Response Transformer Advanced

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Looking for the plugin's configuration parameters? You can find them in the Response Transformer Advanced configuration reference doc.

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

The Response Transformer Advanced plugin is a superset of the open-source Response Transformer plugin.

The advanced plugin adds the following abilities:

• When transforming a JSON payload, transformations are applied to nested JSON objects and arrays. This can be turned off and on using the config.dots_in_keys configuration parameter. See Response Transformer Advanced arrays and nested objects.
• Transformations can be restricted to responses with specific status codes using various config.*.if_status configuration parameters.
• JSON body contents can be restricted to a set of allowed properties with config.allow.json.
• The entire response body can be replaced using config.replace.body.
• Arbitrary transformation functions written in Lua can be applied.
• The plugin will decompress and recompress Gzip-compressed payloads when the Content-Encoding header is gzip.

Notes:

• Transformations on the response body can cause changes in performance. To parse and modify a JSON body, the plugin needs to retain it in memory, which might cause pressure on the worker’s Lua VM when dealing with large bodies (several MB). Because of Nginx’s internals, the Content-Length header will not be set when transforming a response body.
• If the value contains a , then the comma separated format for lists cannot be used. Array notation must be used instead.

Order of execution

The plugin performs the response transformation in the following order:

remove –> replace –> add –> append

Arrays and nested objects

The plugin allows navigating complex JSON objects (arrays and nested objects) when config.dots_in_keys is set to false (the default is true).

• array[*]: Loops through all elements of the array.
• array[N]: Navigates to the nth element of the array (the index of the first element is 1).
• top.sub: Navigates to the sub property of the top object.

These can be combined. For example, config.remove.json: customers[*].info.phone removes all phone properties from inside the info object of all entries in the customers array.

Examples

In these examples, the plugin is enabled on a Route. This would work similarly 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 a 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.

• Remove nested JSON content:

curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --data "name=response-transformer-advanced" \
  --data "config.remove.json=customers.info.phone" \
  --data "config.dots_in_keys=false"

When dots_in_keys is false, the customers.info.phone value is interpreted as nested JSON objects. When dots_in_keys is true (default), customers.info.phone is treated as a single property.

• 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 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 (as specified in RFC 7230).

• 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/$/"

• Explicitly set the type of the added JSON value -1 to be a number (instead of the implicitly inferred type string) if the response code is 500:

curl -X POST http://localhost:8001/routes/{route id}/plugins \
  --data "name=response-transformer-advanced" \
  --data "config.add.json=p1:-1" \
  --data "config.add.json_types=number" \
  --data "config.add.if_status=500"