Socket-Programming

 Establish contact (connection).  Exchange information (bi-directional).  Terminate contact.

3 Network Request Result a client, a server, and network Client Server Client machine Server machine

 Other examples:  Chatroom

 Connection-oriented  Setup the link before communication.  Similar to the phone call. We need the phone number and receiver.  Connectionless  No link needed to be set up before communication.  Similar to send a letter. We need the address and receiver.

6  UDP (User Datagram Protocol) is a protocol that sends independent packets of data, called datagrams, from one computer to another with no guarantees about arrival.  Example applications:  Clock server  Ping  TCP/IP Stack Application (http,ftp,telnet,…) Transport (TCP, UDP,..) Network (IP,..) Link (device driver,..)

7  The TCP and UDP protocols use ports to map incoming data to a particular process running on a computer. server PORT PORT Client TCP TCP or UDP port app port#data Data Packet

Figure 2.6-2: Client socket, welcoming socket and connection socket

 Server waits for client to request a connection.  Client contacts server to establish a connection.  Client sends request.  Server sends reply.  Client and/or server terminate connection.

 Socket  The combination of an IP address and a port number. (RFC 793,original TCP specification)  The name of the Berkeley-derived application programming interfaces (APIs) for applications using TCP/IP protocols.  Two types  Stream socket : reliable two-way connected communication streams  Datagram socket  Socket pair  Specified the two end points that uniquely identifies each TCP connection in an internet.  4-tuple: (client IP address, client port number, server IP address, server port number)

 Some “well-known” ports:  21: ftp  23: telnet  80: http  161: snmp  Check out /etc/services file for complete list of ports and services associated to those ports  Port numbers between are reserved  User level process/services generally use port number value >= 1024

 UDP  Connectionless and unreliable service.  There isn’t an initial handshaking phase.  Doesn’t have a pipe.  transmitted data may be received out of order, or lost  Socket Programming with UDP  No need for a welcoming socket.  No streams are attached to the sockets.  the sending hosts creates “packets” by attaching the IP destination address and port number to each batch of bytes.  The receiving process must unravel to received packet to obtain the packet’s information bytes.

 SOCK_STREAM  TCP  connection oriented, bidirectional  reliable, in-order delivery SOCK_DGRAM  UDP  no connection  unreliable delivery, no guarantee on the order  can send/receive

socket() connect()‏ send() recv() close()... socket() bind() listen() accept() recv() send() close() wait for connection request from next client Client Server

 The package java.net provides support for sockets programming (and more).  Typically you import everything defined in this package with: import java.net.*; Java Socket Programming 16

 The Java API provides datagram communication by means of two classes:  DatagramPacket - Datagram packets are used to implement a connectionless packet delivery service.  DatagramSocket - A datagram socket is the sending or receiving point for a packet delivery service.  DatagramPacket:  getData - Returns the data buffer.  getPort - Returns the port number on the remote host.  getAddress - Returns the IP address.

 DatagramSocket:  send - Sends a datagram packet from this socket.  receive - Receives a datagram packet from this socket.  setSoTimeout - Enable/disable the specified timeout, in milliseconds.  connect - Connects the socket to a remote address for this socket.

InetAddress Socket ServerSocket DatagramSocket DatagramPacket Java Socket Programming 19

 DatagramSocket class  DatagramPacket class needed to specify the payload  incoming or outgoing Java Socket Programming 20

 In Package java.net  java.net.DatagramSocket  A socket for sending and receiving datagram packets.  Constructor and Methods  DatagramSocket(int port): Constructs a datagram socket and binds it to the specified port on the local host machine.  void receive( DatagramPacket p)  void send( DatagramPacket p)  void close() Java Socket Programming 21

DatagramSocket(); DatagramSocket(int port); DatagramSocket(int port, InetAddress a); All can throw SocketException or SecurityException Java Socket Programming 22

void connect(InetAddress, int port); void close(); void receive(DatagramPacket p); void send(DatagramPacket p); Java Socket Programming 23

 Contain the payload  (a byte array  Can also be used to specify the destination address  when not using connected mode UDP Java Socket Programming 24

For receiving: DatagramPacket( byte[] buf, int len); For sending: DatagramPacket( byte[] buf, int len InetAddress a, int port); Java Socket Programming 25

