Hand playback to a native shell (#45)

CarPlay and Android Auto cannot render a web view. Both are template
surfaces, and the only audio they will control is the host's own AVPlayer
or ExoPlayer -- so an app that is "the web UI plus CarPlay" is really "the
web UI whose audio engine is native", and the page had no way to give
playback away.

web/src/native.ts replaces the playback surface of the page's media element
with one that forwards to the host and synthesises the events back. Nothing
in player.ts changes: it only ever speaks to the element, so the player bar,
the row buttons, the EQ bars and the keyboard shortcuts keep working as they
did. Video stays in the page, since CarPlay is audio-only and a native video
layer under a web view buys nothing. In a browser none of it installs.

Position and read are the host's to write. player.ts has been bitten before
by a stale position -- one left paused in another tab saved its older place
over where you had got to -- and a backgrounded web view is exactly that
tab: frozen, holding a time from minutes ago, while the host plays on. So
the beacon becomes a request for the host to save its own clock.

tests/native-bridge.js is what holds the two ends together, and it earned
its place immediately: the src setter called removeAttribute('src'), which
the shim's own override turned into a stop() that switched it back off one
line after enabling it. Silent, and only visible in a car. The stub DOM
moved to tests/dom-stub.js so that test and page-smoke share one harness
rather than two copies.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/dom-stub.js

