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https://github.com/mauriceboe/TREK.git
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Maurice
98 lines
3.7 KiB
TypeScript
98 lines
3.7 KiB
TypeScript
import { TrekShell } from './trekShell';
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/**
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* iOS only. WKWebView runs no service worker for a domain the app does not
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* list at build time, so the app stands in for it: the native side keeps a
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* copy of the start page (TrekShellPlugin.refreshOfflineCopy), and this pulls
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* every chunk of the current build into WebKit's HTTP cache. The server marks
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* them immutable, so a cold start without network can load the stored start
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* page under the server's origin and find all its scripts, including the lazy
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* routes nobody has opened yet.
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*/
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const MANIFEST_URL = '/asset-manifest.json';
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/**
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* Few at a time and at low priority: the warm-up runs while the user already
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* moves through the app, and the page they open must never queue behind it.
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* Measured on a phone: four at normal priority held a first visit to Vacay
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* back by five to seven seconds right after a server update.
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*/
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const CONCURRENCY = 2;
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/** The build whose files are all in the cache; a launch on the same build skips the walk. */
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const WARMED_KEY = 'trek.offlineShellBuild';
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const LOCALE_KEY = /\/i18n\/([^/]+)\/index\.[cm]?js$/;
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interface ManifestChunk {
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file?: string;
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css?: string[];
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assets?: string[];
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}
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/**
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* Every file of the build, without the translations of other languages: only
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* the user's own and English (the fallback) are needed offline, the other 25
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* would cost several megabytes per build for nothing.
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*/
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export function manifestFiles(manifest: unknown, language?: string): string[] {
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if (typeof manifest !== 'object' || manifest === null) return [];
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const keep = new Set(['en', language ?? 'en']);
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const files = new Set<string>();
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for (const [key, chunk] of Object.entries(manifest as Record<string, ManifestChunk>)) {
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const locale = LOCALE_KEY.exec(key)?.[1];
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if (locale && !keep.has(locale)) continue;
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if (typeof chunk?.file === 'string') files.add(chunk.file);
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for (const list of [chunk?.css, chunk?.assets]) {
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if (Array.isArray(list)) list.forEach((f) => typeof f === 'string' && files.add(f));
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}
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}
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return [...files];
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}
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/** True when every file was fetched. */
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async function warmCache(files: string[], fetchFile: (path: string) => Promise<unknown>): Promise<boolean> {
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const queue = [...files];
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let complete = true;
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const worker = async (): Promise<void> => {
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for (let path = queue.shift(); path !== undefined; path = queue.shift()) {
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try {
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await fetchFile(`/${path}`);
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} catch {
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// One missing chunk must not stop the rest; the next launch tries again.
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complete = false;
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}
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}
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};
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await Promise.all(Array.from({ length: CONCURRENCY }, worker));
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return complete;
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}
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function warmedBuild(): string | null {
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try {
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return window.localStorage.getItem(WARMED_KEY);
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} catch {
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return null;
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}
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}
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function rememberWarmed(build: string): void {
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try {
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window.localStorage.setItem(WARMED_KEY, build);
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} catch {
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// Not remembered: the next launch walks the files again, from the cache.
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}
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}
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export async function keepOfflineShellFresh(fetchImpl: typeof fetch = fetch, language?: string): Promise<void> {
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await TrekShell.refreshOfflineCopy();
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const response = await fetchImpl(MANIFEST_URL, { cache: 'no-store' });
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if (!response.ok) return;
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const files = manifestFiles(await response.json(), language);
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// The build and the language together: a new language needs its own chunk.
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const build = `${[...files].sort((a, b) => a.localeCompare(b)).find((f) => /index-[^/]+\.js$/.test(f)) ?? files.length}:${language ?? 'en'}`;
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if (warmedBuild() === build) return;
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const complete = await warmCache(files, (path) =>
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fetchImpl(path, { priority: 'low' } as RequestInit).then((r) => r.blob())
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);
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if (complete) rememberWarmed(build);
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}
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