Restore ability on .NET 9 and later to save dynamic assemblies to disk

CHANGELOG.md

@@ -8,6 +8,7 @@ Breaking Changes:
 
 Enhancements:
 - Minimally improved support for methods having `ref struct` parameter and return types, such as `Span<T>`: Intercepting such methods caused the runtime to throw `InvalidProgramException` and `NullReferenceException` due to forbidden conversions of `ref struct` values when transferring them into & out of `IInvocation` instances. To prevent these exceptions from being thrown, such values now get replaced with `null` in `IInvocation`, and with `default` values in return values and `out` arguments. When proceeding to a target, the target methods likewise receive such nullified values. (@stakx, #665)
+- Restore ability on .NET 9 and later to save dynamic assemblies to disk using `PersistentProxyBuilder` (@stakx, #718)
 - Dependencies were updated
 
 Bugfixes:

ref/Castle.Core-net9.0.cs

@@ -2585,6 +2585,16 @@ public ModuleScope(bool savePhysicalAssembly, bool disableSignedModule, string s
         public string WeakNamedModuleName { get; }
         public static byte[] GetKeyPair() { }
     }
+    public sealed class PersistentProxyBuilder : Castle.DynamicProxy.DefaultProxyBuilder
+    {
+        public PersistentProxyBuilder() { }
+        public event System.EventHandler<Castle.DynamicProxy.PersistentProxyBuilderAssemblyEventArgs>? AssemblyCreated;
+    }
+    public sealed class PersistentProxyBuilderAssemblyEventArgs : System.EventArgs
+    {
+        public System.Reflection.Assembly Assembly { get; }
+        public byte[] AssemblyBytes { get; }
+    }
     public class ProxyGenerationOptions
     {
         public static readonly Castle.DynamicProxy.ProxyGenerationOptions Default;

src/Castle.Core.Tests/DynamicProxy.Tests/PersistentProxyBuilderTestCase.cs

@@ -1,4 +1,4 @@
-// Copyright 2004-2021 Castle Project - http://www.castleproject.org/
+// Copyright 2004-2026 Castle Project - http://www.castleproject.org/
 // 
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -12,14 +12,20 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#if FEATURE_ASSEMBLYBUILDER_SAVE
-
 namespace Castle.DynamicProxy.Tests
 {
 	using System;
+	using System.Collections.Generic;
 	using System.IO;
+	using System.Linq;
+	using System.Reflection;
+
+	using Castle.DynamicProxy.Tests.Interfaces;
+
 	using NUnit.Framework;
 
+#if NET462_OR_GREATER
+
 	[TestFixture]
 	public class PersistentProxyBuilderTestCase
 	{
@@ -44,6 +50,55 @@ public void PersistentProxyBuilder_SavesSignedFile()
 			Assert.IsTrue(path.EndsWith(ModuleScope.DEFAULT_FILE_NAME));
 		}
 	}
-}
 
-#endif
+#elif NET9_0_OR_GREATER
+
+	[TestFixture]
+	[FixtureLifeCycle(LifeCycle.InstancePerTestCase)]
+	public class PersistentProxyBuilderTestCase
+	{
+		private List<Assembly> assemblies;
+		private PersistentProxyBuilder builder;
+
+		[SetUp]
+		public void SetupProxyBuilder()
+		{
+			assemblies = new List<Assembly>();
+			builder = new PersistentProxyBuilder();
+			builder.AssemblyCreated += (object _, PersistentProxyBuilderAssemblyEventArgs e) =>
+			{
+				assemblies.Add(e.Assembly);
+			};
+		}
+
+		[Test]
+		public void SavesOneAssemblyPerProxiedType()
+		{
+			var oneProxyType = builder.CreateInterfaceProxyTypeWithoutTarget(typeof(IOne), Type.EmptyTypes, ProxyGenerationOptions.Default);
+			Assert.AreEqual(1, assemblies.Count);
+
+			var twoProxyType = builder.CreateInterfaceProxyTypeWithoutTarget(typeof(ITwo), Type.EmptyTypes, ProxyGenerationOptions.Default);
+			Assert.AreEqual(2, assemblies.Count);
+
+			var oneAssembly = assemblies[0];
+			var twoAssembly = assemblies[1];
+			Assert.AreSame(oneAssembly, oneProxyType.Assembly);
+			Assert.AreSame(twoAssembly, twoProxyType.Assembly);
+			Assert.AreNotSame(oneAssembly, twoAssembly);
+		}
+
+		[Test]
+		public void TypeCacheWorks()
+		{
+			var proxyType1 = builder.CreateClassProxyType(typeof(object), Type.EmptyTypes, ProxyGenerationOptions.Default);
+			var proxyType2 = builder.CreateClassProxyType(typeof(object), Type.EmptyTypes, ProxyGenerationOptions.Default);
+
+			Assert.AreEqual(1, assemblies.Count);
+			Assert.AreSame(proxyType1, proxyType2);
+			Assert.AreSame(proxyType1.Assembly, proxyType2.Assembly);
+		}
+	}
+
+#endif
+
+}

src/Castle.Core/DynamicProxy/Generators/Emitters/ClassEmitter.cs

@@ -1,4 +1,4 @@
-// Copyright 2004-2025 Castle Project - http://www.castleproject.org/
+// Copyright 2004-2026 Castle Project - http://www.castleproject.org/
 // 
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -412,7 +412,7 @@ public Type BuildType()
 				builder.Generate();
 			}
 
