Quarta parte

Programmazione di rete con UDP
UDP: nessuna connessione
! Invio: il mittente indica
esplicitamente indirizzo IP
e porta del ricevente
! Il ricevente deve
esplicitamente estrarre
indirizzo IP e n. di porta
da pacchetti in arrivo
Applicazioni
Trasferimento non affidabile di
Messaggi tra client e server
UDP: pacchetti possono
essere persi o arrivare
fuori ordine
2: Application Layer
1
Interazione tra client e server
Server (running on hostid)
create socket,
port=x, for
incoming request:
serverSocket =
DatagramSocket()
read request from
serverSocket
write reply to
serverSocket
specifying client
host address,
port umber
Client
create socket,
clientSocket =
DatagramSocket()
Create, address (hostid, port=x,
send datagram request
using clientSocket
read reply from
clientSocket
close
clientSocket
2: Application Layer
2
Classe InetAddress
2: Application Layer
3
Example: Java client (UDP)
import java.io.*;
import java.net.*;
Create
input stream
Create
client socket
Traduzione
Indirizzo
usando DNS
class UDPClient {
public static void main(String args[]) throws Exception
{
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
DatagramSocket clientSocket = new DatagramSocket();
InetAddress IPAddress = InetAddress.getByName("hostname");
byte[] sendData = new byte[1024];
byte[] receiveData = new byte[1024];
String sentence = inFromUser.readLine();
sendData = sentence.getBytes();
2: Application Layer
4
Example: Java client (UDP), cont.
Crea datagramma
con dati da spedire,
lungh., ind. IP, porta
send datagramma
al server
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
clientSocket.send(sendPacket);
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
Ricevi datagramma
dal server
clientSocket.receive(receivePacket);
String modifiedSentence =
new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}
2: Application Layer
5
Example: Java server (UDP)
import java.io.*;
import java.net.*;
Crea Socket
su porta 9876
class UDPServer {
public static void main(String args[]) throws Exception
{
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
while(true)
{
Alloca buffer di
Ricezione pacchetto
Ricevi
pacchetto
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
2: Application Layer
6
Example: Java server (UDP), cont
String sentence = new String(receivePacket.getData());
Estrai ind. IP
da pacchetto
ricevuto
InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();
String capitalizedSentence = sentence.toUpperCase();
sendData = capitalizedSentence.getBytes();
Costruisci
datagramma
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress,
port);
Scrivi datagram
Su socket
serverSocket.send(sendPacket);
}
}
}
Fine ciclo while
Attendi altro datagramma
2: Application Layer
7
2: Application Layer
8