Message Transformation

You can use interceptors in Choreo Connect to carry out transformations and mediation on the requests and responses. Request interceptor gets triggered before sending the request to the backend. Response interceptor gets triggered before responding to the client. Here, an interceptor is a separate microservice that handles the request, response, or both request and response transformations.

If you are an API developer, you can write a custom request/response interceptor microservice in any programming language of your choice by following the Interceptor OpenAPI Definition. Next, for the interceptor to be engaged with Choreo Connect, define the corresponding interceptors using the following OpenAPI extensions in the OpenAPI definition.

Interceptor Corresponding OpenAPI Extension
Request interceptor x-wso2-request-interceptor
Response interceptor x-wso2-response-interceptor

You can define interceptors on an API level (per API) and at resource level (per resource). If a request/response interceptor is on an API level and a resource level, the resource level interceptor overrides the API level interceptor for the resource defined.

The following diagram illustrates the request flow from the client to the backend through the request interceptor service and the response flow from the backend to the client through the response interceptor service.

Choreo Connect Interceptors request flow

Numbers Description
1 Client request
2,3 Request validation flow via the Enforcer
4,5 If the request is valid (i.e. authenticated, not rate-limited etc.), the Router forwards the request to the Interceptor Service and transform the request based on the response from the interceptor service
6,7 Response from the backend
8,9 Response also goes through the Interceptor Service just like during the request flow
10 Response to the client

Adding an interceptor requires the following two steps.

  1. Implement an interceptor microservice adhering to the Interceptor OpenAPI Definition.
  2. Refer to the interceptor service from the client-facing API definition to engage with it in the request/response flow.


The following are not supported during request/response body manipulation.

  • Large payload manipulation. Maximum supported payload size is 1MiB.
  • Content types (e.g., multipart/form-data) with binary payloads.

However, you can use interceptors to modify headers and trailers with the above mentioned scenarios.