TCP/IP Protocol Stack

1. TCP/IP Protocol Stack Application Sockets (Gate to network) TCP UDP IP Device Drivers

2. Programming with Sockets • Sockets are Berkeley software distribution UNIX interface to network protocols • Endpoint of communication, has a type and one associated process • Uses file system model (open-close-read-write) • Internet vs. Unix domain

3. Client-Server Architecture request Process request client response Host: www.vcu.edu Port: 80

4. 4 steps in programming a client • Open a socket. • Open an input and output stream to the socket. • Read from and write to the socket according to the server's protocol. • Clean up.

5. Socket in Java • Two important classes • Socket: a normal socket as communication end • ServerSocket: accept the incoming request • ServerSocket is an analogy to the custom service phone number, it will dispatch your call to a specialized staff--- normal Socket.

6. Client Socket Creation Socket MyClient;MyClient = new Socket("Machine name", PortNumber); SOCKET DESCRIPTOR port (a number) on which the server you want the machine you are trying to open a connection to port numbers between 0 and 1,023 are reserved for for standard services, such as email, FTP, and HTTP. for your server, select one that is greater than 1,023

7. Create Server Socket • If you are programming a server, then this is how you open a socket: • ServerSocket MyService;try {   MyServerice = new ServerSocket(PortNumber);        }        catch (IOException e) {           System.out.println(e);        }

8. Use ServerSocket: listen, accept, and Create connections from clients. Socket clientSocket = null;try {   serviceSocket = MyService.accept();        }catch (IOException e) {   System.out.println(e);} A blocking call, will return when a request arrive

9. Send Data to Socket at Client • PrintStream output;try {   output = new PrintStream(MyClient.getOutputStream());… String inL=“hello”; output.writeBytes(inL+"\n"); • }

10. Read data from Socket at Client • DataInputStream input;try {   input = new DataInputStream(MyClient.getInputStream()); ….. String responseLine = input.readLine(); System.out.println("Server: " + responseLine);}

11. Send Data to Socket at Server • Use the serviceSocket: returned from the accept() call. • PrintStream output;try {   output = new PrintStream(serviceSocket.getOutputStream());output.println(“this is server reply”); • }

12. Read Data From Socket at Server • Same as client case • DataInputStream input;try {      input = new DataInputStream(serviceSocket.getInputStream()); • String req=input.readLine(); • }

13. Close Socket Connection • On the server side: • try {   output.close();   input.close();   serviceSocket.close();    MyService.close();} catch (IOException e) {   System.out.println(e);} • On the client side: • try {        output.close();        input.close();    MyClient.close();} catch (IOException e) {   System.out.println(e);}

14. A Simple Echo Server • // listen and accept connections.// Open input and output streamstry {           clientSocket = echoServer.accept();           is = new DataInputStream (clientSocket.getInputStream()); os = new PrintStream (clientSocket.getOutputStream());// As long as we receive data, echo that data back to the client.          while (true) {             line = is.readLine();             os.println(line);            }        }   catch (IOException e) {           System.out.println(e);        }    }} • import java.io.*;import java.net.*;public class echo3 {    public static void main(String args[]) {        ServerSocket echoServer = null;        String line;        DataInputStream is;        PrintStream os;        Socket clientSocket = null;        try {           echoServer = new ServerSocket(9999);        }        catch (IOException e) {           System.out.println(e);        }  

15. A simple client responseLine = is.readLine(); System.out.println("Server: " + responseLine); responseLine = is.readLine(); System.out.println("Server: " + responseLine); responseLine = is.readLine(); System.out.println("Server: " + responseLine); } smtpSocket = new Socket("128.172.167.167", 9998); os = new DataOutputStream(smtpSocket.getOutputStream()); is = new DataInputStream(smtpSocket.getInputStream()); while (true){ inL=d.readLine(); os.writeBytes(inL+"\n"); if (inL.compareTo("quit")==0) break; // keep on reading from/to the socket till we receive the "Ok" from SMTP, // once we received that then we want to break.

16. Reference • Class ServerSocke • A server socket waits for requests to come in over the network. It performs some operation based on that request, and then possibly returns a result to the requester. • accept() Listens for a connection to be made to this socket and accepts it. • getInetAddress() • Returns the local address of this server socket.

17. Class Socket • This class implements client sockets (also called just "sockets"). A socket is an endpoint for communication between two machines. • Socket(InetAddress address, int port) • connect(SocketAddress endpoint)    Connects this socket to the server. • getPort()    Returns the remote port to which this socket is connected. • getLocalPort()           Returns the local port to which this socket is bound. • getInputStream()           Returns an input stream for this socket. • getOutputStream()           Returns an output stream for this socket. • getInetAddress()           Returns the address to which the socket is connected. • getLocalAddress()           Gets the local address to which the socket is bound.

18. Other Parameters in Socket • Buffer size • Incoming buffer size • Outgoing buffer size • Time out or not • Otherwise a bad read will block your browser for ever. • Status check