TCPIP Protocol Stack

1
TCP/IP Protocol Stack
Application
Sockets
(Gate to network)
TCP
UDP
IP
Device Drivers
2
Programming with Sockets

• Sockets are Berkeley software distribution UNIX
  interface to network protocols
• Endpoint of communication, has a type and one
  associated process
• Uses file system model (open-close-read-write)
• Internet vs. Unix domain

3
Client-Server Architecture
request
Process request
client
response
Host www.vcu.edu Port 80
4
4 steps in programming a client

• Open a socket.
• Open an input and output stream to the socket.
• Read from and write to the socket according to
  the server's protocol.
• Clean up.

5
Socket in Java

• Two important classes
• Socket a normal socket as communication end
• ServerSocket accept the incoming request
• ServerSocket is an analogy to the custom service
  phone number, it will dispatch your call to a
  specialized staff--- normal Socket.

6
Client Socket Creation
Socket MyClientMyClient new Socket("Machine
name", PortNumber)
SOCKET DESCRIPTOR
port (a number) on which the server you want
the machine you are trying to open a connection
to
port numbers between 0 and 1,023 are reserved for
for standard services, such as email, FTP, and
HTTP. for your server, select one that is
greater than 1,023
7
Create Server Socket

• If you are programming a server, then this is how
  you open a socket
• ServerSocket MyServicetry    MyServerice
  new ServerSocket(PortNumber)                ca
  tch (IOException e)           
  System.out.println(e)        

8
Use ServerSocket listen, accept, and Create
connections from clients.

• Socket clientSocket nulltry   
  serviceSocket MyService.accept()        catc
  h (IOException e)    System.out.println(e)

A blocking call, will return when a request arrive
9
Send Data to Socket at Client

• PrintStream outputtry    output new
  PrintStream(MyClient.getOutputStream())
• String inLhello
• output.writeBytes(inL"\n")

10
Read data from Socket at Client

• DataInputStream inputtry    input new
  DataInputStream(MyClient.getInputStream())
• ..
• String responseLine input.readLine()
• System.out.println("Server "
  responseLine)

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Send Data to Socket at Server

• Use the serviceSocket returned from the accept()
  call.

• PrintStream outputtry    output new
  PrintStream(serviceSocket.getOutputStream())outp
  ut.println(this is server reply)

12
Read Data From Socket at Server

• Same as client case
• DataInputStream inputtry       input new
  DataInputStream(serviceSocket.getInputStream())
• String reqinput.readLine()

13
Close Socket Connection

• On the server side
• try    output.close()   input.close()  
  serviceSocket.close()    MyService.close()
  catch (IOException e)    System.out.println(e)
  

• On the client side
• try         output.close()       
  input.close()    MyClient.close() catch
  (IOException e)    System.out.println(e)

14
A Simple Echo Server

• // listen and accept connections.// Open input
  and output streamstry            clientSocket
  echoServer.accept()           is
  new DataInputStream (clientSocket.getInputStream(
  )) os new PrintStream
  (clientSocket.getOutputStream())// As long as
  we receive data, echo that data back to the
  client.          while (true)             
  line is.readLine()            
  os.println(line)                      
  catch (IOException e)           
  System.out.println(e)            

• import java.io.import java.net.public class
  echo3     public static void main(String
  args)         ServerSocket echoServer
  null        String line        DataInputStream
  is        PrintStream os        Socket
  clientSocket null        try           
  echoServer new ServerSocket(9999)           
       catch (IOException e)           
  System.out.println(e)          

15
A simple client

• smtpSocket new Socket("128.172.167.167", 9998)
• os new DataOutputStream(smtpSocket.getOutputStr
  eam())
• is new DataInputStream(smtpSocket.getInputStrea
  m())
• while (true)
• inLd.readLine()
• os.writeBytes(inL"\n")
• if (inL.compareTo("quit")0) break
  
• // keep on reading from/to the socket till we
  receive the "Ok" from SMTP,
• // once we received that then we want to break.

responseLine is.readLine()
System.out.println("Server " responseLine)
responseLine is.readLine()
System.out.println("Server " responseLine)
responseLine is.readLine()
System.out.println("Server " responseLine)

16
Reference

• Class ServerSocke
• A server socket 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.
• accept() Listens for a connection to be made to
  this socket and accepts it.
• getInetAddress()
• Returns the local address of this server socket.

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Class Socket

• This class implements client sockets (also called
  just "sockets"). A socket is an endpoint for
  communication between two machines.
• Socket(InetAddress address, int port)
• connect(SocketAddress endpoint)    Connects this
  socket to the server.
• getPort()    Returns the remote port to which
  this socket is connected.
• getLocalPort()           Returns the local port
  to which this socket is bound.
• getInputStream()           Returns an input
  stream for this socket.
• getOutputStream()           Returns an output
  stream for this socket.
• getInetAddress()           Returns the address
  to which the socket is connected.
• getLocalAddress()           Gets the local
  address to which the socket is bound.

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Other Parameters in Socket

• Buffer size
• Incoming buffer size
• Outgoing buffer size
• Time out or not
• Otherwise a bad read will block your browser for
  ever.
• Status check