Response Transformer plugin

Transform the response sent by the upstream server on the fly before returning the response to the client.

Note on transforming bodies: Be aware of the performance of transformations on the response body. In order to parse and modify a JSON body, the plugin needs to retain it in memory, which might cause pressure on the worker's Lua VM when dealing with large bodies (several MBs). Because of Nginx's internals, the `Content-Length` header will not be set when transforming a response body.

For additional response transformation features, check out the Response Transformer Advanced plugin. Response Transformer Advanced adds the following abilities:

When transforming a JSON payload, transformations are applied to nested JSON objects and arrays. This can be turned off and on using the config.dots_in_keys configuration parameter. See Response Transformed Advanced arrays and nested objects.
Transformations can be restricted to responses with specific status codes using various config.*.if_status configuration parameters.
JSON body contents can be restricted to a set of allowed properties with config.allow.json.
The entire response body can be replaced using config.replace.body.
Arbitrary transformation functions written in Lua can be applied.
The plugin will decompress and recompress Gzip-compressed payloads when the Content-Encoding header is gzip.

Response Transformer Advanced includes the following additional configurations: add.if_status, append.if_status, remove.if_status, replace.body, replace.if_status, transform.functions, transform.if_status, allow.json, rename.if_status, transform.json, and dots_in_keys.

Configuration Reference

This plugin is compatible with DB-less mode.

In DB-less mode, you configure Kong Gateway declaratively. Therefore, the Admin API is mostly read-only. The only tasks it can perform are all related to handling the declarative config, including:

Setting a target's health status in the load balancer
Validating configurations against schemas
Uploading the declarative configuration using the /config endpoint

Enable the plugin on a service

Admin API

Kubernetes

Declarative (YAML)

Konnect Cloud

Kong Manager

For example, configure this plugin on a service by making the following request:

curl -X POST http://{HOST}:8001/services/{SERVICE}/plugins \
    --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

SERVICE is the id or name of the service that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <response-transformer-example>
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Next, apply the KongPlugin resource to a Service by annotating the Service as follows:

apiVersion: v1
kind: Service
metadata:
  name: {SERVICE}
  labels:
    app: {SERVICE}
  annotations:
    konghq.com/plugins: <response-transformer-example>
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: {SERVICE}
  selector:
    app: {SERVICE}

{SERVICE} is the id or name of the service that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any service, consumer, or route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

For example, configure this plugin on a service by adding this section to your declarative configuration file:

plugins:
- name: response-transformer
  service: {SERVICE}
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

SERVICE is the id or name of the service that this plugin configuration will target.

Configure this plugin on a service:

In Konnect Cloud, select the service on the ServiceHub page.
Scroll down to Versions and select the version.
Scroll down to Plugins and click New Plugin.
Find and select the Response Transformer plugin.
Click Create.

Configure this plugin on a service:

In Kong Manager, select the workspace.
From the Dashboard, scroll down to Services and click View for the service row.
Scroll down to plugins and click Add Plugin.
Find and select the Response Transformer plugin.

Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
If the option is available, select Scoped.
Add the service name and ID to the Service field if it is not already prefilled.
Click Create.

Enable the plugin on a route

Admin API

Kubernetes

Declarative (YAML)

Konnect Cloud

Kong Manager

For example, configure this plugin on a route with:

$ curl -X POST http://{HOST}:8001/routes/{ROUTE}/plugins \
    --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

ROUTE is the id or name of the route that this plugin configuration will target.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <response-transformer-example>
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Then, apply it to an ingress (Route or Routes) by annotating the ingress as follows:

apiVersion: networking/v1beta1
kind: Ingress
metadata:
  name: {ROUTE}
  annotations:
    kubernetes.io/ingress.class: kong
    konghq.com/plugins: <response-transformer-example>
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          serviceName: echo
          servicePort: 80

ROUTE is the id or name of the route that this plugin configuration will target.

For example, configure this plugin on a route by adding this section to your declarative configuration file:

plugins:
- name: response-transformer
  route: <route>
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

ROUTE is the id or name of the route that this plugin configuration will target.

Configure this plugin on a route:

In Konnect Cloud, select the service from the ServiceHub page.
Scroll down to Versions and select the version.
Select the route.
Scroll down to Plugins and click Add Plugin.
Find and select the Response Transformer plugin.
Click Create.

Configure this plugin on a route:

In Kong Manager, select the workspace.
From the Dashboard, select Routes in the left navigation.
Click View for the route row.
Scroll down to plugins and click Add Plugin.
Find and select the Response Transformer plugin.

Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
If the option is available, select Scoped.
Add the Route ID if it is not already prefilled.
Click Create.

