src/govpn/cmd/govpn-client/tcp.go

   1 /*
   2 GoVPN -- simple secure free software virtual private network daemon
   3 Copyright (C) 2014-2015 Sergey Matveev <stargrave@stargrave.org>
   4
   5 This program is free software: you can redistribute it and/or modify
   6 it under the terms of the GNU General Public License as published by
   7 the Free Software Foundation, either version 3 of the License, or
   8 (at your option) any later version.
   9
  10 This program is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 GNU General Public License for more details.
  14
  15 You should have received a copy of the GNU General Public License
  16 along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17 */
  18
  19 package main
  20
  21 import (
  22         "encoding/binary"
  23         "io"
  24         "log"
  25         "net"
  26
  27         "govpn"
  28 )
  29
  30 // TCPSender prepends size prefix to each outgoing packet.
  31 type TCPSender struct {
  32         conn *net.TCPConn
  33 }
  34
  35 func (c TCPSender) Write(data []byte) (int, error) {
  36         size := make([]byte, 2)
  37         binary.BigEndian.PutUint16(size, uint16(len(data)))
  38         return c.conn.Write(append(size, data...))
  39 }
  40
  41 func startTCP() (io.Writer, chan []byte, chan struct{}) {
  42         remote, err := net.ResolveTCPAddr("tcp", *remoteAddr)
  43         if err != nil {
  44                 log.Fatalln("Can not resolve remote address:", err)
  45         }
  46         c, err := net.DialTCP("tcp", nil, remote)
  47         conn := TCPSender{c}
  48         if err != nil {
  49                 log.Fatalln("Can not connect TCP:", err)
  50         }
  51         sink := make(chan []byte)
  52         ready := make(chan struct{})
  53         go handleTCP(c, sink, ready)
  54         go func() { ready <- struct{}{} }()
  55         return conn, sink, ready
  56 }
  57
  58 func handleTCP(conn *net.TCPConn, sink chan []byte, ready chan struct{}) {
  59         var err error
  60         var n int
  61         var sizeNbuf int
  62         sizeBuf := make([]byte, 2)
  63         var sizeNeed uint16
  64         var bufN uint16
  65         buf := make([]byte, govpn.MTU)
  66         for {
  67                 <-ready
  68                 if sizeNbuf != 2 {
  69                         n, err = conn.Read(sizeBuf[sizeNbuf:2])
  70                         if err != nil {
  71                                 break
  72                         }
  73                         sizeNbuf += n
  74                         if sizeNbuf != 2 {
  75                                 sink <- nil
  76                                 continue
  77                         }
  78                         sizeNeed = binary.BigEndian.Uint16(sizeBuf)
  79                         if int(sizeNeed) > govpn.MTU-2 {
  80                                 log.Println("Invalid TCP size, skipping")
  81                                 sizeNbuf = 0
  82                                 sink <- nil
  83                                 continue
  84                         }
  85                         bufN = 0
  86                 }
  87         ReadMore:
  88                 if sizeNeed != bufN {
  89                         n, err = conn.Read(buf[bufN:sizeNeed])
  90                         if err != nil {
  91                                 break
  92                         }
  93                         bufN += uint16(n)
  94                         goto ReadMore
  95                 }
  96                 sizeNbuf = 0
  97                 sink <- buf[:sizeNeed]
  98         }
  99 }