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

gm/rebaseline_server/download_actuals.py

Index: gm/rebaseline_server/download_actuals.py
diff --git a/gm/rebaseline_server/download_actuals.py b/gm/rebaseline_server/download_actuals.py
index 636958be6b545c2251628a3b0f65f2d2db0c25d1..96ea74cdfae0df66f9706f514e7a7b715d5ecd4f 100755
--- a/gm/rebaseline_server/download_actuals.py
+++ b/gm/rebaseline_server/download_actuals.py
@@ -105,8 +105,6 @@ class Download(object):
             test_name=test, hash_type=hash_type, hash_digest=hash_digest,
             gm_actuals_root_url=self._gm_actuals_root_url)
         dest_path = os.path.join(dest_dir, config, test + '.png')
-        # TODO(epoger): To speed this up, we should only download files that
-        # we don't already have on local disk.

[epoger, 2014/06/03 20:11:03]

This comment turns out to be misleading... download_actuals.py writes out files
with NON-checksum-based filenames, so we can't easily tell whether the images we
have already downloaded need to be overwritten.

         copy_contents(source_url=source_url, dest_path=dest_path,
                       create_subdirs_if_needed=True)
 
@@ -162,12 +160,33 @@ def copy_contents(source_url, dest_path, create_subdirs_if_needed=False):
       shutil.copyfileobj(fsrc=source_handle, fdst=dest_handle)
 
 
+def gcs_download_file(source_bucket, source_path, dest_path,
+                      create_subdirs_if_needed=False):
+  """ Downloads a single file from Google Cloud Storage to local disk.
+
+  EPOGER: move into a gcs utility module?

[epoger, 2014/06/03 20:11:03]

I think I should move gcs_download_file() and gcs_list_bucket_contents() into a
new gcs_utils.py module before committing this.  Does that sound good to you?

[borenet, 2014/06/03 20:27:47]

Yes, that SGTM, but what's the difference then between "gcs_utils" and
"gs_utils"?  Should one supercede the other?  This is another module which would
be nice to share between buildbot and skia...

[epoger, 2014/06/03 20:39:04]

In this case I went with "gcs_utils.py" because (a) the public API documentation
refers to Google Cloud Storage, and (b) it seemed helpful to be clear that this
is distinct from the gs_utils.py file in buildbot and not using the gsutil
binary.  But I'm happy calling it just about anything.

In buildbot-land, I think we should try to update gs_utils.py to use these API
calls instead of the gsutil binary.  (Ideally, the callers to it won't have to
change at all, unless they want to.)

I agree that it would be good for the two modules to be shared somehow.  I'll
add a TODO when I create the new module.

+
+  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)
+  copy_contents(source_url=source_http_url, dest_path=dest_path,
+                create_subdirs_if_needed=create_subdirs_if_needed)
+
+
 def gcs_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
 
+  EPOGER: move into a gcs utility module?
+
   Args:
     bucket: name of the Google Storage bucket
     subdir: directory within the bucket to list, or None for root directory
@@ -199,6 +218,17 @@ def gcs_list_bucket_contents(bucket, subdir=None):
   return (dirs, files)
 
 
+def get_builders_list(summaries_bucket=GM_SUMMARIES_BUCKET):
+  """ Returns the list of builders we have actual results for.
+
+  Args:
+    summaries_bucket: Google Cloud Storage bucket containing the summary
+        JSON files
+  """
+  dirs, _ = gcs_list_bucket_contents(bucket=GM_SUMMARIES_BUCKET)
+  return dirs
+
+
 def main():
   parser = optparse.OptionParser()
   required_params = []
@@ -234,8 +264,7 @@ def main():
   (params, remaining_args) = parser.parse_args()
 
   if params.list_builders:
-    dirs, _ = gcs_list_bucket_contents(bucket=GM_SUMMARIES_BUCKET)
-    print '\n'.join(dirs)
+    print '\n'.join(get_builders_list())
     return
 
   # Make sure all required options were set,