fix: Show reboot request response in UI

Also make response from api more understandable for non-technical users.

Signed-off-by: Matthias Blankertz <matthias@blankertz.org>

software/frontend/index.html

@@ -154,7 +154,7 @@
         <!-- More screens can be added later -->
     </ul>
     <hr>
-    <button onclick="fetch('/api/v1/reboot/bootloader', {'method': 'POST'});">Reboot to bootloader</button>
+    <button onclick="requestReboot()">Reboot to bootloader</button>
 </div>
 
 <!-- CONFIG EDITOR SCREEN -->
@@ -967,6 +967,14 @@
         return { init, onShow };
     })();
 
+// Misc
+    async function requestReboot() {
+        const resp = await fetch('/api/v1/reboot/bootloader', {'method': 'POST'});
+        if (!resp.ok) {
+            alert('Reboot to bootloader failed: ' + await resp.text());
+        }
+    }
+    
 // Initialization
     Object.values(Screens).forEach(screen => {
         screen.init?.();

software/src/webserver.py

@@ -259,7 +259,7 @@ async def audiofile_delete(request):
 @webapp.route('/api/v1/reboot/<method>', methods=['POST'])
 async def reboot(request, method):
     if hwconfig.get_on_battery():
-        return 'not allowed: no vbus', 403
+        return 'not allowed: usb not connected', 403
 
     if method == 'bootloader':
         leds.set_state(LedManager.REBOOTING)