Reason for WSO2 ESB returns 202 response when an API is called!

Scenario

There's a REST API hosted WSO2 ESB. And when you invoke it, ESB only returns a 202 Accept response similar to follows and no processing is done to the request. And there are no errors printed in the wso2carbon.log too.

HTTP/1.1 202 Accepted
Date: Wed, 25 Feb 2015 13:43:14 GMT
Server: WSO2-PassThrough-HTTP
Transfer-Encoding: chunked
Connection: keep-alive

Reason

The reason for this is, there's no API or a resource that matches the request URL. Let me elaborate more on this. Let's say the request URL is as follows,

https://esb.api.host:8243/myapicontext/myresource/myvar/

If this request returns a response similar to above, following are the possible causes,

1. There's no API with the context="/myapicontext"
2. If there's an API with  context="/myapicontext", it has no resource with uri-template or a url-mapping which matches /myresource/myvar/ portion of the request URL.

Therefore, to fix this issue we should make sure target API and the resource exists in ESB.

In order for the ESB to send  a more meaning full response in case 2 ONLY, add the following sequence to the ESB.

<sequence xmlns="http://ws.apache.org/ns/synapse" name="_resource_mismatch_handler_">
   <payloadFactory media-type="xml">
      <format>
         <tp:fault xmlns:tp="http://test.com">
            <tp:code>404</tp:code>
            <tp:type>Status report</tp:type>
            <tp:message>Not Found</tp:message>
            <tp:description>The requested resource (/$1) is not available.</tp:description>
         </tp:fault>
      </format>
      <args>
      <arg xmlns:ns="http://org.apache.synapse/xsd" xmlns:ns3="http://org.apache.synapse/xsd" expression="$axis2:REST_URL_POSTFIX" evaluator="xml"></arg>
      </args>
   </payloadFactory>
   <property name="NO_ENTITY_BODY" action="remove" scope="axis2"></property>
   <property name="HTTP_SC" value="404" scope="axis2"></property>
   <respond/>
   <drop></drop>
</sequence>

So that the ESB will return a response as follows if there's no matching resource in API,

<tp:fault xmlns:tp="http://test.com">
    <tp:code>404</tp:code>
    <tp:type>Status report</tp:type>
    <tp:message>Not Found</tp:message>
    <tp:description>The requested resource (//myresource/myvar/) is not available.</tp:description>
</tp:fault>