Socket Connections in C#

•Sockets:

–Sockets are used to interface to networks.

–Allows programs to access the network similar to doing file I/O.

–Sockets are stream-based.

–Server waits (listens) for client to request connection.

–When client request is received, server sets up objects for sending and receiving.

–When terminated, server returns to listen phase.

–C# provides objects for sockets.

•Server Function:

–Create an object of TcpListener

•Binds server to port number

–Call Start method

•Begin connection request

–Make connection between server and client

•Returns a Socket object

–Processing phase

•Methods Receive and Send

–Connection-termination phase

•Method Close

• Client Function:– Create object of TcpClient

• Method Connect

– Get a NetworkStream• WriteByte and ReadByte

– Processing phase• Client and server communicate

– Close connection• Method Close

• Simple Server/Client Program:– Start server application (on

server system).

– Start client application (on client system).

– Client requests connection.

– Servers starts stream communication.

– Upon completion server release connection.

Example of Server Chat Program using Sockets

// Fig. 22.1: Server.cs

// Set up a Server that will receive a connection from a client,

// send a string to the client, and close the connection.

using System;

using System.Drawing;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Threading;

using System.Net.Sockets;

using System.IO;

namespace ChatServer

{

// server that awaits client connections (one at a time) and

// allows a conversation between client and server

public class Server : System.Windows.Forms.Form

{

private System.Windows.Forms.TextBox inputTextBox;

private System.Windows.Forms.TextBox displayTextBox;

private Socket connection;

private Thread readThread;

private System.ComponentModel.Container components = null;

private NetworkStream socketStream;

private BinaryWriter writer;

private BinaryReader reader;

// default constructor public Server() { // // Required for Windows Form Designer support // InitializeComponent();

// // TODO: Add any constructor code after InitializeComponent call //

// create a new thread from the server readThread = new Thread( new ThreadStart( RunServer ) ); readThread.Start(); }

/// <summary> /// Clean up any resources being used. /// </summary> protected override void Dispose( bool disposing ) { if( disposing ) { if(components != null) { components.Dispose(); } } base.Dispose( disposing ); }

#region Windows Form Designer generated code

/// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

this.displayTextBox = new System.Windows.Forms.TextBox();

this.inputTextBox = new System.Windows.Forms.TextBox();

this.SuspendLayout();

//

// displayTextBox

//

this.displayTextBox.Location = new System.Drawing.Point(8, 40);

this.displayTextBox.Multiline = true;

this.displayTextBox.Name = "displayTextBox";

this.displayTextBox.ReadOnly = true;

this.displayTextBox.Size = new System.Drawing.Size(272, 208);

this.displayTextBox.TabIndex = 1;

this.displayTextBox.Text = "";

//

// inputTextBox

//

this.inputTextBox.Location = new System.Drawing.Point(8, 8);

this.inputTextBox.Name = "inputTextBox";

this.inputTextBox.Size = new System.Drawing.Size(272, 20);

this.inputTextBox.TabIndex = 0;

this.inputTextBox.Text = "";

this.inputTextBox.KeyDown += new System.Windows.Forms.KeyEventHandler(this.inputTextBox_KeyDown);

// // Server // this.AutoScaleBaseSize = new System.Drawing.Size(5, 13); this.ClientSize = new System.Drawing.Size(292, 261); this.Controls.AddRange(new System.Windows.Forms.Control[] { this.displayTextBox, this.inputTextBox}); this.Name = "Server"; this.Text = "Server"; this.Closing += new System.ComponentModel.CancelEventHandler(this.Server_Closing); this.ResumeLayout(false);

} #endregion

[STAThread] static void Main() { Application.Run( new Server() ); }

protected void Server_Closing( object sender, CancelEventArgs e ) { System.Environment.Exit( System.Environment.ExitCode ); }

// sends the text typed at the server to the client protected void inputTextBox_KeyDown( object sender, KeyEventArgs e ) { // sends the text to the client try { if ( e.KeyCode == Keys.Enter && connection != null ) { writer.Write( "SERVER>>> " + inputTextBox.Text ); displayTextBox.Text += "\r\nSERVER>>> " + inputTextBox.Text;

// if the user at the server signaled termination // sever the connection to the client if ( inputTextBox.Text == "TERMINATE" ) connection.Close();

inputTextBox.Clear(); } } catch ( SocketException ) { displayTextBox.Text += "\nError writing object"; } }

// allows a client to connect and displays the text it sends public void RunServer() { TcpListener listener; int counter = 1;

// wait for a client connection and display the text

// that the client sends

try

{

// Step 1: create TcpListener

listener = new TcpListener( 5000 );

// Step 2: TcpListener waits for connection request

listener.Start();

// Step 3: establish connection upon client request

while ( true )

{

displayTextBox.Text = "Waiting for connection\r\n";

// accept an incoming connection

connection = listener.AcceptSocket();

// create NetworkStream object associated with socket

socketStream = new NetworkStream( connection );

// create objects for transferring data across stream

writer = new BinaryWriter( socketStream );

reader = new BinaryReader( socketStream );

displayTextBox.Text += "Connection " + counter +

" received.\r\n";

// inform client that connection was successfull

writer.Write( "SERVER>>> Connection successful" );

inputTextBox.ReadOnly = false;

string theReply = "";

// Step 4: read String data sent from client

do

{

try

{

// read the string sent to the server

theReply = reader.ReadString();

// display the message

displayTextBox.Text += "\r\n" + theReply;

}

// handle exception if error reading data catch ( Exception ) { break; }

} while ( theReply != "CLIENT>>> TERMINATE" && connection.Connected );

displayTextBox.Text += "\r\nUser terminated connection";

// Step 5: close connection inputTextBox.ReadOnly = true; writer.Close(); reader.Close(); socketStream.Close(); connection.Close();

++counter; } } // end try

catch ( Exception error ) { MessageBox.Show( error.ToString() ); }

} // end method RunServer

} // end class Server}