Enabling the plugin on a consumer

Admin API

Kubernetes

Declarative (YAML)

Kong Manager

For example, configure this plugin on a consumer with:

$ curl -X POST http://{HOST}:8001/consumers/{CONSUMER}/plugins \
    --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

CONSUMER is the id or username of the consumer that this plugin configuration will target.

You can combine consumer.id, service.id, or route.id in the same request, to further narrow the scope of the plugin.

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <response-transformer-example>
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

Then, apply it to a consumer by annotating the KongConsumer resource as follows:

apiVersion: configuration.konghq.com/v1
kind: KongConsumer
metadata:
  name: {CONSUMER}
  annotations:
    konghq.com/plugins: <response-transformer-example>
    kubernetes.io/ingress.class: kong

CONSUMER is the id or username of the consumer that this plugin configuration will target.

Note: The KongPlugin resource only needs to be defined once and can be applied to any Service, Consumer, or Route in the namespace. If you want the plugin to be available cluster-wide, create the resource as a KongClusterPlugin instead of KongPlugin.

For example, configure this plugin on a consumer by adding this section to your declarative configuration file:

plugins:
- name: response-transformer
  consumer: {CONSUMER}
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

CONSUMER is the id or username of the consumer that this plugin configuration will target.

Configure this plugin on a consumer:

In Kong Manager, select the workspace.
From the Dashboard, scroll down to Consumers and click View for the consumer row.
Select the Plugins tab.
Click Add Plugin.
Find and select the Response Transformer plugin.

Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
If the option is available, select Global.
Click Create.

Enable the plugin globally

A plugin which is not associated to any service, route, or consumer is considered global, and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

Admin API

Kubernetes

Declarative (YAML)

Kong Manager

For example, configure this plugin globally with:

$ curl -X POST http://{HOST}:8001/plugins/ \
    --data "name=response-transformer"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one" \
    --data "config.remove.json=json-key-toremove" \
    --data "config.remove.json=another-json-key" \
    --data "config.add.headers=x-new-header:value" \
    --data "config.add.headers=x-another-header:something" \
    --data "config.add.json=new-json-key:some_value" \
    --data "config.add.json=another-json-key:some_value" \
    --data "config.add.json_types=new-json-key:string" \
    --data "config.add.json_types=another-json-key:boolean" \
    --data "config.add.json_types=another-json-key:number" \
    --data "config.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

Create a KongClusterPlugin resource and label it as global:

apiVersion: configuration.konghq.com/v1
kind: KongClusterPlugin
metadata:
  name: <global-response-transformer>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one
  remove:
    json:
    - json-key-toremove
    - another-json-key
  add:
    headers:
    - x-new-header:value
    - x-another-header:something
  add:
    json:
    - new-json-key:some_value
    - another-json-key:some_value
  add:
    json_types:
    - new-json-key:string
    - another-json-key:boolean
    - another-json-key:number
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer

For example, configure this plugin using the plugins: entry in the declarative configuration file:

plugins:
- name: response-transformer
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one
    remove:
      json:
      - json-key-toremove
      - another-json-key
    add:
      headers:
      - x-new-header:value
      - x-another-header:something
    add:
      json:
      - new-json-key:some_value
      - another-json-key:some_value
    add:
      json_types:
      - new-json-key:string
      - another-json-key:boolean
      - another-json-key:number
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

Configure this plugin globally:

In Kong Manager, select the workspace.
From the Dashboard, select Plugins in the left navigation.
Click New Plugin.
Find and select the Response Transformer plugin.

Note: If the plugin is greyed out, then it is not available for your product tier. See Kong Gateway tiers.
If the option is available, set the plugin scope to Global.
Click Create.

