Remove the length field from the index entries in data pack files.

tools/data_pack/data_pack.py

 #!/usr/bin/python
 # Copyright (c) 2011 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """A simple utility function to produce data pack files.
 See base/pack_file* for details.
 """
 
 import struct
 
-FILE_FORMAT_VERSION = 2
+FILE_FORMAT_VERSION = 3
 HEADER_LENGTH = 2 * 4  # Two uint32s. (file version and number of entries)
 
 class WrongFileVersion(Exception):
   pass
 
 def ReadDataPack(input_file):
   """Reads a data pack file and returns a dictionary."""
   data = open(input_file, "rb").read()
   original_data = data
 
   # Read the header.
   version, num_entries = struct.unpack("<II", data[:HEADER_LENGTH])
   if version != FILE_FORMAT_VERSION:
     raise WrongFileVersion
 
   resources = {}
+  if num_entries == 0:
+    return resources
+
   # Read the index and data.
   data = data[HEADER_LENGTH:]
-  kIndexEntrySize = 2 + 2 * 4  # Each entry is 1 uint16 and 2 uint32s.
+  kIndexEntrySize = 2 + 4  # Each entry is a uint16 and a uint32.
   for _ in range(num_entries):
-    id, offset, length = struct.unpack("<HII", data[:kIndexEntrySize])
+    id, offset = struct.unpack("<HI", data[:kIndexEntrySize])
     data = data[kIndexEntrySize:]
-    resources[id] = original_data[offset:offset + length]
+    next_id, next_offset = struct.unpack("<HI", data[:kIndexEntrySize])
+    resources[id] = original_data[offset:next_offset]
 
   return resources
 
 def WriteDataPack(resources, output_file):
   """Write a map of id=>data into output_file as a data pack."""
   ids = sorted(resources.keys())
   file = open(output_file, "wb")
 
   # Write file header.
   file.write(struct.pack("<II", FILE_FORMAT_VERSION, len(ids)))
 
-  # Each entry is 1 uint16 and 2 uint32s.
-  index_length = len(ids) * (2 + 2 * 4)
+  # Each entry is a uint16 and a uint32. We have one extra entry for the last
+  # item.
+  index_length = (len(ids) + 1) * (2 + 4)
 
   # Write index.
   data_offset = HEADER_LENGTH + index_length
   for id in ids:
-    file.write(struct.pack("<HII", id, data_offset, len(resources[id])))
+    file.write(struct.pack("<HI", id, data_offset))
     data_offset += len(resources[id])
 
+  file.write(struct.pack("<HI", 0, data_offset))
+
   # Write data.
   for id in ids:
     file.write(resources[id])
 
 def main():
   # Just write a simple file.
   data = { 1: "", 4: "this is id 4", 6: "this is id 6", 10: "" }
   WriteDataPack(data, "datapack1.pak")
   data2 = { 1000: "test", 5: "five" }
   WriteDataPack(data2, "datapack2.pak")
   print "wrote datapack1 and datapack2 to current directory."
 
 if __name__ == '__main__':
   main()