Google Pub Sub Connector Example¶

The Google Pub/Sub connector allows you to access the Google Cloud Pub/Sub API Version v1 from an integration sequence.

What you'll build¶

Given below is a sample scenario that demonstrates how to work with the WSO2 Google Pub Sub Connector to:

Create a Topic to store company update notifications.
Insert company update notifications to the created topic.
Retrieve company updates from the created topic.

To work with the Google Pub/Sub connector, you need to have a Google Cloud Platform account. Please refer the Setting up the Google Pub Sub Environment documentation to setup an account.

In this scenario, the user needs to create a Topic in Google Cloud Platform account under Big Data. This topic is used to store notifications related to company updates. Once the user invokes the createTopic resource, the subscribing operation also gets triggered simultaneously. Then the user can insert company update notifications to the created topic. Finally, the user can retrieve the company updates from the subscribed topic while invoking the API.

All three operations are exposed via an API. The API with the context /resources has three resources.

/createTopic : Used to create a Topic for store company notifications and subscribe to the topic.
/insertCompanyNotifications : Used to insert company update notifications to the subscribed topic.
/getCompanyNotifications : Used to retrieve information about company updates.

Note: In this example we will be using XPath 2.0 which needs to be enabled in the product as shown below before starting the integration service. If you are using EI 7 or APIM 4.0.0, you need to enable this property by adding the following to the PRODUCT-HOME/conf/deployment.toml file. You can further refer to the Product Configurations. If you are using EI 6, you can enable this property by uncommenting synapse.xpath.dom.failover.enabled=true property in PRODUCT-HOME/conf/synapse.properties file.
[mediation]
synapse.enable_xpath_dom_failover=true

The following diagram shows the overall solution. The user creates a topic, stores some company update notifications, and then receives them back. To invoke each operation, the user uses the same API.

pub-sub connector example

If you do not want to configure this yourself, you can simply get the project and run it.

Set up the integration project¶

Follow the steps in create integration project guide to set up the integration project.

Add integration logic¶

First create an API, which will be where we configure the integration logic. Specify the API name as pubsubApi and API context as /resources.

Adding a Rest API

Configure the API¶

Configure a resource for the createTopic operation

Initialize the connector.
1. Create the /createTopic resource. We will use a URL template called /createTopic and the method will be Post.
2. Navigate into the Connectors pane and select the Googlepubsub Connector section. Then select the init operation.
3. Add the property values into the init operation as shown below. Replace the accessToken, apiUrl, apiVersion with your values.
  - accessToken : The access token that grants access to the Google Pub/Sub API on behalf of a user.
  - apiUrl : The application URL of Google Pub/Sub.
  - apiVersion : The version of the Google Pub/Sub API.
Set up the createTopic operation.
1. Navigate into the Connectors pane and select the createTopic operation listed under Googlepubsub Connector section.
2. The createTopic operation creates a new topic with the name that you specify.
  - projectId : The unique ID of the project within which you want to create a topic.
  - topicName : The name that you want to give the topic that you are creating.
  While invoking the API, topicName values is populated as an input value for the operation.
3. To get the input values in to the API we can use the property mediator. Navigate into the Mediator pane and select the Property mediators.
  
  The parameters available for configuring the Property mediator are as follows:
  
  Note: The properties should be added to the pallet before creating the operation.
4. Add the property mediator to capture the topicName value. The topicName contains the name that you want to give to the topic that you are creating.
  - name : topicName
  - expression : json-eval($.topicName)
Set up the createTopicSubscription operation.
1. Navigate into the Connectors pane and select the Googlepubsub Connector section. Then select the createTopicSubscription operation.
  - projectId : The unique ID of the project within which the topic is created.
  - subscriptionName : The name of the subscription.
  - topicName : The name of the topic for which you want to create a subscription.
  - ackDeadlineSeconds : The maximum time a subscriber can take to acknowledge a message that is received.
2. Add the property mediator to capture the subscriptionName values. This contains the name of the subscription.
  - name : subscriptionName
  - expression : json-eval($.subscriptionName)
3. Add the property mediator to store the name of the created topic value from the response of the createTopic operation.
  - name : nameforsubscription
  - expression : json-eval($.name)
4. Add the property mediator to capture the topic name from the response using the splitting separators in the results.
  - name : test
  - expression : fn:tokenize($ctx:nameforsubscription,'/')[last()]
Forward the backend response to the API caller.

