reland "rebaseline_server: download actual-results.json files from GCS instead of SVN"

tools/pyutils/gs_utils.py

Index: tools/pyutils/gs_utils.py
diff --git a/tools/pyutils/gs_utils.py b/tools/pyutils/gs_utils.py
new file mode 100755
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+++ b/tools/pyutils/gs_utils.py
@@ -0,0 +1,81 @@
+#!/usr/bin/python
+
+"""
+Copyright 2014 Google Inc.
+
+Use of this source code is governed by a BSD-style license that can be
+found in the LICENSE file.
+
+Utilities for accessing Google Cloud Storage.
+
+TODO(epoger): move this into tools/utils for broader use?
+"""
+
+# System-level imports
+import os
+import posixpath
+import sys
+try:
+  from apiclient.discovery import build as build_service
+except ImportError:
+  print ('Missing google-api-python-client.  Please install it; directions '
+         'can be found at https://developers.google.com/api-client-library/'
+         'python/start/installation')
+  raise
+
+# Local imports
+import url_utils
+
+
+def download_file(source_bucket, source_path, dest_path,
+                  create_subdirs_if_needed=False):
+  """ Downloads a single file from Google Cloud Storage to local disk.
+
+  Args:
+    source_bucket: GCS bucket to download the file from
+    source_path: full path (Posix-style) within that bucket
+    dest_path: full path (local-OS-style) on local disk to copy the file to
+    create_subdirs_if_needed: boolean; whether to create subdirectories as
+        needed to create dest_path
+  """
+  source_http_url = posixpath.join(
+      'http://storage.googleapis.com', source_bucket, source_path)
+  url_utils.copy_contents(source_url=source_http_url, dest_path=dest_path,
+                          create_subdirs_if_needed=create_subdirs_if_needed)
+
+
+def list_bucket_contents(bucket, subdir=None):
+  """ Returns files in the Google Cloud Storage bucket as a (dirs, files) tuple.
+
+  Uses the API documented at
+  https://developers.google.com/storage/docs/json_api/v1/objects/list
+
+  Args:
+    bucket: name of the Google Storage bucket
+    subdir: directory within the bucket to list, or None for root directory
+  """
+  # The GCS command relies on the subdir name (if any) ending with a slash.
+  if subdir and not subdir.endswith('/'):
+    subdir += '/'
+  subdir_length = len(subdir) if subdir else 0
+
+  storage = build_service('storage', 'v1')
+  command = storage.objects().list(
+      bucket=bucket, delimiter='/', fields='items(name),prefixes',
+      prefix=subdir)
+  results = command.execute()
+
+  # The GCS command returned two subdicts:
+  # prefixes: the full path of every directory within subdir, with trailing '/'
+  # items: property dict for each file object within subdir
+  #        (including 'name', which is full path of the object)
+  dirs = []
+  for dir_fullpath in results.get('prefixes', []):
+    dir_basename = dir_fullpath[subdir_length:]
+    dirs.append(dir_basename[:-1])  # strip trailing slash
+  files = []
+  for file_properties in results.get('items', []):
+    file_fullpath = file_properties['name']
+    file_basename = file_fullpath[subdir_length:]
+    files.append(file_basename)
+  return (dirs, files)