Simplify CAN and websocket init

In the React app, consolidate DBC cache handling and initialize the WebSocket service only after the DBC is loaded (keeps cleanup on unmount). These changes simplify startup behavior and avoid attempting privileged network commands from the bridge process.

Author: haoruizhou

.gitignore

@@ -238,3 +238,4 @@ test-logs/
 # Ignore generated service worker files
 sw.js
 pecan/src/assets/WFR25.dbc
+WFR25.dbc

kvaser-bridge/src/bridge.py

@@ -93,22 +93,9 @@ async def start(self) -> None:
         # Open CAN bus
         try:
             if config.DEFAULT_CAN_INTERFACE == 'socketcan':
-                import subprocess, shlex
                 ch = config.DEFAULT_SOCKETCAN_CHANNEL
-                # Bring interface down first (ignore errors - may already be down or not exist)
-                subprocess.run(shlex.split(f'ip link set {ch} down'), capture_output=True)
-                result = subprocess.run(
-                    shlex.split(f'ip link set {ch} up type can bitrate {self._bitrate}'),
-                    capture_output=True,
-                )
-                if result.returncode != 0:
-                    stderr = result.stderr.decode(errors='replace').strip()
-                    # Exit 2 with RTNETLINK "busy" means the interface is already UP - that's fine
-                    if result.returncode == 2 and 'busy' in stderr.lower():
-                        log.info('can0 already up, continuing')
-                    else:
-                        # Try opening anyway - maybe it was brought up externally (e.g. with sudo)
-                        log.warning('ip link set %s up returned %d: %s - attempting to open anyway', ch, result.returncode, stderr)
+                # can0 is expected to be already up (via udev rule or manually).
+                # See README: install /etc/udev/rules.d/80-can.rules to auto-bring up on plug-in.
                 self._bus = can.interface.Bus(channel=ch, interface='socketcan')
             else:
                 self._bus = can.interface.Bus(

pecan/src/App.tsx

@@ -63,29 +63,25 @@ function App() {
       if (isUsingCache) {
         setDisplayDefaultBanner(false);
         setDisplayCacheBanner(true);
-        // Persist the state
         localStorage.setItem('dbc-cache-active', 'true');
       } else {
-        // Check if we previously had cache active
         const wasCacheActive = localStorage.getItem('dbc-cache-active') === 'true';
         if (wasCacheActive) {
           console.log("[App] Cache was previously active but not found now");
         }
         localStorage.removeItem('dbc-cache-active');
       }
-    })();
-  }, []);
 
-  // Initialize WebSocket service once when app loads
-  useEffect(() => {
-    webSocketService.initialize();
+      // Initialize WebSocket only after DBC is loaded so the CAN processor
+      // is created with the correct DBC file.
+      webSocketService.initialize();
+    })();
 
-    // Cleanup on unmount
     return () => {
       webSocketService.disconnect();
       serialService.disconnect();
     };
-  }, []); // Empty dependency array = runs once on mount
+  }, []);
 
   return (
     <div className="h-screen flex flex-row overflow-y-auto">