Implicitly execute matched endpoint at the end of middleware pipeline (#1059)

Author: JamesNK

src/Microsoft.AspNetCore.Http/Internal/ApplicationBuilder.cs

@@ -81,6 +81,13 @@ public RequestDelegate Build()
         {
             RequestDelegate app = context =>
             {
+                // Implicitly execute matched endpoint at the end of the pipeline instead of returning 404
+                var endpointRequestDelegate = context.GetEndpoint()?.RequestDelegate;
+                if (endpointRequestDelegate != null)
+                {
+                    return endpointRequestDelegate(context);
+                }
+
                 context.Response.StatusCode = 404;
                 return Task.CompletedTask;
             };

test/Microsoft.AspNetCore.Http.Tests/Internal/ApplicationBuilderTests.cs

@@ -1,7 +1,9 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Features;
 using Xunit;
 
 namespace Microsoft.AspNetCore.Builder.Internal
@@ -20,6 +22,59 @@ public void BuildReturnsCallableDelegate()
             Assert.Equal(404, httpContext.Response.StatusCode);
         }
 
+        [Fact]
+        public void BuildImplicitlyCallsMatchedEndpointAsLastStep()
+        {
+            var builder = new ApplicationBuilder(null);
+            var app = builder.Build();
+
+            var endpointCalled = false;
+            var endpoint = new Endpoint(
+                context =>
+                {
+                    endpointCalled = true;
+                    return Task.CompletedTask;
+                },
+                EndpointMetadataCollection.Empty,
+                "Test endpoint");
+
+            var httpContext = new DefaultHttpContext();
+            httpContext.SetEndpoint(endpoint);
+
+            app.Invoke(httpContext);
+
+            Assert.True(endpointCalled);
+        }
+
+        [Fact]
+        public void BuildDoesNotCallMatchedEndpointWhenTerminated()
+        {
+            var builder = new ApplicationBuilder(null);
+            builder.Use((context, next) =>
+            {
+                // Do not call next
+                return Task.CompletedTask;
+            });
+            var app = builder.Build();
+
+            var endpointCalled = false;
+            var endpoint = new Endpoint(
+                context =>
+                {
+                    endpointCalled = true;
+                    return Task.CompletedTask;
+                },
+                EndpointMetadataCollection.Empty,
+                "Test endpoint");
+
+            var httpContext = new DefaultHttpContext();
+            httpContext.SetEndpoint(endpoint);
+
+            app.Invoke(httpContext);
+
+            Assert.False(endpointCalled);
+        }
+
         [Fact]
         public void PropertiesDictionaryIsDistinctAfterNew()
         {