[Fixes #1836]SupportedMediaTypes for output formatters are incorrectly updated with charset data during requests

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

@@ -177,6 +177,9 @@ namespace Microsoft.AspNet.Mvc
                 throw new InvalidOperationException(Resources.FormatOutputFormatterNoMediaType(GetType().FullName));
             }
 
+            // Clone the media type as we don't want it to affect the next request
+            selectedMediaType = MediaTypeHeaderValue.Parse(selectedMediaType.ToString());
+
             var selectedEncoding = SelectCharacterEncoding(context);
             if (selectedEncoding == null)
             {

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

@@ -120,6 +120,29 @@ namespace Microsoft.AspNet.Mvc.Test
                          formatterContext.SelectedContentType.ToString());
         }
 
+        [Fact]
+        public async Task WriteResponseHeaders_ClonesMediaType()
+        {
+            // Arrange
+            var formatter = new PngImageFormatter();
+            formatter.SupportedMediaTypes.Clear();
+            var mediaType = new MediaTypeHeaderValue("image/png");
+            formatter.SupportedMediaTypes.Add(mediaType);
+            var formatterContext = new OutputFormatterContext();
+            formatterContext.ActionContext = new ActionContext(
+                                    new DefaultHttpContext(), 
+                                    new RouteData(), 
+                                    new ActionDescriptor());
+
+            // Act
+            await formatter.WriteAsync(formatterContext);
+
+            // Assert
+            Assert.NotSame(mediaType, formatterContext.SelectedContentType);
+            Assert.Null(mediaType.Charset);
+            Assert.Equal("image/png; charset=utf-8", formatterContext.SelectedContentType.ToString());
+        }
+
         [Fact]
         public void CanWriteResult_ForNullContentType_UsesFirstEntryInSupportedContentTypes()
         {
@@ -294,7 +317,7 @@ namespace Microsoft.AspNet.Mvc.Test
             public override bool CanWriteResult(OutputFormatterContext context, MediaTypeHeaderValue contentType)
             {
                 // Do not set the selected media Type.
-                // The WriteResponseContentHeader should do it for you.
+                // The WriteResponseHeaders should do it for you.
                 return true;
             }
 
@@ -303,5 +326,19 @@ namespace Microsoft.AspNet.Mvc.Test
                 return Task.FromResult(true);
             }
         }
+
+        private class PngImageFormatter : OutputFormatter
+        {
+            public PngImageFormatter()
+            {
+                SupportedMediaTypes.Add(MediaTypeHeaderValue.Parse("image/png"));
+                SupportedEncodings.Add(Encoding.UTF8);
+            }
+            
+            public override Task WriteResponseBodyAsync([NotNull] OutputFormatterContext context)
+            {
+                return Task.FromResult(true);
+            }
+        }
     }
 }

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

@@ -296,6 +296,50 @@ namespace Microsoft.AspNet.Mvc.FunctionalTests
             Assert.Equal(expectedBody, body);
         }
 
+        [Fact]
+        public async Task JsonFormatter_SupportedMediaType_DoesNotChangeAcrossRequests()
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.CreateClient();
+            var expectedContentType = MediaTypeHeaderValue.Parse("application/json;charset=utf-8");
+            var expectedBody = "{\"MethodName\":\"ReturnJsonResult\"}";
+
+            for (int i = 0; i < 5; i++)
+            {
+                // Act and Assert
+                var response = await client.GetAsync("http://localhost/JsonResult/ReturnJsonResult");
+
+                Assert.Equal(expectedContentType, response.Content.Headers.ContentType);
+                var body = await response.Content.ReadAsStringAsync();
+                Assert.Equal(expectedBody, body);
+            }
+        }
+
+        [Fact]
+        public async Task XmlFormatter_SupportedMediaType_DoesNotChangeAcrossRequests()
+        {
+            // Arrange
+            var server = TestServer.Create(_provider, _app);
+            var client = server.CreateClient();
+            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/xml"));
+            client.DefaultRequestHeaders.AcceptCharset.Add(new StringWithQualityHeaderValue("utf-8"));
+            var expectedContentType = MediaTypeHeaderValue.Parse("application/xml;charset=utf-8");
+            var expectedBody = @"<User xmlns:i=""http://www.w3.org/2001/XMLSchema-instance"" " +
+                                @"xmlns=""http://schemas.datacontract.org/2004/07/ConnegWebSite""><Address>"
+                                + @"One Microsoft Way</Address><Name>John</Name></User>";
+
+            for (int i = 0; i < 5; i++)
+            {
+                // Act and Assert
+                var response = await client.GetAsync("http://localhost/Home/UserInfo");
+
+                Assert.Equal(expectedContentType, response.Content.Headers.ContentType);
+                var body = await response.Content.ReadAsStringAsync();
+                Assert.Equal(expectedBody, body);
+            }
+        }
+
         [Theory]
         [InlineData("UseTheFallback_WithDefaultFormatters")]
         [InlineData("UseTheFallback_UsingCustomFormatters")]

test/WebSites/ConnegWebSite/Controllers/HomeController.cs

@@ -11,5 +11,10 @@ namespace ConnegWebSite
         {
             return new JsonResult("Index Method");
         }
+
+        public User UserInfo()
+        {
+            return new User() { Name = "John", Address = "One Microsoft Way" };
+        }
     }
 }

test/WebSites/ConnegWebSite/Startup.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.Mvc;
 using Microsoft.AspNet.Routing;
 using Microsoft.Framework.DependencyInjection;
 
@@ -18,8 +19,13 @@ namespace ConnegWebSite
             {
                 // Add MVC services to the services container
                 services.AddMvc(configuration);
-            });
 
+                services.Configure<MvcOptions>(options =>
+                {
+                    options.AddXmlDataContractSerializerFormatter();
+                });
+            });
+                        
             // Add MVC to the request pipeline
             app.UseMvc(routes =>
             {