fix(web): improve request cancellation handling in service worker cache (#19217)

web/src/service-worker/cache.ts

@@ -0,0 +1,104 @@
+import { build, files, version } from '$service-worker';
+
+const useCache = true;
+const CACHE = `cache-${version}`;
+
+export const APP_RESOURCES = [
+  ...build, // the app itself
+  ...files, // everything in `static`
+];
+
+let cache: Cache | undefined;
+export async function getCache() {
+  if (cache) {
+    return cache;
+  }
+  cache = await caches.open(CACHE);
+  return cache;
+}
+
+export const isURL = (request: URL | RequestInfo): request is URL => (request as URL).href !== undefined;
+export const isRequest = (request: RequestInfo): request is Request => (request as Request).url !== undefined;
+
+export async function deleteOldCaches() {
+  for (const key of await caches.keys()) {
+    if (key !== CACHE) {
+      await caches.delete(key);
+    }
+  }
+}
+
+const pendingRequests = new Map<string, AbortController>();
+const canceledRequests = new Set<string>();
+
+export async function cancelLoad(urlString: string) {
+  const pending = pendingRequests.get(urlString);
+  if (pending) {
+    canceledRequests.add(urlString);
+    pending.abort();
+    pendingRequests.delete(urlString);
+  }
+}
+
+export async function getCachedOrFetch(request: URL | Request | string) {
+  const response = await checkCache(request);
+  if (response) {
+    return response;
+  }
+
+  const urlString = getCacheKey(request);
+  const cancelToken = new AbortController();
+
+  try {
+    pendingRequests.set(urlString, cancelToken);
+    const response = await fetch(request, {
+      signal: cancelToken.signal,
+    });
+
+    checkResponse(response);
+    await setCached(response, urlString);
+    return response;
+  } catch (error) {
+    if (canceledRequests.has(urlString)) {
+      canceledRequests.delete(urlString);
+      return new Response(undefined, {
+        status: 499,
+        statusText: 'Request canceled: Instructions unclear, accidentally interrupted myself',
+      });
+    }
+    throw error;
+  } finally {
+    pendingRequests.delete(urlString);
+  }
+}
+
+export async function checkCache(url: URL | Request | string) {
+  if (!useCache) {
+    return;
+  }
+  const cache = await getCache();
+  return await cache.match(url);
+}
+
+export async function setCached(response: Response, cacheKey: URL | Request | string) {
+  if (cache && response.status === 200) {
+    const cache = await getCache();
+    cache.put(cacheKey, response.clone());
+  }
+}
+
+function checkResponse(response: Response) {
+  if (!(response instanceof Response)) {
+    throw new TypeError('Fetch did not return a valid Response object');
+  }
+}
+
+export function getCacheKey(request: URL | Request | string) {
+  if (isURL(request)) {
+    return request.toString();
+  } else if (isRequest(request)) {
+    return request.url;
+  } else {
+    return request;
+  }
+}

web/src/service-worker/fetch-event.ts

@@ -1,6 +1,6 @@
 import { version } from '$service-worker';
+import { APP_RESOURCES, checkCache, getCacheKey, setCached } from './cache';
 
-const useCache = true;
 const CACHE = `cache-${version}`;
 
 export const isURL = (request: URL | RequestInfo): request is URL => (request as URL).href !== undefined;
@@ -24,20 +24,14 @@ export async function cancelLoad(urlString: string) {
   }
 }
 
-export async function getCachedOrFetch(request: URL | Request | string, cancelable: boolean = false) {
-  const cached = await checkCache(request);
-  if (cached.response) {
-    return cached.response;
+export async function getCachedOrFetch(request: URL | Request | string) {
+  const response = await checkCache(request);
+  if (response) {
+    return response;
   }
 
   try {
-    if (!cancelable) {
-      const response = await fetch(request);
-      checkResponse(response);
-      return response;
-    }
-
-    return await fetchWithCancellation(request, cached.cache);
+    return await fetchWithCancellation(request);
   } catch {
     return new Response(undefined, {
       status: 499,
@@ -46,7 +40,7 @@ export async function getCachedOrFetch(request: URL | Request | string, cancelab
   }
 }
 
