feat: check if port is busy before starting the server

server/src/wled_controller/__main__.py

@@ -6,6 +6,7 @@ shows a system-tray icon with **Show UI** / **Exit** actions.
 
 import asyncio
 import os
+import socket
 import sys
 import threading
 import time
@@ -43,8 +44,20 @@ def _is_restart() -> bool:
     return os.environ.get("WLED_RESTART", "") == "1"
 
 
+def _check_port(host: str, port: int) -> None:
+    """Exit with a clear message if the port is already in use."""
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
+        sock.settimeout(1)
+        try:
+            sock.bind((host, port))
+        except OSError:
+            logger.error("Port %d is already in use on %s", port, host)
+            sys.exit(1)
+
+
 def main() -> None:
     config = get_config()
+    _check_port(config.server.host, config.server.port)
 
     uv_config = uvicorn.Config(
         "wled_controller.main:app",
@@ -55,16 +68,16 @@ def main() -> None:
     server = uvicorn.Server(uv_config)
     set_server(server)
 
-    use_tray = PYSTRAY_AVAILABLE and (
-        sys.platform == "win32" or _force_tray()
-    )
+    use_tray = PYSTRAY_AVAILABLE and (sys.platform == "win32" or _force_tray())
 
     if use_tray:
         logger.info("Starting with system tray icon")
 
         # Uvicorn in a background thread
         server_thread = threading.Thread(
-            target=_run_server, args=(server,), daemon=True,
+            target=_run_server,
+            args=(server,),
+            daemon=True,
         )
         server_thread.start()
 
@@ -89,9 +102,7 @@ def main() -> None:
         server_thread.join(timeout=10)
     else:
         if not PYSTRAY_AVAILABLE:
-            logger.info(
-                "System tray not available (install pystray for tray support)"
-            )
+            logger.info("System tray not available (install pystray for tray support)")
         server.run()