1#!/usr/bin/env python
2#
3# Copyright (C) 2021 The Android Open Source Project
4#
5# Licensed under the Apache License, Version 2.0 (the "License");
6# you may not use this file except in compliance with the License.
7# You may obtain a copy of the License at
8#
9#      http://www.apache.org/licenses/LICENSE-2.0
10#
11# Unless required by applicable law or agreed to in writing, software
12# distributed under the License is distributed on an "AS IS" BASIS,
13# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14# See the License for the specific language governing permissions and
15# limitations under the License.
16"""replace_bytes is a command line tool to replace bytes in a file.
17
18Typical usage: replace_bytes target_file old_file new_file
19
20  replace bytes of old_file with bytes of new_file in target_file. old_file and new_file should be
21  the same size.
22
23"""
24import argparse
25import sys
26
27
28def ParseArgs(argv):
29    parser = argparse.ArgumentParser(description='Replace bytes')
30    parser.add_argument(
31        'target_file',
32        help='path to the target file.')
33    parser.add_argument(
34        'old_file',
35        help='path to the file containing old bytes')
36    parser.add_argument(
37        'new_file',
38        help='path to the file containing new bytes')
39    return parser.parse_args(argv)
40
41
42def ReplaceBytes(target_file, old_file, new_file):
43    # read old bytes
44    with open(old_file, 'rb') as f:
45        old_bytes = f.read()
46
47    # read new bytes
48    with open(new_file, 'rb') as f:
49        new_bytes = f.read()
50
51    assert len(old_bytes) == len(new_bytes), 'Pubkeys should be the same size. (%d != %d)' % (
52        len(old_bytes), len(new_bytes))
53
54    # replace bytes in target_file
55    with open(target_file, 'r+b') as f:
56        pos = f.read().find(old_bytes)
57        assert pos != -1, 'Pubkey not found'
58        f.seek(pos)
59        f.write(new_bytes)
60
61
62def main(argv):
63    try:
64        args = ParseArgs(argv)
65        ReplaceBytes(args.target_file, args.old_file, args.new_file)
66    except Exception as e:
67        print(e)
68        sys.exit(1)
69
70
71if __name__ == '__main__':
72    main(sys.argv[1:])
73