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+# Copyright 2022 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import asyncio
+import random
+import time
+
+from google.auth import exceptions
+
+# The default amount of retry attempts
+_DEFAULT_RETRY_TOTAL_ATTEMPTS = 3
+
+# The default initial backoff period (1.0 second).
+_DEFAULT_INITIAL_INTERVAL_SECONDS = 1.0
+
+# The default randomization factor (0.1 which results in a random period ranging
+# between 10% below and 10% above the retry interval).
+_DEFAULT_RANDOMIZATION_FACTOR = 0.1
+
+# The default multiplier value (2 which is 100% increase per back off).
+_DEFAULT_MULTIPLIER = 2.0
+
+"""Exponential Backoff Utility
+
+This is a private module that implements the exponential back off algorithm.
+It can be used as a utility for code that needs to retry on failure, for example
+an HTTP request.
+"""
+
+
+class _BaseExponentialBackoff:
+ """An exponential backoff iterator base class.
+
+ Args:
+ total_attempts Optional[int]:
+ The maximum amount of retries that should happen.
+ The default value is 3 attempts.
+ initial_wait_seconds Optional[int]:
+ The amount of time to sleep in the first backoff. This parameter
+ should be in seconds.
+ The default value is 1 second.
+ randomization_factor Optional[float]:
+ The amount of jitter that should be in each backoff. For example,
+ a value of 0.1 will introduce a jitter range of 10% to the
+ current backoff period.
+ The default value is 0.1.
+ multiplier Optional[float]:
+ The backoff multipler. This adjusts how much each backoff will
+ increase. For example a value of 2.0 leads to a 200% backoff
+ on each attempt. If the initial_wait is 1.0 it would look like
+ this sequence [1.0, 2.0, 4.0, 8.0].
+ The default value is 2.0.
+ """
+
+ def __init__(
+ self,
+ total_attempts=_DEFAULT_RETRY_TOTAL_ATTEMPTS,
+ initial_wait_seconds=_DEFAULT_INITIAL_INTERVAL_SECONDS,
+ randomization_factor=_DEFAULT_RANDOMIZATION_FACTOR,
+ multiplier=_DEFAULT_MULTIPLIER,
+ ):
+ if total_attempts < 1:
+ raise exceptions.InvalidValue(
+ f"total_attempts must be greater than or equal to 1 but was {total_attempts}"
+ )
+
+ self._total_attempts = total_attempts
+ self._initial_wait_seconds = initial_wait_seconds
+
+ self._current_wait_in_seconds = self._initial_wait_seconds
+
+ self._randomization_factor = randomization_factor
+ self._multiplier = multiplier
+ self._backoff_count = 0
+
+ @property
+ def total_attempts(self):
+ """The total amount of backoff attempts that will be made."""
+ return self._total_attempts
+
+ @property
+ def backoff_count(self):
+ """The current amount of backoff attempts that have been made."""
+ return self._backoff_count
+
+ def _reset(self):
+ self._backoff_count = 0
+ self._current_wait_in_seconds = self._initial_wait_seconds
+
+ def _calculate_jitter(self):
+ jitter_variance = self._current_wait_in_seconds * self._randomization_factor
+ jitter = random.uniform(
+ self._current_wait_in_seconds - jitter_variance,
+ self._current_wait_in_seconds + jitter_variance,
+ )
+
+ return jitter
+
+
+class ExponentialBackoff(_BaseExponentialBackoff):
+ """An exponential backoff iterator. This can be used in a for loop to
+ perform requests with exponential backoff.
+ """
+
+ def __init__(self, *args, **kwargs):
+ super(ExponentialBackoff, self).__init__(*args, **kwargs)
+
+ def __iter__(self):
+ self._reset()
+ return self
+
+ def __next__(self):
+ if self._backoff_count >= self._total_attempts:
+ raise StopIteration
+ self._backoff_count += 1
+
+ if self._backoff_count <= 1:
+ return self._backoff_count
+
+ jitter = self._calculate_jitter()
+
+ time.sleep(jitter)
+
+ self._current_wait_in_seconds *= self._multiplier
+ return self._backoff_count
+
+
+class AsyncExponentialBackoff(_BaseExponentialBackoff):
+ """An async exponential backoff iterator. This can be used in a for loop to
+ perform async requests with exponential backoff.
+ """
+
+ def __init__(self, *args, **kwargs):
+ super(AsyncExponentialBackoff, self).__init__(*args, **kwargs)
+
+ def __aiter__(self):
+ self._reset()
+ return self
+
+ async def __anext__(self):
+ if self._backoff_count >= self._total_attempts:
+ raise StopAsyncIteration
+ self._backoff_count += 1
+
+ if self._backoff_count <= 1:
+ return self._backoff_count
+
+ jitter = self._calculate_jitter()
+
+ await asyncio.sleep(jitter)
+
+ self._current_wait_in_seconds *= self._multiplier
+ return self._backoff_count