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Source code for google.api_core.retry.retry_streaming_async
# Copyright 2023 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.
"""
Generator wrapper for retryable async streaming RPCs.
"""
from __future__ import annotations
from typing import (
cast,
Any,
Callable,
Iterable,
AsyncIterator,
AsyncIterable,
Awaitable,
TypeVar,
AsyncGenerator,
TYPE_CHECKING,
)
import asyncio
import time
import sys
import functools
from google.api_core.retry.retry_base import _BaseRetry
from google.api_core.retry.retry_base import _retry_error_helper
from google.api_core.retry import exponential_sleep_generator
from google.api_core.retry import build_retry_error
from google.api_core.retry import RetryFailureReason
if TYPE_CHECKING:
if sys.version_info >= (3, 10):
from typing import ParamSpec
else:
from typing_extensions import ParamSpec
_P = ParamSpec("_P") # target function call parameters
_Y = TypeVar("_Y") # yielded values
async def retry_target_stream(
target: Callable[_P, AsyncIterable[_Y] | Awaitable[AsyncIterable[_Y]]],
predicate: Callable[[Exception], bool],
sleep_generator: Iterable[float],
timeout: float | None = None,
on_error: Callable[[Exception], None] | None = None,
exception_factory: Callable[
[list[Exception], RetryFailureReason, float | None],
tuple[Exception, Exception | None],
] = build_retry_error,
init_args: _P.args = (),
init_kwargs: _P.kwargs = {},
**kwargs,
) -> AsyncGenerator[_Y, None]:
"""Create a generator wrapper that retries the wrapped stream if it fails.
This is the lowest-level retry helper. Generally, you'll use the
higher-level retry helper :class:`AsyncRetry`.
Args:
target: The generator function to call and retry.
predicate: A callable used to determine if an
exception raised by the target should be considered retryable.
It should return True to retry or False otherwise.
sleep_generator: An infinite iterator that determines
how long to sleep between retries.
timeout: How long to keep retrying the target.
Note: timeout is only checked before initiating a retry, so the target may
run past the timeout value as long as it is healthy.
on_error: If given, the on_error callback will be called with each
retryable exception raised by the target. Any error raised by this
function will *not* be caught.
exception_factory: A function that is called when the retryable reaches
a terminal failure state, used to construct an exception to be raised.
It takes a list of all exceptions encountered, a retry.RetryFailureReason
enum indicating the failure cause, and the original timeout value
as arguments. It should return a tuple of the exception to be raised,
along with the cause exception if any. The default implementation will raise
a RetryError on timeout, or the last exception encountered otherwise.
init_args: Positional arguments to pass to the target function.
init_kwargs: Keyword arguments to pass to the target function.
Returns:
AsyncGenerator: A retryable generator that wraps the target generator function.
Raises:
ValueError: If the sleep generator stops yielding values.
Exception: a custom exception specified by the exception_factory if provided.
If no exception_factory is provided:
google.api_core.RetryError: If the timeout is exceeded while retrying.
Exception: If the target raises an error that isn't retryable.
"""
target_iterator: AsyncIterator[_Y] | None = None
timeout = kwargs.get("deadline", timeout)
deadline = time.monotonic() + timeout if timeout else None
# keep track of retryable exceptions we encounter to pass in to exception_factory
error_list: list[Exception] = []
target_is_generator: bool | None = None
for sleep in sleep_generator:
# Start a new retry loop
try:
# Note: in the future, we can add a ResumptionStrategy object
# to generate new args between calls. For now, use the same args
# for each attempt.
target_output: AsyncIterable[_Y] | Awaitable[AsyncIterable[_Y]] = target(
*init_args, **init_kwargs
)
try:
# gapic functions return the generator behind an awaitable
# unwrap the awaitable so we can work with the generator directly
target_output = await target_output # type: ignore
except TypeError:
# was not awaitable, continue
pass
target_iterator = cast(AsyncIterable["_Y"], target_output).__aiter__()
if target_is_generator is None:
# Check if target supports generator features (asend, athrow, aclose)
target_is_generator = bool(getattr(target_iterator, "asend", None))
sent_in = None
while True:
## Read from target_iterator
# If the target is a generator, we will advance it with `asend`
# otherwise, we will use `anext`
if target_is_generator:
next_value = await target_iterator.asend(sent_in) # type: ignore
else:
next_value = await target_iterator.__anext__()
## Yield from Wrapper to caller
try:
# yield latest value from target
# exceptions from `athrow` and `aclose` are injected here
sent_in = yield next_value
except GeneratorExit:
# if wrapper received `aclose` while waiting on yield,
# it will raise GeneratorExit here
if target_is_generator:
# pass to inner target_iterator for handling
await cast(AsyncGenerator["_Y", None], target_iterator).aclose()
else:
raise
return
except: # noqa: E722
# bare except catches any exception passed to `athrow`
if target_is_generator:
# delegate error handling to target_iterator
await cast(AsyncGenerator["_Y", None], target_iterator).athrow(
cast(BaseException, sys.exc_info()[1])
)
else:
raise
return
except StopAsyncIteration:
# if iterator exhausted, return
return
# handle exceptions raised by the target_iterator
# pylint: disable=broad-except
# This function explicitly must deal with broad exceptions.
except Exception as exc:
# defer to shared logic for handling errors
_retry_error_helper(
exc,
deadline,
sleep,
error_list,
predicate,
on_error,
exception_factory,
timeout,
)
# if exception not raised, sleep before next attempt
await asyncio.sleep(sleep)
finally:
if target_is_generator and target_iterator is not None:
await cast(AsyncGenerator["_Y", None], target_iterator).aclose()
raise ValueError("Sleep generator stopped yielding sleep values.")
