NoContentFormatter: Writes 204 to the response status code if the value returned is null.

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

@@ -0,0 +1,35 @@
+// 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.Threading.Tasks;
+using Microsoft.AspNet.Mvc.HeaderValueAbstractions;
+
+namespace Microsoft.AspNet.Mvc
+{
+    /// <summary>
+    /// Sets the status code to 204 if the content is null.
+    /// </summary>
+    public class NoContentFormatter : IOutputFormatter
+    {
+        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;
+        }
+
+        public Task WriteAsync(OutputFormatterContext context)
+        {
+            var response = context.ActionContext.HttpContext.Response;
+            response.ContentLength = 0;
+
+            // Only set the status code if its not already set.
+            if (response.StatusCode == 0)
+            {
+                response.StatusCode = 204;
+            }
+
+            return Task.FromResult<bool>(true);
+        }
+    }
+}

src/Microsoft.AspNet.Mvc.Core/Microsoft.AspNet.Mvc.Core.kproj

@@ -32,6 +32,7 @@
     <Compile Include="ActionResults\HttpNotFoundResult.cs" />
     <Compile Include="Formatters\TextPlainFormatter.cs" />
     <Compile Include="HttpMethodAttribute.cs" />
+    <Compile Include="Formatters\NoContentFormatter.cs" />
     <Compile Include="Internal\DecisionTree\DecisionCriterionValue.cs" />
     <Compile Include="Internal\DecisionTree\DecisionCriterionValueEqualityComparer.cs" />
     <Compile Include="Logging\AttributeRouteRouteAsyncValues.cs" />

src/Microsoft.AspNet.Mvc/MvcOptionsSetup.cs

@@ -34,6 +34,7 @@ namespace Microsoft.AspNet.Mvc
             options.ModelBinders.Add(new ComplexModelDtoModelBinder());
 
             // Set up default output formatters.
+            options.OutputFormatters.Add(new NoContentFormatter());
             options.OutputFormatters.Add(new TextPlainFormatter());
             options.OutputFormatters.Add(new JsonOutputFormatter(JsonOutputFormatter.CreateDefaultSettings(),
                                          indent: false));

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

@@ -0,0 +1,107 @@
+// 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;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.AspNet.Http;
+using Microsoft.AspNet.Mvc.HeaderValueAbstractions;
+using Microsoft.AspNet.PipelineCore;
+using Microsoft.AspNet.Routing;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNet.Mvc.Test
+{
+    public class NoContentFormatterTests
+    {
+        public static IEnumerable<object[]> OutputFormatterContextValues_CanWriteType
+        {
+            get
+            {
+                // object value, bool useDeclaredTypeAsString, bool expectedCanwriteResult, bool useNonNullContentType
+                yield return new object[] { "valid value", true, false, true };
+                yield return new object[] { "valid value", false, false, true };
+                yield return new object[] { "", false, false, true };
+                yield return new object[] { "", true, false, true };
+                yield return new object[] { null, true, true, true };
+                yield return new object[] { null, false, true, true };
+                yield return new object[] { null, false, true, false };
+                yield return new object[] { new object(), false, false, true };
+                yield return new object[] { 1232, false, false, true };
+                yield return new object[] { 1232, false, false, false };
+            }
+        }
+
+        [Theory]
+        [MemberData("OutputFormatterContextValues_CanWriteType")]
+        public void CanWriteResult_ReturnsTrueOnlyIfTheValueIsNull(object value,
+                                                                   bool declaredTypeAsString,
+                                                                   bool expectedCanwriteResult,
+                                                                   bool useNonNullContentType)
+        {
+            // Arrange 
+            var typeToUse = declaredTypeAsString ? typeof(string) : typeof(object);
+            var formatterContext = new OutputFormatterContext()
+            {
+                Object = value,
+                DeclaredType = typeToUse,
+                ActionContext = null,
+            };
+            var contetType = useNonNullContentType ? MediaTypeHeaderValue.Parse("text/plain") : null;
+            var formatter = new NoContentFormatter();
+
+            // Act
+            var actualCanWriteResult = formatter.CanWriteResult(formatterContext, contetType);
+
+            // Assert
+            Assert.Equal(expectedCanwriteResult, actualCanWriteResult);
+        }
+
+        [Fact]
+        public async Task WriteAsync_WritesTheStatusCode204_IfNotAlreadySet()
+        {
+            // Arrange 
+            var defaultHttpContext = new DefaultHttpContext();
+
+            // Workaround for https://github.com/aspnet/HttpAbstractions/issues/114
+            defaultHttpContext.Response.StatusCode = 0;
+            var formatterContext = new OutputFormatterContext()
+            {
+                Object = null,
+                ActionContext = new ActionContext(defaultHttpContext, new RouteData(), new ActionDescriptor())
+            };
+
+            var formatter = new NoContentFormatter();
+
+            // Act
+            await formatter.WriteAsync(formatterContext);
+
+            // Assert
+            Assert.Equal(204, defaultHttpContext.Response.StatusCode);
+        }
+
+        [Fact]
+        public async Task WriteAsync_DoesnNotWriteTheStatusCode204_IfStatusCodeIsSetAlready()
+        {
+            // Arrange 
+            var defaultHttpContext = new DefaultHttpContext();
+            defaultHttpContext.Response.StatusCode = 201;
+            var formatterContext = new OutputFormatterContext()
+            {
+                Object = null,
+                ActionContext = new ActionContext(defaultHttpContext, new RouteData(), new ActionDescriptor())
+            };
+
+            var formatter = new NoContentFormatter();
+
+            // Act
+            await formatter.WriteAsync(formatterContext);
+
+            // Assert
+            Assert.Equal(201, defaultHttpContext.Response.StatusCode);
+        }
+    }
+}