 Corresponds to active TCP sockets only!  client sockets  socket returned by accept();  Passive sockets are supported by a different class:  ServerSocket  UDP sockets are supported by  DatagramSocket Java Socket Programming 26

CPSC Application Layer 27 Client process client TCP socket Stream  A stream is a sequence of characters that flow into or out of a process.  An input stream is attached to some input source for the process, e.g., keyboard or socket.  An output stream is attached to an output source, e.g., monitor or socket.

close clientSocket Server (running on hostid) read reply from clientSocket create socket, clientSocket = DatagramSocket() Client Create, address (hostid, port=x, send datagram request using clientSocket create socket, port=x, for incoming request: serverSocket = DatagramSocket() read request from serverSocket write reply to serverSocket specifying client host address, port umber

CPSC Application Layer 29 import java.io.*; import java.net.*; class TCPClient { public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence; BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); Socket clientSocket = new Socket("hostname", 6789); DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream()); Create input stream Create client socket, connect to server Create output stream attached to socket

30  A server (program) runs on a specific computer and has a socket that is bound to a specific port. The server waits and listens to the socket for a client to make a connection request. server Client Connection request port

31  If everything goes well, the server accepts the connection. Upon acceptance, the server gets a new socket bounds to a different port. It needs a new socket (consequently a different port number) so that it can continue to listen to the original socket for connection requests while serving the connected client. server Client Connection port

 socket (): Create a socket  bind(): bind a socket to a local IP address and port #  listen(): passively waiting for connections  connect(): initiating connection to another socket  accept(): accept a new connection  Write(): write data to a socket  Read(): read data from a socket  sendto(): send a datagram to another UDP socket  recvfrom(): read a datagram from a UDP socket  close(): close a socket (tear down the connection)

 In Package java.net  java.net.DatagramSocket  A socket for sending and receiving datagram packets.  Constructor and Methods  DatagramSocket(int port): Constructs a datagram socket and binds it to the specified port on the local host machine.  void receive( DatagramPacket p)  void send( DatagramPacket p)  void close()

import java.io.*; import java.net.*; 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();

DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876); clientSocket.send(sendPacket); DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); clientSocket.receive(receivePacket); String modifiedSentence = new String(receivePacket.getData()); System.out.println("FROM SERVER:" + modifiedSentence); clientSocket.close(); } }

import java.io.*; import java.net.*; 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) { DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length); serverSocket.receive(receivePacket); String sentence = new String(receivePacket.getData());

InetAddress IPAddress = receivePacket.getAddress(); int port = receivePacket.getPort(); String capitalizedSentence = sentence.toUpperCase(); sendData = capitalizedSentence.getBytes(); DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, port); serverSocket.send(sendPacket); }

38 1. Open the Server Socket: ServerSocket server; DataOutputStream os; DataInputStream is; server = new ServerSocket( PORT ); 2. Wait for the Client Request: Socket client = server.accept(); 3. Create I/O streams for communicating to the client is = new DataInputStream( client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 4. Perform communication with client Receive from client: String line = is.readLine(); Send to client: os.writeBytes("Hello\n"); 5. Close sockets: client.close(); For multithreaded server: while(true) { i. wait for client requests (step 2 above) ii. create a thread with “ client ” socket as parameter (the thread creates streams (as in step (3) and does communication as stated in (4). Remove thread once service is provided. }

39 1. Create a Socket Object: client = new Socket( server, port_id ); 2. Create I/O streams for communicating with the server. is = new DataInputStream(client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 3. Perform I/O or communication with the server:  Receive data from the server: String line = is.readLine();  Send data to the server: os.writeBytes("Hello\n"); 4. Close the socket when done: client.close();

40 // SimpleServer.java: a simple server program import java.net.*; import java.io.*; public class SimpleServer { public static void main(String args[]) throws IOException { // Register service on port 1234 ServerSocket s = new ServerSocket(1234); Socket s1=s.accept(); // Wait and accept a connection // Get a communication stream associated with the socket OutputStream s1out = s1.getOutputStream(); DataOutputStream dos = new DataOutputStream (s1out); // Send a string! dos.writeUTF("Hi there"); // Close the connection, but not the server socket dos.close(); s1out.close(); s1.close(); }

