From e5d3cc06f29e2e1da4f495124806ad2e78e88c91 Mon Sep 17 00:00:00 2001
From: Duncan Tourolle <duncan@tourolle.paris>
Date: Tue, 28 Jul 2026 01:32:57 +0200
Subject: [PATCH] fix(android): register WebView JS bridges once; stop
 audio-focus fight
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Locking the screen killed audio on video playback even with the
background-audio toggle armed.

configureWebViewForMedia() ran from onCreate's delayed post AND from
every onResume, re-calling addJavascriptInterface on each pass — five
times in a 45s session. WebView binds injected objects at page-load
time, so re-injecting over a live page leaves JS holding a stale proxy:
the object stays truthy (passing the `bridge()?.` optional chain) while
its methods vanish. Logcat showed 66 "WebView: Unknown object" errors
and, in JS, "TypeError: setEnabled is not a function".

So the toggle turned blue but never reached native. backgroundAudioEnabled
stayed false, onStop never dispatched 'jellytau-background', the handoff
never ran, and audio stopped the instant the screen locked. PiP and audio
focus broke identically.

- Register the bridges exactly once per WebView (identity-compared), and
  split the idempotent settings/chrome-client work into
  configureWebViewSettings() so it still runs on every resume.
- Forward WebView console output to logcat as "JellyTauWeb". The frontend
  was previously invisible to adb, which is what made this bug so hard to
  place; keep it for the next boundary-spanning diagnosis.
- setBackgroundAudioEnabled now reports whether native was actually
  reached instead of silently no-oping, so a dead bridge can never again
  masquerade as an armed toggle.

Removing the re-injection revived a latent conflict it had been masking:
the focus calls started working, and three AUDIOFOCUS_GAIN requesters
inside one uid began fighting — MainActivity, ExoPlayer, and Chromium's
own AudioFocusDelegate. The grant was followed ~45ms later by
AUDIOFOCUS_LOSS, whose handler paused playback, so arming background
audio (or just pressing play) paused the video in a loop.

WebView already manages focus for <video>. Drop the redundant
AndroidAudioFocus bridge, its listeners and its helpers entirely, and
leave focus to whichever engine is actually rendering — consistent with
the player-is-authoritative principle.

Also drops the dead AndroidBackgroundAudio.isSupported() probe, unused
since the button gate moved to platform().

TRACES: UR-040 | IR-025, DR-051 | UT-062
---
 .../com/dtourolle/jellytau/MainActivity.kt    | 170 +++++++++---------
 src/lib/utils/backgroundAudio.test.ts         |  68 +++++++
 src/lib/utils/backgroundAudio.ts              |  27 +--
 3 files changed, 162 insertions(+), 103 deletions(-)
 create mode 100644 src/lib/utils/backgroundAudio.test.ts

diff --git a/src-tauri/android/src/main/java/com/dtourolle/jellytau/MainActivity.kt b/src-tauri/android/src/main/java/com/dtourolle/jellytau/MainActivity.kt
index 469e7fbb..fe5f37b7 100644
--- a/src-tauri/android/src/main/java/com/dtourolle/jellytau/MainActivity.kt
+++ b/src-tauri/android/src/main/java/com/dtourolle/jellytau/MainActivity.kt
@@ -1,10 +1,5 @@
 package com.dtourolle.jellytau
 
-import android.content.Context
-import android.media.AudioAttributes
-import android.media.AudioFocusRequest
-import android.media.AudioManager
-import android.os.Build
 import android.os.Bundle
 import android.os.Handler
 import android.os.Looper
@@ -19,8 +14,6 @@ class MainActivity : TauriActivity() {
   private val handler = Handler(Looper.getMainLooper())
   private var configAttempts = 0
   private val maxConfigAttempts = 10
-  private var audioFocusRequest: AudioFocusRequest? = null
-  private val audioManager by lazy { getSystemService(Context.AUDIO_SERVICE) as AudioManager }
 
   /**
    * Coarse override for whether backgrounding the app should auto-enter PiP.
@@ -50,6 +43,15 @@ class MainActivity : TauriActivity() {
    */
   private var mediaWebView: WebView? = null
 
+  /**
+   * The WebView the @JavascriptInterface bridges have been injected into.
+   *
+   * addJavascriptInterface must run once per WebView instance: re-injecting
+   * over an already-loaded page hands JS a stale proxy whose methods are gone.
+   * Compared by identity so a genuinely new WebView still gets its bridges.
+   */
+  private var bridgesInstalledOn: WebView? = null
+
   override fun onCreate(savedInstanceState: Bundle?) {
     enableEdgeToEdge()
     super.onCreate(savedInstanceState)
@@ -159,19 +161,36 @@ class MainActivity : TauriActivity() {
       android.util.Log.d("MainActivity", "WebView found! Configuring settings...")
       mediaWebView = webView
 
