Add SpanOfCharAsUtf8StringMarshaller and remove ValueUtf8Converter (#121870)

Copilot · jkotas · web-flow · commit 6eb2b9b37b8b · 2025-11-21T08:08:39.000-08:00
Make sure that the thread-local P/Invoke last error is not getting corrupted by marshalling post-actions. Fixes #121868 --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com> Co-authored-by: Jan Kotas <jkotas@microsoft.com>
diff --git a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.MkDir.cs b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.MkDir.cs
@@ -3,20 +3,13 @@
 
 using System;
 using System.Runtime.InteropServices;
-using System.Text;
+using System.Runtime.InteropServices.Marshalling;
 
 internal static partial class Interop
 {
     internal static partial class Sys
     {
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_MkDir", SetLastError = true)]
-        private static partial int MkDir(ref byte path, int mode);
-
-        internal static int MkDir(ReadOnlySpan<char> path, int mode)
-        {
-            using ValueUtf8Converter converter = new(stackalloc byte[DefaultPathBufferSize]);
-            int result = MkDir(ref MemoryMarshal.GetReference(converter.ConvertAndTerminateString(path)), mode);
-            return result;
-        }
+        internal static partial int MkDir([MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> path, int mode);
     }
 }
diff --git a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.ReadLink.cs b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.ReadLink.cs
@@ -4,6 +4,7 @@
 using System;
 using System.Buffers;
 using System.Runtime.InteropServices;
+using System.Runtime.InteropServices.Marshalling;
 using System.Text;
 
 internal static partial class Interop
@@ -21,7 +22,7 @@ internal static partial class Sys
         /// Returns the number of bytes placed into the buffer on success; bufferSize if the buffer is too small; and -1 on error.
         /// </returns>
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_ReadLink", SetLastError = true)]
-        private static partial int ReadLink(ref byte path, ref byte buffer, int bufferSize);
+        private static partial int ReadLink([MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> path, ref byte buffer, int bufferSize);
 
         /// <summary>
         /// Takes a path to a symbolic link and returns the link target path.
@@ -32,18 +33,14 @@ internal static partial class Sys
         {
             const int StackBufferSize = 256;
 
-            // Use an initial buffer size that prevents disposing and renting
-            // a second time when calling ConvertAndTerminateString.
-            using var converter = new ValueUtf8Converter(stackalloc byte[StackBufferSize]);
             Span<byte> spanBuffer = stackalloc byte[StackBufferSize];
             byte[]? arrayBuffer = null;
-            ref byte pathReference = ref MemoryMarshal.GetReference(converter.ConvertAndTerminateString(path));
             while (true)
             {
                 int error = 0;
                 try
                 {
-                    int resultLength = ReadLink(ref pathReference, ref MemoryMarshal.GetReference(spanBuffer), spanBuffer.Length);
+                    int resultLength = ReadLink(path, ref MemoryMarshal.GetReference(spanBuffer), spanBuffer.Length);
 
                     if (resultLength < 0)
                     {
diff --git a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.Rename.cs b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.Rename.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Runtime.InteropServices;
-using System.Text;
+using System.Runtime.InteropServices.Marshalling;
 
 internal static partial class Interop
 {
@@ -17,22 +17,7 @@ internal static partial class Sys
         /// <returns>
         /// Returns 0 on success; otherwise, returns -1
         /// </returns>
-        [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_Rename", StringMarshalling = StringMarshalling.Utf8, SetLastError = true)]
-        internal static partial int Rename(string oldPath, string newPath);
-
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_Rename", SetLastError = true)]
-        internal static partial int Rename(ref byte oldPath, ref byte newPath);
-
-        internal static int Rename(ReadOnlySpan<char> oldPath, ReadOnlySpan<char> newPath)
-        {
-            ValueUtf8Converter converterNewPath = new(stackalloc byte[DefaultPathBufferSize]);
-            ValueUtf8Converter converterOldPath = new(stackalloc byte[DefaultPathBufferSize]);
-            int result = Rename(
-                ref MemoryMarshal.GetReference(converterOldPath.ConvertAndTerminateString(oldPath)),
-                ref MemoryMarshal.GetReference(converterNewPath.ConvertAndTerminateString(newPath)));
-            converterNewPath.Dispose();
-            converterOldPath.Dispose();
-            return result;
-        }
+        internal static partial int Rename([MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> oldPath, [MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> newPath);
     }
 }
diff --git a/src/libraries/Common/src/Interop/Unix/System.Native/Interop.Stat.Span.cs b/src/libraries/Common/src/Interop/Unix/System.Native/Interop.Stat.Span.cs
@@ -3,32 +3,16 @@
 
