WSO2 ESB - Error Codes

Following is the list of error codes used in WSO2 ESB and a brief description about them.

Code	Description
101000	Receiver IO error sending
101001	Receiver IO error receiving
101500	Sender IO error sending
101501	Sender IO error receiving
101503	Connection failed
101504	Connection timed out
101505	Connection closed
101506	HTTP protocol violation
101507	Connect cancel
101508	Connect timeout
101509	Send abort

Error Handling in WSO2 ESB

When a Proxy Service or a Sequence which mediate messages, is considered, error handling would be a key concern. Depending on the error type, we might need to send a fault message, custom response etc.

WSO2 ESB makes our life easier by allowing us to specify a custom fault sequence for error handling. i.e. It gives the flexibility to use mediator and do various tasks even when an error occurred.

Following is a sample sequence which logs the error details and sends a custom message to the client when an error occurs. Further, if you need to send a SOAP Fault, then Fault mediator can be used instead of Payload Factory mediator.

<sequence name="myErrorSequence">
    <header name="To" action="remove"/>
    <property name="RESPONSE" value="true"/>
    <property name="NO_ENTITY_BODY" scope="axis2" action="remove"/>

    <log level="custom">
        <property name="error-message" expression="get-property('ERROR_MESSAGE')"/>
        <property name="error-code" expression="get-property('ERROR_CODE')"/>
        <property name="error-detail" expression="get-property('ERROR_DETAIL')"/>
        <property name="error-exception" expression="get-property('ERROR_EXCEPTION')"/>
    </log>

    <payloadFactory>
        <format>
            <ns:MyResponse xmlns:ns="http://services.samples">
                <ns:Error/>
            </ns:MyResponse>
        </format>
    </payloadFactory>
    <send/>
</sequence> 

As response might be sending even without going to the outSequence, we need to remove the To header and specify the other two properties named RESPONSE and NO_ENTITY_BODY.

You can also get the details of the error occurred using properties named ERROR_MESSAGE, ERROR_CODE, ERROR_DETAIL and ERROR_EXCEPTION.

After you added the above sequence into the configuration, you can refer it as below from a Proxy or a Sequence.

For a Sequence :

<sequence name="mySequence" onerror="myErrorSequence">
.......
</sequence>

For a Proxy Service :

<proxy name="MyProxy" xmlns="http://ws.apache.org/ns/synapse">
    <target faultSequence="myErrorSequence">
    ......
    </target>
</proxy>

Enable Wire Level Logs in WSO2 ESB

When you work with WSO2 ESB, you might need to monitor the wire level data which go through the server. Then, you can simply do that by adding the following entry into the log4j.properties file which can be found at lib/log4j.properties

log4j.category.org.apache.synapse.transport.nhttp.wire=DEBUG

Fixing REST URLs in Send Mediator of WSO2 ESB

There might be situations, that you would need to do REST calls using the send mediator of WSO2 ESB. Then, you might have noticed the endpoint url that you specified in the endpoint configuration, gets suffixed by a url fragment.

This happens when ever you do a REST call using the send mediator. In order to get rid of it, please specify the following property before the send mediator.

<property name="REST_URL_POSTFIX" scope="axis2" action="remove"/>

Sending a Dummy Response from WSO2 ESB

When you play with WSO2 ESB, you might need to send some dummy data as the response of a proxy service or an REST API. In order to do that you will need to specify To, RESPONSE and NO_ENTITY_BODY properties in the inSequence. If the sequence doesn't get called via an HTTP GET, then the property NO_ENTITY_BODY can be removed from the sequence.

Then, the sequence will directly send the response to the client even without going through the outSequence. Using either Enrich or Payload Factory mediator, you can create the response massage manually.

Following is a sample inSequence.

<inSequence>
    <header name="To" action="remove"/>
    <property name="RESPONSE" value="true"/>
    <property name="NO_ENTITY_BODY" scope="axis2" action="remove"/>
    <payloadFactory>
        <format>
            <ns:getQuoteResponse xmlns:ns="http://services.samples">
                <ns:return xmlns:ax21="http://services.samples/xsd">
                    <ax21:change>4.212070096051944</ax21:change>
                    <ax21:earnings>-9.567415587431361</ax21:earnings>
                    <ax21:high>-148.1740146577308</ax21:high>
                    <ax21:symbol>IBM</ax21:symbol>
                </ns:return>
            </ns:getQuoteResponse>
        </format>
    </payloadFactory>
    <send/>
</inSequence>