5417.Java TCP Programming

8/6/2019 5417.Java TCP Programming

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Network

Programming3/23/2011

1Network Programming Rapid Application Development-CS3011

Lecture - 1

Amit Sharma


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Network Programming

Network programming is a branch of computerscience which covers the art of writingapplication programs or software that run onnetworks. These software are known as

Network Programs.3/23/2011 2Network ProgrammingRapid Application Development-CS3011


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Computer NetworkIn Tanenbaum (Author of many

networking books) words Computer Networks can be

described as an interconnectedcollection of autonomouscomputers.

Two computers are said to be interconnected, if they are able to exchange information. By theterm autonomous, it is meant that there shouldnot be any master-slave relationship between thecomputers, that is, all the computers shouldhave the resources to work independently .3/23/2011 3Network ProgrammingRapid Application Development-CS3011


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Network Programs

Send data across the network.

Provide services over a network.

Receives data over a network.

Invoke services across a network.

The main characteristics of network program is that theymust use a computer network inanyway as to perform their job.Network Programs do either of one or all of the following

3/23/2011 4Network ProgrammingRapid Application Development-CS3011


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Networking includes

Network programming includes

Reading and writing network sockets

Encryption and decryption of data

Translating network protocols

Sending data packets to other nodesProviding security to the data

And many more . . .3/23/2011 5Network ProgrammingRapid Application Development-CS3011


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What Network Programs can do

Networking extends the power of a single computer.Network lets one computer communicate withthousands, even millions, of other computers.Network may prove very efficient in the area of Electronic mailApplication ServicesInformation sharing

Parallel computingMessaging servicesWebsite programming

And many more . . .3/23/2011 6Network ProgrammingRapid Application Development-CS3011


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Client ServerModel


Lecture - 2

Amit Sharma


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Networking ModelsFor data communication to take place, a computer

runs a program to request a service fromanother program residing on the destinationcomputer. This is the basic idea behind networkprogramming which means that two computersshould connected to the network and act as aservice requester or service provider.

It is based on, generally, two models-Client - Server ModelPeer-to-Peer Model

From which client-server model is much popularamong the network programmers.



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Client Server Model

to whom the request is made, performs the jobfor the requesting computer. This is the basic

idea of Client-Server Model.

In a network if any hostwishes to receive aservice from a remotecomputer, it executesspecific program toperform the specific

job. Then the computer



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Server and ClientsClient computers are those

who made requests.Server computer respond

the clients and perform

the job requested by theclient.client-server programming

requires experience withmany different technicalskills like, databaseprogramming, networkprotocols, user interfacedesign, transaction

processing, RPCs, etc.

R e q u e s t

Response



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Client-Server Mechanism

1 1

2 2

1. REQUEST: Client initiates a connection, maderequest for the service to server.

2. RESPONSE: Server accept the request, respond

to the client and provide the services to clients.3/23/2011 11Network ProgrammingRapid Application Development-CS3011


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JavaTCP

Programming3/23/2011 12Network ProgrammingRapid Application Development-CS3011

Amit Sharma


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Transmission Control Protocol The TCP is a transport layer protocol. TCP provides reliable , full-duplex connections and

reliable service by ensuring that data is

resubmitted when transmission results in an error. TCP enables two network entities to establish a bi-

directional communications channel for readingand writing streams, that is, sequence of bytes.

The TCP protocol guarantees that bytes will bedelivered to recipient in the order written by thesender.



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Transmission Control Protocol Once the message arrived at the correct IP

address, TCPs main task is error checking . TCP performs congestion control by

controlling the rate with which data is writtento the network in response to networkconditions.

TCP performs an additional service calledflow control .



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Functionsof

TCP3/23/2011 15Network ProgrammingRapid Application Development-CS3011

Lecture - 3

Amit Sharma


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Stream Segmentation

Because the IP protocol only supportstransmission of limited size packets,

TCP must break the stream intosegments for transmission. In order toamortize the cost of transmitting the IP

and TCP headers, it is preferable totransmit packets containing the largestpossible payload.



