Update

src/Grpc.AspNetCore.Server/GrpcEndpointRouteBuilderExtensions.cs

@@ -17,6 +17,7 @@
 #endregion
 
 using System.Diagnostics.CodeAnalysis;
+using Grpc.AspNetCore.Server;
 using Grpc.AspNetCore.Server.Internal;
 using Grpc.AspNetCore.Server.Model.Internal;
 using Grpc.Core;
@@ -31,10 +32,6 @@ namespace Microsoft.AspNetCore.Builder;
 /// </summary>
 public static class GrpcEndpointRouteBuilderExtensions
 {
-    private sealed class ServerServiceDefinitionDummyService
-    {
-    }
-
     /// <summary>
     /// Maps incoming requests to the specified <typeparamref name="TService"/> type.
     /// </summary>
@@ -65,10 +62,7 @@ public static GrpcServiceEndpointConventionBuilder MapGrpcService(this IEndpoint
         ArgumentNullException.ThrowIfNull(builder, nameof(builder));
         ArgumentNullException.ThrowIfNull(serviceDefinition, nameof(serviceDefinition));
 
-        var serviceMethodsRegistry = builder.ServiceProvider.GetRequiredService<ServiceMethodsRegistry>();
-        serviceMethodsRegistry.ServiceDefinitions.Add(serviceDefinition);
-
-        var serviceRouteBuilder = builder.ServiceProvider.GetRequiredService<ServiceRouteBuilder<ServerServiceDefinitionDummyService>>();
+        var serviceRouteBuilder = builder.ServiceProvider.GetRequiredService<ServiceRouteBuilder<ServerServiceDefinitionMarker>>();
         var endpointConventionBuilders = serviceRouteBuilder.Build(builder, serviceDefinition);
 
         return new GrpcServiceEndpointConventionBuilder(endpointConventionBuilders);
@@ -88,10 +82,7 @@ public static GrpcServiceEndpointConventionBuilder MapGrpcService(this IEndpoint
 
         var serviceDefinition = getServiceDefinition(builder.ServiceProvider);
 
-        var serviceMethodsRegistry = builder.ServiceProvider.GetRequiredService<ServiceMethodsRegistry>();
-        serviceMethodsRegistry.ServiceDefinitions.Add(serviceDefinition);
-
-        var serviceRouteBuilder = builder.ServiceProvider.GetRequiredService<ServiceRouteBuilder<ServerServiceDefinitionDummyService>>();
+        var serviceRouteBuilder = builder.ServiceProvider.GetRequiredService<ServiceRouteBuilder<ServerServiceDefinitionMarker>>();
         var endpointConventionBuilders = serviceRouteBuilder.Build(builder, serviceDefinition);
 
         return new GrpcServiceEndpointConventionBuilder(endpointConventionBuilders);

src/Grpc.AspNetCore.Server/GrpcServiceExtensions.cs

@@ -79,7 +79,10 @@ public static IGrpcServerBuilder AddGrpc(this IServiceCollection services)
         services.TryAddEnumerable(ServiceDescriptor.Singleton(typeof(IServiceMethodProvider<>), typeof(BinderServiceMethodProvider<>)));
         services.TryAddEnumerable(ServiceDescriptor.Singleton(typeof(IServiceMethodProvider<>), typeof(ServiceDefinitionMethodProvider<>)));
 
-        return new GrpcServerBuilder(services);
+        var builder = new GrpcServerBuilder(services);
+        builder.AddServiceOptions<ServerServiceDefinitionMarker>(options => options.SuppressCreatingService = true);
+
+        return builder;
 
         static void ConfigureRouting(RouteOptions options)
         {

src/Grpc.AspNetCore.Server/GrpcServiceOptions.cs

@@ -1,4 +1,4 @@
-#region Copyright notice and license
+#region Copyright notice and license
 
 // Copyright 2019 The gRPC Authors
 //
@@ -112,6 +112,8 @@ public IList<ICompressionProvider> CompressionProviders
     /// Get a collection of interceptors to be executed with every call. Interceptors are executed in order.
     /// </summary>
     public InterceptorCollection Interceptors { get; } = new InterceptorCollection();
+
+    internal bool SuppressCreatingService { get; set; }
 }
 
