mokosh/tests/offscreen/port-reconnect-race.test.ts

// tests/offscreen/port-reconnect-race.test.ts
//
// RED-gate tests for debug session empty-archive-port-race
// (.planning/debug/empty-archive-port-race.md).
//
// Empirically pins the two coupled defects observed in Phase 1 UAT Test 3:
//
//   H1  Pre-emptive reconnect at 290 s leaves the ping interval briefly
//       able to fire against a Port whose remote end has been disconnected,
//       throwing "Attempting to use a disconnected port object" — 3
//       uncaught errors observed in the offscreen console.
//
//   H2  REQUEST_BUFFER round-trip silently drops BUFFER when the port is
//       replaced mid-encode (src/offscreen/recorder.ts:597 stale-port
//       refuse) AND when the SW's videoPort is null at request time
//       (src/background/index.ts:128 fast-bailout). The SW then times
//       out (BUFFER_FETCH_TIMEOUT_MS = 2 s) and resolves
//       `{ segments: [] }`, which createArchive's branch at
//       src/background/index.ts:346 silently elides into a video-less
//       archive. Operator-visible result: 88 KB zip with NO
//       video/last_30sec.webm.
//
// These tests drive the REAL src/offscreen/recorder.ts module via the
// established chrome-stub harness (same scaffold as
// tests/offscreen/port.test.ts + handshake.test.ts). No source-code
// re-implementation — the production module is what we're testing.

import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';

interface PortStub {
  name: string;
  // Throw-on-disconnected-postMessage: simulates the real Chrome behaviour
  // documented at https://developer.chrome.com/docs/extensions/develop/concepts/messaging
  // — postMessage on a disconnected Port throws synchronously with
  // "Attempting to use a disconnected port object".
  postMessage: ReturnType<typeof vi.fn>;
  onMessage: {
    addListener: ReturnType<typeof vi.fn>;
    // capture for synthetic dispatch
    _listeners: Array<(msg: unknown) => void>;
  };
  onDisconnect: {
    addListener: (fn: () => void) => void;
    // capture for synthetic dispatch
    _listeners: Array<() => void>;
  };
  disconnect: ReturnType<typeof vi.fn>;
  // test seam — flip this to true to simulate the remote disconnect
  // having taken effect before the next postMessage runs.
  _disconnected: boolean;
}

interface ChromeStub {
  runtime: {
    id: string;
    sendMessage: ReturnType<typeof vi.fn>;
    onMessage: { addListener: ReturnType<typeof vi.fn> };
    connect: () => PortStub;
  };
}

interface GlobalWithChrome {
  chrome?: ChromeStub;
  MediaRecorder?: { isTypeSupported: (mime: string) => boolean };
}

// Build a PortStub whose postMessage throws once `_disconnected` flips true,
// matching Chrome's runtime semantics. The throw is the exact error string
// the offscreen console showed in UAT Test 3 ("Attempting to use a
// disconnected port object"), so the test fails loudly when the bug is
// reproduced — and is silent (pass) once the production code clears the
// ping interval BEFORE the disconnect-detection race window.
function makePortStub(): PortStub {
  const port: PortStub = {
    name: 'video-keepalive',
    postMessage: vi.fn(),
    onMessage: {
      addListener: vi.fn(),
      _listeners: [],
    },
    onDisconnect: {
      addListener: (fn: () => void) => {
        port.onDisconnect._listeners.push(fn);
      },
      _listeners: [],
    },
    disconnect: vi.fn(() => {
      port._disconnected = true;
    }),
    _disconnected: false,
  };
  // Wire onMessage.addListener to capture into _listeners so the test can
  // dispatch REQUEST_BUFFER synthetically.
  port.onMessage.addListener.mockImplementation(
    (fn: (msg: unknown) => void) => {
      port.onMessage._listeners.push(fn);
    }
  );
  // Wire postMessage to throw if the port is disconnected — Chrome's
  // documented behaviour. This is the smoking gun for H1.
  port.postMessage.mockImplementation((msg: unknown) => {
    if (port._disconnected) {
      throw new Error('Attempting to use a disconnected port object');
    }
    return msg;
  });
  return port;
}

function buildChromeStub(ports: PortStub[]): ChromeStub {
  return {
    runtime: {
      id: 'ext-id-test',
      sendMessage: vi.fn(),
      onMessage: { addListener: vi.fn() },
      connect: () => {
        const port = makePortStub();
        ports.push(port);
        return port;
      },
    },
  };
}

