mirror of
https://github.com/octoleo/restic.git
synced 2024-11-16 10:05:25 +00:00
127 lines
5.3 KiB
Go
127 lines
5.3 KiB
Go
// Copyright 2016 Google Inc. 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.
|
|
|
|
/*
|
|
Package pubsub provides an easy way to publish and receive Google Cloud Pub/Sub
|
|
messages, hiding the the details of the underlying server RPCs. Google Cloud
|
|
Pub/Sub is a many-to-many, asynchronous messaging system that decouples senders
|
|
and receivers.
|
|
|
|
Note: This package is in beta. Some backwards-incompatible changes may occur.
|
|
|
|
More information about Google Cloud Pub/Sub is available at
|
|
https://cloud.google.com/pubsub/docs
|
|
|
|
Publishing
|
|
|
|
Google Cloud Pub/Sub messages are published to topics. Topics may be created
|
|
using the pubsub package like so:
|
|
|
|
topic, err := pubsubClient.CreateTopic(context.Background(), "topic-name")
|
|
|
|
Messages may then be published to a topic:
|
|
|
|
res := topic.Publish(ctx, &pubsub.Message{Data: []byte("payload")})
|
|
|
|
Publish queues the message for publishing and returns immediately. When enough
|
|
messages have accumulated, or enough time has elapsed, the batch of messages is
|
|
sent to the Pub/Sub service.
|
|
|
|
Publish returns a PublishResult, which behaves like a future: its Get method
|
|
blocks until the message has been sent to the service.
|
|
|
|
The first time you call Publish on a topic, goroutines are started in the
|
|
background. To clean up these goroutines, call Stop:
|
|
|
|
topic.Stop()
|
|
|
|
Receiving
|
|
|
|
To receive messages published to a topic, clients create subscriptions
|
|
to the topic. There may be more than one subscription per topic; each message
|
|
that is published to the topic will be delivered to all of its subscriptions.
|
|
|
|
Subsciptions may be created like so:
|
|
|
|
sub, err := pubsubClient.CreateSubscription(context.Background(), "sub-name",
|
|
pubsub.SubscriptionConfig{Topic: topic})
|
|
|
|
Messages are then consumed from a subscription via callback.
|
|
|
|
err := sub.Receive(context.Background(), func(ctx context.Context, m *Message) {
|
|
log.Printf("Got message: %s", m.Data)
|
|
m.Ack()
|
|
})
|
|
if err != nil {
|
|
// Handle error.
|
|
}
|
|
|
|
The callback is invoked concurrently by multiple goroutines, maximizing
|
|
throughput. To terminate a call to Receive, cancel its context.
|
|
|
|
Once client code has processed the message, it must call Message.Ack, otherwise
|
|
the message will eventually be redelivered. As an optimization, if the client
|
|
cannot or doesn't want to process the message, it can call Message.Nack to
|
|
speed redelivery. For more information and configuration options, see
|
|
"Deadlines" below.
|
|
|
|
Note: It is possible for Messages to be redelivered, even if Message.Ack has
|
|
been called. Client code must be robust to multiple deliveries of messages.
|
|
|
|
Deadlines
|
|
|
|
The default pubsub deadlines are suitable for most use cases, but may be
|
|
overridden. This section describes the tradeoffs that should be considered
|
|
when overriding the defaults.
|
|
|
|
Behind the scenes, each message returned by the Pub/Sub server has an
|
|
associated lease, known as an "ACK deadline".
|
|
Unless a message is acknowledged within the ACK deadline, or the client requests that
|
|
the ACK deadline be extended, the message will become elegible for redelivery.
|
|
As a convenience, the pubsub package will automatically extend deadlines until
|
|
either:
|
|
* Message.Ack or Message.Nack is called, or
|
|
* the "MaxExtension" period elapses from the time the message is fetched from the server.
|
|
|
|
The initial ACK deadline given to each messages defaults to 10 seconds, but may
|
|
be overridden during subscription creation. Selecting an ACK deadline is a
|
|
tradeoff between message redelivery latency and RPC volume. If the pubsub
|
|
package fails to acknowledge or extend a message (e.g. due to unexpected
|
|
termination of the process), a shorter ACK deadline will generally result in
|
|
faster message redelivery by the Pub/Sub system. However, a short ACK deadline
|
|
may also increase the number of deadline extension RPCs that the pubsub package
|
|
sends to the server.
|
|
|
|
The default max extension period is DefaultReceiveSettings.MaxExtension, and can
|
|
be overridden by setting Subscription.ReceiveSettings.MaxExtension. Selecting a
|
|
max extension period is a tradeoff between the speed at which client code must
|
|
process messages, and the redelivery delay if messages fail to be acknowledged
|
|
(e.g. because client code neglects to do so). Using a large MaxExtension
|
|
increases the available time for client code to process messages. However, if
|
|
the client code neglects to call Message.Ack/Nack, a large MaxExtension will
|
|
increase the delay before the message is redelivered.
|
|
|
|
Authentication
|
|
|
|
See examples of authorization and authentication at
|
|
https://godoc.org/cloud.google.com/go#pkg-examples.
|
|
|
|
Slow Message Processing
|
|
|
|
For use cases where message processing exceeds 30 minutes, we recommend using
|
|
the base client in a pull model, since long-lived streams are periodically killed
|
|
by firewalls. See the example at https://godoc.org/cloud.google.com/go/pubsub/apiv1#example-SubscriberClient-Pull-LengthyClientProcessing
|
|
*/
|
|
package pubsub // import "cloud.google.com/go/pubsub"
|