Response Transformer Advanced plugin

Kong Enterprise only: This plugin is only available with a Kong Enterprise subscription. Please inquire about Kong Enterprise by contacting us, or start a free trial today.

Transform the response sent by the upstream server on the fly on Kong, 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.

Configuration Reference

You can configure this plugin using the Kong Admin API or through declarative configuration, which involves directly editing the Kong configuration file.

Enabling the plugin on a Service

Kong Admin API

Kubernetes

Declarative (YAML)

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

$ curl -X POST http://<admin-hostname>:8001/services/<service>/plugins \
    --data "name=response-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one:application/json" \
    --data "config.remove.headers=x-list-of-values:v1,v2,v3" \
    --data "config.remove.headers=Set-Cookie:/JSESSIONID=.*/" \
    --data "config.remove.headers=x-another-regex://status/$/" \
    --data "config.remove.headers=x-one-more-regex:/^/begin//" \
    --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.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <response-transformer-advanced-example>
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one:application/json
    - x-list-of-values:v1,v2,v3
    - Set-Cookie:/JSESSIONID=.*/
    - x-another-regex://status/$/
    - x-one-more-regex:/^/begin//
  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
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer-advanced

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-advanced-example>
spec:
  ports:
  - port: 80
    targetPort: 80
    protocol: TCP
    name: <service>
  selector:
    app: <service>

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-advanced
  service: <service>
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one:application/json
      - x-list-of-values:v1,v2,v3
      - Set-Cookie:/JSESSIONID=.*/
      - x-another-regex://status/$/
      - x-one-more-regex:/^/begin//
    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
    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.

Enabling the plugin on a Route

Kong Admin API

Kubernetes

Declarative (YAML)

For example, configure this plugin on a Route with:

$ curl -X POST http://<admin-hostname>:8001/routes/<route>/plugins \
    --data "name=response-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one:application/json" \
    --data "config.remove.headers=x-list-of-values:v1,v2,v3" \
    --data "config.remove.headers=Set-Cookie:/JSESSIONID=.*/" \
    --data "config.remove.headers=x-another-regex://status/$/" \
    --data "config.remove.headers=x-one-more-regex:/^/begin//" \
    --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.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

First, create a KongPlugin resource:

apiVersion: configuration.konghq.com/v1
kind: KongPlugin
metadata:
  name: <response-transformer-advanced-example>
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one:application/json
    - x-list-of-values:v1,v2,v3
    - Set-Cookie:/JSESSIONID=.*/
    - x-another-regex://status/$/
    - x-one-more-regex:/^/begin//
  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
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer-advanced

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-advanced-example>
spec:
  rules:
  - host: examplehostname.com
    http:
      paths:
      - path: /bar
        backend:
          serviceName: echo
          servicePort: 80

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

plugins:
- name: response-transformer-advanced
  route: <route>
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one:application/json
      - x-list-of-values:v1,v2,v3
      - Set-Cookie:/JSESSIONID=.*/
      - x-another-regex://status/$/
      - x-one-more-regex:/^/begin//
    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
    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.

Enabling the plugin on a Consumer

Kong Admin API

Kubernetes

Declarative (YAML)

For example, configure this plugin on a Consumer with:

$ curl -X POST http://<admin-hostname>:8001/consumers/<consumer>/plugins \
    --data "name=response-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one:application/json" \
    --data "config.remove.headers=x-list-of-values:v1,v2,v3" \
    --data "config.remove.headers=Set-Cookie:/JSESSIONID=.*/" \
    --data "config.remove.headers=x-another-regex://status/$/" \
    --data "config.remove.headers=x-one-more-regex:/^/begin//" \
    --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.append.headers=x-existing-header:some_value" \
    --data "config.append.headers=x-another-header:some_value"

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-advanced-example>
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one:application/json
    - x-list-of-values:v1,v2,v3
    - Set-Cookie:/JSESSIONID=.*/
    - x-another-regex://status/$/
    - x-one-more-regex:/^/begin//
  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
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer-advanced

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-advanced-example>
    kubernetes.io/ingress.class: kong

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

plugins:
- name: response-transformer-advanced
  consumer: <consumer>
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one:application/json
      - x-list-of-values:v1,v2,v3
      - Set-Cookie:/JSESSIONID=.*/
      - x-another-regex://status/$/
      - x-one-more-regex:/^/begin//
    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
    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.

Enabling 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.

Kong Admin API

Kubernetes

Declarative (YAML)

For example, configure this plugin globally with:

$ curl -X POST http://<admin-hostname>:8001/plugins/ \
    --data "name=response-transformer-advanced"  \
    --data "config.remove.headers=x-toremove" \
    --data "config.remove.headers=x-another-one:application/json" \
    --data "config.remove.headers=x-list-of-values:v1,v2,v3" \
    --data "config.remove.headers=Set-Cookie:/JSESSIONID=.*/" \
    --data "config.remove.headers=x-another-regex://status/$/" \
    --data "config.remove.headers=x-one-more-regex:/^/begin//" \
    --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.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-advanced>
  annotations:
    kubernetes.io/ingress.class: kong
  labels:
    global: \"true\"
config: 
  remove:
    headers:
    - x-toremove
    - x-another-one:application/json
    - x-list-of-values:v1,v2,v3
    - Set-Cookie:/JSESSIONID=.*/
    - x-another-regex://status/$/
    - x-one-more-regex:/^/begin//
  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
  append:
    headers:
    - x-existing-header:some_value
    - x-another-header:some_value
plugin: response-transformer-advanced

