# Copyright 2019, Google LLC All rights reserved. # # 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. from __future__ import absolute_import import os import typing from typing import cast, Any, Callable, Optional, Sequence, Union import warnings from google.auth.credentials import AnonymousCredentials # type: ignore from google.oauth2 import service_account # type: ignore from google.cloud.pubsub_v1 import types from google.cloud.pubsub_v1.subscriber import futures from google.cloud.pubsub_v1.subscriber._protocol import streaming_pull_manager from google.pubsub_v1.services.subscriber import client as subscriber_client from google.pubsub_v1 import gapic_version as package_version if typing.TYPE_CHECKING: # pragma: NO COVER from google.cloud.pubsub_v1 import subscriber from google.pubsub_v1.services.subscriber.transports.grpc import ( SubscriberGrpcTransport, ) __version__ = package_version.__version__ class Client(subscriber_client.SubscriberClient): """A subscriber client for Google Cloud Pub/Sub. This creates an object that is capable of subscribing to messages. Generally, you can instantiate this client with no arguments, and you get sensible defaults. Args: kwargs: Any additional arguments provided are sent as keyword keyword arguments to the underlying :class:`~google.cloud.pubsub_v1.gapic.subscriber_client.SubscriberClient`. Generally you should not need to set additional keyword arguments. Optionally, regional endpoints can be set via ``client_options`` that takes a single key-value pair that defines the endpoint. Example: .. code-block:: python from google.cloud import pubsub_v1 subscriber_client = pubsub_v1.SubscriberClient( # Optional client_options = { "api_endpoint": REGIONAL_ENDPOINT } ) """ def __init__(self, **kwargs: Any): # Sanity check: Is our goal to use the emulator? # If so, create a grpc insecure channel with the emulator host # as the target. if os.environ.get("PUBSUB_EMULATOR_HOST"): kwargs["client_options"] = { "api_endpoint": os.environ.get("PUBSUB_EMULATOR_HOST") } kwargs["credentials"] = AnonymousCredentials() # Instantiate the underlying GAPIC client. super().__init__(**kwargs) self._target = self._transport._host self._closed = False @classmethod def from_service_account_file( # type: ignore[override] cls, filename: str, **kwargs: Any ) -> "Client": """Creates an instance of this client using the provided credentials file. Args: filename: The path to the service account private key json file. kwargs: Additional arguments to pass to the constructor. Returns: A Subscriber :class:`~google.cloud.pubsub_v1.subscriber.client.Client` instance that is the constructed client. """ credentials = service_account.Credentials.from_service_account_file(filename) kwargs["credentials"] = credentials return cls(**kwargs) from_service_account_json = from_service_account_file # type: ignore[assignment] @property def target(self) -> str: """Return the target (where the API is). Returns: The location of the API. """ return self._target @property def closed(self) -> bool: """Return whether the client has been closed and cannot be used anymore. .. versionadded:: 2.8.0 """ return self._closed @property def api(self): """The underlying gapic API client. .. versionchanged:: 2.10.0 Instead of a GAPIC ``SubscriberClient`` client instance, this property is a proxy object to it with the same interface. .. deprecated:: 2.10.0 Use the GAPIC methods and properties on the client instance directly instead of through the :attr:`api` attribute. """ msg = ( 'The "api" property only exists for backward compatibility, access its ' 'attributes directly thorugh the client instance (e.g. "client.foo" ' 'instead of "client.api.foo").' ) warnings.warn(msg, category=DeprecationWarning) return super() def subscribe( self, subscription: str, callback: Callable[["subscriber.message.Message"], Any], flow_control: Union[types.FlowControl, Sequence] = (), scheduler: Optional["subscriber.scheduler.ThreadScheduler"] = None, use_legacy_flow_control: bool = False, await_callbacks_on_shutdown: bool = False, ) -> futures.StreamingPullFuture: """Asynchronously start receiving messages on a given subscription. This method starts a background thread to begin pulling messages from a Pub/Sub subscription and scheduling them to be processed using the provided ``callback``. The ``callback`` will be called with an individual :class:`google.cloud.pubsub_v1.subscriber.message.Message`. It is the responsibility of the callback to either call ``ack()`` or ``nack()`` on the message when it finished processing. If an exception occurs in the callback during processing, the exception is logged and the message is ``nack()`` ed. The ``flow_control`` argument can be used to control the rate of at which messages are pulled. The settings are relatively conservative by default to prevent "message hoarding" - a situation where the client pulls a large number of messages but can not process them fast enough leading it to "starve" other clients of messages. Increasing these settings may lead to faster throughput for messages that do not take a long time to process. The ``use_legacy_flow_control`` argument disables enforcing flow control settings at the Cloud Pub/Sub server, and only the client side flow control will be enforced. This method starts the receiver in the background and returns a *Future* representing its execution. Waiting on the future (calling ``result()``) will block forever or until a non-recoverable error is encountered (such as loss of network connectivity). Cancelling the future will signal the process to shutdown gracefully and exit. .. note:: This uses Pub/Sub's *streaming pull* feature. This feature properties that may be surprising. Please take a look at https://cloud.google.com/pubsub/docs/pull#streamingpull for more details on how streaming pull behaves compared to the synchronous pull method. Example: .. code-block:: python from google.cloud import pubsub_v1 subscriber_client = pubsub_v1.SubscriberClient() # existing subscription subscription = subscriber_client.subscription_path( 'my-project-id', 'my-subscription') def callback(message): print(message) message.ack() future = subscriber_client.subscribe( subscription, callback) try: future.result() except KeyboardInterrupt: future.cancel() # Trigger the shutdown. future.result() # Block until the shutdown is complete. Args: subscription: The name of the subscription. The subscription should have already been created (for example, by using :meth:`create_subscription`). callback: The callback function. This function receives the message as its only argument and will be called from a different thread/ process depending on the scheduling strategy. flow_control: The flow control settings. Use this to prevent situations where you are inundated with too many messages at once. scheduler: An optional *scheduler* to use when executing the callback. This controls how callbacks are executed concurrently. This object must not be shared across multiple ``SubscriberClient`` instances. use_legacy_flow_control (bool): If set to ``True``, flow control at the Cloud Pub/Sub server is disabled, though client-side flow control is still enabled. If set to ``False`` (default), both server-side and client-side flow control are enabled. await_callbacks_on_shutdown: If ``True``, after canceling the returned future, the latter's ``result()`` method will block until the background stream and its helper threads have been terminated, and all currently executing message callbacks are done processing. If ``False`` (default), the returned future's ``result()`` method will not block after canceling the future. The method will instead return immediately after the background stream and its helper threads have been terminated, but some of the message callback threads might still be running at that point. Returns: A future instance that can be used to manage the background stream. """ flow_control = types.FlowControl(*flow_control) manager = streaming_pull_manager.StreamingPullManager( self, subscription, flow_control=flow_control, scheduler=scheduler, use_legacy_flow_control=use_legacy_flow_control, await_callbacks_on_shutdown=await_callbacks_on_shutdown, ) future = futures.StreamingPullFuture(manager) manager.open(callback=callback, on_callback_error=future.set_exception) return future def close(self) -> None: """Close the underlying channel to release socket resources. After a channel has been closed, the client instance cannot be used anymore. This method is idempotent. """ transport = cast("SubscriberGrpcTransport", self._transport) transport.grpc_channel.close() self._closed = True def __enter__(self) -> "Client": if self._closed: raise RuntimeError("Closed subscriber cannot be used as context manager.") return self def __exit__(self, exc_type, exc_val, exc_tb): self.close()