When you are invoke the created resource, the request for the message is going through the /createTopic resource. Finally, it is passed to the Respond mediator. The Respond Mediator stops the processing of the current message and sends the message back to the client as a response.
1. Add the respond mediator to the Design view.
2. Once you have setup the sequences and API, you can see the /createTopic resource as shown below.

Configure a resource for the publishMessage operation

Initialize the connector.
Initialize the connector. You can use the same configuration to initialize the connector. Please follow the steps given in section 1 for setting up the init operation to the createTopic operation.
Set up the publishMessage operation. Navigate into the Connectors pane and select the Googlepubsub Connector section. Then select the publishMessage operation.
- projectId : The unique ID of the project within which the topic is created.
- topicName : The name of the topic for which you want to create a subscription.
- data : The message payload.
Add the property mediator to capture the topicName values.
- name : topicName
- expression : json-eval($.topicName)
Add the property mediator to capture the data values.
- name : data
- expression : json-eval($.data)

Configure a resource for the pullMessage operation

Initialize the connector.
Initialize the connector. You can use the same configuration to initialize the connector. Please follow the steps given in section 1 for setting up the init operation for the createTopic operation
Set up the pullMessage operation. Navigate into the Connectors pane and select the Googlepubsub Connector section. Then select the pullMessage operation.
- projectId : The unique ID of the project within which the topic is created.
- subscriptionName : The name of the topic for which you want to create a subscription.
- maxMessages : The maximum number of messages to retrieve.
- returnImmediately : Set this to true if you want the server to respond immediately.
Add the property mediator to capture the subscriptionName values. Follow the steps given in createTopicSubscription operation.

pubsubApi.xml

<?xml version="1.0" encoding="UTF-8"?>
<api context="/resources" name="pubsubApi" xmlns="http://ws.apache.org/ns/synapse">
    <resource methods="POST" url-mapping="/createTopic">
        <inSequence>
            <property expression="json-eval($.topicName)" name="topicName" scope="default" type="STRING"/>
            <property expression="json-eval($.subscriptionName)" name="subscriptionName" scope="default" type="STRING"/>
            <googlepubsub.init>
                <accessToken>ya29.a0AfH6SMA0MU0Frk_7gNnA79QUWQGnalPXvmkoA4MYS8p8Mt9OSC5SUqqcqIjcrP-_ollVB9gpeg3SufbCpASMCWyHcVCN6ZMCbqz4IdQqRVi8Kt22tI6gR5zvgtWn1qFWnYnGQ6Ehqi_mS9k0PL_R-kQcl-AkqveA8ZY</accessToken>
                <apiUrl>https://pubsub.googleapis.com</apiUrl>
                <apiVersion>v1</apiVersion>
            </googlepubsub.init>
            <googlepubsub.createTopic>
                <projectId>ei-connector-improvement</projectId>
                <topicName>{$ctx:topicName}</topicName>
            </googlepubsub.createTopic>
            <property expression="json-eval($.name)" name="nameforsubscription" scope="default" type="STRING"/>
            <property expression="fn:tokenize($ctx:nameforsubscription,'/')[last()]" name="test" scope="default" type="STRING" xmlns:fn="http://www.w3.org/2005/xpath-functions"/>
            <googlepubsub.init>
                <accessToken>ya29.a0AfH6SMA0MU0Frk_7gNnA79QUWQGnalPXvmkoA4MYS8p8Mt9OSC5SUqqcqIjcrP-_ollVB9gpeg3SufbCpASMCWyHcVCN6ZMCbqz4IdQqRVi8Kt22tI6gR5zvgtWn1qFWnYnGQ6Ehqi_mS9k0PL_R-kQcl-AkqveA8ZY</accessToken>
                <apiUrl>https://pubsub.googleapis.com</apiUrl>
                <apiVersion>v1</apiVersion>
            </googlepubsub.init>
            <googlepubsub.createTopicSubscription>
                <projectId>ei-connector-improvement</projectId>
                <subscriptionName>{$ctx:subscriptionName}</subscriptionName>
                <topicName>{$ctx:test}</topicName>
                <ackDeadlineSeconds>30</ackDeadlineSeconds>
            </googlepubsub.createTopicSubscription>
            <respond/>
        </inSequence>
        <faultSequence/>
    </resource>
    <resource methods="POST" url-mapping="/insertcompanynotifications">
        <inSequence>
            <property expression="json-eval($.topicName)" name="topicName" scope="default" type="STRING"/>
            <property expression="json-eval($.data)" name="data" scope="default" type="STRING"/>
            <googlepubsub.init>
                <accessToken>ya29.a0AfH6SMA0MU0Frk_7gNnA79QUWQGnalPXvmkoA4MYS8p8Mt9OSC5SUqqcqIjcrP-_ollVB9gpeg3SufbCpASMCWyHcVCN6ZMCbqz4IdQqRVi8Kt22tI6gR5zvgtWn1qFWnYnGQ6Ehqi_mS9k0PL_R-kQcl-AkqveA8ZY</accessToken>
                <apiUrl>https://pubsub.googleapis.com</apiUrl>
                <apiVersion>v1</apiVersion>
            </googlepubsub.init>
            <googlepubsub.publishMessage>
                <projectId>ei-connector-improvement</projectId>
                <topicName>{$ctx:topicName}</topicName>
                <data>{$ctx:data}</data>
            </googlepubsub.publishMessage>
            <respond/>
        </inSequence>
        <faultSequence/>
    </resource>
    <resource methods="POST" url-mapping="/getcompanynotifictions">
        <inSequence>
            <property expression="json-eval($.subscriptionName)" name="subscriptionName" scope="default" type="STRING"/>
            <googlepubsub.init>
                <accessToken>ya29.a0AfH6SMDDFZCdoo37Tb48MrJU-ZnNoyrYqNY8r5cgWX0kD7n3GBhZr_TbicfvywjKwGYaZEBV50_yGINVOhZr_4jFMu2O03c87NiDCBpKW5zdsnl3x9iWdsosjDoE7uAGEKKLikPgnKfcgilGB2d-MBzu_c2e53kXG6A</accessToken>
                <apiUrl>https://pubsub.googleapis.com</apiUrl>
                <apiVersion>v1</apiVersion>
            </googlepubsub.init>
            <googlepubsub.pullMessage>
                <projectId>ei-connector-improvement</projectId>
                <subscriptionName>{$ctx:subscriptionName}</subscriptionName>
                <maxMessages>2</maxMessages>
                <returnImmediately>false</returnImmediately>
            </googlepubsub.pullMessage>
            <respond/>
        </inSequence>
        <faultSequence/>
    </resource>
</api>

