blob: feb5bd910a12694ce6dff14302189b93a55ce718 [file] [log] [blame]
# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Block diff utility."""
import optparse
import sys
class BlockDiffError(Exception):
def BlockDiff(block_size, file1, file2, name1, name2, max_length=-1):
"""Performs a binary diff of two files by blocks.
block_size: the size of a block to diff by
file1: first file object
file2: second file object
name1: name of first file (for error reporting)
name2: name of second file (for error reporting)
max_length: the maximum length to read/diff in bytes (optional)
A list of (start, length) pairs representing block extents that differ
between the two files.
BlockDiffError if there were errors while diffing.
if max_length < 0:
max_length = sys.maxint
diff_list = []
num_blocks = extent_start = extent_length = 0
while max_length or extent_length:
read_length = min(max_length, block_size)
data1 =
data2 =
if len(data1) != len(data2):
raise BlockDiffError('read %d bytes from %s but %d bytes from %s' %
(len(data1), name1, len(data2), name2))
if data1 != data2:
# Data is different, mark it down.
if extent_length:
# Stretch the current diff extent.
extent_length += 1
# Start a new diff extent.
extent_start = num_blocks
extent_length = 1
elif extent_length:
# Record the previous extent.
diff_list.append((extent_start, extent_length))
extent_length = 0
# Are we done reading?
if not data1:
max_length -= len(data1)
num_blocks += 1
return diff_list
def main(argv):
# Parse command-line arguments.
parser = optparse.OptionParser(
usage='Usage: %prog FILE1 FILE2',
description='Compare FILE1 and FILE2 by blocks.')
parser.add_option('-b', '--block-size', metavar='NUM', type=int, default=4096,
help='the block size to use (default: %default)')
parser.add_option('-m', '--max-length', metavar='NUM', type=int, default=-1,
help='maximum number of bytes to compared')
opts, args = parser.parse_args(argv[1:])
name1, name2 = args
except ValueError:
parser.error('unexpected number of arguments')
# Perform the block diff.
with open(name1) as file1:
with open(name2) as file2:
diff_list = BlockDiff(opts.block_size, file1, file2, name1, name2,
except BlockDiffError as e:
print >> sys.stderr, 'Error:', e
return 2
# Print the diff, if such was found.
if diff_list:
total_diff_blocks = 0
for extent_start, extent_length in diff_list:
total_diff_blocks += extent_length
print('%d->%d (%d)' %
(extent_start, extent_start + extent_length, extent_length))
print 'total diff: %d blocks' % total_diff_blocks
return 1
return 0
if __name__ == '__main__':