// Top-level snapshots of the real timer APIs — captured at module load,
// BEFORE any test runs, so they survive a test that fails before its
// inline restore code. The afterEach below restores unconditionally.
const ORIGINAL_SET_INTERVAL = globalThis.setInterval;
const ORIGINAL_CLEAR_INTERVAL = globalThis.clearInterval;
const ORIGINAL_SET_TIMEOUT = globalThis.setTimeout;
const ORIGINAL_CLEAR_TIMEOUT = globalThis.clearTimeout;

describe('port reconnect race (RED — confirms empty-archive-port-race H1+H2)', () => {
  beforeEach(() => {
    vi.resetModules();
    (globalThis as unknown as GlobalWithChrome).MediaRecorder = {
      isTypeSupported: vi.fn().mockReturnValue(true),
    };
  });

  afterEach(() => {
    globalThis.setInterval = ORIGINAL_SET_INTERVAL;
    globalThis.clearInterval = ORIGINAL_CLEAR_INTERVAL;
    globalThis.setTimeout = ORIGINAL_SET_TIMEOUT;
    globalThis.clearTimeout = ORIGINAL_CLEAR_TIMEOUT;
  });

  // ──────────────────────────────────────────────────────────────────────
  // H1 — ping fires against disconnected port and throws
  // ──────────────────────────────────────────────────────────────────────
  //
  // Production code path (src/offscreen/recorder.ts:623-625):
  //   pingIntervalId = setInterval(() => {
  //     keepalivePort?.postMessage({ type: 'PING' });   // throws if disconnected
  //   }, PORT_PING_MS);
  //
  // The `?.` only guards against keepalivePort === null. After the SW
  // (or the SW's idle-eviction, or a remote disconnect) tears down the
  // port, the offscreen-side Port reference is still non-null but
  // postMessage throws synchronously with "Attempting to use a
  // disconnected port object". The interval is cleared only in the
  // onDisconnect handler — there's a race window during which the next
  // queued interval callback fires before onDisconnect runs.
  //
  // Test strategy: intercept setInterval to capture the ping callback,
  // then synthetically disconnect the port (without firing onDisconnect
  // first — mimicking the race), then invoke the captured ping callback
  // and assert it does NOT throw an uncaught error.
  it('H1: ping callback handles a remotely-disconnected port without throwing', async () => {
    const ports: PortStub[] = [];
    const stub = buildChromeStub(ports);
    (globalThis as unknown as GlobalWithChrome).chrome = stub;

    // Intercept setInterval to capture the ping callback for direct invocation.
    const intervalCallbacks: Array<() => void> = [];
    globalThis.setInterval = ((cb: () => void, _ms: number) => {
      intervalCallbacks.push(cb);
      return 999 as unknown as ReturnType<typeof setInterval>;
    }) as typeof globalThis.setInterval;
    // No-op clearInterval — the test wants to keep the callback callable
    // even after the production code attempts a clear, to expose the
    // race-window assumption.
    globalThis.clearInterval = (() => {}) as typeof globalThis.clearInterval;

    await import('../../src/offscreen/recorder');

    expect(ports.length).toBe(1);
    expect(intervalCallbacks.length).toBeGreaterThanOrEqual(1);

    const port = ports[0];
    const pingCb = intervalCallbacks[0];

    // Simulate the race: the remote side of the port has been
    // disconnected (e.g. SW eviction, ~5 min cap, port glitch) but the
    // offscreen's onDisconnect handler has NOT yet run, so the interval
    // is still installed and keepalivePort is still non-null on the
    // offscreen side.
    port._disconnected = true;

    // The PRODUCTION ping callback must not throw — either by checking
    // port.postMessage safety first, or by wrapping the call in
    // try/catch, or by removing the interval at first postMessage
    // failure. Whatever the fix, an uncaught throw here would surface
    // as the "Attempting to use a disconnected port object" error the
    // operator observed in UAT Test 3.
    expect(() => pingCb()).not.toThrow();

  });

