Extract endpoint metadata during ActionModel creation

Author: mkArtakMSFT

src/Mvc/Mvc.Core/src/ApplicationModels/DefaultApplicationModelProvider.cs

@@ -1,9 +1,11 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Mvc.ActionConstraints;
 using Microsoft.AspNetCore.Mvc.ApiExplorer;
 using Microsoft.AspNetCore.Mvc.Filters;
@@ -349,9 +351,43 @@ internal PropertyModel CreatePropertyModel(PropertyInfo propertyInfo)
         applicableAttributes.AddRange(routeAttributes);
         AddRange(actionModel.Selectors, CreateSelectors(applicableAttributes));
 
+        AddReturnTypeMetadata(actionModel.Selectors, methodInfo);
+
         return actionModel;
     }
 
+    [UnconditionalSuppressMessage("AssemblyLoadTrimming", "IL2026:RequiresUnreferencedCode",
+        Justification = "The method utilizes reflection to get information about the return type of an action")]
+    internal static void AddReturnTypeMetadata(IList<SelectorModel> selectors, MethodInfo methodInfo)
+    {
+        // Get metadata from return type
+        var returnType = methodInfo.ReturnType;
+        if (CoercedAwaitableInfo.IsTypeAwaitable(returnType, out var coercedAwaitableInfo))
+        {
+            returnType = coercedAwaitableInfo.AwaitableInfo.ResultType;
+        }
+
+        if (returnType is not null && typeof(IEndpointMetadataProvider).IsAssignableFrom(returnType))
+        {
+            // Return type implements IEndpointMetadataProvider
+            var builder = new InertEndpointBuilder();
+            var invokeArgs = new object[2];
+            invokeArgs[0] = methodInfo;
+            invokeArgs[1] = builder;
+            EndpointMetadataPopulator.PopulateMetadataForEndpointMethod.MakeGenericMethod(returnType).Invoke(null, invokeArgs);
+
+            // The metadata is added to the builder's metadata collection.
+            // We need to populate the selectors with that metadata.
+            foreach (var metadata in builder.Metadata)
+            {
+                foreach (var selector in selectors)
+                {
+                    selector.EndpointMetadata.Add(metadata);
+                }
+            }
+        }
+    }
+
     private string CanonicalizeActionName(string actionName)
     {
         const string Suffix = "Async";

src/Mvc/Mvc.Core/src/Routing/ActionEndpointFactory.cs

@@ -543,12 +543,4 @@ private static RequestDelegate CreateRequestDelegate()
             return invoker!.InvokeAsync();
         };
     }
-
-    private sealed class InertEndpointBuilder : EndpointBuilder
-    {
-        public override Endpoint Build()
-        {
-            return new Endpoint(RequestDelegate, new EndpointMetadataCollection(Metadata), DisplayName);
-        }
-    }
 }

src/Mvc/Mvc.Core/src/Routing/InertEndpointBuilder.cs

@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+
+namespace Microsoft.AspNetCore.Mvc.Routing;
+
+internal sealed class InertEndpointBuilder : EndpointBuilder
+{
+    public override Endpoint Build()
+    {
+        return new Endpoint(RequestDelegate, new EndpointMetadataCollection(Metadata), DisplayName);
+    }
+}

src/Mvc/Mvc.Core/test/ApplicationModels/DefaultApplicationModelProviderTest.cs

@@ -1243,6 +1243,45 @@ public void CreateActionModel_InheritedAttributeRoutesOverridden()
         Assert.Contains(selectorModel.AttributeRouteModel.Attribute, action.Attributes);
     }
 