-async function fetchWithCancellation(request: URL | Request | string, cache: Cache) {
+async function fetchWithCancellation(request: URL | Request | string) {
   const cacheKey = getCacheKey(request);
   const cancelToken = new AbortController();
 
@@ -57,44 +51,26 @@ async function fetchWithCancellation(request: URL | Request | string, cache: Cac
     });
 
     checkResponse(response);
-    setCached(response, cache, cacheKey);
+    setCached(response, cacheKey);
     return response;
   } finally {
     pendingLoads.delete(cacheKey);
   }
 }
 
-async function checkCache(url: URL | Request | string) {
-  if (!useCache) {
-    return;
-  }
-  const cache = await caches.open(CACHE);
-  const response = await cache.match(url);
-  return { cache, response };
-}
-
-async function setCached(response: Response, cache: Cache, cacheKey: URL | Request | string) {
-  if (response.status === 200) {
-    cache.put(cacheKey, response.clone());
-  }
-}
-
 function checkResponse(response: Response) {
   if (!(response instanceof Response)) {
-    throw new TypeError('invalid response from fetch');
+    throw new TypeError('Fetch did not return a valid Response object');
   }
 }
 
-function getCacheKey(request: URL | Request | string) {
-  if (isURL(request)) {
-    return request.toString();
-  } else if (isRequest(request)) {
-    return request.url;
-  } else {
-    return request;
-  }
+function isIgnoredFileType(pathname: string): boolean {
+  return /\.(png|ico|txt|json|ts|ttf|css|js|svelte)$/.test(pathname);
 }
 
+function isIgnoredPath(pathname: string): boolean {
+  return /^\/(src|api)(\/.*)?$/.test(pathname) || /^\/(node_modules|@vite|@id)(\/.*)?$/.test(pathname);
+}
 function isAssetRequest(pathname: string): boolean {
   return /^\/api\/assets\/[a-f0-9-]+\/(original|thumbnail)/.test(pathname);
 }
@@ -105,12 +81,30 @@ export function handleFetchEvent(event: FetchEvent): void {
   }
 
   const url = new URL(event.request.url);
+
+  // Only handle requests to the same origin
   if (url.origin !== self.location.origin) {
     return;
   }
 
-  if (isAssetRequest(url.pathname)) {
-    event.respondWith(getCachedOrFetch(event.request, true));
+  // Do not cache app resources
+  if (APP_RESOURCES.includes(url.pathname)) {
     return;
   }
+
+  // Cache requests for thumbnails
+  if (isAssetRequest(url.pathname)) {
+    event.respondWith(getCachedOrFetch(event.request));
+    return;
+  }
+
+  // Do not cache ignored file types or paths
+  if (isIgnoredFileType(url.pathname) || isIgnoredPath(url.pathname)) {
+    return;
+  }
+
+  // At this point, the only remaining requests for top level routes
+  // so serve the Svelte SPA fallback page
+  const slash = new URL('/', url.origin);
+  event.respondWith(getCachedOrFetch(slash));
 }

web/src/service-worker/index.ts

@@ -3,7 +3,8 @@
 /// <reference lib="esnext" />
 /// <reference lib="webworker" />
 import { installBroadcastChannelListener } from './broadcast-channel';
-import { deleteOldCaches, handleFetchEvent } from './fetch-event';
+import { deleteOldCaches } from './cache';
+import { handleFetchEvent } from './fetch-event';
 
 const sw = globalThis as unknown as ServiceWorkerGlobalScope;
 
@@ -14,6 +15,7 @@ const handleActivate = (event: ExtendableEvent) => {
 
 const handleInstall = (event: ExtendableEvent) => {
   event.waitUntil(sw.skipWaiting());
+  // do not preload app resources
 };
 
 sw.addEventListener('install', handleInstall, { passive: true });