  // ──────────────────────────────────────────────────────────────────────
  // H2 — BUFFER lost on stale-port reconnect; SW left with empty segments
  // ──────────────────────────────────────────────────────────────────────
  //
  // Production code path (src/offscreen/recorder.ts:547-604):
  //   const finalized = getSegments();
  //   ...
  //   for (let idx = 0; idx < allSegments.length; idx++) {
  //     const data = await blobToBase64(segment);   // ←── async window
  //     transferred.push(...);
  //   }
  //   if (keepalivePort !== portAtRequest) {
  //     logger.warn('port replaced during encode; dropping BUFFER response');
  //     return;
  //   }
  //   portAtRequest.postMessage({ type: 'BUFFER', segments: transferred });
  //
  // When the SW issues REQUEST_BUFFER during the ~10-50 ms reconnect
  // window, the offscreen captures `portAtRequest = keepalivePort`,
  // awaits the per-segment base64 encode (~150 ms for 3 segments), and
  // by the time the encode completes the pre-emptive reconnect has
  // swapped `keepalivePort` to a fresh Port. The guard correctly
  // refuses to post on the stale Port. HOWEVER, no retry is issued —
  // the SW's getVideoBufferFromOffscreen times out after 2 s and
  // resolves `{ segments: [] }`. createArchive then takes the silent
  // no-video branch (src/background/index.ts:350-352). The archive
  // ships without video.
  //
  // This RED test pins the contract: when REQUEST_BUFFER arrives AND
  // segments exist, BUFFER (with the encoded segments) MUST reach SOME
  // live port, either:
  //   (a) by retrying on the freshly-connected port, OR
  //   (b) by re-issuing REQUEST_BUFFER on the new port from the
  //       reconnect handler when there's an unanswered request in
  //       flight.
  // Whatever the strategy, silent loss with non-empty buffer is the
  // bug. The current production code drops the response on the floor.
  it('H2: REQUEST_BUFFER mid-reconnect must NOT drop BUFFER when segments exist', async () => {
    const ports: PortStub[] = [];
    const stub = buildChromeStub(ports);
    (globalThis as unknown as GlobalWithChrome).chrome = stub;

    const recorder = await import('../../src/offscreen/recorder');

    // 1) Seed the ring buffer with 3 real Blob segments via the test
    //    seam (recorder.ts:85 — pushSegmentForTest). Each segment is a
    //    plausible WebM head (EBML magic + filler bytes). The 3 ×
    //    payload ensures the for-loop body actually awaits — opening
    //    the real reconnect race window.
    const ebmlMagic = new Uint8Array([0x1a, 0x45, 0xdf, 0xa3]);
    recorder.resetBuffer();
    for (let i = 0; i < 3; i++) {
      const payload = new Uint8Array(1024);
      payload.set(ebmlMagic, 0);
      payload.fill(i + 1, ebmlMagic.length);
      recorder.pushSegmentForTest(
        new Blob([payload], { type: 'video/webm' })
      );
    }
    expect(recorder.getSegments().length).toBe(3);

    expect(ports.length).toBe(1);
    const oldPort = ports[0];
    expect(oldPort.onMessage._listeners.length).toBeGreaterThanOrEqual(1);

    // 2) SW issues REQUEST_BUFFER — synthetically dispatch to the
    //    captured onPortMessage listener. The production code kicks off
    //    encodeAndSendBuffer which awaits 3 blobToBase64 calls.
    //
    //    Under the Option C protocol the request carries a requestId the
    //    SW generates per call; the offscreen echoes it on the BUFFER
    //    response. This test uses a literal id since it's not driving
    //    the SW — only the recorder's onPortMessage path.
    const requestId = 'h2-test-id';
    oldPort.onMessage._listeners[0]({
      type: 'REQUEST_BUFFER',
      requestId,
    });

    // 3) Mid-encode, the pre-emptive reconnect fires. Simulate by
    //    firing onDisconnect on the old port — production code's
    //    handler runs `keepalivePort = null` then `connectPort()`
    //    which spawns a new PortStub. The keepalivePort reference now
    //    points to the new port; the in-flight portAtRequest in the
    //    encode loop still points to oldPort, so the stale-port guard
    //    at line 597 will trigger.
    oldPort.onDisconnect._listeners.forEach((fn) => fn());

    // After reconnect a NEW port exists.
    expect(ports.length).toBeGreaterThanOrEqual(2);
    const newPort = ports[ports.length - 1];

    // 4) Drain enough microtasks for the encode loop to complete and
    //    the post-await guard to evaluate. blobToBase64 awaits
    //    `blob.arrayBuffer()` (1 microtask) ×3 + the guard check.
    //    Generous: drain 32 microtasks then a macrotask. This is
    //    deterministic — vitest's Node env exposes setImmediate
    //    semantics via setTimeout(_, 0).
    for (let i = 0; i < 32; i++) {
      await Promise.resolve();
    }
    await new Promise<void>((resolve) => setTimeout(resolve, 0));
    for (let i = 0; i < 32; i++) {
      await Promise.resolve();
    }

