Par2Parser.py

   1 #!/usr/bin/env python
   2 # vim: set ts=4 sts=4 sw=4 textwidth=92:
   3
   4 ################################################################################
   5 # The PAR2 Parser
   6 #
   7 # This was stolen from cfv (see http://cfv.sourceforge.net/ for a copy)
   8 ################################################################################
   9
  10 import struct, errno, os
  11
  12 def get_full_filename (dir, file):
  13         return os.path.abspath (os.path.expanduser (os.path.join (dir, file)))
  14
  15 def chompnulls(line):
  16         p = line.find('\0')
  17         if p < 0: return line
  18         else:     return line[:p]
  19
  20 def get_protected_files (dir, filename):
  21         """Get all of the filenames that are protected by the par2
  22         file given as the filename"""
  23
  24         full_filename = get_full_filename (dir, filename)
  25
  26         try:
  27                 file = open(full_filename, 'rb')
  28         except:
  29                 print 'Could not open %s' % (full_filename, )
  30                 raise EnvironmentError, (errno.EINVAL, 'can not open par2 file')
  31
  32         pkt_header_fmt = '< 8s Q 16s 16s 16s'
  33         pkt_header_size = struct.calcsize(pkt_header_fmt)
  34         file_pkt_fmt = '< 16s 16s 16s Q'
  35         file_pkt_size = struct.calcsize(file_pkt_fmt)
  36         main_pkt_fmt = '< Q I'
  37         main_pkt_size = struct.calcsize(main_pkt_fmt)
  38
  39         seen_file_ids = {}
  40         expected_file_ids = None
  41         filenames = []
  42
  43         while 1:
  44                 try:
  45                         d = file.read(pkt_header_size)
  46                 except OverflowError:
  47                         raise EnvironmentError, (errno.EINVAL, 'bad par2 file')
  48                 if not d:
  49                         break
  50
  51                 magic, pkt_len, pkt_md5, set_id, pkt_type = struct.unpack(pkt_header_fmt, d)
  52
  53                 if pkt_type == 'PAR 2.0\0FileDesc':
  54                         file_id, file_md5, file_md5_16k, file_size = \
  55                                 struct.unpack(file_pkt_fmt, d[:file_pkt_size])
  56
  57                         if seen_file_ids.get(file_id) is None:
  58                                 seen_file_ids[file_id] = 1
  59                                 filename = chompnulls(d[file_pkt_size:])
  60                                 filenames.append(filename)
  61
  62                 elif pkt_type == "PAR 2.0\0Main\0\0\0\0":
  63                         try:
  64                                 d = file.read(pkt_len - pkt_header_size)
  65                         except OverflowError:
  66                                 raise EnvironmentError, (errno.EINVAL, 'corrupt par2 file')
  67
  68                         if expected_file_ids is None:
  69                                 expected_file_ids = []
  70                                 slice_size, num_files = struct.unpack(main_pkt_fmt, d[:main_pkt_size])
  71                                 num_nonrecovery = (len(d)-main_pkt_size)/16 - num_files
  72
  73                                 for i in range(main_pkt_size,main_pkt_size+(num_files+num_nonrecovery)*16,16):
  74                                         expected_file_ids.append(d[i:i+16])
  75
  76                 else:
  77                         try:
  78                                 file.seek(pkt_len - pkt_header_size, 1)
  79                         except OverflowError, IOError:
  80                                 raise EnvironmentError, (errno.EINVAL, 'corrupt par2 file')
  81
  82         if expected_file_ids is None:
  83                 raise EnvironmentError, (errno.EINVAL, \
  84                         "corrupt or unsupported par2 file - no main packet found")
  85
  86         for id in expected_file_ids:
  87                 if not seen_file_ids.has_key(id):
  88                         raise EnvironmentError, (errno.EINVAL, \
  89                                 "corrupt or unsupported par2 file - " \
  90                                 "expected file description packet not found")
  91
  92         return filenames
  93
  94 def main ():
  95         pass
  96
  97 if __name__ == '__main__':
  98         main ()
  99