Support overriding MsQuic.dll in the application directory on Windows.

src/libraries/Common/src/System/AppContextSwitchHelper.cs

@@ -0,0 +1,35 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Globalization;
+
+namespace System
+{
+    internal static class AppContextSwitchHelper
+    {
+        internal static bool GetBooleanConfig(string switchName, bool defaultValue = false) =>
+            AppContext.TryGetSwitch(switchName, out bool value) ? value : defaultValue;
+
+        internal static bool GetBooleanConfig(string switchName, string envVariable, bool defaultValue = false)
+        {
+            if (AppContext.TryGetSwitch(switchName, out bool value))
+            {
+                return value;
+            }
+
+            if (Environment.GetEnvironmentVariable(envVariable) is string str)
+            {
+                if (str == "1" || string.Equals(str, bool.TrueString, StringComparison.OrdinalIgnoreCase))
+                {
+                    return true;
+                }
+                if (str == "0" || string.Equals(str, bool.FalseString, StringComparison.OrdinalIgnoreCase))
+                {
+                    return false;
+                }
+            }
+
+            return defaultValue;
+        }
+    }
+}

src/libraries/System.Net.Quic/src/System.Net.Quic.csproj

@@ -25,6 +25,7 @@
     <Compile Include="System\Net\Quic\**\*.cs" Exclude="System\Net\Quic\*.Unsupported.cs"/>
     <!-- System.Net common -->
     <Compile Include="$(CommonPath)DisableRuntimeMarshalling.cs" Link="Common\DisableRuntimeMarshalling.cs" />
+    <Compile Include="$(CommonPath)System\AppContextSwitchHelper.cs" Link="Common\System\AppContextSwitchHelper.cs" />
     <Compile Include="$(CommonPath)System\Net\SafeHandleCache.cs" Link="Common\System\Net\SafeHandleCache.cs" />
     <Compile Include="$(CommonPath)System\Net\ArrayBuffer.cs" Link="Common\System\Net\ArrayBuffer.cs" />
     <Compile Include="$(CommonPath)System\Net\MultiArrayBuffer.cs" Link="Common\System\Net\MultiArrayBuffer.cs" />

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/MsQuicApi.cs

@@ -4,6 +4,7 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Net.Sockets;
+using System.IO;
 using System.Runtime.InteropServices;
 using Microsoft.Quic;
 using static Microsoft.Quic.MsQuic;
@@ -75,7 +76,7 @@ private MsQuicApi(QUIC_API_TABLE* apiTable)
     static MsQuicApi()
     {
         bool loaded = false;
-        IntPtr msQuicHandle;
+        IntPtr msQuicHandle = IntPtr.Zero;
         Version = default;
 
         // MsQuic is using DualMode sockets and that will fail even for IPv4 if AF_INET6 is not available.
@@ -94,7 +95,7 @@ static MsQuicApi()
             // Windows ships msquic in the assembly directory next to System.Net.Quic, so load that.
             // For single-file deployments, the assembly location is an empty string so we fall back
             // to AppContext.BaseDirectory which is the directory containing the single-file executable.
-            string path = typeof(MsQuicApi).Assembly.Location is string assemblyLocation && !string.IsNullOrEmpty(assemblyLocation)
+            string path = !ShouldUseAppLocalMsQuic() && typeof(MsQuicApi).Assembly.Location is string assemblyLocation && !string.IsNullOrEmpty(assemblyLocation)
                 ? System.IO.Path.GetDirectoryName(assemblyLocation)!
                 : AppContext.BaseDirectory;
 
@@ -278,4 +279,7 @@ private static bool IsTls13Disabled(bool isServer)
 #endif
         return false;
     }
+
+    private static bool ShouldUseAppLocalMsQuic() => AppContextSwitchHelper.GetBooleanConfig(
+        "System.Net.Quic.AppLocalMsQuic");
 }

src/libraries/System.Net.Quic/src/System/Net/Quic/Internal/MsQuicConfiguration.Cache.cs