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Stream Reassembly

The TCP streams that are transmitted as IPpackets may arrive at the destination indifferent order than the order sent. TCPmust be able to handle out-of-order deliveryand still reassemble the data in the ordertransmitted. TCP addresses this problem by

counting the number of bytes transmitted inthe stream and identifying each of the firststream byte it carries.



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Handling Packet loss IP packets carrying segments of the stream may be

lost in the way. TCP must be able to detect the factthat a packet has been lost and arrange

retransmission. TCP deletes packets loss by positive receiver

acknowledgements. When a TCP packet arrives,the receivers TCP protocol implementation will

send a TCP packet to the sender acknowledgingreceipt. If the sender fails to receiveacknowledgement by a certain deadline, it willretransmit the packet.



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Data Corruption Detection The IP protocol only protects its own header and

does not make any guarantees on the payloadcontents. It is therefore possible that one or more bitsin the payload may be corrupted due to transmissionerror.

For this payloads summary is computed and storedin the packets header. The receiver of the packet

then independently computes the summary of thedata received, using the same algorithm andcompares it to summary stored in header. Thisalgorithm protects against all 1-bit errors and somemultiple bit errors.3/23/2011 19Network ProgrammingRapid Application Development-CS3011


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Java TCP Programming

The programming model of TCPcommunication in Java, rely

completely on the sockets and ports .Because TCP is a stream protocol, itallows to send arbitrary amount of

data rather rely on class to encapsulatedata within TCP packets.



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Sockets

Java programs communicate through aprogramming abstraction called socket. A socketis one end-point of a two-way communicationlink between two computers (or programs)running on a network. A socket is bound to a portnumber so that the TCP layer can identify the

application that data is destined to be sent.

PORT

PORT



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Ports

One mechanism that is commonly used by networkprotocols, and in particular the Internettransport layer protocols, is port addressing.Every network service is associated with one ormore ports on one or more IP interfaces of itshost device. Typically, integer numbers are used

to identify different ports. In order to contact anetwork service, it is therefore necessary toprovide both the IP address of its host, as well asport number it is using.



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Stream Socket



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Package java.net

The Java language supports TCP programmingthrough the java.net.Socket and

java.net.ServerSocket classes. Java clients

connect to TCP servers by creating instances of the java.net.Socket class . Similarly, Java serverslisten for java clients by creating

java.net.ServerSocket class. Connections areconfigured through the methods of these twoclasses. Actual network communications,however, are performed using the java.iopackage streaming classes.3/23/2011 24Network ProgrammingRapid Application Development-CS3011


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Client Program

A client is a network program residing onlocal computer, who requests for any serviceto the server. A client program is a finiteprocess which means that it is started by theuser and terminates when the service iscomplete.

For example, Web Browser is a network client which requests to the Web Server to readfiles, view images or download documents

or images on the local computer.3/23/2011 25Network ProgrammingRapid Application Development-CS3011


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Functioning of Client

A client opens the communication channel usingthe IP address of the remote host and the well-known port address of the specific servercomputer. After a channel is active, the clientsends its request and receives a response. Therequest-response part may be repeated forseveral times. At the end, the client closes the

communication channel.

SERVER CLIENTConnection

Request

PORT



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Structure of Client ProgramClient program use TCP/IP sockets for communication

with server. The structure of basic client program is

A new socket instance is created using a constructor of Socket class.

The socket attempts to connect to a remote host, passingand IP address (or URL) and a port number.

Socket socket = new Socket(sap_server,1234);

Where sap_server is the URL and 1234 is port numberwhere it listens.

Once the client connects, the client and server interactaccording to protocol.

Finally the server, the client or both close the sockets.3/23/2011 27Network ProgrammingRapid Application Development-CS3011


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Server Program

A server is a remote computer on a network whichprovides services to the clients. When it starts,it opens the channel for incoming requests fromclients, but it never initiates a service until it isrequested to do so.

A server program is an infinite process. When it is

starts in runs infinitely unless a problemarises. It waits for incoming requests fromclients. When a request arrives, it responds tothe request either iteratively or concurrently.



