FetchEvent

Extend the lifetime of a fetch event with waitUntil and passThroughOnException.

The cloudflare package exposes two FetchEvent lifecycle methods.

WaitUntil

cloudflare.WaitUntil keeps the worker alive after the response has been sent. Use it for logging, analytics, cache writes, and other work that should not delay the client.

func handler(w http.ResponseWriter, req *http.Request) {
	cloudflare.WaitUntil(func() {
		// runs after the response is returned
		writeAnalytics(req)
	})
	w.Write([]byte("ok"))
}

WaitUntil accepts a synchronous func() — run slow work inside it, and the Workers runtime waits for it to finish before terminating the invocation.

PassThroughOnException

cloudflare.PassThroughOnException forwards the request to the origin server when the worker throws an unhandled exception, instead of returning a runtime error response. It needs a route or custom domain configured on the worker.

func handler(w http.ResponseWriter, req *http.Request) {
	cloudflare.PassThroughOnException()
	// if this handler panics, the request goes to the origin
}

Example project

_examples/fetch-event combines both methods with a reverse proxy.