How to update a nodeset variable?

[#1]

Hi,

I'm creating a proxy that modifies a single field in a large json payload, before passing to the backend.

So I use the extract variable policy to extract the whole payload :

<ExtractVariables async="false" continueOnError="false" enabled="true" name="Extract-Request-Data">
    <DisplayName>Extract-Request-Data</DisplayName>
    <JSONPayload>
        <Variable name="body" type="nodeset">
            <JSONPath>$ </JSONPath>
        </Variable>
    </JSONPayload>
    <Source clearPayload="false">request</Source>
    <VariablePrefix>Request-Data</VariablePrefix>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
</ExtractVariables>

Then I tried updating that variable with a assignmessage liek this:

<AssignMessage async="false" continueOnError="false" enabled="true" name="Update-Request-Message">
    <DisplayName>Update-Request-Message</DisplayName>
    <IgnoreUnresolvedVariables>true</IgnoreUnresolvedVariables>
    <AssignVariable>
        <Name>Request-Data.body.theField</Name>
        <Ref>Callout-Response-Data.body.fieldValue</Ref>
    </AssignVariable>
    <AssignTo createNew="false" transport="http" type="request"/>
</AssignMessage>

Unfortunately, the assign message has no effect. All I can see in the tracing is Request-Data.body.theField != (empty)

I also tried to do the update in a JS policy without luck.

Any advice on how this can be done? I don't want extract and copy 20 something fields just to update one field.

Thanks

[#2]

Easiest thing to do is work directly with the content in a JavaScript policy. Something like:

var calloutBody = context.getVariable("Callout-Response-Data.content");

var calloutJson = JSON.parse(calloutBody);

// make your changes

context.setVariable("Callout-Response-Data.content", JSON.stringify(calloutJson));