Add toggleable modifier key support

src/SwitchifyPc.App/App.xaml.cs

@@ -19,6 +19,7 @@
 using SwitchifyPc.Windows.Bluetooth;
 using SwitchifyPc.Windows.CursorOverlay;
 using SwitchifyPc.Windows.Input;
+using SwitchifyPc.Windows.ModifierOverlay;
 using SwitchifyPc.Windows.Startup;
 using SwitchifyPc.Windows.Updates;
 using SwitchifyPc.Protocol;
@@ -44,6 +45,7 @@ public partial class App : System.Windows.Application
     private DesktopCommandExecutor? commandExecutor;
     private MouseRepeatController? mouseRepeatController;
     private WindowsCursorOverlayNotifier? cursorOverlay;
+    private WindowsModifierKeyOverlayNotifier? modifierOverlay;
     private DispatcherTimer? pairingExpiryTimer;
     private AppThemeManager? themeManager;
     private bool isQuitting;
@@ -117,6 +119,8 @@ protected override void OnExit(ExitEventArgs e)
         bluetoothServer = null;
         cursorOverlay?.Dispose();
         cursorOverlay = null;
+        modifierOverlay?.Dispose();
+        modifierOverlay = null;
         themeManager?.Dispose();
         themeManager = null;
         commandExecutor = null;
@@ -275,7 +279,8 @@ private async Task StartBluetoothAsync()
             SendInputWindowsNativeInput nativeInput = new();
             WindowsDesktopInputAdapter inputAdapter = new(nativeInput, pointerSettingsStore.Load());
             cursorOverlay = new WindowsCursorOverlayNotifier(nativeInput, cursorOverlaySettingsStore);
-            commandExecutor = new DesktopCommandExecutor(inputAdapter, cursorOverlay);
+            modifierOverlay = new WindowsModifierKeyOverlayNotifier(nativeInput);
+            commandExecutor = new DesktopCommandExecutor(inputAdapter, cursorOverlay, modifierOverlay: modifierOverlay);
             mouseRepeatController = new MouseRepeatController(commandExecutor, mouseRepeatSettingsStore);
             ControlSession controlSession = new(
                 new CommandAuthValidator(pairingStore),
@@ -328,10 +333,11 @@ private void HandleBluetoothEvent(BluetoothHelperEvent helperEvent)
 
                         if (commandExecutor is not null)
                         {
-                            await commandExecutor.ReleaseHeldMouseButtonsAsync();
+                            await commandExecutor.ReleaseHeldInputsAsync();
                         }
 
                         cursorOverlay?.EndControlSession();
+                        modifierOverlay?.EndControlSession();
                     }
                     break;
                 case BluetoothDiagnosticEvent diagnostic:

src/SwitchifyPc.Core/Control/ControlSession.cs

@@ -86,14 +86,16 @@ public async Task<ControlSessionResult> ProcessMessageAsync(string rawMessage, C
                 await StopRepeatAsync(failedDeviceId!).ConfigureAwait(false);
             }
 
+            await commandExecutor.ReleaseHeldInputsAsync(cancellationToken).ConfigureAwait(false);
+            commandExecutor.EndControlSession();
             return ControlSessionResult.Response(ErrorResponse(RequestIdOrNull(request), auth.Reason ?? "invalid_auth", "Command authentication failed."))
                 with { AuthFailureReason = auth.Reason ?? "invalid_auth" };
         }
 
         if (type == "connection.disconnecting")
         {
             await StopRepeatAsync(auth.DeviceId ?? "").ConfigureAwait(false);
-            await commandExecutor.ReleaseHeldMouseButtonsAsync(cancellationToken).ConfigureAwait(false);
+            await commandExecutor.ReleaseHeldInputsAsync(cancellationToken).ConfigureAwait(false);
             commandExecutor.EndControlSession();
             return WithAuth(AckOrNoResponse(request), auth);
         }
@@ -147,6 +149,13 @@ public async Task<ControlSessionResult> ProcessMessageAsync(string rawMessage, C
 
     public Task StopAllRepeatsAsync() => mouseRepeatController?.StopAllAsync() ?? Task.CompletedTask;
 
