Allow muxer behind Windows symlink (#99576)

The current logic for the muxer (dotnet.exe) doesn't resolve through symlinks
on Windows. For instance, it looks next to the entry point path for things like
hostfxr. This means that you cannot use a symlink to dotnet.exe, as it will look
next to your symlink for the runtime, rather than next to the target of the symlink.

This PR fixes the problem just for the muxer. To do so, it introduces a new API:
fullpath. The existing realpath API has the behavior of always resolving symlinks
on Unix, and never resolving symlinks on Windows. The new `fullpath` API replicates
this behavior, while the old `realpath` API is changed to always resolve symlinks on
both Unix and Windows. Then, the realpath API is used in appropriate places when
resolving paths relative to the muxer to guarantee resolving through symlinks on
all platforms.

Fixes #83314

src/installer/tests/AppHost.Bundle.Tests/BundleExtractToSpecificPath.cs

@@ -31,7 +31,7 @@ private void AbsolutePath()
             var bundleDir = Directory.GetParent(bundledApp.Path);
             bundleDir.Should().OnlyHaveFiles(new[]
             {
-                Binaries.GetExeFileNameForCurrentPlatform(app.Name),
+                Binaries.GetExeName(app.Name),
                 $"{app.Name}.pdb"
             });
 

src/installer/tests/HostActivation.Tests/InvalidHost.cs

@@ -90,16 +90,16 @@ public SharedTestState()
                 BaseDirectory = TestArtifact.Create(nameof(InvalidHost));
                 Directory.CreateDirectory(BaseDirectory.Location);
 
-                RenamedDotNet = Path.Combine(BaseDirectory.Location, Binaries.GetExeFileNameForCurrentPlatform("renamed"));
+                RenamedDotNet = Path.Combine(BaseDirectory.Location, Binaries.GetExeName("renamed"));
                 File.Copy(Binaries.DotNet.FilePath, RenamedDotNet);
 
-                UnboundAppHost = Path.Combine(BaseDirectory.Location, Binaries.GetExeFileNameForCurrentPlatform("unbound"));
+                UnboundAppHost = Path.Combine(BaseDirectory.Location, Binaries.GetExeName("unbound"));
                 File.Copy(Binaries.AppHost.FilePath, UnboundAppHost);
 
                 if (OperatingSystem.IsWindows())
                 {
                     // Mark the apphost as GUI, but don't bind it to anything - this will cause it to fail
-                    UnboundAppHostGUI = Path.Combine(BaseDirectory.Location, Binaries.GetExeFileNameForCurrentPlatform("unboundgui"));
+                    UnboundAppHostGUI = Path.Combine(BaseDirectory.Location, Binaries.GetExeName("unboundgui"));
                     File.Copy(Binaries.AppHost.FilePath, UnboundAppHostGUI);
                     PEUtils.SetWindowsGraphicalUserInterfaceBit(UnboundAppHostGUI);
                 }

src/installer/tests/HostActivation.Tests/NativeHosting/ComhostSideBySide.cs

@@ -116,7 +116,7 @@ public SharedTestState()
                     }
                 }
 
-                string comsxsName = Binaries.GetExeFileNameForCurrentPlatform("comsxs");
+                string comsxsName = Binaries.GetExeName("comsxs");
                 ComSxsPath = Path.Combine(comsxsDirectory, comsxsName);
                 File.Copy(
                     Path.Combine(RepoDirectoriesProvider.Default.HostTestArtifacts, comsxsName),

src/installer/tests/HostActivation.Tests/NativeHosting/SharedTestStateBase.cs

@@ -21,7 +21,7 @@ public SharedTestStateBase()
             _baseDirArtifact = TestArtifact.Create("nativeHosting");
             BaseDirectory = _baseDirArtifact.Location;
 
-            string nativeHostName = Binaries.GetExeFileNameForCurrentPlatform("nativehost");
+            string nativeHostName = Binaries.GetExeName("nativehost");
             NativeHostPath = Path.Combine(BaseDirectory, nativeHostName);
 
