SOCKET原理（转载）

SOCKET原理

一、套接字（socket）概念

　　套接字（socket）是通信的基石，是支持TCP/IP协议的网络通信的基本操作单元。它是网络通信过程中端点的抽象表示，包含进行网络通信必须的五种信息：连接使用的协议，本地主机的IP地址，本地进程的协议端口，远地主机的IP地址，远地进程的协议端口。

　　应用层通过传输层进行数据通信时，TCP会遇到同时为多个应用程序进程提供并发服务的问题。多个TCP连接或多个应用程序进程可能需要通过同一个 TCP协议端口传输数据。为了区别不同的应用程序进程和连接，许多计算机操作系统为应用程序与TCP／IP协议交互提供了套接字(Socket)接口。应 用层可以和传输层通过Socket接口，区分来自不同应用程序进程或网络连接的通信，实现数据传输的并发服务。

二、建立socket连接

　　建立Socket连接至少需要一对套接字，其中一个运行于客户端，称为ClientSocket ，另一个运行于服务器端，称为ServerSocket 。

　　套接字之间的连接过程分为三个步骤：服务器监听，客户端请求，连接确认。

1. 服务器监听：服务器端套接字并不定位具体的客户端套接字，而是处于等待连接的状态，实时监控网络状态，等待客户端的连接请求 
2. 客户端请求：指客户端的套接字提出连接请求，要连接的目标是服务器端的套接字。为此，客户端的套接字必须首先描述它要连接的服务器的套接字，指出服务器端套接字的地址和端口号，然后就向服务器端套接字提出连接请求。
3. 连接确认：当服务器端套接字监听到或者说接收到客户端套接字的连接请求时，就响应客户端套接字的请求，建立一个新的线程，把服务器端套接字的描述发给客户 端，一旦客户端确认了此描述，双方就正式建立连接。而服务器端套接字继续处于监听状态，继续接收其他客户端套接字的连接请求。

三、SOCKET连接与TCP连接

　　创建Socket连接时，可以指定使用的传输层协议，Socket可以支持不同的传输层协议（TCP或UDP），当使用TCP协议进行连接时，该Socket连接就是一个TCP连接。

四、Socket连接与HTTP连接 

　　由于通常情况下Socket连接就是TCP连接，因此Socket连接一旦建立，通信双方即可开始相互发送数据内容，直到双方连接断开。但在实际网络应用 中，客户端到服务器之间的通信往往需要穿越多个中间节点，例如路由器、网关、防火墙等，大部分防火墙默认会关闭长时间处于非活跃状态的连接而导致 Socket 连接断连，因此需要通过轮询告诉网络，该连接处于活跃状态。

　　而HTTP连接使用的是“请求—响应”的方式，不仅在请求时需要先建立连接，而且需要客户端向服务器发出请求后，服务器端才能回复数据。

　　很多情况下，需要服务器端主动向客户端推送数据，保持客户端与服务器数据的实时与同步。此时若双方建立的是Socket连接，服务器就可以直接将数据传送 给客户端；若双方建立的是HTTP连接，则服务器需要等到客户端发送一次请求后才能将数据传回给客户端，因此，客户端定时向服务器端发送连接请求，不仅可 以保持在线，同时也是在“询问”服务器是否有新的数据，如果有就将数据传给客户端。

五、Socket服务端与客户端通信示意图

六、服务端与客户端代码

　　1、服务端

　　（1）服务端窗口设计

namespace SocketForm
{
    partial class Form1
    {
        /// <summary>
        /// 必需的设计器变量。
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// 清理所有正在使用的资源。
        /// </summary>
        /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows 窗体设计器生成的代码