test/Microsoft.AspNet.Mvc.Core.Test/Microsoft.AspNet.Mvc.Core.Test.kproj

@@ -30,8 +30,11 @@
     <Compile Include="ActionResults\RedirectResultTest.cs" />
     <Compile Include="ActionResults\RedirectToActionResultTest.cs" />
     <Compile Include="ActionResults\RedirectToRouteResultTest.cs" />
+    <Compile Include="ActionResults\RedirectResultTest.cs" />
+    <Compile Include="DefaultActionDiscoveryConventionsActionSelectionTests.cs" />
     <Compile Include="AntiXsrf\AntiForgeryOptionsTests.cs" />
     <Compile Include="Filters\ProducesAttributeTests.cs" />
+    <Compile Include="Formatters\NoContentFormatterTests.cs" />
     <Compile Include="Formatters\OutputFormatterTests.cs" />
     <Compile Include="Formatters\TextPlainFormatterTests.cs" />
     <Compile Include="DefaultViewComponentActivatorTests.cs" />
@@ -58,6 +61,7 @@
     <Compile Include="OptionDescriptors\ValueProviderFactoryDescriptorTest.cs" />
     <Compile Include="OptionDescriptors\ViewEngineDescriptorTest.cs" />
     <Compile Include="OptionDescriptors\ViewEngineDscriptorExtensionsTest.cs" />
+    <Compile Include="MediaTypeWithQualityHeaderValueTests.cs" />
     <Compile Include="ParameterBinding\ModelBindingHelperTest.cs" />
     <Compile Include="AntiXsrf\AntiForgeryTokenSerializerTest.cs" />
     <Compile Include="AntiXsrf\ITokenProvider.cs" />

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

@@ -189,65 +189,5 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
             var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
             Assert.Equal(expectedBody, body);
         }
-
-
-        [InlineData("ReturnTaskOfString")]
-        [InlineData("ReturnTaskOfObject_StringValue")]
-        [InlineData("ReturnString")]
-        [InlineData("ReturnObject_StringValue")]
-        [InlineData("ReturnString_NullValue")]
-        public async Task TextPlainFormatter_ReturnsTextPlainContentType(string actionName)
-        {
-            // Arrange
-            var server = TestServer.Create(_provider, _app);
-            var client = server.Handler;
-            var expectedContentType = "text/plain;charset=utf-8";
-            var expectedBody = actionName;
-
-            // Act
-            var result = await client.GetAsync("http://localhost/TextPlain/" + actionName);
-
-            // Assert
-            Assert.Equal(expectedContentType, result.HttpContext.Response.ContentType);
-            var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
-            Assert.Equal(expectedBody, body);
-        }
-
-        [InlineData("ReturnTaskOfObject_ObjectValue")]
-        [InlineData("ReturnObject_ObjectValue")]
-        [InlineData("ReturnObject_NullValue")]
-        public async Task TextPlainFormatter_DoesNotSelectTextPlainFormatterForNonStringValue(string actionName)
-        {
-            // Arrange
-            var server = TestServer.Create(_provider, _app);
-            var client = server.Handler;
-            var expectedContentType = "application/json;charset=utf-8";
-            var expectedBody = actionName;
-
-            // Act
-            var result = await client.GetAsync("http://localhost/TextPlain/" + actionName);
-
-            // Assert
-            Assert.Equal(expectedContentType, result.HttpContext.Response.ContentType);
-            var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
-        }
-
-        [InlineData("ReturnString_NullValue")]
-        public async Task TextPlainFormatter_DoesNotWriteNullValue(string actionName)
-        {
-            // Arrange
-            var server = TestServer.Create(_provider, _app);
-            var client = server.Handler;
-            var expectedContentType = "text/plain;charset=utf-8";
-            string expectedBody = null;
-
-            // Act
-            var result = await client.GetAsync("http://localhost/TextPlain/" + actionName);
-
-            // Assert
-            Assert.Equal(expectedContentType, result.HttpContext.Response.ContentType);
-            var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
-            Assert.Equal(expectedBody, body);
-        }
     }
 }

test/Microsoft.AspNet.Mvc.FunctionalTests/Microsoft.AspNet.Mvc.FunctionalTests.kproj

