public class FileApiResult : IHttpActionResult
    {
        public string FileName { get; set; }

        public Stream Content { get; set; }

        public string ContentType { get; set; }

        public long? ContentLength { get; set; }

        public string DispositionType { get; set; }

        public Task<HttpResponseMessage> ExecuteAsync(CancellationToken cancellationToken)
        {
            var result =
                new HttpResponseMessage(HttpStatusCode.OK)
                {
                    Content = new StreamContent(Content)
                };

            result.Content.Headers.ContentDisposition =
                new ContentDispositionHeaderValue(DispositionType ?? DispositionTypeNames.Attachment)
                {
                    FileNameStar = FileName
                };

            result.Content.Headers.ContentType =
                new MediaTypeHeaderValue(ContentType ?? MediaTypeNames.Application.Octet);

            if (ContentLength.HasValue)
                result.Content.Headers.ContentLength = ContentLength;

            return Task.FromResult(result);
        }
    }