+    public async Task EndControlSessionAsync(CancellationToken cancellationToken = default)
+    {
+        await StopAllRepeatsAsync().ConfigureAwait(false);
+        await commandExecutor.ReleaseHeldInputsAsync(cancellationToken).ConfigureAwait(false);
+        commandExecutor.EndControlSession();
+    }
+
     private static ControlSessionResult WithAuth(ControlSessionResult result, AuthValidationResult auth)
     {
         return result with

src/SwitchifyPc.Core/Control/RemoteControlSession.cs

@@ -133,7 +133,7 @@ public RemoteSessionResult ExpirePendingPairingRequests()
 
     public void RemoveConnection(string connectionId)
     {
-        _ = commandSession.StopAllRepeatsAsync();
+        _ = commandSession.EndControlSessionAsync();
         string[] requestIds = pendingConnectionsByRequestId
             .Where(entry => entry.Value.ConnectionId == connectionId)
             .Select(entry => entry.Key)

src/SwitchifyPc.Core/Input/DesktopCommandExecutor.cs

@@ -15,14 +15,21 @@ public sealed class DesktopCommandExecutor
 
     private readonly IDesktopInputAdapter adapter;
     private readonly ICursorOverlayNotifier? cursorOverlay;
+    private readonly IModifierKeyOverlayNotifier? modifierOverlay;
     private readonly Func<double> now;
     private readonly Dictionary<string, TextInputStreamState> textInputStreams = new(StringComparer.Ordinal);
+    private readonly HashSet<string> activeModifierKeys = new(StringComparer.Ordinal);
     private string? activeDragButton;
 
-    public DesktopCommandExecutor(IDesktopInputAdapter adapter, ICursorOverlayNotifier? cursorOverlay = null, Func<double>? now = null)
+    public DesktopCommandExecutor(
+        IDesktopInputAdapter adapter,
+        ICursorOverlayNotifier? cursorOverlay = null,
+        Func<double>? now = null,
+        IModifierKeyOverlayNotifier? modifierOverlay = null)
     {
         this.adapter = adapter;
         this.cursorOverlay = cursorOverlay;
+        this.modifierOverlay = modifierOverlay;
         this.now = now ?? (() => DateTimeOffset.UtcNow.ToUnixTimeMilliseconds());
     }
 
@@ -52,6 +59,8 @@ public async Task<CommandExecutionResult> ExecuteAsync(JsonElement command, Canc
                 "mouse.rightClick" => await RightClickMouseAsync(cancellationToken),
                 "mouse.scroll" => await ScrollMouseAsync(payload, cancellationToken),
                 "keyboard.key" => await PressKeyAsync(payload.GetProperty("key").GetString() ?? "", cancellationToken),
+                "keyboard.modifierDown" => await SetModifierAsync(payload.GetProperty("key").GetString() ?? "", down: true, cancellationToken),
+                "keyboard.modifierUp" => await SetModifierAsync(payload.GetProperty("key").GetString() ?? "", down: false, cancellationToken),
                 "keyboard.shortcut" => await PressShortcutAsync(payload.GetProperty("keys"), cancellationToken),
                 "keyboard.typeText" => await TypeTextAsync(payload.GetProperty("text").GetString() ?? "", cancellationToken),
                 "keyboard.textStream.open" => OpenTextInputStream(command.GetProperty("deviceId").GetString() ?? "", payload.GetProperty("streamId").GetString() ?? ""),
@@ -79,18 +88,21 @@ public async Task<CommandExecutionResult> ExecuteAsync(JsonElement command, Canc
 
