服务器如何知道要与之通信的特定客户端的地址？

Question

There is a server and multiple clients. The server accepts the connection requests from multiple clients. The sockets created are stored in an array. There is a list box in my application. On selecting a particular item it refers to the corresponding socket in the array of sockets (eg if I select first item, it will consider first socket in the array). But the problem is - as the clients can connect to the server in random fashion how the server keep tracks of the clients if it has to send data to a particular client. Here is my code:

static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        int i=0;
        TcpListener listener = new TcpListener(8888);

        listener.Start();

        while(true)
        {
            Socket soc = listener.AcceptSocket();
            socarray[i] = soc;
            i++;
            if (i == NUMBEROFCLIENTS)
                break;


        }


       // Thread writetodatabase = new Thread(datawrite);
      //  writetodatabase.Start();

        Application.Run(new Form1());


    }
      private void button5_Click(object sender, EventArgs e)
    {
        if (listBox1.Text == "Reader1")
        {
            reader_flag = 1;
            toolStripStatusLabel1.Text = "reader1 selected";
            a = toolStripStatusLabel1.Text;
        }

        if (listBox1.Text == "Reader2")
        {
            reader_flag = 2;
            toolStripStatusLabel1.Text = "reader2 selected";
            a = toolStripStatusLabel1.Text;

        }

     }


          namespace WindowsFormsApplication1
     {
           public partial class Form1 : Form
         {
            string a;
            public static int reader_flag = 0;

              public Form1()
             {
                InitializeComponent();
              }
            private void Form1_Load(object sender, System.EventArgs e)
          {


            }


      private void button2_Click(object sender, EventArgs e)
     {
        Form3 formmm = new Form3();
        formmm.Show();
     }



    private void button4_Click(object sender, EventArgs e)
    {
        Form2 formm = new Form2();
        formm.Show();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        try
        {

            byte[] bytesFrom = new Byte[1000];
            Program.socarray[0].Receive(bytesFrom);
            char[] stuffed =  System.Text.Encoding.UTF8.GetString(bytesFrom).ToCharArray();

            int i;
            char escape='@';

            List<char> unstuffed = new List<char>();

             for(i=0;i<stuffed.Length;i++)

             {

              if(stuffed[i]==escape)

                {
                   i++;
                   unstuffed.Add(stuffed[i]);

                 }

               else

                {

                 unstuffed.Add(stuffed[i]);

                }

              }
                  unstuffed.RemoveAt(0);
                  unstuffed.RemoveAt(unstuffed.Count-1);


                  char[] final;
                  final = unstuffed.ToArray();
                  string foo = new string(final);
                  textBox1.Text = foo;



System.IO.File.WriteAllText(@"C:\Users\cdac\Desktop\server\server\TextFile2.txt", foo);

                 }
           finally { }

             }

            private void textBox1_TextChanged(object sender, EventArgs e)
             {

             }

       private void button3_Click(object sender, EventArgs e)
       {
        Form4 mm = new Form4();
        mm.Show();
       }

        private void toolStripStatusLabel1_Click(object sender, EventArgs e)
      {
          toolStripStatusLabel1.Text = a;
      }

      private void button5_Click(object sender, EventArgs e)
      {
        if (listBox1.Text == "Reader1")
        {
            reader_flag = 1;
            toolStripStatusLabel1.Text = "reader1 selected";
            a = toolStripStatusLabel1.Text;
        }

        if (listBox1.Text == "Reader2")
        {
            reader_flag = 2;
            toolStripStatusLabel1.Text = "reader2 selected";
            a = toolStripStatusLabel1.Text;

        }

    }

    private void button6_Click(object sender, EventArgs e)
    {
        string MyConString = "server=localhost;" +
               "database=cdac;"+
               "User Id=root;"

               +"password=cdac56;";
            MySqlConnection connection = new MySqlConnection(MyConString);
            MySqlCommand command = connection.CreateCommand();
            MySqlDataReader Reader;
            connection.Open();

               //StreamReader reader = new StreamReader("C:\\tag_log_030610.txt");
               StreamReader reader = new StreamReader("C:\\Users\\cdac\\Desktop\\server\\server\\TextFile2.txt");

               string line;
                while ((line = reader.ReadLine()) != null)
                {
                    string[] parts = line.Split(';');
                   //command.CommandText = "insert into st_attn(rollno,Th_attn,Name) values('" + parts[0] + "','" + parts[1] + "','" + parts[2] + "')";

                    command.CommandText = "insert into st_attn(rollno) values('" + parts[0] + "')";



                    Reader = command.ExecuteReader();
                }





            }

    private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
    {

    }


    }
}

Answer 1

Client-Server apps ALWAYS start with a request from the client to the server. No matter if it's a business app, a game, a website, a webservice or even something to tell the time, the client will always first ask the server.

This means that if you're using sockets, you will always have to let the request come from the client. He will send a request to the server. The server will then keep a record internally of where they can find the client. This is kept in the Endpoint property of the Socket. But normally, you will not have to worry about this unless you're working with push apps.