feat: create request projects for basic CQRS

src/request.dispatcher/Geekeey.Request.Dispatcher.csproj

@@ -0,0 +1,36 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <IsPackable>true</IsPackable>
+  </PropertyGroup>
+
+  <PropertyGroup>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(Configuration)' == 'Debug'">
+    <InternalsVisibleTo Include="Geekeey.Request.Dispatcher.Tests" />
+  </ItemGroup>
+
+  <PropertyGroup>
+    <PackageReadmeFile>package-readme.md</PackageReadmeFile>
+    <PackageDescription>Simple mediator implementation in .NET with minimal dependencies.</PackageDescription>
+    <PackageIcon>package-icon.png</PackageIcon>
+    <PackageProjectUrl>https://code.geekeey.de/geekeey/request/src/branch/main/src/request.dispatcher</PackageProjectUrl>
+    <PackageLicenseExpression>EUPL-1.2</PackageLicenseExpression>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <None Include=".\package-icon.png" Pack="true" PackagePath="\" Visible="false" />
+    <None Include=".\package-readme.md" Pack="true" PackagePath="\" Visible="false" />
+    <None Include="..\..\LICENSE.md" Pack="true" PackagePath="\" Visible="false" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.DependencyInjection.Abstractions" />
+    <PackageReference Include="Microsoft.Extensions.Options" />
+  </ItemGroup>
+
+</Project>

src/request.dispatcher/IRequestDispatcher.cs

@@ -0,0 +1,28 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Defines functionality to dispatch requests to their corresponding handlers.
+/// </summary>
+public interface IRequestDispatcher
+{
+	/// <summary>
+	/// Asynchronously send a request to a handler producing a scalar value.
+	/// </summary>
+	/// <param name="request">Request object</param>
+	/// <param name="cancellationToken">Optional cancellation token</param>
+	/// <typeparam name="TResponse">Response type</typeparam>
+	/// <returns>A task that represents the send operation. The task result contains the handler response</returns>
+	Task<TResponse> DispatchAsync<TResponse>(IScalarRequest<TResponse> request, CancellationToken cancellationToken = default);
+
+	/// <summary>
+	/// Asynchronously send a request to a handler producing a stream value.
+	/// </summary>
+	/// <param name="request">Request object</param>
+	/// <param name="cancellationToken">Optional cancellation token</param>
+	/// <typeparam name="TResponse">Response type</typeparam>
+	/// <returns>The created async enumerable, representing the stream of responses.</returns>
+	IAsyncEnumerable<TResponse> DispatchAsync<TResponse>(IStreamRequest<TResponse> request, CancellationToken cancellationToken = default);
+}

src/request.dispatcher/IRequestDispatcherBuilder.cs

@@ -0,0 +1,19 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Represents a builder for configuring and registering request dispatchers and their related components.
+/// </summary>
+public interface IRequestDispatcherBuilder
+{
+	/// <summary>
+	/// Gets the <see cref="IServiceCollection"/> associated with the request dispatcher builder.
+	/// Provides access to the underlying service collection for configuring dependencies
+	/// and registering services required by the request dispatcher.
+	/// </summary>
+	IServiceCollection Services { get; }
+}

src/request.dispatcher/IScalarPipelineBehavior.cs

@@ -0,0 +1,35 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+#pragma warning disable CA1711
+#pragma warning disable CA1716
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Represents a behavior in the request pipeline, allowing interception, modification,
+/// or chaining of asynchronous stream requests and responses.
+/// </summary>
+/// <typeparam name="TRequest">The type of the request being handled. Must implement <see cref="IScalarRequest{TResponse}"/>.</typeparam>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+public interface IScalarRequestBehavior<in TRequest, TResponse> where TRequest : IScalarRequest<TResponse>
+{
+	/// <summary>
+	/// Handles the asynchronous processing of a request, allowing behavior customization
+	/// such as interception, modification, or chaining of the request and its response.
+	/// </summary>
+	/// <param name="request">The request instance being processed.</param>
+	/// <param name="next">The next delegate in the pipeline to execute after the custom behavior.</param>
+	/// <param name="cancellationToken">A token to monitor for cancellation requests.</param>
+	/// <returns>A task that represents the asynchronous operation. The task result contains the response from the request.</returns>
+	Task<TResponse> HandleAsync(TRequest request, ScalarHandlerDelegate<TResponse> next, CancellationToken cancellationToken);
+}
+
+/// <summary>
+/// Represents the delegate responsible for handling asynchronous requests in a pipeline.
+/// </summary>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+/// <param name="request">The asynchronous request being processed.</param>
+/// <param name="cancellationToken">A token for monitoring cancellation requests.</param>
+/// <returns>A task, that represents the asynchronous operation, containing the response of type <typeparamref name="TResponse"/>.</returns>
+public delegate Task<TResponse> ScalarHandlerDelegate<TResponse>(IScalarRequest<TResponse> request, CancellationToken cancellationToken);

