Fix for 1071: Output Formatters should be invoked for writing out the response.

src/Microsoft.AspNet.Mvc.Core/Formatters/HttpNoContentOutputFormatter.cs

@@ -13,11 +13,23 @@ namespace Microsoft.AspNet.Mvc
     /// </summary>
     public class HttpNoContentOutputFormatter : IOutputFormatter
     {
+        /// <summary>
+        /// Indicates whether to select this formatter if the returned value from the action
+        /// is null.
+        /// </summary>
+        public bool TreatNullValueAsNoContent { get; set; } = true;
+
         public bool CanWriteResult(OutputFormatterContext context, MediaTypeHeaderValue contentType)
         {
             // ignore the contentType and just look at the content.
             // This formatter will be selected if the content is null. 
-            return context.Object == null;
+            // We check for Task as a user can directly create an ObjectContentResult with the unwrapped type.
+            if(context.DeclaredType == typeof(void) || context.DeclaredType == typeof(Task))
+            {
+                return true;
+            }
+
+            return TreatNullValueAsNoContent && context.Object == null;
         }
 
         public IReadOnlyList<MediaTypeHeaderValue> GetSupportedContentTypes(

src/Microsoft.AspNet.Mvc.Core/ReflectedActionInvoker.cs

@@ -80,7 +80,11 @@ namespace Microsoft.AspNet.Mvc
             if (declaredReturnType == typeof(void) ||
                 declaredReturnType == typeof(Task))
             {
-                return new NoContentResult();
+                return new ObjectResult(null)
+                {
+                    // Treat the declared type as void, which is the unwrapped type for Task.
+                    DeclaredType = typeof(void)
+                };
             }
 
             // Unwrap potential Task<T> types. 

test/Microsoft.AspNet.Mvc.Core.Test/Formatters/NoContentFormatterTests.cs

@@ -37,10 +37,10 @@ namespace Microsoft.AspNet.Mvc.Test
 
         [Theory]
         [MemberData(nameof(OutputFormatterContextValues_CanWriteType))]
-        public void CanWriteResult_ReturnsTrueOnlyIfTheValueIsNull(object value,
-                                                                   bool declaredTypeAsString,
-                                                                   bool expectedCanwriteResult,
-                                                                   bool useNonNullContentType)
+        public void CanWriteResult_ByDefault_ReturnsTrue_IfTheValueIsNull(object value,
+                                                                          bool declaredTypeAsString,
+                                                                          bool expectedCanwriteResult,
+                                                                          bool useNonNullContentType)
         {
             // Arrange 
             var typeToUse = declaredTypeAsString ? typeof(string) : typeof(object);
@@ -60,6 +60,58 @@ namespace Microsoft.AspNet.Mvc.Test
             Assert.Equal(expectedCanwriteResult, actualCanWriteResult);
         }
 
+        [Theory]
+        [InlineData(typeof(void))]
+        [InlineData(typeof(Task))]
+        public void CanWriteResult_ReturnsTrue_IfReturnTypeIsVoidOrTask(Type declaredType)
+        {
+            // Arrange 
+            var formatterContext = new OutputFormatterContext()
+            {
+                Object = "Something non null.",
+                DeclaredType = declaredType,
+                ActionContext = null,
+            };
+            var contetType = MediaTypeHeaderValue.Parse("text/plain");
+            var formatter = new HttpNoContentOutputFormatter();
+
+            // Act
+            var actualCanWriteResult = formatter.CanWriteResult(formatterContext, contetType);
+
+            // Assert
+            Assert.True(actualCanWriteResult);
+        }
+
+        [Theory]
+        [InlineData(null, true, true)]
+        [InlineData(null, false, false)]
+        [InlineData("some value", true, false)]
+        public void 
+            CanWriteResult_ReturnsTrue_IfReturnValueIsNullAndTreatNullValueAsNoContentIsNotSet(string value,
+                                                                                      bool treatNullValueAsNoContent,
+                                                                                      bool expectedCanwriteResult)
+        {
+            // Arrange 
+            var formatterContext = new OutputFormatterContext()
+            {
+                Object = value,
+                DeclaredType = typeof(string),
+                ActionContext = null,
+            };
+
+            var contetType = MediaTypeHeaderValue.Parse("text/plain");
+            var formatter = new HttpNoContentOutputFormatter()
+            {
+                TreatNullValueAsNoContent = treatNullValueAsNoContent
+            };
+
+            // Act
+            var actualCanWriteResult = formatter.CanWriteResult(formatterContext, contetType);
+
+            // Assert
+            Assert.Equal(expectedCanwriteResult, actualCanWriteResult);
+        }
+
         [Fact]
         public async Task WriteAsync_WritesTheStatusCode204()
         {

test/Microsoft.AspNet.Mvc.Core.Test/ReflectedActionInvokerTest.cs

@@ -1234,13 +1234,17 @@ namespace Microsoft.AspNet.Mvc
         [Theory]
         [InlineData(typeof(void))]
         [InlineData(typeof(Task))]
-        public void CreateActionResult_Types_ReturnsNoContentResultForTaskAndVoidReturnTypes(Type type)
+        public void CreateActionResult_Types_ReturnsObjectResultForTaskAndVoidReturnTypes(Type type)
         {
             // Arrange & Act
-            var result = ReflectedActionInvoker.CreateActionResult(type, null).GetType();
+            var result = ReflectedActionInvoker.CreateActionResult(type, null);
 
