Change a Script’s MIME Type Output

The DataWeave examples show how to differentiate the output MIME type from the MIME type in which the output data is formatted. Such differentiation enables a Mule application to output a MIME type that clients can use to determine how to render the application’s output data. An example is HTTP, which uses the MIME type to generate its Content-Type header.

Before you begin, note that 2.x versions of DataWeave are used by Mule 4 apps. For DataWeave in Mule 3 apps, refer to DataWeave version 1.2 examples. For other DataWeave versions, you can use the version selector in the DataWeave table of contents.

The first example uses the "problem details" standard for APIs. The standard requires the application/problem+json content type in the response header and a JSON-formatted response body that contains specific keys.

The example is a Mule flow that handles HTTP requests but always fails. The failure triggers the error handler, which sets the status code to 400 and uses a DataWeave script to produce a response that conforms to the standard.

The DataWeave output directive output application/problem+json with json instructs the script to produce a response with the application/problem+json MIME type and a JSON-formatted body.

A client that receives the 400 error uses the Content-Type: application/problem+json in the response to determine that it can handle the response data in the standard way, for example, using the title key it expects. By contrast, the MIME type Content-Type: application/json, without problem+, fails to indicate whether the client can handle the error in that way.

Mule Flow:

<flow name="problemDetailFlow">
		<http:listener config-ref="HTTP_Listener_config" path="/test">
			<http:error-response statusCode="#[vars.statusCode]" >
				<http:body ><![CDATA[#[payload]]]></http:body>
			</http:error-response>
		</http:listener>
		<raise-error doc:name="Raise error" type="CUSTOM:FORCED" description="This is a manual error to force the execution of the error handler."/>
		<error-handler >
			<on-error-propagate>
				<set-variable value="#[400]" variableName="statusCode"/>
				<ee:transform>
					<ee:message>
						<ee:set-payload><![CDATA[%dw 2.0
output application/problem+json with json
---
{
  "type": "https://example.org/out-of-stock",
  title: "Out of Stock",
  status: vars.statusCode,
  detail: "Item B00027Y5QG is no longer available",
  product: "B00027Y5QG"
}]]></ee:set-payload>
					</ee:message>
				</ee:transform>
			</on-error-propagate>
		</error-handler>
	</flow>

Response:

HTTP/1.1 400 Bad Request
Content-Type: application/problem+json; charset=UTF-8
Content-Length: 173
Date: Thu, 02 Apr 2020 19:48:23 GMT
Connection: close

[data-source-url=modules/ROOT/pages/_partials/cookbook-dw/change-script-output-mime-ex1-partial-solution]
{
  "type": "https://example.org/out-of-stock",
  "title": "Out of Stock",
  "status": 400,
  "detail": "Item B00027Y5QG is no longer available",
  "product": "B00027Y5QG"
}

In the next example, the Mule flow returns text/markdown content generated by DataWeave as simple text. A browser that supports Markdown might render the input as bulleted content according to the rules of Markdown instead of rendering it in plain text with asterisks.

Mule Flow:

<flow name="listFlow">
  <http:listener config-ref="HTTP_Listener_config" path="/some.md"/>
  <ee:transform>
    <ee:message>
      <ee:set-payload ><![CDATA[%dw 2.0
output text/markdown with text
---
"* idea 1
* some other idea"]]></ee:set-payload>
    </ee:message>
  </ee:transform>
</flow>

Response:

HTTP/1.1 200
Content-Type: text/markdown; charset=UTF-8
Content-Length: 26
Date: Thu, 02 Apr 2020 21:28:36 GMT

* idea 1
* some other idea

Change a Script’s MIME Type Output

See Also