kmime_codec_base64.cpp

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/*  -*- c++ -*-
    kmime_codec_base64.cpp

    KMime, the KDE Internet mail/usenet news message library.
    Copyright (c) 2001 Marc Mutz <mutz@kde.org>

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.
*/
#include "kmime_codec_base64.h"

#include <kdebug.h>

#include <cassert>

using namespace KMime;

namespace KMime {

// codec for base64 as specified in RFC 2045
//class Base64Codec;
//class Base64Decoder;
//class Base64Encoder;

// codec for the B encoding as specified in RFC 2047
//class Rfc2047BEncodingCodec;
//class Rfc2047BEncodingEncoder;
//class Rfc2047BEncodingDecoder;

//@cond PRIVATE
static const uchar base64DecodeMap[128] = {
  64, 64, 64, 64, 64, 64, 64, 64,  64, 64, 64, 64, 64, 64, 64, 64,
  64, 64, 64, 64, 64, 64, 64, 64,  64, 64, 64, 64, 64, 64, 64, 64,

  64, 64, 64, 64, 64, 64, 64, 64,  64, 64, 64, 62, 64, 64, 64, 63,
  52, 53, 54, 55, 56, 57, 58, 59,  60, 61, 64, 64, 64, 64, 64, 64,

  64,  0,  1,  2,  3,  4,  5,  6,   7,  8,  9, 10, 11, 12, 13, 14,
  15, 16, 17, 18, 19, 20, 21, 22,  23, 24, 25, 64, 64, 64, 64, 64,

  64, 26, 27, 28, 29, 30, 31, 32,  33, 34, 35, 36, 37, 38, 39, 40,
  41, 42, 43, 44, 45, 46, 47, 48,  49, 50, 51, 64, 64, 64, 64, 64
};

static const char base64EncodeMap[64] = {
  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
  'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
  'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
  'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
  'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
  'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
  'w', 'x', 'y', 'z', '0', '1', '2', '3',
  '4', '5', '6', '7', '8', '9', '+', '/'
};
//@endcond

class Base64Decoder : public Decoder
{
  uint mStepNo;
  uchar mOutbits;
  bool mSawPadding : 1;

  protected:
    friend class Base64Codec;
    Base64Decoder( bool withCRLF=false )
      : Decoder( withCRLF ), mStepNo( 0 ), mOutbits( 0 ),
        mSawPadding( false ) {}

  public:
    virtual ~Base64Decoder() {}

    bool decode( const char* &scursor, const char * const send,
                 char* &dcursor, const char * const dend );
    // ### really needs no finishing???
    bool finish( char* &dcursor, const char * const dend )
      {
        Q_UNUSED( dcursor ); Q_UNUSED( dend );
        return true;
      }
};

class Base64Encoder : public Encoder
{
  uint mStepNo;
  uint mWrittenPacketsOnThisLine;
  uchar mNextbits;
  bool mInsideFinishing : 1;

  protected:
    friend class Rfc2047BEncodingCodec;
    friend class Rfc2047BEncodingEncoder;
    friend class Base64Codec;
    Base64Encoder( bool withCRLF=false )
      : Encoder( withCRLF ), mStepNo( 0 ), mWrittenPacketsOnThisLine( 0 ),
        mNextbits( 0 ), mInsideFinishing( false ) {}

    bool generic_finish( char* &dcursor, const char * const dend,
                         bool withLFatEnd );

  public:
    virtual ~Base64Encoder() {}

    bool encode( const char* &scursor, const char * const send,
                 char* &dcursor, const char * const dend );

    bool finish( char* &dcursor, const char * const dend );

  protected:
    bool writeBase64( uchar ch, char* &dcursor, const char * const dend )
      { return write( base64EncodeMap[ ch ], dcursor, dend ); }
};

class Rfc2047BEncodingEncoder : public Base64Encoder
{
  protected:
    friend class Rfc2047BEncodingCodec;
    Rfc2047BEncodingEncoder( bool withCRLF=false )
      : Base64Encoder( withCRLF ) {}

  public:
    bool encode( const char* &scursor, const char * const send,
                 char* &dcursor, const char * const dend );
    bool finish( char* &dcursor, const char * const dend );
};