@@ -0,0 +1,131 @@
+// The stub DOM the page's script is loaded against, shared by page-smoke.js and
+// native-bridge.js. It is deliberately thin: enough for every handler the script wires at load
+// to find what it reaches for, and no more.
+//
+// `media` swaps the bare `#audio` proxy for something with the parts of HTMLMediaElement that
+// matter -- a prototype carrying the real accessors, and events that actually dispatch -- because
+// native.ts replaces that surface on the element and a proxy that answers everything would prove
+// nothing about whether it worked.
+const vm = require('vm');
+
+function makeContext(html, script, { media = false } = {}) {
+  // Ids in the page, and in the markup the script builds for its dialogs.
+  const ids = new Set([...(html + script).matchAll(/\bid=(?:"([^"]+)"|([^\s>"']+))/g)].map(m => m[1] || m[2]));
+  const missing = [];
+
+  const el = (name) => new Proxy({ style: { setProperty(){}, getPropertyValue(){ return ''; } }, dataset: {}, classList: { add(){}, remove(){}, toggle(){}, contains(){ return false; } },
+    value: '', textContent: '', innerHTML: '', hidden: false, children: [], firstElementChild: null,
+    appendChild(){}, removeChild(){}, remove(){}, insertAdjacentHTML(){}, addEventListener(){},
+    setAttribute(){}, getAttribute(){ return null; }, select(){}, setSelectionRange(){}, focus(){},
+    replaceWith(){}, querySelector(){ return el('nested'); }, querySelectorAll(){ return []; },
+    play(){ return Promise.resolve(); }, pause(){}, closest(){ return null; } },
+    { get: (t, k) => k in t ? t[k] : undefined, set: (t, k, v) => (t[k] = v, true) });
+
+  const body = el('body');
+  const audio = media ? makeMediaElement() : null;
+  if (media) {
+    // native.ts reads has-video off the body to decide whether the host takes the file, so this
+    // one has to be a real set rather than something that always says no.
+    const classes = new Set();
+    body.classList = {
+      add: c => classes.add(c), remove: c => classes.delete(c),
+      toggle: (c, on) => (on === undefined ? (classes.has(c) ? classes.delete(c) : classes.add(c)) : on ? classes.add(c) : classes.delete(c)),
+      contains: c => classes.has(c),
+    };
+  }
+
+  const document = {
+    querySelector(sel) {
+      if (sel === '#audio' && audio) return audio;
+      if (sel.startsWith('#') && !ids.has(sel.slice(1))) { missing.push(sel); return null; }
+      return el(sel);
+    },
+    querySelectorAll: () => [],
+    createElement: () => el('created'),
+    addEventListener(){}, body,
+    documentElement: { dataset: {} },
+  };
+
+  const ctx = {
+    document, console,
+    window: { isSecureContext: false, addEventListener(){} },
+    localStorage: { getItem: () => null, setItem(){}, removeItem(){} },
+    navigator: { clipboard: undefined, sendBeacon(){}, mediaSession: undefined },
+    fetch: (url) => Promise.resolve({
+      ok: true, status: 200, text: () => Promise.resolve(''),
+      json: () => Promise.resolve(
+        String(url).includes('/api/settings')
+          ? { schedule: 'every 60m', every_mins: 60, download_dir: '/tmp', max_total_gb: 0, max_age_days: 0 }
+          : String(url).includes('/api/users')
+            ? [{ id: 1, name: 'admin', admin: true, password: true }, { id: 2, name: 'sam', admin: false, password: false }]
+            : /\/api\/(popular|directory)/.test(String(url))
+              ? [{ id: 'f', title: 'A Feed', image: null, subscribers: 2, subscribed: true },
+                 { id: 'g', title: null, image: null, subscribers: 1, subscribed: false }]
+              : /entries/.test(String(url)) ? { total: 0, entries: [] } : []),
+    }),
+    EventSource: function () { this.close = () => {}; },
+    MediaMetadata: function () {},
+    Blob: function () {},
+    setTimeout, clearTimeout, setInterval, clearInterval,
+    confirm: () => false, prompt: () => null, alert(){},
+    Date, Math, JSON, Object, Array, String, Number, Promise, Error, FormData: function(){},
+    URLSearchParams, encodeURIComponent, decodeURIComponent, parseInt, parseFloat, isNaN,
+  };
+  if (media) {
+    ctx.HTMLMediaElement = MediaElement;
+    ctx.Event = Event;
+    ctx.isFinite = isFinite;
+    ctx.CSS = { escape: s => String(s) };
+  }
+  ctx.globalThis = ctx;
+  ctx.window.location = { href: '', hash: '' };
+  ctx.location = ctx.window.location;
+
+  return { ctx, missing, audio, body, ids };
+}
+
+/* ---- just enough HTMLMediaElement for the shim to be worth testing ---- */
+
+function Event(type) { this.type = type; }
+
+function MediaElement() {
+  this._src = ''; this._t = 0; this._dur = NaN; this._paused = true;
+  this._ready = 0; this._vol = 1; this._rate = 1;
+  this._listeners = {};
+  this.dataset = {}; this.classList = { add(){}, remove(){}, toggle(){}, contains(){ return false; } };
+  // Every call that reached the real element, so a test can say the host took over rather than
+  // the element quietly playing as well.
+  this.calls = [];
+}
+MediaElement.prototype.play = function(){ this.calls.push('play'); this._paused = false; return Promise.resolve(); };
+MediaElement.prototype.pause = function(){ this.calls.push('pause'); this._paused = true; };
+MediaElement.prototype.load = function(){ this.calls.push('load'); };
+MediaElement.prototype.addEventListener = function(name, fn, opts){
+  (this._listeners[name] || (this._listeners[name] = [])).push({ fn, once: !!(opts && opts.once) });
+};
+MediaElement.prototype.dispatchEvent = function(ev){
+  for (const l of (this._listeners[ev.type] || []).slice()) {
+    if (l.once) this._listeners[ev.type] = this._listeners[ev.type].filter(x => x !== l);
+    l.fn(ev);
+  }
+  return true;
+};
+MediaElement.prototype.removeAttribute = function(name){ this.calls.push('removeAttribute:' + name); if (name === 'src') this._src = ''; };
+MediaElement.prototype.setAttribute = function(){};
+MediaElement.prototype.getAttribute = function(){ return null; };
+const accessor = (k, field, log) => Object.defineProperty(MediaElement.prototype, k, {
+  configurable: true,
+  get(){ return this[field]; },
+  set(v){ if (log) this.calls.push(k + ':' + v); this[field] = v; },
+});
+accessor('src', '_src', true);
+accessor('currentTime', '_t', true);
+accessor('volume', '_vol');
+accessor('playbackRate', '_rate');
+Object.defineProperty(MediaElement.prototype, 'duration', { configurable: true, get(){ return this._dur; } });
+Object.defineProperty(MediaElement.prototype, 'paused', { configurable: true, get(){ return this._paused; } });
+Object.defineProperty(MediaElement.prototype, 'readyState', { configurable: true, get(){ return this._ready; } });
+
+function makeMediaElement(){ return new MediaElement(); }
+
+module.exports = { makeContext, vm };

