Cloudflare Worker times out for the client, but all the work completes and no timeout error given (inspected with console.log/ `wrangler tail`) - cloudflare-workers

Question

My published Cloudflare Worker (wrangler publish --env environment_name) is timing out for clients, but not when
running locally (e.g. by using cfworker, a nice tool to emulate cloudflare workers locally)
or running in preview (wrangler preview --env environment_name).
A summary of my worker:
addEventListener('fetch', async (event) => {
const fetchEvent = event as FetchEvent
const results = await doSomeWork() // returns a promise
return fetchEvent.respondWith(new Response(JSON.stringify(results)))
})
My wrangler tail (production logs) output does complete (after I placed console.log statements in doSomeWork. There were no errors, and I got {"outcome":"ok"... in wrangler tail. I would have expected to get error code 1102 (Worker exceeded CPU time limit.) if time-out was happening.

Answer 1

It turns out that addEventListener cannot be passed an async function (or one that returns a promise). The fetchEvent.respondWith does accept a promise however. This is not written in the documentation, but I discovered this in lib.webworker.d.ts.
To do asynchronous work, you must return a promise to fetchEvent.respondWith instead:
So your alternatives are to:
Pass a promise to respondWith
addEventListener('fetch' (event) => {
const fetchEvent = event as FetchEvent
const responsePromise = doSomeWork().then((results) => new Response(JSON.stringify(results))
return fetchEvent.respondWith(responsePromise))
})
Or pass the result of an async function to respondWith (still a promise, I told you, you must return a promise)
addEventListener('fetch' (event) => {
const fetchEvent = event as FetchEvent
const responsePromise =
return fetchEvent.respondWith(async () => {
// I would put this async function in a different file (handlers.ts/.js), and name it `doSomeWorkHandler` to make it more readable though
const results = await doSomeWork()
return new Response(JSON.stringify({hello: "world"}))
}))
})
Why no timeout error?
The reason the timeout error doesn't happen is because even though Cloudflare Workers limits your CPU execution time to 10ms on the free plan, it doesn't stop your worker because you're not using the CPU in this bug/ edge case. It's doing nothing.