     public async Task ReleaseHeldMouseButtonsAsync(CancellationToken cancellationToken = default)
     {
-        if (activeDragButton is null) return;
-        string button = activeDragButton;
-        await adapter.SetMouseButtonDownAsync(button, false, cancellationToken);
-        activeDragButton = null;
-        cursorOverlay?.SetDragActive(false);
-        cursorOverlay?.Hide();
+        await ReleaseHeldInputsAsync(cancellationToken).ConfigureAwait(false);
+    }
+
+    public async Task ReleaseHeldInputsAsync(CancellationToken cancellationToken = default)
+    {
+        await ReleaseHeldMouseButtonAsync(cancellationToken).ConfigureAwait(false);
+        await ReleaseHeldModifiersAsync(cancellationToken).ConfigureAwait(false);
     }
 
     public void EndControlSession()
     {
         activeDragButton = null;
+        activeModifierKeys.Clear();
         cursorOverlay?.EndControlSession();
+        modifierOverlay?.EndControlSession();
     }
 
     private async Task<CommandExecutionResult> MoveMouseAsync(JsonElement payload, CancellationToken cancellationToken)
@@ -171,6 +183,37 @@ private async Task<CommandExecutionResult> PressKeyAsync(string key, Cancellatio
         return CommandExecutionResult.Success;
     }
 
+    private async Task<CommandExecutionResult> SetModifierAsync(string key, bool down, CancellationToken cancellationToken)
+    {
+        if (down)
+        {
+            if (activeModifierKeys.Contains(key))
+            {
+                return CommandExecutionResult.Success;
+            }
+
+            await adapter.SetKeyDownAsync(key, true, cancellationToken);
+            activeModifierKeys.Add(key);
+            UpdateModifierOverlay();
+            return CommandExecutionResult.Success;
+        }
+
+        if (!activeModifierKeys.Remove(key))
+        {
+            return CommandExecutionResult.Success;
+        }
+
+        try
+        {
+            await adapter.SetKeyDownAsync(key, false, cancellationToken);
+            return CommandExecutionResult.Success;
+        }
+        finally
+        {
+            UpdateModifierOverlay();
+        }
+    }
+
     private async Task<CommandExecutionResult> PressShortcutAsync(JsonElement keysElement, CancellationToken cancellationToken)
     {
         string[] keys = keysElement.EnumerateArray().Select(key => key.GetString() ?? "").ToArray();
@@ -310,6 +353,56 @@ private static bool IsMouseCommand(string type)
         return type is "mouse.move" or "mouse.click" or "mouse.doubleClick" or "mouse.rightClick" or "mouse.scroll" or "mouse.dragStart" or "mouse.dragEnd";
     }
 
+    private async Task ReleaseHeldMouseButtonAsync(CancellationToken cancellationToken)
+    {
+        if (activeDragButton is null) return;
+        string button = activeDragButton;
+        activeDragButton = null;
+        await adapter.SetMouseButtonDownAsync(button, false, cancellationToken);
+        cursorOverlay?.SetDragActive(false);
+        cursorOverlay?.Hide();
+    }
+
+    private async Task ReleaseHeldModifiersAsync(CancellationToken cancellationToken)
+    {
+        foreach (string key in new[] { "Meta", "Shift", "Alt", "Ctrl" })
+        {
+            if (!activeModifierKeys.Remove(key)) continue;
+            try
+            {
+                await adapter.SetKeyDownAsync(key, false, cancellationToken);
+            }
+            finally
+            {
+                UpdateModifierOverlay();
+            }
+        }
+    }
+
+    private void UpdateModifierOverlay()
+    {
+        modifierOverlay?.SetActiveModifiers(ActiveModifierLabels());
+    }
+
+    private IReadOnlyList<string> ActiveModifierLabels()
+    {
+        List<string> labels = [];
+        foreach (string key in new[] { "Ctrl", "Alt", "Shift", "Meta" })
+        {
+            if (activeModifierKeys.Contains(key))
+            {
+                labels.Add(DisplayModifierLabel(key));
+            }
+        }
+
+        return labels;
+    }
+
+    private static string DisplayModifierLabel(string key)
+    {
+        return key == "Meta" ? "Start" : key;
+    }
+
     private static string TextInputStreamKey(string deviceId, string streamId)
     {
         return $"{deviceId}:{streamId}";