-			var type = typeBuilder.CreateTypeInfo();
+			var type = moduleScope.BuildType(typeBuilder);
 
 			return type;
 		}

src/Castle.Core/DynamicProxy/ModuleScope.cs

@@ -1,4 +1,4 @@
-// Copyright 2004-2021 Castle Project - http://www.castleproject.org/
+// Copyright 2004-2026 Castle Project - http://www.castleproject.org/
 // 
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -311,50 +311,59 @@ internal ModuleBuilder ObtainDynamicModuleWithWeakName()
 
 		private ModuleBuilder CreateModule(bool signStrongName)
 		{
-			var assemblyName = GetAssemblyName(signStrongName);
+			var assemblyBuilder = CreateAssembly(signStrongName);
 			var moduleName = signStrongName ? StrongNamedModuleName : WeakNamedModuleName;
-#if FEATURE_APPDOMAIN
+#if NET462_OR_GREATER
 			if (savePhysicalAssembly)
 			{
-				AssemblyBuilder assemblyBuilder;
-				try
-				{
-					assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(
-						assemblyName, AssemblyBuilderAccess.RunAndSave, signStrongName ? StrongNamedModuleDirectory : WeakNamedModuleDirectory);
-				}
-				catch (ArgumentException e)
-				{
-					if (signStrongName == false && e.StackTrace.Contains("ComputePublicKey") == false)
-					{
-						// I have no idea what that could be
-						throw;
-					}
-					var message = string.Format(
-						"There was an error creating dynamic assembly for your proxies - you don't have permissions " +
-						"required to sign the assembly. To workaround it you can enforce generating non-signed assembly " +
-						"only when creating {0}. Alternatively ensure that your account has all the required permissions.",
-						GetType());
-					throw new ArgumentException(message, e);
-				}
-				var module = assemblyBuilder.DefineDynamicModule(moduleName, moduleName, false);
-				return module;
+				return assemblyBuilder.DefineDynamicModule(moduleName, moduleName, false);
 			}
 			else
-#endif
 			{
-#if FEATURE_APPDOMAIN
-				var assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(
-					assemblyName, AssemblyBuilderAccess.Run);
+				return assemblyBuilder.DefineDynamicModule(moduleName);
+			}
 #else
-				var assemblyBuilder = AssemblyBuilder.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
+			return assemblyBuilder.DefineDynamicModule(moduleName);
 #endif
+		}
 
-				var module = assemblyBuilder.DefineDynamicModule(moduleName);
-				return module;
+		internal virtual AssemblyBuilder CreateAssembly(bool signStrongName)
+		{
+			var assemblyName = GetAssemblyName(signStrongName);
+			try
+			{
+#if NET462_OR_GREATER
+				if (savePhysicalAssembly)
+				{
+					return AppDomain.CurrentDomain.DefineDynamicAssembly(
+						assemblyName,
+						AssemblyBuilderAccess.RunAndSave,
+						signStrongName ? StrongNamedModuleDirectory : WeakNamedModuleDirectory);
+				}
+				else
+				{
+					return AppDomain.CurrentDomain.DefineDynamicAssembly(
+						assemblyName,
+						AssemblyBuilderAccess.Run);
+				}
+#else
+				return AssemblyBuilder.DefineDynamicAssembly(
+					assemblyName,
+					AssemblyBuilderAccess.Run);
+#endif
+			}
+			catch (ArgumentException e) when (signStrongName || e.StackTrace?.Contains("ComputePublicKey") == true)
+			{
+				var message = string.Format(
+					"There was an error creating dynamic assembly for your proxies - you don't have permissions " +
+					"required to sign the assembly. To workaround it you can enforce generating non-signed assembly " +
+					"only when creating {0}. Alternatively ensure that your account has all the required permissions.",
+					GetType());
+				throw new ArgumentException(message, e);
 			}
 		}
 
-		private AssemblyName GetAssemblyName(bool signStrongName)
+		internal AssemblyName GetAssemblyName(bool signStrongName)
 		{
 			var assemblyName = new AssemblyName {
 				Name = signStrongName ? strongAssemblyName : weakAssemblyName
@@ -372,6 +381,15 @@ private AssemblyName GetAssemblyName(bool signStrongName)
 			return assemblyName;
 		}
 
