(config.CIDR)
	localAddr, err := net.ResolveUDPAddr("udp", config.LocalAddr)
	if err != nil {
		log.Fatalln("failed to get UDP socket:", err)
	}
	conn, err := net.ListenUDP("udp", localAddr)
	if err != nil {
		log.Fatalln("failed to listen on UDP socket:", err)
	}
	defer conn.Close()
	forwarder := &Forwarder{localConn: conn}
	go forwarder.forward(iface, conn)
	buf := make([]byte, 1500)
	for {
		n, cliAddr, err := conn.ReadFromUDP(buf)
		if err != nil || n == 0 {
			forwarder.cliConnMap.Delete(cliAddr.String())
			continue
		}
		b := buf[:n]
		// decrypt data
		cipher.Decrypt(&b)
		iface.Write(b)
		forwarder.cliConnMap.LoadOrStore(cliAddr.String(), cliAddr)
	}
}

func (f *Forwarder) forward(iface *water.Interface, conn *net.UDPConn) {
	packet := make([]byte, 1500)
	for {
		n, err := iface.Read(packet)
		if err != nil || n == 0 {
			continue
		}
		b := packet[:n]
		// encrypt data
		cipher.Encrypt(&b)
		fd := ForwardData{localConn: conn, data: b}
		f.cliConnMap.Range(fd.walk)
	}
}

func (f *ForwardData) walk(key, value interface{}) bool {
	f.localConn.WriteToUDP(f.data, value.(*net.UDPAddr))
	return true
}