StreamFormatter.cs

public class StreamFormatter : MediaTypeFormatter
    {
        private readonly MediaTypeHeaderValue _mediaType;

        /// <summary>
        /// Default constructor
        /// </summary>
        /// <param name="mediaType"></param>
        public StreamFormatter(MediaTypeHeaderValue mediaType)
        {
            _mediaType = mediaType;
        }

        /// <summary>
        /// Queries whether this <see cref="T:System.Net.Http.Formatting.MediaTypeFormatter"/> can deserialize an object of the specified type.
        /// </summary>
        /// <returns>
        /// true if the <see cref="T:System.Net.Http.Formatting.MediaTypeFormatter"/> can deserialize the type; otherwise, false.
        /// </returns>
        /// <param name="type">The type to deserialize.</param>
        public override bool CanReadType(Type type)
        {
            return false;
        }

        /// <summary>
        /// Sets the default headers for content that will be formatted using this formatter. This method is called from the <see cref="T:System.Net.Http.ObjectContent"/> constructor. This implementation sets the Content-Type header to the value of mediaType if it is not null. If it is null it sets the Content-Type to the default media type of this formatter. If the Content-Type does not specify a charset it will set it using this formatters configured <see cref="T:System.Text.Encoding"/>. 
        /// </summary>
        /// <param name="type">The type of the object being serialized. See <see cref="T:System.Net.Http.ObjectContent"/>.</param><param name="headers">The content headers that should be configured.</param><param name="mediaType">The authoritative media type. Can be null.</param>
        public override void SetDefaultContentHeaders(Type type, HttpContentHeaders headers, MediaTypeHeaderValue mediaType)
        {
            base.SetDefaultContentHeaders(type, headers, _mediaType);
        }

        /// <summary>
        /// Queries whether this <see cref="T:System.Net.Http.Formatting.MediaTypeFormatter"/> can serializean object of the specified type.
        /// </summary>
        /// <returns>
        /// true if the <see cref="T:System.Net.Http.Formatting.MediaTypeFormatter"/> can serialize the type; otherwise, false.
        /// </returns>
        /// <param name="type">The type to serialize.</param>
        public override bool CanWriteType(Type type)
        {
            return type.IsSubclassOf(typeof(Stream)) || type == typeof(Stream);
        }

        /// <summary>
        /// Asynchronously writes an object of the specified type.
        /// </summary>
        /// <returns>
        /// A <see cref="T:System.Threading.Tasks.Task"/> that will perform the write.
        /// </returns>
        /// <param name="type">The type of the object to write.</param><param name="value">The object value to write.  It may be null.</param><param name="writeStream">The <see cref="T:System.IO.Stream"/> to which to write.</param><param name="content">The <see cref="T:System.Net.Http.HttpContent"/> if available. It may be null.</param><param name="transportContext">The <see cref="T:System.Net.TransportContext"/> if available. It may be null.</param><param name="cancellationToken">The token to cancel the operation.</param><exception cref="T:System.NotSupportedException">Derived types need to support writing.</exception>
        public override async Task WriteToStreamAsync(Type type, object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken)
        {
            using (var source = (Stream)value)
                await source.CopyToAsync(writeStream);
        }
    }