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Handlers

URL Forward Handler

The URL Forward handler proxies requests to a different API without writing any code. It appends the incoming path section of the URL onto the specified baseUrl property, making it ideal for creating API gateways and backend proxying.

How It Works

If you have an incoming request with URL: https://my-gateway.com/pizza/cheese/size/large

And a URL forward handler with baseUrl of https://my-backend.com/folder, the gateway makes a request to: https://my-backend.com/folder/pizza/cheese/size/large

By default, query parameters are forwarded automatically.

Setup via Portal

The Forward Handler can be added to any route using the Route Designer. Open the Route Designer by navigating to the Code 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:

Code
https://${env.BASE_HOST_NAME}/${method}/${params.productId}

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.

Code
"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": []
        }
      }
    }
  }
}

Options

The URL Forward handler accepts the following options:

• baseUrl (required): The base URL where the incoming pathname will be appended

  • Type: string
  • Supports template interpolation with environment variables and request properties
  • Example: "https://api.example.com" or "${env.BACKEND_URL}"

• forwardSearch (optional): Controls whether query parameters are forwarded

  • Type: boolean
  • Default: true
  • When true, query string is automatically included in forwarded URL

• followRedirects (optional): Controls redirect handling behavior

  • Type: boolean
  • Default: false
  • When false, redirects aren't followed - status and location header are returned as received
  • When true, redirects are automatically followed

Complete Example

Code
// routes.oas.json handler configuration
{
  "handler": {
    "export": "urlForwardHandler",
    "module": "$import(@zuplo/runtime)",
    "options": {
      "baseUrl": "${env.BACKEND_URL}",
      "forwardSearch": true,
      "followRedirects": false
    }
  }
}

Different Backends per Environment

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

For example,

Code
${env.BASE_PATH}

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

Code
https://example.com/foo/bar

Related Documentation

• URL Rewrite Handler - For more complex URL transformations
• Custom Handler - Building custom request handlers
• Environment Variables - Configuration management
• ZuploRequest - Request object reference
• ZuploContext - Context object reference