-      // Add JavaScript interface for audio focus control
-      webView.addJavascriptInterface(object : Any() {
-        @JavascriptInterface
-        fun requestAudioFocus() {
-          handler.post { this@MainActivity.requestAudioFocus() }
-        }
+      // Register the @JavascriptInterface bridges EXACTLY ONCE per WebView.
+      //
+      // configureWebViewForMedia() runs from onCreate's delayed post AND from
+      // every onResume (plus each WebView re-find), so this used to re-inject
+      // all four bridges repeatedly - 5 times in a 45s session. WebView binds
+      // injected objects at page-load time; re-injecting over a live page
+      // leaves JS holding a stale proxy. The object stays truthy while its
+      // methods vanish, which surfaced as a flood of
+      // "WebView: Unknown object" chromium errors and, in JS,
+      // "TypeError: setEnabled is not a function".
+      //
+      // The visible bug: the background-audio toggle turned blue but never
+      // reached native, so backgroundAudioEnabled stayed false, onStop never
+      // dispatched 'jellytau-background', and a locked screen killed audio
+      // instantly (UR-040). Audio focus and PiP broke the same way.
+      //
+      // The settings/WebChromeClient work below is idempotent and must keep
+      // running on resume; only the bridge injection is one-shot.
+      if (webView === bridgesInstalledOn) {
+        android.util.Log.d("MainActivity", "JS bridges already installed on this WebView - skipping re-injection")
+        configureWebViewSettings(webView)
+        return
+      }
+      bridgesInstalledOn = webView
 
-        @JavascriptInterface
-        fun abandonAudioFocus() {
-          handler.post { this@MainActivity.abandonAudioFocus() }
-        }
-      }, "AndroidAudioFocus")
-      android.util.Log.d("MainActivity", "JavaScript interface 'AndroidAudioFocus' added")
+      // NOTE: there is deliberately no "AndroidAudioFocus" bridge. Manual focus
+      // requests from the WebView competed with Chromium's own
+      // AudioFocusDelegate and with ExoPlayer, and the resulting
+      // AUDIOFOCUS_LOSS paused playback. See the comment on the video listeners
+      // in configureWebViewSettings().
 
       // Add JavaScript interface for picture-in-picture control.
       // enterPip/canEnterPip must run on the main thread; @JavascriptInterface
@@ -212,10 +231,6 @@ class MainActivity : TauriActivity() {
           backgroundAudioEnabled = enabled
           android.util.Log.d("MainActivity", "backgroundAudioEnabled = $enabled")
         }
-
-        /** Whether background audio is available on this device (needs PiP-era APIs unnecessary; audio service always present on Android). */
-        @JavascriptInterface
-        fun isSupported(): Boolean = true
       }, "AndroidBackgroundAudio")
       android.util.Log.d("MainActivity", "JavaScript interface 'AndroidBackgroundAudio' added")
 
@@ -248,6 +263,21 @@ class MainActivity : TauriActivity() {
         dispatchWebEvent("jellytau-network-changed")
       }
 
+      configureWebViewSettings(webView)
+
+    } catch (e: Exception) {
+      android.util.Log.e("MainActivity", "Failed to configure WebView for media", e)
+    }
+  }
+
+  /**
+   * WebView settings, chrome client and the video-unmute script.
+   *
+   * Split out from the bridge injection because this half is idempotent and
+   * must re-run on every resume, whereas addJavascriptInterface must not.
+   */
+  private fun configureWebViewSettings(webView: WebView) {
+    try {
       // Set WebChromeClient to handle video playback and audio focus
       webView.webChromeClient = object : WebChromeClient() {
         override fun onShowCustomView(view: View?, callback: CustomViewCallback?) {
@@ -259,6 +289,21 @@ class MainActivity : TauriActivity() {
           super.onHideCustomView()
           android.util.Log.d("MainActivity", "Video exited fullscreen")
         }
+
+        /**
+         * Forward WebView console output to logcat under the "JellyTauWeb" tag.
+         *
+         * Without this the frontend is invisible to `adb logcat`, which makes
+         * diagnosing anything that spans the JS/native boundary (the
+         * background-audio handoff in particular) guesswork.
+         */
+        override fun onConsoleMessage(msg: android.webkit.ConsoleMessage): Boolean {
+          android.util.Log.d(
+            "JellyTauWeb",
+            "${msg.message()} (${msg.sourceId()}:${msg.lineNumber()})"
+          )
+          return true
+        }
       }
       android.util.Log.d("MainActivity", "WebChromeClient configured")
 
