Enabling WSO2 ESB APIs to Pass-Through response Content-Types

This post explains how to configure WSO2ESB 4.5.x to Pass-Through response Content-Types.

WSO2 ESB is build to work on soap environments therefore WSO2 ESB (proxy service) always sends the response message in the same Content Type of the request, which is the expected behaviour.
This works fine for SOAP, because the incoming message to the proxy service and the outgoing  messages from the proxy service are both SOAP messages.

But this is not the case for REST calls, there can be cases where the proxy service need to mimic the actual service as it is.
E.g. Client sends the request in the Content-Type to be "application/json" and the Actual service receives the request in the same "application/json"  Content-Type and responds in the Content-Type of "text/plain" which the client can Accept.

This can be achieved using Message Relays, but in any case if you need to achieve this for your custom formatters you have to manually set these Content-Type as below.

<api name="api_content_type_passthrough" context="/esbsanitycheck">
  <resource methods="POST GET DELETE PUT">
     <inSequence>
        <send>
           <endpoint key="ep_esb_sanity_check"/>
        </send>
     </inSequence>
     <outSequence>
        <property name="messageType" expression="$trp:Content-Type" scope="axis2"/>
        <property name="ContentType" expression="$trp:Content-Type" scope="axis2"/>
        <send/>
     </outSequence>
  </resource>
</api>