Asp.net web api, text/html, text/plain formatter

HtmlFormatter.cs

    public class HtmlFormatter : MediaTypeFormatter
    {
        public HtmlFormatter()
        {
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
            SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/plain"));
        }

        protected override bool CanReadType(Type type)
        {
            return false;
        }

        protected override bool CanWriteType(Type type)
        {
            return typeof(string) == type;
        }

        protected override Task OnWriteToStreamAsync(Type type, object value, Stream stream, HttpContentHeaders contentHeaders, FormatterContext formatterContext, TransportContext transportContext)
        {
            using (var writer = new StreamWriter(stream))
            {
                writer.WriteLine("Hijacked..");
                writer.WriteLine(value.ToString());
                writer.WriteLine("  ..egad!");
            }

            var tcs = new TaskCompletionSource<Stream>();
            tcs.SetResult(stream);
            return tcs.Task;
        }
    }