URL Forward Handler

The URL Forward handler can be used to proxy requests to a different API without writing any code. It simply appends the incoming path section of the URL onto the specified baseUrl property. For example:

If you have an incoming request with url


And you have a URL forward handler with a baseUrl of https://my-backend.com/folder - the gateway will make a request to

https://my-backend.com/folder/pizza/cheese/size/large. By default it will forward any search parameters.

Setup via Portal#

The Forward Handler can be added to any route using the Route Designer. Open the Route Designer by navigating to the Files tab then click routes.oas.json. Inside any route, select URL Forward from the Request Handlers drop-down.

In the text box enter the URL to rewrite the request. Values can be mixed into the URL string using Javascript string interpolation syntax. For example:


The following objects are available for substitution:

  • env - the environment object, to access Environment Variables
  • request: ZuploRequest - the full ZuploRequest object
  • context: ZuploContext - the ZuploContext object without functions.
  • params: Record<string, string> - The parameters of the route. For example, params.productId would be the value of :productId in a route.
  • query: Record<string, string> - The query parameters of the route. For example, query.filterBy would be the value of ?filterBy=VALUE.
  • headers: Headers - the incoming request's headers object
  • url: string - The full incoming request as a string
  • host: string - The host portion of the incoming URL
  • hostname: string - The hostname portion of the incoming URL
  • pathname: string - The pathname portion of the incoming URL
  • port: string - The port portion of the incoming URL
  • search - The search portion of the incoming URL

Use the following methods to encode portions of the URL:

  • encodeURIComponent: The encodeURIComponent() function encodes a URI by replacing each instance of certain characters with escape sequences.
  • e: An alias to encodeURIComponent to help keep URLs more readable. Can be used like ${e(params.productId)}

Example Values#

A few examples of the values of various substitutions.

  • ${headers.get("content-type")} - "application/json"
  • ${host} - "example.com:8080"
  • ${hostname} - "example.com"
  • ${method} - "GET"
  • ${origin} - "https://example.com"
  • ${params.productId} - ":productId"
  • ${pathname} - "/v1/products/:productId"
  • ${port} - "8080"
  • ${protocol} - "https:"
  • ${query.category} - "cars"
  • ${search} - "?category=cars"
  • ${url} - "https://example.com:8080/v1/products/:productId?category=cars"
  • ${env.BASE_URL} - "https://example.com"

Setup via routes.oas.json#

The URL Forward handler can also be added manually to the routes.oas.json file with the following route configuration.

"paths": { "/forward-test": { "x-zuplo-path": { "pathMode": "open-api" }, "get": { "summary": "Testing forward handler", "x-zuplo-route": { "corsPolicy": "none", "handler": { "export": "urlForwardHandler", "module": "$import(@zuplo/runtime)", "options": { "baseUrl": "${env.BASE_URL}" } }, "policies": { "inbound": [] } } } } }


The URL Rewrite handler can be configured via options to support common use-cases.

  • baseUrl - the base URL the incoming pathname will be appended to.
  • forwardSearch - The query string will be automatically included in the rewritten url.
  • followRedirects - Determines if redirects should be followed when fetching the rewrite url . When set to false or not specified, redirects will not be followed - the status and location header will be returned as received.

Different Backends per Environment#

It's common to want a different backend for your production, staging and preview environments. This can be easily achieved by using environment variables to specify the origin of the backend.

For example,


A url rewrite like this will combine the BASE_PATH environment variable, say https://example.com

Custom Code Outbound