邮箱账号验证类【共享】基于pop3

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using System;
using System.IO;
using System.Net.Security;
using System.Net.Sockets;
using System.Text;

namespace WindowsFormsApplication1
{
    /// <summary>
    /// 提供通过 POP3 协议进行电子信箱账号验证的功能。
    /// </summary>
    public sealed class POP3AccountValidator
    {
        #region ValidateResults enum

        /// <summary>
        /// 表示验证结果的枚举值。
        /// </summary>
        public enum ValidateResults
        {
            /// <summary>
            /// 未指定。
            /// </summary>
            None = 0,

            /// <summary>
            /// 连接失败。
            /// </summary>
            ConnectFailed = 1,

            /// <summary>
            /// 无效的登录账号。
            /// </summary>
            InvalidUserName = 2,

            /// <summary>
            /// 无效的登录密码。
            /// </summary>
            InvalidPassword = 3,

            /// <summary>
            /// 登录成功。
            /// </summary>
            Success = 4,

            /// <summary>
            /// 验证过程发生异常。
            /// </summary>
            Error = 5,
        }

        #endregion

        private const string _CRLF = "\r\n";
        private readonly bool _useSSL;

        /// <summary>
        /// 初始化 <see cref="POP3AccountValidator"/> 类的新实例。
        /// </summary>
        /// <param name="server">指定 POP3 服务器。</param>
        public POP3AccountValidator(string server) : this(server, 110) { }

        /// <summary>
        /// 初始化 <see cref="POP3AccountValidator"/> 类的新实例。
        /// </summary>
        /// <param name="server">指定 POP3 服务器。</param>
        /// <param name="port">指定 POP3 服务器端口号。</param>
        public POP3AccountValidator(string server, int port) : this(server, port, false) { }

        /// <summary>
        /// 初始化 <see cref="POP3AccountValidator"/> 类的新实例。
        /// </summary>
        /// <param name="server">指定 POP3 服务器。</param>
        /// <param name="port">指定 POP3 服务器端口号。</param>
        /// <param name="useSSL">指定一个值，该值指示验证过程是否使用 SSL 加密协议。</param>
        public POP3AccountValidator(string server, int port, bool useSSL)
        {
            if (String.IsNullOrWhiteSpace(server)) throw new ArgumentOutOfRangeException("server");
            if (port < 1 || port > 65535) throw new ArgumentOutOfRangeException("port");

            this.Server = server;
            this.Port = port;
            this._useSSL = useSSL;
        }

        /// <summary>
        /// 获取 POP3 服务器。
        /// </summary>
        public string Server { get; private set; }

        /// <summary>
        /// 获取 POP3 服务器端口号。
        /// </summary>
        public int Port { get; private set; }

        private static ValidateResults _Validate(Stream stream, string username, string password)
        {
            var data = "USER " + username + _CRLF;

            using (var reader = new StreamReader(stream))
            {
                if (!reader.ReadLine().Contains("+OK")) return ValidateResults.ConnectFailed;

                var charData = Encoding.ASCII.GetBytes(data);

                stream.Write(charData, 0, charData.Length);

                if (!reader.ReadLine().Contains("+OK")) return ValidateResults.InvalidUserName;

                data = "PASS " + password + _CRLF;
                charData = Encoding.ASCII.GetBytes(data);

                stream.Write(charData, 0, charData.Length);

                return reader.ReadLine().Contains("+OK") ? ValidateResults.Success : ValidateResults.InvalidPassword;
            }
        }

        /// <summary>
        /// 验证电子信箱账号。
        /// </summary>
        /// <param name="username">电子信箱账号。</param>
        /// <param name="password">电子信箱密码。</param>
        /// <returns>返回 <see cref="ValidateResults"/> 枚举值之一。</returns>
        public ValidateResults Validate(string username, string password)
        {
            if (username == null) throw new ArgumentNullException("username");
            if (password == null) throw new ArgumentNullException("password");

            try
            {
                using (var tcpClient = new TcpClient(this.Server, this.Port))
                {
                    using (var tcpStream = tcpClient.GetStream())
                    {
                        if (!this._useSSL) return _Validate(tcpStream, username, password);

                        using (var sslStream = new SslStream(tcpStream, false))
                        {
                            sslStream.AuthenticateAsClient(this.Server);

                            return _Validate(sslStream, username, password);
                        }
                    }
                }
            }
            catch
            {
                return ValidateResults.Error;
            }
        }
    }
}