             // Copy over native host

src/installer/tests/HostActivation.Tests/NativeUnitTests.cs

@@ -15,7 +15,7 @@ public class NativeUnitTests
         [Fact]
         public void Native_Test_Fx_Ver()
         {
-            string testPath = Path.Combine(RepoDirectoriesProvider.Default.HostTestArtifacts, Binaries.GetExeFileNameForCurrentPlatform("test_fx_ver"));
+            string testPath = Path.Combine(RepoDirectoriesProvider.Default.HostTestArtifacts, Binaries.GetExeName("test_fx_ver"));
 
             Command testCommand = Command.Create(testPath);
             testCommand

src/installer/tests/HostActivation.Tests/SelfContainedAppLaunch.cs

@@ -95,7 +95,7 @@ public void RenameApphost()
         {
             var app = sharedTestState.App.Copy();
 
-            var renamedAppExe = app.AppExe + Binaries.GetExeFileNameForCurrentPlatform("renamed");
+            var renamedAppExe = app.AppExe + Binaries.GetExeName("renamed");
             File.Move(app.AppExe, renamedAppExe, true);
 
             Command.Create(renamedAppExe)

src/installer/tests/HostActivation.Tests/SymbolicLinks.cs

@@ -22,11 +22,11 @@ public SymbolicLinks(SymbolicLinks.SharedTestState fixture)
         }
 
         [Theory]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
         [InlineData ("a/b/SymlinkToApphost")]
         [InlineData ("a/SymlinkToApphost")]
         public void Run_apphost_behind_symlink(string symlinkRelativePath)
         {
+            symlinkRelativePath = Binaries.GetExeName(symlinkRelativePath);
             using (var testDir = TestArtifact.Create("symlink"))
             {
                 Directory.CreateDirectory(Path.Combine(testDir.Location, Path.GetDirectoryName(symlinkRelativePath)));
@@ -43,13 +43,14 @@ public void Run_apphost_behind_symlink(string symlinkRelativePath)
         }
 
         [Theory]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
         [InlineData ("a/b/FirstSymlink", "c/d/SecondSymlink")]
         [InlineData ("a/b/FirstSymlink", "c/SecondSymlink")]
         [InlineData ("a/FirstSymlink", "c/d/SecondSymlink")]
         [InlineData ("a/FirstSymlink", "c/SecondSymlink")]
         public void Run_apphost_behind_transitive_symlinks(string firstSymlinkRelativePath, string secondSymlinkRelativePath)
         {
+            firstSymlinkRelativePath = Binaries.GetExeName(firstSymlinkRelativePath);
+            secondSymlinkRelativePath = Binaries.GetExeName(secondSymlinkRelativePath);
             using (var testDir = TestArtifact.Create("symlink"))
             {
                 // second symlink -> apphost
@@ -71,15 +72,14 @@ public void Run_apphost_behind_transitive_symlinks(string firstSymlinkRelativePa
             }
         }
 
-        //[Theory]
-        //[InlineData("a/b/SymlinkToFrameworkDependentApp")]
-        //[InlineData("a/SymlinkToFrameworkDependentApp")]
-        [Fact(Skip = "Currently failing in OSX with \"No such file or directory\" when running Command.Create. " +
+        [Theory]
+        [InlineData("a/b/SymlinkToFrameworkDependentApp")]
+        [InlineData("a/SymlinkToFrameworkDependentApp")]
+        [SkipOnPlatform(TestPlatforms.OSX, "Currently failing in OSX with \"No such file or directory\" when running Command.Create. " +
             "CI failing to use stat on symbolic links on Linux (permission denied).")]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
-        public void Run_framework_dependent_app_behind_symlink(/*string symlinkRelativePath*/)
+        public void Run_framework_dependent_app_behind_symlink(string symlinkRelativePath)
         {
-            var symlinkRelativePath = string.Empty;
+            symlinkRelativePath = Binaries.GetExeName(symlinkRelativePath);
 
             using (var testDir = TestArtifact.Create("symlink"))
             {
@@ -96,14 +96,14 @@ public void Run_framework_dependent_app_behind_symlink(/*string symlinkRelativeP
             }
         }
 
