Networking in Java

1. Networking in Java Representation and Management of Data on the Internet

2. Client-Server Model Port 80 Client application 132.65.32.29 Server application 64.208.34.100 www.google.com Client application 132.68.7.11

3. Clients • Client - initiates connection • retrieves data • displays data • responds to user input • requests more data • Examples: • Web Browser • Chat Program • PC accessing files

4. Servers • Server - responds to connection • receives request for data • looks it up • delivers it • Examples: • Web Server • Database Server • Domain Name Server

5. Networking Basics • Communication layers: Application (HTTP, FTP, Telnet) Our Applications Transport (TCP, UDF) Network (IP) Link (device, driver,…)

6. Application Layer DATA Transport Layer HEADER DATA Internet Layer HEADER HEADER DATA Network Layer HEADER HEADER HEADER DATA Internet Architecture Model

7. TCP and UDP • TCP (Transmission Control Protocol) • connection-based protocol • provides a reliable flow of data between two computers • UDP (User Datagram Protocol) • a protocol that sends independent packets of data, called datagrams, from one computer to another • arrival of datagrams is not gaurantees • UDP is not connection-based like TCP

8. How to Choose TCP or UDP • Use TCP when reliability is critical: • HTTP • FTP • Telnet • Use UDP when reliability is not critical: • Ping • Clock • Audio and Video transmission • NFS – Network File System

9. Host and Port • Destination in the Internet is identified by host + port • a 32 bits IP-address • a 16 bits port • Q: Why don’t we specify the port in a Web browser? • Ports 0-1023 are restricted • Do not use them

10. Destination of a Connection • Q: How does an HTTP request ‘knows’ where is the server to which it is intended? • Q: How does an HTTP response ‘knows’ where is the server to which it is intended? • Q: There can be more then one application (ever some servers) running on the same host, how do we know to which application a message is intended?

11. A Connection to Many Applications • Q: There can be many applications that are on the same time connected to the same host, (for example, many browser and one search engine) How do we send the right transmission to each client? • A: By adding the IP address of the client and the port of the client to the IP packets

12. mail client web browser Known Ports Client Application • Some known ports are • 20, 21: FTP • 23: telnet • 25: SMTP • 43: whois • 80: HTTP • 119: NNTP 21 23 25 43 80 119

13. Internet Addresses • InetAddress – a final class that represents Internet Protocol (IP) addresses and the names of hosts • Getting the InetAdddress • getLocalHost • Returns the local host • getByName(String host) • For the given host name one of its IP addresses is returned • getAllByName(String host) • For a given host name all its IP addresses are returned

14. Methods of InetAddress • getHostAddress • Returns the IP address of the host • The address is in the form “%d.%d.%d.%d” • getHostName • Returns the name of the host

15. Protocol Host Name Port Number File Name Reference Working with URLs • URL (Uniform Resource Locator) - a reference (an address) to a resource on the Internet http://www.cs.huji.ac.il:80/~dbi/main.html#notes

16. Creating URLs • The class URL is defined in the package java.net • Basic constructor: URL w3c = new URL("http://www.w3.org/"); • Relative links: • Are created from baseURL + relativeURL URL amaya = new URL(w3c, “Amaya/Amaya.html”); URL jigsaw = new URL(w3c, “Jigsaw/#Getting”);

17. Creating URLs (cont.) • The following two are equivalent: URL dbiNotes = new URL(“http://www.cs.huji.ac.il:80/” + ”~dbi/main.html#notes”); URL dbiNotes = new URL(“http”, “www.cs.huji.ac.il”, 80, “~dbi/main.html#notes”); • Construction of URLs can throw MalformedURLException

18. Why Do We Need the URL Class? • The main usage of URL is for parsing URLs • getting the protocol • getting the host • getting the port • getting the file name • getting the reference • An example of parsing a URL

19. Running the Example

20. Running the Example Java URLInfo http://www.cs.huji.ac.il Java URLInfo http://www.cs.huji.ac.il:80/~dbi/main.html#notes Protocol: http Host: www.cs.huji.ac.il File name: Port: -1 Reference: null Protocol: http Host: www.cs.huji.ac.il File name: /~dbi/main.html Port: 80 Reference: notes

21. openStream BufferedReader InputStreamReader readLine Page Content Reading From A URL url

22. Reading From a URL • Example of reading from a given URL: UrlReader.java • For reading a URL using a proxy, we do the following: Java –Dhttp.proxyHost=wwwproxy.cs.huji.ac.il –Dhttp.proxyPort=8080 UrlReader url

23. Java UrlReader url The content of the file Reading …

24. openConnection URLConnection getOutputStream println getInputStream PrintWriter Page InputStreamReader BufferedReader readLine Connecting to A URL url

25. Interacting with a CGI script • Create a URL • Open a connection to the URL • Set output capability on the URLConnection • Get an output stream from the connection • This output stream is connected to the standard input stream of the cgi-bin script on the server • Write to the output stream • Close the output stream

26. HTTP/1.1 200 OK <HTML> … </HTML> HTTP connections • You can create a connection to an HTTP server with an object HttpURLConnection • This object extends the URLConnection object • getResponseCode • getResponseMessage • setRequestMethod • Look in the Java API

27. URLEncoder • contains a utility method encode for converting a string into an encoded format • To convert a string, each character is examined in turn: • The ASCII characters 'a' – 'z', 'A' – 'Z', '0' – '9', ".", "-", "*", "_" remain the same • Space is converted into a plus sign '+' • All other characters are converted into the 3-character string "%xy", where xy is the two-digit hexadecimal representation of the lower 8-bits of the character

28. URL Connection Example • The next example connects to a CGI script on www.walla.co.il – a search tool is given a word to search SearchWalla

29. Sockets • Communication is between sockets • A socket is one end-point of a two-way communication link between two programs running on the network • A socket has a binding to a port to which it listens • A socket implementation gives us the ability to read from it and write to it as if it is a file

30. In Sockets • A socket ‘knows’ the followings • The port number of the remote host • The host name (InetAddress) of the remote host • The local port to which it is bound • The local address of its local host

31. Sockets • The server has a socket that listen to a known port, e.g., Web server and port 80 • The server waits (listening to the socket) till a client requests a connection • A client requests a connection on the known host and port of the server • Q: What should the server do so that it can serve other clients as well?

