As of January 1, 2020 this library no longer supports Python 2 on the latest released version.
Library versions released prior to that date will continue to be available. For more information please
visit Python 2 support on Google Cloud.
Source code for google.cloud.pubsub_v1.subscriber.client
# 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 pkg_resources
from google.auth.credentials import AnonymousCredentials
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.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
try:
__version__ = pkg_resources.get_distribution("google-cloud-pubsub").version
except pkg_resources.DistributionNotFound:
# Distribution might not be available if we are not running from within
# a PIP package.
__version__ = "0.0"
_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["client_options"] = {
"api_endpoint": os.environ.get("PUBSUB_EMULATOR_HOST")
}
kwargs["credentials"] = AnonymousCredentials()
# Instantiate the underlying GAPIC client.
self._api = subscriber_client.SubscriberClient(**kwargs)
self._target = self._api._transport._host
[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 self._target
@property
def api(self):
"""The underlying gapic API client."""
return self._api
[docs] def subscribe(
self,
subscription,
callback,
flow_control=(),
scheduler=None,
use_legacy_flow_control=False,
await_callbacks_on_shutdown=False,
):
"""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 (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. This object must not be shared
across multiple SubscriberClients.
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 (bool):
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 :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,
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
[docs] def close(self):
"""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.
"""
self.api._transport.grpc_channel.close()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.close()