tests/native-bridge.js

@@ -0,0 +1,117 @@
+// The page inside a native shell: web/src/native.ts should take playback off the element and
+// hand it to the host, while everything in player.ts carries on talking to the element.
+//
+// This is the check that the shim and player.ts still agree. The surface native.ts replaces --
+// play, pause, src, currentTime, duration, paused, readyState, the events -- is player.ts's
+// alone, so a change there that steps outside it would otherwise break the app in a car, on a
+// road, with nothing to look at.
+//
+//   node tests/native-bridge.js
+const { makeContext, vm } = require('./dom-stub.js');
+const { buildPage } = require('../web/build.mjs');
+
+const { html, js: script } = buildPage('index.html');
+
+let failed = 0;
+const ok = (cond, what) => { if (!cond) { console.error('FAIL: ' + what); failed++; } };
+
+/* ---- a browser: nothing installs ---- */
+{
+  const { ctx } = makeContext(html, script, { media: true });
+  vm.createContext(ctx);
+  vm.runInContext(script, ctx, { filename: 'browser', timeout: 5000 });
+  ok(ctx.window.ipxNative === undefined, 'the bridge installed in a plain browser');
+  const audio = ctx.document.querySelector('#audio');
+  audio.src = '/media/1';
+  ok(audio.calls.includes('src:/media/1'), 'a browser did not set the real src');
+}
+
+/* ---- inside the shell ---- */
+const posted = [];
+const { ctx, audio, body } = makeContext(html, script, { media: true });
+ctx.window.webkit = { messageHandlers: { ipx: { postMessage: m => posted.push(m) } } };
+vm.createContext(ctx);
+vm.runInContext(script, ctx, { filename: 'shell', timeout: 5000 });
+
+const last = t => [...posted].reverse().find(m => m.t === t);
+const since = () => posted.splice(0, posted.length);
+
+ok(ctx.window.ipxNative && ctx.window.ipxNative.version === 1, 'window.ipxNative is not there for the host to call');
+ok(last('ready'), 'the host was never told the bridge is in');
+since();
+
+// What play() does: player.ts fills in `player`, marks the body, sets the src, then plays.
+const entry = { guid: 'g1', feed_id: 'f', title: 'Episode One', image: null, position: 0, duration: 1800, read: false,
+  enclosures: [{ id: 42, mime: 'audio/mpeg', path: '/downloads/f/ep1.mp3', url: 'https://x/ep1.mp3' }] };
+vm.runInContext('S.feeds=[{id:"f",title:"A Feed",image:"/art.jpg"}]', ctx);
+vm.runInContext('player.guid="g1";player.feed="f";player.enc=42;player.entry=E', Object.assign(ctx, { E: entry }));
+
+body.classList.toggle('has-video', false);
+audio.calls.length = 0;
+audio.src = '/media/42';
+
+const load = last('load');
+ok(load, 'setting the src told the host nothing');
+if (load) {
+  ok(load.url === '/media/42' && load.enc === 42, 'the host was not told which file');
+  ok(load.feedId === 'f' && load.guid === 'g1', 'the host cannot save a position without the feed and guid');
+  ok(load.title === 'Episode One' && load.feedTitle === 'A Feed', 'now-playing has nothing to show');
+  ok(load.artwork === '/art.jpg', "the feed's art did not stand in for an episode without its own");
+}
+ok(!audio.calls.some(c => c.startsWith('src:')), 'the element loaded the file as well as the host');
+ok(audio.calls.includes('load'), 'the element was not made to let go of what it held');
+
+// player.ts sets currentTime=0 straight after the src.
+since();
+audio.currentTime = 0;
+ok(last('seek') && last('seek').to === 0, 'a seek did not reach the host');
+
+since();
+audio.play();
+ok(last('play'), 'play did not reach the host');
+ok(!audio.calls.includes('play'), 'the element played too -- two engines on one file');
+
+// The host answers, and the page must move as it would have on its own.
+let played = 0, timed = 0;
+audio.addEventListener('play', () => played++);
+audio.addEventListener('timeupdate', () => timed++);
+ctx.window.ipxNative.on({ t: 'state', playing: true });
+ok(played === 1, 'the page never saw the host start playing');
+ok(audio.paused === false, 'audio.paused still says paused while the host plays');
+
+ctx.window.ipxNative.on({ t: 'meta', dur: 1800 });
+ok(audio.duration === 1800, 'the duration the host measured did not reach the page');
+ok(audio.readyState > 0, 'readyState stayed 0, which is what stops a position being saved');
+
+ctx.window.ipxNative.on({ t: 'time', cur: 30 });
+ok(audio.currentTime === 30, "the host's clock did not reach the page");
+ok(timed > 0, 'no timeupdate, so the player bar would sit at zero');
+
+// The 15-second key: a read and a write through the shim.
+since();
+audio.currentTime -= 15;
+ok(last('seek') && last('seek').to === 15, 'back 15 seconds did not land at 15');
+
+// Position saving is the host's: a frozen WebView must not write a time from minutes ago.
+since();
+const saved = ctx.navigator.sendBeacon('/api/entries/f/g1/position', {});
+ok(saved === true, 'sendBeacon reported a failure the page would treat as unsaved');
+ok(last('position') && /\/position$/.test(last('position').url), 'the position write did not become a request to the host');
+
+// Closing the player has to stop the host, not just blank the element.
+since();
+audio.removeAttribute('src');
+ok(last('stop'), 'closing the player left the host playing');
+
+// Video stays on the element: CarPlay is audio-only, and a native video layer under a WebView
+// buys nothing.
+since();
+audio.calls.length = 0;
+body.classList.toggle('has-video', true);
+audio.src = '/media/99';
+ok(!last('load'), 'a video was handed to the host');
+ok(audio.calls.includes('src:/media/99'), 'a video did not play on the element');
+
+if (failed) { console.error(`\n${failed} failed`); process.exit(1); }
+console.log('OK: native-bridge: the host takes playback and the page follows it');
+process.exit(0);

