Response Transformer Advanced

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: an entity that makes requests for Kong to proxy; it represents either a user or an external service.
• 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-advanced"  \
    --data "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//" \
    --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} is 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}/plugins \
    --data "name=response-transformer-advanced"  \
    --data "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//" \
    --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} is the id or name 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/consumers/{consumer}/plugins \
    --data "name=response-transformer-advanced" \
     \
    --data "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//" \
    --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"

{consumer} is the id or username of the Consumer that this plugin configuration will target.

You can combine consumer.id and service.id in the same request, to furthermore narrow the scope of the plugin.

Global plugins

• Using a database, all plugins can be configured using the http://kong:8001/plugins/ endpoint.
• Without a database, all plugins can be configured via the plugins: entry on the declarative configuration file.

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

• 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"]}}}'

• 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"

• 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"]}}}'

• 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" \

• 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" \

• 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" \

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/$/" \