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Functioning of Server

On server side, if everything goes well, the serveraccepts the connection. Upon acceptance the severgets a new socket bound to a different port. Itneeds a new socket (and consequently a differentport number) so that it can continue to listen tothe original socket for connection requests while

tending to the needs of the connected client.

SERVER CLIENTCommunication

Channel

PORT

PORT

P O R T



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Structure of Server ProgramThe basic steps for the coding of server program in Java are

Instance of server socket is created which listens onselected port number, using the constructors of ServerSocket class.

ServerSocket serverSocket = new ServerSocket(1234);The above code will create a serverSocket which wouldlisten on port number 1234 .This instance listens for connection on the desired port. Itwaits for client until it attempts to connect. It uses accept() method to establish the connection.Once a client connects, the accept() method returns aninstance of the socket class, which it uses as a receivingsocket. Client "sending" sockets and servers receivingsockets comes from the same Java class, Socket class.3/23/2011 30Network ProgrammingRapid Application Development-CS3011


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Structure of Server Program(Contd.)

The client and server interact according to protocol.Java servers typically use getInputStream() and getOutputStream() to handle socket communication.

Either server or client, or both close the socket.

The server returns to listening for connection on itsdesignated port.

Incoming connection requests are stored by theoperating system in a FIFO queue. Those requestswill block while the server is handing clientinteractions. But with Java, network developer canemploy a new thread to handle another client in case

of servicing the client for longer or indefinite time.3/23/2011 31Network ProgrammingRapid Application Development-CS3011


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Creating a Client Program

The java.net.Socket of a java.netpackage implements client side of a

two-way connection between Javaprogram and another program on thenetwork. By using this class instead of

relying on native code, Java programcan communicate over network inplatform independent fashion.



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Creating a Client Socket

The java.net.Socket class provides aconstructor, which takes an IP address andport number and attempts to establish a

connection.The signature of this constructor is

Socket(InetAddress, int port)throws IOException;

Throwing the java.io.IOException exception

signals communication error.3/23/2011 33Network ProgrammingRapid Application Development-CS3011


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Although the signature of the constructorsonly declares the java.io.IOException ,

users can determine the reasonprogrammatically using followingsubclasses of java.io.IOException .

java.net.NoRouteToHostException java.net.ConnectException



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Another constructor is provided for use withhost names, or IP addresses represented asStrings. The signature is

Socket(String host,int port)throws IOException;

This constructor may also throw an additional

IOException subclass called java.net.UnknownHostException if the hostname can not be resolved, or string

representation of the IP address is invalid.3/23/2011 35Network ProgrammingRapid Application Development-CS3011


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There is another equivalent constructor with theprevious constructor, which is much moreconvenient Socket(InetAddress.getByName(host),port);



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3/23/2011 Network ProgrammingRapid Application Development-CS3011 37

Lecture - 4

Creating Clientand Server Socket

Amit Sharma


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Example demonstrating Socket Creation

import java.net.*;import java.io.*;public class SimpleClient {

public static void main(String[] args) {String host = sap_server;int port = 1234;try {

System.out.println(Attempting to connect to TCP

service on host + host + and port: + port);Socket s = new Socket(host,port);System.out.println(Connection Established . . .);

}3/23/2011 38Network ProgrammingRapid Application Development-CS3011


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Example (contd.)

catch(UnknownHostException ue) {

System.out.println(Trouble: + ue.getMessage());}catch(IOException ioe) {

System.out.println(Trouble: + ioe.getMessage());}

}}



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Reading / Writing Socket

The Socket class provides two methods, one forobtaining an input stream for reading bytesand one for obtaining an output stream forwriting byte-stream to the output stream.

