Implement Linux locator

examples/AvaloniaCrossPlat/ConsoleLogger.cs

@@ -0,0 +1,22 @@
+using System;
+using Microsoft.Extensions.Logging;
+
+namespace AvaloniaCrossPlat;
+
+public class ConsoleLogger : ILogger
+{
+    public void Log<TState>(LogLevel logLevel, EventId eventId, TState state, Exception exception, Func<TState, Exception, string> formatter)
+    {
+        Console.WriteLine(formatter(state, exception));
+    }
+
+    public bool IsEnabled(LogLevel logLevel)
+    {
+        return true;
+    }
+
+    public IDisposable BeginScope<TState>(TState state)
+    {
+        return null;
+    }
+}

examples/AvaloniaCrossPlat/Program.cs

@@ -13,7 +13,7 @@ class Program
     public static void Main(string[] args)
     {
         VelopackApp.Build()
-            .Run();
+            .Run(new ConsoleLogger());
 
         BuildAvaloniaApp()
             .StartWithClassicDesktopLifetime(args);

src/Velopack.Packaging.Unix/Commands/LinuxPackCommandRunner.cs

@@ -49,10 +49,12 @@ Categories=Development;
 """);
 
             File.Copy(Options.Icon, Path.Combine(dir.FullName, Options.PackId + Path.GetExtension(Options.Icon)), true);
+            var helper = new HelperExe(Log);
 
             var bin = dir.CreateSubdirectory("usr").CreateSubdirectory("bin");
             CopyFiles(new DirectoryInfo(packDir), bin, progress, true);
             File.WriteAllText(Path.Combine(bin.FullName, "sq.version"), nuspecText);
+            File.Copy(helper.UpdateNixPath, Path.Combine(bin.FullName, "UpdateNix"), true);
             progress(100);
             return Task.FromResult(dir.FullName);
         }

src/Velopack.Packaging.Unix/HelperExe.cs

@@ -24,6 +24,7 @@ public class HelperExe : HelperFile
         var tool = AppImageTool;
         Chmod.ChmodFileAsExecutable(tool);
         InvokeAndThrowIfNonZero(tool, new[] { appDir, outputFile }, null);
+        Chmod.ChmodFileAsExecutable(outputFile);
     }
 
     [SupportedOSPlatform("osx")]

src/Velopack/Locators/LinuxVelopackLocator.cs

@@ -1,11 +1,14 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Runtime.Versioning;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Logging;
 using NuGet.Versioning;
+using Velopack.NuGet;
 
 namespace Velopack.Locators
 {
@@ -43,6 +46,9 @@ namespace Velopack.Locators
         /// <summary> A pointer to /var/tmp/{velopack}, a location on linux which is semi-persistent. </summary>
         public string PersistentVelopackDir => CreateSubDirIfDoesNotExist("/var/tmp", "velopack");
 
+        /// <summary> File path of the .AppImage which mounted and ran this application. </summary>
+        public string AppImagePath => Environment.GetEnvironmentVariable("APPIMAGE");
+
         /// <summary>
         /// Creates a new <see cref="OsxVelopackLocator"/> and auto-detects the
         /// app information from metadata embedded in the .app.
@@ -54,8 +60,34 @@ namespace Velopack.Locators
                 throw new NotSupportedException("Cannot instantiate LinuxVelopackLocator on a non-linux system.");
 
             Log.Info($"Initialising {nameof(LinuxVelopackLocator)}");
+            
+            // are we inside a mounted .AppImage?
+            var ourPath = VelopackRuntimeInfo.EntryExePath;
+            var ix = ourPath.IndexOf("/usr/bin/", StringComparison.InvariantCultureIgnoreCase);
+            if (ix <= 0) {
+                Log.Warn($"Unable to locate .AppImage root from '{ourPath}'");
+                return;
+            }
 
-            throw new NotImplementedException();
+            var rootDir = ourPath.Substring(0, ix);
+            var contentsDir = Path.Combine(rootDir, "usr", "bin");
+            var updateExe = Path.Combine(contentsDir, "UpdateNix");
+            var metadataPath = Path.Combine(contentsDir, Utility.SpecVersionFileName);
+
+            if (!String.IsNullOrEmpty(AppImagePath) && File.Exists(AppImagePath)) {
+                if (File.Exists(updateExe) && NuspecManifest.TryParseFromFile(metadataPath, out var manifest)) {
+                    Log.Info("Located valid manifest file at: " + metadataPath);
+                    AppId = manifest.Id;
+                    RootAppDir = rootDir;
+                    AppContentDir = contentsDir;
+                    UpdateExePath = updateExe;
+                    CurrentlyInstalledVersion = manifest.Version;
+                } else {
+                    logger.Error("Unable to locate UpdateNix in " + contentsDir);
+                }
+            } else {
+                logger.Error("Unable to locate .AppImage ($APPIMAGE)");
+            }
         }
     }
 }