1# Copyright 2014 The Chromium Authors. All rights reserved.
2# Use of this source code is governed by a BSD-style license that can be
3# found in the LICENSE file.
4
5"""This module fetches and syncs prebuilts from Google Cloud Storage (GCS).
6
7See prebuilts/README for a description of the respository <> GCS sync mechanism.
8"""
9
10import hashlib
11import logging
12import os
13import urllib
14
15from memory_inspector import constants
16
17
18# Bypass the GCS download logic in unittests and use the *_ForTests mock.
19in_test_harness = False
20
21
22def GetIfChanged(local_file_path):
23  """Downloads the file from GCS, only if the local one is outdated."""
24  is_changed = _IsChanged(local_file_path)
25
26  # In test harness mode we are only interested in checking that the proper
27  # .sha1 files have been checked in (hence the call to _IsChanged() above).
28  if in_test_harness:
29    return _GetIfChanged_ForTests(local_file_path)
30
31  if not is_changed:
32    return
33  obj_name = _GetRemoteFileID(local_file_path)
34  url = constants.PREBUILTS_BASE_URL + obj_name
35  logging.info('Downloading %s prebuilt from %s.' % (local_file_path, url))
36  urllib.urlretrieve(url, local_file_path)
37  assert(not _IsChanged(local_file_path)), ('GCS download for %s failed.' %
38                                            local_file_path)
39
40
41def _IsChanged(local_file_path):
42  """Checks whether the local_file_path exists and matches the expected hash."""
43  is_changed = True
44  expected_hash = _GetRemoteFileID(local_file_path)
45  if os.path.exists(local_file_path):
46    with open(local_file_path, 'rb') as f:
47      local_hash = hashlib.sha1(f.read()).hexdigest()
48    is_changed = (local_hash != expected_hash)
49  return is_changed
50
51
52def _GetRemoteFileID(local_file_path):
53  """Returns the checked-in hash which identifies the name of file in GCS."""
54  hash_path = local_file_path + '.sha1'
55  with open(hash_path, 'rb') as f:
56    return f.read(1024).rstrip()
57
58
59def _GetIfChanged_ForTests(local_file_path):
60  """This is the mock version of |GetIfChanged| used only in unittests."""
61  # Just truncate / create an empty file.
62  open(local_file_path, 'wb').close()
63