    // CONTRACT — pick exactly one:
    //
    //   (a) BUFFER posted on the NEW port (segments encoded, retry on
    //       fresh port works), OR
    //   (b) BUFFER posted on the OLD port (encode completed and the
    //       post squeezed in before the swap took effect — acceptable
    //       because the SW's per-request listener is still bound to it
    //       and the SW gets the data).
    //
    // The current production code posts NEITHER when the reconnect
    // arrives between the await and the post (the line 597 guard
    // returns silently). This assertion FAILS today, proving the H2
    // bug. The fix must surface SOME signal that the SW can act on —
    // silent loss when the buffer is non-empty is the bug.

    const oldPortBuffers = oldPort.postMessage.mock.calls.filter(
      (call: unknown[]) =>
        typeof call[0] === 'object' &&
        call[0] !== null &&
        (call[0] as { type?: unknown }).type === 'BUFFER'
    );
    const newPortBuffers = newPort.postMessage.mock.calls.filter(
      (call: unknown[]) =>
        typeof call[0] === 'object' &&
        call[0] !== null &&
        (call[0] as { type?: unknown }).type === 'BUFFER'
    );

    const totalBuffersPosted = oldPortBuffers.length + newPortBuffers.length;
    // Stronger assertion: when BUFFER reaches a port, it must carry
    // the 3 segments we seeded. A 0-segment BUFFER is the silent-loss
    // shape and should not satisfy the contract.
    const allBufferCalls = [...oldPortBuffers, ...newPortBuffers];
    const segmentBearingBuffers = allBufferCalls.filter((call) => {
      const msg = call[0] as { segments?: unknown };
      return Array.isArray(msg.segments) && msg.segments.length > 0;
    });
    expect(totalBuffersPosted).toBeGreaterThanOrEqual(1);
    expect(segmentBearingBuffers.length).toBeGreaterThanOrEqual(1);

    // Cleanup test seam state so we don't bleed segments across tests.
    recorder.resetBuffer();
  });

  // ──────────────────────────────────────────────────────────────────────
  // H1.b — externally-disconnected port path. The original 290 s
  // pre-emptive setTimeout is gone (Option C retired it — see the
  // "Bisect Results" section of empty-archive-port-race.md). What
  // remains is the same H1 race shape, just triggered by a different
  // path: the SW side (or Chrome's idle eviction, or a network glitch)
  // can mark the remote end of the port as disconnected; the local
  // postMessage then throws synchronously with the same Chrome error
  // string. The fix's try/catch + reconnect path must absorb that.
  // ──────────────────────────────────────────────────────────────────────
  it('H1.b: externally-disconnected port — ping path absorbs the throw and reconnects cleanly', async () => {
    const ports: PortStub[] = [];
    const stub = buildChromeStub(ports);
    (globalThis as unknown as GlobalWithChrome).chrome = stub;

    const intervalCallbacks: Array<() => void> = [];
    globalThis.setInterval = ((cb: () => void, _ms: number) => {
      intervalCallbacks.push(cb);
      return 100 as unknown as ReturnType<typeof setInterval>;
    }) as typeof globalThis.setInterval;
    globalThis.clearInterval = (() => {}) as typeof globalThis.clearInterval;

    await import('../../src/offscreen/recorder');

    expect(ports.length).toBe(1);
    expect(intervalCallbacks.length).toBeGreaterThanOrEqual(1);

    const oldPort = ports[0];
    const pingCb = intervalCallbacks[0];

    // Simulate an EXTERNAL disconnect: the remote end of the port has
    // been torn down (SW eviction, port glitch, network blip), but the
    // local onDisconnect handler hasn't fired yet — this is exactly the
    // half-open state that the original H1 race weaponised.
    oldPort._disconnected = true;

    // Fire the ping. Under the legacy code this threw with "Attempting
    // to use a disconnected port object"; under the Option C fix the
    // ping callback wraps postMessage in try/catch and initiates a
    // clean reconnect via reconnectPort(). The test asserts BOTH that
    // no Uncaught Error escapes AND that a fresh port has been
    // requested (the visible side-effect of the reconnect path).
    expect(() => pingCb()).not.toThrow();
    expect(ports.length).toBeGreaterThanOrEqual(2);

  });
});