src/request.dispatcher/IScalarRequest.cs

@@ -0,0 +1,14 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Represents a request that produces a response of a specified type.
+/// This interface serves as a marker for distinguishing request types,
+/// enabling their integration into request-based pipelines or dispatch mechanisms.
+/// </summary>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+public interface IScalarRequest<out TResponse>
+{
+}

src/request.dispatcher/IScalarRequestHandler.cs

@@ -0,0 +1,20 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Defines a handler for processing requests of a specific type and returning a response.
+/// </summary>
+/// <typeparam name="TRequest">The type of the request to be handled. Must implement <see cref="IScalarRequest{TResponse}"/>.</typeparam>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+public interface IScalarRequestHandler<in TRequest, TResponse> where TRequest : IScalarRequest<TResponse>
+{
+	/// <summary>
+	/// Processes a scalar request and returns a response asynchronously.
+	/// </summary>
+	/// <param name="request">The request object to be processed.</param>
+	/// <param name="cancellationToken">A token to observe for cancellation requests.</param>
+	/// <returns>A task representing the asynchronous operation, containing the response of type <typeparamref name="TResponse"/>.</returns>
+	Task<TResponse> HandleAsync(TRequest request, CancellationToken cancellationToken = default);
+}

src/request.dispatcher/IStreamPipelineBehavior.cs

@@ -0,0 +1,35 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+#pragma warning disable CA1711
+#pragma warning disable CA1716
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Represents a behavior in the request pipeline, allowing interception, modification,
+/// or chaining of asynchronous stream requests and responses.
+/// </summary>
+/// <typeparam name="TRequest">The type of the request being processed. Must implement <see cref="IStreamRequest{TResponse}"/>.</typeparam>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+public interface IStreamRequestBehavior<in TRequest, TResponse> where TRequest : IStreamRequest<TResponse>
+{
+	/// <summary>
+	/// Handles the asynchronous processing of a request, allowing behavior customization
+	/// such as interception, modification, or chaining of the request and its response.
+	/// </summary>
+	/// <param name="request">The request instance being processed.</param>
+	/// <param name="next">The next delegate in the pipeline to execute after the custom behavior.</param>
+	/// <param name="cancellationToken">A token to monitor for cancellation requests.</param>
+	/// <returns>An asynchronous stream of <typeparamref name="TResponse"/> representing the processed response.</returns>
+	IAsyncEnumerable<TResponse> HandleAsync(TRequest request, StreamHandlerDelegate<TResponse> next, CancellationToken cancellationToken);
+}
+
+/// <summary>
+/// Represents the delegate responsible for handling asynchronous requests in a pipeline.
+/// </summary>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+/// <param name="request">The asynchronous request being processed.</param>
+/// <param name="cancellationToken">A token for monitoring cancellation requests.</param>
+/// <returns>An asynchronous stream of responses of type <typeparamref name="TResponse"/>.</returns>
+public delegate IAsyncEnumerable<TResponse> StreamHandlerDelegate<TResponse>(IStreamRequest<TResponse> request, CancellationToken cancellationToken);

src/request.dispatcher/IStreamRequest.cs

@@ -0,0 +1,14 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Represents a request that produces a response of a specified type.
+/// This interface serves as a marker for distinguishing request types,
+/// enabling their integration into request-based pipelines or dispatch mechanisms.
+/// </summary>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+public interface IStreamRequest<out TResponse>
+{
+}

src/request.dispatcher/IStreamRequestHandler.cs

@@ -0,0 +1,21 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Defines a handler for processing streaming requests of a specific type and producing
+/// a stream of responses.
+/// </summary>
+/// <typeparam name="TRequest">The type of the request to handle. This must implement <see cref="IStreamRequest{TResponse}"/>.</typeparam>
+/// <typeparam name="TResponse">The type of the response produced by the implementing request handler.</typeparam>
+public interface IStreamRequestHandler<in TRequest, out TResponse> where TRequest : IStreamRequest<TResponse>
+{
+	/// <summary>
+	/// Handles a streaming request and returns a stream of responses asynchronously.
+	/// </summary>
+	/// <param name="request">The request object to be processed.</param>
+	/// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+	/// <returns>An asynchronous stream of responses of type <typeparamref name="TResponse"/>.</returns>
+	IAsyncEnumerable<TResponse> HandleAsync(TRequest request, CancellationToken cancellationToken);
+}

