InetAddress Class

1
InetAddress Class
2
Demonstrating InetAddress Class
3
Network File Access
4
URL Class- Example Constructor Calls
5
Methods in URL Class
6
Demonstration of URL Class Methods
7
Java Sockets
NETWORK COMMUNICATIONS USING SOCKETS Socket
- abstraction used to facilitate TCP/IP network
communications Formally a socket consists of an
IP address and a port number. Java 1.1 supports
most of the Berkley Sockets standard. (This has
its roots in the BSD UNIX specification) PORT
NUMBERS
8
COMMON WELL-KNOWN PORTS

• Service Port Function
• HTTP 80 WebHTTPS 443 Web (secure)FTP 20,21
  File transferFTPS 989,990 File transfer
  (secure)Telnet 23 Remote loginSSH 22 Remote
  login (secure)DNS 53 Host naming
• SMTP 25 Internet mailPOP3 110 Client
  accessIMAP 143 Client access
• NNTP 119 Usenet newsgroupsNNTPS 563 Usenet
  newsgroups (secure)IRC 194 Chat
• NTP 123 Network time
• SNMP 161,162 Network managementCMIP 163,164
  Network management
• Kerberos 88 AuthenticationNetBIOS 137-139
  DOS/Windows naming
• http//www.iss.net/security_center/advice/Exploits
  /Ports/default.htm

9
Sockets for Clients

• Sockets are higher level abstraction of hosts
  native networking software
• Sockets allow a programmer to treat a network
  connection as to just another stream
• Onto which bytes can be written
• From which bytes can be read
• Sockets shield the programmer with lower level
  details of network , such as error detection,
  packet sizes, packet retransmission etc.

10
Socket Basics

• A Socket is a connection between two hosts. It
  can perform seven basic operations
• Connect to a remote machine
• Send Data
• Receive Data
• Close a Connection
• Javas Socket Class, which is used by both client
  and servers has methods corresponding to these
  four operations.

11
Socket Basics

• The remaining three operations needed by servers,
  which wait for clients to connect to them are
  implemented by ServerSocket Class.
• Bind to a port
• Listen for incoming data
• Accept connections from remote machines on the
  bound port.

12
Java Programs /Client Sockets

• Java Programs use Client Sockets in the following
  fashion
• The program creates a new socket with a
  constructor
• The Socket attempts to connect to a remote host.
• Once the connection is established, the local and
  remote hosts get input and output streams from
  the socket and use those streams to send and data
  to each other
• When transmission of data is complete, one or
  both sides close the connection.

13
The Socket Class

• The java.net.Socket Class is javas fundamental
  class for performing client-side TCP operations.
  Methods of this class can be classified into
• The Constructors
• Getting Information about the Socket
• Closing the Socket
• Setting Socket Options
• Class of Service

14
The Constructors

• Each Socket Constructor lets you specify
• The Host and Port you want to connect to.
• Hosts maybe specified as an InetAddress or a
  String.
• Ports are always specified as int values from 0
  to 65535.
• Two of the constructors lets you specify the
  local address and the local port from which data
  will be sent.

15
Constructor 1

• public Socket(String host, int port) throws
  UnknownHostException, I0Exception
• try
• Socket s new Socket(www.uwstout.edu,
  80)
• //send receive data
• catch (UnknownHostException ex)
• System.err.println(ex)
• break
• catch (IOException ex)
• System.err.println(ex)

It creates a TCP Socket to the specified port on
the specified host.
16
Low-Port Scanner using Constructor 1
Find out which of the first 1,024 ports seem to
be hosting TCP servers on a specified host

• import java.net.
• import java.io.
• public class LowPortScanner
• public static void main(String args)
• String host "localhost"
• if (args.length gt 0)
• host args0
• for (int i 1 i lt 1024 i)
• try
• Socket s new Socket(host, i)
• System.out.println(
• "There is a server on port " i " of
  " host)
• catch (UnknownHostException e)
• System.err.println(e)
• break
• catch (IOException e)

17
What can this program do?

• Helps you understand what your system is doing
• You can find possible entrance points for
  attackers.
• Someone is running a server on some port that is
  consuming bandwidth.
• Dont use this program to probe a machine that
  you dont own.

