[Fixes #1183] Response uses chunked encoding when returning a string

Author: kichalla

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

@@ -51,7 +51,9 @@ public override async Task WriteResponseBodyAsync(OutputFormatterContext context
             }
 
             var response = context.ActionContext.HttpContext.Response;
-            using (var writer = new StreamWriter(response.Body, context.SelectedEncoding, 1024, leaveOpen: true))
+
+            using (var delegatingStream = new DelegatingStream(response.Body))
+            using (var writer = new StreamWriter(delegatingStream, context.SelectedEncoding, 1024, leaveOpen: true))
             {
                 await writer.WriteAsync(valueAsString);
             }

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

@@ -54,22 +54,29 @@ public void CanWriteResult_ReturnsTrueForStringTypes(object value, bool useDecla
         public async Task WriteAsync_DoesNotWriteNullStrings()
         {
             // Arrange
+            Encoding encoding = Encoding.UTF8;
+            var memoryStream = new MemoryStream();
+            var response = new Mock<HttpResponse>();
+            response.SetupProperty<long?>(o => o.ContentLength);
+            response.SetupGet(r => r.Body).Returns(memoryStream);
+            var mockHttpContext = new Mock<HttpContext>();
+            mockHttpContext.Setup(o => o.Response).Returns(response.Object);
+
             var formatter = new TextPlainFormatter();
             var formatterContext = new OutputFormatterContext()
             {
                 Object = null,
-                DeclaredType = typeof(string), 
+                DeclaredType = typeof(string),
+                ActionContext = new ActionContext(mockHttpContext.Object, new RouteData(), new ActionDescriptor()),
+                SelectedEncoding = encoding
             };
 
-            var tempMemoryStream = new MemoryStream();
-            var mockHttpContext = new Mock<HttpContext>();
-            mockHttpContext.SetupGet(o => o.Response.Body)
-                           .Returns(tempMemoryStream);
             // Act
             await formatter.WriteResponseBodyAsync(formatterContext);
 
             // Assert
-            Assert.Equal(0, tempMemoryStream.Length);
+            Assert.Equal(0, memoryStream.Length);
+            response.VerifySet(r => r.ContentLength = It.IsAny<long?>(), Times.Never());
         }
     }
 }