Codebase audit fixes: stability, performance, accessibility

- Fix CORS: set allow_credentials=False (token auth, not cookies)
- Add threading.Lock for position cache thread safety
- Add shutdown_executor() for clean ThreadPoolExecutor cleanup
- Dedicated ThreadPoolExecutors for script/callback execution
- Fix Mutagen file handle leaks with try/finally close
- Reduce idle WebSocket polling (0.5s → 2.0s when no clients)
- Add :focus-visible styles for playback control buttons
- Add aria-label to icon-only header buttons
- Dynamic album art alt text for screen readers
- Persist MDI icon cache to localStorage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

media_server/main.py

@@ -87,6 +87,13 @@ async def lifespan(app: FastAPI):
 
     # Stop WebSocket status monitor
     await ws_manager.stop_status_monitor()
+
+    # Clean up platform-specific resources
+    import platform as _platform
+    if _platform.system() == "Windows":
+        from .services.windows_media import shutdown_executor
+        shutdown_executor()
+
     logger.info("Media Server shutting down")
 
 
@@ -103,10 +110,11 @@ def create_app() -> FastAPI:
     app.add_middleware(GZipMiddleware, minimum_size=1000)
 
     # Add CORS middleware for cross-origin requests
+    # Token auth is via Authorization header, not cookies, so credentials are not needed
     app.add_middleware(
         CORSMiddleware,
         allow_origins=["*"],
-        allow_credentials=True,
+        allow_credentials=False,
         allow_methods=["*"],
         allow_headers=["*"],
     )

media_server/routes/callbacks.py

@@ -5,6 +5,7 @@ import logging
 import re
 import subprocess
 import time
+from concurrent.futures import ThreadPoolExecutor
 from typing import Any
 
 from fastapi import APIRouter, Depends, HTTPException, status
@@ -17,6 +18,9 @@ from ..config_manager import config_manager
 router = APIRouter(prefix="/api/callbacks", tags=["callbacks"])
 logger = logging.getLogger(__name__)
 
+# Dedicated executor for callback/subprocess execution
+_callback_executor = ThreadPoolExecutor(max_workers=4, thread_name_prefix="callback")
+
 
 class CallbackInfo(BaseModel):
     """Information about a configured callback."""
@@ -127,10 +131,10 @@ async def execute_callback(
     logger.info(f"Executing callback for debugging: {callback_name}")
 
     try:
-        # Execute in thread pool to not block
+        # Execute in dedicated thread pool to not block the default executor
         loop = asyncio.get_event_loop()
         result = await loop.run_in_executor(
-            None,
+            _callback_executor,
             lambda: _run_callback(
                 command=callback_config.command,
                 timeout=callback_config.timeout,

media_server/routes/scripts.py

@@ -5,6 +5,7 @@ import logging
 import re
 import subprocess
 import time
+from concurrent.futures import ThreadPoolExecutor
 from typing import Any
 
 from fastapi import APIRouter, Depends, HTTPException, status
@@ -16,6 +17,9 @@ from ..config_manager import config_manager
 from ..services.websocket_manager import ws_manager
 
 router = APIRouter(prefix="/api/scripts", tags=["scripts"])
+
+# Dedicated executor for script/subprocess execution (avoids blocking the default pool)
+_script_executor = ThreadPoolExecutor(max_workers=4, thread_name_prefix="script")
 logger = logging.getLogger(__name__)
 
 
@@ -101,10 +105,10 @@ async def execute_script(
             # Append arguments to command
             command = f"{command} {' '.join(args)}"
 
-        # Execute in thread pool to not block
+        # Execute in dedicated thread pool to not block the default executor
         loop = asyncio.get_event_loop()
         result = await loop.run_in_executor(
-            None,
+            _script_executor,
             lambda: _run_script(
                 command=command,
                 timeout=script_config.timeout,

media_server/services/metadata_service.py

@@ -28,6 +28,7 @@ class MetadataService:
             if audio is None:
                 return {"error": "Unable to read audio file"}
 
+            try:
                 metadata = {
                     "type": "audio",
                     "filename": file_path.name,
@@ -83,6 +84,9 @@ class MetadataService:
                     metadata["title"] = file_path.stem
 
                 return metadata
+            finally:
+                if hasattr(audio, 'close'):
+                    audio.close()
 
         except ImportError:
             logger.error("mutagen library not installed, cannot extract metadata")
@@ -117,6 +121,7 @@ class MetadataService:
                     "title": file_path.stem,
                 }
 