        /// <summary>
        /// 设计器支持所需的方法 - 不要
        /// 使用代码编辑器修改此方法的内容。
        /// </summary>
        private void InitializeComponent()
        {
            this.panel1 = new System.Windows.Forms.Panel();
            this.tb_ip = new System.Windows.Forms.TextBox();
            this.lb_Ip = new System.Windows.Forms.Label();
            this.lb_port = new System.Windows.Forms.Label();
            this.tb_port = new System.Windows.Forms.TextBox();
            this.bt_connnect = new System.Windows.Forms.Button();
            this.listBox1 = new System.Windows.Forms.ListBox();
            this.txt_msg = new System.Windows.Forms.TextBox();
            this.bt_send = new System.Windows.Forms.Button();
            this.panel1.SuspendLayout();
            this.SuspendLayout();
            // 
            // panel1
            // 
            this.panel1.Controls.Add(this.bt_connnect);
            this.panel1.Controls.Add(this.lb_port);
            this.panel1.Controls.Add(this.tb_port);
            this.panel1.Controls.Add(this.lb_Ip);
            this.panel1.Controls.Add(this.tb_ip);
            this.panel1.Location = new System.Drawing.Point(21, 12);
            this.panel1.Name = "panel1";
            this.panel1.Size = new System.Drawing.Size(580, 70);
            this.panel1.TabIndex = 0;
            // 
            // tb_ip
            // 
            this.tb_ip.Location = new System.Drawing.Point(44, 18);
            this.tb_ip.Name = "tb_ip";
            this.tb_ip.Size = new System.Drawing.Size(100, 21);
            this.tb_ip.TabIndex = 0;
            this.tb_ip.Text = "127.0.0.1";
            // 
            // lb_Ip
            // 
            this.lb_Ip.AutoSize = true;
            this.lb_Ip.Location = new System.Drawing.Point(15, 21);
            this.lb_Ip.Name = "lb_Ip";
            this.lb_Ip.Size = new System.Drawing.Size(23, 12);
            this.lb_Ip.TabIndex = 1;
            this.lb_Ip.Text = "IP:";
            // 
            // lb_port
            // 
            this.lb_port.AutoSize = true;
            this.lb_port.Location = new System.Drawing.Point(158, 24);
            this.lb_port.Name = "lb_port";
            this.lb_port.Size = new System.Drawing.Size(35, 12);
            this.lb_port.TabIndex = 3;
            this.lb_port.Text = "Port:";
            // 
            // tb_port
            // 
            this.tb_port.Location = new System.Drawing.Point(199, 21);
            this.tb_port.Name = "tb_port";
            this.tb_port.Size = new System.Drawing.Size(100, 21);
            this.tb_port.TabIndex = 2;
            this.tb_port.Text = "80";
            // 
            // bt_connnect
            // 
            this.bt_connnect.Location = new System.Drawing.Point(316, 15);
            this.bt_connnect.Name = "bt_connnect";
            this.bt_connnect.Size = new System.Drawing.Size(132, 42);
            this.bt_connnect.TabIndex = 4;
            this.bt_connnect.Text = "开始监听";
            this.bt_connnect.UseVisualStyleBackColor = true;
            this.bt_connnect.Click += new System.EventHandler(this.bt_connnect_Click);
            // 
            // listBox1
            // 
            this.listBox1.FormattingEnabled = true;
            this.listBox1.ItemHeight = 12;
            this.listBox1.Location = new System.Drawing.Point(21, 112);
            this.listBox1.Name = "listBox1";
            this.listBox1.Size = new System.Drawing.Size(580, 124);
            this.listBox1.TabIndex = 1;
            // 
            // txt_msg
            // 
            this.txt_msg.Location = new System.Drawing.Point(21, 255);
            this.txt_msg.Multiline = true;
            this.txt_msg.Name = "txt_msg";
            this.txt_msg.Size = new System.Drawing.Size(424, 73);
            this.txt_msg.TabIndex = 2;
            // 
            // bt_send
            // 
            this.bt_send.Location = new System.Drawing.Point(471, 266);
            this.bt_send.Name = "bt_send";
            this.bt_send.Size = new System.Drawing.Size(119, 52);
            this.bt_send.TabIndex = 3;
            this.bt_send.Text = "发送";
            this.bt_send.UseVisualStyleBackColor = true;
            this.bt_send.Click += new System.EventHandler(this.bt_send_Click);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(695, 340);
            this.Controls.Add(this.bt_send);
            this.Controls.Add(this.txt_msg);
            this.Controls.Add(this.listBox1);
            this.Controls.Add(this.panel1);
            this.Name = "Form1";
            this.Text = "SocketForm";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.panel1.ResumeLayout(false);
            this.panel1.PerformLayout();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Panel panel1;
        private System.Windows.Forms.Button bt_connnect;
        private System.Windows.Forms.Label lb_port;
        private System.Windows.Forms.TextBox tb_port;
        private System.Windows.Forms.Label lb_Ip;
        private System.Windows.Forms.TextBox tb_ip;
        private System.Windows.Forms.ListBox listBox1;
        private System.Windows.Forms.TextBox txt_msg;
        private System.Windows.Forms.Button bt_send;
    }
}

 

　　（2）服务端逻辑设计

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Windows.Forms;

namespace SocketForm
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void bt_connnect_Click(object sender, EventArgs e)
        {

            try
            {
                //点击开始监听时 在服务端创建一个负责监听IP和端口号的Socket
                Socket socketWatch = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                IPAddress ip = IPAddress.Any;
                //创建对象端口
                IPEndPoint point = new IPEndPoint(ip, Convert.ToInt32(tb_port.Text));

                socketWatch.Bind(point);//绑定端口号
                ShowMsg("监听成功!");
                socketWatch.Listen(10);//设置监听