 using System;
 using System.Runtime.InteropServices;
-using System.Text;
+using System.Runtime.InteropServices.Marshalling;
 
 internal static partial class Interop
 {
     internal static partial class Sys
     {
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_Stat", SetLastError = true)]
-        internal static partial int Stat(ref byte path, out FileStatus output);
-
-        internal static int Stat(ReadOnlySpan<char> path, out FileStatus output)
-        {
-            var converter = new ValueUtf8Converter(stackalloc byte[DefaultPathBufferSize]);
-            int result = Stat(ref MemoryMarshal.GetReference(converter.ConvertAndTerminateString(path)), out output);
-            converter.Dispose();
-            return result;
-        }
+        internal static partial int Stat([MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> path, out FileStatus output);
 
         [LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_LStat", SetLastError = true)]
-        internal static partial int LStat(ref byte path, out FileStatus output);
-
-        internal static int LStat(ReadOnlySpan<char> path, out FileStatus output)
-        {
-            var converter = new ValueUtf8Converter(stackalloc byte[DefaultPathBufferSize]);
-            int result = LStat(ref MemoryMarshal.GetReference(converter.ConvertAndTerminateString(path)), out output);
-            converter.Dispose();
-            return result;
-        }
+        internal static partial int LStat([MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> path, out FileStatus output);
     }
 }
diff --git a/src/libraries/Common/src/System/Runtime/InteropServices/SpanOfCharAsUtf8StringMarshaller.cs b/src/libraries/Common/src/System/Runtime/InteropServices/SpanOfCharAsUtf8StringMarshaller.cs
@@ -0,0 +1,75 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace System.Runtime.InteropServices.Marshalling
+{
+    /// <summary>
+    /// Marshaller for ReadOnlySpan&lt;char&gt; to UTF-8 strings.
+    /// </summary>
+    [CustomMarshaller(typeof(ReadOnlySpan<char>), MarshalMode.ManagedToUnmanagedIn, typeof(ManagedToUnmanagedIn))]
+    internal static unsafe class SpanOfCharAsUtf8StringMarshaller
+    {
+        /// <summary>
+        /// Custom marshaller to marshal a ReadOnlySpan&lt;char&gt; as a UTF-8 unmanaged string.
+        /// </summary>
+        internal ref struct ManagedToUnmanagedIn
+        {
+            /// <summary>
+            /// Gets the requested buffer size for optimized marshalling.
+            /// </summary>
+            public static int BufferSize => 0x100;
+
+            private byte* _unmanagedValue;
+            private bool _allocated;
+
+            /// <summary>
+            /// Initializes the marshaller with a ReadOnlySpan&lt;char&gt; and requested buffer.
+            /// </summary>
+            /// <param name="managed">The managed ReadOnlySpan&lt;char&gt; with which to initialize the marshaller.</param>
+            /// <param name="buffer">The request buffer whose size is at least <see cref="BufferSize"/>.</param>
+            public void FromManaged(ReadOnlySpan<char> managed, Span<byte> buffer)
+            {
+                _allocated = false;
+
+                const int MaxUtf8BytesPerChar = 3;
+
+                // >= for null terminator
+                // Use the cast to long to avoid the checked operation
+                if ((long)MaxUtf8BytesPerChar * managed.Length >= buffer.Length)
+                {
+                    // Calculate accurate byte count when the provided stack-allocated buffer is not sufficient
+                    int exactByteCount = checked(Encoding.UTF8.GetByteCount(managed) + 1); // + 1 for null terminator
+                    if (exactByteCount > buffer.Length)
+                    {
+                        buffer = new Span<byte>((byte*)NativeMemory.Alloc((nuint)exactByteCount), exactByteCount);
+                        _allocated = true;
+                    }
+                }
+
+                // Unsafe.AsPointer is safe since buffer must be pinned
+                _unmanagedValue = (byte*)Unsafe.AsPointer(ref MemoryMarshal.GetReference(buffer));
+
+                int byteCount = Encoding.UTF8.GetBytes(managed, buffer);
+                buffer[byteCount] = 0; // null-terminate
+            }
+
+            /// <summary>
+            /// Converts the current managed ReadOnlySpan&lt;char&gt; to an unmanaged string.
+            /// </summary>
+            /// <returns>An unmanaged string.</returns>
