This document discusses socket programming in C. It begins with an introduction to sockets, describing them as an interface between applications and networks that allows processes to communicate. It then covers the client-server model and types of sockets like stream and datagram. The main socket APIs are explained, including functions for creating, binding, listening, connecting, sending, receiving and closing sockets. Examples of socket programming with UDP and TCP are provided, showing the typical functions used in each case. The document concludes by noting that files can also be sent over sockets and models for handling multiple clients like process, thread and worker pools.

1. Socket Programming
in C
connecting
processes
Dipak Kumar Swain
MCA 4th Semester
Regd No-1105227024

2. Overview
• 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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3. Introduction 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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4. Client 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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5. Client 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
1343
Client
192.168.0.2
Server
80
1343
Client
192.168.0.3
192.168.0.1
5488
Client
192.168.0.2
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6. Types 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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7. Socket APIs
Socket System Call – create an end
Socket System Call UDP Socketend
Some Essential System calls used byCall –Bind createaddress
TCP & – an IP an
Bind Systemfor communication
Bind System Call –Bind an IP address
point socket for communication
point socket
Listen System Call:– Used by Server
Listen System Call:– Used by
• socket ( ):
and port number with a socket Server
and port<sys/socket.h> socket
number with a
#includein TCP for passively waiting
#includeSystem for passively waiting
<sys/socket.h>
Connect in TCP Call – Initiates a
Connect
Process System Call – Initiates a
Process
#include <sys/socket.h>
#include <sys/socket.h>
• bind( ):
Accept SystemTCPSocket. a
Accept SystemCall:– Accept a
connection on TCP Socket. type, int
connection on domain, int
for connection domain, int type, int
for connection Call:– Accept
int socket(intCall– Send data to
int socket(int
Send Systemsockfd, Send data to
Send SystemCallclient
connection from client socket.
connection from – struct
int bind(<sys/socket.h>socket.
int
int bind(<sys/socket.h>
• listen( ):
#includeTCP socket. Receive data from
#includeTCP sockfd, struct
protocol);intsocket.Receive data from
protocol); Call –
Recv System Call –
Recv System
another <sys/socket.h> addrlen);
another *serv_addr, int
sockaddr<sys/socket.h> addrlen);
#includeSystemCall – Send datagram
sockaddr *serv_addr,Send
int
#include
Sendto System Call integer datagram
Sendto TCPunsigned –intstruct
another an unsigned integercalled
another <sys/socket.h> backlog);
int listen( intintsockfd, struct
• connect( ):
intconnect( int sockfd,
listen( intsockfd,
sockfd,
Returns TCPsocket. intbacklog);
connect(socket.
Returns <sys/socket.h>
#include anSystemCallstructcalled
#include System Call– Receive
Recvfromonintsockfd, struct
Recvfrom*addr,
intthe specified UDP socket.
to the specified sockfd, – Receive
intaccept(*addr, intsocket.
to accept(int UDP addrlen);
#include0<sys/socket.h>
Returnsdescriptorint addrlen);
#include on Call
sockaddr<sys/socket.h> the
Returns 0on success
socketSystemsockfd,Closes*msg, int
sockaddr int success void
socketdescriptor – void the
Returns 0 int success *addrlen); int
Close Systemsockfd,Closes*msg,
• accept( ):
int send( packet from*addrlen); int
Returns 0 packet from void *msg,
Close
int send( on success void *msg,
datagram *addr, int another UDP int
datagram *addr, int
sockaddrintintCall – void *msg, int
sockaddr sockfd,
int sendto( intsockfd, another UDP
int sendto(
sockfd,
int recv( intsockfd, void *msg, int
int recv( on success
communication channel between
size, int 0 on flags, between
communication
Returns flag);success struct sockaddr
size, int 0 int
Returns
socket flag); flags, struct sockaddr
socket a non-negative descriptor
• send( ):
noOfbytes, int channeldescriptoron
noOfbytes,
Returns server.
size, int flag);
Returns server.
size, int flag);
client & numbersockfd,void *msg,senton
client & a non-negative *msg,int on
Returns*sock_length);
Returns number of characters int
int recvfrom( int sockfd, void
int int
*to,recvfrom( int of characters sent on
*to, int
success *sock_length);
success
• recv( ):
Returns number of characters sent on
Returns int flags,struct sockaddr *from,
noOfbytes,number of characters sent on
int close(intflags,of bytes written*from,
noOfbytes,
int close(intsockfd);
sockfd);
success number of bytes writtento
success number struct
Returnsorint on error sockaddr to
Returnsor-1 on error
success
int *sock_length);
success -1
int *sock_length);
• sendto( ):
Returnonon success & sockfd is the
Returnonsuccess or & on error
socket 0 on success -1 sockfd is the
socket 0 success or -1 on error
Returnsdescriptorofbyteswill befrom
Returnsnumber which read from
socket descriptorofwhich will be
socket number bytes read
• recvfrom( ):
socket on success or -1 on error
socket
closed. on success or -1 on error
closed.
• close( ):
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8. Socket Programming With UDP
Client
Server
socket
socket
bind
sendto
recvfrom
Request
Response
recvfrom
sendto
close
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9. Socket Programming With TCP
Client
Server
socket
socket
bind
listen
connect
Connect
3-way handshake
accept
send/recv
recv/send
close
close
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10. Conclusion
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 Model
Thread Model
Worker Pool Model
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11. References
• 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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