Create a multipart response with WSO2 ESB - wso2

Question

I'm trying to create a WSO2 ESB proxy that would generate an HTTP multipart response, basically with 2 parts: XML and an attached binary file (an image for example).
The sequence would be as follow:
the service is exposed as an HTTP GET request
we first call an endpoint that returns a binary file
we create an XML that describe the binary file
we mix the 2 elements together and provide the multipart response
(XML + binary file)
After several attempts and looking around on samples and forums I couldn't find how to solve this particular case.
I've managed to call the endpoint. I can see in the debug logs that the response is transferred as binary in the soap internal message.
I suspect I then need to use the MultipartFormDataFormatter. As far as I understand the code of the formatter, it takes all the child nodes of the body of the internal soap message to create one part by child.
So I've tried to append my XML content as a sibling node of the binary node (the message looks as expected in the logs), and force the ContentType with :
<property name="messageType" value="multipart/form-data" scope="axis2"/>
<property name="ContentType" value="multipart/form-data" scope="axis2"/>
to be sure to call the correct formatter.
Unfortunately this does not seem to work, the response is indeed in multipart/form-data, but with zero bytes data.
Any help?
Thanks
Yannick

Answer 1

You need to enable Binary Relay builders in axis2.xml file to use the multipart/form-data message formatting.
<messageBuilder contentType="multipart/form-data"
class="org.wso2.carbon.relay.BinaryRelayBuilder"/>
<messageFormatter contentType="multipart/form-data"
class="org.wso2.carbon.relay.ExpandingMessageFormatter"/>

Answer 2

Thanks for your answer.
I've made several tests, by enabling Binary Relay builders, but I did not get the exact multipart response I was expecting.
So, I've finally created my own Formatter. It constructs the multipart response from the body children, and looks for some specific properties to specify header information such as part content id, transfer encoding and content type.

Answer 3

Maybe this will be useful to someone else:
You can set the multipart builders by uncommenting the following property in /repository/conf/axis2/axis2.xml file
<messageBuilder contentType="multipart/related" class="org.wso2.carbon.relay.BinaryRelayBuilder"/>
As per our understanding requirement here is to make a single response message using an xml content and a png attachment received from different endpoints.
In order to accomplish your goal, we can use a custom mediator. By using a custom class mediator you can build a response with xml metadata and png images.
Writing a java class to build the message with both responses could be the best way to achieve this in WSO2 way. You can use message builder and crate message methods to create the message in the way that you want. And you can use the class mediator, which can be found in this documentation to use it with ESB
As a further clarification, please note that the enrich mediator attaches the given resources.