@@ -287,29 +332,18 @@ class MainActivity : TauriActivity() {
               video.volume = 1.0;
               console.log('[Android] Video unmuted, volume:', video.volume, 'muted:', video.muted);
 
-              // Add event listeners to manage audio focus
-              video.addEventListener('play', function() {
-                console.log('[Android] Video play event - requesting audio focus');
-                if (typeof AndroidAudioFocus !== 'undefined') {
-                  AndroidAudioFocus.requestAudioFocus();
-                }
-                console.log('[Android] Video state - muted:', this.muted, 'volume:', this.volume);
-              });
-
-              video.addEventListener('pause', function() {
-                console.log('[Android] Video pause event - abandoning audio focus');
-                if (typeof AndroidAudioFocus !== 'undefined') {
-                  AndroidAudioFocus.abandonAudioFocus();
-                }
-              });
-
-              video.addEventListener('ended', function() {
-                console.log('[Android] Video ended event - abandoning audio focus');
-                if (typeof AndroidAudioFocus !== 'undefined') {
-                  AndroidAudioFocus.abandonAudioFocus();
-                }
-              });
-
+              // NOTE: deliberately no audio-focus calls here.
+              //
+              // WebView already manages audio focus for <video> through
+              // Chromium's own AudioFocusDelegate. Requesting AUDIOFOCUS_GAIN
+              // again from MainActivity made two requesters compete inside one
+              // uid: the grant was immediately followed by AUDIOFOCUS_LOSS
+              // (~45ms), whose handler paused playback - so arming background
+              // audio, or simply pressing play, paused the video in a loop.
+              //
+              // ExoPlayer is the third potential owner and stays authoritative
+              // for native playback (JellyTauPlayer manages its own focus).
+              // Leave focus to whichever engine is actually rendering.
               video.addEventListener('volumechange', function() {
                 console.log('[Android] Video volume changed - volume:', this.volume, 'muted:', this.muted);
               });
@@ -356,48 +390,4 @@ class MainActivity : TauriActivity() {
     return null
   }
 
