TCP socket application

1. TCP socket application Architecture of Client-Server Applications Java Socket Programming Client Application Server Application norly@ftsm.ukm.my

2. Evolution of Application Architectures norly@ftsm.ukm.my

3. Java – is one of the earliest programming language to support 3-tier and n-tier architecture. • Java’s strength is in developing enterprisesoftware (J2EE) as it simplify developer’s job in implementing the newer application architecture – from 3-tier to n-tier to mobile. norly@ftsm.ukm.my

4. 3-tier Client-Server Application norly@ftsm.ukm.my

5. A Bug Tracking System (3-tier) norly@ftsm.ukm.my

6. Socket-based Client-Server Application : ALI BABA norly@ftsm.ukm.my

7. TCP overview • Unlike UDP which is concerned with the transmission of packets of data, TCP establishes a "virtual connection" between two machines through which streams of data may be sent. • TCP guarantees delivery and order, providing a reliable byte communication stream between client and server that supports two-way communication. norly@ftsm.ukm.my

8. Establish a virtual connection Transmit data back and forth Terminate the connection norly@ftsm.ukm.my

9. TCP uses IP (Internet Protocol) to establish the connection between machines. • This connection provides an interface that allows streams of bytes to be sent and received, and transparently converts the data into IP datagram packets. • The virtual connection between two machines is represented by a socket. norly@ftsm.ukm.my

10. What is a socket? • Original idea came from UNIX • “The network is just like a file system” • Read and write a stream of data “to the network” through socket • Stream? ( recall : using package java.io ) • A socket is bound to a port number so that the TCP layer can identify the correct application for the data norly@ftsm.ukm.my

11. A little background • Socket provides the TCP/IP communication protocol • Introduced in 1981- UNIX BSD 4.2 • Later Sun build RPC and NFS over the socket • Is supported by all OS • WinSocks for Windows 3.1 • Built into Windows 95, … and NT • For other OS – it is not new • Is the De Facto in network communication norly@ftsm.ukm.my

12. agreed port any port socket socket message client server other ports Internet address = 138.37.94.248 Internet address = 138.37.88.249 Communication between processes : using port and socket • Port: The destination of a message • Socket: The final point for processes communication • Each socket is associated with UDP or TCP norly@ftsm.ukm.my

13. Like ports in UDP, ports in TCP are also represented by a number in the range 1 - 65535. • Ports below 1024 are restricted to use by well-known services. For example, • Telnet (port 23) • SMTP (port 25) • HTTP (port 80) • POP3 (port 110) norly@ftsm.ukm.my

14. TCP vs UDP • TCP sockets are different from UDP sockets: • TCP sockets are connected to a single machine. • UDP sockets only send and receive packets of data. • TCP allows transmission of data through byte streams. They are converted into datagram packets for transmission over the network without programmer intervention. norly@ftsm.ukm.my

15. Advantages of TCP over UDP • Automatic Error Control • Data transmission is more dependable. Delivery of data is guaranteed - lost data packets are retransmitted. • By means of a timer, TCP retransmits a packet if an acknowledgement is not received from the recipient within a specified amount of time. norly@ftsm.ukm.my

16. Reliability • As packets are delivered by IP, they will frequently arrive out of order. However, each packet contains a sequence number. Using this sequence number and queuing out-of-order packets, TCP is able to pass arriving packets to the application in the correct sequence. norly@ftsm.ukm.my

17. Ease of Use • Network programmers will find programming communication via TCP sockets far simpler than via datagram packets. This is because data sent and received can be treated as a continuous stream (like I/O streams). The data need not be packaged into discrete units like UDP. norly@ftsm.ukm.my

18. Socket Operations • TCP sockets can perform a variety of operations: • Establish a connection to a remote host • Send data to a remote host • Receive data from a remote host • Close a connection norly@ftsm.ukm.my

19. There is a special type of socket that provides a service that will bind to a specific port number. Normally used only in servers, this socket can perform the following operations: • Bind to a local port • Accept incoming connections from remote hosts • Unbind from a local port norly@ftsm.ukm.my

20. TCP and the Client/Server Paradigm • In network programming, applications that use sockets are divided into clients and servers. • A client is software that initiates a connection and sends requests. • A server is software that listens for connections and processes requests. norly@ftsm.ukm.my

21. Note that in the context of UDP programming, no actual connection is established. UDP applications may both initiate and receive requests on the same socket. • In the client/server paradigm, when there is a connection between two applications, one must be a client and the other must be a server. norly@ftsm.ukm.my

22. Network Clients • Network clients initiate connections and control network transactions. • The server fulfills the requests of the client but not the other way round. • The network client speaks to the server using a network protocol. E.g an HTTP client communicates with an HTTP server using HTTP. norly@ftsm.ukm.my