The streams are represented as java.io.InputStream java.io.OutputStream



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Reading / Writing Socket

An exception java.io.IOException will bethrown in this case. The signatures are java.io.InputStream getInputStream()

throws IOException; java.io.OutputStream getOutputStream()

throws IOException; Once the input and output streams for the

socket have been obtained, it is up toapplication to determine the contents of

communication.3/23/2011 41Network ProgrammingRapid Application Development-CS3011


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Getting Socket Information

Connection oriented sockets may becharacterized by set:

The four methods for querying the Socket are InetAddress getInetAddress() throws IOException;int getPort() throws IOException;InetAddress getLocalAddress() throws IOException;int getLocalPort() throws IOException;



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Terminating Socket

The close() method requests asynchronoustermination of the socket connection.

The close() method will return immediately, evenif data written before invocation has notcompleted transmission.

void close() throws IOException;


E l ill t ti g di g/ iti g th gh S k t


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Example illustrating reading/writing through Socket/* EchoClient implements a client,, that connects to the EchoServer. The

EchoServer simply receives data from client and echoes it back. */

import java.net.*;import java.io.*;public class EchoClient {

public static void main(String[] args) {

Socket echoSocket = null;PrintWriter out = null;BufferedReader in = null;try {echoSocket = new Socket(sap_server,4444);out = new PrintWriter(echoSocket.getOutputStream(),true);


E ample ill strating reading/ riting thro gh Socket


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Example illustrating reading/writing through Socket

in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream());

} catch(UnknownHostException ue) {System.out.println(Trouble: + ue.getMessage());

} catch(IOException ioe) {

System.out.println(Trouble: + ioe.getMessage());}BufferedReader stdIn = new BufferedReader(new

InputStreamReader(System.in));




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String userInput;while(!(userInput = stdIn.readLine()).equals(quit)) {

out.println(userInput);System.out.println(Echo: + in.readLine());

}out.close();in.close();stdIn.close();echoSocket.close();

}}



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Server Side TCP Programming

In order to accept network connections a Javaprogram must create an instance of

java.net.ServerSocket.Server sockets are not directly used to perform

any network communication. Instead, they actas factories that create a java.net.Socket objectfor every incoming TCP communicationrequest.

Programs create the server socket, bind to aspecific port on one or more interfaces, and

then invoke the blocking accept() method.3/23/2011 47Network ProgrammingRapid Application Development-CS3011


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Creating Server Socket

The basic ServerSocket constructor takes asingle argument, the TCP port number used inbinding.

The constructor may fail due to an I/O error, ordue to a security error. The signature of theconstructor is

ServerSocket(int port) throwsIOException,SecurityException;

Port is not permitted to listen more than one

process at the same point of time.3/23/2011 48Network ProgrammingRapid Application Development-CS3011


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Accepting Socket

The main task of server socket is to receiveincoming connection requests and generate a

java.net.Socket object that encapsulates each

request.Incoming connections are queued until the

program retrieves them one at a time by

invoking the accept() method.The accept() method takes no arguments, andreturns the next connection in the queue.


Example SimpleServer java


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Example -- SimpleServer.javaimport java.net.*;import java.io.*;

public class SimpleServer {public static void main(String args[]) {

ServerSocket server = null;port = 1234;

try {System.out.println(Attempting to bind a TCP port + port);server = new ServerSocket(port);

} catch(SecurityException se) {System.out.println(Trouble : + se.getMessage());

} catch(IOException ioe) {System.out.println(Trouble : + ioe.getMessage());


Example contd


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Example contd.try {

Socket socket = server.accept();

System.out.println(Accepting connection from: +socket.getInetAddress().getHostName());

socket.close();} catch(SecurityException se) {

System.out.println(Trouble : + se.getMessage());} catch(IOException ioe) {

System.out.println(Trouble : + ioe.getMessage());

}}

}



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Getting ServerSocket Info

Server socket objects have two identifyingattributes: the port number and theInetAddress they are bound to.

The java.net.ServerSocket class providesmethods to query two values

The getInetAddress() method returns the IP

address of the interface to which the serversocket is bound.

The getLocalPort() returns the port the server

socket is bound to.3/23/2011 52Network ProgrammingRapid Application Development-CS3011


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Terminating ServerSocket

A server socket may be terminated simply byinvoking the no argument close () method.

