Request Transformer Advanced

Transform client requests before they reach the upstream server. The plugin lets you match portions of incoming requests using regular expressions, save those matched strings into variables, and substitute the strings into transformed requests via flexible templates.

The Request Transformer Advanced plugin builds on the open-source Request Transformer plugin with the following enhanced capability:

• Limit the list of allowed parameters in the request body. Set this up with the allow.body configuration parameter.

Notes:

• If the value contains a , (comma), then the comma-separated format for lists 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

You can use any of the current request headers, query parameters, and captured URI groups as templates to populate supported config fields.

To escape a template, wrap it inside quotes and pass inside another template. For example:

$('$(something_that_needs_to_escaped)')

Note: The plugin creates a non-mutable table of request headers, query strings, and captured URIs before transformation. So any update or removal of parameters used in the 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 prefixing 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 which routes requests to the mockbin.com upstream service:

curl -X POST http://localhost:8001/services \
    --data 'name=test' \
    --data 'url=http://mockbin.com/requests'

Create a route for the test service, capturing a user_id field from the third segment of the request path:

Kubernetes users: Version 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. For example $(uri_captures[1]) obtains the value of the first capture group.

curl -X POST http://localhost:8001/services/test/routes --data "name=test_user" \
    --data-urlencode 'paths=~/requests/user/(?<user_id>\w+)'

Enable the request-transformer-advanced plugin to add a new header, x-user-id, whose value is being set from the captured group in the route path specified above:

curl -XPOST http://localhost:8001/routes/test_user/plugins --data "name=request-transformer-advanced" --data "config.add.headers=x-user-id:\$(uri_captures['user_id'])"

Now send a request with a user id in the route path:

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

You should notice in the response that the x-user-id header has been added with a value of foo.

Order of Execution

This plugin performs the response transformation in the following order:

• remove → rename → 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"

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"

Add multiple headers passing config as a 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"]}}}'

Add a query string 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"

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" \

Add multiple headers and query string 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" \