Encoder *Base64Codec::makeEncoder( bool withCRLF ) const
{
  return new Base64Encoder( withCRLF );
}

Decoder *Base64Codec::makeDecoder( bool withCRLF ) const
{
  return new Base64Decoder( withCRLF );
}

Encoder *Rfc2047BEncodingCodec::makeEncoder( bool withCRLF ) const
{
  return new Rfc2047BEncodingEncoder( withCRLF );
}

/********************************************************/
/********************************************************/
/********************************************************/

bool Base64Decoder::decode( const char* &scursor, const char * const send,
                            char* &dcursor, const char * const dend )
{
  while ( dcursor != dend && scursor != send ) {
    uchar ch = *scursor++;
    uchar value;

    // try converting ch to a 6-bit value:
    if ( ch < 128 ) {
      value = base64DecodeMap[ ch ];
    } else {
      value = 64;
    }

    // ch isn't of the base64 alphabet, check for other significant chars:
    if ( value >= 64 ) {
      if ( ch == '=' ) {
        // padding:
        if ( mStepNo == 0 || mStepNo == 1 ) {
          if ( !mSawPadding ) {
            // malformed
            kWarning() << "Base64Decoder: unexpected padding"
              "character in input stream";
          }
          mSawPadding = true;
          break;
        } else if ( mStepNo == 2 ) {
          // ok, there should be another one
        } else if ( mStepNo == 3 ) {
          // ok, end of encoded stream
          mSawPadding = true;
          break;
        }
        mSawPadding = true;
        mStepNo = ( mStepNo + 1 ) % 4;
        continue;
      } else {
        // non-base64 alphabet
        continue;
      }
    }

    if ( mSawPadding ) {
      kWarning() << "Base64Decoder: Embedded padding character"
        "encountered!";
      return true;
    }

    // add the new bits to the output stream and flush full octets:
    switch ( mStepNo ) {
    case 0:
      mOutbits = value << 2;
      break;
    case 1:
      *dcursor++ = (char)( mOutbits | value >> 4 );
      mOutbits = value << 4;
      break;
    case 2:
      *dcursor++ = (char)( mOutbits | value >> 2 );
      mOutbits = value << 6;
      break;
    case 3:
      *dcursor++ = (char)( mOutbits | value );
      mOutbits = 0;
      break;
    default:
      assert( 0 );
    }
    mStepNo = ( mStepNo + 1 ) % 4;
  }

  // return false when caller should call us again:
  return scursor == send;
} // Base64Decoder::decode()

bool Base64Encoder::encode( const char* &scursor, const char * const send,
                            char* &dcursor, const char * const dend )
{
  const uint maxPacketsPerLine = 76 / 4;

  // detect when the caller doesn't adhere to our rules:
  if ( mInsideFinishing ) {
    return true;
  }

  while ( scursor != send && dcursor != dend ) {
    // properly empty the output buffer before starting something new:
    // ### fixme: we can optimize this away, since the buffer isn't
    // written to anyway (most of the time)
    if ( mOutputBufferCursor && !flushOutputBuffer( dcursor, dend ) ) {
      return scursor == send;
    }

    uchar ch = *scursor++;
    // mNextbits   // (part of) value of next sextet

    // check for line length;
    if ( mStepNo == 0 && mWrittenPacketsOnThisLine >= maxPacketsPerLine ) {
      writeCRLF( dcursor, dend );
      mWrittenPacketsOnThisLine = 0;
    }

    // depending on mStepNo, extract value and mNextbits from the
    // octet stream:
    switch ( mStepNo ) {
    case 0:
      assert( mNextbits == 0 );
      writeBase64( ch >> 2, dcursor, dend ); // top-most 6 bits -> output
      mNextbits = ( ch & 0x3 ) << 4; // 0..1 bits -> 4..5 in mNextbits
      break;
    case 1:
      assert( ( mNextbits & ~0x30 ) == 0 );
      writeBase64( mNextbits | ch >> 4, dcursor, dend ); // 4..7 bits -> 0..3 in value
      mNextbits = ( ch & 0xf ) << 2; // 0..3 bits -> 2..5 in mNextbits
      break;
    case 2:
      assert( ( mNextbits & ~0x3C ) == 0 );
      writeBase64( mNextbits | ch >> 6, dcursor, dend ); // 6..7 bits -> 0..1 in value
      writeBase64( ch & 0x3F, dcursor, dend ); // 0..5 bits -> output
      mNextbits = 0;
      mWrittenPacketsOnThisLine++;
      break;
    default:
      assert( 0 );
    }
    mStepNo = ( mStepNo + 1 ) % 3;
  }