+		internal void ResetModules()
+		{
+			lock (moduleLocker)
+			{
+				moduleBuilder = null;
+				moduleBuilderWithStrongName = null;
+			}
+		}
+
 #if FEATURE_ASSEMBLYBUILDER_SAVE
 		/// <summary>
 		///   Saves the generated assembly with the name and directory information given when this <see cref = "ModuleScope" /> instance was created (or with
@@ -539,10 +557,15 @@ public void LoadAssemblyIntoCache(Assembly assembly)
 		}
 #endif
 
-		internal TypeBuilder DefineType(bool inSignedModulePreferably, string name, TypeAttributes flags)
+		internal virtual TypeBuilder DefineType(bool inSignedModulePreferably, string name, TypeAttributes flags)
 		{
 			var module = ObtainDynamicModule(disableSignedModule == false && inSignedModulePreferably);
 			return module.DefineType(name, flags);
 		}
+
+		internal virtual Type BuildType(TypeBuilder typeBuilder)
+		{
+			return typeBuilder.CreateTypeInfo()!;
+		}
 	}
 }

src/Castle.Core/DynamicProxy/PersistentProxyBuilder.cs

@@ -1,4 +1,4 @@
-// Copyright 2004-2021 Castle Project - http://www.castleproject.org/
+// Copyright 2004-2026 Castle Project - http://www.castleproject.org/
 // 
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -12,12 +12,15 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#if FEATURE_ASSEMBLYBUILDER_SAVE
-
 #nullable enable
 
 namespace Castle.DynamicProxy
 {
+	using System;
+	using System.Reflection;
+
+#if NET462_OR_GREATER
+
 	/// <summary>
 	///   ProxyBuilder that persists the generated type.
 	/// </summary>
@@ -46,6 +49,40 @@ public PersistentProxyBuilder() : base(new ModuleScope(true))
 			return ModuleScope.SaveAssembly();
 		}
 	}
-}
 
-#endif
+#elif NET9_0_OR_GREATER
+
+	/// <summary>
+	///   <see cref="IProxyBuilder"/> that allows you to persist proxy types.
+	///   Each generated proxy type will be placed in its own separate assembly.
+	/// </summary>
+	public sealed class PersistentProxyBuilder : DefaultProxyBuilder
+	{
+		/// <summary>
+		///   Initializes a new instance of the <see cref = "PersistentProxyBuilder" /> class.
+		/// </summary>
+		public PersistentProxyBuilder()
+			: this(new PersistentProxyBuilderModuleScope())
+		{
+		}
+
+		private PersistentProxyBuilder(PersistentProxyBuilderModuleScope scope)
+			: base(scope)
+		{
+			scope.AssemblyCreated += OnAssemblyCreated;
+		}
+
+		/// <summary>
+		///   Raised when a new proxy type assembly has been created and loaded into the runtime.
+		/// </summary>
+		public event EventHandler<PersistentProxyBuilderAssemblyEventArgs>? AssemblyCreated;
+
+		private void OnAssemblyCreated(Assembly assembly, byte[] assemblyBytes)
+		{
+			AssemblyCreated?.Invoke(this, new PersistentProxyBuilderAssemblyEventArgs(assembly, assemblyBytes));
+		}
+	}
+
+#endif
+
+}

src/Castle.Core/DynamicProxy/PersistentProxyBuilderAssemblyEventArgs.cs

@@ -0,0 +1,53 @@
+// Copyright 2004-2026 Castle Project - http://www.castleproject.org/
+//
+// 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.
+
+#if NET9_0_OR_GREATER
+
+#nullable enable
+
+namespace Castle.DynamicProxy
+{
+	using System;
+	using System.Reflection;
+
+	/// <summary>
+	///   Provides data for the <see cref="PersistentProxyBuilder.AssemblyCreated"/> event.
+	/// </summary>
+	public sealed class PersistentProxyBuilderAssemblyEventArgs : EventArgs
+	{
+		/// <summary>
+		///   Initializes a new instance of the <see cref="PersistentProxyBuilderAssemblyEventArgs"/> class.
+		/// </summary>
+		/// <param name="assembly">The assembly that has been created and loaded into the runtime.</param>
+		/// <param name="assemblyBytes">The raw bytes of the created assembly (can be saved as a DLL file).</param>
+		internal PersistentProxyBuilderAssemblyEventArgs(Assembly assembly, byte[] assemblyBytes)
+		{
+			Assembly = assembly;
+			AssemblyBytes = assemblyBytes;
+		}
+
+		/// <summary>
+		///   The assembly that has been created and loaded into the runtime.
+		/// </summary>
+		public Assembly Assembly { get; }
+
+		/// <summary>
+		///   The raw bytes of the created assembly (can be saved as a DLL file).
+		/// </summary>
+		/// <remarks></remarks>
+		public byte[] AssemblyBytes { get; }
+	}
+}
+
+#endif