Get the project¶

You can download the ZIP file and extract the contents to get the project code.

Tip

You may need to update the simulator details and make other such changes before deploying and running this project.

Deployment¶

In order to deploy and run the project, refer the build and run guide.

Test¶

Invoke the API as shown below using the curl command. Curl application can be downloaded from here.

Create a Topic for store company update notifications.

Sample request

  curl -v POST -d '{"topicName":"CompanyUpdates","subscriptionName": "SubscriptionForCompanyUpdates"}' "http://localhost:8290/resources/createTopic" -H "Content-Type:application/json"

Expected response

{
    "name": "projects/ei-connector-improvement/subscriptions/SubscriptionForCompanyUpdates",
    "topic": "projects/ei-connector-improvement/topics/CompanyUpdates",
    "pushConfig": {},
    "ackDeadlineSeconds": 30,
    "messageRetentionDuration": "604800s",
    "expirationPolicy": {
        "ttl": "2678400s"
    }
}

You will see the results from G-Cloud console

Created Topic.
Created subscription for the Topic that you specify in the G-Cloud.
Insert company update notifications to the created topic.

Sample request

  curl -v POST -d '{"topicName":"CompanyUpdates", "data":"This is first notification"}' "http://localhost:8290/resources/insertcompanynotifications" -H "Content-Type:application/json"

Expected response

{
    "messageIds": [
        "1268617220412368"
    ]
}

3. Retrieve company updates from the created topic.

Sample request

  curl -v POST -d '{"subscriptionName":"SubscriptionForCompanyUpdates"}' "http://localhost:8290/resources/getcompanynotifictions" -H "Content-Type:application/json"

Expected response

{
    "receivedMessages": [
        {
            "ackId": "ISE-MD5FU0RQBhYsXUZIUTcZCGhRDk9eIz81IChFEgIIFAV8fXFYW3VfVBoHUQ0Zcnxmd2NTQQhXRFB_VVsRDXptXFcnUA8fentgcmhYEwUDR1B4V3Pr67-C9PCXYxclSpuLu6xvM8byp5xMZho9XxJLLD5-NjNFQV5AEkw9BkRJUytDCypYEU4E",
            "message": {
                "data": "VGhpcyBpcyBmaXJzdCBub3RpZmljYXRpb24=",
                "messageId": "1268617220412368",
                "publishTime": "2020-06-09T15:36:35.632Z"
            }
        }
    ]
}

You will see the results from G-Cloud console

View published company update notification.