fix: add ConnectionError to default retry (#445)

This adds python built-in [ConnectionError](https://docs.python.org/3/library/exceptions.html#ConnectionError) to default retryable types. ConnectionError was recently added in the [BigQuery library](googleapis/python-bigquery#571) to allow retries. Fixes #426 🦕

Author: cojenco

google/cloud/storage/retry.py

@@ -21,7 +21,14 @@
 import json
 
 
-_RETRYABLE_TYPES = (
+# ConnectionError is a built-in exception only in Python3 and not in Python2.
+try:
+ _RETRYABLE_STDLIB_TYPES = (ConnectionError,)
+except NameError:
+ _RETRYABLE_STDLIB_TYPES = ()
+
+
+_RETRYABLE_TYPES = _RETRYABLE_STDLIB_TYPES + (
  api_exceptions.TooManyRequests, # 429
  api_exceptions.InternalServerError, # 500
  api_exceptions.BadGateway, # 502
@@ -30,6 +37,7 @@
  requests.ConnectionError,
 )
 
+
 # Some retriable errors don't have their own custom exception in api_core.
 _ADDITIONAL_RETRYABLE_STATUS_CODES = (408,)
 

tests/unit/test_retry.py

@@ -19,6 +19,14 @@
 import mock
 
 
+try:
+ ConnectionError
+except NameError:
+ _HAS_STDLIB_CONNECTION_ERROR = False
+else:
+ _HAS_STDLIB_CONNECTION_ERROR = True
+
+
 class Test_should_retry(unittest.TestCase):
  def _call_fut(self, exc):
  from google.cloud.storage import retry
@@ -56,9 +64,22 @@ def test_w_google_api_call_error_miss(self):
  self.assertFalse(self._call_fut(exc))
 
  def test_w_requests_connection_error(self):
+ import requests
+
+ exc = requests.ConnectionError()
+ self.assertTrue(self._call_fut(exc))
+
+ def test_miss_w_stdlib_error(self):
  exc = ValueError("testing")
  self.assertFalse(self._call_fut(exc))
 
+ @unittest.skipUnless(
+ _HAS_STDLIB_CONNECTION_ERROR, "No builtin 'ConnectionError' in Python 2",
+ )
+ def test_w_stdlib_connection_error(self):
+ exc = ConnectionError()
+ self.assertTrue(self._call_fut(exc))
+
 
 class TestConditionalRetryPolicy(unittest.TestCase):
  def _make_one(self, retry_policy, conditional_predicate, required_kwargs):