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