@@ -31,6 +31,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="BasicTests.cs" />
+    <Compile Include="OutputFormattterTests.cs" />
     <Compile Include="ConnegTests.cs" />
     <Compile Include="AntiForgeryTests.cs" />
     <Compile Include="ModelBindingTests.cs" />

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

@@ -0,0 +1,85 @@
+// 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;
+using System.Threading.Tasks;
+using ConnegWebsite;
+using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.TestHost;
+using Xunit;
+
+namespace Microsoft.AspNet.Mvc.FunctionalTests
+{
+    public class OutputFormatterTests
+    {
+        private readonly IServiceProvider _provider = TestHelper.CreateServices("ConnegWebsite");
+        private readonly Action<IBuilder> _app = new Startup().Configure;
+
+        [Theory]
+        [InlineData("ReturnTaskOfString")]
+        [InlineData("ReturnTaskOfObject_StringValue")]
+        [InlineData("ReturnString")]
+        [InlineData("ReturnObject_StringValue")]
+        public async Task TextPlainFormatter_ForStringValues_GetsSelectedReturnsTextPlainContentType(string actionName)
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.Handler;
+            var expectedContentType = "text/plain;charset=utf-8";
+            var expectedBody = actionName;
+
+            // Act
+            var result = await client.GetAsync("http://localhost/TextPlain/" + actionName);
+
+            // Assert
+            Assert.Equal(expectedContentType, result.HttpContext.Response.ContentType);
+            var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
+            Assert.Equal(expectedBody, body);
+        }
+
+        [Theory]
+        [InlineData("ReturnTaskOfObject_ObjectValue")]
+        [InlineData("ReturnObject_ObjectValue")]
+        public async Task JsonOutputFormatter_ForNonStringValue_GetsSelected(string actionName)
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.Handler;
+            var expectedContentType = "application/json;charset=utf-8";
+            var expectedBody = actionName;
+
+            // Act
+            var result = await client.GetAsync("http://localhost/TextPlain/" + actionName);
+
+            // Assert
+            Assert.Equal(expectedContentType, result.HttpContext.Response.ContentType);
+            var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
+        }
+
+        [Theory]
+        [InlineData("ReturnTaskOfString_NullValue")]
+        [InlineData("ReturnTaskOfObject_StringValue")]
+        [InlineData("ReturnTaskOfObject_NullValue")]
+        [InlineData("ReturnObject_NullValue")]
+        public async Task NoContentFormatter_ForNullValue_GetsSelectedAndWritesResponse(string actionName)
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.Handler;
+            string expectedContentType = null;
+
+            // ReadBodyAsString returns empty string instead of null.
+            string expectedBody = "";
+
+            // Act
+            var result = await client.GetAsync("http://localhost/NoContent/" + actionName);
+
+            // Assert
+            Assert.Equal(expectedContentType, result.HttpContext.Response.ContentType);
+            var body = await result.HttpContext.Response.ReadBodyAsStringAsync();
+            Assert.Equal(expectedBody, body);
+            Assert.Equal(204, result.HttpContext.Response.StatusCode);
+            Assert.Equal(0, result.HttpContext.Response.ContentLength);
+        }
+    }
+}

test/WebSites/ConnegWebSite/ConnegWebsite.kproj

@@ -31,6 +31,7 @@
     <Compile Include="Controllers\ProducesContentBaseController.cs" />
     <Compile Include="Controllers\ProducesContentOnClassController.cs" />
     <Compile Include="Controllers\HomeController.cs" />
+    <Compile Include="Controllers\NoContentController.cs" />
     <Compile Include="Controllers\TextPlainController.cs" />
     <Compile Include="Models\User.cs" />
     <Compile Include="ContentType.cs" />

test/WebSites/ConnegWebSite/Controllers/NoContentController.cs

@@ -0,0 +1,31 @@
+// 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.Threading.Tasks;
+using Microsoft.AspNet.Mvc;
+
+namespace ConnegWebsite
+{
+    public class NoContentController : Controller
+    {
+        public Task<string> ReturnTaskOfString_NullValue()
+        {
+            return Task.FromResult<string>(null);
+        }
+
+        public Task<object> ReturnTaskOfObject_NullValue()
+        {
+            return Task.FromResult<object>(null);
+        }
+
+        public string ReturnString_NullValue()
+        {
+            return null;
+        }
+
+        public object ReturnObject_NullValue()
+        {
+            return null;
+        }
+    }
+}

test/WebSites/ConnegWebSite/Controllers/TextPlainController.cs

@@ -30,7 +30,7 @@ namespace ConnegWebsite
 
         public object ReturnObject_StringValue()
         {
-            return "";
+            return "ReturnObject_StringValue";
         }
 
         public object ReturnObject_ObjectValue()