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# Copyright 2017 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.
"""Helpers for wrapping low-level gRPC methods with common functionality.
This is used by gapic clients to provide common error mapping, retry, timeout,
pagination, and long-running operations to gRPC methods.
"""
from google.api_core import general_helpers
from google.api_core import grpc_helpers
from google.api_core import timeout
from google.api_core.gapic_v1 import client_info
USE_DEFAULT_METADATA = object()
DEFAULT = object()
"""Sentinel value indicating that a retry or timeout argument was unspecified,
so the default should be used."""
def _is_not_none_or_false(value):
return value is not None and value is not False
def _apply_decorators(func, decorators):
"""Apply a list of decorators to a given function.
``decorators`` may contain items that are ``None`` or ``False`` which will
be ignored.
"""
decorators = filter(_is_not_none_or_false, reversed(decorators))
for decorator in decorators:
func = decorator(func)
return func
def _determine_timeout(default_timeout, specified_timeout, retry):
"""Determines how timeout should be applied to a wrapped method.
Args:
default_timeout (Optional[Timeout]): The default timeout specified
at method creation time.
specified_timeout (Optional[Timeout]): The timeout specified at
invocation time. If :attr:`DEFAULT`, this will be set to
the ``default_timeout``.
retry (Optional[Retry]): The retry specified at invocation time.
Returns:
Optional[Timeout]: The timeout to apply to the method or ``None``.
"""
# If timeout is specified as a number instead of a Timeout instance,
# convert it to a ConstantTimeout.
if isinstance(specified_timeout, (int, float)):
specified_timeout = timeout.ConstantTimeout(specified_timeout)
if isinstance(default_timeout, (int, float)):
default_timeout = timeout.ConstantTimeout(default_timeout)
if specified_timeout is DEFAULT:
specified_timeout = default_timeout
if specified_timeout is default_timeout:
# If timeout is the default and the default timeout is exponential and
# a non-default retry is specified, make sure the timeout's deadline
# matches the retry's. This handles the case where the user leaves
# the timeout default but specifies a lower deadline via the retry.
if (
retry
and retry is not DEFAULT
and isinstance(default_timeout, timeout.ExponentialTimeout)
):
return default_timeout.with_deadline(retry._deadline)
else:
return default_timeout
return specified_timeout
class _GapicCallable(object):
"""Callable that applies retry, timeout, and metadata logic.
Args:
target (Callable): The low-level RPC method.
retry (google.api_core.retry.Retry): The default retry for the
callable. If ``None``, this callable will not retry by default
timeout (google.api_core.timeout.Timeout): The default timeout
for the callable. If ``None``, this callable will not specify
a timeout argument to the low-level RPC method by default.
metadata (Sequence[Tuple[str, str]]): Additional metadata that is
provided to the RPC method on every invocation. This is merged with
any metadata specified during invocation. If ``None``, no
additional metadata will be passed to the RPC method.
"""
def __init__(self, target, retry, timeout, metadata=None):
self._target = target
self._retry = retry
self._timeout = timeout
self._metadata = metadata
def __call__(self, *args, **kwargs):
"""Invoke the low-level RPC with retry, timeout, and metadata."""
# Note: Due to Python 2 lacking keyword-only arguments we use kwargs to
# extract the retry and timeout params.
timeout_ = _determine_timeout(
self._timeout,
kwargs.pop("timeout", self._timeout),
# Use only the invocation-specified retry only for this, as we only
# want to adjust the timeout deadline if the *user* specified
# a different retry.
kwargs.get("retry", None),
)
retry = kwargs.pop("retry", self._retry)
if retry is DEFAULT:
retry = self._retry
# Apply all applicable decorators.
wrapped_func = _apply_decorators(self._target, [retry, timeout_])
# Add the user agent metadata to the call.
if self._metadata is not None:
metadata = kwargs.get("metadata", [])
# Due to the nature of invocation, None should be treated the same
# as not specified.
if metadata is None:
metadata = []
metadata = list(metadata)
metadata.extend(self._metadata)
kwargs["metadata"] = metadata
return wrapped_func(*args, **kwargs)
def wrap_method(
func,
default_retry=None,
default_timeout=None,
client_info=client_info.DEFAULT_CLIENT_INFO,
):
"""Wrap an RPC method with common behavior.
This applies common error wrapping, retry, and timeout behavior a function.
The wrapped function will take optional ``retry`` and ``timeout``
arguments.
For example::
import google.api_core.gapic_v1.method
from google.api_core import retry
from google.api_core import timeout
# The original RPC method.
def get_topic(name, timeout=None):
request = publisher_v2.GetTopicRequest(name=name)
return publisher_stub.GetTopic(request, timeout=timeout)
default_retry = retry.Retry(deadline=60)
default_timeout = timeout.Timeout(deadline=60)
wrapped_get_topic = google.api_core.gapic_v1.method.wrap_method(
get_topic, default_retry)
# Execute get_topic with default retry and timeout:
response = wrapped_get_topic()
# Execute get_topic without doing any retying but with the default
# timeout:
response = wrapped_get_topic(retry=None)
# Execute get_topic but only retry on 5xx errors:
my_retry = retry.Retry(retry.if_exception_type(
exceptions.InternalServerError))
response = wrapped_get_topic(retry=my_retry)
The way this works is by late-wrapping the given function with the retry
and timeout decorators. Essentially, when ``wrapped_get_topic()`` is
called:
* ``get_topic()`` is first wrapped with the ``timeout`` into
``get_topic_with_timeout``.
* ``get_topic_with_timeout`` is wrapped with the ``retry`` into
``get_topic_with_timeout_and_retry()``.
* The final ``get_topic_with_timeout_and_retry`` is called passing through
the ``args`` and ``kwargs``.
The callstack is therefore::
method.__call__() ->
Retry.__call__() ->
Timeout.__call__() ->
wrap_errors() ->
get_topic()
Note that if ``timeout`` or ``retry`` is ``None``, then they are not
applied to the function. For example,
``wrapped_get_topic(timeout=None, retry=None)`` is more or less
equivalent to just calling ``get_topic`` but with error re-mapping.
Args:
func (Callable[Any]): The function to wrap. It should accept an
optional ``timeout`` argument. If ``metadata`` is not ``None``, it
should accept a ``metadata`` argument.
default_retry (Optional[google.api_core.Retry]): The default retry
strategy. If ``None``, the method will not retry by default.
default_timeout (Optional[google.api_core.Timeout]): The default
timeout strategy. Can also be specified as an int or float. If
``None``, the method will not have timeout specified by default.
client_info
(Optional[google.api_core.gapic_v1.client_info.ClientInfo]):
Client information used to create a user-agent string that's
passed as gRPC metadata to the method. If unspecified, then
a sane default will be used. If ``None``, then no user agent
metadata will be provided to the RPC method.
Returns:
Callable: A new callable that takes optional ``retry`` and ``timeout``
arguments and applies the common error mapping, retry, timeout,
and metadata behavior to the low-level RPC method.
"""
func = grpc_helpers.wrap_errors(func)
if client_info is not None:
user_agent_metadata = [client_info.to_grpc_metadata()]
else:
user_agent_metadata = None
return general_helpers.wraps(func)(
_GapicCallable(
func, default_retry, default_timeout, metadata=user_agent_metadata
)
)