[docs]class AsyncStreamingRetry(_BaseRetry):
"""Exponential retry decorator for async streaming rpcs.
This class returns an AsyncGenerator when called, which wraps the target
stream in retry logic. If any exception is raised by the target, the
entire stream will be retried within the wrapper.
Although the default behavior is to retry transient API errors, a
different predicate can be provided to retry other exceptions.
Important Note: when a stream is encounters a retryable error, it will
silently construct a fresh iterator instance in the background
and continue yielding (likely duplicate) values as if no error occurred.
This is the most general way to retry a stream, but it often is not the
desired behavior. Example: iter([1, 2, 1/0]) -> [1, 2, 1, 2, ...]
There are two ways to build more advanced retry logic for streams:
1. Wrap the target
Use a ``target`` that maintains state between retries, and creates a
different generator on each retry call. For example, you can wrap a
grpc call in a function that modifies the request based on what has
already been returned:
.. code-block:: python
async def attempt_with_modified_request(target, request, seen_items=[]):
# remove seen items from request on each attempt
new_request = modify_request(request, seen_items)
new_generator = await target(new_request)
async for item in new_generator:
yield item
seen_items.append(item)
retry_wrapped = AsyncRetry(is_stream=True,...)(attempt_with_modified_request, target, request, [])
2. Wrap the retry generator
Alternatively, you can wrap the retryable generator itself before
passing it to the end-user to add a filter on the stream. For
example, you can keep track of the items that were successfully yielded
in previous retry attempts, and only yield new items when the
new attempt surpasses the previous ones:
.. code-block:: python
async def retryable_with_filter(target):
stream_idx = 0
# reset stream_idx when the stream is retried
def on_error(e):
nonlocal stream_idx
stream_idx = 0
# build retryable
retryable_gen = AsyncRetry(is_stream=True, ...)(target)
# keep track of what has been yielded out of filter
seen_items = []
async for item in retryable_gen:
if stream_idx >= len(seen_items):
yield item
seen_items.append(item)
elif item != previous_stream[stream_idx]:
raise ValueError("Stream differs from last attempt")"
stream_idx += 1
filter_retry_wrapped = retryable_with_filter(target)
Args:
predicate (Callable[Exception]): A callable that should return ``True``
if the given exception is retryable.
initial (float): The minimum amount of time to delay in seconds. This
must be greater than 0.
maximum (float): The maximum amount of time to delay in seconds.
multiplier (float): The multiplier applied to the delay.
timeout (Optional[float]): How long to keep retrying in seconds.
Note: timeout is only checked before initiating a retry, so the target may
run past the timeout value as long as it is healthy.
on_error (Optional[Callable[Exception]]): A function to call while processing
a retryable exception. Any error raised by this function will
*not* be caught.
is_stream (bool): Indicates whether the input function
should be treated as a stream function (i.e. an AsyncGenerator,
or function or coroutine that returns an AsyncIterable).
If True, the iterable will be wrapped with retry logic, and any
failed outputs will restart the stream. If False, only the input
function call itself will be retried. Defaults to False.
To avoid duplicate values, retryable streams should typically be
wrapped in additional filter logic before use.
deadline (float): DEPRECATED use ``timeout`` instead. If set it will
override ``timeout`` parameter.
"""
[docs] def __call__(
self,
func: Callable[..., AsyncIterable[_Y] | Awaitable[AsyncIterable[_Y]]],
on_error: Callable[[Exception], Any] | None = None,
) -> Callable[_P, Awaitable[AsyncGenerator[_Y, None]]]:
"""Wrap a callable with retry behavior.
Args:
func (Callable): The callable or stream to add retry behavior to.
on_error (Optional[Callable[Exception]]): If given, the
on_error callback will be called with each retryable exception
raised by the wrapped function. Any error raised by this
function will *not* be caught. If on_error was specified in the
constructor, this value will be ignored.
Returns:
Callable: A callable that will invoke ``func`` with retry
behavior.
"""
if self._on_error is not None:
on_error = self._on_error
@functools.wraps(func)
async def retry_wrapped_func(
*args: _P.args, **kwargs: _P.kwargs
) -> AsyncGenerator[_Y, None]:
"""A wrapper that calls target function with retry."""
sleep_generator = exponential_sleep_generator(
self._initial, self._maximum, multiplier=self._multiplier
)
return retry_target_stream(
func,
self._predicate,
sleep_generator,
self._timeout,
on_error,
init_args=args,
init_kwargs=kwargs,
)
return retry_wrapped_func
