Layout compilation error not showing in browser - GitHub WebFX #286

An exception thrown in a layout (or for that matter anything that is a rendering time exception)
is not bubbling to the end user.

The reason is that the StreamWrite is flushing because it's in a dispose pattern.
The solution is to wrap the stream and prevent writes/flushes if an exception has been thrown.

At the same time we stop writing BOM out to html files by default.

Also specified charset explicitly - so there is matches the encoding of the page.

src/Microsoft.AspNet.Mvc.Core/ActionResults/ViewResult.cs

@@ -31,11 +31,23 @@ namespace Microsoft.AspNet.Mvc
 
             using (view as IDisposable)
             {
-                context.HttpContext.Response.ContentType = "text/html";
+                context.HttpContext.Response.ContentType = "text/html; charset=utf-8";
-                using (var writer = new StreamWriter(context.HttpContext.Response.Body, Encoding.UTF8, 1024, leaveOpen: true))
+                var wrappedStream = new StreamWrapper(context.HttpContext.Response.Body);
+                using (var writer = new StreamWriter(wrappedStream, new UTF8Encoding(false), 1024, leaveOpen: true))
                 {
-                    var viewContext = new ViewContext(context, view, ViewData, writer);
+                    try
-                    await view.RenderAsync(viewContext);
+                    {
+                        var viewContext = new ViewContext(context, view, ViewData, writer);
+                        await view.RenderAsync(viewContext);
+                    }
+                    catch
+                    {
+                        // Need to prevent writes/flushes on dispose because the StreamWriter will flush even if nothing
+                        // got written. This leads to a response going out on the wire prematurely in case an exception
+                        // is being thrown inside the try catch block.
+                        wrappedStream.BlockWrites = true;
+                        throw;
+                    }
                 }
             }
         }
@@ -57,5 +69,80 @@ namespace Microsoft.AspNet.Mvc
 
             return result.View;
         }
+
+        private class StreamWrapper : Stream
+        {
+            private readonly Stream _wrappedStream;
+
+            public StreamWrapper([NotNull] Stream stream)
+            {
+                _wrappedStream = stream;
+            }
+
+            public bool BlockWrites { get; set;}
+
+            public override bool CanRead
+            {
+                get { return _wrappedStream.CanRead; }
+            }
+
+            public override bool CanSeek
+            {
+                get { return _wrappedStream.CanSeek; }
+            }
+
+            public override bool CanWrite
+            {
+                get { return _wrappedStream.CanWrite; }
+            }
+
+            public override void Flush()
+            {
+                if (!BlockWrites)
+                {
+                    _wrappedStream.Flush();
+                }
+            }
+
+            public override long Length
+            {
+                get { return _wrappedStream.Length; }
+            }
+
+            public override long Position
+            {
+                get
+                {
+                    return _wrappedStream.Position;
+                }
+                set
+                {
+                    _wrappedStream.Position = value;
+                }
+            }
+
+            public override int Read(byte[] buffer, int offset, int count)
+            {
+                return _wrappedStream.Read(buffer, offset, count);
+            }
+
+            public override long Seek(long offset, SeekOrigin origin)
+            {
+                return Seek(offset, origin);
+            }
+
+            public override void SetLength(long value)
+            {
+                SetLength(value);
+            }
+
+            public override void Write(byte[] buffer, int offset, int count)
+            {
+                if (!BlockWrites)
+                {
+                    _wrappedStream.Write(buffer, offset, count);
+                }
+            }
+        }
     }
 }