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         "log"
  24         "net"
  25
  26         "govpn"
  27 )
  28
  29 // TCPSender prepends size prefix to each outgoing packet.
  30 type TCPSender struct {
  31         conn *net.TCPConn
  32 }
  33
  34 func (c TCPSender) Write(data []byte) (int, error) {
  35         size := make([]byte, 2)
  36         binary.BigEndian.PutUint16(size, uint16(len(data)))
  37         return c.conn.Write(append(size, data...))
  38 }
  39
  40 func (c TCPSender) Reorderable() bool {
  41         return false
  42 }
  43
  44 func startTCP() (govpn.RemoteConn, chan []byte, chan struct{}) {
  45         remote, err := net.ResolveTCPAddr("tcp", *remoteAddr)
  46         if err != nil {
  47                 log.Fatalln("Can not resolve remote address:", err)
  48         }
  49         c, err := net.DialTCP("tcp", nil, remote)
  50         conn := TCPSender{c}
  51         if err != nil {
  52                 log.Fatalln("Can not connect TCP:", err)
  53         }
  54         sink := make(chan []byte)
  55         ready := make(chan struct{})
  56         go handleTCP(c, sink, ready)
  57         go func() { ready <- struct{}{} }()
  58         return conn, sink, ready
  59 }
  60
  61 func handleTCP(conn *net.TCPConn, sink chan []byte, ready chan struct{}) {
  62         var err error
  63         var n int
  64         var sizeNbuf int
  65         sizeBuf := make([]byte, 2)
  66         var sizeNeed uint16
  67         var bufN uint16
  68         buf := make([]byte, govpn.MTU)
  69         for {
  70                 <-ready
  71                 if sizeNbuf != 2 {
  72                         n, err = conn.Read(sizeBuf[sizeNbuf:2])
  73                         if err != nil {
  74                                 break
  75                         }
  76                         sizeNbuf += n
  77                         if sizeNbuf != 2 {
  78                                 sink <- nil
  79                                 continue
  80                         }
  81                         sizeNeed = binary.BigEndian.Uint16(sizeBuf)
  82                         if int(sizeNeed) > govpn.MTU-2 {
  83                                 log.Println("Invalid TCP size, skipping")
  84                                 sizeNbuf = 0
  85                                 sink <- nil
  86                                 continue
  87                         }
  88                         bufN = 0
  89                 }
  90         ReadMore:
  91                 if sizeNeed != bufN {
  92                         n, err = conn.Read(buf[bufN:sizeNeed])
  93                         if err != nil {
  94                                 break
  95                         }
  96                         bufN += uint16(n)
  97                         goto ReadMore
  98                 }
  99                 sizeNbuf = 0
 100                 sink <- buf[:sizeNeed]
 101         }
 102 }