Signage/tests/browser/media-cache.test.ts

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);
  });
});