42 def read_le_short(f):  argument
44   return struct.unpack("<H", f.read(2))[0]
46 def read_le_long(f):  argument
48   return struct.unpack("<L", f.read(4))[0]
50 def read_byte(f):  argument
52   return struct.unpack("B", f.read(1))[0]
54 def skip_bytes(f, n):  argument
56   f.seek(n, os.SEEK_CUR)
58 def skip_short(f):  argument
60   skip_bytes(f, 2)
62 def skip_byte(f):  argument
64   skip_bytes(f, 1)
66 def rewind_bytes(f, n):  argument
68   skip_bytes(f, -n)
70 def rewind_short(f):  argument
72   rewind_bytes(f, 2)
370   def commit(self, f):  argument
375     f.seek(0)
399       record = f.read(32)
403         f.write("\0" * self.fs.bytes_per_cluster)
404         f.seek(-self.fs.bytes_per_cluster, os.SEEK_CUR)
405         record = f.read(32)
414     f.seek(-(record_count * 32), os.SEEK_CUR)
415     f.write(entry)
428     f = self.fs.f
429     f.seek(self.fs.data_start() + self.idx)
434     ret = f.read(count)
439     f = self.fs.f
440     f.seek(self.fs.data_start() + self.idx)
445     f.write(data)
457     f = open(path, "r+b")
459     self.f = f
461     f.seek(0xb)
462     bytes_per_sector = read_le_short(f)
463     sectors_per_cluster = read_byte(f)
467     reserved_sectors = read_le_short(f)
471     fat_count = read_byte(f)
474     self.root_entries = read_le_short(f)
476     skip_short(f) # Image size. Sort of. Useless field.
477     skip_byte(f) # Media type. We don't care.
479     self.fat_size = read_le_short(f) * bytes_per_sector
496     f = self.f
497     f.seek(FAT_TABLE_START + head_cluster * 2)
503       head_cluster = read_le_short(f)
504       f.seek(FAT_TABLE_START + head_cluster * 2)
508   def read_dentry(self, f=None):  argument
513     f = f or self.f
521       skip_bytes(f, 11)
522       attributes = read_byte(f)
523       rewind_bytes(f, 12)
530       seq = read_byte(f)
531       chars = f.read(10)
532       skip_bytes(f, 3) # Various hackish nonsense
533       chars += f.read(12)
534       skip_short(f) # Lots more nonsense
535       chars += f.read(4)
541     ind = read_byte(f)
544       skip_bytes(f, 31)
553       skip_bytes(f, 31)
556     shortname = ind + f.read(7).rstrip()
557     ext = f.read(3).rstrip()
558     skip_bytes(f, 15) # Assorted flags, ctime/atime/mtime, etc.
559     first_cluster = read_le_short(f)
560     size = read_le_long(f)
581     f = self.f
602         f.seek(self.data_start() + bytes_from_data_start)
603         line = f.read(size_now)
614       f.seek(FAT_TABLE_START + head_cluster * 2)
616       head_cluster = read_le_short(f)
626     f = self.f
627     f.write(struct.pack("<H", entry))
628     skip_bytes(f, self.fat_size - 2)
629     f.write(struct.pack("<H", entry))
630     rewind_bytes(f, self.fat_size)
639     f = self.f
640     f.seek(FAT_TABLE_START + 4)
648       data = read_le_short(f)
690       f.seek(FAT_TABLE_START + cluster * 2)
703     f = self.f
705     f.seek(entry_offset)
706     assert read_le_short(f) == 0xFFFF, "Extending from middle of chain"
709     f.seek(entry_offset)
721     f = self.f
734         f.seek(cluster_file_offset + max(0, start_byte - current_offset))
735         f.write(data[data_begin:data_end])
740         f.seek(FAT_TABLE_START + current_cluster * 2)
741         next_cluster = read_le_short(f)
763     with open(item, 'rb') as f:
764       directory.new_file(os.path.basename(item), f)