Console FTP in C#

using System;

namespace HB.Web.Pop3
{
	/// <summary>
	/// Represents a message on a Pop3 server.
	/// </summary>
	public struct Message : IComparable
	{
		/// <summary>
		/// Creates a new Pop3 server message.
		/// </summary>
		/// <param name="id">The ID of the pop3 message.</param>
		/// <param name="length">The length of the pop3 message.</param>
		/// <exception cref="ArgumentNullException">When parameter id is null.</exception>
		public Message(string id, long length)
		{
			if(id == null)
				throw new ArgumentNullException("id");
			this.id = id;
			this.length = length;
		}

		/// <summary>
		/// Gets the length in bytes of the message.
		/// </summary>
		public long Length
		{
			get
			{
				return length;
			}
		}

		/// <summary>
		/// Gets the unique ID of the message.
		/// </summary>
		public string Id
		{
			get
			{
				return id;
			}
		}

		/// <summary>
		/// Compares the current instance with another <see cref="Message"/>.
		/// </summary>
		/// <param name="obj">An <see cref="Object"/> to compare.</param>
		/// <returns>A 32-bit signed integer that indicates the relative order of the comparands.</returns>
		/// <exception cref="ArgumentException">When parameter obj is not the same type as this instance.</exception>
		/// <remarks>The <see cref="ID"/> is compared.</remarks>
		public int CompareTo(object obj)
		{
			if(!(obj is Message))
				throw new ArgumentException("obj is not the same type as this instance.");
			return Id.CompareTo(((Message)obj).Id);
		}

		/// <summary>
		/// Returns the <see cref="ID"/> of the <see cref="Message"/>.
		/// </summary>
		/// <returns>The <see cref="ID"/> and <see cref="Length"/> of the <see cref="Message"/>.</returns>
		public override string ToString()
		{
			return Id + " " + Length;
		}

		/// <summary>
		/// Determines if this instance of <see cref="Message"/>
		/// is equal to another object.
		/// </summary>
		/// <param name="obj">The object to compare.</param>
		/// <returns>true if parameter obj is of type <see cref="Message"/>
		/// and equal to the this instance.</returns>
		public override bool Equals(object obj)
		{
			return ((obj is Message) && (this == (Message)obj));
		}

		/// <summary>
		/// Determines if two instances of type <see cref="Message"/>
		/// are equal to each other.
		/// </summary>
		/// <param name="lhs">A <see cref="Message"/> to compare.</param>
		/// <param name="rhs">A <see cref="Message"/> to compare.</param>
		/// <returns>true if both objects are of type <see cref="Message"/>
		/// with the same <see cref="Id"/>.</returns>
		public static bool operator ==(Message lhs, Message rhs)
		{
			if(((object)lhs == null) && ((object)rhs == null))
				return true;
			if(((object)lhs == null) || ((object)rhs == null))
				return false;
			return lhs.Id == rhs.Id;
		}

		/// <summary>
		/// Determines if two instances of type <see cref="Message"/>
		/// are not equal to each other.
		/// </summary>
		/// <param name="lhs">A <see cref="Message"/> to compare.</param>
		/// <param name="rhs">A <see cref="Message"/> to compare.</param>
		/// <returns>true if the objects are not equal.</returns>
		/// <remarks>Negates the result of the equals operator.</remarks>
		public static bool operator !=(Message lhs, Message rhs)
		{
			return !(lhs == rhs);
		}

		private string id;
		private long length;
	}
}