             // Assert
-            Assert.Equal(typeof(NoContentResult), (result));
+            var objectResult = Assert.IsType<ObjectResult>(result);
+
+            // Since we unwrap the Task type to void, the expected type will always be void.
+            Assert.Equal(typeof(void), objectResult.DeclaredType);
+            Assert.Null(objectResult.Value);
         }
 
         public static IEnumerable<object[]> CreateActionResult_ReturnsObjectContentResultData

test/Microsoft.AspNet.Mvc.FunctionalTests/OutputFormattterTests.cs

@@ -57,10 +57,9 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
         }
 
         [Theory]
-        [InlineData("ReturnTaskOfString_NullValue")]
-        [InlineData("ReturnTaskOfObject_NullValue")]
-        [InlineData("ReturnObject_NullValue")]
-        public async Task NoContentFormatter_ForNullValue_GetsSelectedAndWritesResponse(string actionName)
+        [InlineData("ReturnTask")]
+        [InlineData("ReturnVoid")]
+        public async Task NoContentFormatter_ForVoidAndTaskReturnType_GetsSelectedAndWritesResponse(string actionName)
         {
             // Arrange
             var server = TestServer.Create(_provider, _app);
@@ -77,5 +76,50 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
             Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
             Assert.Equal(0, response.Content.Headers.ContentLength);
         }
+
+        [Theory]
+        [InlineData("ReturnTaskOfString_NullValue")]
+        [InlineData("ReturnTaskOfObject_NullValue")]
+        [InlineData("ReturnObject_NullValue")]
+        public async Task NoContentFormatter_ForNullValue_ByDefault_GetsSelectedAndWritesResponse(string actionName)
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.CreateClient();
+
+            // Act
+            var response = await client.GetAsync("http://localhost/NoContent/" + actionName);
+
+            // Assert
+            Assert.Null(response.Content.Headers.ContentType);
+            var body = await response.Content.ReadAsStringAsync();
+            // Response body is empty instead of null.
+            Assert.Empty(body);
+            Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
+            Assert.Equal(0, response.Content.Headers.ContentLength);
+        }
+
+        [Theory]
+        [InlineData("ReturnTaskOfString_NullValue")]
+        [InlineData("ReturnTaskOfObject_NullValue")]
+        [InlineData("ReturnObject_NullValue")]
+        public async Task 
+            NoContentFormatter_ForNullValue_AndTreatNullAsNoContentFlagSetToFalse_DoesNotGetSelected(string actionName)
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.CreateClient();
+
+            // Act
+            var response = await client.GetAsync("http://localhost/NoContentDoNotTreatNullValueAsNoContent/" +
+                                                 actionName);
+
+            // Assert
+            Assert.Null(response.Content.Headers.ContentType);
+            var body = await response.Content.ReadAsStringAsync();
+            // Response body is empty instead of null.
+            Assert.Empty(body);
+            Assert.Equal(HttpStatusCode.NotAcceptable, response.StatusCode);
+        }
     }
 }

test/WebSites/BasicWebSite/Controllers/HomeController.cs

@@ -34,7 +34,7 @@ namespace BasicWebSite.Controllers
         public async Task ActionReturningTask()
         {
             // TODO: #1077. With HttpResponseMessage, there seems to be a race between the write operation setting the
-            // header to 200 and NoContentResult returned by the action invoker setting it to 204.
+            // header to 200 and HttpNoContentOutputFormatter which sets the header to 204.
             Context.Response.StatusCode = 204;
             await Context.Response.WriteAsync("Hello world");
         }

test/WebSites/ConnegWebSite/Controllers/NoContentController.cs

@@ -27,5 +27,14 @@ namespace ConnegWebsite
         {
             return null;
         }
+
+        public Task ReturnTask()
+        {
+            return Task.FromResult<bool>(true);
+        }
+
+        public void ReturnVoid()
+        {
+        }
     }
 }

test/WebSites/ConnegWebSite/Controllers/NoContentDoNotTreatNullValueAsNoContentController.cs

@@ -0,0 +1,44 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Mvc;
+
+namespace ConnegWebsite
+{
+    public class NoContentDoNotTreatNullValueAsNoContentController : Controller
+    {
+        public override void OnActionExecuted(ActionExecutedContext context)
+        {
+            var result = context.Result as ObjectResult;
+            if (result != null)
+            {
+                var noContentFormatter = new HttpNoContentOutputFormatter() { TreatNullValueAsNoContent = false };
+                result.Formatters.Add(noContentFormatter);
+            }
+
+            base.OnActionExecuted(context);
+        }
+
+        public Task<string> ReturnTaskOfString_NullValue()
+        {
+            return Task.FromResult<string>(null);
+        }
+
+        public Task<object> ReturnTaskOfObject_NullValue()
+        {
+            return Task.FromResult<object>(null);
+        }
+
+        public object ReturnObject_NullValue()
+        {
+            return null;
+        }
+
+        public string ReturnString_NullValue()
+        {
+            return null;
+        }
+    }
+}