C#：一个增强的TcpClient（一）连接

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本文介绍了一个使用C#实现的TcpClientPlus类，该类通过异步方式连接到远程主机，并支持设置连接超时。文中详细解释了如何通过自定义状态对象来管理连接过程中的状态，并在异步操作完成后进行相应的处理。

using System;
using System.Net;
using System.Net.Sockets;
using System.Threading;

namespace Splash.Net.Sockets
{
    /// <summary>
    /// 异步连接状态对象
    /// </summary>
    internal class AsyncConnectStateObject
    {
        public ManualResetEvent eventDone;
        public TcpClient client;
        public Exception exception;
    }

    /// <summary>
    /// 实现TcpClient的异步连接
    /// </summary>
    public partial class TcpClientPlus
    {
        /// <summary>
        /// 设置连接超时值
        /// </summary>
        public Int32 ConnectTimeout = Timeout.Infinite;

        /// <summary>
        /// 异步连接
        /// </summary>
        /// <param name="hostname">主机名</param>
        /// <param name="port">端口号</param>
        public void AsyncConnect(String hostname, Int32 port)
        {
            // 用户定义对象
            AsyncConnectStateObject State = new AsyncConnectStateObject
            {   // 将事件状态设置为非终止状态，导致线程阻止
                eventDone = new ManualResetEvent(false),
                client = this,
                exception = null
            };

            // 开始一个对远程主机连接的异步请求
            BeginConnect(hostname, port, new AsyncCallback(AsyncConnectCallback), State);

            // 等待操作完成信号
            if (State.eventDone.WaitOne(ConnectTimeout, false))
            {   // 接收到信号
                if (State.exception != null) throw State.exception;
            }
            else
            {   // 超时异常
                Close();
                throw new TimeoutException();
            }
        }

        /// <summary>
        /// 异步连接
        /// </summary>
        /// <param name="address">IP地址</param>
        /// <param name="port">端口号</param>
        public void AsyncConnect(IPAddress address, Int32 port)
        {
            // 用户定义对象
            AsyncConnectStateObject State = new AsyncConnectStateObject
            {   // 将事件状态设置为非终止状态，导致线程阻止
                eventDone = new ManualResetEvent(false),
                client = this,
                exception = null
            };

            // 开始一个对远程主机连接的异步请求
            BeginConnect(address, port, new AsyncCallback(AsyncConnectCallback), State);

            // 等待操作完成信号
            if (State.eventDone.WaitOne(ConnectTimeout, false))
            {   // 接收到信号
                if (State.exception != null) throw State.exception;
            }
            else
            {   // 超时异常
                Close();
                throw new TimeoutException();
            }
        }

        /// <summary>
        /// 异步连接回调函数
        /// </summary>
        /// <param name="ar">异步操作结果</param>
        private static void AsyncConnectCallback(IAsyncResult ar)
        {
            AsyncConnectStateObject State = ar.AsyncState as AsyncConnectStateObject;
            try
            {   // 异步接受传入的连接尝试
                State.client.EndConnect(ar);
            }

            catch (Exception e)
            {   // 异步连接异常
                State.exception = e;
            }

            finally
            {   // 将事件状态设置为终止状态，线程继续                
                State.eventDone.Set();
            }
        }
    }
}