DataWeave Headers Transformation Policy

Policy name

DataWeave Headers Transformation

Summary

Transforms headers of request or response traffic with a DataWeave script

Category

Transformation

First Flex Gateway version available

v1.12.0

Returned Status Codes

400 - The DataWeave script failed to execute or returned an invalid result

Summary

The DataWeave Headers Transformation policy transforms request or response headers with a DataWeave script. The script receives headers and the message body, and returns a map of header names to values. In the request or response, the gateway removes existing headers and runs the script with header bindings. The script output must be a map. Each entry becomes a header. For multi-value headers, use a list of values.

Configure Policy Parameters

Flex Gateway Local Mode

In Local Mode, you apply the policy to your API via declarative configuration files. Refer to the following policy definition and table of parameters:

- policyRef:
    name: dataweave-headers-transformation-flex
  config:
    script: <string>           // REQUIRED - DataWeave script
    requestFlow: <string>      // REQUIRED - "onRequest" or "onResponse"
    requiresPayload: <boolean> // OPTIONAL, default: false

Parameter Required Default Value Description

Parameter	Required	Default Value	Description
`script`	Required	—	A DataWeave script that returns a map of header names to values. The script receives `attributes.headers`. If `requiresPayload` is true, the script also receives the message body in the `payload` binding.
`requestFlow`	Required	—	Whether the policy transforms the request or response body. Supported values: `onRequest` or `onResponse`.
`requiresPayload`	Optional	false	If true, the script receives the message body in the `payload` binding. The gateway buffers the body for the transformation.

script

Required

—

A DataWeave script that returns a map of header names to values. The script receives attributes.headers. If requiresPayload is true, the script also receives the message body in the payload binding.

requestFlow

Required

—

Whether the policy transforms the request or response body. Supported values: onRequest or onResponse.

requiresPayload

Optional

false

If true, the script receives the message body in the payload binding. The gateway buffers the body for the transformation.

Resource Configuration Example

This example adds custom headers with conditional logic. When the header custom-client-header is set to fixed_client, the gateway replaces it with custom-123123231231231231. Otherwise, the gateway uses the header value or client-id-not-set:

  policies:
    - policyRef:
        name: dataweave-headers-transformation-flex
      config:
        script: |
          {
            "custom_client_secret": "fixed_secret_123123231231231231",
            "custom_client_id": if (attributes.headers.'custom-client-header'?)
              attributes.headers.'custom-client-header' match {
                case literalMatch: "fixed_client" -> "custom-123123231231231231"
                else -> attributes.headers.'custom-client-header'
              }
            else "client-id-not-set"
          }

To append custom headers using payload data, for example to add the payload id to a custom header, set requiresPayload: true and include payload in the script:

  policies:
    - policyRef:
        name: dataweave-headers-transformation-flex
      config:
        script: |
          attributes.headers ++ {
            "custom_client_id_from_payload": payload.id,
            "custom_client_secret_from_payload": payload.secret
          }
        requiresPayload: true

Managed Flex Gateway and Flex Gateway Connected Mode

When you apply the policy to your API instance from the UI, the following parameters are displayed:

Parameter	Description
Policy type	DataWeave Headers Transformation
Script	The DataWeave script that returns a map of headers
Request flow	The flow where the policy applies: request or response
Requires payload	Whether the script requires the message body
Method & Resource conditions	The option to add configurations to a select few or all methods and resources of the API

Parameter

Description

Policy type

DataWeave Headers Transformation

Script

The DataWeave script that returns a map of headers

Request flow

The flow where the policy applies: request or response

Requires payload

Whether the script requires the message body

Method & Resource conditions

The option to add configurations to a select few or all methods and resources of the API