Response Transformer

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

Terminology

• plugin: a plugin executing actions inside Kong before or after a request has been proxied to the upstream API.
• Service: the Kong entity representing an external upstream API or microservice.
• Route: the Kong entity representing a way to map downstream requests to upstream services.
• Consumer: the Kong entity representing a developer or machine using the API. When using Kong, a Consumer only communicates with Kong which proxies every call to the said upstream API.
• Credential: a unique string associated with a Consumer, also referred to as an API key.
• upstream service: this refers to your own API/service sitting behind Kong, to which client requests are forwarded.

Configuration

Enabling the plugin on a Service

Configure this plugin on a Service by making the following request:

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

• service: the id or name of the Service that this plugin configuration will target.

Enabling the plugin on a Route

Configure this plugin on a Route with:

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

• route_id: the id of the Route that this plugin configuration will target.

Enabling the plugin on a Consumer

You can use the http://localhost:8001/plugins endpoint to enable this plugin on specific Consumers:

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

Where consumer_id is the id of the Consumer we want to associate with this plugin.

You can combine consumer_id and service_id

in the same request, to furthermore narrow the scope of the plugin.

Global plugins

All plugins can be configured using the http://kong:8001/plugins/ endpoint. A plugin which is not associated to any Service, Route or Consumer (or API, if you are using an older version of Kong) is considered "global", and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

Parameters

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

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 –> 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" \
  --data "config.add.headers[1]=h1:v1" \
  --data "config.add.headers[2]=h2:v1"

upstream response headers | proxied response headers — | — h1: v1 | <ul><li>h1: v1</li><li>h2: v1</li></ul> —

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

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

upstream response headers | proxied response headers — | — h1: v1 | <ul><li>h1: v1</li><li>h2: v1</li></ul> —

• 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", "config": {"add": {"headers": ["h1:v2", "h2:v1"]}}}'

upstream response headers | proxied response headers — | — h1: v1 | <ul><li>h1: v1</li><li>h2: v1</li></ul> —

• Add a body property and a header:

$ curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --data "name=response-transformer" \
  --data "config.add.json=p1:v1,p2=v2" \
  --data "config.add.headers=h1: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", "config": {"append": {"headers": ["h1:v2", "h2:v1"]}, "remove": {"json": ["p1"]}}}'