Working with Project Subscriptions in Google Pub/Sub

[Overview] [Operation details] [Sample configuration]

Overview

The following operations allow you to work with project subscriptions. Click an operation name to see details on how to use it.

For a sample proxy service that illustrates how to work with project subscriptions, see Sample configuration.

Operation	Description
createTopicSubscription	Creates a subscription to a specified topic.
pullMessage	Retrieves messages from the server.

Operation details

This section provides details on each of the operations.

Creating a topic subscription

The createTopicSubscription operation creates a subscription to a topic that you specify.

createTopicSubscription

<googlepubsub.createTopicSubscription>
    <topicName>{$ctx:topicName}</topicName>
    <projectId>{$ctx:projectId}</projectId>
    <ackDeadlineSeconds>{$ctx:ackDeadlineSeconds}</ackDeadlineSeconds>
    <subscriptionName>{$ctx:subscriptionName}</subscriptionName>
    <pushEndpoint>{$ctx:pushEndpoint}</pushEndpoint>
    <attributes>{$ctx:attributes}</attributes>
</googlepubsub.createTopicSubscription>

Properties

topicName: The name of the topic for which you want to create a subscription.
projectId: The unique ID of the project within which the topic is created.
subscriptionName: The name of the subscription.
ackDeadlineSeconds[Optional]: The maximum time a subscriber can take to acknowledge a message that is received.
pushendpoint [Optional]: The URL that specifies the endpoint to which messages should be pushed.
attributes [Optional]: Additional endpoint configuration attributes.

Sample request

Following is a sample request that can be handled by the createTopicSubscription operation.

createTopicSubscription

{
  "apiUrl":"https://pubsub.googleapis.com",
  "apiVersion":"v1",
  "accessToken": "ya29.GlwABYxVvbJG2NhgX_NQhxjtF_0G9bzf0FEj_shNWgF_GXmYFpwIxjeYQF0XQXrBjjcrJukforOeyTAHoFfSQW0x-OrrZ2lj47Z6k6DAYZuUv3ZhJMl-ll4mvouAbc",
  "topicName":"topicA",
  "projectId":"rising-parser-123456",
  "subscriptionName":"mysubA",
  "ackDeadlineSeconds":"30",
  "pushEndpoint": "https://example.com/push",
  "attributes": {"key": "value1","key2":"values2"} 
}

Related Google pub/sub documentation

https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/create

Retrieving messages from the server

The pullMessage operation retrieves messages that are published to a topic.

pullMessage

<googlepubsub.pullMessage>
    <topicName>{$ctx:topicName}</topicName>
    <projectId>{$ctx:projectId}</projectId>
    <subscriptionName>{$ctx:subscriptionName}</subscriptionName>
    <maxMessages>{$ctx:maxMessages}</maxMessages>
    <returnImmediately>{$ctx:returnImmediately}</returnImmediately>
</googlepubsub.pullMessage>

Properties

topicName: The name of the topic to which the subscription belongs.
projectId: The unique ID of the project within which the topic is created.
subscriptionName: The name of the subscription from which messages should be pulled.
maxMessages[Optional]: The maximum number of messages to retrieve.
returnImmediately[Optional]: Set this to true if you want the server to respond immediately.

Sample request

Following is a sample request that can be handled by the pullMessage operation.

pullMessage

{
  "apiUrl":"https://pubsub.googleapis.com",
  "apiVersion":"v1",
  "accessToken": "ya29.GlwABYxVvbJG2NhgX_NQhxjtF_0G9bzf0FEj_shNWgF_GXmYFpwIxjeYQF0XQXrBjjcrJukforOeyTAHoFfSQW0x-OrrZ2lj47Z6k6DAYZuUv3ZhJMl-ll4mvouAbc",
  "topicName":"topicA",
  "projectId":"rising-parser-123456",
  "subscriptionName":"mysubA",
  "maxMessages":"2",
  "returnImmediately":"false"
}

Related Google Pub/Sub documentation

https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.subscriptions/pull

Sample configuration

Following is a sample proxy service that illustrates how to connect to Google Pub/Sub with the init operation, and then use the createTopicSubscription operation. The sample request for this proxy can be found in createTopicSubscription sample request. You can use this sample as a template for using other operations in this category.

Sample Proxy

<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
 name="createTopicSubscription"
 startOnLoad="true"
 statistics="disable"
 trace="disable"
 transports="http,https">
 <target>
 <inSequence>
 		<property expression="json-eval($.accessToken)" name="accessToken"/>
 		<property expression="json-eval($.apiUrl)" name="apiUrl"/>
		<property expression="json-eval($.apiVersion)" name="apiVersion"/>
 		<property expression="json-eval($.topicName)"  name="topicName"/>
        <property expression="json-eval($.projectId)" name="projectId"/>
        <property expression="json-eval($.subscriptionName)" name="subscriptionName"/>
        <property expression="json-eval($.ackDeadlineSeconds)"  name="ackDeadlineSeconds"/>
 		<googlepubsub.init>
 			<apiUrl>{$ctx:apiUrl}</apiUrl>
			<apiVersion>{$ctx:apiUrl}</apiVersion>
 			<accessToken>{$ctx:accessToken}</accessToken>
 		</googlepubsub.init>
 		<googlepubsub.createTopicSubscription>
             <topicName>{$ctx:topicName}</topicName>
             <projectId>{$ctx:projectId}</projectId>
             <ackDeadlineSeconds>{$ctx:ackDeadlineSeconds}</ackDeadlineSeconds>
             <subscriptionName>{$ctx:subscriptionName}</subscriptionName>
        </googlepubsub.createTopicSubscription>
 		<respond/>
 </inSequence>
 <outSequence>
 	<log/>
 	<send/>
 </outSequence>
 </target>
</proxy>