ci/display-scenarios

@@ -4,3 +4,4 @@
 two-pages
 session-blip
 stream-failure
+stream-recycle

src/browser/storage.ts

@@ -36,6 +36,9 @@ export interface SignageMediaCache {
    * can never leave a screen with less than it had. */
   prune(keep: readonly string[]): Promise<void>;
   count(): Promise<number>;
+  /** Gives back every local URL this cache handed out. Called when a display stops; a URL handed
+   * out before this is no longer valid afterwards. */
+  release(): void;
 }
 
 /** The stable key a native image's bytes are cached under. Deliberately built from identity, never
@@ -86,6 +89,9 @@ export function createMemoryMediaCache(): SignageMediaCache {
       }
       return Promise.resolve();
     },
+    release(): void {
+      // Holds plain URLs, nothing the browser has to be given back.
+    },
     store(key: string, url: string): Promise<string | undefined> {
       stored.set(key, url);
       return Promise.resolve(url);
@@ -179,14 +185,45 @@ export function createBrowserMediaCache(scope: typeof globalThis = globalThis):
     return `${origin}/${key}`;
   }
 
-  async function localUrl(cache: Cache, url: string): Promise<string | undefined> {
+  /**
-    const response = await cache.match(url);
+   * The one object URL each cached slide is rendered from, by cache entry.
+   *
+   * An object URL pins its blob in the browser until it is revoked. Every state refresh looks every
+   * cached slide up again, so minting a URL per lookup leaked a blob per slide per refresh, and
+   * within minutes the browser refused the display's own requests for want of resources. So each
+   * entry gets exactly one URL, revoked when the entry is pruned or replaced, and all of them when
+   * the display stops.
+   */
+  const objectUrls = new Map<string, string>();
+
+  function forget(request: string): void {
+    const url = objectUrls.get(request);
+    if (url !== undefined) {
+      objectUrls.delete(request);
+      URL.revokeObjectURL(url);
+    }
+  }
+
+  async function localUrl(cache: Cache, request: string): Promise<string | undefined> {
+    const existing = objectUrls.get(request);
+    if (existing !== undefined) {
+      return existing;
+    }
+    const response = await cache.match(request);
     if (!response) {
       return undefined;
     }
     try {
       const blob = await response.blob();
-      return URL.createObjectURL(blob);
+      // Two lookups of one slide can be in flight at once; the first to finish wins, and the other
+      // gives its URL straight back rather than leaving it pinned.
+      const raced = objectUrls.get(request);
+      if (raced !== undefined) {
+        return raced;
+      }
+      const url = URL.createObjectURL(blob);
+      objectUrls.set(request, url);
+      return url;
     } catch {
       return undefined;
     }
@@ -220,6 +257,7 @@ export function createBrowserMediaCache(scope: typeof globalThis = globalThis):
         for (const request of await cache.keys()) {
           if (!retained.has(request.url)) {
             await cache.delete(request);
+            forget(request.url);
           }
         }
       } catch {
@@ -227,6 +265,12 @@ export function createBrowserMediaCache(scope: typeof globalThis = globalThis):
       }
     },
 
+    release(): void {
+      for (const request of [...objectUrls.keys()]) {
+        forget(request);
+      }
+    },
+
     async store(key: string, url: string): Promise<string | undefined> {
       const cache = await open();
       if (!cache) {
@@ -242,6 +286,8 @@ export function createBrowserMediaCache(scope: typeof globalThis = globalThis):
         // Stored under the *stable* key, so the next refresh's freshly signed URL finds these
         // bytes instead of downloading them again.
         await cache.put(cacheRequest(key), response.clone());
+        // New bytes under this key: the URL for the old ones is given back before one is made.
+        forget(cacheRequest(key));
         return localUrl(cache, cacheRequest(key));
       } catch {
         return undefined;

src/display/controller.ts

@@ -715,6 +715,8 @@ export function createDisplayController(options: DisplayControllerOptions): Disp
       exitOffline();
       await stage?.destroy();
       stage = undefined;
+      // After the stage is gone, so nothing on screen still points at a released URL.
+      media.release();
     },
   };
 