+    [Fact]
+    public void CreateActionModel_PopulatesReturnTypeEndpointMetadata() {
+        // Arrange
+        var builder = new TestApplicationModelProvider();
+        var typeInfo = typeof(TypedResultsReturningActionsController).GetTypeInfo();
+        var actionName = nameof(TypedResultsReturningActionsController.Get);
+
+        // Act
+        var action = builder.CreateActionModel(typeInfo, typeInfo.AsType().GetMethod(actionName));
+
+        // Assert
+        Assert.NotNull(action.Selectors);
+        Assert.All(action.Selectors, selector =>
+        {
+            Assert.NotNull(selector.EndpointMetadata);
+            Assert.Contains(selector.EndpointMetadata, m => m is ProducesResponseTypeMetadata);
+        });
+        var metadata = action.Selectors[0].EndpointMetadata.OfType<ProducesResponseTypeMetadata>().Single();
+        Assert.Equal(200, metadata.StatusCode);
+    }
+
+    [Fact]
+    public void AddReturnTypeMetadata_ExtractsMetadataFromReturnType()
+    {
+        // Arrange
+        var selector = new SelectorModel();
+        var selectors = new List<SelectorModel> { selector };
+        var actionMethod = typeof(TypedResultsReturningActionsController).GetMethod(nameof(TypedResultsReturningActionsController.Get));
+
+        // Act
+        DefaultApplicationModelProvider.AddReturnTypeMetadata(selectors, actionMethod);
+
+        // Assert
+        Assert.NotNull(selector.EndpointMetadata);
+        Assert.Single(selector.EndpointMetadata);
+        Assert.IsType<ProducesResponseTypeMetadata>(selector.EndpointMetadata.Single()); 
+        Assert.Equal(200, ((ProducesResponseTypeMetadata)selector.EndpointMetadata[0]).StatusCode);
+    }
+
     [Fact]
     public void ControllerDispose_ExplicitlyImplemented_IDisposableMethods_AreTreatedAs_NonActions()
     {
@@ -1711,6 +1750,16 @@ public void Details() { }
         public void List() { }
     }
 
+    private class TypedResultsReturningActionsController : Controller
+    {
+        [HttpGet]
+        public Http.HttpResults.Ok<Foo> Get() => TypedResults.Ok<Foo>(new Foo { Info = "Hello" });
+    }
+
+    public class Foo {
+        public required string Info { get; set; }
+    }
+
     private class CustomHttpMethodsAttribute : Attribute, IActionHttpMethodProvider
     {
         private readonly string[] _methods;

src/Mvc/Mvc.Core/test/Microsoft.AspNetCore.Mvc.Core.Test.csproj

@@ -12,6 +12,7 @@
   <ItemGroup>
     <Reference Include="FSharp.Core" />
     <Reference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" />
+    <Reference Include="Microsoft.AspNetCore.Http.Results" />
     <ProjectReference Include="..\..\shared\Mvc.Core.TestCommon\Microsoft.AspNetCore.Mvc.Core.TestCommon.csproj" />
     <ProjectReference Include="..\..\shared\Mvc.TestDiagnosticListener\Microsoft.AspNetCore.Mvc.TestDiagnosticListener.csproj" />
 

src/Shared/EndpointMetadataPopulator.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Http;
 internal static class EndpointMetadataPopulator
 {
     private static readonly MethodInfo PopulateMetadataForParameterMethod = typeof(EndpointMetadataPopulator).GetMethod(nameof(PopulateMetadataForParameter), BindingFlags.NonPublic | BindingFlags.Static)!;
-    private static readonly MethodInfo PopulateMetadataForEndpointMethod = typeof(EndpointMetadataPopulator).GetMethod(nameof(PopulateMetadataForEndpoint), BindingFlags.NonPublic | BindingFlags.Static)!;
+    internal static readonly MethodInfo PopulateMetadataForEndpointMethod = typeof(EndpointMetadataPopulator).GetMethod(nameof(PopulateMetadataForEndpoint), BindingFlags.NonPublic | BindingFlags.Static)!;
 
     public static void PopulateMetadata(MethodInfo methodInfo, EndpointBuilder builder, IEnumerable<ParameterInfo>? parameters = null)
     {