41 // SimpleClient.java: a simple client program import java.net.*; import java.io.*; public class SimpleClient { public static void main(String args[]) throws IOException { // Open your connection to a server, at port 1234 Socket s1 = new Socket("mundroo.cs.mu.oz.au",1234); // Get an input file handle from the socket and read the input InputStream s1In = s1.getInputStream(); DataInputStream dis = new DataInputStream(s1In); String st = new String (dis.readUTF()); System.out.println(st); // When done, just close the connection and exit dis.close(); s1In.close(); s1.close(); }

42  Run Server on mundroo.cs.mu.oz.au  java SimpleServer &  Run Client on any machine (including mundroo):  java SimpleClient Hi there  If you run client when server is not up:  sockets [1:147] java SimpleClient Exception in thread "main" java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:320) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:133) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:120) at java.net.Socket. (Socket.java:273) at java.net.Socket. (Socket.java:100) at SimpleClient.main(SimpleClient.java:6)

43  A socket is an endpoint of a two-way communication link between two programs running on the network.  A socket is bound to a port number so that the TCP layer can identify the application that data destined to be sent.  Java’s.net package provides two classes:  Socket – for implementing a client  ServerSocket – for implementing a server

44 1. Open the Server Socket: ServerSocket server; DataOutputStream os; DataInputStream is; server = new ServerSocket( PORT ); 2. Wait for the Client Request: Socket client = server.accept(); 3. Create I/O streams for communicating to the client is = new DataInputStream( client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 4. Perform communication with client Receive from client: String line = is.readLine(); Send to client: os.writeBytes("Hello\n"); 5. Close sockets: client.close(); For multithreaded server: while(true) { i. wait for client requests (step 2 above) ii. create a thread with “ client ” socket as parameter (the thread creates streams (as in step (3) and does communication as stated in (4). Remove thread once service is provided. }

45 1. Create a Socket Object: client = new Socket( server, port_id ); 2. Create I/O streams for communicating with the server. is = new DataInputStream(client.getInputStream() ); os = new DataOutputStream( client.getOutputStream() ); 3. Perform I/O or communication with the server:  Receive data from the server: String line = is.readLine();  Send data to the server: os.writeBytes("Hello\n"); 4. Close the socket when done: client.close();

46 // SimpleServer.java: a simple server program import java.net.*; import java.io.*; public class SimpleServer { public static void main(String args[]) throws IOException { // Register service on port 1234 ServerSocket s = new ServerSocket(1234); Socket s1=s.accept(); // Wait and accept a connection // Get a communication stream associated with the socket OutputStream s1out = s1.getOutputStream(); DataOutputStream dos = new DataOutputStream (s1out); // Send a string! dos.writeUTF("Hi there"); // Close the connection, but not the server socket dos.close(); s1out.close(); s1.close(); }

47 // SimpleClient.java: a simple client program import java.net.*; import java.io.*; public class SimpleClient { public static void main(String args[]) throws IOException { // Open your connection to a server, at port 1234 Socket s1 = new Socket("mundroo.cs.mu.oz.au",1234); // Get an input file handle from the socket and read the input InputStream s1In = s1.getInputStream(); DataInputStream dis = new DataInputStream(s1In); String st = new String (dis.readUTF()); System.out.println(st); // When done, just close the connection and exit dis.close(); s1In.close(); s1.close(); }

48  Run Server on mundroo.cs.mu.oz.au  java SimpleServer &  Run Client on any machine (including mundroo):  java SimpleClient Hi there  If you run client when server is not up:  sockets [1:147] java SimpleClient Exception in thread "main" java.net.ConnectException: Connection refused at java.net.PlainSocketImpl.socketConnect(Native Method) at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:320) at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:133) at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:120) at java.net.Socket. (Socket.java:273) at java.net.Socket. (Socket.java:100) at SimpleClient.main(SimpleClient.java:6)

49  TCP (Transport Control Protocol) is a connection- oriented protocol that provides a reliable flow of data between two computers.  Example applications:  HTTP  FTP  Telnet  TCP/IP Stack Application (http,ftp,telnet,…) Transport (TCP, UDP,..) Network (IP,..) Link (device driver,..)