socket programming

Socket ProgrammingSocket Programming

Ameera Almasoud

1Based on Jignesh Patel & Palanivel Rathinam,Socket Programming:connecting processes presentation

Overview

Introduction to SocketsA generic Client-Server applicationProgramming Client-Server in JavaReferences

Based on Jignesh Patel & Palanivel Rathinam,Socket Programming:connecting processes presentationAmeera Almasoud 2

Introduction to Sockets


Introduction to SocketsPorts:A port is a special number present in the data packet. Ports are typically used to map data to a particular process

running on a computer.Internet Assigned Numbers Authority (IANA) is

responsible for assigning TCP and UDP port numbers to specific used.Well-known ports (0-1023)Registered ports (1024-49151)Dynamic and/or Private ports (49152-65535)

Ameera AlmasoudBased on Jignesh Patel & Palanivel Rathinam,Socket

Programming:connecting processes presentation 4

Introduction to SocketsWhat are Sockets?

End-point of interprocess communication.

An interface through which processes can send / receive information.A socket can perform 7 basic operations:

Connect to a remote machine

Send data

Receive data

Close a connection

Bind to a port

Listen for incoming data

Accept connections from remote machines on the bound port



Why Sockets?Used in Interprocess Communication (N/W Programming):

Making phone calls over the Internet (Skype). Send instant messages (MSN). Playing games with other people. E-Commerce: any shopping site such as: Amazon.

Sockets are also known as Application Programming Interface (API)Sockets are used in a client/server environment.The TCP, UDP and IP protocols reside in the host operating System.




Introduction to SocketsThe Client-Server model

Most interprocess communication uses client-server model

Client & Server are two processes that wants to communicate with each other

The Client process connects to the Server process, to make a request for information/services own by the Server.

Once the connection is established between Client process and Server process, they can start sending / receiving information.


Introduction to Sockets What exactly creates a Socket?

<IP address, Port #> tuple What makes a connection?

{Source<IP address, Port #> , Destination <IP address, Port #>} i.e. source socket – destination socket pair uniquely identifies a connection.

A client may have multiple connections with the same server. Two clients may have the same port numbers (2 connections).

Example

Based on Jignesh Patel & Palanivel Rathinam,Socket Programming:connecting processes presentation

Server

Client

Client

192.168.0.1

192.168.0.2

192.168.0.2

80

1343

5488

Client192.168.0.3

1343

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Socket Types STREAM – uses TCP which is reliable, stream oriented protocol DATAGRAM – uses UDP which is unreliable, message oriented

protocol RAW – provides RAW data transfer directly over IP protocol (no

transport layer) Sockets can use

“unicast” ( for a particular IP address destination) “multicast” ( a set of destinations – 224.x.x.x) “broadcast” (direct and limited) “Loopback” address i.e. 127.x.x.x


A generic Client-Server application


A generic TCP application algorithm for TCP client

Find the IP address and port number of server Create a TCP socket Connect the socket to server (Server must be up and listening for

new requests) Send/ receive data with server using the socket Close the connection

algorithm for TCP server Find the IP address and port number of server Create a TCP server socket Bind the server socket to server IP and Port number (this is the port

to which clients will connect) Accept a new connection from client

returns a client socket that represents the client which is connected

Send/ receive data with client using the client socket Close the connection with client


A generic UDP applicationalgorithm for UDP client

Find the IP address and port number of serverCreate a UDP socketSend/ receive data with server using the socketClose the connection

algorithm for UDP serverFind the IP address and port number of serverCreate a UDP server socketBind the server socket to server IP and Port

number (this is the port to which clients will send)Send/ receive data with client using the client

socketClose the connection with client


Programming Client-Server in Java


Programming TCP Client-Server in Java All the classes related to sockets are in the java.net package, so

makesure to import that package when you program sockets.

