Kong Enterprise only: This plugin is only available with a Kong Enterprise subscription.
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The Request Transformer plugin for Kong Enterprise builds on the Kong version of this plugin with enhanced capabilities to match portions of incoming requests using regular expressions, save those matched strings into variables, and substitute those strings into transformed requests via flexible templates.


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.
  • API: a legacy entity used to represent your upstream services. Deprecated in favor of Services since CE 0.13.0 and EE 0.32.

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=request-transformer-advanced" 

  • 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=request-transformer-advanced" 

  • 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=request-transformer-advanced" \
    --data "consumer_id={consumer_id}" 

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.

Enabling the plugin on an API

If you are using an older version of Kong with the legacy API entity (deprecated in favor of Services since CE 0.13.0 and EE 0.32.), you can configure this plugin on top of such an API by making the following request:

$ curl -X POST http://kong:8001/apis/{api}/plugins \
    --data "name=request-transformer-advanced" 

  • api: either id or name of the API that this plugin configuration will target.

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:

form parameterdefaultdescription
nameThe name of the plugin to use, in this case request-transformer-advanced
service_idThe id of the Service which this plugin will target.
route_idThe id of the Route which this plugin will target.
enabledtrueWhether this plugin will be applied.
consumer_idThe id of the Consumer which this plugin will target.
api_idThe id of the API which this plugin will target. Note: The API Entity is deprecated in favor of Services since CE 0.13.0 and EE 0.32.
config.http_method
optional

Changes the HTTP method for the upstream request

config.remove.headers
optional

List of header names. Unset the headers with the given name.

config.remove.querystring
optional

List of querystring names. Remove the querystring if it is present.

config.remove.body
optional

List of parameter names. Remove the parameter if and only if content-type is one the following [application/json, multipart/form-data, application/x-www-form-urlencoded] and parameter is present.

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.querystring
optional

List of queryname:value pairs. If and only if the querystring name is already set, replace its old value with the new one. Ignored if the header is not already set.

config.replace.uri
optional

Updates the upstream request URI with given value. This value can only be used to update the path part of the URI, not the scheme, nor the hostname.

config.replace.body
optional

List of paramname:value pairs. If and only if content-type is one the following [application/json, multipart/form-data, application/x-www-form-urlencoded] and the parameter is already present, replace its old value with the new one. Ignored if the parameter is not already present.

config.rename.headers
optional

List of headername:value pairs. If and only if the header is already set, rename the header. The value is unchanged. Ignored if the header is not already set.

config.rename.querystring
optional

List of queryname:value pairs. If and only if the field name is already set, rename the field name. The value is unchanged. Ignored if the field name is not already set.

config.rename.body
optional

List of parameter name:value pairs. Rename the parameter name if and only if content-type is one the following [application/json, multipart/form-data, application/x-www-form-urlencoded] and parameter is present.

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.querystring
optional

List of queryname:value pairs. If and only if the querystring name is not already set, set a new querystring with the given value. Ignored if the querystring name is already set.

config.add.body
optional

List of paramname:value pairs. If and only if content-type is one the following [application/json, multipart/form-data, application/x-www-form-urlencoded] and the parameter is not present, add a new parameter with the given value to form-encoded body. Ignored if the parameter is already present.

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.querystring
optional

List of queryname:value pairs. If the querystring is not set, set it with the given value. If it is already set, a new querystring with the same name and the new value will be set.

config.append.body
optional

List of paramname:value pairs. If the content-type is one the following [application/json, application/x-www-form-urlencoded], add a new parameter with the given value if the parameter is not present, otherwise if it is already present, the two values (old and new) will be aggregated in an array.

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

Template as Value

User can use any of the the current request headers, query params, and captured URI named groups as template to populate above supported config fields.

Request Param Template
header $(headers. or $(headers['']) or 'optional_default')
querystring $(query_params. or $(query_params['query-param-name']) or 'optional_default')
captured URIs $(uri_captures. or $(uri_captures['group-name']) or 'optional_default')

To escape a template, wrap it inside quotes and pass inside another template.
Ex. $(‘$(some_needs_to_escaped)’)

Note: Plugin creates a non mutable table of request headers, querystrings, and captured URIs before transformation. So any update or removal of params used in template does not affect the rendered value of template.

Examples Using Template as Value

Add an API test with uris configured with a named capture group user_id

$ curl -X POST http://localhost:8001/apis \
    --data 'name=test' \
    --data 'upstream_url=http://mockbin.com' \
    --data-urlencode 'uris=/requests/user/(?<user_id>\w+)' \
    --data "strip_uri=false"

Enable the ‘request-transformer-advanced’ plugin to add a new header x-consumer-id and its value is being set with the value sent with header x-user-id or with the default value alice is header is missing.

$ curl -X POST http://localhost:8001/apis/test/plugins \
    --data "name=request-transformer-advanced" \
    --data-urlencode "config.add.headers=x-consumer-id:\$(headers['x-user-id'] or 'alice')" \
    --data "config.remove.headers=x-user-id"

Now send a request without setting header x-user-id

$ curl -i -X GET localhost:8000/requests/user/foo

Plugin will add a new header x-consumer-id with value alice before proxying request upstream. Now try sending request with header x-user-id set

$ curl -i -X GET localhost:8000/requests/user/foo \
  -H "X-User-Id:bob"

This time plugin will add a new header x-consumer-id with value sent along with header x-user-id, i.e.bob

Order of Execution

Plugin performs the response transformation in following order

remove –> replace –> add –> append

Configuration Examples

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

$ curl -X POST http://localhost:8001/apis/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers[1]=h1:v1" \
  --data "config.add.headers[2]=h2:v1"
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1

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

$ curl -X POST http://localhost:8001/apis/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers=h1:v1,h2:v2"
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1

Add multiple headers passing config as JSON body:

$ curl -X POST http://localhost:8001/apis/mockbin/plugins \
  --header 'content-type: application/json' \
  --data '{"name": "request-transformer-advanced", "config": {"add": {"headers": ["h1:v2", "h2:v1"]}}}'
Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1

Add a querystring and a header:

$ curl -X POST http://localhost:8001/apis/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.querystring=q1:v2,q2=v1" \
  --data "config.add.headers=h1:v1"

Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1
h3: v1 h1: v1, h2: v1, h3: v1
Incoming Request Querystring Upstream Proxied Querystring
?q1=v1 ?q1=v1&q2=v1
  ?q1=v2&q2=v1

Append multiple headers and remove a body parameter:

$ curl -X POST http://localhost:8001/apis/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers=h1:v2,h2:v1" \
  --data "config.remove.body=p1" \

Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h1: v2, h2: v1
Incoming URL Encoded Body Upstream Proxied URL Encoded Body
p1=v1&p2=v1 p2=v1
p2=v1 p2=v1

Add multiple headers and querystring parameters if not already set:

$ curl -X POST http://localhost:8001/apis/mockbin/plugins \
  --data "name=request-transformer-advanced" \
  --data "config.add.headers=h1:v1,h2:v1" \
  --data "config.add.querystring=q1:v2,q2:v1" \

Incoming Request Headers Upstream Proxied Headers
h1: v1 h1: v1, h2: v1
h3: v1 h1: v1, h2: v1, h3: v1
Incoming Request Querystring Upstream Proxied Querystring
?q1=v1 ?q1=v1&q2=v1
  ?q1=v2&q2=v1