@@ -16,27 +16,9 @@ namespace System.Net.Quic;
 
 internal static partial class MsQuicConfiguration
 {
-    private const string DisableCacheEnvironmentVariable = "DOTNET_SYSTEM_NET_QUIC_DISABLE_CONFIGURATION_CACHE";
-    private const string DisableCacheCtxSwitch = "System.Net.Quic.DisableConfigurationCache";
-
-    internal static bool ConfigurationCacheEnabled { get; } = GetConfigurationCacheEnabled();
-
-    private static bool GetConfigurationCacheEnabled()
-    {
-        // AppContext switch takes precedence
-        if (AppContext.TryGetSwitch(DisableCacheCtxSwitch, out bool value))
-        {
-            return !value;
-        }
-        // check environment variable second
-        else if (Environment.GetEnvironmentVariable(DisableCacheEnvironmentVariable) is string envVar)
-        {
-            return !(envVar == "1" || envVar.Equals("true", StringComparison.OrdinalIgnoreCase));
-        }
-
-        // enabled by default
-        return true;
-    }
+    internal static bool ConfigurationCacheEnabled { get; } = !AppContextSwitchHelper.GetBooleanConfig(
+        "System.Net.Quic.DisableConfigurationCache",
+        "DOTNET_SYSTEM_NET_QUIC_DISABLE_CONFIGURATION_CACHE");
 
     private static readonly MsQuicConfigurationCache s_configurationCache = new MsQuicConfigurationCache();
 

src/libraries/System.Net.Quic/tests/FunctionalTests/MsQuicTests.cs

@@ -720,7 +720,7 @@ public async Task ConnectWithClientCertificate(bool sendCertificate, ClientCertS
             await serverConnection.DisposeAsync();
         }
 
-        [Fact]
+        [ConditionalFact(typeof(QuicTestCollection), nameof(QuicTestCollection.IsUsingSchannelBackend))]
         [PlatformSpecific(TestPlatforms.Windows)]
         public async Task Server_CertificateWithEphemeralKey_Throws()
         {
@@ -764,7 +764,7 @@ public async Task Server_CertificateWithEphemeralKey_Throws()
             }
         }
 
-        [Fact]
+        [ConditionalFact(typeof(QuicTestCollection), nameof(QuicTestCollection.IsUsingSchannelBackend))]
         [PlatformSpecific(TestPlatforms.Windows)]
         public async Task Client_CertificateWithEphemeralKey_Throws()
         {

src/libraries/System.Net.Quic/tests/FunctionalTests/QuicTestBase.cs

@@ -44,6 +44,18 @@ public abstract class QuicTestBase : IDisposable
         public const int PassingTestTimeoutMilliseconds = 4 * 60 * 1000;
         public static TimeSpan PassingTestTimeout => TimeSpan.FromMilliseconds(PassingTestTimeoutMilliseconds);
 
+        static QuicTestBase()
+        {
+            // Opt in to run with OpenSSL version on MsQuic on older windows where Schannel
+            // version is not supported.
+            //
+            // This has to happen here in order to be called before QuicTestBase.IsSupported
+            if (PlatformDetection.IsWindows10OrLater && !QuicTestCollection.IsWindowsVersionWithSchannelSupport())
+            {
+                AppContext.SetSwitch("System.Net.Quic.AppLocalMsQuic", true);
+            }
+        }
+
         public QuicTestBase(ITestOutputHelper output)
         {
             _output = output;

src/libraries/System.Net.Quic/tests/FunctionalTests/QuicTestCollection.cs

@@ -26,8 +26,9 @@ public unsafe class QuicTestCollection : ICollectionFixture<QuicTestCollection>,
     public QuicTestCollection()
     {
         string msQuicLibraryVersion = GetMsQuicLibraryVersion();
+        string tlsBackend = IsUsingSchannelBackend() ? "Schannel" : "OpenSSL";
         // If any of the reflection bellow breaks due to changes in "System.Net.Quic.MsQuicApi", also check and fix HttpStress project as it uses the same hack.
-        Console.WriteLine($"MsQuic {(IsSupported ? "supported" : "not supported")} and using '{msQuicLibraryVersion}'.");
+        Console.WriteLine($"MsQuic {(IsSupported ? "supported" : "not supported")} and using '{msQuicLibraryVersion}' {(IsSupported ? $"({tlsBackend})" : "")}.");
 