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

Form Parameter	Description
`name` required Type: string	The name of the plugin, in this case `response-transformer`.
`service.id` Type: string	The ID of the Service the plugin targets.
`route.id` Type: string	The ID of the Route the plugin targets.
`consumer.id` Type: string	The ID of the Consumer the plugin targets.
`enabled` required Type: boolean Default value: `true`	Whether this plugin will be applied.
`config.remove.headers` optional Type: array of string elements	List of header names. Unset the header(s) with the given name.
`config.remove.json` optional Type: array of string elements	List of property names. Remove the property from the JSON body if it is present.
`config.rename.headers` optional Type: array of string elements	List of `original_header_name:new_header_name` pairs. If the header `original_headername` is already set, rename it to `new_headername`. Ignored if the header is not already set.
`config.replace.headers` optional Type: array of string elements	List of `headername:value` pairs. If and only if the header is already set, replace its old value with the new one. Ignored if the header is not already set.
`config.replace.json` optional Type: array of string elements	List of `property:value` pairs. If and only if the parameter is already present, replace its old value with the new one. Ignored if the parameter is not already present.
`config.replace.json_types` optional Type: array of string elements	List of JSON type names. Specify the types of the JSON values returned when replacing JSON properties. Each string element can be one of: boolean, number, or string.
`config.add.headers` optional Type: array of string elements	List of `headername:value` pairs. If and only if the header is not already set, set a new header with the given value. Ignored if the header is already set.
`config.add.json` optional Type: array of string elements	List of `property:value` pairs. If and only if the property is not present, add a new property with the given value to the JSON body. Ignored if the property is already present.
`config.add.json_types` optional Type: array of string elements	List of JSON type names. Specify the types of the JSON values returned when adding a new JSON property. Each string element can be one of: boolean, number, or string.
`config.append.headers` optional Type: array of string elements	List of `headername:value` pairs. If the header is not set, set it with the given value. If it is already set, a new header with the same name and the new value will be set. Each string element can be one of: boolean, number, or string.
`config.append.json` optional Type: array of string elements	List of `property:value` pairs. If the property is not present in the JSON body, add it with the given value. If it is already present, the two values (old and new) will be aggregated in an array.
`config.append.json_types` optional Type: array of string elements	List of JSON type names. Specify the types of the JSON values returned when appending JSON properties. Each string element can be one of: boolean, number, or string.

Note: if the value contains a , then the comma separated format for lists cannot be used. The array notation must be used instead.

Order of execution

Plugin performs the response transformation in following order

remove –> rename –> replace –> add –> append

Examples

In these examples we have the plugin enabled on a Route. This would work similar for Services.

Add multiple headers by passing each header:value pair separately:

With a database

Without a database

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.headers[1]=h1:v1" \
  --data "config.add.headers[2]=h2:v1"

plugins:
- name: response-transformer
  route: {route}
  config:
    add:
      headers: ["h1:v1", "h2:v2"]

upstream response headers	proxied response headers
h1: v1	h1: v1 h2: v1

Add multiple headers by passing comma separated header:value pair (only possible with a database):

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.headers=h1:v1,h2:v2"

upstream response headers	proxied response headers
h1: v1	h1: v1 h2: v1

Add multiple headers passing config as JSON body (only possible with a database):

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "response-transformer", "config": {"add": {"headers": ["h1:v2", "h2:v1"]}}}'

upstream response headers	proxied response headers
h1: v1	h1: v1 h2: v1

Add a body property and a header:

With a database

Without a database

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.json=p1:v1,p2=v2" \
  --data "config.add.headers=h1:v1"

plugins:
- name: response-transformer
  route: {route}
  config:
    add:
      json: ["p1:v1", "p2=v2"]
      headers: ["h1:v1"]

upstream response headers	proxied response headers
h1: v2	h1: v2 h2: v1
h3: v1	h1: v1 h2: v1 h3: v1

upstream response JSON body	proxied response body
{}	{“p1” : “v1”, “p2”: “v2”}
{“p1” : “v2”}	{“p1” : “v2”, “p2”: “v2”}

Append multiple headers and remove a body property:

With a database

Without a database

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "response-transformer", "config": {"append": {"headers": ["h1:v2", "h2:v1"]}, "remove": {"json": ["p1"]}}}'

plugins:
- name: response-transformer
  route: {route}
  config:
    append:
      headers: ["h1:v2", "h2:v1"]
    remove:
      json: ["p1"]

upstream response headers	proxied response headers
h1: v1	h1: v1 h1: v2 h2: v1

upstream response JSON body	proxied response body
{“p2”: “v2”}	{“p2”: “v2”}
{“p1” : “v1”, “p2” : “v1”}	{“p2”: “v2”}

Explicitly set the type of the added JSON value -1 to be a number (instead of the implicitly inferred type string) if the response code is 500:

$ curl -X POST http://localhost:8001/routes/{route}/plugins \
  --data "name=response-transformer" \
  --data "config.add.json=p1:-1" \
  --data "config.add.json_types=number"

About this Plugin
Plugin Version	1.0.x
Made by	Kong Inc.
Categories	Transformations
DB-less compatible?	Yes
Konnect Cloud compatible?	Yes
Compatible protocols	`http` `https`
Version Compatibility
Kong Gateway 2.8.x 2.7.x 2.6.x 2.5.x 2.4.x 2.3.x 2.2.x 2.1.x 1.5.x 1.3-x 0.36-x Kong Gateway (OSS) 2.8.x 2.7.x 2.6.x 2.5.x 2.4.x 2.3.x 2.2.x 2.1.x 2.0.x 1.5.x 1.4.x 1.3.x 1.2.x 1.1.x 1.0.x 0.14.x 0.13.x