Idempotent Design Pattern in Mule 4
How to restrict the duplicate request payload in Mule 4 API by adapting an idempotent-message-validator component. This is demonstrated through a simple POC.
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Sometimes the same request message gets delivered more than once. It could be that the message receiver is not sure whether the message has been successfully delivered or not, or it could be that the code is not configured to check duplicates.
To get rid of duplicates, we have to adapt an idempotent design pattern, which will send unique messages to the system.
Mulesoft provided the idempotent-message-validator component, and we can easily achieve this without much coding.
I have prepared a simple POC to describe how to use the idempotent-message-validator component to restrict the incoming duplicate request payload in Mule 4 API.
Requirement
In any project, it is a basic requirement to process a unique request payload.
In this POC, we will be executing the flow successfully if there is no duplicate email id in the requests.
POC
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns:doc="http://www.mulesoft.org/schema/mule/documentation" xmlns:json="http://www.mulesoft.org/schema/mule/json" xmlns:os="http://www.mulesoft.org/schema/mule/os" xmlns:ee="http://www.mulesoft.org/schema/mule/ee/core" xmlns="http://www.mulesoft.org/schema/mule/core" xmlns:apikit="http://www.mulesoft.org/schema/mule/mule-apikit" xmlns:http="http://www.mulesoft.org/schema/mule/http" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.mulesoft.org/schema/mule/json http://www.mulesoft.org/schema/mule/json/current/mule-json.xsd http://www.mulesoft.org/schema/mule/ee/core http://www.mulesoft.org/schema/mule/ee/core/current/mule-ee.xsd http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd http://www.mulesoft.org/schema/mule/mule-apikit http://www.mulesoft.org/schema/mule/mule-apikit/current/mule-apikit.xsd http://www.mulesoft.org/schema/mule/os http://www.mulesoft.org/schema/mule/os/current/mule-os.xsd">
<http:listener-config name="duplicate-check-httpListenerConfig">
<http:listener-connection host="${http.private.host}" port="${http.private.port}" />
</http:listener-config>
<apikit:config name="duplicate-check-config" api="duplicate-check-api.raml" outboundHeadersMapName="outboundHeaders" httpStatusVarName="httpStatus" />
<configuration-properties doc:name="Configuration properties" doc:id="18cff226-2fbc-44ed-8053-420aa52d5165" file="properties/${mule.env}-properties.yaml" />
<flow name="duplicate-check-main">
<http:listener config-ref="duplicate-check-httpListenerConfig" path="${http.private.path}">
<reconnect frequency="${http.private.reconnect.frequency}" count="${http.private.reconnect.attempts}"/>
<http:response statusCode="#[vars.httpStatus default 200]">
<http:headers><![CDATA[#[vars.outboundHeaders default {}]]]></http:headers>
</http:response>
<http:error-response statusCode="#[vars.httpStatus default 500]">
<http:body><![CDATA[#[payload]]]></http:body>
<http:headers><![CDATA[#[vars.outboundHeaders default {}]]]></http:headers>
</http:error-response>
</http:listener>
<apikit:router config-ref="duplicate-check-config" />
</flow>
<flow name="post:\user_register:duplicate-check-config">
<flow-ref doc:name="check-duplicate-message" doc:id="f708d25c-923a-43ca-8551-64858be9e982" name="check-duplicate-message"/>
<ee:transform doc:name="Store the information successfully" doc:id="313b0077-13ba-4bf9-b0c5-122e4616cb08" >
<ee:message >
<ee:set-payload ><![CDATA[%dw 2.0
output application/json
---
{
"message" : "User details stored successfully."
}]]></ee:set-payload>
</ee:message>
</ee:transform>
<error-handler >
<on-error-propagate enableNotifications="true" logException="true" doc:name="On Error Propagate" doc:id="a52c6ae8-a8f5-4300-aa9a-4a43b45e0d83" type="ANY">
<ee:transform doc:name="Prepare Error Payload" doc:id="f0f65cbf-fa19-48fb-ad02-6e63ea1424af" >
<ee:message >
<ee:set-payload resource="dwl/prepareError.dwl" />
</ee:message>
</ee:transform>
</on-error-propagate>
</error-handler>
</flow>
<sub-flow name="check-duplicate-message" doc:id="1ce86c01-2e24-49b3-bf17-764747a252b8" >
<set-variable value='#[%dw 2.0
output application/json
---
write(payload.email,"application/json")]' doc:name="Set email variable" doc:id="4c342f3b-be44-4b10-86a6-949b3717180a" variableName="uniqueEmailCheck" mimeType="application/json"/>
<idempotent-message-validator doc:name="Idempotent Message Validator" doc:id="744f1b97-4ef7-4206-acca-1c4cdcaedaa8" idExpression="#[%dw 2.0
output text/plain
import dw::Crypto
---
Crypto::hashWith(vars.uniqueEmailCheck as Binary,'SHA-1')]">
<os:private-object-store entryTtl="${duplicate_check_os.entry_ttl}" expirationInterval="${duplicate_check_os.expiration_interval}" expirationIntervalUnit="DAYS" entryTtlUnit="DAYS" />
</idempotent-message-validator>
<remove-variable doc:name="Remove Variable" doc:id="71d94db7-d7bc-4506-b835-419dc59727c5" variableName="uniqueEmailCheck"/>
</sub-flow>
</mule>
Git Reference
You can find the complete executable code here, and to test the POC, the postman script is here.
Test Output
Happy Scenario (First Request)
For the first request where the email is new, it will accept the request and will respond like this:
Error Scenario (Second Request With Same Payload)
For the second request where the email id is the same as first, it will raise an error by the idempotent-message-validator component and we can prepare the output like this:
Conclusion
This POC is just to give an idea about the idempotent-message-validator component. It can be enhanced as per your requirement.
An important point of this component is that it uses ObjectStore to keep the records, so we have to consider the cost and usage of memory while designing.
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