Re-use the singlefilehost instead of using a fresh one to reduce package size

build.ps1

@@ -38,7 +38,6 @@ Copy-Item "$In\Win32\Setup.exe" -Destination "$BinOut"
 Copy-Item "$In\Win32\StubExecutable.exe" -Destination "$BinOut"
 Copy-Item "$PSScriptRoot\vendor\rcedit.exe" -Destination "$BinOut"
 Copy-Item "$PSScriptRoot\vendor\signtool.exe" -Destination "$BinOut"
-Copy-Item "$PSScriptRoot\vendor\singlefilehost.exe" -Destination "$BinOut"
 Copy-Item -Path "$PSScriptRoot\vendor\7za.exe" -Destination "$BinOut"
 
 # Clean up files we do not need to create a nuget package

src/Squirrel.CommandLine.Windows/DotnetUtil.cs

@@ -119,26 +119,20 @@ namespace Squirrel.CommandLine
         {
             using var _ = Utility.GetTempDirectory(out var tmpdir);
             var sourceName = Path.GetFileNameWithoutExtension(sourceFile);
+            var newAppHost = Path.Combine(tmpdir, sourceName + ".exe");
 
-            // extract Update.exe to tmp dir
-            Log.Info("Extracting Update.exe resources to temp directory");
+            // extract bundled Update.exe assets to tmp dir
+            Log.Info("Extracting Update.exe resources");
+            File.Copy(sourceFile, newAppHost);
             DumpPackageAssemblies(sourceFile, tmpdir);
 
-            // create new app host
-            var newAppHost = Path.Combine(tmpdir, sourceName + ".exe");
-            HostWriter.CreateAppHost(
-                HelperExe.SingleFileHostPath, // input file
-                newAppHost, // output file
-                sourceName + ".dll", // entry point, relative to apphost
-                true, // isGui?
-                Path.Combine(tmpdir, sourceName + ".dll") // copy exe resources from?
-            );
-
-            // set new icon
+            // set new icon (which eradicates bundled assets)
             Log.Info("Patching Update.exe icon");
             HelperExe.SetExeIcon(newAppHost, iconPath);
+            HostWriter.ResetBundle(newAppHost);
 
-            // create new bundle
+            // re-append bundled assets to exe
+            Log.Info("Re-packing Update.exe bundle");
             var bundlerOutput = Path.Combine(tmpdir, "output");
             Directory.CreateDirectory(bundlerOutput);
             var bundler = new Bundler(
@@ -151,8 +145,6 @@ namespace Squirrel.CommandLine
                 false,
                 sourceName
             );
-
-            Log.Info("Re-packing Update.exe bundle");
             var singleFile = GenerateBundle(bundler, tmpdir, bundlerOutput);
 
             // copy to requested location
@@ -167,7 +159,7 @@ namespace Squirrel.CommandLine
 
             using (var memoryMappedPackage = MemoryMappedFile.CreateFromFile(packageFileName, FileMode.Open, null, 0, MemoryMappedFileAccess.Read)) {
                 using (var packageView = memoryMappedPackage.CreateViewAccessor(0, 0, MemoryMappedFileAccess.Read)) {
-                    var manifest = DotnetUtil.ReadManifest(packageView, bundleHeaderOffset);
+                    var manifest = ReadManifest(packageView, bundleHeaderOffset);
                     foreach (var entry in manifest.Entries) {
                         Stream contents;
 

src/Squirrel.CommandLine.Windows/HelperExe.cs

@@ -18,7 +18,6 @@ namespace Squirrel.CommandLine
         public static string UpdatePath
             => FindHelperFile("Update.exe", p => Microsoft.NET.HostModel.AppHost.HostWriter.IsBundle(p, out var _));
         public static string StubExecutablePath => FindHelperFile("StubExecutable.exe");
-        public static string SingleFileHostPath => FindHelperFile("singlefilehost.exe");
 
         // private so we don't expose paths to internal tools. these should be exposed as a helper function
         private static string SignToolPath => FindHelperFile("signtool.exe");

src/Squirrel.CommandLine/HostModel/AppHost/HostWriter.cs

@@ -209,8 +209,37 @@ namespace Microsoft.NET.HostModel.AppHost
         /// Check if the an AppHost is a single-file bundle
         /// </summary>
         /// <param name="appHostFilePath">The path of Apphost to check</param>
-        /// <param name="bundleHeaderOffset">An out parameter containing the offset of the bundle header (if any)</param>
         /// <returns>True if the AppHost is a single-file bundle, false otherwise</returns>
+        public static void ResetBundle(string appHostFilePath)
+        {
+            byte[] bundleSignature = {
+                // 32 bytes represent the bundle signature: SHA-256 for ".net core bundle"
+                0x8b, 0x12, 0x02, 0xb9, 0x6a, 0x61, 0x20, 0x38,
+                0x72, 0x7b, 0x93, 0x02, 0x14, 0xd7, 0xa0, 0x32,
+                0x13, 0xf5, 0xb9, 0xe6, 0xef, 0xae, 0x33, 0x18,
+                0xee, 0x3b, 0x2d, 0xce, 0x24, 0xb3, 0x6a, 0xae
+            };
+
+            void ResetBundleHeader()
+            {
+                using (var memoryMappedFile = MemoryMappedFile.CreateFromFile(appHostFilePath))
+                {
+                    using (MemoryMappedViewAccessor accessor = memoryMappedFile.CreateViewAccessor())
+                    {
+                        int position = BinaryUtils.SearchInFile(accessor, bundleSignature);
+                        if (position == -1)
+                        {
+                            throw new PlaceHolderNotFoundInAppHostException(bundleSignature);
+                        }
+                        
+                        accessor.WriteArray(position - sizeof(long), new byte[sizeof(long)], 0, sizeof(long));
+                    }
+                }
+            }
+
+            RetryUtil.RetryOnIOError(ResetBundleHeader);
+        }
+        
         public static bool IsBundle(string appHostFilePath, out long bundleHeaderOffset)
         {
             byte[] bundleSignature = {