src/request.dispatcher/RequestDispatcher.cs

@@ -0,0 +1,48 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using System.Collections.Concurrent;
+using System.Reflection.Metadata;
+
+[assembly: MetadataUpdateHandler(typeof(Geekeey.Request.Dispatcher.RequestDispatcher))]
+
+namespace Geekeey.Request.Dispatcher;
+
+internal sealed class RequestDispatcher : IRequestDispatcher
+{
+	private static readonly ConcurrentDictionary<(Type, Type), ScalarRequestInvoker> ScalarRequestHandlers = new();
+	private static readonly ConcurrentDictionary<(Type, Type), StreamRequestInvoker> StreamRequestHandlers = new();
+
+	private readonly IServiceProvider _serviceProvider;
+
+	public RequestDispatcher(IServiceProvider serviceProvider)
+	{
+		_serviceProvider = serviceProvider;
+	}
+
+	public Task<TResponse> DispatchAsync<TResponse>(IScalarRequest<TResponse> request, CancellationToken cancellationToken = default)
+	{
+		ArgumentNullException.ThrowIfNull(request);
+
+		var handler = ScalarRequestHandlers.GetOrAdd((request.GetType(), typeof(TResponse)), static key =>
+		{
+			var type = typeof(ScalarRequestInvoker<,>).MakeGenericType(key.Item1, key.Item2);
+			return (ScalarRequestInvoker)Activator.CreateInstance(type)!;
+		});
+
+		return ((ScalarRequestInvoker<TResponse>)handler).HandleAsync(request, _serviceProvider, cancellationToken);
+	}
+
+	public IAsyncEnumerable<TResponse> DispatchAsync<TResponse>(IStreamRequest<TResponse> request, CancellationToken cancellationToken = default)
+	{
+		ArgumentNullException.ThrowIfNull(request);
+
+		var handler = StreamRequestHandlers.GetOrAdd((request.GetType(), typeof(TResponse)), static key =>
+		{
+			var type = typeof(StreamRequestInvoker<,>).MakeGenericType(key.Item1, key.Item2);
+			return (StreamRequestInvoker)Activator.CreateInstance(type)!;
+		});
+
+		return ((StreamRequestInvoker<TResponse>)handler).HandleAsync(request, _serviceProvider, cancellationToken);
+	}
+}

