BuildBucket recipe module can expose properties.

scripts/slave/recipe_modules/buildbucket/api.py

 # Copyright 2016 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.
 
 """API for interacting with the buildbucket service directly.
 
 Instead of triggering jobs by emitting annotations then handled by the master,
 this module allows slaves to directly post requests to buildbucket.
 """
 
 import json
 import os
 import uuid
 
 from recipe_engine import recipe_api
 
 
 class BuildbucketApi(recipe_api.RecipeApi):
   """A module for interacting with buildbucket."""
 
+  def __init__(self, *args, **kwargs):
+    super(BuildbucketApi, self).__init__(*args, **kwargs)
+    self._properties = None
+
   def get_config_defaults(self):
     if self.m.platform.is_win:
       return {'PLATFORM': 'win'}
     return {'PLATFORM': 'default'}
 
   def _configure_defaults(self):
     """Apply default configuration if no configuration has been set.
 
     Ideally whoever uses this api will explicitly set the configuration by
     doing `api.buildbucket.set_config('production_buildbucket')`, but to make
     this module usable even in case they don't configure it, we set the default
     to the production instance of buildbucket."""
     # There's only two items in this module's configuration, the path to the
     # buildbucket cli client binary and the buildbucket hostname, this default
     # configuration will override them.
     if not self.c or not self.c.complete():
       self.set_config('production_buildbucket')
 
   def _tags_for_build(self, bucket, parameters, override_tags=None):
-    buildbucket_info = self.m.properties.get('buildbucket', {})
-    if isinstance(buildbucket_info, basestring):  # pragma: no cover
-      buildbucket_info = json.loads(buildbucket_info)
+    buildbucket_info = self.properties or {}
     original_tags_list = buildbucket_info.get('build', {}).get('tags', [])
 
     original_tags = dict(t.split(':', 1) for t in original_tags_list)
     new_tags = {'user_agent': 'recipe'}
 
     if 'buildset' in original_tags:
       new_tags['buildset'] = original_tags['buildset']
     builder_name = parameters.get('builder_name')
     if builder_name:
       new_tags['builder'] = builder_name
     if bucket.startswith('master.'):
       new_tags['master'] = bucket[7:]
 
     new_tags.update(override_tags or {})
     return sorted([':'.join((x, y)) for x, y in new_tags.iteritems()])
 
+  @property
+  def properties(self):
+    """Returns (dict-like or None): The BuildBucket properties, if present."""
+    if self._properties is None:
+      # Not cached, load and deserialize from properties.
+      props = self.m.properties.get('buildbucket')
+      if props is not None:
+        if isinstance(props, basestring):
+          props = json.loads(props)
+        self._properties = props
+    return self._properties
 
   def put(self, builds, service_account=None, **kwargs):
     """Puts a batch of builds.
 
     Args:
       builds (list): A list of dicts, where keys are:
         'bucket': (required) name of the bucket for the request.
         'parameters' (dict): (required) arbitrary json-able parameters that a
           build system would be able to interpret.
         'tags': (optional) a dict(str->str) of tags for the build. These will
@@ skipping 30 matching lines @@
   def _call_service(self, command, args, service_account=None, **kwargs):
     # TODO: Deploy buildbucket client using cipd.
     self._configure_defaults()
     step_name = kwargs.pop('name', 'buildbucket.' + command)
     if service_account:
       args = ['--service-account-json', service_account] + args
     args = [str(self.c.buildbucket_client_path), command, '--host',
             self.c.buildbucket_host] + args
     return self.m.step(
         step_name, args, stdout=self.m.json.output(), **kwargs)