tests/browser/media-cache.test.ts

@@ -0,0 +1,119 @@
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { createBrowserMediaCache, type SignageMediaCache } from "../../src/browser/storage.js";
+
+/**
+ * The Cache Storage media cache hands out object URLs, and every live one pins its blob in the
+ * browser until it is revoked.
+ *
+ * Every state refresh looks up every cached slide, so a cache that minted a fresh URL per lookup
+ * leaked one blob per slide per refresh. In a real browser that exhausted blob storage within
+ * minutes: the display's own state requests then failed with `net::ERR_INSUFFICIENT_RESOURCES` and
+ * it fell back to its offline banner on a perfectly good network.
+ */
+
+/** Just enough Cache Storage: one named cache, keyed by request URL. */
+function fakeCacheStorage() {
+  const entries = new Map<string, { body: ArrayBuffer; type: string }>();
+  const cache = {
+    async delete(request: Request | string): Promise<boolean> {
+      return entries.delete(typeof request === "string" ? request : request.url);
+    },
+    async keys(): Promise<Request[]> {
+      return [...entries.keys()].map((url) => new Request(url));
+    },
+    async match(request: Request | string): Promise<Response | undefined> {
+      const entry = entries.get(typeof request === "string" ? request : request.url);
+      return entry
+        ? new Response(entry.body, { headers: { "content-type": entry.type } })
+        : undefined;
+    },
+    async put(request: Request | string, response: Response): Promise<void> {
+      entries.set(typeof request === "string" ? request : request.url, {
+        body: await response.arrayBuffer(),
+        type: response.headers.get("content-type") ?? "application/octet-stream",
+      });
+    },
+  };
+  return { open: async () => cache } as unknown as CacheStorage;
+}
+
+describe("Signage's media cache and object URLs", () => {
+  const realCreate = URL.createObjectURL;
+  const realRevoke = URL.revokeObjectURL;
+  let live: Set<string>;
+  let media: SignageMediaCache;
+
+  beforeEach(() => {
+    live = new Set();
+    let next = 0;
+    URL.createObjectURL = () => {
+      next += 1;
+      const url = `blob:test/${next}`;
+      live.add(url);
+      return url;
+    };
+    URL.revokeObjectURL = (url: string) => {
+      live.delete(url);
+    };
+    media = createBrowserMediaCache({
+      caches: fakeCacheStorage(),
+      fetch: async () =>
+        new Response(new Uint8Array([1, 2, 3]), { headers: { "content-type": "image/webp" } }),
+      location: { origin: "https://api.example.test" },
+    } as unknown as typeof globalThis);
+  });
+
+  afterEach(() => {
+    URL.createObjectURL = realCreate;
+    URL.revokeObjectURL = realRevoke;
+  });
+
+  const keys = ["slide/a", "slide/b", "slide/c"];
+
+  it("keeps one live object URL per cached slide, however often it is looked up", async () => {
+    for (const key of keys) {
+      await media.store(key, `https://files.example.test/${key}?sig=1`);
+    }
+    // A state refresh looks every slide up again; a long-running display does this for months.
+    for (let refresh = 0; refresh < 100; refresh += 1) {
+      for (const key of keys) {
+        await media.find(key);
+      }
+    }
+    expect(live.size).toBe(keys.length);
+  });
+
+  it("hands out the same URL for the same bytes", async () => {
+    await media.store("slide/a", "https://files.example.test/a?sig=1");
+    const first = await media.find("slide/a");
+    const second = await media.find("slide/a");
+    expect(first).toBeDefined();
+    expect(second).toBe(first);
+  });
+
+  it("revokes a pruned slide's URL", async () => {
+    for (const key of keys) {
+      await media.store(key, `https://files.example.test/${key}?sig=1`);
+      await media.find(key);
+    }
+    await media.prune(["slide/a"]);
+    expect(live.size).toBe(1);
+    expect(await media.find("slide/b")).toBeUndefined();
+  });
+
+  it("revokes the URL it replaces when a slide is stored again", async () => {
+    await media.store("slide/a", "https://files.example.test/a?sig=1");
+    await media.store("slide/a", "https://files.example.test/a?sig=2");
+    await media.find("slide/a");
+    expect(live.size).toBe(1);
+  });
+
+  it("releases every URL it handed out when the display stops", async () => {
+    for (const key of keys) {
+      await media.store(key, `https://files.example.test/${key}?sig=1`);
+      await media.find(key);
+    }
+    media.release();
+    expect(live.size).toBe(0);
+  });
+});