  if ( mOutputBufferCursor ) {
    flushOutputBuffer( dcursor, dend );
  }

  return scursor == send;
}

bool Rfc2047BEncodingEncoder::encode( const char* &scursor,
                                      const char * const send,
                                      char* &dcursor,
                                      const char * const dend )
{
  // detect when the caller doesn't adhere to our rules:
  if ( mInsideFinishing ) {
    return true;
  }

  while ( scursor != send && dcursor != dend ) {
    // properly empty the output buffer before starting something new:
    // ### fixme: we can optimize this away, since the buffer isn't
    // written to anyway (most of the time)
    if ( mOutputBufferCursor && !flushOutputBuffer( dcursor, dend ) ) {
      return scursor == send;
    }

    uchar ch = *scursor++;
    // mNextbits   // (part of) value of next sextet

    // depending on mStepNo, extract value and mNextbits from the
    // octet stream:
    switch ( mStepNo ) {
    case 0:
      assert( mNextbits == 0 );
      writeBase64( ch >> 2, dcursor, dend ); // top-most 6 bits -> output
      mNextbits = ( ch & 0x3 ) << 4; // 0..1 bits -> 4..5 in mNextbits
      break;
    case 1:
      assert( ( mNextbits & ~0x30 ) == 0 );
      writeBase64( mNextbits | ch >> 4, dcursor, dend ); // 4..7 bits -> 0..3 in value
      mNextbits = ( ch & 0xf ) << 2; // 0..3 bits -> 2..5 in mNextbits
      break;
    case 2:
      assert( ( mNextbits & ~0x3C ) == 0 );
      writeBase64( mNextbits | ch >> 6, dcursor, dend ); // 6..7 bits -> 0..1 in value
      writeBase64( ch & 0x3F, dcursor, dend ); // 0..5 bits -> output
      mNextbits = 0;
      break;
    default:
      assert( 0 );
    }
    mStepNo = ( mStepNo + 1 ) % 3;
  }

  if ( mOutputBufferCursor ) {
    flushOutputBuffer( dcursor, dend );
  }

  return scursor == send;
}

bool Base64Encoder::finish( char* &dcursor, const char * const dend )
{
  return generic_finish( dcursor, dend, true );
}

bool Rfc2047BEncodingEncoder::finish( char* & dcursor,
                                      const char * const dend )
{
  return generic_finish( dcursor, dend, false );
}

bool Base64Encoder::generic_finish( char* &dcursor, const char * const dend,
                                    bool withLFatEnd )
{
  if ( mInsideFinishing ) {
    return flushOutputBuffer( dcursor, dend );
  }

  if ( mOutputBufferCursor && !flushOutputBuffer( dcursor, dend ) ) {
    return false;
  }

  mInsideFinishing = true;

  //
  // writing out the last mNextbits...
  //
  switch ( mStepNo ) {
  case 1: // 2 mNextbits waiting to be written. Needs two padding chars:
  case 2: // 4 or 6 mNextbits waiting to be written. Completes a block
    writeBase64( mNextbits, dcursor, dend );
    mNextbits = 0;
    break;
  case 0: // no padding, nothing to be written, except possibly the CRLF
    assert( mNextbits == 0 );
    break;
  default:
    assert( 0 );
  }

  //
  // adding padding...
  //
  switch ( mStepNo ) {
  case 1:
    write( '=', dcursor, dend );
    // fall through:
  case 2:
    write( '=', dcursor, dend );
    // fall through:
  case 0: // completed an quartet - add CRLF
    if ( withLFatEnd ) {
      writeCRLF( dcursor, dend );
    }
    return flushOutputBuffer( dcursor, dend );
  default:
    assert( 0 );
  }
  return true; // asserts get compiled out
}

} // namespace KMime