Closing the server socket will not affectconnections that have already been returnedby an accept () invocation.

The signature is as follows void close () throws IO Exception;


Example the server side of the Echo Client


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Example the server side of the Echo Client

import java.net.*;import java.io.*;public class EchoServer {

public static void main(String args[]) {Socket clientSocket;ServerSocket serverSocket;int port = 4444;try {

//Creating ServerSocket instanceserverSocket = new ServerSocket(port);

} catch(SecurityException se) {System.out.println (Trouble : + se.getMessage());

} catch(IOException ioe) {System.out.println (Trouble : + ioe.getMessage());


try {


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try { //Server is accepting connectionclientSocket = serverSocket.accept();

// Initializing I/O streamsPrintWriter out = new PrintWriter(clientSocket.getOutputStream(),true);BufferedReader in = new BufferedReader(new

InputStreamReader (clientSocket.getInputStream())); //Server is ready to start conversation

//Initiate conversation with ClientString inputLine;do {

inputLine = in .readLine();out .println (Received : + inputLine);

}while(!( inputLine.equalsIgnoreCase (quit)));


//Close all IO streams and sockets


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//Close all IO streams and sockets

in.close();out.close();

clientSocket.close();serverSocket.close();

} catch(IOException ioe) {System.out.println (Trouble : + ioe.getMessage());}

}}



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Chat Messenger


Lecture - 5

Application of Network Programming


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Example illustrating ChatClient through Socket Programming


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import java.net.*;import java.io.*;public class ChatClient {

public static void main(String[] args){ Socket echoSocket = null;

PrintWriter out = null;

BufferedReader in = null;try {

echoSocket = new Socket("127.0.0.1",4444);out = new PrintWriter(echoSocket.getOutputStream(),true);

in = new BufferedReader( newInputStreamReader(echoSocket.getInputStream())) ;

}

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Rapid Application Development-CS3011



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} catch(UnknownHostException ue) {

System.out.ptintln (Trouble: + ue.getMessage());} catch(IOException ioe) {

System.out.ptintln (Trouble: + ioe.getMessage());}

BufferedReader stdIn = new BufferedReader(newInputStreamReader(System.in));

String userInput;

3/23/2011 61Network Programming




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System.out.println("Received : " + in .readLine());do{

System.out.print("Send : ");userInput = stdIn .readLine();out .println(userInput);System.out.println("Received : " + in .readLine());

}while(! (userInput.equalsIgnoreCase("bye"));

out.close();in.close();stdIn.close();echoSocket.close();

}

} 3/23/2011 62Network Programming



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3/23/2011Network Programming

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Chat Server

// Example illustrating ChatServer through Socket Programming


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import java.net.*;import java.io.*;public class ChatServer {

public static void main(String args[]){

Socket clientSocket;ServerSocket serverSocket = null;int port = 4444;

try{ //Creating ServerSocket instance

serverSocket = new ServerSocket(port);}catch(SecurityException se) {System.out.println("Trouble : " + se.getMessage());

}catch(IOException ioe) {

System.out.println("Trouble : " + ioe.getMessage()); }



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//Server is accepting connectionclientSocket = serverSocket.accept();

// Initializing I/O streamsPrintWriter out = new PrintWriter(clientSocket.getOutputStream());

BufferedReader in = new BufferedReader(newInputStreamReader(clientSocket.getInputStream()));

BufferedReader stdIn = new BufferedReader(newInputStreamReader(System.in));

//Server is ready to start conversation //Initiate conversation with Client

String inputLine, userInput;out .println("Server is listening on port " + port);



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do {inputLine = in .readLine();System.out.println("Received : " + inputLine);

System.out.print("Send : ");userInput = stdIn .readLine();out .println(userInput);

}while(!(userInput.equalsIgnoreCase("bye")));

//Close all IO streams and socketsin.close();

out.close();clientSocket.close();serverSocket.close();

}}

A ig t


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Assignment

Create a Chat Messenger with GUI using AWT and Event Handling.

Documents

5417.Java TCP Programming