-  private fun requestAudioFocus() {
-    android.util.Log.d("MainActivity", "Requesting audio focus for video playback")
-
-    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
-      val audioAttributes = AudioAttributes.Builder()
-        .setUsage(AudioAttributes.USAGE_MEDIA)
-        .setContentType(AudioAttributes.CONTENT_TYPE_MOVIE)
-        .build()
-
-      audioFocusRequest = AudioFocusRequest.Builder(AudioManager.AUDIOFOCUS_GAIN)
-        .setAudioAttributes(audioAttributes)
-        .setAcceptsDelayedFocusGain(true)
-        .setOnAudioFocusChangeListener { focusChange ->
-          android.util.Log.d("MainActivity", "Audio focus changed: $focusChange")
-        }
-        .build()
-
-      val result = audioManager.requestAudioFocus(audioFocusRequest!!)
-      android.util.Log.d("MainActivity", "Audio focus request result: $result")
-    } else {
-      @Suppress("DEPRECATION")
-      val result = audioManager.requestAudioFocus(
-        { focusChange ->
-          android.util.Log.d("MainActivity", "Audio focus changed: $focusChange")
-        },
-        AudioManager.STREAM_MUSIC,
-        AudioManager.AUDIOFOCUS_GAIN
-      )
-      android.util.Log.d("MainActivity", "Audio focus request result (legacy): $result")
-    }
-  }
-
-  private fun abandonAudioFocus() {
-    android.util.Log.d("MainActivity", "Abandoning audio focus")
-
-    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
-      audioFocusRequest?.let {
-        audioManager.abandonAudioFocusRequest(it)
-      }
-    } else {
-      @Suppress("DEPRECATION")
-      audioManager.abandonAudioFocus { }
-    }
-  }
 }
diff --git a/src/lib/utils/backgroundAudio.test.ts b/src/lib/utils/backgroundAudio.test.ts
new file mode 100644
index 00000000..a068e4f8
--- /dev/null
+++ b/src/lib/utils/backgroundAudio.test.ts
@@ -0,0 +1,68 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { setBackgroundAudioEnabled } from "./backgroundAudio";
+
+/**
+ * Bridge-reporting contract for the background-audio toggle.
+ *
+ * TRACES: UR-040 | IR-025, DR-051 | UT-062
+ *
+ * Regression guard for the "screen lock kills video audio" bug: MainActivity
+ * re-ran configureWebViewForMedia() on every onResume, re-calling
+ * addJavascriptInterface over a live page. WebView then served a stale proxy —
+ * `window.AndroidBackgroundAudio` stayed truthy but its methods were gone, so
+ * `setEnabled` threw `TypeError: e.setEnabled is not a function`.
+ *
+ * The old implementation swallowed that with `bridge()?.setEnabled(...)` inside
+ * a try/catch returning void, so the UI showed "armed" while native never got
+ * the flag — and onStop's `if (backgroundAudioEnabled)` guard never dispatched
+ * `jellytau-background`. Audio died the instant the screen locked.
+ *
+ * setBackgroundAudioEnabled must therefore REPORT whether native was actually
+ * reached, so a dead bridge can never masquerade as an armed toggle.
+ */
+describe("setBackgroundAudioEnabled", () => {
+  beforeEach(() => {
+    delete (window as unknown as Record<string, unknown>).AndroidBackgroundAudio;
+    vi.restoreAllMocks();
+  });
+
+  it("reports success when the bridge is present and the call lands", () => {
+    const setEnabled = vi.fn();
+    window.AndroidBackgroundAudio = { setEnabled };
+
+    expect(setBackgroundAudioEnabled(true)).toBe(true);
+    expect(setEnabled).toHaveBeenCalledWith(true);
+  });
+
+  it("reports failure when the bridge object is absent entirely", () => {
+    expect(setBackgroundAudioEnabled(true)).toBe(false);
+  });
+
+  it("reports failure for a stale proxy whose methods are gone", () => {
+    // The exact shape of the bug: object present (so `?.` passes) but the
+    // method is missing after re-injection over a live page.
+    window.AndroidBackgroundAudio = {} as unknown as typeof window.AndroidBackgroundAudio;
+
+    expect(setBackgroundAudioEnabled(true)).toBe(false);
+  });
+
+  it("reports failure when the bridge method throws", () => {
+    window.AndroidBackgroundAudio = {
+      setEnabled: () => {
+        throw new TypeError("e.setEnabled is not a function");
+      },
+    };
+
+    expect(setBackgroundAudioEnabled(true)).toBe(false);
+  });
+
+  it("never throws out to the caller — the toggle must not break the player", () => {
+    window.AndroidBackgroundAudio = {
+      setEnabled: () => {
+        throw new Error("boom");
+      },
+    };
+
+    expect(() => setBackgroundAudioEnabled(false)).not.toThrow();
+  });
+});
diff --git a/src/lib/utils/backgroundAudio.ts b/src/lib/utils/backgroundAudio.ts
index c788e35a..037c8ca5 100644
--- a/src/lib/utils/backgroundAudio.ts
+++ b/src/lib/utils/backgroundAudio.ts
@@ -20,7 +20,6 @@
 
 interface AndroidBackgroundAudioBridge {
   setEnabled(enabled: boolean): void;
-  isSupported(): boolean;
 }
 
 declare global {
@@ -34,25 +33,27 @@ function bridge(): AndroidBackgroundAudioBridge | undefined {
   return window.AndroidBackgroundAudio;
 }
 
-/** Whether background audio is available — used to decide if the toggle renders. */
-export function isBackgroundAudioSupported(): boolean {
-  try {
-    return bridge()?.isSupported() ?? false;
-  } catch (err) {
-    console.warn("[BgAudio] isSupported check failed:", err);
-    return false;
-  }
-}
-
 /**
  * Arm/disarm background-audio mode for the current video. When armed, the native
  * side runs the audio handoff on background instead of entering PiP.
  */
-export function setBackgroundAudioEnabled(enabled: boolean): void {
+export function setBackgroundAudioEnabled(enabled: boolean): boolean {
+  const b = bridge();
+  if (!b) {
+    // The button is gated on platform(), not on this bridge, so it can render
+    // before/without the bridge existing. Silently no-oping here leaves the UI
+    // showing "armed" while native never learns — and the handoff then never
+    // fires on lock. Report it so callers can retry.
+    console.warn("[BgAudio] setEnabled: bridge missing, native NOT armed");
+    return false;
+  }
   try {
-    bridge()?.setEnabled(enabled);
+    b.setEnabled(enabled);
+    console.log("[BgAudio] setEnabled ->", enabled);
+    return true;
   } catch (err) {
     console.warn("[BgAudio] Failed to set enabled:", err);
+    return false;
   }
 }