compress.cc

   1 /*
   2  * Copyright (c) 2001, Robert Collins.
   3  *
   4  *     This program is free software; you can redistribute it and/or modify
   5  *     it under the terms of the GNU General Public License as published by
   6  *     the Free Software Foundation; either version 2 of the License, or
   7  *     (at your option) any later version.
   8  *
   9  *     A copy of the GNU General Public License can be found at
  10  *     http://www.gnu.org/
  11  *
  12  * Written by Robert Collins  <rbtcollins@hotmail.com>
  13  *
  14  */
  15
  16 #include "compress.h"
  17 #include "compress_gz.h"
  18 #include "compress_bz.h"
  19 #include "compress_xz.h"
  20 #include "compress_zstd.h"
  21 #include <string.h>
  22
  23 /* In case you are wondering why the file magic is not in one place:
  24  * It could be. But there is little (any?) benefit.
  25  * What is important is that the file magic required for any _task_ is centralised.
  26  * One such task is identifying compresss
  27  *
  28  * to federate into each class one might add a magic parameter to the constructor, which
  29  * the class could test itself.
  30  */
  31
  32 #define longest_magic 18 /* ZStandard longest frame header (magic is only 4 bytes) */
  33
  34 io_stream *
  35 compress::decompress (io_stream * original)
  36 {
  37   if (!original)
  38     return NULL;
  39   char magic[longest_magic];
  40   if (original->peek (magic, longest_magic) > 0)
  41     {
  42       if (memcmp (magic, "\037\213", 2) == 0)
  43         {
  44           /* tar */
  45           compress_gz *rv = new compress_gz (original);
  46           if (!rv->error ())
  47             return rv;
  48           /* else */
  49           rv->release_original();
  50           delete rv;
  51           return NULL;
  52         }
  53       else if (compress_zstd::is_zstd (magic, 18))
  54         {
  55           compress_zstd *rv = new compress_zstd (original);
  56           if (!rv->error ())
  57             return rv;
  58           /* else */
  59           rv->release_original();
  60           delete rv;
  61           return NULL;
  62         }
  63       else if (memcmp (magic, "BZh", 3) == 0)
  64         {
  65           compress_bz *rv = new compress_bz (original);
  66           if (!rv->error ())
  67             return rv;
  68           /* else */
  69           rv->release_original();
  70           delete rv;
  71           return NULL;
  72         }
  73       else if (compress_xz::is_xz_or_lzma (magic, 14))
  74         {
  75           compress_xz *rv = new compress_xz (original);
  76           if (!rv->error ())
  77             return rv;
  78           /* else */
  79           rv->release_original();
  80           delete rv;
  81           return NULL;
  82         }
  83     }
  84   return NULL;
  85 }
  86
  87 compress::~compress () {}