23. Port numbers are used to enable clients to locate server applications. E.g. a web server uses port 80. norly@ftsm.ukm.my

24. Network Servers • The role of the network server is to bind to a specific port and to listen for new connections. • Unlike the client, the server must run continually in the hope that some client will want its services. • The server runs indefinitely. Normally, it is automatically started when the host computer of the server is started. norly@ftsm.ukm.my

25. Some servers can handle only one connection at a time, while others can handle many connections concurrently, through the use of threads. • Some protocols (e.g. HTTP/1.0) normally allow only one request per connection. Others, like POP3, support a sequence of requests. • Servers answer the client request by sending either a response or an error message. norly@ftsm.ukm.my

26. Socket Types • In Java, there are 4 main socket types: • ServerSocket • Socket • DatagramSocket • MulticastSocket • Accessible by importing java.net.*; norly@ftsm.ukm.my

27. TCP Sockets and Java • Java provide the following classes for TCP sockets: • java.net.Socket • java.net.ServerSocket • The Socket class should be used when writing client software. • The ServerSocket class should be used when writing server software. norly@ftsm.ukm.my

28. Socket Class • Socket objects represent client sockets, and is a communication channel between two TCP communications ports belonging to one or two machines. norly@ftsm.ukm.my

29. There are several constructors for the Socket class. • The easiest way to create a socket is shown below: Socket mySocket; try { mySocket = new Socket("www.aol.com", 80); } catch (Exception e) { … } norly@ftsm.ukm.my

30. Socket Constructors • From 8 constructors, 4 are commonly used: • public Socket(InetAddress address, int port) • Throws java.io.IOException, java.lang.SecurityException Creates a stream socket and connects it to the specified port number at the specified IP address. . • public Socket(InetAddress address, int port, InetAddress localAddr, int localPort) • Throws java.io.IOException, java.lang.SecurityException Creates a socket and connects it to the specified remote address on the specified remote port. • public Socket(String host, int port) • Throws java.io.IOException, java.lang.SecurityException Creates a stream socket and connects it to the specified port number on the named host. • public Socket(String host, int port, InetAddress localAddr, int localPort) • Throws java.net.UnknownHostException, java.io.IOException, java.lang.SecurityException Creates a socket and connects it to the specified remote host on the specified remote port. norly@ftsm.ukm.my

31. Reading from and Writing to TCP Sockets • In Java, once a socket is created, it is connected and ready to read/write by using the socket's input and output streams. Use the methods getInputStream() and getOutputStream() to access those streams. norly@ftsm.ukm.my

32. Socket socket; • InputStreamReader isr; • BufferedReader br; • PrintStream ps; • try { • socket = new Socket("www.aol.com",80); • isr = new InputStreamReader(socket.getInputStream()); • br = new BufferedReader(isr); • ps = new PrintStream(socket.getOutputStream()); • } catch (Exception e) { • … • } • Example: norly@ftsm.ukm.my

33. Methods of class Socket Returned stream depends on TCP flow control and error correction. • public InputStream getInputStream(); Returns an input stream for this socket. • public OutputStream getOutputStream(); Returns an output stream for this socket. • public void close(); Closes this socket. • public int getPort(); Returns a remote port associated to the socket. • public InetAddress getInetAddress(); Returns an address associated to the socket. • public int getLocalPort(); Returns a local port associated to the socket. norly@ftsm.ukm.my

34. Server Socket • Server socket is bound to a certain port of a local host • When it is successfully bound to a port, it immediately listens to any attempt of incoming connection • When a server detects an attempt of incoming connection, it accept the connection • This creates a socket which handles communication between the client and server norly@ftsm.ukm.my

35. ServerSocket Class • java.net.ServerSocket represents the serve socket • ServerSocket object is created on a local port and calls method accept() to listen to incoming connection • accept() will block until a connection is detected. Then it returns a Socket object that handles communication with a client norly@ftsm.ukm.my

36. The easiest way to create a socket to listen at a certain port is shown below: ServerSocket mySocket; try { mySocket = new ServerSocket(80); } catch (Exception e) { … } norly@ftsm.ukm.my

37. ServerSocket Constructors • Some of the other constructors: • ServerSocket(int port) • Throws java.io.IOException, java.lang.SecurityException • If port is 0, then any free port will be used. • By default, the queue size is set to 50. • ServerSocket(int port, int maxClients) • Throws java.io.IOException, java.lang.SecurityException • Allocates sufficient space to the queue to support the specified number of client sockets. norly@ftsm.ukm.my

38. Methods of class ServerSocket • public Socket accept(); • Listens for a connection to be made to this socket and accepts it. • public void close(); • Closes this socket. • public InetAddress getInetAddress(); • Returns the local address of this server socket. norly@ftsm.ukm.my