-        [Fact(Skip = "Currently failing in OSX with \"No such file or directory\" when running Command.Create. " +
-                     "CI failing to use stat on symbolic links on Linux (permission denied).")]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
+        [Fact]
+        [SkipOnPlatform(TestPlatforms.OSX, "Currently failing in OSX with \"No such file or directory\" when running Command.Create. " +
+            "CI failing to use stat on symbolic links on Linux (permission denied).")]
         public void Run_framework_dependent_app_with_runtime_behind_symlink()
         {
             using (var testDir = TestArtifact.Create("symlink"))
             {
-                var dotnetSymlink = Path.Combine(testDir.Location, "dotnet");
+                var dotnetSymlink = Path.Combine(testDir.Location, Binaries.GetExeName("dotnet"));
 
                 using var symlink = new SymLink(dotnetSymlink, TestContext.BuiltDotNet.BinPath);
                 Command.Create(sharedTestState.FrameworkDependentApp.AppExe)
@@ -117,7 +117,6 @@ public void Run_framework_dependent_app_with_runtime_behind_symlink()
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
         public void Put_app_directory_behind_symlink()
         {
             var app = sharedTestState.SelfContainedApp.Copy();
@@ -138,7 +137,6 @@ public void Put_app_directory_behind_symlink()
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
         public void Put_dotnet_behind_symlink()
         {
             using (var testDir = TestArtifact.Create("symlink"))
@@ -156,7 +154,6 @@ public void Put_dotnet_behind_symlink()
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
         public void Put_app_directory_behind_symlink_and_use_dotnet()
         {
             var app = sharedTestState.SelfContainedApp.Copy();
@@ -177,7 +174,6 @@ public void Put_app_directory_behind_symlink_and_use_dotnet()
         }
 
         [Fact]
-        [SkipOnPlatform(TestPlatforms.Windows, "Creating symbolic links requires administrative privilege on Windows, so skip test.")]
         public void Put_satellite_assembly_behind_symlink()
         {
             var app = sharedTestState.LocalizedApp.Copy();

src/installer/tests/Microsoft.NET.HostModel.Tests/Bundle/BundlerConsistencyTests.cs

@@ -23,7 +23,7 @@ public BundlerConsistencyTests(SharedTestState fixture)
             sharedTestState = fixture;
         }
 
-        private static string BundlerHostName = Binaries.GetExeFileNameForCurrentPlatform(SharedTestState.AppName);
+        private static string BundlerHostName = Binaries.GetExeName(SharedTestState.AppName);
         private Bundler CreateBundlerInstance(BundleOptions bundleOptions = BundleOptions.None, Version version = null, bool macosCodesign = true)
             => new Bundler(BundlerHostName, sharedTestState.App.GetUniqueSubdirectory("bundle"), bundleOptions, targetFrameworkVersion: version, macosCodesign: macosCodesign);
 

src/installer/tests/TestUtils/Binaries.cs

@@ -15,7 +15,7 @@ namespace Microsoft.DotNet.CoreSetup.Test
 {
     public static class Binaries
     {
-        public static string GetExeFileNameForCurrentPlatform(string exeName) =>
+        public static string GetExeName(string exeName) =>
             exeName + (RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? ".exe" : string.Empty);
 
         public static (string, string) GetSharedLibraryPrefixSuffix()
@@ -37,7 +37,7 @@ public static string GetSharedLibraryFileNameForCurrentPlatform(string libraryNa
 
         public static class AppHost
         {
-            public static string FileName = GetExeFileNameForCurrentPlatform("apphost");
+            public static string FileName = GetExeName("apphost");
             public static string FilePath = Path.Combine(RepoDirectoriesProvider.Default.HostArtifacts, FileName);
         }
 
@@ -52,7 +52,7 @@ public static class CoreClr
 
         public static class DotNet
         {
-            public static string FileName = GetExeFileNameForCurrentPlatform("dotnet");
+            public static string FileName = GetExeName("dotnet");
             public static string FilePath = Path.Combine(RepoDirectoriesProvider.Default.HostArtifacts, FileName);
         }
 
