Add milo_service to perf dashboard.

dashboard/dashboard/services/milo_service.py

+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""An interface to the milo service, which provides buildbot information.
+
+The protocol buffer defining the API is located here:
+https://github.com/luci/luci-go/blob/master/milo/api/proto/buildbot.proto
+
+The API basically returns the same thing as the buildbot JSON API. We use the
+milo API instead of raw buildbot json because this is the method supported by
+Chrome infra team; the data is available longer and pinging the API does not
+DOS buildbot pages.
+"""
+
+import base64
+import json
+
+from google.appengine.api import urlfetch
+
+_BUILDBOT_JSON_URL = (
+    'https://luci-milo.appspot.com/prpc/milo.Buildbot/'
+    'GetBuildbotBuildJSON')
+
+
+def GetBuildbotBuildInfo(master, builder, build_num):
+  body = json.dumps({
+      'master': master,
+      'builder': builder,
+      'build_num': int(build_num)
+  })
+  headers = {
+      'Accept': 'application/json',
+      'Content-Type': 'application/json',
+  }
+  try:
+    response = urlfetch.fetch(
+        url=_BUILDBOT_JSON_URL,
+        method=urlfetch.POST,
+        payload=body,
+        headers=headers)
+  except urlfetch.Error:
+    return None
+  if response.status_code != 200:
+    return None
+
+  # Unwrap the gRPC message
+  resp = json.loads(response.content[5:])  # Remove the jsonp header.

[eakuefner, 2017/01/09 21:30:31]

Is there documentation on their jsonp format anywhere, or did you just figure it
out by inspecting responses manually? Is this built-in to grpc? I'm just asking
because this seems like it might be fragile, so the more we know about the magic
number 5, the better.

[sullivan, 2017/01/09 21:57:16]

I added a comment; this is a really common prefix used for security purposes.

+  # Decompress and unmarshal the json message.
+  data = base64.b64decode(resp['data'])
+  if not data:
+    return None
+  result = json.loads(data)
+  # Convert properties and steps lists to dicts
+  properties = {p[0] : p[1] for p in result['properties']}
+  result['properties'] = properties
+  steps = {step['name'] : step for step in result['steps']}
+  result['steps'] = steps
+  result['masterName'] = master
+  return result