src/request.dispatcher/RequestDispatcherBuilderExtensions.cs

@@ -0,0 +1,174 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using System.Reflection;
+using System.Runtime.CompilerServices;
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+
+using static Geekeey.Request.Dispatcher.RequestDispatcherOptions;
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Provides extension methods for configuring <see cref="IRequestDispatcherBuilder"/>
+/// with additional capabilities such as searching and registering request handlers in assemblies or adding types directly.
+/// </summary>
+public static class RequestDispatcherBuilderExtensions
+{
+	/// <summary>
+	/// Searches for request handler types within the specified assembly and adds them to the request dispatcher
+	/// configuration.
+	/// </summary>
+	/// <remarks>
+	/// Prefer the generated <c>Add&lt;Name&gt;(builder)</c> extensions for assemblies that directly reference
+	/// <c>Geekeey.Request.Dispatcher</c>. This runtime scanning API remains supported, but nested request handlers are rejected
+	/// during registration and generated registration should not be mixed with <see cref="SearchHandlerInAssembly(IRequestDispatcherBuilder, Assembly)"/>
+	/// for the same assembly.
+	/// </remarks>
+	/// <param name="builder">The <see cref="IRequestDispatcherBuilder"/> to configure.</param>
+	/// <param name="assembly">The assembly to search for request handler types.</param>
+	/// <returns>The <see cref="IRequestDispatcherBuilder"/> instance for further configuration.</returns>
+	public static IRequestDispatcherBuilder SearchHandlerInAssembly(this IRequestDispatcherBuilder builder, Assembly assembly)
+	{
+		ArgumentNullException.ThrowIfNull(builder);
+
+		var exports = assembly.GetTypes()
+			.Where(type => type is { IsClass: true, IsAbstract: false })
+			.Where(IsRequestHandlerImplementationType);
+
+		builder.Add(exports);
+
+		return builder;
+	}
+
+	/// <summary>
+	/// Searches for request handler types within the specified assembly and adds them to the request dispatcher
+	/// configuration with the given service lifetime.
+	/// </summary>
+	/// <remarks>
+	/// Prefer the generated <c>Add&lt;Name&gt;(builder, lifetime)</c> extensions for assemblies that directly reference
+	/// <c>Geekeey.Request.Dispatcher</c>. This runtime scanning API remains supported, but nested request handlers are rejected
+	/// during registration and generated registration should not be mixed with <see cref="SearchHandlerInAssembly(IRequestDispatcherBuilder, Assembly, ServiceLifetime)"/>
+	/// for the same assembly.
+	/// </remarks>
+	/// <param name="builder">The <see cref="IRequestDispatcherBuilder"/> to configure.</param>
+	/// <param name="assembly">The assembly to search for request handler types.</param>
+	/// <param name="lifetime">The lifetime with which the request handlers are registered in the dependency injection container.</param>
+	/// <returns>The <see cref="IRequestDispatcherBuilder"/> instance for further configuration.</returns>
+	public static IRequestDispatcherBuilder SearchHandlerInAssembly(this IRequestDispatcherBuilder builder, Assembly assembly, ServiceLifetime lifetime)
+	{
+		ArgumentNullException.ThrowIfNull(builder);
+
+		var exports = assembly.GetTypes()
+			.Where(type => type is { IsClass: true, IsAbstract: false })
+			.Where(IsRequestHandlerImplementationType);
+
+		builder.Add(exports, lifetime);
+
+		return builder;
+	}
+
+	/// <summary>
+	/// Adds the specified type to the request dispatcher configuration for inspection.
+	/// </summary>
+	/// <param name="builder">The <see cref="IRequestDispatcherBuilder"/> to configure.</param>
+	/// <param name="type">The type to be added to the request dispatcher configuration.</param>
+	/// <returns>The <see cref="IRequestDispatcherBuilder"/> instance for further configuration.</returns>
+	public static IRequestDispatcherBuilder Add(this IRequestDispatcherBuilder builder, Type type)
+	{
+		ArgumentNullException.ThrowIfNull(builder);
+		ValidateNoNestedRequestHandlers([type]);
+
