FileContent

FileContent.cs

public class FileContent : HttpContent
    {
        private const int DefaultBufferSize = 1024 * 64;

        private readonly string _fileName;
        private readonly FileInfo _fileInfo;

        public FileContent(string fileName, MediaTypeHeaderValue contentType = null)
        {
            Headers.ContentType = contentType ?? new MediaTypeHeaderValue("application/octet-stream");

            if (string.IsNullOrWhiteSpace(fileName))
            {
                throw new ArgumentNullException("fileName");
            }
            _fileInfo = new FileInfo(fileName);
            if (!_fileInfo.Exists)
            {
                throw new FileNotFoundException(string.Empty, fileName);
            }

            _fileName = fileName;

        }

        public string FileName
        {
            get { return _fileName; }
        }


        protected override bool TryComputeLength(out long length)
        {
            length = _fileInfo.Length;
            return true;
        }


        protected override Task SerializeToStreamAsync(Stream stream, TransportContext context)
        {
            using(var fileStream = new FileStream(_fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite,
                                         DefaultBufferSize, FileOptions.Asynchronous | FileOptions.SequentialScan)) {

                fileStream.CopyTo(stream);

            };

            return Task.FromResult<object>(null);

        }

    }

Probably would be better to do the throws on null fileName or file.Exist == false before setting the Headers.ContentType.

Also, would be much cooler to use await fileStream.CopyToAsync when on platforms that would allow it...