+            public byte* ToUnmanaged() => _unmanagedValue;
+
+            /// <summary>
+            /// Frees any allocated unmanaged memory.
+            /// </summary>
+            public void Free()
+            {
+                if (_allocated)
+                    NativeMemory.Free(_unmanagedValue);
+            }
+        }
+    }
+}
diff --git a/src/libraries/Common/src/System/Text/ValueUtf8Converter.cs b/src/libraries/Common/src/System/Text/ValueUtf8Converter.cs
diff --git a/src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj b/src/libraries/System.Diagnostics.Process/src/System.Diagnostics.Process.csproj
@@ -273,8 +273,8 @@
              Link="Common\Interop\Unix\Interop.ResourceLimits.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.PathConf.cs"
              Link="Common\Interop\Unix\Interop.PathConf.cs" />
-    <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs"
-             Link="Common\System\Text\ValueUtf8Converter.cs" />
+    <Compile Include="$(CommonPath)System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs"
+             Link="Common\System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.WaitId.cs"
              Link="Common\Interop\Unix\Interop.WaitId.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.WaitPid.cs"
diff --git a/src/libraries/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj b/src/libraries/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj
@@ -115,8 +115,8 @@
              Link="Common\Microsoft\Win32\SafeHandles\SafeCreateHandle.OSX.cs" />
     <Compile Include="$(CommonPath)Microsoft\Win32\SafeHandles\SafeEventStreamHandle.OSX.cs"
              Link="Common\Microsoft\Win32\SafeHandles\SafeEventStreamHandle.OSX.cs" />
-    <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs"
-             Link="Common\System\Text\ValueUtf8Converter.cs" />
+    <Compile Include="$(CommonPath)System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs"
+             Link="Common\System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj b/src/libraries/System.Net.Ping/src/System.Net.Ping.csproj
@@ -68,8 +68,8 @@
              Link="Common\Interop\Unix\System.Native\Interop.Socket.cs" />
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.SocketAddress.cs"
              Link="Common\Interop\Unix\System.Native\Interop.SocketAddress.cs" />
-    <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs"
-             Link="Common\System\Text\ValueUtf8Converter.cs" />
+    <Compile Include="$(CommonPath)System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs"
+             Link="Common\System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetPlatformIdentifier)' != '' and '$(TargetPlatformIdentifier)' != 'windows' and '$(IsApplePlatform)' != 'true'">
diff --git a/src/libraries/System.Net.Ping/tests/FunctionalTests/System.Net.Ping.Functional.Tests.csproj b/src/libraries/System.Net.Ping/tests/FunctionalTests/System.Net.Ping.Functional.Tests.csproj
@@ -36,7 +36,7 @@
              Link="Common\System\Net\NetworkInformation\UnixCommandLinePing.cs" />
     <Compile Include="$(CommonTestPath)System\Net\Capability.RawSocketPermissions.cs"
              Link="Common\System\Net\Capability.RawSocketPermissions.cs" />
-    <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs"
-             Link="Common\System\Text\ValueUtf8Converter.cs" />
+    <Compile Include="$(CommonPath)System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs"
+             Link="Common\System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs" />
   </ItemGroup>
 </Project>
diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2567,8 +2567,8 @@
     <Compile Include="$(CommonPath)Interop\Unix\System.Native\Interop.Write.cs">
       <Link>Common\Interop\Unix\System.Native\Interop.Write.cs</Link>
     </Compile>
-    <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs">
-      <Link>Common\System\Text\ValueUtf8Converter.cs</Link>
+    <Compile Include="$(CommonPath)System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs">
+      <Link>Common\System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs</Link>
     </Compile>
     <Compile Include="$(CommonPath)System\IO\PathInternal.Unix.cs">
       <Link>Common\System\IO\PathInternal.Unix.cs</Link>
diff --git a/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Unix.cs b/src/libraries/System.Private.CoreLib/src/System/IO/FileSystem.Unix.cs
@@ -674,14 +674,14 @@ internal static void CreateHardLink(string path, string pathToTarget)
 
