Inter-Process Communication (IPC): Network Programming using TCP Java

Inter-Process Communication (IPC): Network Programming using TCP Java Sockets Dr. Rajkumar Buyya Cloud Computing and Distributed Systems (CLOUDS) Laboratory School of Computing and Information Systems The University of Melbourne, Australia http://www.buyya.com 1

Agenda Introduction Networking Basics Understanding Ports and Sockets Java Sockets Implementing a Server Implementing a Client Sample Examples Conclusions 2

Introduction Internet and WWW have emerged as global ubiquitous media for communication and are changing the way we conduct science, engineering, and commerce They are also changing the way we learn, live, enjoy, communicate, interact, engage, work, etc. It appears like the modern life activities are getting completely drive by the Internet 3

Internet Applications Serving Local and Remote Users PC client Internet Server Local Area Network PDA 4

Increasing Demand for Internet Applications To take advantage of opportunities presented by the Internet, businesses are continuously seeking new and innovative ways and means for offering their services via the Internet. This created a huge demand for software designers with skills to create new Internet-enabled applications or migrate existing/legacy applications to the Internet platform. Object-oriented Java technologies—Sockets, threads, RMI, clustering, Web services—have emerged as leading solutions for creating portable, efficient, and maintainable large and complex Internet applications. 5

Elements of Client-Server Computing/Communication a client, a server, and network ue req st result network client server Processes follow protocols that define a set of rules that must be observed by participants: How the data exchange is encoded? How events (sending, receiving) are synchronized (ordered) so that participants can send and receive data in a coordinated manner? In face-to-face communication, humans beings follow unspoken protocols based on eye contact, body language, gesture. 6

Networking Basics Physical/Link Layer Internet/Network Layer Functionalities for transmission of signals representing a stream of data from one computer to another IP (Internet Protocols) – a packet of data to be addressed to a remote computer and delivered Transport Layer Functionalities for delivering data packets to a specific process on a remote computer TCP (Transmission Control Protocol) UDP (User Datagram Protocol) Programming Interface: Sockets Applications Layer Message exchange between standard or user applications: TCP/IP Stack Application (http,ftp,telnet, ) Transport (TCP, UDP,.) Internet/Network (IP,.) Physical/Link (device driver,.) HTTP, FTP, Telnet, Skype, 7

Networking Basics TCP (Transmission Control Protocol) is a connectionoriented communication protocol that provides a reliable flow of data between two computers. Analogy: Speaking on Phone Example applications: HTTP, FTP, Telnet Skype uses TCP for call signalling, and both UDP and TCP for transporting media traffic. TCP/IP Stack Application (http,ftp,telnet, ) Transport (TCP, UDP,.) Internet/Network (IP,.) Physical/Link (device driver,.) 8

Networking Basics UDP (User Datagram Protocol) is a connectionless communication protocol that sends independent packets of data, called datagrams, from one computer to another with no guarantees about arrival or order of arrival Similar to sending multiple emails/letters to friends, each containing part of a message. Example applications: Clock server Ping Live streaming (events/sports broadcasting) TCP/IP Stack Application (http,ftp,telnet, ) Transport (TCP, UDP,.) Network (IP,.) Link (device driver,.) 9

TCP Vs UDP Communication A A B Connection-Oriented Communication B Connectionless Communication 10

Understanding Ports The TCP and UDP protocols use ports to map incoming data to a particular process running on a computer. server P o r t app app app app port port port port TCP or UDP Data TCP Client Packet port# data 11

Understanding Ports Port is represented by a positive (16-bit) integer value Some ports have been reserved to support common/well known services: ftp 21/tcp telnet 23/tcp smtp 25/tcp http 80/tcp login 513/tcp https://en.wikipedia.org/wiki/List of TCP and UDP port numbers User-level processes/services generally use port number value 1024 12

Sockets Sockets provide an interface for programming networks at the transport layer Network communication using Sockets is very much similar to performing file I/O In fact, socket handle is treated like file handle. The streams used in file I/O operation are also applicable to socket-based I/O Socket-based communication is programming language independent. That means, a socket program written in Java language can communicate with a program written in Java or non-Java socket programs. 13

Socket Communication 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. port server Connection request Client 14

Socket Communication 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. port port server Connection port Client 15

Sockets and Java Socket Classes 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 16

