miru/app/sw.js

self.addEventListener('install', e => {
	self.skipWaiting();
});

self.addEventListener('activate', e => {
	return self.clients.claim()
})

self.addEventListener('fetch', evt => {
	const { request } = evt
	const { url, method, headers } = request
	if (!url.includes(self.registration.scope + 'webtorrent/')) return null

	function getConsumer(clients) {
		return new Promise(rs => {
			// Use race condition for whoever controls the response stream
			for (const client of clients) {
				const mc = new MessageChannel()
				const { port1, port2 } = mc
				port1.onmessage = evt => {
					rs([evt.data, mc])
				}
				client.postMessage({
					url,
					method,
					headers: [...headers],
					scope: self.registration.scope
				}, [port2])
			}
		})
	}

	evt.respondWith(
		clients.matchAll({ type: 'window', includeUncontrolled: true })
			.then(getConsumer)
			.then(([data, mc]) => {
				let tm = null
				const body = data.body === 'stream' ? new ReadableStream({
					pull(controller) {
						return new Promise(rs => {
							mc.port1.onmessage = evt => {
								if (evt.data) {
									controller.enqueue(evt.data) // evt.data is Uint8Array
								} else {
									clearTimeout(tm)
									controller.close() // evt.data is null, means the stream ended
									mc.port1.onmessage = null
								}
								rs()
							}

							clearTimeout(tm)
							tm = setTimeout(() => {
								controller.close()
								mc.port1.postMessage(false) // send timeout
								mc.port1.onmessage = null
								rs()
							}, 5000)

							mc.port1.postMessage(true) // send a pull request
						})
					},
					cancel() {
						// This event is never executed
						mc.port1.postMessage(false) // send a cancel request
					}
				}) : data.body

				return new Response(body, data)
			})
			.catch(console.error)
	)
})