+            try:
                 metadata = {
                     "type": "video",
                     "filename": file_path.name,
@@ -151,6 +156,9 @@ class MetadataService:
                     metadata["title"] = file_path.stem
 
                 return metadata
+            finally:
+                if hasattr(video, 'close'):
+                    video.close()
 
         except ImportError:
             logger.error("mutagen library not installed, cannot extract metadata")

media_server/services/websocket_manager.py

@@ -251,7 +251,7 @@ class ConnectionManager:
                     has_clients = len(self._active_connections) > 0
 
                 if not has_clients:
-                    await asyncio.sleep(self._poll_interval)
+                    await asyncio.sleep(2.0)  # Sleep longer when no clients connected
                     continue
 
                 status = await get_status_func()

media_server/services/windows_media.py

@@ -2,6 +2,8 @@
 
 import asyncio
 import logging
+import threading
+import time as _time
 from concurrent.futures import ThreadPoolExecutor
 from typing import Optional, Any
 
@@ -16,8 +18,10 @@ _executor = ThreadPoolExecutor(max_workers=2, thread_name_prefix="winrt")
 # Global storage for current album art (as bytes)
 _current_album_art_bytes: bytes | None = None
 
+# Lock protecting _position_cache and _track_skip_pending from concurrent access
+_position_lock = threading.Lock()
+
 # Global storage for position tracking
-import time as _time
 _position_cache = {
     "track_id": "",
     "base_position": 0.0,
@@ -224,6 +228,7 @@ def _sync_get_media_status() -> dict[str, Any]:
                         is_playing = result["state"] == "playing"
                         current_title = result.get('title', '')
 
+                        with _position_lock:
                             # Check if track skip is pending and title changed
                             skip_just_completed = False
                             if _track_skip_pending["active"]:
@@ -483,6 +488,11 @@ def _sync_seek(position: float) -> bool:
         return False
 
 
+def shutdown_executor() -> None:
+    """Shut down the WinRT thread pool executor."""
+    _executor.shutdown(wait=False)
+
+
 class WindowsMediaController(MediaController):
     """Media controller for Windows using WinRT and pycaw."""
 
@@ -602,7 +612,7 @@ class WindowsMediaController(MediaController):
 
         result = await self._run_command("next")
         if result:
-            # Set flag to force position to 0 until title changes
+            with _position_lock:
                 _track_skip_pending["active"] = True
                 _track_skip_pending["old_title"] = old_title
                 _track_skip_pending["skip_time"] = _time.time()
@@ -620,7 +630,7 @@ class WindowsMediaController(MediaController):
 
         result = await self._run_command("previous")
         if result:
-            # Set flag to force position to 0 until title changes
+            with _position_lock:
                 _track_skip_pending["active"] = True
                 _track_skip_pending["old_title"] = old_title
                 _track_skip_pending["skip_time"] = _time.time()

media_server/static/css/styles.css

@@ -824,6 +824,20 @@ button:disabled {
     transform: scale(1.05);
 }
 
+.controls button:focus-visible {
+    outline: 2px solid var(--accent);
+    outline-offset: 3px;
+    box-shadow: 0 0 0 4px rgba(29, 185, 84, 0.25);
+}
+
+.mute-btn:focus-visible,
+.mini-control-btn:focus-visible,
+.vinyl-toggle-btn:focus-visible {
+    outline: 2px solid var(--accent);
+    outline-offset: 2px;
+    box-shadow: 0 0 0 4px rgba(29, 185, 84, 0.25);
+}
+
 .controls button.primary {
     width: 56px;
     height: 56px;

