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 func() {
  54                 var err error
  55                 var n int
  56                 var sizeNbuf int
  57                 sizeBuf := make([]byte, 2)
  58                 var sizeNeed uint16
  59                 var bufN uint16
  60                 buf := make([]byte, govpn.MTU)
  61                 for {
  62                         <-ready
  63                         if sizeNbuf != 2 {
  64                                 n, err = c.Read(sizeBuf[sizeNbuf:2])
  65                                 if err != nil {
  66                                         break
  67                                 }
  68                                 sizeNbuf += n
  69                                 if sizeNbuf == 2 {
  70                                         sizeNeed = binary.BigEndian.Uint16(sizeBuf)
  71                                         if sizeNeed > uint16(govpn.MTU)-2 {
  72                                                 log.Println("Invalid TCP size, skipping")
  73                                                 sizeNbuf = 0
  74                                                 sink <- nil
  75                                                 continue
  76                                         }
  77                                         bufN = 0
  78                                 }
  79                         }
  80                 ReadMore:
  81                         if sizeNeed != bufN {
  82                                 n, err = c.Read(buf[bufN:sizeNeed])
  83                                 if err != nil {
  84                                         break
  85                                 }
  86                                 bufN += uint16(n)
  87                                 goto ReadMore
  88                         }
  89                         sizeNbuf = 0
  90                         sink <- buf[:sizeNeed]
  91                 }
  92         }()
  93         go func() { ready <- struct{}{} }()
  94         return conn, sink, ready
  95 }