@@ -84,7 +84,7 @@ public static class NetHost
 
         public static class SingleFileHost
         {
-            public static string FileName = GetExeFileNameForCurrentPlatform("singlefilehost");
+            public static string FileName = GetExeName("singlefilehost");
             public static string FilePath = Path.Combine(RepoDirectoriesProvider.Default.HostArtifacts, FileName);
         }
 

src/installer/tests/TestUtils/SingleFileTestApp.cs

@@ -92,7 +92,7 @@ public string Bundle(BundleOptions options, out Manifest manifest, Version? bund
         {
             string bundleDirectory = GetUniqueSubdirectory("bundle");
             var bundler = new Bundler(
-                Binaries.GetExeFileNameForCurrentPlatform(AppName),
+                Binaries.GetExeName(AppName),
                 bundleDirectory,
                 options,
                 targetFrameworkVersion: bundleVersion,

src/installer/tests/TestUtils/SymbolicLinking.cs → src/installer/tests/TestUtils/SymLink.cs

@@ -35,7 +35,7 @@ private static bool MakeSymbolicLink(string symbolicLinkName, string targetFileN
             errorMessage = string.Empty;
             if (OperatingSystem.IsWindows())
             {
-                if (!CreateSymbolicLink(symbolicLinkName, targetFileName, SymbolicLinkFlag.IsFile))
+                if (!CreateSymbolicLink(symbolicLinkName, targetFileName, SymbolicLinkFlag.IsFile | SymbolicLinkFlag.AllowUnprivilegedCreate))
                 {
                     int errno = Marshal.GetLastWin32Error();
                     errorMessage = $"CreateSymbolicLink failed with error number {errno}";

src/installer/tests/TestUtils/TestApp.cs

@@ -185,7 +185,7 @@ private void LoadAssets()
         {
             Directory.CreateDirectory(Location);
             AppDll = Path.Combine(Location, $"{AssemblyName}.dll");
-            AppExe = Path.Combine(Location, Binaries.GetExeFileNameForCurrentPlatform(AssemblyName));
+            AppExe = Path.Combine(Location, Binaries.GetExeName(AssemblyName));
             DepsJson = Path.Combine(Location, $"{AssemblyName}.deps.json");
             RuntimeConfigJson = Path.Combine(Location, $"{AssemblyName}.runtimeconfig.json");
             RuntimeDevConfigJson = Path.Combine(Location, $"{AssemblyName}.runtimeconfig.dev.json");

src/native/corehost/corehost.cpp

@@ -112,6 +112,8 @@ int exe_start(const int argc, const pal::char_t* argv[])
     initialize_static_createdump();
 #endif
 
+    // Use realpath to find the path of the host, resolving any symlinks.
+    // hostfxr (for dotnet) and the app dll (for apphost) are found relative to the host.
     pal::string_t host_path;
     if (!pal::get_own_executable_path(&host_path) || !pal::realpath(&host_path))
     {
@@ -148,7 +150,7 @@ int exe_start(const int argc, const pal::char_t* argv[])
     {
         trace::info(_X("Detected Single-File app bundle"));
     }
-    else if (!pal::realpath(&app_path))
+    else if (!pal::fullpath(&app_path))
     {
         trace::error(_X("The application to execute does not exist: '%s'."), app_path.c_str());
         return StatusCode::LibHostAppRootFindFailure;

src/native/corehost/fxr/command_line.cpp

@@ -145,7 +145,7 @@ namespace
         if (mode == host_mode_t::apphost)
         {
             app_candidate = host_info.app_path;
-            doesAppExist = bundle::info_t::is_single_file_bundle() || pal::realpath(&app_candidate);
+            doesAppExist = bundle::info_t::is_single_file_bundle() || pal::fullpath(&app_candidate);
         }
         else
         {
@@ -169,7 +169,7 @@ namespace
                 }
             }
 
-            doesAppExist = pal::realpath(&app_candidate);
+            doesAppExist = pal::fullpath(&app_candidate);
             if (!doesAppExist)
             {
                 trace::verbose(_X("Application '%s' does not exist."), app_candidate.c_str());