32. Client Requests for a Connection Port 8090 Port: 8090 LocalPort: 80 Localhost: www.google.com Remotehost: 132.65.32.29 Port 80 Client application 132.65.32.29 Port: 8888 LocalPort: 80 Localhost: www.google.com Remotehost: 132.68.7.11 Port 8888 Client application Server application 132.68.7.11 64.208.34.100 www.google.com

33. Socket • Class Socket – implements the client side of the connection • Class ServerSocket – implements the server side of the connection

34. host Socket port getInputStream BufferedReader InputStreamReader readLine Page Content Using a Socket

35. Using a Socket // Constructors (partial list) public Socket() public Socket(InetAddress address, int port); public Socket(String host, int port); // Methods (partial list) public void close(); public InetAddress getInetAddress(); public int getLocalPort(); public InputStream getInputStream(); public OutputStream getOutputStream(); public int getPort(); public String toString();

36. Using a Socket (client) • A client: • Opens a socket (with a binding to which port?) • Opens an input stream and output stream to the socket • Reads from and write to the stream according to the client’s protocol • Closes the streams • Closes the socket

37. Using a Socket (cont.) • A server: • Open a socket • Open an input stream and output stream to the socket • Read from and write to the stream according to the server's protocol • Close the streams • Close the socket

38. A Client Example • The following is a client that connects to a Time Server (port 13) and returns the curret time TimeClient

39. java TimeClient Tue Mar 13 12:42:09 2001 Running the TimeClient

40. The size or requests queue with default of 50 requests What happens when a running program reaches accept()? ServerSocket // Constructors (partial list) public ServerSocket(int port); public ServerSocket(int port, int count); // Methods (partial list) public Socket accept(); public void close(); public InetAddress getInetAddress(); public int getLocalPort(); public String toString(); Why don’t we have getPort in addition to getLocalPort?

41. A Server Example • The following is a time server that returns the time: TimeServer • Note: When the ServerSocket constructor is given port number 0, a random free port is chosen

42. More on Server Socket • A ServerSocket waits for requests to come in over the network • It performs some operation based on that request, and then possibly returns a result to the requester • The actual work of the ServerSocket is performed by an instance of the SocketImpl class • The abstract class SocketImpl is a common superclass of all classes that actually implement sockets • It is used to create both client and server sockets

44. Server side import java.net.*; import java.io.*; // A server that says 'hello' class HelloServer { public static void main(String[] args) { int port = Integer.parseInt(args[0]); ServerSocket server = null; try { server = new ServerSocket(port); } catch (IOException ioe) { System.err.println("Couldn't run"+ "server on port "+port); return; }

45. Server side while(true) { try { Socket connection = server.accept(); BufferedReader reader = new BufferedReader( new InputStreamReader( connection.getInputStream())); PrintWriter writer = new PrintWriter( new OutputStreamWriter( connection.getOutputStream())); String clientName = reader.readLine(); writer.println("Hello "+clientName); writer.flush(); } catch (IOException ioe1) {} }

46. Client side import java.net.*; import java.io.*; // A client of an HelloServer class HelloClient { public static void main(String[] args) { String hostname = args[0]; int port = Integer.parseInt(args[1]); Socket connection = null; try { connection = new Socket(hostname, port); } catch (IOException ioe) { System.err.println("Connection failed"); return; }

47. Client side try { BufferedReader reader = new BufferedReader( new InputStreamReader( connection.getInputStream())); PrintWriter writer = new PrintWriter( new OutputStreamWriter( connection.getOutputStream())); writer.println(args[2]); // client name String reply = reader.readLine(); System.out.println("Server reply: "+reply); writer.flush(); } catch (IOException ioe1) { } }

48. Datagrams • Datagram packets are used to implement a connectionless, packet based, delivery service • Each message is routed from one machine to another based solely on information contained within that packet • Multiple packets sent from one machine to another might be routed differently, and might arrive in any order • Packets may be lost or duplicated during transit • The class DatagramPacket represents a datagram in Java

49. DatagramPacket Class //Constructors public DatagramPacket(byte ibuf[], int ilength); public DatagramPacket( byte ibuf[], int ilength, InetAddress iaddr, int iport); // Methods public synchronized InetAddress getAddress(); public synchronized int getPort(); public synchornized byte[] getData(); int getLength(); void setAddress(InetAddress iaddr); void setPort(int iport); void setData(byte ibuf[]); void setLength(int ilength);

50. DatagramSocket • This class represents a socket for sending and receiving datagram packets • Addressing information for outgoing packets is contained in the packet header • A socket that is used to read incoming packets must be bound to an address (sockets that are used for sending must be bound as well, but in most cases it is done automatically) • There is no special datagram server socket class • Since packets can be lost, the ability to set timeouts is important