         if (IsSupported)
         {
@@ -97,6 +98,13 @@ void DumpCounter(QUIC_PERFORMANCE_COUNTERS counter)
         Console.WriteLine($"Unobserved exceptions of {s_unobservedExceptions.Count} different types: {Environment.NewLine}{string.Join(Environment.NewLine + new string('=', 120) + Environment.NewLine, s_unobservedExceptions.Select(pair => $"Count {pair.Value}: {pair.Key}"))}");
     }
 
+    internal static bool IsWindowsVersionWithSchannelSupport()
+    {
+        // copied from MsQuicApi implementation to avoid triggering the static constructor
+        Version minWindowsVersion = new Version(10, 0, 20145, 1000);
+        return OperatingSystem.IsWindowsVersionAtLeast(minWindowsVersion.Major, minWindowsVersion.Minor, minWindowsVersion.Build, minWindowsVersion.Revision);
+    }
+
     private static Version GetMsQuicVersion()
     {
         Type msQuicApiType = Type.GetType("System.Net.Quic.MsQuicApi, System.Net.Quic");
@@ -111,6 +119,13 @@ private static Version GetMsQuicVersion()
         return (string)msQuicApiType.GetProperty("MsQuicLibraryVersion", BindingFlags.NonPublic | BindingFlags.Static).GetGetMethod(true).Invoke(null, Array.Empty<object?>());
     }
 
+    internal static bool IsUsingSchannelBackend()
+    {
+        Type msQuicApiType = Type.GetType("System.Net.Quic.MsQuicApi, System.Net.Quic");
+
+        return (bool)msQuicApiType.GetProperty("UsesSChannelBackend", BindingFlags.NonPublic | BindingFlags.Static).GetGetMethod(true).Invoke(null, Array.Empty<object?>());
+    }
+
     private static QUIC_API_TABLE* GetApiTable()
     {
         Type msQuicApiType = Type.GetType("System.Net.Quic.MsQuicApi, System.Net.Quic");

src/libraries/System.Net.Quic/tests/FunctionalTests/System.Net.Quic.Functional.Tests.csproj

@@ -42,4 +42,22 @@
   <ItemGroup>
     <PackageReference Include="System.Net.TestData" Version="$(SystemNetTestDataVersion)" />
   </ItemGroup>
+
+  <!-- Support running tests on older windows by explicitly including OpenSSL version of MsQuic,
+       The binary will be used only if "System.Net.Quic.AppLocalMsQuic" appctx switch is 'true',
+       Which we manually flip in the test setup on appropriate platform. -->
+  <ItemGroup Condition="'$(TargetPlatformIdentifier)' == 'windows'">
+    <PackageReference Include="Microsoft.Native.Quic.MsQuic.OpenSSL"
+                      Version="$(MicrosoftNativeQuicMsQuicSchannelVersion)"
+                      PrivateAssets="all"
+                      GeneratePathProperty="true" />
+
+  </ItemGroup>
+  <Target Name="CopyCustomContent" AfterTargets="Build" BeforeTargets="PrepareForRun" Condition="'$(TargetPlatformIdentifier)' == 'windows'">
+    <Copy SourceFiles="$(PkgMicrosoft_Native_Quic_MsQuic_OpenSSL)\build\native\bin\x64\msquic.dll" DestinationFolder="$(OutDir)" />
+  </Target>
+  <Target Name="CopyCustomContentOnPublish" AfterTargets="Publish" BeforeTargets="PrepareForRun" Condition="'$(TargetPlatformIdentifier)' == 'windows'">
+    <Copy SourceFiles="$(PkgMicrosoft_Native_Quic_MsQuic_OpenSSL)\build\native\bin\x64\msquic.dll" DestinationFolder="$(PublishDir)" />
+  </Target>
+
 </Project>