Normally, workers are designed to return some kind of HTTP Response and exit immediately upon receiving an HTTP request. FetchEvent can extend these life cycles.

WaitUntil

WaitUntil extends the lifetime of the "fetch" event. It accepts an asynchronous task which the Workers runtime will execute without blocking the response. The worker will not be terminated until those tasks are completed.

PassThroughOnException

PassThroughOnException prevents a runtime error response when the Worker script throws an unhandled exception. Instead, the request forwards to the origin server as if it had not gone through the worker.

Example

Usecase

You have decided to implement a log stream API to capture all access logs. You must edit the Headers so that the user's API token is not logged. If an unknown error occurs during this process, the entire service will be down, which must be avoided. In such cases, declare PassThroughOnException first and use WaitUntil for logging.

Setup

This example worker is triggered by Routes. To try this example, add your site to cloudflare and add some records(A and CNAME, etc.) so that you can actually access the website. If your domain is sub.example.com, edit wrangler.toml as following:

routes = [
    { pattern = "sub.example.com/*", zone_name = "example.com" }
]

The workers is executed if the URL matches sub.example.com/*.

Development

Requirements

This project requires these tools to be installed globally.

wrangler
tinygo

Commands

make dev     # run dev server
make build   # build Go Wasm binary
make deploy # deploy worker