+		builder.Services.AddOptions<RequestDispatcherOptions>()
+			.Configure(options => options.Inspect([type]));
+
+		return builder;
+	}
+
+	/// <summary>
+	/// Adds the specified type to the request dispatcher configuration.
+	/// This also adds the type to the service collection with the specified lifetime,
+	/// allowing it to be resolved as a dependency in request handlers and behaviors.
+	/// </summary>
+	/// <param name="builder">The <see cref="IRequestDispatcherBuilder"/> used to configure the request dispatcher.</param>
+	/// <param name="type">The type to be added to the request dispatcher configuration.</param>
+	/// <param name="lifetime">The lifetime scope of the type in the service container.</param>
+	/// <returns>The <see cref="IRequestDispatcherBuilder"/> instance for further configuration.</returns>
+	public static IRequestDispatcherBuilder Add(this IRequestDispatcherBuilder builder, Type type, ServiceLifetime lifetime)
+	{
+		ArgumentNullException.ThrowIfNull(builder);
+		ValidateNoNestedRequestHandlers([type]);
+
+		builder.Services.AddOptions<RequestDispatcherOptions>()
+			.Configure(options => options.Inspect([type]));
+
+		builder.Services.Add(new ServiceDescriptor(type, type, lifetime));
+
+		return builder;
+	}
+
+	/// <summary>
+	/// Adds the specified collection of types to the request dispatcher configuration for inspection.
+	/// </summary>
+	/// <param name="builder">The <see cref="IRequestDispatcherBuilder"/> to configure.</param>
+	/// <param name="type">The collection of types to be added to the request dispatcher configuration.</param>
+	/// <returns>The <see cref="IRequestDispatcherBuilder"/> instance for further configuration.</returns>
+	public static IRequestDispatcherBuilder Add(this IRequestDispatcherBuilder builder, IEnumerable<Type> type)
+	{
+		ArgumentNullException.ThrowIfNull(builder);
+
+		var types = ValidateNoNestedRequestHandlers([.. type]);
+
+		builder.Services.AddOptions<RequestDispatcherOptions>()
+			.Configure(options => options.Inspect(types));
+
+		return builder;
+	}
+
+	/// <summary>
+	/// Adds the specified collection of types to the request dispatcher configuration for inspection.
+	/// This also adds the specified collection of types to the service collection with the specified lifetime,
+	/// allowing it to be resolved as a dependency in request handlers and behaviors.
+	/// </summary>
+	/// <param name="builder">The <see cref="IRequestDispatcherBuilder"/> to configure.</param>
+	/// <param name="type">The collection of types to be added to the request dispatcher configuration.</param>
+	/// <param name="lifetime">The lifetime scope of the types in the service container.</param>
+	/// <returns>The <see cref="IRequestDispatcherBuilder"/> instance for further configuration.</returns>
+	public static IRequestDispatcherBuilder Add(this IRequestDispatcherBuilder builder, IEnumerable<Type> type, ServiceLifetime lifetime)
+	{
+		ArgumentNullException.ThrowIfNull(builder);
+
+		var types = ValidateNoNestedRequestHandlers([.. type]);
+
+		builder.Services.AddOptions<RequestDispatcherOptions>()
+			.Configure(options => options.Inspect(types));
+
+		builder.Services.Add(types.Select(export => new ServiceDescriptor(export, export, lifetime)));
+
+		return builder;
+	}
+
+	private static IReadOnlyCollection<Type> ValidateNoNestedRequestHandlers(IReadOnlyCollection<Type> types, [CallerMemberName] string? invoker = null)
+	{
+		var nestedHandlers = types
+			.Where(type => type is { IsClass: true, IsAbstract: false, IsNested: true })
+			.Where(IsRequestHandlerImplementationType)
+			.Select(type => type.FullName ?? type.Name)
+			.OrderBy(static name => name, StringComparer.Ordinal)
+			.ToArray();
+
+		if (nestedHandlers.Length > 0)
+		{
+			throw new InvalidOperationException($"Nested request handlers are not supported by {invoker}: {string.Join(", ", nestedHandlers)}");
+		}
+
+		return types;
+	}
+
+	private static bool IsRequestHandlerImplementationType(Type type)
+	{
+		return type.GetInterfaces().Any(IsRequestHandlerType);
+	}
+}

