src/pppfilter.cc

   1 ///
   2 /// \file       pppfilter.cc
   3 ///             Data filter class, to morph PPP data into something that
   4 ///             the Blackberry / Rogers / ISP can handle.
   5 ///             This logic is based partly on XmBlackBerry's
   6 ///             gprs_protocol_fix.c program.
   7 ///
   8
   9 /*
  10     Copyright (C) 2008-2013, Net Direct Inc. (http://www.netdirect.ca/)
  11
  12     This program is free software; you can redistribute it and/or modify
  13     it under the terms of the GNU General Public License as published by
  14     the Free Software Foundation; either version 2 of the License, or
  15     (at your option) any later version.
  16
  17     This program is distributed in the hope that it will be useful,
  18     but WITHOUT ANY WARRANTY; without even the implied warranty of
  19     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  20
  21     See the GNU General Public License in the COPYING file at the
  22     root directory of this project for more details.
  23 */
  24
  25 #include "pppfilter.h"
  26 #include <string.h>
  27
  28 namespace Barry {
  29
  30 //////////////////////////////////////////////////////////////////////////////
  31 // PppFilter class
  32
  33 PppFilter::PppFilter()
  34         : m_ppp_mode(false)
  35         , m_last(0x7e)
  36 {
  37 }
  38
  39 //
  40 // Filter
  41 //
  42 /// Copy PPP data from src to dest, creating needed space in dest,
  43 /// and inserting missing 0x7e characters wherever they are detected.
  44 /// Starts writing at the start of the dest buffer + destoffset.
  45 ///
  46 void PppFilter::Filter(Data &dest, const Data &src, unsigned int destoffset)
  47 {
  48         const unsigned char *b = src.GetData(), *e = src.GetData() + src.GetSize();
  49         size_t needed = src.GetSize() / 2 * 3 + 4 + destoffset; // worst case
  50         unsigned char *buf = dest.GetBuffer(needed) + destoffset;
  51         unsigned char *put = buf;
  52
  53         while( b != e ) {
  54                 // if last character was 0x7e, then next one must be,
  55                 // or else we insert it ourselves
  56                 if( m_last == 0x7e ) {
  57                         m_last = 0;
  58                         if( *b != 0x7e )
  59                                 *put++ = 0x7e;
  60                         else
  61                                 *put++ = *b++;
  62                 }
  63
  64                 // copy all non-0x7e chars verbatim
  65                 while( b != e && *b != 0x7e ) {
  66                         *put++ = *b++;
  67                 }
  68
  69                 if( b != e ) {  // if b!=e then *b == 0x7e and must keep going
  70                         *put++ = *b++;
  71                         m_last = 0x7e;
  72                 }
  73         }
  74
  75         dest.ReleaseBuffer(put - buf + destoffset);
  76 }
  77
  78 //
  79 // Write
  80 //
  81 /// If PPP mode has not been detected, just return the data buffer.
  82 /// If in PPP mode, then filter data into internal write buffer,
  83 /// inserting any missing 0x7e characters and return reference
  84 /// to internal write buffer.
  85 ///
  86 const Data& PppFilter::Write(const Data &data)
  87 {
  88         if( data.GetSize() == 0 )
  89                 return data;    // nothing to do
  90
  91         const unsigned char *b = data.GetData();
  92
  93         if( !m_ppp_mode ) {
  94                 if( *b == 0x7e ) {
  95                         m_ppp_mode = true;
  96                         // fall through
  97                 }
  98                 else {
  99                         // not in ppp mode yet, so just pass the buffer
 100                         // straight back to the caller
 101                         return data;
 102                 }
 103         }
 104
 105         Filter(m_writeBuf, data, 0);
 106         return m_writeBuf;
 107 }
 108
 109 //
 110 // Write (with prepend)
 111 //
 112 /// Same as Write(data), but makes sure that prepend bytes are available
 113 /// at the beginning of the returned buffer.
 114 /// If not in PPP mode, the extra bytes are still provided.
 115 ///
 116 Data& PppFilter::Write(const Data &data, unsigned int prepend)
 117 {
 118         const unsigned char *b = data.GetData(), *e = data.GetData() + data.GetSize();
 119
 120         if( !m_ppp_mode ) {
 121                 if( b != e && *b == 0x7e ) {
 122                         m_ppp_mode = true;
 123                         // fall through
 124                 }
 125                 else {
 126                         // make space, copy, return
 127                         unsigned int size = data.GetSize() + prepend;
 128                         unsigned char *buf = m_writeBuf.GetBuffer(size);
 129                         memcpy(&buf[prepend], data.GetData(), data.GetSize());
 130                         m_writeBuf.ReleaseBuffer(size);
 131                         return m_writeBuf;
 132                 }
 133         }
 134
 135         Filter(m_writeBuf, data, prepend);
 136         return m_writeBuf;
 137 }
 138
 139 } // namespace Barry
 140