WcfWebApi Content-Disposition

JpgProcessor.cs

public class JpgProcessor : MediaTypeFormatter
{
    public JpgProcessor()
    {
        SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/jpg"));
    }
    protected override object OnReadFromStream(Type type, Stream stream, HttpContentHeaders contentHeaders)
    {
        throw new NotImplementedException();
    }

    protected override void OnWriteToStream(Type type, object value, Stream stream, HttpContentHeaders contentHeaders, TransportContext context)
    {
        var pathToImage= value as string;
        var path = HttpContext.Current.Server.MapPath(pathToImage);

        // This does not work!
        contentHeaders.ContentDisposition = new ContentDispositionHeaderValue("attachment") {FileName = "test.jpg"};

        using (var file = new FileStream(path, FileMode.Open))
        {
            file.CopyTo(stream);
        }
    }
}