PubSub: Making thread.Policy.on_exception more robust. (#4444)

- Adding special handling for API core exceptions
- Retrying on both types of idempotent error

Towards #4234.

Author: dhermes

google/cloud/pubsub_v1/subscriber/policy/base.py

@@ -21,6 +21,7 @@
 import random
 import time
 
+from google.api_core import exceptions
 import six
 
 from google.cloud.pubsub_v1 import types
@@ -65,6 +66,10 @@ class BasePolicy(object):
     """
 
     _managed_ack_ids = None
+    _RETRYABLE_STREAM_ERRORS = (
+        exceptions.DeadlineExceeded,
+        exceptions.ServiceUnavailable,
+    )
 
     def __init__(self, client, subscription,
                  flow_control=types.FlowControl(), histogram_data=None):

google/cloud/pubsub_v1/subscriber/policy/thread.py

@@ -153,10 +153,9 @@ def on_exception(self, exception):
 
         This will cause the stream to exit loudly.
         """
-        # If this is DEADLINE_EXCEEDED, then we want to retry.
-        # That entails just returning None.
-        deadline_exceeded = grpc.StatusCode.DEADLINE_EXCEEDED
-        if getattr(exception, 'code', lambda: None)() == deadline_exceeded:
+        # If this is in the list of idempotent exceptions, then we want to
+        # retry. That entails just returning None.
+        if isinstance(exception, self._RETRYABLE_STREAM_ERRORS):
             return
 
         # Set any other exception on the future.

tests/unit/pubsub_v1/subscriber/test_policy_base.py

@@ -14,11 +14,15 @@
 
 import time
 
+from google.api_core import exceptions
+from google.auth import credentials
+import grpc
 import mock
 
-from google.auth import credentials
 from google.cloud.pubsub_v1 import subscriber
 from google.cloud.pubsub_v1 import types
+from google.cloud.pubsub_v1.gapic import subscriber_client_config
+from google.cloud.pubsub_v1.subscriber.policy import base
 from google.cloud.pubsub_v1.subscriber.policy import thread
 
 
@@ -28,6 +32,23 @@ def create_policy(flow_control=types.FlowControl()):
     return thread.Policy(client, 'sub_name_d', flow_control=flow_control)
 
 
+def test_idempotent_retry_codes():
+    # Make sure the config matches our hard-coded tuple of exceptions.
+    interfaces = subscriber_client_config.config['interfaces']
+    retry_codes = interfaces['google.pubsub.v1.Subscriber']['retry_codes']
+    idempotent = retry_codes['idempotent']
+
+    status_codes = tuple(
+        getattr(grpc.StatusCode, name, None)
+        for name in idempotent
+    )
+    expected = tuple(
+        exceptions.exception_class_for_grpc_status(status_code)
+        for status_code in status_codes
+    )
+    assert base.BasePolicy._RETRYABLE_STREAM_ERRORS == expected
+
+
 def test_ack_deadline():
     policy = create_policy()
     assert policy.ack_deadline == 10

tests/unit/pubsub_v1/subscriber/test_policy_thread.py

@@ -17,8 +17,8 @@
 from concurrent import futures
 import threading
 
+from google.api_core import exceptions
 from google.auth import credentials
-import grpc
 import mock
 import pytest
 from six.moves import queue
@@ -90,8 +90,19 @@ def test_on_callback_request():
 
 def test_on_exception_deadline_exceeded():
     policy = create_policy()
-    exc = mock.Mock(spec=('code',))
-    exc.code.return_value = grpc.StatusCode.DEADLINE_EXCEEDED
+
+    details = 'Bad thing happened. Time out, go sit in the corner.'
+    exc = exceptions.DeadlineExceeded(details)
+
+    assert policy.on_exception(exc) is None
+
+
+def test_on_exception_unavailable():
+    policy = create_policy()
+
+    details = 'UNAVAILABLE. Service taking nap.'
+    exc = exceptions.ServiceUnavailable(details)
+
     assert policy.on_exception(exc) is None