Copies part of a stream to another stream.

StreamExtensions.cs

using System;
using System.Diagnostics.Contracts;
using System.IO;

namespace Virtlink
{
    /// <summary>
    /// Extension methods for <see cref="Stream"/> objects.
    /// </summary>
    /// <example>
    /// Usage example:
    /// <code>
    /// string inputFilename = @"input.bin";
    /// string outputFilename = @"output.bin";
    /// using (var input = File.OpenRead(inputFilename))
    /// using (var output = File.Create(outputFilename))
    /// {
    ///     input.Seek(0x1000, SeekOrigin.Begin);
    ///     input.CopyPartTo(output, 0x2000);
    /// }
    /// </code>
    /// </example>
    /// <remarks>
    /// Created by Virtlink. Original source code on GitHub:
    /// <see href="https://gist.github.com/Virtlink/9337057"/>.
    /// </remarks>
    public static class StreamExtensions
    {
        /// <summary>
        /// Copies a specific number of bytes from the current position of the
        /// source stream to the current position of the destination stream.
        /// </summary>
        /// <param name="source">The source stream.</param>
        /// <param name="destination">The destination stream.</param>
        /// <param name="count">The number of bytes to copy.</param>
        /// <param name="bufferSize">The size of the buffer to use.
        /// The default is 4096.</param>
        public static void CopyPartTo(this Stream source, Stream destination, int count, int bufferSize)
        {
            #region Contract
            Contract.Requires<ArgumentNullException>(source != null);
            Contract.Requires<ArgumentNullException>(destination != null);
            Contract.Requires<ArgumentOutOfRangeException>(count >= 0);
            Contract.Requires<ArgumentOutOfRangeException>(bufferSize > 0);
            #endregion
            byte[] buffer = new byte[bufferSize];
            int read;
            while (count > 0 && (read = source.Read(buffer, 0, Math.Min(buffer.Length, count))) > 0)
            {
                count -= read;
                destination.Write(buffer, 0, read);
            }
        }

        /// <summary>
        /// Copies a specific number of bytes from the current position of the
        /// source stream to the current position of the destination stream.
        /// </summary>
        /// <param name="source">The source stream.</param>
        /// <param name="destination">The destination stream.</param>
        /// <param name="count">The number of bytes to copy.</param>
        public static void CopyPartTo(this Stream source, Stream destination, int count)
        {
            #region Contract
            Contract.Requires<ArgumentNullException>(source != null);
            Contract.Requires<ArgumentNullException>(destination != null);
            Contract.Requires<ArgumentOutOfRangeException>(count >= 0);
            #endregion
            CopyPartTo(source, destination, count, 0x1000);
        }
    }
}