rsutil/par2parser.py

   1 #!/usr/bin/env python
   2 # vim: set ts=4 sts=4 sw=4 textwidth=92:
   3
   4 """
   5 Module which holds PAR2 file parsing functions.
   6
   7 Much of this code was borrowed from the excellent cfv project.
   8 See http://cfv.sourceforge.net/ for a copy.
   9 """
  10
  11 __author__    = "Ira W. Snyder (devel@irasnyder.com)"
  12 __copyright__ = "Copyright (c) 2006,2007 Ira W. Snyder (devel@irasnyder.com)"
  13 __license__   = "GNU GPL v2 (or, at your option, any later version)"
  14
  15 #    par2parser.py -- PAR2 file parsing utility
  16 #
  17 #    Copyright (C) 2006,2007  Ira W. Snyder (devel@irasnyder.com)
  18 #
  19 #    This program is free software; you can redistribute it and/or modify
  20 #    it under the terms of the GNU General Public License as published by
  21 #    the Free Software Foundation; either version 2 of the License, or
  22 #    (at your option) any later version.
  23 #
  24 #    This program is distributed in the hope that it will be useful,
  25 #    but WITHOUT ANY WARRANTY; without even the implied warranty of
  26 #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  27 #    GNU General Public License for more details.
  28 #
  29 #    You should have received a copy of the GNU General Public License
  30 #    along with this program; if not, write to the Free Software
  31 #    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  32
  33
  34 import struct, errno, os, md5
  35
  36 def chompnulls(line):
  37         p = line.find('\0')
  38         if p < 0: return line
  39         else:     return line[:p]
  40
  41 def get_protected_files (dir, filename):
  42         """Get all of the filenames that are protected by the par2
  43         file given as the filename"""
  44
  45         assert os.path.isdir (dir) # MUST be a valid directory
  46         assert os.path.isfile (os.path.join (dir, filename))
  47
  48         full_filename = os.path.join (dir, filename)
  49
  50         try:
  51                 file = open(full_filename, 'rb')
  52         except:
  53                 print 'Could not open %s' % (full_filename, )
  54                 return []
  55
  56         # We always want to do crc checks
  57         docrcchecks = True
  58
  59         pkt_header_fmt = '< 8s Q 16s 16s 16s'
  60         pkt_header_size = struct.calcsize(pkt_header_fmt)
  61         file_pkt_fmt = '< 16s 16s 16s Q'
  62         file_pkt_size = struct.calcsize(file_pkt_fmt)
  63         main_pkt_fmt = '< Q I'
  64         main_pkt_size = struct.calcsize(main_pkt_fmt)
  65
  66         seen_file_ids = {}
  67         expected_file_ids = None
  68         filenames = []
  69
  70         # This try is here to ensure that we close the open file before
  71         # returning. Since this code was (pretty much) borrowed verbatim
  72         # from the cfv project, I didn't want to refactor it to make file
  73         # closing more sane, so I just used a try / finally clause.
  74         try:
  75                 while 1:
  76                         d = file.read(pkt_header_size)
  77                         if not d:
  78                                 break
  79
  80                         magic, pkt_len, pkt_md5, set_id, pkt_type = struct.unpack(pkt_header_fmt, d)
  81
  82                         if docrcchecks:
  83                                 control_md5 = md5.new()
  84                                 control_md5.update(d[0x20:])
  85                                 d = file.read(pkt_len - pkt_header_size)
  86                                 control_md5.update(d)
  87
  88                                 if control_md5.digest() != pkt_md5:
  89                                         raise EnvironmentError, (errno.EINVAL, \
  90                                                 "corrupt par2 file - bad packet hash")
  91
  92                         if pkt_type == 'PAR 2.0\0FileDesc':
  93                                 if not docrcchecks:
  94                                         d = file.read(pkt_len - pkt_header_size)
  95
  96                                 file_id, file_md5, file_md5_16k, file_size = \
  97                                         struct.unpack(file_pkt_fmt, d[:file_pkt_size])
  98
  99                                 if seen_file_ids.get(file_id) is None:
 100                                         seen_file_ids[file_id] = 1
 101                                         filename = chompnulls(d[file_pkt_size:])
 102                                         filenames.append(filename)
 103
 104                         elif pkt_type == "PAR 2.0\0Main\0\0\0\0":
 105                                 if not docrcchecks:
 106                                         d = file.read(pkt_len - pkt_header_size)
 107
 108                                 if expected_file_ids is None:
 109                                         expected_file_ids = []
 110                                         slice_size, num_files = struct.unpack(main_pkt_fmt, d[:main_pkt_size])
 111                                         num_nonrecovery = (len(d)-main_pkt_size)/16 - num_files
 112
 113                                         for i in range(main_pkt_size,main_pkt_size+(num_files+num_nonrecovery)*16,16):
 114                                                 expected_file_ids.append(d[i:i+16])
 115
 116                         else:
 117                                 if not docrcchecks:
 118                                         file.seek(pkt_len - pkt_header_size, 1)
 119
 120                 if expected_file_ids is None:
 121                         raise EnvironmentError, (errno.EINVAL, \
 122                                 "corrupt or unsupported par2 file - no main packet found")
 123
 124                 for id in expected_file_ids:
 125                         if not seen_file_ids.has_key(id):
 126                                 raise EnvironmentError, (errno.EINVAL, \
 127                                         "corrupt or unsupported par2 file - " \
 128                                         "expected file description packet not found")
 129         finally:
 130                 file.close ()
 131
 132         return filenames
 133
 134 def main ():
 135         pass
 136
 137 if __name__ == '__main__':
 138         main ()
 139