Update OS version detection to get version directly from Windows

src/Grpc.Net.Client/Internal/NtDll.cs

@@ -0,0 +1,69 @@
+#region Copyright notice and license
+
+// Copyright 2019 The gRPC Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+#if !NET5_0_OR_GREATER
+
+using System.Runtime.InteropServices;
+
+namespace Grpc.Net.Client.Internal;
+
+internal static class NtDll
+{
+    [DllImport("ntdll.dll", SetLastError = true, CharSet = CharSet.Unicode)]
+    internal static extern NTSTATUS RtlGetVersion(ref OSVERSIONINFOEX versionInfo);
+
+    internal static Version DetectWindowsVersion()
+    {
+        var osVersionInfo = new OSVERSIONINFOEX { OSVersionInfoSize = Marshal.SizeOf(typeof(OSVERSIONINFOEX)) };
+
+        if (RtlGetVersion(ref osVersionInfo) != NTSTATUS.STATUS_SUCCESS)
+        {
+            throw new InvalidOperationException($"Failed to call internal {nameof(RtlGetVersion)}.");
+        }
+
+        return new Version(osVersionInfo.MajorVersion, osVersionInfo.MinorVersion, osVersionInfo.BuildNumber, 0);
+    }
+
+    internal enum NTSTATUS : uint
+    {
+        /// <summary>
+        /// The operation completed successfully. 
+        /// </summary>
+        STATUS_SUCCESS = 0x00000000
+    }
+
+    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
+    internal struct OSVERSIONINFOEX
+    {
+        // The OSVersionInfoSize field must be set to Marshal.SizeOf(typeof(OSVERSIONINFOEX))
+        public int OSVersionInfoSize;
+        public int MajorVersion;
+        public int MinorVersion;
+        public int BuildNumber;
+        public int PlatformId;
+        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
+        public string CSDVersion;
+        public ushort ServicePackMajor;
+        public ushort ServicePackMinor;
+        public short SuiteMask;
+        public byte ProductType;
+        public byte Reserved;
+    }
+}
+
+#endif

src/Grpc.Net.Client/Internal/OperatingSystem.cs

@@ -39,13 +39,23 @@ internal sealed class OperatingSystem : IOperatingSystem
 
     private OperatingSystem()
     {
-        IsBrowser = RuntimeInformation.IsOSPlatform(OSPlatform.Create("browser"));
 #if NET5_0_OR_GREATER
         IsAndroid = System.OperatingSystem.IsAndroid();
+        IsWindows = System.OperatingSystem.IsWindows();
+        IsBrowser = System.OperatingSystem.IsBrowser();
+        OSVersion = Environment.OSVersion.Version;
 #else
         IsAndroid = false;
-#endif
         IsWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
-        OSVersion = Environment.OSVersion.Version;
+        IsBrowser = RuntimeInformation.IsOSPlatform(OSPlatform.Create("browser"));
+
+        // Older versions of .NET report an OSVersion.Version based on Windows compatibility settings.
+        // For example, if an app running on Windows 11 is configured to be "compatible" with Windows 10
+        // then the version returned is always Windows 10.
+        //
+        // Get correct Windows version directly from Windows by calling RtlGetVersion.
+        // https://www.pinvoke.net/default.aspx/ntdll/RtlGetVersion.html
+        OSVersion = IsWindows ? NtDll.DetectWindowsVersion() : Environment.OSVersion.Version;
+#endif
     }
 }

test/Grpc.Net.Client.Tests/OperatingSystemTests.cs

@@ -0,0 +1,43 @@
+#region Copyright notice and license
+
+// Copyright 2019 The gRPC Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using Grpc.Net.Client.Internal;
+using NUnit.Framework;
+using OperatingSystem = Grpc.Net.Client.Internal.OperatingSystem;
+
+namespace Grpc.Net.Client.Tests;
+
+public class OperatingSystemTests
+{
+#if !NET5_0_OR_GREATER
+    [Test]
+    [Platform("Windows", Reason = "Only runs on Windows where ntdll.dll is present.")]
+    public void DetectWindowsVersion_Windows_MatchesEnvironment()
+    {
+        // It is safe to compare Environment.OSVersion.Version on netfx because tests have no compatibilty setting.
+        Assert.AreEqual(Environment.OSVersion.Version, NtDll.DetectWindowsVersion());
+    }
+#endif
+
+    [Test]
+    public void OSVersion_ModernDotNet_MatchesEnvironment()
+    {
+        // It is safe to compare Environment.OSVersion.Version on netfx because tests have no compatibilty setting.
+        Assert.AreEqual(Environment.OSVersion.Version, OperatingSystem.Instance.OSVersion);
+    }
+}