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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