Java Sockets Server ServerSocket(1234) Output/write stream Client Input/read stream Socket(“128.250.22.134”, 1234) It can be host name like “clouds.cis.unimelb.edu.au” 17

Implementing a Server 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. } 18

Implementing a Client 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(); 19

A simple server (simplified code) // 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(); } } 20

A simple client (simplified code) // 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(“clouds.cis.unimelb.edu.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(); } } 21

Run Run Server on mundroo.cs.mu.oz.au Run Client on any machine (including mundroo): [raj@mundroo] java SimpleServer & [raj@mundroo] java SimpleClient Hi there If you run client when server is not up: [raj@mundroo] 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. init (Socket.java:273) at java.net.Socket. init (Socket.java:100) at SimpleClient.main(SimpleClient.java:6) 22

Socket Exceptions try { Socket client new Socket(host, port); handleConnection(client); } catch(UnknownHostException uhe) { System.out.println("Unknown host: " host); uhe.printStackTrace(); } catch(IOException ioe) { System.out.println("IOException: " ioe); ioe.printStackTrace(); } 23

ServerSocket & Exceptions public ServerSocket(int port) throws IOException Creates a server socket on a specified port A port of 0 creates a socket on any free port. You can use getLocalPort() to identify the (assigned) port on which this socket is listening The maximum queue length for incoming connection indications (a request to connect) is set to 50. If a connection indication arrives when the queue is full, the connection is refused Throws: IOException - if an I/O error occurs when opening the socket SecurityException - if a security manager exists and its checkListen method doesn't allow the operation 24

Server in Loop: Always up // SimpleServerLoop.java: a simple server program that runs forever in a single thead import java.net.*; import java.io.*; public class SimpleServerLoop { public static void main(String args[]) throws IOException { // Register service on port 1234 ServerSocket s new ServerSocket(1234); while(true) { 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(); } } } 25

Java API for UDP Programming Java API provides datagram communication by means of two classes DatagramPacket Msg length Host serverPort DatagramSocket 26

UDP Client: Sends a Message and Gets reply import java.net.*; import java.io.*; public class UDPClient { public static void main(String args[]){ // args give message contents and server hostname // "Usage: java UDPClient message Host name Port number " DatagramSocket aSocket null; try { aSocket new DatagramSocket(); byte [] m args[0].getBytes(); InetAddress aHost InetAddress.getByName(args[1]); int serverPort 6789; // Or Integer.valueOf(args[2]).intValue() if use Port number args[2] DatagramPacket request new DatagramPacket(m, args[0].length(), aHost, serverPort); aSocket.send(request); byte[] buffer new byte[1000]; DatagramPacket reply new DatagramPacket(buffer, buffer.length); aSocket.receive(reply); System.out.println("Reply: " new String(reply.getData())); } catch (SocketException e){System.out.println("Socket: " e.getMessage());} catch (IOException e){System.out.println("IO: " e.getMessage());} finally { if(aSocket ! null) aSocket.close(); } } } 27

UDP Sever: repeatedly received a request and sends it back to the client import java.net.*; import java.io.*; public class UDPServer{ public static void main(String args[]){ DatagramSocket aSocket null; try{ aSocket new DatagramSocket(6789); // fixed port number byte[] buffer new byte[1000]; while(true){ DatagramPacket request new DatagramPacket(buffer, buffer.length); aSocket.receive(request); DatagramPacket reply new DatagramPacket(request.getData(), request.getLength(), request.getAddress(), request.getPort()); aSocket.send(reply); } }catch (SocketException e){System.out.println("Socket: " e.getMessage());} catch (IOException e) {System.out.println("IO: " e.getMessage());} finally {if(aSocket ! null) aSocket.close();} } } 28

Multithreaded Server: For Serving Multiple Clients Concurrently Client Process 2 Server Process Server threads Client Process 1 29

Summary Programming client/server applications in Java is fun and challenging Programming socket programming in Java is much easier than doing it in other languages such as C TCP for Connection-oriented communication, more reliable, flow control UDP for connection-less communication Keywords: Clients, servers, TCP/IP, port number, sockets, Java sockets 30

References Chapter 13: Socket Programming R. Buyya, S. Selvi, X. Chu, “Object Oriented Programming with Java: Essentials and Applications”, McGraw Hill, New Delhi, India, 2009. Sample chapters at book website: http://www.buyya.com/java/ 31