media_server/static/index.html

@@ -74,12 +74,12 @@
             <div class="header-toolbar">
                 <div id="headerLinks" class="header-links"></div>
                 <div class="accent-picker">
-                    <button class="header-btn" onclick="toggleAccentPicker()" title="Accent color">
+                    <button class="header-btn" onclick="toggleAccentPicker()" title="Accent color" aria-label="Accent color">
                         <span class="accent-dot" id="accentDot"></span>
                     </button>
                     <div class="accent-picker-dropdown" id="accentDropdown"></div>
                 </div>
-                <button class="header-btn" onclick="toggleTheme()" data-i18n-title="player.theme" title="Toggle theme" id="theme-toggle">
+                <button class="header-btn" onclick="toggleTheme()" data-i18n-title="player.theme" title="Toggle theme" aria-label="Toggle theme" id="theme-toggle">
                     <svg id="theme-icon-sun" viewBox="0 0 24 24" style="display: none;">
                         <path d="M12 7c-2.76 0-5 2.24-5 5s2.24 5 5 5 5-2.24 5-5-2.24-5-5-5zM2 13h2c.55 0 1-.45 1-1s-.45-1-1-1H2c-.55 0-1 .45-1 1s.45 1 1 1zm18 0h2c.55 0 1-.45 1-1s-.45-1-1-1h-2c-.55 0-1 .45-1 1s.45 1 1 1zM11 2v2c0 .55.45 1 1 1s1-.45 1-1V2c0-.55-.45-1-1-1s-1 .45-1 1zm0 18v2c0 .55.45 1 1 1s1-.45 1-1v-2c0-.55-.45-1-1-1s-1 .45-1 1zM5.99 4.58c-.39-.39-1.03-.39-1.41 0-.39.39-.39 1.03 0 1.41l1.06 1.06c.39.39 1.03.39 1.41 0s.39-1.03 0-1.41L5.99 4.58zm12.37 12.37c-.39-.39-1.03-.39-1.41 0-.39.39-.39 1.03 0 1.41l1.06 1.06c.39.39 1.03.39 1.41 0 .39-.39.39-1.03 0-1.41l-1.06-1.06zm1.06-10.96c.39-.39.39-1.03 0-1.41-.39-.39-1.03-.39-1.41 0l-1.06 1.06c-.39.39-.39 1.03 0 1.41s1.03.39 1.41 0l1.06-1.06zM7.05 18.36c.39-.39.39-1.03 0-1.41-.39-.39-1.03-.39-1.41 0l-1.06 1.06c-.39.39-.39 1.03 0 1.41s1.03.39 1.41 0l1.06-1.06z"/>
                     </svg>
@@ -92,7 +92,7 @@
                     <option value="ru">RU</option>
                 </select>
                 <span class="header-toolbar-sep"></span>
-                <button class="header-btn header-btn-logout" onclick="clearToken()" data-i18n-title="auth.logout.title" title="Clear saved token">
+                <button class="header-btn header-btn-logout" onclick="clearToken()" data-i18n-title="auth.logout.title" title="Clear saved token" aria-label="Logout">
                     <svg viewBox="0 0 24 24"><path d="M17 7l-1.41 1.41L18.17 11H8v2h10.17l-2.58 2.58L17 17l5-5zM4 5h8V3H4c-1.1 0-2 .9-2 2v14c0 1.1.9 2 2 2h8v-2H4V5z"/></svg>
                 </button>
             </div>

media_server/static/js/app.js

@@ -1368,6 +1368,13 @@
             currentState = status.state;
             updatePlaybackState(status.state);
 
+            // Update album art alt text for accessibility
+            const altText = status.title && status.artist
+                ? `${status.artist} – ${status.title}`
+                : status.title || t('player.no_media');
+            dom.albumArt.alt = altText;
+            dom.miniAlbumArt.alt = altText;
+
             // Update album art (skip if same track to avoid redundant network requests)
             const artworkSource = status.album_art_url || null;
             const artworkKey = `${status.title || ''}|${status.artist || ''}|${artworkSource || ''}`;
@@ -3468,7 +3475,16 @@ async function toggleDisplayPower(monitorId, monitorName) {
 // Header Quick Links
 // ============================================================
 
-const mdiIconCache = {};
+// In-memory + localStorage cache for MDI icons (persists across reloads)
+const mdiIconCache = (() => {
+    try {
+        return JSON.parse(localStorage.getItem('mdiIconCache') || '{}');
+    } catch { return {}; }
+})();
+
+function _persistMdiCache() {
+    try { localStorage.setItem('mdiIconCache', JSON.stringify(mdiIconCache)); } catch {}
+}
 
 async function fetchMdiIcon(iconName) {
     // Parse "mdi:icon-name" → "icon-name"
@@ -3480,6 +3496,7 @@ async function fetchMdiIcon(iconName) {
         if (response.ok) {
             const svg = await response.text();
             mdiIconCache[name] = svg;
+            _persistMdiCache();
             return svg;
         }
     } catch (e) {