SOCKET PROGRAMMING (lập TRÌNH MẠNG cơ bản SLIDE)

SOCKET PROGRAMMING


Introduction

 The socket API is an Interprocessing Communication (IPC) programming
interface originally provided as part of the Berkeley UNIX operating
system.

 It has been ported to all modern operating systems, including Sun
Solaris and Windows systems.

 It is a de facto standard for programming IPC, and is the basis of
more sophisticated IPC interface such as remote procedure call and
remote method invocation.

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The conceptual model of the socket API

P ro c ess A

P ro c ess B

a socket
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The socket API

 A socket API provides a programming construct termed a socket. A
process wishing to communicate with another process must create an
instance, or instantiate, such a construct

 The two processes then issues operations provided by the API to send
and receive data.

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Connection-oriented & connectionless datagram socket



A socket programming construct can make use of either the UDP or TCP protocol.



Sockets that use UDP for transport are known as datagram sockets, while sockets that use
TCP are termed stream sockets.



Datagram sockets can support both connectionless and connection-oriented

communication at the application layer. This is so because even though datagrams are sent or
received without the notion of connections at the transport layer, the runtime support of the
socket API can create and maintain logical connections for datagrams exchanged between two
processes, as you will see in the next section

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Connection-oriented & connectionless datagram socket

sock et
A P I r u n t im e
suppo r t

P roce ss A

P roce ss B

sock et
A P I r u n t im e
suppo r t

tr a n s p o r t la y e r s o ftw a r e

tr a n s p o r t la y e r s o ftw a r e

c o n n e c t io n le s s d a ta g r a m s o c k e t
a d a ta g r a m

a lo g ic a l c o n n e c t io n c r e a t e d a n d m a in t a in e d
b y t h e r u n t im e s u p p o r t o f t h e d a t a g r a m
socket A P I
sock e t
A P I r u n t im e
su pp o r t

P rocess A

P roce ss B

sock e t
A P I r u n t im e
su p po r t

tr a n s p o r t la y e r s o ft w a r e

tr a n s p o r t la y e r s o ftw a r e

c o n n e c t io n - o r ie n t e d d a t a g r a m s o c k e t

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Networking Basics
 Computers running on the Internet communicate to each other using either the Transmission
Control Protocol (TCP) or the User Datagram Protocol (UDP)

 TCP
 When two applications want to communicate to each other reliably, they establish a

connection and send data back and forth over that connection
 TCP provides a point-to-point channel for applications that require reliable

communications. The Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), and
Telnet are all examples of applications that require a reliable communication channel

 UDP
 The UDP protocol provides for communication that is not guaranteed between two

applications on the network. UDP is not connection-based like TCP. Rather, it sends
independent packets of data, called datagrams, from one application to another

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Client-Server
 Client - initiates connection
 retrieves data,
 displays data,
 responds to user input,
 requests more data

 Examples:
 Web Browser
 Chat Program

 PC accessing files

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Client-Server
 Server - responds to connection
 receives request for data,
 looks it up,
 delivers it

 Examples:
 Web Server
 Database Server
 Domain Name Server
 Stock Quote Server

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Client-Server

 Difference between client and server is semantic
 It’s all just peers talking to each other
 Protocol - roles, vocabulary, rules for communication (more later)

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TCP/IP: The Internet Protocol

Application Layer (HTTP, FTP, SMTP)

Transport Layer (TCP, UDP)

Internet Layer (IP)

Physical Network

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TCP/UDP/IP

 IP
 raw packets
 the “Internet Layer”

 TCP
 data stream
 reliable, ordered
 the “Transport Layer”

 UDP
 user datagrams (packets)
 unreliable, unordered
 the “Transport Layer”

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The Three ‘I’s
 internet
 any IP-based network

 Internet
 the big, famous, world-wide IP network

 intranet
 a corporate LAN-based IP network

 extranet
 accessing corporate data across the Internet

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Sockets and Ports

 Port: a meeting place on a host
 one service per port
 1-1023 = well-known services
 1024+ = experimental services, temporary

 Socket: a two-way connection

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Well-Known Ports
 20,21: FTP
 23: telnet
 25: SMTP
 43: whois
 80: HTTP
 119: NNTP
 1099: RMI

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Sockets and Ports (Diagram)

port 13

Time Service

port 80

Web Service

Client

Socket

Socket

Server

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Understanding Ports

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Communication between Applications Using Ports

Local ports identify the application establishing a connection from other
programs, allowing multiple TCP applications to run on the same

machine.

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Transmission Control Protocol

TCP establishes a virtual connection to transmit data

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TCP Programmning in Java
ServerSocket server = new ServerSocket(port);
Socket serverSoc = server.accept();

Socket clientSoc = new Socket(serverAdd,port);

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TCP Programmning in Java
OutputStream outClient =
clientSoc.getOutputStream();

InputStream inServer =
serverSoc.getInputStream();
stream

Server

Client

InputStream inClient =
clientSoc.getInputStream();
OutputStream outServer =
serverSoc.getOutputStream();
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Socket Basics
 A socket is a connection between two hosts. It can perform seven 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

 Java's Socket class, which is used by both clients and servers, has methods that correspond to the
first four of these operations. The last three operations are needed only by servers, which wait for
clients to connect to them. They are implemented by the ServerSocket class

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Program using client socket

1.
2.
3.

The program creates a new socket with a Socket( ) constructor.
The socket attempts to connect to the remote host.
Once the connection is established, the local and remote hosts get input and
output streams from the socket and use those streams to send data to each
other. This connection is full-duplex; both hosts can send and receive data
simultaneously.

4.

When the transmission of data is complete, one or both sides close the
connection. Some protocols, such as HTTP 1.0, require the connection to be
closed after each request is serviced. Others, such as FTP, allow multiple
requests to be processed in a single connection.

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Socket Basics - Constructors
public Socket(String host, int port) throws UnknownHostException,
IOException

This constructor creates a TCP socket to the specified port on the specified host and
attempts to connect to the remote host. For example:
try {
Socket toOReilly = new

Socket("www.oreilly.com",

80);
// send and receive data...
} catch (UnknownHostException e) {
System.err.println(e);
} catch (IOException e) {
System.err.println(e);
}

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LowPortScanner Program
import java.net.*;
import java.io.*;
public class LowPortScanner {
public static void main(String[] args) {

String host = "localhost";
if (args.length > 0) host = args[0];
for (int i = 1; i < 1024; i++) {
try {
System.out.print("Scanning on port : "+i +" ; ");
Socket s = new Socket(host, i);
System.out.println("There is a server on port " + i + " of "+host);
}
catch (UnknownHostException e) {
System.out.println("The Server adress is unknown");
break;
}
catch (IOException e) {
System.out.println("The Server is not found");
}
}}}

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