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

plugins:
- name: response-transformer-advanced
  config: 
    remove:
      headers:
      - x-toremove
      - x-another-one:application/json
      - x-list-of-values:v1,v2,v3
      - Set-Cookie:/JSESSIONID=.*/
      - x-another-regex://status/$/
      - x-one-more-regex:/^/begin//
    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
    append:
      headers:
      - x-existing-header:some_value
      - x-another-header:some_value

Parameters

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

Form Parameter	Description
`name`	The name of the plugin to use, in this case `response-transformer-advanced`.
`service.id`	The ID of the Service the plugin targets.
`route.id`	The ID of the Route the plugin targets.
`consumer.id`	The ID of the Consumer the plugin targets.
`enabled` default value: `true`	Whether this plugin will be applied.
`config.remove.headers` optional	List of header_name[:header_value]. If only header_name is given, unset the header field with the given header_name. If header_name:header_value is given, remove a specific header_value. If header_value starts and ends with a ‘/’ (slash character), then it is considered to be a regular expression. Note that as per https://httpwg.org/specs/rfc7230.html#field.order multiple header values with the same header name are allowed if the entire field value for that header field is defined as a comma-separated list or the header field is a Set-Cookie header field.
`config.remove.json` optional	List of property names. Remove the property from the JSON body if it is present.
`config.remove.if_status` optional	List of response status codes or status code ranges to which the transformation will apply. Empty means all response codes.
`config.rename.headers` optional	List of headername:value pairs. Renames header with headername to new name.
`config.replace.headers` optional	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	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	List of JSON type names. Specify the types of the JSON values returned when replacing JSON properties.
`config.replace.body` optional	String with which to replace the entire response body
`config.replace.if_status` optional	List of response status codes or status code ranges to which the transformation will apply. Empty means all response codes
`config.add.headers` optional	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	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	List of JSON type names. Specify the types of the JSON values returned when adding a new JSON property.
`config.add.if_status` optional	List of response status codes or status code ranges to which the transformation will apply. Empty means all response codes
`config.append.headers` optional	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.
`config.append.json` optional	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	List of JSON type names. Specify the types of the JSON values returned when appending JSON properties.
`config.append.if_status` optional	List of response status codes or status code ranges to which the transformation will apply. Empty means all response codes
`config.allow.json` optional	Set of parameter names. Only allowed parameters are present in the JSON response body.
`config.transform.functions` optional	Set of Lua functions to perform arbitrary transforms in a response JSON body.
`config.transform.if_status` optional	List of response status codes or ranges to which the arbitrary transformation applies. Leaving empty implies that the transformations apply to all response codes.

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

The plugin performs the response transformation in following order:

remove –> 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:

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

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

Add multiple headers by passing comma separated header:value pair:

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --data "name=response-transformer-advanced" \
  --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:

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "response-transformer-advanced", "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:

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

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "response-transformer-advanced", "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”}

Replace entire response body if response code is 500

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --data "name=response-transformer-advanced" \
  --data "config.replace.body='{\"error\": \"internal server error\"}'" \
  --data "config.replace.if_status=500"

Note: the plugin doesn’t validate the value in config.replace.body against the content type as defined in the Content-Type response header.

Perform arbitrary transforms to a JSON body

Use the power of embedding Lua to perform arbitrary transformations on JSON bodies. Transformation functions receive an argument with the JSON body, and must return the transformed response body:

-- transform.lua
-- this function transforms
-- { "foo": "something", "something": "else" }
-- into
-- { "foobar": "hello world", "something": "else" }
return function (data)
  if type(data) ~= "table" then
    return data
  end

  -- remove foo key
  data["foo"] = nil

  -- add a new key
  data["foobar"] = "hello world"

  return data
end

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  -F "name=response-transformer-advanced" \
  -F "config.transform.functions=@transform.lua"
  -F "config.transform.if_status=200"

Remove the entire header field with a given header name

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

upstream response headers	proxied response headers
h1:v1,v2,v3	{}
h2:v2	{}

Remove a specific header value of a given header field

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

upstream response headers	proxied response headers
h1:v1,v2,v3	h1:v3

Remove a specific header value from a comma-separated list of a header values

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

upstream response headers	proxied response headers
h1:v1,v2,v3	h1:v3

Note: the plugin doesn’t remove header values if the values are not separated by commas, unless it’s a Set-Cookie header field. RFC reference: https://httpwg.org/specs/rfc7230.html#field.order

Remove a specific header value defined by a regular expression

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --data "name=response-transformer-advanced" \
  --data "config.remove.headers=h1:/JSESSIONID=.*/, h2://status/$/" \

upstream response headers	proxied response headers
h1:JSESSIONID=1876832,path=/	h1:path=/
h2:/match/status/,/status/no-match/	h2:/status/no-match/

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 id}/plugins \
  --data "name=response-transformer-advanced" \
  --data "config.add.json=p1:-1" \
  --data "config.add.json_types=number" \
  --data "config.add.if_status=500"

About this Plugin
Made by
Categories	Transformations
Bundled with...
Kong Enterprise 2.1.x 1.5.x 1.3-x 0.36-x 0.35-x