18
Constructor 2

• public Socket(InetAddress host, int port) throws
  I0Exception
• try
• InetAddress theAddress InetAddress.getByN
  ame(www.uwstout.edu)
• Socket theSocket new Socket(theAddress,
  80)
• //send receive data
• catch (UnknownHostException ex)
• System.err.println(ex)
• catch (IOException ex)
• System.err.println(ex)

• It creates a TCP Socket to the specified port on
  the specified host.
• It differs from previous constructor by using a
  InetAddress object to specify the host name
  tather than host name

19
High-Port Scanner using Constructor 2

• import java.net.
• import java.io.
• public class HighPortScanner
• public static void main(String args)
• String host "localhost"
• if (args.length gt 0)
• host args0
• try
• InetAddress theAddress InetAddress.getByNa
  me(host)
• for (int i 1024 i lt 65536 i)
• try
• Socket theSocket new
  Socket(theAddress, i)
• System.out.println("There is a server
  on port " i " of " host)
• catch (IOException ex)
• // must not be a server on this port
• // end for

Find out which of the ports at or above 1,024
seem to be hosting TCP servers.
20
Constructor 3

• public Socket(String host, int port, InetAddress
  interface, int localport) throws I0Exception,
  UnknownHostException

• It creates a TCP Socket to the specified port on
  the specified host.
• It connects to the host and port specified in the
  first two arguments.
• It connects from the local network interface and
  port specified by the last two arguments.
• If 0 is passed for the localPort argument, Java
  chooses a random available port between 1,024 to
  65535.

21
Constructor 4

• public Socket(InetAddress host, int port,
  InetAddress interface, int localport) throws
  I0Exception, UnknownHostException

• It creates a TCP Socket to the specified port on
  the specified host.
• It connects to the host and port specified in the
  first two arguments.
• It connects from the local network interface and
  port specified by the last two arguments.
• If 0 is passed for the localPort argument, Java
  chooses a random available port between 1,024 to
  65535.
• Identical to previous one except that host to
  connect to is passed as an InetAddress, not a
  String

22
Getting Information About a Socket

• Getting Address of Remote Host
• Getting Port Information to which the Socket
  is connected to on the remote host.
• Getting Address of Local Host
• Getting Port Information of local host from
  which the Socket is connected.
• To read data from the socket into the program
• To write data into the socket from your
  application

23
Getting Address of Remote Host

• public InetAddress getInetAddress( )
• try
• Socket theSocket new Socket(java.sun.com
  , 80)
• InetAddress host theSocket.getInetAddress(
  )
• System.out.println(Connected to remote host
  host)
• //end try
• catch (UnknownHostException ex)
• System.err.println(ex)
• catch (IOException ex)
• System.err.println(ex)

24
Port Information on Remote Host

• public int getPort( )
• try
• Socket theSocket new Socket(java.sun.com
  , 80)
• int port theSocket.getPort( )
• System.out.println(Connected to remote port
  port)
• //end try
• catch (UnknownHostException ex)
• System.err.println(ex)
• catch (IOException ex)
• System.err.println(ex)

25
Port Information of Local Host

• public int getLocalPort( )
• try
• Socket theSocket new Socket(java.sun.com
  , 80)
• int localPort theSocket.getLocalPort( )
• System.out.println(Connected from local
  port localPort)
• //end try
• catch (UnknownHostException ex)
• System.err.println(ex)
• catch (IOException ex)
• System.err.println(ex)

26
Getting Address of Local Host

• public InetAddress getLocalAddress( )
• try
• Socket theSocket new Socket(hostname,
  80)
• InetAddress localAddress theSocket.getLocalA
  ddress( )
• System.out.println(Connected from local
  Address localAddress)
• //end try
• catch (UnknownHostException ex)
• System.err.println(ex)
• catch (IOException ex)
• System.err.println(ex)

27
Get a Sockets Information

• import java.net.
• import java.io.
• public class SocketInfo
• public static void main(String args)
• for (int i 0 i lt args.length i)
• try
• Socket theSocket new Socket(argsi,
  80)
• System.out.println("Connected to "
  theSocket.getInetAddress()
• " on port " theSocket.getPort() "
  from port "
• theSocket.getLocalPort() " of "
• theSocket.getLocalAddress())
• // end try
• catch (UnknownHostException ex)
• System.err.println("I can't find "
  argsi)
• catch (SocketException ex)

• Read a list of hostnames from the command lines.
• Attempt to open a socket to each one.
• Use the four methods to print the remote host,
  the remote part, the local host and the local port

28
Reading Data From Program

• public InputStream getInputStream( ) throws
  IOException
• getInputStream( ) returns an input stream that
  can read data from socket into the program.
• Chain this InputStream to a filter stream or
  reader that offers more functionality
  DataInputStream or InputStreamReader.
• Buffer the input by chaining it to a
  BufferedInputStream and/or a BufferedReader.

