Adding configuration to auto-register request processors

src/MediatR/MicrosoftExtensionsDI/MediatrServiceConfiguration.cs

@@ -64,6 +64,11 @@ public class MediatRServiceConfiguration
     /// </summary>
     public List<ServiceDescriptor> RequestPostProcessorsToRegister { get; } = new();
 
+    /// <summary>
+    /// Automatically register processors during assembly scanning
+    /// </summary>
+    public bool AutoRegisterRequestProcessors { get; set; }
+
     /// <summary>
     /// Register various handlers from assembly containing given type
     /// </summary>

src/MediatR/Registration/ServiceRegistrar.cs

@@ -21,13 +21,25 @@ public static void AddMediatRClasses(IServiceCollection services, MediatRService
         ConnectImplementationsToTypesClosing(typeof(IRequestExceptionHandler<,,>), services, assembliesToScan, true, configuration);
         ConnectImplementationsToTypesClosing(typeof(IRequestExceptionAction<,>), services, assembliesToScan, true, configuration);
 
-        var multiOpenInterfaces = new[]
+        if (configuration.AutoRegisterRequestProcessors)
+        {
+            ConnectImplementationsToTypesClosing(typeof(IRequestPreProcessor<>), services, assembliesToScan, false, configuration);
+            ConnectImplementationsToTypesClosing(typeof(IRequestPostProcessor<,>), services, assembliesToScan, false, configuration);
+        }
+
+        var multiOpenInterfaces = new List<Type>
         {
             typeof(INotificationHandler<>),
             typeof(IRequestExceptionHandler<,,>),
             typeof(IRequestExceptionAction<,>)
         };
 
+        if (configuration.AutoRegisterRequestProcessors)
+        {
+            multiOpenInterfaces.Add(typeof(IRequestPreProcessor<>));
+            multiOpenInterfaces.Add(typeof(IRequestPostProcessor<,>));
+        }
+
         foreach (var multiOpenInterface in multiOpenInterfaces)
         {
             var arity = multiOpenInterface.GetGenericArguments().Length;

test/MediatR.Tests/MicrosoftExtensionsDI/PipelineTests.cs

@@ -846,6 +846,29 @@ public void Should_handle_open_behaviors_registration_from_a_single_type()
         });
     }
 
+    [Fact]
+    public void Should_auto_register_processors_when_configured()
+    {
+        var cfg = new MediatRServiceConfiguration
+        {
+            AutoRegisterRequestProcessors = true
+        };
+
+        var output = new Logger();
+        IServiceCollection services = new ServiceCollection();
+        services.AddSingleton(output);
+
+        cfg.RegisterServicesFromAssemblyContaining<Ping>();
+
+        services.AddMediatR(cfg);
+
+        var provider = services.BuildServiceProvider();
+
+        provider.GetServices(typeof(IRequestPreProcessor<Ping>)).Count().ShouldBeGreaterThan(0);
+        provider.GetServices(typeof(IRequestPostProcessor<Ping, Pong>)).Count().ShouldBeGreaterThan(0);
+    }
+
+
     public sealed record FooRequest : IRequest;
 
     public interface IBlogger<T>