Source code for google.cloud.pubsub_v1.subscriber.client

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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#     http://www.apache.org/licenses/LICENSE-2.0
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# Unless required by applicable law or agreed to in writing, software
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from __future__ import absolute_import

import os
import pkg_resources

import grpc

from google.api_core import grpc_helpers
from google.oauth2 import service_account

from google.cloud.pubsub_v1 import _gapic
from google.cloud.pubsub_v1 import types
from google.cloud.pubsub_v1.gapic import subscriber_client
from google.cloud.pubsub_v1.gapic.transports import subscriber_grpc_transport
from google.cloud.pubsub_v1.subscriber import futures
from google.cloud.pubsub_v1.subscriber._protocol import streaming_pull_manager


__version__ = pkg_resources.get_distribution("google-cloud-pubsub").version

_BLACKLISTED_METHODS = (
    "publish",
    "from_service_account_file",
    "from_service_account_json",
)


[docs]@_gapic.add_methods(subscriber_client.SubscriberClient, blacklist=_BLACKLISTED_METHODS) class Client(object): """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 (dict): 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): # 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["channel"] = grpc.insecure_channel( target=os.environ.get("PUBSUB_EMULATOR_HOST") ) # Use a custom channel. # We need this in order to set appropriate default message size and # keepalive options. if "transport" not in kwargs: channel = kwargs.pop("channel", None) if channel is None: channel = grpc_helpers.create_channel( credentials=kwargs.pop("credentials", None), target=self.target, scopes=subscriber_client.SubscriberClient._DEFAULT_SCOPES, options={ "grpc.max_send_message_length": -1, "grpc.max_receive_message_length": -1, "grpc.keepalive_time_ms": 30000, }.items(), ) # cannot pass both 'channel' and 'credentials' kwargs.pop("credentials", None) transport = subscriber_grpc_transport.SubscriberGrpcTransport( channel=channel ) kwargs["transport"] = transport # Add the metrics headers, and instantiate the underlying GAPIC # client. self._api = subscriber_client.SubscriberClient(**kwargs)
[docs] @classmethod def from_service_account_file(cls, filename, **kwargs): """Creates an instance of this client using the provided credentials file. Args: filename (str): 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 @property def target(self): """Return the target (where the API is). Returns: str: The location of the API. """ return subscriber_client.SubscriberClient.SERVICE_ADDRESS @property def api(self): """The underlying gapic API client.""" return self._api
[docs] def subscribe(self, subscription, callback, flow_control=(), scheduler=None): """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. 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() Args: subscription (str): The name of the subscription. The subscription should have already been created (for example, by using :meth:`create_subscription`). callback (Callable[~google.cloud.pubsub_v1.subscriber.message.Message]): 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 (~google.cloud.pubsub_v1.types.FlowControl): The flow control settings. Use this to prevent situations where you are inundated with too many messages at once. scheduler (~google.cloud.pubsub_v1.subscriber.scheduler.Scheduler): An optional *scheduler* to use when executing the callback. This controls how callbacks are executed concurrently. Returns: A :class:`~google.cloud.pubsub_v1.subscriber.futures.StreamingPullFuture` 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 ) future = futures.StreamingPullFuture(manager) manager.open(callback=callback, on_callback_error=future.set_exception) return future