1. Comunicação entre processos baseada em troca de mensagens através de sockets sobre IP Alcides Calsavara

2. Sockets Basic TCP/IP mechanism Three access facilities: –connection-oriented: Socket, ServerSocket –datagram-oriented: DatagramSocket MulticastSocket –raw IP data: SocketImpl

3. Connection-oriented sockets Built over TCP/IP Reliable services: no data losses in the network data ordering is insured Trade-off: slower than datagrams Data streams can be created Asymmetric behaviors client side Vs. server side

4. Connection: client actions 1. Open the communication socket import java.io.* ; // streams import java.net.* ; // sockets Socket clientSocket = new Socket (“www.javasoft.com”, 80) ;

5. Connection: client actions 2. Get socket input/output streams: DataInputStream inbound = new DataInputStream ( clientSocket.getInputStream( ) ) ; DataOutputStream outbound = new DataOutputStream ( clientSocket.getOutputStream( ) ) ;

6. Connection: client actions 3. Use the input/output streams outbound.writeInt( 3 ); outbound.writeUTF( “Hello” ); int k = inbound.readInt( ); String s = inbound.readUTF() ;...

7. Connection: client actions 4. Close in/out streams inbound.close () ; outbound.close () ; 5. Close the socket clientSocket.close() ;

8. Connection: server actions 1. Create server-side socket: ServerSocket serverSocket = new ServerSocket (80, 5) ; 2. Wait for client connections: Socket clientSocket = serverSocket.accept () ;

9. Connection: server actions 3. Create client in/out streams: DataInputStream inbound = new DataInputStream ( clientSocket.getInputStream( ) ) ; DataOutputStream outbound = new DataOutputStream ( clientSocket.getOutputStream( ) ) ;

10. Connection: server actions 4. Dialog with the client: int k = inbound.readInt( ); String s = inbound.readUTF() ; outbound.writeInt( 3 ); outbound.writeUTF( “Hello” );

11. Connection: server actions 5. Close streams and client socket: inbound.close () ; outbound.close () ; clientSocket.close() ; 6. Close server-side socket: serverSocket.close() ;

12. Datagram sockets Based on UDP/IP unreliable service: messages can be lost messages ordering is not guaranteed but it’s much faster the TCP/IP Each message is a “datagram”: [sender, receiver, contents]

13. Datagram, sender side 1. Client socket creation: // sender socket doesn’t need // a special port number DatagramSocket clientSocket = new DatagramSocket () ;

14. Datagram, sender side 2. Build and send the datagram: InetAddress addr=InetAddress.getByName (“www.javasoft.com”) ; String toSend = “That’s my question!” ; byte[] buffer = toSend.getBytes() ; // datagram to receiver’s port 4545 DatagramPacket question = new DatagramPacket (buffer, buffer.length, addr, 4545) ; clientSocket.send (question) ;

15. Datagram, sender side 3. Receive and open the answer: DatagramPacket answer = new DatagramPacket (new byte[512], 512); clientSocket.receive (answer) ; System.out.println (answer.getData() + “\n” + answer.getLength() + “\n” + answer.getAddress() + “\n” + answer.getPort() ) ;

16. Datagram, sender side 4. Close the client socket: clientSocket.close() ;

17. Datagram, receiver side 1. Create a server socket: // listens on port 4545 DatagramSocket serverSocket = new DatagramSocket (4545) ;

18. Datagram, receiver side 2. Receive a datagram: DatagramPacket question = new DatagramPacket (new byte[512], 512) ; serverSocket.receive (question) ;

19. Datagram, receiver side 3. Send the answer datagram: String toSend = “That’s the answer !” ; byte[] buffer = toSend.getBytes() ; DatagramPacket answer = new DatagramPacket (buffer, buffer.length, question.getAddress(), // sender info question.getPort() ) ; // sender info serverSocket.send (answer) ;

20. Datagram, receiver side 4. Close the server socket: serverSocket.close() ;