Only allow a single instance to run

src/Keyden.App/AgentK.cs

@@ -386,6 +386,16 @@ private class KeyInfo
 	}
 	private readonly Dictionary<string, KeyInfo> KeyInfos = new();
 
+	public void AddActivity(string title, string description, string icon = "fa-circle-info", ActivityImportance importance = ActivityImportance.Normal)
+	{
+		NewActivity?.Invoke(new ActivityItem()
+		{
+			Title = title,
+			Description = description,
+			Icon = icon,
+			Importance = importance,
+		});
+	}
 
 	private AuthRequired QueryAuth(SshKey key, SshKeyOptions options, ClientInfo clientInfo)
 	{

src/Keyden.App/App.axaml.cs

@@ -7,11 +7,17 @@
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
 
-using Keyden.ViewModels;
 using Keyden.Views;
 using Avalonia.Controls;
 using System.Text.Json;
 using System.Text;
+using System.IO.Pipes;
+using System.Globalization;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Reflection.Metadata;
+using System.Threading;
+using System.Threading.Tasks;
 
 namespace Keyden;
 
@@ -55,8 +61,122 @@ public static T GetKeyedService<T>(object? key) where
 	private SshAgent? Agent { get; set; }
 	private KeydenSettings? Settings { get; set; }
 
+	public static string AppPipePath
+	{
+		get
+		{
+			if (false&&RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
+			{
+				return $"{Environment.UserName}/keyden";
+			}
+
+			if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
+			{
+				var uid = Unix.Getuid().ToString(CultureInfo.InvariantCulture);
+				var socketDirectory = $"/run/user/{uid}";
+
+				// check for legacy linux systems
+				if (!Directory.Exists(socketDirectory))
+					socketDirectory = Directory.Exists("/run") ? "/run" : "/var/run";
+
+				if (!Directory.Exists(socketDirectory))
+					return "keyden";
+
+				socketDirectory += "/keyden";
+				var socketPath = $"{socketDirectory}/keyden.sock";
+
+				if (!Directory.Exists(socketDirectory))
+					Directory.CreateDirectory(socketDirectory);
+				return socketPath;
+			}
+
+			if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+			{
+				var uid = Unix.Getuid().ToString(CultureInfo.InvariantCulture);
+				return $"/var/run/{uid}-keyden.sock";
+			}
+
+			return "keyden";
+		}
+	}
+
+	private async void MainAppPipeThread(CancellationToken ct)
+	{
+		var agentK = GetService<AgentK>();
+		try
+		{
+			using var pipeServer = new NamedPipeServerStream(
+					pipeName: AppPipePath,
+					direction: PipeDirection.InOut,
+					maxNumberOfServerInstances: NamedPipeServerStream.MaxAllowedServerInstances,
+					transmissionMode: PipeTransmissionMode.Byte,
+					options: PipeOptions.Asynchronous | PipeOptions.WriteThrough | PipeOptions.CurrentUserOnly | PipeOptions.FirstPipeInstance,
+					inBufferSize: 1,
+			outBufferSize: 1);
+
+
+			while (!ct.IsCancellationRequested)
+			{
+				try
+				{
+					await pipeServer.WaitForConnectionAsync(ct);
+					var byteRead = pipeServer.ReadByte();
+					if (byteRead == 0x0A)
+					{
+						agentK.AddActivity("Keyden opened", "Another Keyden instance was opened, showing main window instead.");
+
+						ShowMainWindow();
+						pipeServer.WriteByte(0xA0);
+						pipeServer.Flush();
+						await Task.Delay(100);
+					}
+				}
+				catch (OperationCanceledException) { }
+				catch (IOException) { }
+				catch (Exception ex)
+				{
+					agentK.AddActivity("Error in single instance host", ex.ToString(), "fa-circle-exclamation", ViewModels.ActivityImportance.Warning);
+				}
+				finally
+				{
+					if (pipeServer.IsConnected)
+						pipeServer.Disconnect();
+				}
+			}
+		}
+		catch (Exception ex)
+		{
+			agentK.AddActivity("Critical error in single instance host", ex.ToString(), "fa-circle-exclamation", ViewModels.ActivityImportance.Critical);
+		}
+	}
+
+	private CancellationTokenSource AppPipeCts = new();
+
 	public override void OnFrameworkInitializationCompleted()
 	{
+		Exception? singleInstanceEx = null;
+		if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime)
+		{
+			try
+			{
+				using var client = new NamedPipeClientStream(pipeName: AppPipePath);
+				client.Connect(100);
+				if (client.IsConnected)
+				{
+					client.WriteByte(0x0A);
+					client.Flush();
+					if (client.ReadByte() == 0xA0)
+						Environment.Exit(0);
+				}
+			}
+			catch (IOException) { }
+			catch (TimeoutException) { }
+			catch (Exception ex)
+			{
+				singleInstanceEx = ex;
+			}
+		}
+
 		var collection = new ServiceCollection();
 
 		collection.AddSingleton(SystemServices);
@@ -70,18 +190,31 @@ public override void OnFrameworkInitializationCompleted()
 		if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
 		{
 			desktop.ShutdownMode = ShutdownMode.OnExplicitShutdown;
-
 			bool isAutomaticStart =
 				SystemServices.IsAutomaticStart ||
 				desktop.Args?.Contains("--hide") == true;
 
 			if (!isAutomaticStart)
 				ShowMainWindow();
+
+			MainAppPipeThread(AppPipeCts.Token);
+			desktop.Exit += DesktopAppExit;
 		}
 		else if (ApplicationLifetime is ISingleViewApplicationLifetime singleViewPlatform)
 			singleViewPlatform.MainView = new MainView();
 
 		base.OnFrameworkInitializationCompleted();
+
+		if (singleInstanceEx is not null)
+		{
+			var agentK = GetService<AgentK>();
+			agentK.AddActivity("Error in single instance client", singleInstanceEx.ToString(), "fa-circle-exclamation", ViewModels.ActivityImportance.Critical);
+		}
+	}
+
+	private void DesktopAppExit(object? sender, ControlledApplicationLifetimeExitEventArgs e)
+	{
+		AppPipeCts.Cancel();
 	}
 
 	private static SettingsWindow? SettingsWindow { get; set; }

src/Keyden.Core/ISystemServices.cs

@@ -1,6 +1,5 @@
 using System;
 using System.Diagnostics;
-using System.Diagnostics.CodeAnalysis;
 using System.IO.Pipes;
 using System.Threading;
 using System.Threading.Tasks;
@@ -13,7 +12,7 @@ public interface ISystemServices
 	bool IsAutomaticStart { get; }
 
 	TimeSpan UserIdleDuration { get; }
-	public event EventHandler<EventArgs> MachineLocked;
+	event EventHandler<EventArgs> MachineLocked;
 
 	Task<AuthResult> TryAuthUser(
 			AuthRequired authRequired,