Response Body

Enable Response Modifying Middleware

In order for responses to be processed by Tyk as they return via the proxy, the response middleware must be loaded for the API definition. Unlike inbound middleware, these processors are loaded only as required and must therefore be registered in advance. To do so is very simple, just add them to your API definition as follows:

"response_processors": [
  {
    "name": "response_body_transform",
    "options": {}
  }
]

For the header injector response middleware, it is possible to set global response injection headers. This means that they do not need to be set on a version-level. Any headers set up in the options section of the response headers object will be applied to all replies.

Response Body Transformation

Setting up response transforms in your API definition is very similar to setting up request transforms, we simply use the transform_response section of the API Definition instead:

"extended_paths": {
  "ignored": [],
  "white_list": [],
  "black_list": [],
  "cache": ["get"],
  "transform": [],
  "transform_response": [
    {
      "path": "widgets/{id}",
      "method": "POST",
      "template_data": {
          "template_mode": "file",
          "template_source": "./templates/transform_test.tmpl"
      }
    }
  ],
  "transform_headers": []
}

Tyk will load and evaluate the template on start, if you modify the template, you will need to restart The Gateway in order for the changes to take effect.

The field representations are:

path: The path to match.
method : The method to match.
template_data.input_type: either xml or json, this represents the type of data for the parser to expect.
template_source: Either a file path, or a base64 encoded representation of your template.
template_mode: Set to blob for a base64 template and file for a file path in the template source.

Fixing Response Headers that Leak Upstream Server Data

A middleware called header_transform, added in v2.1, ensures headers such as Location and Link reflect the outward facade of your API Gateway and also align with the expected response location to be terminated at the gateway, not the hidden upstream proxy:

"response_processors": [
  {
    "name": "header_transform",
    "options": {
      "rev_proxy_header_cleanup": {
          "headers": ["Link", "Location"],
          "target_host": "http://TykHost:TykPort"
      }
    }
  }
]

In this configuration, you set the headers to target and the target host to replace the values with. In the above example, the Link and Location headers will be modified from the server-generated response, with the protocol, domain and port of the value set in target_host.

(This is not supported in the Dashboard yet.)

Go Template Functions

For increasing the functions available to the built in Go templating, we have bundled the Sprig Library (v2) which provides over 70 additional functions for transformations.

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