All the input/output stream classes are in the java.io package, include this also

How to open a socket? If you are programming a client, then you would create an

object of Socket class

Machine name is the machine you are trying to open a connection to,

PortNumber is the port (a number) on which the server you are trying toconnect to is running. select one that is greater than 1,023.


Socket MyClient;try { MyClient = new Socket("Machine name", PortNumber);}catch (IOException e) { System.out.println(e);}

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Programming TCP Client-Server in Java If you are programming a server, then this is how you open a

socket:

When implementing a server you also need to create a socket object from the ServerSocket in order to listen for and accept connections from clients.


ServerSocket MyService;try {

MyServerice = new ServerSocket(PortNumber); } catch (IOException e) { System.out.println(e); }

Socket clientSocket = null;try {

clientSocket = MyService.accept();}catch (IOException e) {

System.out.println(e);}

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Programming TCP Client-Server in Java How to create an input stream?

On the client side, you can use the DataInputStream class to create an input stream to receive response from the server:

The class DataInputStream allows you to read lines of text and Java primitive data types in a portable way. It has methods such as read, readChar, readInt, readDouble, and readLine,.

On the server side, you can use DataInputStream to receive input fromthe client:


DataInputStream input;try { input = new DataInputStream(MyClient.getInputStream());}catch (IOException e) { System.out.println(e);}

DataInputStream input;try { input = new DataInputStream(clientSocket.getInputStream());}catch (IOException e) { System.out.println(e);}

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Programming TCP Client-Server in Java How to create an output stream?

On the client side, you can create an output stream to send informationto the server socket using the class PrintStream or DataOutputStreamof java.io:

The class PrintStream has methods for displaying textual representationof Java primitive data types. Its write and println methods are important.Also, you may want to use the DataOutputStream:


PrintStream output;try { output = new PrintStream(MyClient.getOutputStream());}catch (IOException e) { System.out.println(e);}

DataOutputStream output;try { output = new DataOutputStream(MyClient.getOutputStream());}catch (IOException e) { System.out.println(e);}

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Programming TCP Client-Server in Java On the server side

you can use the class PrintStream to send information to the client.

Note: You can use the class DataOutputStream as mentioned previously.


PrintStream output;try { output = new PrintStream(clientSocket.getOutputStream());}catch (IOException e) { System.out.println(e);}

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Programming TCP Client-Server in Java How to close sockets?

You should always close the output and input stream before you close the socket.

On the client side:

On the server side:


try { output.close(); input.close(); MyClient.close();}catch (IOException e) { System.out.println(e);}

try { output.close(); input.close(); clientSocket.close(); MyService.close();}catch (IOException e) { System.out.println(e);}

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Programming UDP Client-Server in Java How to open a datagram socket?

If you are programming a client, then you would create an object of DatagramSocket class

If you are programming a server, then this is how you open a socket:


try { DatagramSocket socket = new DatagramSocket();}catch (IOException e) { System.out.println(e);}

DatagramSocket socket = null;try {

socket = new DatagramSocket(4445);} catch (IOException e) { System.out.println(e); }

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Programming UDP Client-Server in Java How to send/receive on Datagram sockets?

On the client side, you can use the DatagramPacket class To send data

To receive data


byte[] buf = new byte[256];InetAddress address = InetAddress.getByName(args[0]);DatagramPacket packet = new DatagramPacket(buf,

buf.length, address, 4445);socket.send(packet);

packet = new DatagramPacket(buf, buf.length);socket.receive(packet);String received = new String(packet.getData());System.out.println(“Received from server: " + received);

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Programming UDP Client-Server in Java How to send/receive on Datagram sockets?

On the Server side, you can use the DatagramPacket class To receive data

To send data

How to close a Datagram socket?


byte[] buf = new byte[256];DatagramPacket packet = new DatagramPacket(buf, buf.length);socket.receive(packet);

InetAddress address = packet.getAddress();int port = packet.getPort();packet = new DatagramPacket(buf, buf.length, address, port);socket.send(packet);

socket.close();

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