src/SwitchifyPc.Core/Input/DesktopInputAdapter.cs

@@ -8,6 +8,7 @@ public interface IDesktopInputAdapter
     Task DoubleClickMouseAsync(string button, CancellationToken cancellationToken = default);
     Task ScrollMouseAsync(double dx, double dy, CancellationToken cancellationToken = default);
     Task PressKeyAsync(string key, CancellationToken cancellationToken = default);
+    Task SetKeyDownAsync(string key, bool down, CancellationToken cancellationToken = default);
     Task PressShortcutAsync(IReadOnlyList<string> keys, CancellationToken cancellationToken = default);
     Task TypeTextAsync(string text, CancellationToken cancellationToken = default);
     Task TypeCharacterAsync(string text, CancellationToken cancellationToken = default);
@@ -33,3 +34,9 @@ public interface ICursorOverlayNotifier
     void MarkControlActive();
     void SetDragActive(bool active);
 }
+
+public interface IModifierKeyOverlayNotifier
+{
+    void SetActiveModifiers(IReadOnlyCollection<string> activeModifiers);
+    void EndControlSession();
+}

src/SwitchifyPc.Protocol/ProtocolConstants.cs

@@ -24,6 +24,8 @@ public static class ProtocolConstants
         "mouse.dragStart",
         "mouse.dragEnd",
         "keyboard.key",
+        "keyboard.modifierDown",
+        "keyboard.modifierUp",
         "keyboard.shortcut",
         "keyboard.typeText",
         "keyboard.textStream.open",
@@ -53,6 +55,8 @@ public static class ProtocolConstants
         "mouse.dragStart",
         "mouse.dragEnd",
         "keyboard.key",
+        "keyboard.modifierDown",
+        "keyboard.modifierUp",
         "keyboard.shortcut",
         "keyboard.typeText",
         "keyboard.textStream.char",
@@ -103,6 +107,14 @@ public static class ProtocolConstants
         KeyboardKeys.Concat(["Ctrl", "Alt", "Shift", "Meta", "A", "C", "V", "X", "Z", "Y"]),
         StringComparer.Ordinal);
 
+    public static readonly IReadOnlySet<string> ModifierKeys = new HashSet<string>(StringComparer.Ordinal)
+    {
+        "Ctrl",
+        "Alt",
+        "Shift",
+        "Meta"
+    };
+
     public static readonly IReadOnlySet<string> MediaActions = new HashSet<string>(StringComparer.Ordinal)
     {
         "playPause",

src/SwitchifyPc.Protocol/ProtocolValidator.cs

@@ -148,6 +148,10 @@ private static ProtocolValidationResult ValidateCommandPayload(string type, Json
                 TryGetString(payload, "key", out string? key) && ProtocolConstants.KeyboardKeys.Contains(key)
                     ? Valid(payload)
                     : Invalid("invalid_payload", "Keyboard key is invalid."),
+            "keyboard.modifierDown" or "keyboard.modifierUp" =>
+                TryGetString(payload, "key", out string? modifierKey) && ProtocolConstants.ModifierKeys.Contains(modifierKey)
+                    ? Valid(payload)
+                    : Invalid("invalid_payload", "Modifier key is invalid."),
             "keyboard.shortcut" => ValidateShortcutPayload(payload),
             "keyboard.typeText" =>
                 TryGetString(payload, "text", out string? text) && IsSafeTextPayload(text)

src/SwitchifyPc.Tests/BluetoothControlFrameProcessorTests.cs

@@ -198,6 +198,12 @@ public Task PressKeyAsync(string key, CancellationToken cancellationToken = defa
             return Task.CompletedTask;
         }
 
+        public Task SetKeyDownAsync(string key, bool down, CancellationToken cancellationToken = default)
+        {
+            Calls.Add($"setKeyDown:{key}:{down}");
+            return Task.CompletedTask;
+        }
+
         public Task PressShortcutAsync(IReadOnlyList<string> keys, CancellationToken cancellationToken = default)
         {
             Calls.Add($"pressShortcut:{string.Join("+", keys)}");

src/SwitchifyPc.Tests/BluetoothRemoteFrameProcessorTests.cs

@@ -320,6 +320,12 @@ public Task PressKeyAsync(string key, CancellationToken cancellationToken = defa
             return Task.CompletedTask;
         }
 
