The Request Transformer plugin for Kong Gateway 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.
Configuration Reference
Enable the plugin on a service
Enable the plugin on a route
Enabling the plugin on a consumer
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.
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 request-transformer-advanced . |
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.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 [ |
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 [ |
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 [ |
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 [ |
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 [ |
config.whitelist.body
optional |
Set of parameter name. If and only if content-type is one the following [ |
Notes:
- If the value contains a
,
then the comma separated format cannot be used. The array notation must be used instead. - The
X-Forwarded-*
fields are non-standard header fields written by Nginx to inform the upstream about client details and can’t be overwritten by this plugin. If you need to overwrite these header fields, see the post-function plugin in Serverless Functions.
Template as Value
User can use any of the the current request headers, query params, and captured URI groups as template to populate above supported config fields.
Request Param | Template |
---|---|
header | $(headers.<header-name>) or $(headers["<header-name>"]) ) |
querystring | $(query_params.<query-param-name>) or $(query_params["<query-param-name>"]) ) |
captured URIs | $(uri_captures.<group-name>) or $(uri_captures["<group-name>"]) ) |
To escape a template, wrap it inside quotes and pass inside another template.
Ex. $(‘$(some_needs_to_escaped)’)
Note: The 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.
Advanced templates
The content of the placeholder $(...)
is evaluated as a Lua expression, so
logical operators may be used. For example:
Header-Name:$(uri_captures["user-id"] or query_params["user"] or "unknown")
This will first look for the path parameter (uri_captures
); if not found, it will
return the query parameter; or if that also doesn’t exist, it returns the default
value ‘“unknown”’.
Constant parts can be specified as part of the template outside the dynamic
placeholders. For example, creating a basic-auth header from a query parameter
called auth
that only contains the base64-encoded part:
Authorization:Basic $(query_params["auth"])
Lambdas are also supported if wrapped as an expression like this:
$((function() ... implementation here ... end)())
A complete lambda example for pefixing a header value with “Basic “ if not already there:
Authorization:$((function()
local value = headers.Authorization
if not value then
return
end
if value:sub(1, 6) == "Basic " then
return value -- was already properly formed
end
return "Basic " .. value -- added proper prefix
end)())
NOTE: Especially in multi-line templates like the example above, make sure not to add any trailing white-space or new-lines. Since these would be outside the placeholders, they would be considered part of the template, and hence would be appended to the generated value.
The environment is sandboxed, meaning that Lambda’s will not have access to any
library functions, except for the string methods (like sub()
in the example
above).
Examples Using Template as Value
Add a Service named test
with uris
configured with a named capture group user_id
:
$ curl -X POST http://localhost:8001/services \
--data 'name=test' \
--data 'upstream_url=http://mockbin.com' \
--data-urlencode 'uris=/requests/user/(?<user_id>\w+)' \
--data "strip_uri=false"
v1beta1
of the Ingress
specification does not allow the use of named regex capture groups in paths.
If you use the ingress controller, you should use unnamed groups, e.g.
(\w+)/
instead of (?<user_id>\w+)
. You can access
these based on their order in the URL path, e.g. $(uri_captures[1])
will obtain the value of the first capture group.
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/services/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
This plugin performs the response transformation in the following order:
remove –> replace –> add –> append
Configuration Examples
Add multiple headers by passing each header:value pair separately:
$ curl -X POST http://localhost:8001/services/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/services/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/services/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/services/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/services/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/services/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 |