CPSC 441 Tutorial TCP Server. Department of Computer Science University of Calgary

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1 CPSC 441 Tutorial TCP Server Department of Computer Science University of Calgary

2 TCP Socket Client Server Connection Request Server Listening on welcoming socket Client Socket Server Socket Data

3 Simple TCP Server public class TCPServer public static void main(string[] args) String s; ServerSocket serversocket = null; Socket socket = null; Listen on port 8888 Create streams // Listen on port 8888 serversocket = new ServerSocket(8888); socket = serversocket.accept(); Connected to client PrintWriter outputstream = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8")); Scanner inputstream = new Scanner(socket.getInputStream(), "UTF-8");

4 Receive message from the client and respond. Exit on bye while(true) s = inputstream.nextline(); System.out.println(s); if(s.equalsignorecase("bye")) outputstream.println("bye"); outputstream.flush(); break; outputstream.println(s); outputstream.flush(); catch (Exception e) System.out.println("Error: " + e.getmessage()); finally if (socket!= null) socket.close();

5 catch (IOException ex) // ignore if (serversocket!= null) serversocket.close(); catch (IOException ex) // ignore // close finally block // close main block // close class block

6 Drawback v Cannot handle multiple clients v Quick fix: Add a while loop v Iterative Server

7 Iterative TCP Server public class TCPServer public static void main(string[] args) String s; ServerSocket serversocket = null; Listen on port 8888 Create streams serversocket = new ServerSocket(8888); while(true) // Listen on port 8888 Socket socket = null; socket = serversocket.accept(); Connected to client PrintWriter outputstream = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), "UTF-8")); Scanner inputstream = new Scanner(socket.getInputStream(), "UTF-8");

8 Receive message from the client and respond. Exit on bye while(true) s = inputstream.nextline(); System.out.println(s); if(s.equalsignorecase("bye")) outputstream.println("bye"); outputstream.flush(); break; outputstream.println(s); outputstream.flush(); catch (Exception e) System.out.println( Client Error: " + e.getmessage()); finally if (socket!= null) socket.close();

9 catch (IOException ex) // ignore // close finally // close inner while loop // close outer block catch (Exception e) System.out.println( Server Error: " + e.getmessage()); finally if (serversocket!= null) serversocket.close(); catch (IOException ex) // ignore // close finally // close outer while loop //close main close class

10 Drawback v After a connection is made with a client, server will not respond to a second client (while the first is still being served) v Solution: Use threads

11 Case: Multi-threaded TCP Server public class TCPServer_Multithreaded extends Thread private Socket connection; public TCPServer_Multithreaded(Socket socket) this.connection = socket; public static void main(string[] args) ServerSocket serversocket; serversocket = new ServerSocket(8888); while(true) Listen on port 8888 Socket socket = serversocket.accept(); TCPServer_Multithreaded tcpconn = new TCPServer_Multithreaded(socket); tcpconn.start(); //close inner catch (Exception e) // related to this particular client -- Ignore anyway //close while // close catch (Exception e) //related to server Ignore // close main New thread to handle this connection

12 // Override run method of Thread Class --- following will be executed for each client public void run() Note the signature String s; of method run () PrintWriter outputstream = new PrintWriter(new OutputStreamWriter(connection.getOutputStream(), "UTF-8")); Scanner inputstream = new Scanner(connection.getInputStream(), "UTF-8"); // Respond to messages from the client while(true) s = inputstream.nextline(); System.out.println(s); // exit if message from client is "bye if(s.equalsignorecase("bye")) outputstream.println("bye"); outputstream.flush(); break; outputstream.println(s); outputstream.flush(); // close while // close catch (Exception e) // Ignore Exception How to pass argument to thread? Check the constructor Logic for handling the client should be inside the run() method

13 finally if (connection!= null) connection.close(); catch (IOException ex) // ignore //close // close if // close finally // close run method // close class

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