tests/page-smoke.js

@@ -7,7 +7,7 @@
 // and every server-side test passed too, because the server was fine.
 //
 //   node tests/page-smoke.js
-const vm = require('vm');
+const { makeContext, vm } = require('./dom-stub.js');
 const PAGE = process.argv[2] || 'index.html';
 
 const { buildPage } = require('../web/build.mjs');
@@ -19,57 +19,7 @@ if (!/<link rel=stylesheet href="?\/app\.css\?v=[0-9a-f]{12}"?>/.test(html) && P
 if (!new RegExp(`<script src="?/${file.replace('.', '\\.')}\\?v=[0-9a-f]{12}"?>`).test(html)) {
   console.error(`FAIL: the page does not load /${file}?v=<hash>`); process.exit(1);
 }
-// Ids in the page, and in the markup the script builds for its dialogs.
-const ids = new Set([...(html + script).matchAll(/\bid=(?:"([^"]+)"|([^\s>"']+))/g)].map(m => m[1] || m[2]));
-
-const missing = [];
-const el = (name) => new Proxy({ style: { setProperty(){}, getPropertyValue(){ return ''; } }, dataset: {}, classList: { add(){}, remove(){}, toggle(){}, contains(){ return false; } },
-  value: '', textContent: '', innerHTML: '', hidden: false, children: [], firstElementChild: null,
-  appendChild(){}, removeChild(){}, remove(){}, insertAdjacentHTML(){}, addEventListener(){},
-  setAttribute(){}, getAttribute(){ return null; }, select(){}, setSelectionRange(){}, focus(){},
-  replaceWith(){}, querySelector(){ return el('nested'); }, querySelectorAll(){ return []; },
-  play(){ return Promise.resolve(); }, pause(){}, closest(){ return null; } },
-  { get: (t, k) => k in t ? t[k] : undefined, set: (t, k, v) => (t[k] = v, true) });
-
-const document = {
-  querySelector(sel) {
-    if (sel.startsWith('#') && !ids.has(sel.slice(1))) { missing.push(sel); return null; }
-    return el(sel);
-  },
-  querySelectorAll: () => [],
-  createElement: () => el('created'),
-  addEventListener(){}, body: el('body'),
-  documentElement: { dataset: {} },
-};
-
-const ctx = {
-  document, console,
-  window: { isSecureContext: false, addEventListener(){} },
-  localStorage: { getItem: () => null, setItem(){}, removeItem(){} },
-  navigator: { clipboard: undefined, sendBeacon(){}, mediaSession: undefined },
-  fetch: (url) => Promise.resolve({
-    ok: true, status: 200, text: () => Promise.resolve(''),
-    json: () => Promise.resolve(
-      String(url).includes('/api/settings')
-        ? { schedule: 'every 60m', every_mins: 60, download_dir: '/tmp', max_total_gb: 0, max_age_days: 0 }
-        : String(url).includes('/api/users')
-          ? [{ id: 1, name: 'admin', admin: true, password: true }, { id: 2, name: 'sam', admin: false, password: false }]
-          : /\/api\/(popular|directory)/.test(String(url))
-            ? [{ id: 'f', title: 'A Feed', image: null, subscribers: 2, subscribed: true },
-               { id: 'g', title: null, image: null, subscribers: 1, subscribed: false }]
-            : /entries/.test(String(url)) ? { total: 0, entries: [] } : []),
-  }),
-  EventSource: function () { this.close = () => {}; },
-  MediaMetadata: function () {},
-  Blob: function () {},
-  setTimeout, clearTimeout, setInterval, clearInterval,
-  confirm: () => false, prompt: () => null, alert(){},
-  Date, Math, JSON, Object, Array, String, Number, Promise, Error, FormData: function(){},
-  URLSearchParams, encodeURIComponent, decodeURIComponent, parseInt, parseFloat, isNaN,
-};
-ctx.globalThis = ctx;
-ctx.window.location = { href: '', hash: '' };
-ctx.location = ctx.window.location;
+const { ctx, missing } = makeContext(html, script);
 
 try {
   vm.createContext(ctx);