buildbucket: add retry API.

appengine/cr-buildbucket/api.py

Index: appengine/cr-buildbucket/api.py
diff --git a/appengine/cr-buildbucket/api.py b/appengine/cr-buildbucket/api.py
index eb5a568456f48dd3702f476f666854726cf675ae..ddc531779b2a41a3949972de76bca6b707654db5 100644
--- a/appengine/cr-buildbucket/api.py
+++ b/appengine/cr-buildbucket/api.py
@@ -287,6 +287,29 @@ class BuildBucketApi(remote.Service):
       for req, build in zip(request.builds, build_futures)]
     return res
 
+  ##################################  RETRY   ##################################
+
+  class RetryRequestMessage(messages.Message):
+    client_operation_id = messages.StringField(1)
+    lease_expiration_ts = messages.IntegerField(2)
+    pubsub_callback = messages.MessageField(PubSubCallbackMessage, 3)
+
+  @buildbucket_api_method(
+    id_resource_container(RetryRequestMessage),
+    BuildResponseMessage,
+    path='builds/{id}/retry', http_method='PUT')
+  @auth.public
+  def retry(self, request):
+    """Retries an existing build."""
+    build = service.retry(
+      request.id,
+      lease_expiration_date=parse_datetime(request.lease_expiration_ts),
+      client_operation_id=request.client_operation_id,
+      pubsub_callback=pubsub_callback_from_message(request.pubsub_callback),
+    )
+    return build_to_response_message(build, include_lease_key=True)
+
+
   ##################################  SEARCH   #################################