Middleware scripts

Middleware scripts act as intermediaries within the CDN request workflow, allowing you to insert custom logic that modifies requests or responses as they pass through the CDN.

Use cases

Authentication and authorization — Verify credentials and manage session tokens at the edge
Header injection and manipulation — Add, modify, or remove HTTP headers on requests and responses
Response body transformation — Rewrite HTML, inject scripts, or modify content before delivery
A/B testing and feature flags — Route users to different versions based on headers or cookies
Request routing and redirects — Direct traffic based on path, geolocation, or custom logic
Security enhancements — Implement rate limiting, IP filtering, or bot protection

Benefits

Middleware scripts provide the flexibility to integrate complex logic into the CDN request flow without modifying backend infrastructure. By processing requests and responses directly at the edge, these scripts improve the overall speed and efficiency of content delivery while reducing reliance on backend processing power.

The `servePullZone` function

The servePullZone function creates a middleware handler that integrates with your Pull Zone. It returns a chainable object for adding request and response middleware.

import * as BunnySDK from "@bunny.net/edgescript-sdk";

BunnySDK.net.http
  .servePullZone({ url: "https://your-origin.com" })
  .onOriginRequest((ctx) => {
    // Modify or intercept requests
    return Promise.resolve(ctx.request);
  })
  .onOriginResponse((ctx) => {
    // Modify responses
    return Promise.resolve(ctx.response);
  });

Function signature

servePullZone(options: { url: string }): PullZoneHandler

Option	Type	Description
`url`	`string`	The origin URL to proxy requests to. Only used during local development; in production, the Pull Zone origin is used.

The url option is only used during local development. When deployed to bunny.net, requests are proxied to the origin configured in your Pull Zone settings.

Middleware methods

The servePullZone function returns a PullZoneHandler object with chainable middleware methods:

`onClientRequest`

Preview

If your PullZone is configured to execute script before cache, you’ll have access to this function.

Intercepts requests before they are sent to the cache. You can modify the request or short-circuit by returning a response directly.

onClientRequest(
  middleware: (ctx: { request: Request }) => Promise<Response> | Response | Promise<Request> | Request | void
): PullZoneHandler

Property	Type	Description
`ctx.request`	`Request`	The incoming request object

Return value:

Return Promise<Request> to continue to the origin with the (modified) request
Return Promise<Response> to short-circuit and respond immediately without hitting the cache

`onClientResponse`

Preview

If your PullZone is configured to execute script before cache, you’ll have access to this function.

Intercepts requests before they are returned to the user even after you return a cached response.

onClientResponse(
  middleware: (ctx: { request: Request; response: Response }) => Promise<Response> | Response
): PullZoneHandler

Property	Type	Description
`ctx.request`	`Request`	The original request object
`ctx.response`	`Response`	The response from the origin server

Return value:

Return Promise<Response> or Response with the (modified) response to send to the client.

`onOriginRequest`

Intercepts requests before they are sent to the origin server. You can modify the request or short-circuit by returning a response directly.

onOriginRequest(
  middleware: (ctx: { request: Request }) => Promise<Request> | Promise<Response>
): PullZoneHandler

Property	Type	Description
`ctx.request`	`Request`	The incoming request object

Return value:

Return Promise<Request> to continue to the origin with the (modified) request
Return Promise<Response> to short-circuit and respond immediately without hitting the origin

`onOriginResponse`

Intercepts responses from the origin server before they are sent to the client. Modifications occur before the response is cached.

onOriginResponse(
  middleware: (ctx: { request: Request; response: Response }) => Promise<Response>
): PullZoneHandler

Property	Type	Description
`ctx.request`	`Request`	The original request object
`ctx.response`	`Response`	The response from the origin server

Return value:

Return Promise<Response> with the (modified) response to send to the client

Enable Before Cache Scripts

Preview To enable Middleware script to run before cache, you’ll need to enable it at your PullZone level. Navigate to your Pull Zone, then go to General > Origin and enable Run script before cache.

Learn more about before cache execution.

Workflow

When a client makes a request to a Pull Zone, the request passes through middleware at different stages:

If your PullZone is configured to execute script before cache, you’ll run the onClientRequest and onClientResponse if those are registered.

onClientRequest - Called before the request is sent to the cache. Modify the request or return a response to short-circuit.
onOriginRequest - Called before the request is sent to the origin (so if the cache is giving a MISS). Modify the request or return a response to short-circuit.
Origin fetch - The request is sent to your origin server.
onOriginResponse - Called after the origin responds. Modify the response before it’s sent to the client and cached.
onClientResponse - Called just before a Response is sent to the client expect if you short circuit it at the onClientRequest layer.

Example

This example implements access control based on feature flags and adds a custom header to responses:

import * as BunnySDK from "@bunny.net/edgescript-sdk";

BunnySDK.net.http
  .servePullZone({ url: "https://echo.free.beeceptor.com/" })
  .onOriginRequest((ctx) => {
    const optFT = ctx.request.headers.get("feature-flags");
    const featureFlags = optFT
      ? optFT.split(",").map((v) => v.trimStart())
      : [];

    // Route-based matching and feature flag check
    const path = new URL(ctx.request.url).pathname;
    if (path === "/d") {
      if (!featureFlags.includes("route-d-preview")) {
        // Short-circuit: return response without hitting origin
        return Promise.resolve(
          new Response("You cannot use this route.", { status: 400 }),
        );
      }
    }

    // Continue to origin with the request
    return Promise.resolve(ctx.request);
  })
  .onOriginResponse((ctx) => {
    // Add custom header to response
    ctx.response.headers.append("X-Via", "MyMiddleware");
    return Promise.resolve(ctx.response);
  });

Local development

You can run middleware scripts locally using Deno:

deno run -A script.ts

Test with curl:

# Blocked - missing required feature flag
curl http://127.0.0.1:8080/d --header 'feature-flags: something-else'

# Allowed - has required feature flag
curl http://127.0.0.1:8080/d --header 'feature-flags: route-d-preview, something-else'

Documentation

Script Types

Deployment

Observability

APIs

Reference

Use cases

Benefits

The `servePullZone` function

Function signature

Middleware methods

`onClientRequest`

`onClientResponse`

`onOriginRequest`

`onOriginResponse`

Enable Before Cache Scripts

Workflow

Example

Local development

​Use cases

​Benefits

​The servePullZone function

​Function signature

​Middleware methods

​onClientRequest

​onClientResponse

​onOriginRequest

​onOriginResponse

​Enable Before Cache Scripts

​Workflow

​Example

​Local development

Use cases

Benefits

The `servePullZone` function

Function signature

Middleware methods

`onClientRequest`

`onClientResponse`

`onOriginRequest`

`onOriginResponse`

Enable Before Cache Scripts

Workflow

Example

Local development