Conditionally modify upstream response body in Kong

[stiti-bacem]

I'm currently working with Kong and I need to modify the body of upstream responses based on certain conditions. Specifically, I want to modify the body only if the request is a POST request. I've tried using the "response transformer" plugin, but I can't figure out how to add this specific condition.

Here are the points I need clarification on:

Did I misconfigure the "response transformer" plugin?
Is it possible to add such a condition with the existing plugin?
Do I need to develop a custom plugin to achieve this functionality?
I configured the "response transformer" plugin to modify the response body. The plugin works, but it applies the transformation to all response bodies regardless of the request method. I expected to find an option to conditionally apply the transformation based on the request method (only for POST requests), but I couldn't locate such an option in the plugin's configuration.

[hanshuebner]

@stiti-bacem In order to restrict a plugin to specific HTTP methods, you can create a separate route for POST requests and add the plugin to it.

_format_version: "2.1"

services:
- name: example-service
  url: http://web
  routes:
    - name: post-route
      paths:
        - /
      methods:
        - POST
      plugins:
        - name: response-transformer
          config:
            add:
              json:
                - "hello: world"

    - name: default-route
      paths:
        - /

[stiti-bacem]

Hello @hanshuebner

Thank you for your response.

Indeed, on the project I am working on, it is not possible to do that. I cannot create a route exclusively for POST requests to apply the plugin. The routes I have are allowed to use all HTTP requests (GET, POST, PUT, DELETE, etc.).

I only want to modify the body of all POST requests. Is it possible to do this using Kong plugins? I have already developed a custom plugin that works correctly, but I wanted to know if we can use a Kong plugin directly without developing a new one ourselves.

[hanshuebner]

It is possible to do this using a plugin that is attached to the route. If you don't want to do that, you'll need a custom plugin.