Or you can just create your own MediaTypeFormatter. I use this for text/html. If you add text/plain to it, it'll work for you too:
public class TextMediaTypeFormatter : MediaTypeFormatter
{
public TextMediaTypeFormatter()
{
SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
}
public override Task<object> ReadFromStreamAsync(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger)
{
return ReadFromStreamAsync(type, readStream, content, formatterLogger, CancellationToken.None);
}
public override async Task<object> ReadFromStreamAsync(Type type, Stream readStream, HttpContent content, IFormatterLogger formatterLogger, CancellationToken cancellationToken)
{
using (var streamReader = new StreamReader(readStream))
{
return await streamReader.ReadToEndAsync();
}
}
public override bool CanReadType(Type type)
{
return type == typeof(string);
}
public override bool CanWriteType(Type type)
{
return false;
}
}
Finally you have to assign this to the HttpMethodContext.ResponseFormatter property.