Socket Connections in C#

1. Socket Connections in C# C# 213 Project Apr. 28, 2004 Gary Laatsch

2. 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.

3. 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

4. Client Function: • Create object of TcpClient • Method Connect • Get a NetworkStream • WriteByte and ReadByte • Processing phase • Client and server communicate • Close connection • Method Close

5. 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.

6. Example of Server Chat Program using Sockets

7. // 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;

8. // 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 ); }

9. #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);

10. // // 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 ); }

11. // 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;

12. // 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";

13. // 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; }

14. // 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 }