                //创建监听线程
                Thread thread = new Thread(Listen);
                thread.IsBackground = true;
                thread.Start(socketWatch);
            }
            catch { }
           
        }
       
        /// <summary>
        /// 等待客户端的连接 并且创建与之通信的Socket
        /// </summary>
        Socket socketSend;
        void Listen(object o)
        {
            try
            {
                Socket socketWatch = o as Socket;
                while (true)
                {
                    socketSend = socketWatch.Accept();//等待接收客户端连接
                    ShowMsg(socketSend.RemoteEndPoint.ToString() + ":" + "连接成功!");
                    //开启一个新线程，执行接收消息方法
                    Thread r_thread = new Thread(Received);
                    r_thread.IsBackground = true;
                    r_thread.Start(socketSend);
                }
            }
            catch { }
        }
        /// <summary>
        /// 服务器端不停的接收客户端发来的消息
        /// </summary>
        /// <param name="o"></param>
        void Received(object o)
        {
            try
            {
                Socket socketSend = o as Socket;
                while (true)
                {
                    //客户端连接服务器成功后，服务器接收客户端发送的消息
                    byte[] buffer = new byte[1024 * 1024 * 3];
                    //实际接收到的有效字节数
                    int len = socketSend.Receive(buffer);
                    if (len == 0)
                    {
                        break;
                    }
                    string str = Encoding.UTF8.GetString(buffer, 0, len);
                    ShowMsg(socketSend.RemoteEndPoint + ":" + str);
                }
            }
            catch { }
        }
        /// <summary>
        /// 服务器向客户端发送消息
        /// </summary>
        /// <param name="str"></param>
        void Send(string str) {
            byte[] buffer = Encoding.UTF8.GetBytes(str);
            socketSend.Send(buffer);
        }

        void ShowMsg(string msg)
        {
            listBox1.Items.Add(msg + "
");
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Control.CheckForIllegalCrossThreadCalls = false;
        }

        private void bt_send_Click(object sender, EventArgs e)
        {
            Send(txt_msg.Text.Trim());
        }
    }
}

 

　　2、客户端

　　（1）客户端窗口设计

namespace SocketClient
{
    partial class Form1
    {
        /// <summary>
        /// 必需的设计器变量。
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// 清理所有正在使用的资源。
        /// </summary>
        /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows 窗体设计器生成的代码