29
Writing Data into Socket

• public OutputStream getOutputStream( ) throws
  IOException
• Writer out
• try
• Socket http new Socket(www.uwstout.edu,80)
• OutputStream raw http.getOutputStream()
• OutputStream buffered new BufferedOutputStream(
  raw)
• out new OutputStreamWriter(buffered,ASCII)
• out.write(GET /HTTP 1.0 \r\n\r\n)
• //read the server response
• catch(Exception ex)
• System.err.println(ex)
• Finally
• try
• out.close()
• catch(Exception ex

• getOutputStream( ) returns a raw OutputStream for
  writing data from your application to the other
  end of socket.
• Chain this OutputStream to a more convenient
  class DataOutputStream or OutputStreamWriter.
• Also, if possible use buffers.

30
An Echo Client

• import java.net.
• import java.io.
• public class EchoClient
• public static void main(String args)
• String hostname "localhost"
• if (args.length gt 0)
• hostname args0
• PrintWriter out null
• BufferedReader networkIn null
• try
• Socket theSocket new Socket(hostname, 7)
• networkIn new BufferedReader(
• new InputStreamReader(theSocket.getInputStr
  eam()))
• BufferedReader userIn new BufferedReader(

31
An Echo Client

• while (true)
• String theLine userIn.readLine()
• if (theLine.equals(".")) break
• out.println(theLine)
• out.flush()
• System.out.println(networkIn.readLine())
• // end try
• catch (IOException ex)
• System.err.println(ex)
• finally
• try
• if (networkIn ! null) networkIn.close()
  
• if (out ! null) out.close()
• catch (IOException ex)

32
Closing the Socket

• Socket closes automatically when
• One of its two streams closes.
• When the program ends
• When its garbage collected
• It is a bad practice to assume a system will
  close the sockets for you, especially for
  programs that might run for an indefinite period
  of time.
• When you are through with a socket you should
  call its close() method to disconnect
• public void close() throws IOException

33
Closing the Socket

• Socket connection null
• try
• connection new Socket( www.java.com, 13)
• // interact with the socket
• //end try
• catch(UnknownHostException ex)
• System.err.println(ex)
• finally
• if(connection ! null) connection.close()

• Once a Socket has been closed, its InetAddress,
  port number, local address, and local port number
  are still accessible through getNAME methods.
• However, although you can still call
  getInputStream() and getOutputStream(),
  attempting to read data from the InputStream or
  write data to the OutputStream throws an
  IOException

34
Socket Status Methods

• public boolean isClosed()
• If the socket has never been connected in the
  first place, it returns false
• public boolean isConnected()
• It does not tell you if the socket is currently
  connected to a remote host.
• It tells you if a socket has ever been connected
  to a remote host.
• To tell if a socket is currently open, you need
  to check that
• isConnected() returns TRUE
• isClosed() returns FALSE

35
Sockets for Servers

• Why Server Sockets?
• Client Sockets by themselves are not enough
  unless they can talk to a server.
• Socket discussed earlier is not sufficient for
  writing servers.
• To create a Socket you need to know the Internet
  host you want to connect to
• When you are writing a server
• You do know who would contact you
• When they would contact you.

36
ServerSocket Class

• Java provides ServerSocket Class that represents
  server sockets.
• A server socket runs on the server and listens
  for incoming TCP connections.
• Each Server socket listens on a particular port
  on the server machine.
• When a client on a remote host attempts to
  connect to that port
• The server wakes up
• Negotiates the connection between the client and
  the server.
• Returns a regular Socket object representing the
  socket between the two hosts.

37
Server Socket Behavior Overview

• Server sockets waits for connections, while
  client sockets initiate connections.
• Once a ServerSocket has set up a connection
• The server uses a regular Socket object to send
  data to the client
• Data always travel over the regular socket.

