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vendor/cloud.google.com/go/pubsub/doc.go

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+// 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 experimental and may make backwards-incompatible changes.
+
+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:
+
+ msgIDs, err := topic.Publish(ctx, &pubsub.Message{
+	Data: []byte("payload"),
+ })
+
+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", topic, 0, nil)
+
+Messages are then consumed from a subscription via an iterator:
+
+ // Construct the iterator
+ it, err := sub.Pull(context.Background())
+ if err != nil {
+	// handle err ...
+ }
+ defer it.Stop()
+
+ // Consume N messages
+ for i := 0; i < N; i++ {
+ 	msg, err := it.Next()
+ 	if err == iterator.Done {
+ 		break
+ 	}
+ 	if err != nil {
+ 		// handle err ...
+ 		break
+ 	}
+
+ 	log.Print("got message: ", string(msg.Data))
+ 	msg.Done(true)
+ }
+
+The message iterator returns messages one at a time, fetching batches of
+messages behind the scenes as needed. Once client code has processed the
+message, it must call Message.Done, otherwise the message will eventually be
+redelivered. For more information and configuration options, see "Deadlines"
+below.
+
+Note: It is possible for Messages to be redelivered, even if Message.Done 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.Done 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 DefaultMaxExtension, and can be overridden
+by passing a MaxExtension option to Subscription.Pull. 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.Done, 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.
+*/
+package pubsub // import "cloud.google.com/go/pubsub"