        /// <summary>
        /// 设计器支持所需的方法 - 不要
        /// 使用代码编辑器修改此方法的内容。
        /// </summary>
        private void InitializeComponent()
        {
            this.panel1 = new System.Windows.Forms.Panel();
            this.lb_ip = new System.Windows.Forms.Label();
            this.txt_ip = new System.Windows.Forms.TextBox();
            this.txt_port = new System.Windows.Forms.TextBox();
            this.lb_port = new System.Windows.Forms.Label();
            this.bt_connect = new System.Windows.Forms.Button();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.txt_msg = new System.Windows.Forms.TextBox();
            this.bt_send = new System.Windows.Forms.Button();
            this.panel1.SuspendLayout();
            this.SuspendLayout();
            // 
            // panel1
            // 
            this.panel1.Controls.Add(this.bt_connect);
            this.panel1.Controls.Add(this.txt_port);
            this.panel1.Controls.Add(this.lb_port);
            this.panel1.Controls.Add(this.txt_ip);
            this.panel1.Controls.Add(this.lb_ip);
            this.panel1.Location = new System.Drawing.Point(12, 12);
            this.panel1.Name = "panel1";
            this.panel1.Size = new System.Drawing.Size(463, 75);
            this.panel1.TabIndex = 0;
            // 
            // lb_ip
            // 
            this.lb_ip.AutoSize = true;
            this.lb_ip.Location = new System.Drawing.Point(14, 23);
            this.lb_ip.Name = "lb_ip";
            this.lb_ip.Size = new System.Drawing.Size(23, 12);
            this.lb_ip.TabIndex = 0;
            this.lb_ip.Text = "IP:";
            // 
            // txt_ip
            // 
            this.txt_ip.Location = new System.Drawing.Point(43, 20);
            this.txt_ip.Name = "txt_ip";
            this.txt_ip.Size = new System.Drawing.Size(100, 21);
            this.txt_ip.TabIndex = 1;
            this.txt_ip.Text = "127.0.0.1";
            // 
            // txt_port
            // 
            this.txt_port.Location = new System.Drawing.Point(207, 23);
            this.txt_port.Name = "txt_port";
            this.txt_port.Size = new System.Drawing.Size(100, 21);
            this.txt_port.TabIndex = 3;
            this.txt_port.Text = "2001";
            // 
            // lb_port
            // 
            this.lb_port.AutoSize = true;
            this.lb_port.Location = new System.Drawing.Point(166, 29);
            this.lb_port.Name = "lb_port";
            this.lb_port.Size = new System.Drawing.Size(35, 12);
            this.lb_port.TabIndex = 2;
            this.lb_port.Text = "port:";
            // 
            // bt_connect
            // 
            this.bt_connect.Location = new System.Drawing.Point(313, 9);
            this.bt_connect.Name = "bt_connect";
            this.bt_connect.Size = new System.Drawing.Size(113, 47);
            this.bt_connect.TabIndex = 4;
            this.bt_connect.Text = "连接";
            this.bt_connect.UseVisualStyleBackColor = true;
            this.bt_connect.Click += new System.EventHandler(this.bt_connect_Click);
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(12, 103);
            this.textBox1.Multiline = true;
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(463, 114);
            this.textBox1.TabIndex = 1;
            // 
            // txt_msg
            // 
            this.txt_msg.Location = new System.Drawing.Point(12, 246);
            this.txt_msg.Multiline = true;
            this.txt_msg.Name = "txt_msg";
            this.txt_msg.Size = new System.Drawing.Size(291, 54);
            this.txt_msg.TabIndex = 2;
            // 
            // bt_send
            // 
            this.bt_send.Location = new System.Drawing.Point(325, 246);
            this.bt_send.Name = "bt_send";
            this.bt_send.Size = new System.Drawing.Size(113, 54);
            this.bt_send.TabIndex = 3;
            this.bt_send.Text = "发送";
            this.bt_send.UseVisualStyleBackColor = true;
            this.bt_send.Click += new System.EventHandler(this.bt_send_Click);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(493, 323);
            this.Controls.Add(this.bt_send);
            this.Controls.Add(this.txt_msg);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.panel1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.panel1.ResumeLayout(false);
            this.panel1.PerformLayout();
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Panel panel1;
        private System.Windows.Forms.Label lb_ip;
        private System.Windows.Forms.Button bt_connect;
        private System.Windows.Forms.TextBox txt_port;
        private System.Windows.Forms.Label lb_port;
        private System.Windows.Forms.TextBox txt_ip;
        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.TextBox txt_msg;
        private System.Windows.Forms.Button bt_send;
    }
}

 

　　（2）客户端逻辑设计

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Windows.Forms;

namespace SocketClient
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        Socket socketSend;
        private void bt_connect_Click(object sender, EventArgs e)
        {
            try
            {
                //创建客户端Socket，获得远程ip和端口号
                socketSend = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                IPAddress ip = IPAddress.Parse(txt_ip.Text);
                IPEndPoint point = new IPEndPoint(ip, Convert.ToInt32(txt_port.Text));

                socketSend.Connect(point);
                ShowMsg("连接成功!");
                //开启新的线程，不停的接收服务器发来的消息
                Thread c_thread = new Thread(Received);
                c_thread.IsBackground = true;
                c_thread.Start();
            }
            catch (Exception){
                ShowMsg("IP或者端口号错误...");
            }
 
        }
        void ShowMsg(string str)
        {
            textBox1.AppendText(str + "
");
        }
        /// <summary>
        /// 接收服务端返回的消息
        /// </summary>
        void Received()
        {
            while (true)
            {
                try
                {
                    byte[] buffer = new byte[1024 * 1024 * 3];
                    //实际接收到的有效字节数
                    int len = socketSend.Receive(buffer);
                    if (len == 0)
                    {
                        break;
                    }
                    string str = Encoding.UTF8.GetString(buffer, 0, len);
                    ShowMsg(socketSend.RemoteEndPoint + ":" + str);
                }
                catch { }
            }
        } 
        /// <summary>
        /// 向服务器发送消息
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void bt_send_Click(object sender, EventArgs e)
        {
            try
            {
                string msg = txt_msg.Text.Trim();
                byte[] buffer = new byte[1024 * 1024 * 3];
                buffer = Encoding.UTF8.GetBytes(msg);
                socketSend.Send(buffer);
            }
            catch { }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Control.CheckForIllegalCrossThreadCalls = false;
        }
    }
}

 

七、运行效果

　　1、服务端

　　2、客户端