Middleware scripts

Middleware scripts sit inside the CDN request flow. Your logic runs on requests on their way in and on responses on their way out, so you can change how traffic behaves without touching your backend, and the work happens at the edge rather than on your origin. A middleware script can run at two points in the request flow:

Origin hooks (onOriginRequest, onOriginResponse) run between the cache and your origin. They run only on a cache MISS. This is the default.
Client hooks (onClientRequest, onClientResponse) run between the client and the cache. They run on every request, including cache hits. To use them, enable Run script before cache in your Pull Zone, under General > Origin. See before cache execution.

One script can use both types of hooks.

Choose a hook

Hook	Runs	Runs on a cache HIT	Needs Run script before cache	Example uses (not a complete list)
`onClientRequest`	Before the cache lookup	Yes	Yes	Verify credentials, rate limiting, IP filtering, bot protection, A/B tests, redirects
`onOriginRequest`	Before the request goes to the origin	No	No	Add or remove headers on the request to the origin, such as a secret the origin checks
`onOriginResponse`	After the origin responds, before cache	No	No	Rewrite HTML or the response body, set headers that are cached with the response
`onClientResponse`	Before the response goes to the client	Yes	Yes	Add headers to every response, including cached responses

Origin hooks run only on a cache MISS. The CDN serves a cached response without them. An access check in onOriginRequest does not protect cached content. For access control, enable before cache execution, and put the check in onClientRequest.

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@0.13.0";

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`

This hook runs only when your Pull Zone has before cache execution enabled. If it is off, the hook does not run, and no error shows.

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 cache lookup with the (modified) request. On a cache MISS, the request then goes to the origin.
Return Promise<Response> to short-circuit and respond immediately without hitting the cache. onClientResponse does not run for this response.

`onClientResponse`

This hook runs only when your Pull Zone has before cache execution enabled.

Intercepts responses before they are returned to the user, including responses served from the cache.

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. It runs only on a cache MISS. 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. The CDN handles this response like an origin response, so it can be cached.

`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

Before cache execution is turned on per Pull Zone. 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:

onClientRequest and onClientResponse run only when your Pull Zone has before cache execution enabled.

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 only when the cache returns 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, unless you short-circuited at the onClientRequest layer.

Example

This example gates a route behind a feature flag, and adds a custom header to responses from the origin. The flag check runs in onClientRequest, so it also applies to cached responses. Enable before cache execution to run it.

import * as BunnySDK from "@bunny.net/edgescript-sdk@0.13.0";

BunnySDK.net.http
  .servePullZone({ url: "https://echo.free.beeceptor.com/" })
  .onClientRequest((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 the cache or the origin
        return Promise.resolve(
          new Response("You cannot use this route.", { status: 400 }),
        );
      }
    }

    // Continue to the cache lookup with the request
    return Promise.resolve(ctx.request);
  })
  .onOriginResponse((ctx) => {
    // Add custom header to the response before it is cached
    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

Choose a hook

The `servePullZone` function

Function signature

Middleware methods

`onClientRequest`

`onClientResponse`

`onOriginRequest`

`onOriginResponse`

Enable before cache scripts

Workflow

Example

Local development

​Choose a hook

​The servePullZone function

​Function signature

​Middleware methods

​onClientRequest

​onClientResponse

​onOriginRequest

​onOriginResponse

​Enable before cache scripts

​Workflow

​Example

​Local development

Choose a hook

The `servePullZone` function

Function signature

Middleware methods

`onClientRequest`

`onClientResponse`

`onOriginRequest`

`onOriginResponse`

Enable before cache scripts

Workflow

Example

Local development