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Request-Reply

This page explains how you can implement a sample scenario of Request-Reply EIP using WSO2 Micro Integrator.

Introduction to Request-Reply

The Request-Reply EIP facilitates two-way communication by ensuring that a sender gets a response or reply back from the receiver after sending a request message. This pattern sends a pair of Request-Reply messages, each on its own channel.

Info

For more information, refer to Request-Reply documentation.

Request reply

Sample scenario

The example scenario illustrates how a request for a service is made through one channel, and the response from the service is returned to the requester on a separate channel.

The diagram below depicts how to simulate the example scenario.

Request reply

Before digging into implementation details, let's take a look at the relationship between the example scenario and the Request-Reply EIP by comparing their core components.

Request-Reply EIP (Figure 1) Request-Reply Example Scenario (Figure 2)
Requestor Simple Stock Quote Client
Request Channel Send, Endpoint
Replier Stock Quote Service Instance
Reply Channel Send, Endpoint

Synapse configuration of the artifacts

Given below is the synapse configuration of this sample.

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="RequestReplyProxy" startOnLoad="true" transports="http https" xmlns="http://ws.apache.org/ns/synapse">
   <target>
      <inSequence>
         <sequence key="RequestProcessSeq"/>
         <call>
            <endpoint key="SimpleStockQuoteServiceEp"/>
         </call>
         <sequence key="ResponseProcessSeq"/>
         <respond/>
      </inSequence>
   </target>
</proxy>

<?xml version="1.0" encoding="UTF-8"?>
<sequence name="RequestProcessSeq" trace="disable" xmlns="http://ws.apache.org/ns/synapse">
   <header name="Action" xmlns:wsa="http://www.w3.org/2005/08/addressing" action="set" scope="default" value="urn:getQuote"/>
</sequence>

<?xml version="1.0" encoding="UTF-8"?>
<sequence name="ResponseProcessSeq" trace="disable" xmlns="http://ws.apache.org/ns/synapse">
   <enrich description="">
      <source clone="true" type="inline">
         <ResponseEnvelopeWrapper></ResponseEnvelopeWrapper>
      </source>
      <target action="child" type="body"/>
   </enrich>
</sequence>

Let's investigate the elements of the configuration in detail.

  • Request Process Sequence - When a client sends a message, it is picked up by this sequence.
  • Call Mediator - The call mediator sends the message to the endpoint running on port 9000.
  • Response Process Sequence - The response from the endpoint can be further processed through this sequence.
  • Respond Mediator - The respond mediator will direct the message back to the requesting client.

Set up the sample scenario

Follow the below instructions to simulate this sample scenario.

  1. Install WSO2 Micro Integrator.

    Info

    Follow the Install the Micro Integrator Runtime documentation for more information.

  2. Launch Visual Studio Code with the Micro Integrator for VS Code extension (MI for VS Code) installed.

    Info

    Follow the Install Micro Integrator for VS Code documentation for a complete installation guide.

  3. Download the backend service.

  4. Extract the downloaded zip file.

  5. Open a terminal, and navigate to the axis2Server/bin/ directory inside the extracted folder.

  6. Execute the following command to start the axis2server with the SimpleStockQuote backend service:

    sh axis2server.sh

    axis2server.bat

  7. Download the artifacts of the sample.

    Download ZIP

  8. Import the artifacts to WSO2 MI.

    Click File -> Open Folder -> Select the extracted ZIP file to import the downloaded ZIP file.

  9. Start the project in the WSO2 MI server.

    For instructions, go to Build and Run Documentation.

Execute the sample

Send the following request to the above proxy service.

POST /services/RequestReplyProxy HTTP/1.1
Host: localhost:8290
Content-Type: text/xml

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Header/>
   <soapenv:Body>
      <ser:getQuote xmlns:ser="http://services.samples" xmlns:xsd="http://services.samples/xsd">
         <ser:request>
            <xsd:symbol>IBM</xsd:symbol>
         </ser:request>
      </ser:getQuote>
   </soapenv:Body>
</soapenv:Envelope>

Analyze the output

A message similar to the one below appears in the simple axis2server.

Fri Aug 09 00:23:15 IST 2024 samples.services.SimpleStockQuoteService :: Generating quote for : IBM

You can view the response as follows.

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
    <ResponseEnvelopeWrapper xmlns="http://ws.apache.org/ns/synapse">
        <soapenv:Envelope>
            <soapenv:Header/>
            <soapenv:Body>
                <ns:getQuoteResponse xmlns:ns="http://services.samples">
                    <ns:return xmlns:ax21="http://services.samples/xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="ax21:GetQuoteResponse">
                        <ax21:change>4.2113329121535985</ax21:change>
                        <ax21:earnings>12.835575447763125</ax21:earnings>
                        <ax21:high>169.56462892544192</ax21:high>
                        <ax21:last>164.91134732838054</ax21:last>
                        <ax21:lastTradeTimestamp>Sun Aug 11 22:57:48 IST 2024</ax21:lastTradeTimestamp>
                        <ax21:low>-164.53083186503255</ax21:low>
                        <ax21:marketCap>4.370714333403162E7</ax21:marketCap>
                        <ax21:name>IBM Company</ax21:name>
                        <ax21:open>172.04078135604772</ax21:open>
                        <ax21:peRatio>24.822545511157507</ax21:peRatio>
                        <ax21:percentageChange>2.2584407962867004</ax21:percentageChange>
                        <ax21:prevClose>186.47081292003838</ax21:prevClose>
                        <ax21:symbol>IBM</ax21:symbol>
                        <ax21:volume>19826</ax21:volume>
                    </ns:return>
                </ns:getQuoteResponse>
            </soapenv:Body>
        </soapenv:Envelope>
    </ResponseEnvelopeWrapper>
</soapenv:Envelope>