         internal static FileSystemInfo? ResolveLinkTarget(string linkPath, bool returnFinalTarget, bool isDirectory)
         {
-            ValueStringBuilder sb = new(Interop.DefaultPathBufferSize);
+            ValueStringBuilder sb = new(stackalloc char[Interop.DefaultPathBufferSize]);
             sb.Append(linkPath);
 
             string? linkTarget = Interop.Sys.ReadLink(linkPath);
             if (linkTarget == null)
             {
-                sb.Dispose();
                 Interop.Error error = Interop.Sys.GetLastError();
+                sb.Dispose();
                 // Not a link, return null
                 if (error == Interop.Error.EINVAL)
                 {
diff --git a/src/libraries/System.Security.Cryptography/src/System.Security.Cryptography.csproj b/src/libraries/System.Security.Cryptography/src/System.Security.Cryptography.csproj
@@ -1066,8 +1066,8 @@
              Link="Common\System\Security\Cryptography\SP800108HmacCounterKdfImplementationManaged.cs" />
     <Compile Include="$(CommonPath)System\Text\UrlBase64Encoding.cs"
              Link="Common\System\Text\UrlBase64Encoding.cs" />
-    <Compile Include="$(CommonPath)System\Text\ValueUtf8Converter.cs"
-             Link="Common\System\Text\ValueUtf8Converter.cs" />
+    <Compile Include="$(CommonPath)System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs"
+             Link="Common\System\Runtime\InteropServices\SpanOfCharAsUtf8StringMarshaller.cs" />
     <Compile Include="System\Security\Cryptography\AesCcm.OpenSsl.cs" />
     <Compile Include="System\Security\Cryptography\AesGcm.OpenSsl.cs" />
     <Compile Include="System\Security\Cryptography\AesImplementation.OpenSsl.cs" />

Original file line number	Diff line number	Diff line change
`@@ -3,20 +3,13 @@`
`3`	`3`
`4`	`4`	`using System;`
`5`	`5`	`using System.Runtime.InteropServices;`
`6`		`-using System.Text;`
	`6`	`+using System.Runtime.InteropServices.Marshalling;`
`7`	`7`
`8`	`8`	`internal static partial class Interop`
`9`	`9`	`{`
`10`	`10`	`internal static partial class Sys`
`11`	`11`	`{`
`12`	`12`	`[LibraryImport(Libraries.SystemNative, EntryPoint = "SystemNative_MkDir", SetLastError = true)]`
`13`		`- private static partial int MkDir(ref byte path, int mode);`
`14`		`-`
`15`		`- internal static int MkDir(ReadOnlySpan<char> path, int mode)`
`16`		`- {`
`17`		`- using ValueUtf8Converter converter = new(stackalloc byte[DefaultPathBufferSize]);`
`18`		`- int result = MkDir(ref MemoryMarshal.GetReference(converter.ConvertAndTerminateString(path)), mode);`
`19`		`- return result;`
`20`		`- }`
	`13`	`+ internal static partial int MkDir([MarshalUsing(typeof(SpanOfCharAsUtf8StringMarshaller))] ReadOnlySpan<char> path, int mode);`
`21`	`14`	`}`
`22`	`15`	`}`