Sockets for clients

1
Sockets for clients

• Lecture 6

2

• Data Communication across Internet
• Socket basics
• Socket Class
• Socket Exceptions
• Socket Addresses
• Examples

3
Data Communication across Internet

• Data is transmitted in packets of fixed size
  called datagrams
• Each datagram contains a header a payload
• Header has the address port to which the data
  is going, from where it came other housekeeping
  info
• Data can be carried by a number of datagrams
• Pkts could be lost or could arrive in different
  order
• Sockets are used to setup this connection

4
Socket basics

• Is a connection between two hosts
• Has seven basic opns
• Connect to a remote machine (both client
  server)
• Send data (both client server)
• Receive data (both client server)
• Close a connection (both client server)
• Bind to a port (only server)
• Listen for incoming data (only server)
• Accept connections from remote machine on the
  bound port (only server)

5
Java socket class

• Used by both clients servers
• How it works
• Pgm creates a new socket with a constructor
• Socket attempts to connect to the remote host
• Once connection is established, the local
  remote hosts get input and output streams from
  the socket and use those streams to send data to
  each other (Full-duplex)
• When the transmission of data is complete, one or
  both sides close the connection.

6
Socket class cont..

• The methods of the Socket class set up and tear
  down constructions and set various socket
  options.
• TCP connections are reliable and uses the
  Streams interface
• The constructors allow you to specify the host
  and the port you want to connect to

7
The constructors

• Public Socket(String host, int port) throws
  UnknownHostException
• try
• Socket toUNB new Socket (www.unb.ca,80)
• //send and receive data
• catch (UnknownHostException ex)
• System.err.println(ex)

8
Socket class constructors cont..

• Public Socket(InetAddress host, int port) throws
  IOException
• try
• InetAddress UNB InetAddress.getByName
  (www.unb.ca)
• Socket UNBSocket new Socket (unb,80)
• //send and receive data
• catch (UnknownHostException ex)
• System.err.println(ex)
• Catch (IOException ex)
• System.err.println(ex)

9
Getting info about a socket

• Find the host that the socket was connected to
• Public InetAddress getinetAddress()
• try(
• Socket theSocket new Socket (UNB.ca, 80)
• InetAddress host the Socket.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)

10
Getting info about a socket cont..

• Find the port the socket was connected to
• Public InetAddress getinetAddress()
• try(
• Socket theSocket new Socket (UNB.ca, 80)
• int port the Socket.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)
• Similarly there are TWO more methods
• Public int getLocalPort()
• Public int getLocalAddress()
• Examples http//www.cafeaulait.org/books/jnp3/exa
  mples/09/

11
Input and Output streams

• Public inputStream getInputStream() throws
  Exception
• Public outputStream getoutputStream() throws
  Exception
• Example
• A day time protocol client

12
Closing the socket

• Public void close() throws IOException
• Socket connection null
• try
• InetAddress UNB InetAddress.getByName
  (www.unb.ca)
• Socket UNBSocket new Socket (unb,80)
• //send and receive data
• catch (UnknownHostException ex)
• System.err.println(ex)
• Catch (IOException ex)
• System.err.println(ex)
• finally
• If (connection ! null) connection.close()

13
Setting socket options

• TCP-NODELAY
• SO_BINDADDR
• SO_TIMEOUT
• SO_LINGER
• SO_SNDBUF
• SO_RCVBUF
• SO_KEEPALIVE
• OOBINLINE

14
Class of service

• Java lets you inspect and set the class of
  service for a socket
• Public int getTrafficClass() throws
  SocketException
• Public void setTrafficClass(int trafficClass)
  throws SocketException
• 0x02 Low cost
• 0x04 High reliability
• 0x08 Maximum throughput
• 0x10 Maximum delay
• Examples Socket s new Socket (www.unb.ca,80)
• s. setTrafficClass(0x02)
• Socket s new Socket (www.unb.ca,80)
• s.setTrafficClass (0x08 / 0x10)

15
Examples from book

• http//www.cafeaulait.org/books/jnp3/examples/09/

16
Finger Protocol

• Written by Les Earnest Earl Killiar Brian
  Harvey at MIT
• Straight forward protocol based on TCP using port
  79
• Defined in RFC 1288
• Gives user info in the .plan file
• Example http//www.cafeaulait.org/books/jnp3/exam
  ples/09/

17
Whois

• Simple directory service protocol RFC 954
• Example http//www.cafeaulait.org/books/jnp3/exam
  ples/09/