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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.

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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

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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.

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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);
  });

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Function signature

servePullZone(options: { url: string }): PullZoneHandler
OptionTypeDescription
urlstringThe 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.

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Middleware methods

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

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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
PropertyTypeDescription
ctx.requestRequestThe 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

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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
PropertyTypeDescription
ctx.requestRequestThe original request object
ctx.responseResponseThe response from the origin server
Return value:
  • Return Promise<Response> with the (modified) response to send to the client

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Workflow

When a client makes a request to a Pull Zone, the request passes through middleware at different stages:
  1. onOriginRequest - Called before the request is sent to the origin. Modify the request or return a response to short-circuit.
  2. Origin fetch - The request is sent to your origin server (skipped if short-circuited).
  3. onOriginResponse - Called after the origin responds. Modify the response before it’s sent to the client and cached.

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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);
  });

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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'