Refactor: speed up reject parsing

Build/lib/fetch-assets.ts

@@ -0,0 +1,61 @@
+import picocolors from 'picocolors';
+import { defaultRequestInit, fetchWithRetry } from './fetch-retry';
+
+class CustomAbortError extends Error {
+  public readonly name = 'AbortError';
+  public readonly digest = 'AbortError';
+}
+
+const sleepWithAbort = (ms: number, signal: AbortSignal) => new Promise<void>((resolve, reject) => {
+  signal.throwIfAborted();
+  signal.addEventListener('abort', stop);
+  Bun.sleep(ms).then(done).catch(doReject);
+
+  function done() {
+    signal.removeEventListener('abort', stop);
+    resolve();
+  }
+  function stop(this: AbortSignal) {
+    reject(this.reason);
+  }
+  function doReject(reason: unknown) {
+    signal.removeEventListener('abort', stop);
+    reject(reason);
+  }
+});
+
+export async function fetchAssets(url: string, fallbackUrls: string[] | readonly string[]) {
+  const controller = new AbortController();
+
+  const fetchMainPromise = fetchWithRetry(url, { signal: controller.signal, ...defaultRequestInit })
+    .then(r => r.text())
+    .then(text => {
+      controller.abort();
+      return text;
+    });
+  const createFetchFallbackPromise = async (url: string, index: number) => {
+    // Most assets can be downloaded within 250ms. To avoid wasting bandwidth, we will wait for 500ms before downloading from the fallback URL.
+    try {
+      await sleepWithAbort(500 + (index + 1) * 20, controller.signal);
+    } catch {
+      console.log(picocolors.gray('[fetch cancelled early]'), picocolors.gray(url));
+      throw new CustomAbortError();
+    }
+    if (controller.signal.aborted) {
+      console.log(picocolors.gray('[fetch cancelled]'), picocolors.gray(url));
+      throw new CustomAbortError();
+    }
+    const res = await fetchWithRetry(url, { signal: controller.signal, ...defaultRequestInit });
+    const text = await res.text();
+    controller.abort();
+    return text;
+  };
+
+  return Promise.any([
+    fetchMainPromise,
+    ...fallbackUrls.map(createFetchFallbackPromise)
+  ]).catch(e => {
+    console.log(`Download Rule for [${url}] failed`);
+    throw e;
+  });
+}