78 lines
2.5 KiB
TypeScript
78 lines
2.5 KiB
TypeScript
import { Comlink } from '@/deps.ts';
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import './handlers/abortsignal.ts';
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import type { FetchWorker } from './fetch.worker.ts';
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const worker = new Worker(new URL('./fetch.worker.ts', import.meta.url), { type: 'module' });
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const client = Comlink.wrap<typeof FetchWorker>(worker);
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// Wait for the worker to be ready before we start using it.
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const ready = new Promise<void>((resolve) => {
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const handleEvent = () => {
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self.removeEventListener('message', handleEvent);
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resolve();
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};
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worker.addEventListener('message', handleEvent);
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});
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/**
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* Fetch implementation with a Web Worker.
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* Calling this performs the fetch in a separate CPU thread so it doesn't block the main thread.
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*/
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const fetchWorker: typeof fetch = async (...args) => {
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await ready;
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const [url, init] = serializeFetchArgs(args);
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const { body, signal, ...rest } = init;
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const result = await client.fetch(url, { ...rest, body: await prepareBodyForWorker(body) }, signal);
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return new Response(...result);
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};
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/** Take arguments to `fetch`, and turn them into something we can send over Comlink. */
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function serializeFetchArgs(args: Parameters<typeof fetch>): [string, RequestInit] {
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const request = normalizeRequest(args);
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const init = requestToInit(request);
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return [request.url, init];
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}
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/** Get a `Request` object from arguments to `fetch`. */
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function normalizeRequest(args: Parameters<typeof fetch>): Request {
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return new Request(...args);
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}
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/** Get the body as a type we can transfer over Web Workers. */
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async function prepareBodyForWorker(
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body: BodyInit | undefined | null,
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): Promise<ArrayBuffer | Blob | string | undefined | null> {
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if (!body || typeof body === 'string' || body instanceof ArrayBuffer || body instanceof Blob) {
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return body;
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} else {
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const response = new Response(body);
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return await response.arrayBuffer();
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}
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}
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/**
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* Convert a `Request` object into its serialized `RequestInit` format.
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* `RequestInit` is a subset of `Request`, just lacking helper methods like `json()`,
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* making it easier to serialize (exceptions: `body` and `signal`).
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*/
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function requestToInit(request: Request): RequestInit {
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return {
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method: request.method,
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headers: [...request.headers.entries()],
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body: request.body,
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referrer: request.referrer,
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referrerPolicy: request.referrerPolicy,
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mode: request.mode,
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credentials: request.credentials,
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cache: request.cache,
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redirect: request.redirect,
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integrity: request.integrity,
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keepalive: request.keepalive,
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signal: request.signal,
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};
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}
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export { fetchWorker };
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