+        public Task SetKeyDownAsync(string key, bool down, CancellationToken cancellationToken = default)
+        {
+            Calls.Add($"setKeyDown:{key}:{down}");
+            return Task.CompletedTask;
+        }
+
         public Task PressShortcutAsync(IReadOnlyList<string> keys, CancellationToken cancellationToken = default)
         {
             Calls.Add($"pressShortcut:{string.Join("+", keys)}");

src/SwitchifyPc.Tests/ControlSessionTests.cs

@@ -56,6 +56,20 @@ public async Task SuppressesResponseForNoAckCommands()
         Assert.Equal(["moveMouseBy:10,-2"], adapter.Calls);
     }
 
+    [Fact]
+    public async Task AuthenticatedModifierCommandsRouteToExecutor()
+    {
+        FakeInputAdapter adapter = new();
+        ControlSession session = CreateSession(adapter);
+
+        ControlSessionResult down = await session.ProcessMessageAsync(SignedCommand("keyboard.modifierDown", new { key = "Ctrl" }));
+        ControlSessionResult up = await session.ProcessMessageAsync(SignedCommand("keyboard.modifierUp", new { key = "Ctrl" }, id: "request-2"));
+
+        Assert.True(down.HasResponse);
+        Assert.True(up.HasResponse);
+        Assert.Equal(["setKeyDown:Ctrl:True", "setKeyDown:Ctrl:False"], adapter.Calls);
+    }
+
     [Fact]
     public async Task RejectsInvalidJsonAndMalformedPayloads()
     {
@@ -121,24 +135,27 @@ public async Task AuthenticatedRepeatStartExecutesInitialCommandAndStopAcknowled
     }
 
     [Fact]
-    public async Task DisconnectingReleasesHeldMouseButtons()
+    public async Task DisconnectingReleasesHeldInputs()
     {
         FakeInputAdapter adapter = new();
         FakeCursorOverlay overlay = new();
         ControlSession session = CreateSession(adapter, overlay);
 
         await session.ProcessMessageAsync(SignedCommand("mouse.dragStart", new { button = "left" }, id: "request-1"));
-        ControlSessionResult result = await session.ProcessMessageAsync(SignedCommand("connection.disconnecting", new { }, id: "request-2"));
+        await session.ProcessMessageAsync(SignedCommand("keyboard.modifierDown", new { key = "Ctrl" }, id: "request-2"));
+        ControlSessionResult result = await session.ProcessMessageAsync(SignedCommand("connection.disconnecting", new { }, id: "request-3"));
 
         Assert.True(result.HasResponse);
         Assert.Equal(
             [
                 "setMouseButtonDown:left:True",
-                "setMouseButtonDown:left:False"
+                "setKeyDown:Ctrl:True",
+                "setMouseButtonDown:left:False",
+                "setKeyDown:Ctrl:False"
             ],
             adapter.Calls);
         Assert.Equal([true, false], overlay.DragActiveChanges);
-        Assert.Equal(1, overlay.HideCount);
+        Assert.Equal(2, overlay.HideCount);
         Assert.Equal(1, overlay.EndSessionCount);
     }
 
@@ -301,6 +318,12 @@ public Task PressKeyAsync(string key, CancellationToken cancellationToken = defa
             return Task.CompletedTask;
         }
 
+        public Task SetKeyDownAsync(string key, bool down, CancellationToken cancellationToken = default)
+        {
+            Calls.Add($"setKeyDown:{key}:{down}");
+            return Task.CompletedTask;
+        }
+
         public Task PressShortcutAsync(IReadOnlyList<string> keys, CancellationToken cancellationToken = default)
         {
             Calls.Add($"pressShortcut:{string.Join("+", keys)}");