System.IO.Stream to System.IO.File

public static class IOExtensions
{
    public static void SaveToFile(this System.IO.Stream stream, string fileFullPath)
    {
        System.Diagnostics.Debug.Assert(string.IsNullOrEmpty(fileFullPath) == false);
        if (stream.Length == 0) return;

        using (System.IO.FileStream fileStream = System.IO.File.Create(fileFullPath))
        {
            const int bufferSize = 0x100;
            byte[] buffer = new byte[bufferSize];
            int bytesRead = 0;
            while ((bytesRead = stream.Read(buffer, 0, bufferSize)) > 0)
            {
                fileStream.Write(buffer, 0, bytesRead);
            }
        }
    }
}