 /// <summary>

src/Grpc.AspNetCore.Server/Model/Internal/ServiceDefinitionMethodProvider.cs

@@ -20,6 +20,7 @@
 using Grpc.AspNetCore.Server.Internal;
 using Grpc.Core;
 using Grpc.Shared;
+using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.Logging;
 
 namespace Grpc.AspNetCore.Server.Model.Internal;
@@ -54,25 +55,37 @@ public ProviderServiceBinder(ServiceMethodProviderContext<TService> context)
         public override void AddMethod<TRequest, TResponse>(Method<TRequest, TResponse> method, UnaryServerMethod<TRequest, TResponse>? handler)
         {
             ArgumentNullThrowHelper.ThrowIfNull(handler, nameof(handler));
-            _context.AddUnaryMethod(method, new List<object>(), (service, request, context) => handler(request, context));
+            _context.AddUnaryMethod(method, CreateMetadata(), (service, request, context) => handler(request, context));
         }
 
         public override void AddMethod<TRequest, TResponse>(Method<TRequest, TResponse> method, DuplexStreamingServerMethod<TRequest, TResponse>? handler)
         {
             ArgumentNullThrowHelper.ThrowIfNull(handler, nameof(handler));
-            _context.AddDuplexStreamingMethod(method, new List<object>(), (service, request, response, context) => handler(request, response, context));
+            _context.AddDuplexStreamingMethod(method, CreateMetadata(), (service, request, response, context) => handler(request, response, context));
         }
 
         public override void AddMethod<TRequest, TResponse>(Method<TRequest, TResponse> method, ServerStreamingServerMethod<TRequest, TResponse>? handler)
         {
             ArgumentNullThrowHelper.ThrowIfNull(handler, nameof(handler));
-            _context.AddServerStreamingMethod(method, new List<object>(), (service, request, response, context) => handler(request, response, context));
+            _context.AddServerStreamingMethod(method, CreateMetadata(), (service, request, response, context) => handler(request, response, context));
         }
 
         public override void AddMethod<TRequest, TResponse>(Method<TRequest, TResponse> method, ClientStreamingServerMethod<TRequest, TResponse>? handler)
         {
             ArgumentNullThrowHelper.ThrowIfNull(handler, nameof(handler));
-            _context.AddClientStreamingMethod(method, new List<object>(), (service, request, context) => handler(request, context));
+            _context.AddClientStreamingMethod(method, CreateMetadata(), (service, request, context) => handler(request, context));
+        }
+
+        private static List<object> CreateMetadata()
+        {
+            // Accepting CORS preflight means gRPC will allow requests with OPTIONS + preflight headers.
+            // If CORS middleware hasn't been configured then the request will reach gRPC handler.
+            // gRPC will return 405 response and log that CORS has not been configured.
+            var metadata = new List<object>
+            {
+                new HttpMethodMetadata(new[] { "POST" }, acceptCorsPreflight: true)
+            };
+            return metadata;
         }
     }
 }

src/Grpc.AspNetCore.Server/Model/Internal/ServiceMethodsRegistry.cs

@@ -16,8 +16,6 @@
 
 #endregion
 
-using Grpc.Core;
-
 namespace Grpc.AspNetCore.Server.Model.Internal;
 
 /// <summary>
@@ -26,6 +24,4 @@ namespace Grpc.AspNetCore.Server.Model.Internal;
 internal sealed class ServiceMethodsRegistry
 {
     public List<MethodModel> Methods { get; } = new List<MethodModel>();
-
-    public List<ServerServiceDefinition> ServiceDefinitions { get; } = new List<ServerServiceDefinition>();
 }

src/Grpc.AspNetCore.Server/ServerServiceDefinitionMarker.cs

@@ -0,0 +1,23 @@
+#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
+
+namespace Grpc.AspNetCore.Server;
+
+internal sealed class ServerServiceDefinitionMarker
+{
+}

src/Shared/Server/MethodOptions.cs

@@ -121,6 +121,7 @@ public static MethodOptions Create(IEnumerable<GrpcServiceOptions> serviceOption
         bool? enableDetailedErrors = null;
         string? responseCompressionAlgorithm = null;
         CompressionLevel? responseCompressionLevel = null;
+        bool? suppressCreatingService = null;
 
         foreach (var options in serviceOptions.Reverse())
         {
@@ -139,6 +140,7 @@ public static MethodOptions Create(IEnumerable<GrpcServiceOptions> serviceOption
             enableDetailedErrors ??= options.EnableDetailedErrors;
             responseCompressionAlgorithm ??= options.ResponseCompressionAlgorithm;
             responseCompressionLevel ??= options.ResponseCompressionLevel;
+            suppressCreatingService ??= options.SuppressCreatingService;
         }
 
         var interceptors = new InterceptorCollection();
@@ -153,7 +155,7 @@ public static MethodOptions Create(IEnumerable<GrpcServiceOptions> serviceOption
             enableDetailedErrors: enableDetailedErrors,
             responseCompressionAlgorithm: responseCompressionAlgorithm,
             responseCompressionLevel: responseCompressionLevel,
-            suppressCreatingService: true
+            suppressCreatingService: suppressCreatingService ?? false
         );
     }