38
Life cycle of a server program

• A new ServerSocket is created on a particular
  port using a ServerSocket() constructor.
• The ServerSocket listens for incoming connection
  attempts on that port using its accept() method.
  accept() blocks until a client attempts o make a
  connection, at which point accept() returns a
  Socket object connecting the client and Server

39
Life cycle of a server program

• Depending on the type of server, either the
  Sockets getInputStream() method,
  getOutputStream() method, or both are called to
  get input and output streams that communicate
  with the client.
• He server and the client interact according to an
  agreed-upon protocol until it is time to close
  the connection.
• The server, the client , or both close the
  connection.
• The server returns to step 2 and waits for the
  next connection.

40
The Constructors

• public ServerSocket(int port) throws
  BindException, IOException
• public ServerSocket(int port, int queueLength)
  throws BindException, IOException
• public ServerSocket(int port, int queueLength,
  InetAddress bindAddress) throws IOException
• public ServerSocket() throws IOException

41
Constructor 1

• public ServerSocket(int port) throws
  BindException, IOException
• Creates a Server Socket on the port specified by
  the argument
• try
• ServerSocket httpd new ServerSocket(80)
• catch (IOException ex)
• System.err.println(ex)
• // end catch

42
Local Port Scanner

• import java.net.
• import java.io.
• public class LocalPortScanner
• public static void main(String args)
• for (int port 1 port lt 65535 port)
• try
• // the next line will fail and drop into
  the catch block if
• // there is already a server running on
  the port
• ServerSocket server new
  ServerSocket(port)
• catch (IOException ex)
• System.out.println("There is a server on
  port " port ".")
• // end catch
• // end for

43
Constructor 2

• public ServerSocket(int port, int queueLength)
  throws BindException, IOException
• Creates a Server Socket on the port specified
  with a queue length of your choosing.
• queueLength Length of queue for incoming
  connection requests
• try
• ServerSocket httpd new ServerSocket(5776,100)
• catch (IOException ex)
• System.err.println(ex)
• // end catch

44
Constructor 3

• public ServerSocket(int port, int queueLength,
  InetAddress bindAddress) throws BindException,
  IOException
• Binds a Server Socket to the port specified with
  a specified queue length.
• queueLength Length of queue for incoming
  connection requests
• try
• ServerSocket httpd new ServerSocket(5776,10,Ine
  tAddress.getByName(192.168.210.122)
• catch (IOException ex)
• System.err.println(ex)
• // end catch

45
Constructor 4

• public ServerSocket() throws IOException
• It creates a ServerSocket object but does not
  actually bind to a port so it cannot initially
  accept connections.
• It can be bound later using the bind() functions
• public void bind(SocketAddress endpoint) throws
  IOException
• public void bind(SocketAddress endpoint, int
  queueLength) throws IOException
• ServerSocket ss new ServerSocket()
• SocketAddress http new InetSocketAddress(80)
• ss.bind(http)

46
Accepting and Closing Connections

• public Socket accept() throws IOException
• This method blocks it stops the flow of
  execution and waits until a client connects.
• When a client does connect, the accept() method
  returns a Socket object.
• You use the streams returned by this Sockets
  getInputStream() and getOutputStream() methods to
  communicate with the client

47
Example Code

• ServerSocket server new ServerSocket(5776)
• while(true)
• Socket connection server.accept()
• OutputStreamWriter out new OutputStreamWriter(c
  onnection.getOutputStream())
• out.write(Youve connected to this server.
  Bye-Bye now.\r\n)
• connection.close()

48
Closing the Socket

• public void close() throws IOException
• Close the server socket so that it frees up port
  for other programs to use it.
• Closing ServerSocket is different than closing
  Socket
• ServerSockets are automatically closed when a
  program dies.
• public boolean isClosed()
• public boolean isBound()
• public static boolean isOpen(ServerSocket ss)
• returns ss.isBound() ! ss.isClosed()

49
Other Methods

• public InetAddress getInetAddress()
• Returns the address being used by the server.
• ServerSocket httpd new ServerSocket(80)
• InetAddress ia httpd.getInetAddress()
• public int getLocalPort()
• Lets you find out what port you are listening on
• public void setSoTimeOut(int timeout) throws
  SocketException
• public int getSoTimeOut() throws IOException

50
Example illustrating get Methods

• import java.net.
• import java.io.
• public class RandomPort
• public static void main(String args)
• try
• ServerSocket server new ServerSocket(0)
• System.out.println("This server runs on
  port "
• server.getLocalPort())
• catch (IOException ex)
• System.err.println(ex)