1 / 24

Block 10: Datagram

Learn about Datagram sockets, data exchange, DatagramSocket API, key methods, constructors, and program flow in client-server programming with examples in Java this week.

dbone
Télécharger la présentation

Block 10: Datagram

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Block 10: Datagram Jin Sa Client-server Programming

  2. Datagram and examples this week • Next week, move multicast from next term. • Last week of the term: no CSP lecture on 20 Dec, but available in 2P18 • Assignment JOptionPane not considered GUI implementation for this assignment Client-server Programming

  3. Datagram sockets and stream sockets • A socket programming construct can use either the UDP or TCP protocol. • Sockets that use UDP for transport are known as datagram sockets, while sockets that use TCP are termed stream sockets. Client-server Programming

  4. Datagram socket • The datagram socket API supports the exchange of discrete units of data • Datagram sockets usually are used to support connectionless communication • No need to establish connection • But each time we need to include the receiver’s address Client-server Programming

  5. The Java Datagram Socket API In Java, two classes are provided for the datagram socket API: • the DatagramSocketclass for the sockets. • the DatagramPacket class for the datagram exchanged. Client-server Programming

  6. The Data Structures in the sender and receiver programs for datagram socket Client-server Programming

  7. The Java Datagram Socket API To send a datagram to another process, a process: • creates a DatagramPacket object that represents the datagram itself. This object carries • the payload data as a reference to a byte array, • the destination address (the host ID and port number to which the receiver’s socket is bound. • Creates a DatagramSocket, and issues a call to the send method in the DatagramSocketobject, specifying a reference to the DatagramPacket object as an argument Client-server Programming

  8. The Java Datagram Socket API • In the receiving process, a DatagramSocket object must also be instantiated and bound to a local port. (The port number in the datagram packet of the sender must agree with this port number. ) • To receive datagrams sent to the socket, the process creates a datagramPacket object which references a byte array • Calls the receivemethod in the DatagramSocket object, specifying as argument a reference to the DatagramPacket object. Client-server Programming

  9. Key Methods and Constructors for Datagram -- DatagramSocket • DatagramSocket() constructor, used if no need to receive datagram • DatagramSocket(int port) constructor, used if need to receive packet. The port number can then be specified in the datagram packet sent by the other process. • void close() to close the datagram socket Client-server Programming

  10. Key Methods and Constructors for Datagram-- DatagramSocket • void send(DatagramPacket p) to send the datagram packet pointed by p using this datagram socket • void receive(DatagramPacket p) to receive a datagram packet, p will refer to the packet • void setSoTimeout(int timeout) Sets a timeout period for the blocking receive operations Client-server Programming

  11. Key Methods and Constructors for Datagram -- DatagramPacket • DatagramPacket(byte[] buf,int l) constructor for receiving packets of length l, data received will be stored in buf • DatagramPacket(byte[] buf,int l,InetAddress ipAddress, int port) constructor for sending packets to the socket bound to the port number on the receiving host. Client-server Programming

  12. The program flow in the sender and receiver programs Receiver program Sender program Create a datagram socket Place data in a byte array Create a datagram packet, specifying the data array and the receiver’s address (IP address and port same as in the receiver’s port number) Invoke the send method of the socket with a reference to the datagram packet Create a datagram socket and bind it to a local port number Create a byte array for receiving the data Create a datagram packet, specifying the data array Invoke the receive method of the socket with a reference to the datagram packet Extract the data from the byte array Client-server Programming

  13. Setting timeout • To avoid indefinite blocking, a timeout can be set with a socket object. • Once set, the timeout will be in effect for all blocking operations. Client-server Programming

  14. Example • Sender – version 1 • Create a datagram socket • Put the message “Hello!” in a byte array • Create a datagram packet with the receiver’s address and port number, and the byte array • Send datagram in the packet through the datagram socket • Receiver – version 1 • Create a datagram socket bound to a port (e.g.12345) • Create a datagram packet includes a reference to a byte array • Receive a data packet through the datagram socket • On E:clientserverprogramming0708 Client-server Programming

  15. Sender – version 1 InetAddress receiverHost = InetAddress.getByName("localhost"); int receiverPort = 12345; String message = "hello"; DatagramSocket mySocket = new DatagramSocket(); byte[ ] buffer = message.getBytes( ); DatagramPacket datagram = new DatagramPacket(buffer, buffer.length, receiverHost, receiverPort); mySocket.send(datagram); mySocket.close( ); Client-server Programming

  16. Receiver – version 1 final int MAX_LEN = 10; DatagramSocket mySocket = new DatagramSocket(port); byte[ ] buffer = new byte[MAX_LEN]; DatagramPacket datagram = new DatagramPacket(buffer, MAX_LEN); mySocket.setSoTimeout(5000); mySocket.receive(datagram); String message = new String(buffer); System.out.println(message); mySocket.close( ); Client-server Programming

  17. In class exercises • Study the two programs: Sender.java and Receiver.java (send is non blocking, and receive is blocking) • Explain what happens when you run Receiver first and then Sender (see slide 18) • Explain what happens when you run Sender first and then Receiver (see slide 19) • Explain what happens when you run Receiver twice without running Sender. • Explain the effect of setting a timeout. • Explain what happens when you replace the message “hello!” with “hello, how are you?” Client-server Programming

  18. Client-server Programming

  19. Client-server Programming

  20. Issues to remember • Sockets normally provide non-blocking send and blocking receive • The method receive blocks until a datagram packet is received as seen in Receiver, unless it sets a time out period. • Synchronisation of the events, e.g. send before receive or receive before send • If infinitely blocked, use timeout, length of the timeout period • Size of the buffer for holding the data Client-server Programming

  21. More datagram APIs DatagramPacket datagram = new DatagramPacket(buffer, MAX_LEN) datagram.getAddress(); //returns address of datagram packet sender datagram.getPort(); //returns port of sender datagram.getLength(); //returns length of packet Client-server Programming

  22. Example • Sender – version 2 • Create a datagram socket • Put the message “Hello!” in a byte array • Create a datagram packet with the receiver’s address and port number, and the byte array • Send datagram in the packet through the datagram socket • Receive a reply from the Receiver • Receiver – version 2 • Create a datagram socket bound to a port (12345) • Create a datagram packet includes a reference to a byte array • Receive a datagram packet through the datagram socket • Get the sender’s address and port number from the datagram packet • Send a reply to the Sender using the address and the port number obtained from the datagram packet • On E:clientserverprogramming0708 Client-server Programming

  23. Sender – version 2 … DatagramSocket mySocket = new DatagramSocket(); byte[ ] buffer = message.getBytes( ); DatagramPacket datagram = new DatagramPacket(buffer, buffer.length, receiverHost, receiverPort); mySocket.send(datagram); //Now waiting for acknowledgement from receiver."); mySocket.receive(datagram); String ack=new String(buffer); System.out.println("The receiver's reply is; "+ack); mySocket.close( ); Client-server Programming

  24. Receiver – version 2 DatagramPacket datagram = new DatagramPacket(buffer, MAX_LEN); mySocket.receive(datagram); String message = new String(buffer); System.out.println(message); //send a reply back to the sender Scanner in=new Scanner(System.in); System.out.println("Enter your name to send to the sender:"); String name=in.nextLine();//delay so that sender is ready buffer=name.getBytes(); DatagramPacket datagram2= new DatagramPacket(buffer,buffer.length, datagram.getAddress(),datagram.getPort()); mySocket.send(datagram2); mySocket.close( ); Client-server Programming

More Related