39. When a ServerSocket object is created, it attempts to bind to the port on the local host given by the port argument. • If another server socket is already listening to the port, then a java.net.BindException, a subclass of IOException, is thrown. • No more than one process or thread can listen to a particular port at a time. This includes non-Java processes or threads. • For example, if there's already an HTTP server running on port 80, you won't be able to bind to port 80. norly@ftsm.ukm.my

40. If you want your process to wait (listening) incoming connections at a specified port, ServerSocket class allow it to detect the incoming connection: ServerSocket outSock = new ServerSocket (8888); while (true) { Socket inSock = outSock.accept(); handleConnection(inSock); inSock.close(); } norly@ftsm.ukm.my

41. Accepting and Processing Requests from TCP Clients • The most important function of a server socket is to accept client sockets. Once a client socket is obtained, the server can perform all the "real work" of server programming, which involves reading from and writing to the socket to implement a network protocol. • Example: a mail server that provides access to stored messages would listen to commands and send back message contents. norly@ftsm.ukm.my

42. ServerSocket server; BufferedReader reader; PrintWriter writer; server = new ServerSocket(13); while (true) { Socket client = server.accept(); reader = new BufferedReader( new InputStreamReader( client.getInputStream())); writer = new PrintWriter( new OutputStreamWriter( client.getOutputStream())); … } • Example: norly@ftsm.ukm.my

43. ALI BABA Client-Server Apps norly@ftsm.ukm.my

44. Client Application • The example consists of two applications which is executed separately • The client app is implemented as NyietInSengClient class norly@ftsm.ukm.my

45. BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in)); String fromServer; String fromUser; while ((fromServer = in.readLine()) != null) { System.out.println("Server: " + fromServer); if (fromServer.equals("tata titi tutu")) break; fromUser = stdIn.readLine(); if (fromUser != null) { System.out.println("Client: " + fromUser); out.println(fromUser); } } out.close(); in.close(); stdIn.close(); nisSocket.close(); } } import java.io.*; import java.net.*; public class NyietInSengClient { public static void main(String[] args) throws IOException { Socket nisSocket = null; PrintWriter out = null; BufferedReader in = null; try { nisSocket = new Socket("localhost", 8888); out = new PrintWriter(nisSocket.getOutputStream(), true); in = new BufferedReader(newInputStreamReader(nisSocket.getInputStream())); } catch (UnknownHostException e) { System.err.println("Don't know about host: localhost."); System.exit(1); } catch (IOException e) { System.err.println("Couldn't get I/O for the connection to: localhost."); System.exit(1); } norly@ftsm.ukm.my

46. Server Application • Server app is implemented using 2 classes: • NyietInSengServer • NyietInSengServer contains the main() method for the server app. It listens at a port, accepts connection, read from and write to the socket. norly@ftsm.ukm.my

47. PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true); BufferedReader in = new BufferedReader( new InputStreamReader(clientSocket.getInputStream())); String inputLine, outputLine; NyietInSengProtocol nis = new NyietInSengProtocol(); outputLine = nis.processInput(null); out.println(outputLine); while ((inputLine = in.readLine()) != null) { outputLine = nis.processInput(inputLine); out.println(outputLine); if (outputLine.equals("tata titi tutu")) break; } out.close(); in.close(); clientSocket.close(); serverSocket.close(); } } import java.net.*; import java.io.*; public class NyietInSengServer { public static void main(String[] args) throws IOException { ServerSocket serverSocket = null; try { serverSocket = new ServerSocket(8888); } catch (IOException e) { System.err.println("Could not listen on port: 8888."); System.exit(1); } Socket clientSocket = null; try { clientSocket = serverSocket.accept(); } catch (IOException e) { System.err.println("Accept failed."); System.exit(1); } norly@ftsm.ukm.my

48. Server Application • NyietInSengProtocol • NyietInSengProtocol provides the jokes. It tracks the current joke, current status (SENTTOKTOK, SENTCLUE, etc) and returns jokes text based on the current status. • It implements the communication protocol agreed by the client and server. norly@ftsm.ukm.my

49. Server Application • The server app begins by creating a ServerSocket object to listen (wait) at a specified port. When selecting a port number use the one not defined for other services. NyietInSengServer waits at port 8888 because 8/8 is my birthdate (ONG) and port 8888 is not used in my computer environment try { serverSocket = new ServerSocket(8888); } catch (IOException e) { System.out.println("Could not listen on port: 8888"); System.exit(-1); } norly@ftsm.ukm.my

50. Server Application • Constructor ServerSocket throws an exception if it cannot listen to the specified port (in used). • In this kes NyietInSengServer has no other choice than to end the program. (exit). norly@ftsm.ukm.my