NET0183Lec31

NET0183 Networks and Communications

Lecture 31The Socket API

8/25/2009 1NET0183 Networks and Communications

by Dr Andy Brooks

Lecture powerpoints from the recommended textbook are by Lami Kaya, [email protected] powerpoints are 2009 Pearson Education Inc.Their content has sometimes been edited by Andy Brooks.

socket/tengill

8/25/2009NET0183 Networks and Communications

by Dr Andy Brooks2

The recommended textbook is Computer Networks and Internets by Douglas E. Comerhttp://www.coursesmart.com/0136066992/?a=1773944www.pearson-books.com/student (for additional discounts and offers)

Socket @ Webopedia 31. mars 2010


by Dr Andy Brooks3

http://www.webopedia.com/TERM/s/socket.html

(1) In UNIX and some other operating systems, a software object that connects an application to a network protocol. In UNIX, for example, a program can send and receive TCP/IP messages by opening a socket and reading and writing data to and from the socket. This simplifies program development because the programmer need only worry about manipulating the socket and can rely on the operating system to actually transport messages across the network correctly. Note that a socket in this sense is completely soft - it's a software object, not a physical component.

4Socket: a door between an application process and a transport protocol (e.g. TCP)

process

TCP withbuffers,variables

socket

controlled byapplicationdeveloper

controlled byoperating

system

host orserver

process

TCP withbuffers,variables

socket

controlled byapplicationdeveloper

controlled byoperatingsystem

host orserver

internet

from Kurose and Ross

2009 Pearson Education Inc., Upper Saddle River, NJ. All rights reserved. 5

3.13 Network Programming and the Socket API

The interface an application uses to specify communication is known as an Application Program Interface (API).

One particular API has emerged as the de facto standard for software that communicates over the Internet. This API is

known as the socket API, commonly abbreviated sockets.

The socket API is available for many OS such as Microsoft's Windows systems as well as various UNIX systems,

including Linux.

sockets/tenglar


3.15 Parameters and the Socket API

Socket programming differs from conventional I/O.

An application must specify details such as :

the address of a remote computer

the protocol port number

whether the application will act as a client or as a server

To avoid having a single socket function with many parameters, designers of the socket API chose to

define many functions.

An application creates a socket, and then invokes functions.


Figure 3.7 A summary of the major functions in the socket API.


3.16 Socket Calls in a Client and Server

Figure 3.8 illustrates the sequence of socket calls made by a typical client and server that use a stream connection.

The server waits for the client to send data.

In practice, some applications arrange for the server to send first (i.e. send and recv are called in the reverse order).


Figure 3.8 Illustration of the sequence of socket functions called by a client and

server using the stream paradigm.

10

How does this all work in Java?A brief overview follows...

8/25/2009 NET0183 Networks and Communications by Dr Andy Brooks

Simple, example client-server in Java.

11

AdditionClient.java RunAdditionClient.javaAdditionServer.java RunAdditionServer.javaThe source code files are on NET0183 website.


by Dr Andy Brooks

The client sends two numbers to the server.The server computes the addition and sends the result back to the client.Window dialogues are used to report behaviour to let us see what is happening.

Socket and ServerSocket classes in Java

Socket knows about: opening a connection

sending data

receiving data

closing a connection

ServerSocket knows about: binding to a port

listening for incoming data

accepting connections


by Dr Andy Brooks12


by Dr Andy Brooks13

import java.net.*;

import java.io.*;

import javax.swing.*;

public class AdditionServer extends JFrame

{

private JTextArea textWindow = new JTextArea();

private int port;

// the constructor

public AdditionServer(int portIn)

{

port = portIn;

setTitle("Addition Server");

add("Center",textWindow);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setSize(400, 300);

setVisible(true);

startServer();

}

AdditionServer.java


by Dr Andy Brooks14

AdditionServer.java

private void startServer()

{

// declare a "general" socket and a server socket

Socket connection;

ServerSocket listenSocket;

// declare low level and high level objects for input

InputStream inStream;

DataInputStream inDataStream;

// declare low level and high level objects for output

OutputStream outStream;

DataOutputStream outDataStream;

// declare other variables

String client;

int first, second, sum;

boolean connected;


by Dr Andy Brooks15

AdditionServer.javawhile(true){

try {

// create a server socket

listenSocket = new ServerSocket(port);

textWindow.append("Listening on port " + port + "\n");

// listen for a connection from the client

connection = listenSocket.accept ();

connected = true;

// create an input stream from the client

inStream = connection.getInputStream();

inDataStream = new DataInputStream(inStream);

// create an output stream to the client

outStream = connection.getOutputStream ();

outDataStream = new DataOutputStream (outStream );

// wait for a string from the client

client = inDataStream.readUTF();

textWindow.append("Connection established with "

+ client + "\n" );


by Dr Andy Brooks16

AdditionServer.java

while(connected)

{

//read an integer from the client

first = inDataStream.readInt();

textWindow.append( "First number received: "

+ first + "\n");

//read an integer from the client

second = inDataStream.readInt();

textWindow.append( "Second number received: "

+ second + "\n");

sum = first + second;

textWindow.append( "Sum returned: "

+ sum + "\n");

//send the sum to the client

outDataStream.writeInt(sum);

}

}

catch (IOException e)

{

connected = false;

}}}}


by Dr Andy Brooks17

RunAdditionServer.java

public class RunAdditionServer {

/**

* @param args

*/

public static void main(String[] args) {

new AdditionServer(8901);

}

}


by Dr Andy Brooks18

Simple, example client-server in Java.Extracts from the Java API.

listenSocket = new ServerSocket(port); Creates a server socket, bound to the specified port. A

port of 0 creates a socket on any free port. The maximum queue length for incoming connection indications (a request to connect) is set to 50. If a connection indication arrives when the queue is full, the connection is refused.

connection = listenSocket.accept (); Listens for a connection to be made to this socket and

accepts it. The method blocks until a connection is made. A new Socket s is created and, if there is a security manager, the security manager's checkAccept method is called with s.getInetAddress().getHostAddress() and s.getPort() as its arguments to ensure the operation is allowed. This could result in a SecurityException.

Documents

NET0183Lec31