Socket programming in C

Socket Programmingin C

Socket Programmingin C

connecting processes

Dipak Kumar Swain

MCA 4th Semester

Regd No-1105227024

OverviewOverview

• Introduction to Sockets

• A generic Client-Server application

• Types of Socket

• Socket APIs• Socket Programming with TCP

• Socket Programming with UDP

• Conclusion

• References

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Introduction to SocketsIntroduction to Sockets

What is a Sockets?

• Socket is an interface between application and network which is used for communication between processes

• Data can be sent to or received through a socket from another process running on the same machine or a different machine

• Socket internally represents the three things:– Protocol

– IP address

– Port number

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Client Server ApplicationClient Server Application

Most interprocess communication uses client-server model• Server waits for client to request a connection and Client contacts

server to establish a connection.

• Client sends request and Server sends reply.

• Client and/or server terminate connection.

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Client Server ApplicationClient Server Application

• What makes a connection?

{Source<IP address, Port #> , Destination <IP address, Port #>}

i.e. source socket – destination socket pair uniquely identifies a connection.

• Example

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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Types of SocketTypes of Socket

Two essential types of sockets :

– STREAM Socket – Treat communications as a continuous stream of characters.

– DATAGRAM Socket– Read entire messages at once.

Stream Socket(SOCK_TCP) Datagram

Socket(SOCK_DGRAM)

TCP UDP

Connection Oriented Connection Less

Reliable Delivery Unreliable Delivery

In-Order Guaranteed No-Order Guaranteed

Bidirectional Can Send Or Receive

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Socket APIsSocket APIs

Some Essential System calls used by TCP & UDP Socket

• socket ( ):

• bind( ):

• listen( ):

• connect( ):

• accept( ):

• send( ):

• recv( ):

• sendto( ):

• recvfrom( ):

• close( ):

Socket System Call – create an end point socket for communication

#include <sys/socket.h>

int socket(int domain, int type, int protocol);

Returns an unsigned integer called socket descriptor

Socket System Call – create an end point socket for communication

#include <sys/socket.h>

int socket(int domain, int type, int protocol);

Returns an unsigned integer called socket descriptor

Bind System Call –Bind an IP address and port number with a socket

#include <sys/socket.h>

int bind( int sockfd, struct sockaddr *serv_addr, int addrlen);

Returns 0 on success

Bind System Call –Bind an IP address and port number with a socket

#include <sys/socket.h>

int bind( int sockfd, struct sockaddr *serv_addr, int addrlen);

Returns 0 on success

Listen System Call:– Used by Server Process in TCP for passively waiting for connection

#include <sys/socket.h>

int listen( int sockfd, int backlog);

Returns 0 on success

Listen System Call:– Used by Server Process in TCP for passively waiting for connection

#include <sys/socket.h>

int listen( int sockfd, int backlog);

Returns 0 on success

Connect System Call – Initiates a connection on TCP Socket.

#include <sys/socket.h>

int connect( int sockfd, struct sockaddr *addr, int addrlen);

Returns 0 on success

Connect System Call – Initiates a connection on TCP Socket.

#include <sys/socket.h>

int connect( int sockfd, struct sockaddr *addr, int addrlen);

Returns 0 on success

Accept System Call:– Accept a connection from client socket.

#include <sys/socket.h>

int accept( int sockfd, struct sockaddr *addr, int *addrlen);

Returns a non-negative descriptor on success

Accept System Call:– Accept a connection from client socket.

#include <sys/socket.h>

int accept( int sockfd, struct sockaddr *addr, int *addrlen);

Returns a non-negative descriptor on success

Send System Call – Send data to another TCP socket.

#include <sys/socket.h>int send( int sockfd, void *msg, int size, int flag);Returns number of characters sent on success

Send System Call – Send data to another TCP socket.

#include <sys/socket.h>int send( int sockfd, void *msg, int size, int flag);Returns number of characters sent on success

Recv System Call – Receive data from another TCP socket.#include <sys/socket.h>int recv( int sockfd, void *msg, int size, int flag);

Returns number of characters sent on success or -1 on error

Recv System Call – Receive data from another TCP socket.#include <sys/socket.h>int recv( int sockfd, void *msg, int size, int flag);

Returns number of characters sent on success or -1 on error

Sendto System Call – Send datagram to the specified UDP socket.int sendto( int sockfd, void *msg, int noOfbytes, int flags, struct sockaddr *to, int *sock_length);Returns number of bytes written to socket on success or -1 on error

Sendto System Call – Send datagram to the specified UDP socket.int sendto( int sockfd, void *msg, int noOfbytes, int flags, struct sockaddr *to, int *sock_length);Returns number of bytes written to socket on success or -1 on error

Recvfrom System Call – Receive datagram packet from another UDP socketint recvfrom( int sockfd, void *msg, int noOfbytes, int flags, struct sockaddr *from, int *sock_length);

Returns number of bytes read from socket on success or -1 on error

Recvfrom System Call – Receive datagram packet from another UDP socketint recvfrom( int sockfd, void *msg, int noOfbytes, int flags, struct sockaddr *from, int *sock_length);

Returns number of bytes read from socket on success or -1 on error

Close System Call – Closes the communication channel between client & server.int close(int sockfd);

Return 0 on success & sockfd is the socket descriptor which will be closed.

Close System Call – Closes the communication channel between client & server.int close(int sockfd);

Return 0 on success & sockfd is the socket descriptor which will be closed.

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Socket Programming With UDPSocket Programming With UDP

socket socket

recvfrom

sendto

sendto

recvfrom

bind

close

ServerClient

Request

Response

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Socket Programming With TCPSocket Programming With TCP

Client Server

socket

connect

send/recv

close

accept

listen

bind

socket

recv/send

close

Connect

3-way handshake

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ConclusionConclusion

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Not only message can send but also a file can send through Socket.

To handle multiple client simultaneously , we can use the following models at server side:

Process ModelThread ModelWorker Pool Model

ReferencesReferences

• Cystem Programming at the Roots… By Susant K Rout and T Prabakaran

• UNIX Network Programming, by Richard Stevens.

• LINUX man page

Accessible through following command– man 2 <system_call_name>

– E.g. man 2 socket

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