src/request.dispatcher/RequestDispatcherOptions.cs

@@ -0,0 +1,207 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using System.Collections;
+using System.Collections.Concurrent;
+
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Geekeey.Request.Dispatcher;
+
+internal sealed class RequestDispatcherOptions
+{
+	private readonly List<Type> _search = [];
+	private readonly Lazy<TypeIndex> _behaviorsTypeIndex;
+	private readonly Lazy<TypeIndex> _handlersTypeIndex;
+
+	public RequestDispatcherOptions()
+	{
+		_behaviorsTypeIndex = new Lazy<TypeIndex>(() => new BehaviorTypeIndex(_search.Distinct()));
+		_handlersTypeIndex = new Lazy<TypeIndex>(() => new HandlerTypeIndex(_search.Distinct()));
+	}
+
+	public void Inspect(IEnumerable<Type> assembly)
+	{
+		if (_behaviorsTypeIndex.IsValueCreated || _handlersTypeIndex.IsValueCreated)
+		{
+			throw new InvalidOperationException("The type index has already been created. Cannot inspect new assemblies.");
+		}
+
+		_search.AddRange(assembly);
+	}
+
+	public IEnumerable<T> GetRequestBehaviors<T>(IServiceProvider services)
+	{
+		return _behaviorsTypeIndex.Value.Resolve<T>(services);
+	}
+
+	public IEnumerable<T> GetRequestHandlers<T>(IServiceProvider services)
+	{
+		return _handlersTypeIndex.Value.Resolve<T>(services);
+	}
+
+	private abstract class TypeIndex
+	{
+		private readonly ConcurrentDictionary<Type, Func<IServiceProvider, IEnumerable>> _cache = new();
+
+		protected readonly Dictionary<Type, List<Type>> _closedTypeInfo = [];
+		protected readonly List<Type> _openTypeInfo = [];
+
+		protected TypeIndex(IEnumerable<Type> collection, Func<Type, bool> predicate)
+		{
+			foreach (var type in collection)
+			{
+				if (type.IsGenericTypeDefinition)
+				{
+					if (type.GetInterfaces().Any(predicate))
+					{
+						_openTypeInfo.Add(type);
+					}
+				}
+				else
+				{
+					foreach (var @interface in type.GetInterfaces().Where(predicate))
+					{
+						(_closedTypeInfo.TryGetValue(@interface, out var list) ? list : _closedTypeInfo[@interface] = []).Add(type);
+					}
+				}
+			}
+		}
+
+		public IEnumerable<T> Resolve<T>(IServiceProvider services)
+		{
+			return (IEnumerable<T>)_cache.GetOrAdd(typeof(T), CreateResolverFactory<T>)(services);
+		}
+
+		protected abstract IReadOnlyList<Type> IsAssignableTo(Type type);
+
+		private Func<IServiceProvider, IEnumerable<T>> CreateResolverFactory<T>(Type @interface)
+		{
+			var list = IsAssignableTo(@interface);
+			return ResolverFactory;
+
+			IEnumerable<T> ResolverFactory(IServiceProvider services)
+			{
+				foreach (var type in list)
+				{
+					yield return (T)ActivatorUtilities.GetServiceOrCreateInstance(services, type);
+				}
+			}
+		}
+	}
+
+	internal static bool IsRequestHandlerType(Type type)
+	{
+		return type.IsGenericType &&
+			   (type.GetGenericTypeDefinition() == typeof(IScalarRequestHandler<,>) ||
+				type.GetGenericTypeDefinition() == typeof(IStreamRequestHandler<,>));
+	}
+
+	private sealed class HandlerTypeIndex(IEnumerable<Type> collection)
+		: TypeIndex(collection, IsRequestHandlerType)
+	{
+		protected override IReadOnlyList<Type> IsAssignableTo(Type @interface)
+		{
+			var result = new List<Type>();
+
+			if (_closedTypeInfo.TryGetValue(@interface, out var list))
+			{
+				result.AddRange(list);
+			}
+
+			var requestType = @interface.GetGenericArguments()[0];
+			_ = @interface.GetGenericArguments()[1];
+
+			foreach (var type in _openTypeInfo)
+			{
+				try
+				{
+					// open type case one: Handler<TRequest> : IRequestHandler<TRequest, TOutput>
+					// We try to close it with the request type.
+					var impl = type.MakeGenericType(requestType);
+					if (impl.IsAssignableTo(@interface))
+					{
+						result.Add(impl);
+					}
+				}
+				catch (ArgumentException)
+				{
+				}
+
+				try
+				{
+					// open type case two: Handler<T> : IRequestHandler<WrapperRequest<T>, TOutput>
+					// If the request is generic, we try to close the handler with the request's generic arguments.
+					if (requestType.IsGenericType)
+					{
+						var impl = type.MakeGenericType(requestType.GetGenericArguments());
+						if (impl.IsAssignableTo(@interface))
+						{
+							result.Add(impl);
+						}
+					}
+				}
+				catch (ArgumentException)
+				{
+				}
+			}
+
+			return result;
+		}
+	}
+
+	internal static bool IsRequestBehaviorType(Type type)
+	{
+		return type.IsGenericType &&
+			   (type.GetGenericTypeDefinition() == typeof(IScalarRequestBehavior<,>) ||
+				type.GetGenericTypeDefinition() == typeof(IStreamRequestBehavior<,>));
+	}
+
+	private sealed class BehaviorTypeIndex(IEnumerable<Type> collection)
+		: TypeIndex(collection, IsRequestBehaviorType)
+	{
+		protected override IReadOnlyList<Type> IsAssignableTo(Type @interface)
+		{
+			var result = new List<Type>();
+
+			if (_closedTypeInfo.TryGetValue(@interface, out var list))
+			{
+				result.AddRange(list);
+			}
+
+			var requestType = @interface.GetGenericArguments()[0];
+			var responseType = @interface.GetGenericArguments()[1];
+
+			foreach (var behaviour in _openTypeInfo)
+			{
+				try
+				{
+					// open type case one: Behaviour<TRequest, TResponse> : IRequestBehaviour<TRequest, TResponse>
+					var impl = behaviour.MakeGenericType(requestType, responseType);
+					if (impl.IsAssignableTo(@interface))
+					{
+						result.Add(impl);
+					}
+				}
+				catch (ArgumentException)
+				{
+				}
+
+				try
+				{
+					// open type case two: Behaviour<T> : IRequestBehaviour<WrapperRequest<T>, TResponse>
+					var impl = behaviour.MakeGenericType(requestType.GetGenericArguments());
+					if (impl.IsAssignableTo(@interface))
+					{
+						result.Add(impl);
+					}
+				}
+				catch (ArgumentException)
+				{
+				}
+			}
+
+			return result;
+		}
+	}
+}

