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This week, we’re going to study complementary pattern to Request-Reply known as Return Address.

When do I use this pattern?

This pattern is applied whenever the asynchronous Request-Reply pattern is used. In Messaging, a message flows from one participant to another. This applies to both Request message and Reply message. When a request message is sent to a participant, how would the receiving participant know where to send the reply?

Imagine receiving emails from NoReply type of email addresses. You wouldn’t know whom to respond. In Emails, a Reply-To header can be set to inform receiver whom to respond. For example, when a meeting in Google Calendar is changed, a notification email is received from calendar-notification@google.com, however, a Reply-To field contains the email of the person who changed the event.

Similarly, a reply-to header can be specified in a JMS message to let the processor of the message know where to send the response.

Return Address in CPI

In CPI, we’ll use AMQP adapter to implement Return Address pattern. For getting started with AMQP Adapter, read Mandy‘s blog on Connecting to Messaging Systems using the AMQP Adapter. First, customer information is enqueued in the ‘customers’ queue. The receiver processes the message in the ‘customers’ queue and puts the response in the queue specified by the ‘JMSReplyTo’ header. Finally, CPI processes responses from ‘customerresponses’ queue.

Step 1: Enqueueing Customer

Integration Flow

This integration flow starts immediately after deployment, prepares the input message, and enqueues it using AMQP Adapter.

Steps

Start Immediately

This is a Timer Start step with the schedule of Run Once.

Prepare Input Message

This Content Modifier step sets the body as follows:

<Customer>
    <Id>1</Id>
    <Name>SAP</Name>
</Customer>

This step also sets the Return Address by using ‘JMSReplyTo’ header. The ‘JMSReplyTo’ header is set to ‘customerresponses’.

Enqueueing

This step enqueues the customer in a Microsoft Service Bus queue using AMQP Receiver Adapter.

Here’s the configuration for AMQP Adapter:

Step 2: Processing Customer

I have coded this step in CPI. Generally, this step will be performed by the receiver system.

Integration Flow

This integration flow dequeues customer from ‘customers’ queue and replaces the body with the response and enqueues the response in queue specified by ‘JMSReplyTo’ header.

Dequeueing Customer

This step reads from ‘customers’ queue for processing using AMQP Sender Adapter.

Here’s the configuration of AMQP Adapter:

Enqueueing Response

This step enqueues the response in the queue specified by ‘JMSReplyTo’ header.

Here’s the configuration of AMQP Adapter:

Step 3: Processing Response

Integration Flow

This integration flow reads from response queue ‘customerresponses’ and logs the response for monitoring.

Dequeueing Response

This step reads responses from ‘customerresponses’ queue.

Here’s the configuration of AMQP Adapter:

Log

This Groovy Script step logs the response for monitoring.

import com.sap.gateway.ip.core.customdev.util.Message

def Message processData(Message message) {
    
    def messageLog = messageLogFactory.getMessageLog(message)
    messageLog.addAttachmentAsString('Response', message.getBody(String), null)
    
    return message
}

Output

The response message is logged for monitoring:

<Response>
    <Result>SUCCESS</Result>
</Response>

Conclusion

Return Address pattern applies when the reply is needed asynchronously. The sender must specify where it wants to receive the response in a predetermined header in the request message.

The Missing Piece of The Puzzle

Here, the responses are being read from ‘customerresponses’ queue, however, it is unknown for which request they are for. This can be achieved using the Correlation Identifier which is the pattern for next week.

References/Further Readings

• Return Address Pattern in Enterprise Integration Patterns
• Mandy‘s blog on Connecting to Messaging Systems using the AMQP Adapter
• CPI Components
  • Timer Start
  • Content Modifier
  • AMQP Receiver Adapter
  • AMQP Sender Adapter
  • Groovy Script

Hope this helps,
Bala

P.S.: All three flows should soon be available as Integration Recipes when my pull request is approved and merged. In the meantime, you can download the iFlow zips from my fork on GitHub.

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