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Overview

Transformations allow you to dynamically modify requests and responses. That includes headers, query string parameters and body.
This section describes API-scoped transformations. Transformations defined on an API level are applied to requests/responses to that API, regardless of the product the customer is subscribed to.
Transformations defined on an API level are always applied first.Read about product-scoped transformations.
One of the use-cases for transformations is to authenticate Nadles API Gateway in your API backend by API key. Learn how to configure Nadles to send an API key to your backend.

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How it works

To configure transformations, navigate to APIs → select API → Transformations.

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Headers

The transformation will add/replace/remove headers in a request or response. Header names are case-insensitive.

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Add

Adds a new header, even if there is already one with the same name.
ExampleOriginal request:
GET / HTTP/1.1
X-Some-Header: some-value
Transformation:
Add header "X-Some-Header" with value "another-value".
Transformed request:
GET / HTTP/1.1
X-Some-Header: some-value
X-Some-Header: another-value

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Replace

Replaces header(s) with a new value. If there are several headers with the given name, they’re removed and replaced with the new value.
ExampleOriginal request:
GET / HTTP/1.1
X-Some-Header: first-value
X-Some-Header: second-value
Transformation:
Replace header "X-Some-Header" with value "third-value".
Transformed request:
GET / HTTP/1.1
X-Some-Header: third-value

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Remove

Removes all headers with the given name.
ExampleOriginal request:
GET / HTTP/1.1
X-Some-Header: first-value
X-Some-Header: second-value
Transformation:
Remove header "X-Some-Header".
Transformed request:
GET / HTTP/1.1

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Query string parameters

The transformation will add/replace/remove query string parameters in a request. Query string parameter names are case-sensitive.

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Add

Adds a new query string parameter, even if there is already one or more with the same name.
ExampleOriginal request:
GET /?param1=100 HTTP/1.1
Transformation:
Add query string parameter "param2" with value "test-value".
Transformed request:
GET /?param1=100&param2=test-value HTTP/1.1

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Replace

Replaces query string parameter(s) with a new value. If there are several query string parameters with the given name, they’re removed and replaced with the new value.
ExampleOriginal request:
GET /?param1=100 HTTP/1.1
Transformation:
Replace query string parameter "param1" with value 200.
Transformed request:
GET /?param1=200 HTTP/1.1

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Remove

Removes all query string parameters with the given name.
ExampleOriginal request:
GET /?param1=100 HTTP/1.1
Transformation:
Remove query string parameter "param1".
Transformed request:
GET / HTTP/1.1

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Body

The transformation will add/replace/remove request/response body.

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Add

Adds a new body. If a request or response already has a body, it’s left unchanged.
ExampleOriginal request:
POST / HTTP/1.1
Transformation:
Add body with value {"testkey": "testvalue"}
Transformed request:
POST / HTTP/1.1

{"testkey": "testvalue"}

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Replace

Replaces the body with a new value. If there is no body yet, it’s added.
ExampleOriginal request:
POST / HTTP/1.1

{"originalkey": "originalvalue"}
Transformation:
Replace body with value {"newkey": "newvalue"}
Transformed request:
POST / HTTP/1.1

{"newkey": "newvalue"}

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Remove

Removes the body.
ExampleOriginal request:
POST / HTTP/1.1

{"key": "value"}
Transformation:
Remove body.
Transformed request:
POST / HTTP/1.1

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Expressions

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JavaScript

You can use JavaScript expressions in your transformations to make them even more dynamic. Expressions must evaluate to a new string value for the header/query string parameter/body.

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Examples

Example — News APISay, you provide an API endpoint that returns contents of a news article. E.g.,
{
    "id": "b6355c53-44a3-464b-bc9e-759749cdb3ec",
    "title": "The title",
    "content": "Some long article body"
}
For your “Free” product, you’d like to return only the first 120 characters of article body.With the following transformation added to the “Free” product, you configure Nadles API Gateway to do that:Note that the expression evaluation result is used as the new value for the response body.

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Expression variables

There are several variables you can use in your expressions.
Path parameters
path.params.* — placeholder values specified in the endpoint URL.
ExampleIf an endpoint URL is /resource/{resourceId}and the HTTP request URL is /resource/801d49c2-ca05-42b1-97af-baf0ddf36ba3,then there will be a variable path.params.resourceId with value "801d49c2-ca05-42b1-97af-baf0ddf36ba3".
path.params.resourceId // "801d49c2-ca05-42b1-97af-baf0ddf36ba3"
Path parameter names are case-sensitive.
Client IP address
request.remote_addr — Client IP address.
Request headers
request.headers['header-name'] — Request header values.
Example
request.headers['content-type'] == 'application/json'
Header names must be in lower case.
Request query string parameters
request.query['query_string_parameter_name'] — Request query string parameters.
Example
request.query['page'] > 100
Query string parameter names are case-sensitive.
Request body
request.body — Request body.
Example
request.body.length > 1000
Response variables are only available in response transformations.
Response status code
response.statusCode — HTTP status code of the response from the upstream.
Example
response.statusCode == 200
Response headers
response.headers['header-name'] — Response header values.
Example
response.headers['content-type'] == 'application/json'
Header names must be in lower case.
Response body
response.body — Raw response body.
Example
response.body.length > 0

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jq

You can also use jq expressions for transformations.
jq is like sed for JSON data - you can use it to slice and filter and map and transform JSON with the same ease that sed, awk, grep and friends let you play with text.
Unlike JavaScript expressions, the result of jq transformation does not necessarily have to be a string. If the expression result is not a string, it’s encoded as JSON.

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Examples

Example — News APISay, you provide an API endpoint that returns contents of a news article. E.g.,
{
    "id": "b6355c53-44a3-464b-bc9e-759749cdb3ec",
    "title": "The title",
    "content": "Some long article body"
}
For your “Free” product, you’d like to return only the first 120 characters of article body.The following jq expression will do the job:Note that the expression evaluation result is used as the new value for the response body.

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Expression input

The followind is passed as input (.) to your jq expressions: