Open Source API Gateway

Scripting with Groovy, JavaScript and SpEL

Membrane API Gateway can be extended with small scripts and expressions. Scripts can read and change headers and bodies, build responses, transform JSON or steer the flow of a request.

All three languages share the same built-in variables and functions:

Samples

Set a Header with Groovy

api:
  port: 2000
  flow:
    - request:
        - groovy:
            src: |
              header.put('X-Request-Method', method)
              CONTINUE
  target:
    url: https://api.predic8.de
api:
  port: 2000
  flow:
    - request:
        - groovy:
            src: |
              header.put('X-Request-Method', method)
              CONTINUE
  target:
    url: https://api.predic8.de

End a script with CONTINUE when it only changes values. Otherwise the value of the last expression may become the new body.

Return a Response from Groovy

api:
  port: 2000
  flow:
    - groovy:
        src: |
          Response.ok()
            .contentType("application/json")
            .header("X-Foo", "bar")
            .body('{"success": true}')
            .build()
api:
  port: 2000
  flow:
    - groovy:
        src: |
          Response.ok()
            .contentType("application/json")
            .header("X-Foo", "bar")
            .body('{"success": true}')
            .build()

Build JSON with JavaScript

api:
  port: 2000
  flow:
    - request:
        - javascript:
            src: |
              // Returned object becomes the JSON body
              ({ id: params.get('id')?.[0], city: params.get('city')?.[0] })
    - return:
        contentType: application/json
api:
  port: 2000
  flow:
    - request:
        - javascript:
            src: |
              // Returned object becomes the JSON body
              ({ id: params.get('id')?.[0], city: params.get('city')?.[0] })
    - return:
        contentType: application/json

Compute Values with SpEL

api:
  port: 2000
  flow:
    - request:
        - if:
            test: isJSON() and jsonPath('$.total') > 100
            flow:
              - setHeader:
                  name: X-Priority
                  value: high
    - response:
        - setHeader:
            name: X-Method
            value: ${method}
  target:
    url: https://api.predic8.de
api:
  port: 2000
  flow:
    - request:
        - if:
            test: isJSON() and jsonPath('$.total') > 100
            flow:
              - setHeader:
                  name: X-Priority
                  value: high
    - response:
        - setHeader:
            name: X-Method
            value: ${method}
  target:
    url: https://api.predic8.de

Render a Template with Groovy

api:
  port: 2000
  flow:
    - response:
        - template:
            contentType: text/plain
            src: |
              Method: ${method}
              Path: ${path}
              Date: ${new Date()}
    - return:
        status: 200
api:
  port: 2000
  flow:
    - response:
        - template:
            contentType: text/plain
            src: |
              Method: ${method}
              Path: ${path}
              Date: ${new Date()}
    - return:
        status: 200

Tutorials and Examples

The Membrane distribution contains runnable tutorials. Start Membrane in the tutorial folder with the YAML file as argument and follow the instructions in the file.