src/request.dispatcher/ScalarRequestInvoker.cs

@@ -0,0 +1,47 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+
+namespace Geekeey.Request.Dispatcher;
+
+internal abstract class ScalarRequestInvoker
+{
+	public abstract Task<object?> HandleAsync(object request, IServiceProvider serviceProvider, CancellationToken cancellationToken);
+}
+
+internal abstract class ScalarRequestInvoker<TResponse> : ScalarRequestInvoker
+{
+	public abstract Task<TResponse> HandleAsync(IScalarRequest<TResponse> request, IServiceProvider serviceProvider, CancellationToken cancellationToken);
+}
+
+internal sealed class ScalarRequestInvoker<TRequest, TResponse> : ScalarRequestInvoker<TResponse>
+	where TRequest : IScalarRequest<TResponse>
+{
+	public override async Task<object?> HandleAsync(object request, IServiceProvider serviceProvider, CancellationToken cancellationToken)
+	{
+		return await HandleAsync((IScalarRequest<TResponse>)request, serviceProvider, cancellationToken).ConfigureAwait(false);
+	}
+
+	public override Task<TResponse> HandleAsync(IScalarRequest<TResponse> request, IServiceProvider serviceProvider, CancellationToken cancellationToken)
+	{
+		var options = serviceProvider.GetRequiredService<IOptions<RequestDispatcherOptions>>().Value;
+
+		var pipeline = options.GetRequestBehaviors<IScalarRequestBehavior<TRequest, TResponse>>(serviceProvider)
+			.Reverse()
+			.Aggregate((ScalarHandlerDelegate<TResponse>)Head, Chain);
+
+		return pipeline(request, cancellationToken);
+
+		static ScalarHandlerDelegate<TResponse> Chain(ScalarHandlerDelegate<TResponse> next, IScalarRequestBehavior<TRequest, TResponse> filter)
+		{
+			return (req, ct) => filter.HandleAsync((TRequest)req, next, ct);
+		}
+
+		Task<TResponse> Head(IScalarRequest<TResponse> r, CancellationToken ct)
+		{
+			return options.GetRequestHandlers<IScalarRequestHandler<TRequest, TResponse>>(serviceProvider).First().HandleAsync((TRequest)r, ct);
+		}
+	}
+}

src/request.dispatcher/ServiceCollectionExtensions.cs

@@ -0,0 +1,50 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
+
+namespace Geekeey.Request.Dispatcher;
+
+/// <summary>
+/// Provides extension methods for configuring and registering request dispatchers and their dependencies.
+/// </summary>
+public static class ServiceCollectionExtensions
+{
+	/// <summary>
+	/// Adds the request dispatcher services to the specified <see cref="IServiceCollection"/>.
+	/// </summary>
+	/// <param name="services">The service collection to which the request dispatcher services will be added.</param>
+	/// <returns>An instance of <see cref="IRequestDispatcherBuilder"/> to configure the request dispatcher.</returns>
+	public static IRequestDispatcherBuilder AddRequestDispatcher(this IServiceCollection services)
+	{
+		ArgumentNullException.ThrowIfNull(services);
+
+		services.AddOptions<RequestDispatcherOptions>();
+		services.TryAddTransient<IRequestDispatcher, RequestDispatcher>();
+
+		return new RequestDispatcherBuilder(services);
+	}
+
+	/// <summary>
+	/// Adds the request dispatcher services to the specified <see cref="IServiceCollection"/>
+	/// and configures it using the provided <see cref="Action{T}"/>.
+	/// </summary>
+	/// <param name="services">The service collection to which the request dispatcher services will be added.</param>
+	/// <param name="configure">A delegate to configure the request dispatcher builder.</param>
+	/// <returns>The service collection with the request dispatcher services added.</returns>
+	public static IServiceCollection AddRequestDispatcher(this IServiceCollection services, Action<IRequestDispatcherBuilder> configure)
+	{
+		ArgumentNullException.ThrowIfNull(services);
+		ArgumentNullException.ThrowIfNull(configure);
+
+		configure(services.AddRequestDispatcher());
+
+		return services;
+	}
+
+	private sealed class RequestDispatcherBuilder(IServiceCollection services) : IRequestDispatcherBuilder
+	{
+		public IServiceCollection Services { get; } = services;
+	}
+}

src/request.dispatcher/StreamRequestInvoker.cs

@@ -0,0 +1,52 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+using System.Runtime.CompilerServices;
+
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+
+namespace Geekeey.Request.Dispatcher;
+
+internal abstract class StreamRequestInvoker
+{
+	public abstract IAsyncEnumerable<object?> HandleAsync(object request, IServiceProvider serviceProvider, CancellationToken cancellationToken);
+}
+
+internal abstract class StreamRequestInvoker<TResponse> : StreamRequestInvoker
+{
+	public abstract IAsyncEnumerable<TResponse> HandleAsync(IStreamRequest<TResponse> request, IServiceProvider serviceProvider, CancellationToken cancellationToken);
+}
+
+internal sealed class StreamRequestInvoker<TRequest, TResponse> : StreamRequestInvoker<TResponse>
+	where TRequest : IStreamRequest<TResponse>
+{
+	public override async IAsyncEnumerable<object?> HandleAsync(object request, IServiceProvider serviceProvider, [EnumeratorCancellation] CancellationToken cancellationToken)
+	{
+		await foreach (var item in HandleAsync((IStreamRequest<TResponse>)request, serviceProvider, cancellationToken))
+		{
+			yield return item;
+		}
+	}
+
+	public override IAsyncEnumerable<TResponse> HandleAsync(IStreamRequest<TResponse> request, IServiceProvider serviceProvider, CancellationToken cancellationToken)
+	{
+		var options = serviceProvider.GetRequiredService<IOptions<RequestDispatcherOptions>>().Value;
+
+		var pipeline = options.GetRequestBehaviors<IStreamRequestBehavior<TRequest, TResponse>>(serviceProvider)
+			.Reverse()
+			.Aggregate((StreamHandlerDelegate<TResponse>)Head, Chain);
+
+		return pipeline(request, cancellationToken);
+
+		static StreamHandlerDelegate<TResponse> Chain(StreamHandlerDelegate<TResponse> next, IStreamRequestBehavior<TRequest, TResponse> filter)
+		{
+			return (req, ct) => filter.HandleAsync((TRequest)req, next, ct);
+		}
+
+		IAsyncEnumerable<TResponse> Head(IStreamRequest<TResponse> r, CancellationToken ct)
+		{
+			return options.GetRequestHandlers<IStreamRequestHandler<TRequest, TResponse>>(serviceProvider).First().HandleAsync((TRequest)r, ct);
+		}
+	}
+}

src/request.dispatcher/package-readme.md

@@ -0,0 +1,68 @@
+## Features
+
+- **Simple interfaces:** no complex constraints, just marker interfaces that work.
+- **Minmal dependencies:** only depends on `Microsoft.Extensions.DependencyInjection.Abstractions` and the
+  `Microsoft.Extensions.Options` package.
+
+## Getting Started
+
+### Install the NuGet package:
+
+```shell
+dotnet add package Geekeey.Request.Dispatcher
+```
+
+You may need to add our NuGet feed to your nuget.config this can be done by running the following command:
+
+```shell
+dotnet nuget add source -n geekeey https://code.geekeey.de/api/packages/geekeey/nuget/index.json
+```
+
+### Usage
+
+```csharp
+public static Task<int> Main()
+{
+  var collection = new ServiceCollection();
+  collection.AddRequestDispatcher(builder => builder
+      .SearchHandlerInAssembly(typeof(ScalarHandler).Assembly)
+      .Add(typeof(ScalarBehavior)));
+  await using var provider = collection.BuildServiceProvider();
+  var dispatcher = provider.GetRequiredService<IRequestDispatcher>();
+
+  var request = new ScalarRequest { Value = "Hello" };
+  var result = await dispatcher.DispatchAsync(request);
+
+  Console.WriteLine(result);
+  return 0;
+}
+
+public class ScalarRequest : IScalarRequest<string>
+{
+  public string Value { get; set; } = string.Empty;
+}
+
+public class ScalarHandler : IScalarRequestHandler<ScalarRequest, string>
+{
+  public Task<string> HandleAsync(ScalarRequest request, CancellationToken cancellationToken)
+  {
+    return Task.FromResult($"{request.Value} World");
+  }
+}
+
+public class ScalarBehavior : IScalarRequestBehavior<ScalarRequest, string>
+{
+  public async Task<string> HandleAsync(ScalarRequest request, ScalarHandlerDelegate<string> next, CancellationToken cancellationToken)
+  {
+    Console.WriteLine("Before");
+    var result = await next(request, cancellationToken);
+    Console.WriteLine("After");
+    return result;
+  }
+}
+```
+
+## Behaviour of the Handlers
+
+Handlers are resolved from either the DI container or are created on the fly but can receive arguments from the DI
+container when being constructed. The same also applied for the request pipeline behaviours.