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EX NO 2 INTRODUCTION TO SOCKET PROGRAMMING

Aim:

To study about the basics of Socket in Network Programming

Network Programming

Network programming involves writing programs that communicate with other programs

across a computer N/W. One program is normally called the client and the other the server.

!ommon e"amples in the T!P/#P are web clients $browsers% & Web Servers 'TP clients &

server and Telnet clients & servers.

To facilitate communication between unrelated processes and to standardi(e network

programming an )P# is needed. There are two such )P#s*

+. Sockets sometimes called ,-erkeley Sockets. 0T# $0/open transport interface%

Socket

#n T!P/#P an addressable point that consists of an #P address and a T!P or 12P port

member that provides application with access to T!P/#P protocol is called Socket.

) socket is an abstraction that represents an endpoint of communication. The operations

that can be performed on a socket include control operations $such as associating a port number

with the socket initiating or accepting a connection on the socket or destroying the socket% data

transfer operations $such as writing data through the socket to some other application or reading

data from some other application through the socket% and status operations $such as finding the#P address associated with the socket%. The complete set of operations that can be performed on a

socket constitutes the Socket API $)pplication Programming #nterface%.

Str!ct!re

Structures are used in socket programming to hold information about the address. The

generic socket address structure is defined below*

struct sockaddr

3

unsigned short sa4family5 /6 address family 6/

char sa4data7+895 /6 +8 bytes of protocol address6/

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IP"# Socket A$$re Str!ct!re

This structure is also called as ;#nternet socket address structure header.

struct in4addr 3

in4addr4t s4addr5 /6 ?@bit #Pv8 address network byte ordered 6/

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struct sockaddr4in3

unit4t sin4len5 /6 length of structure $+A byte% 6/

sa4family4t sin4family5 /6)'4#NBT6/

in4port4t sin4port5 /6 +A@bit T!P or 12P port number 6/

/6 network byte ordered 6/

struct in4addr sin4addr5 /6?@bit #pv8 address network byte ordered 6/

char sin4(ero7C95 /6 unused D initiali(e to all (eroes 6/

:5

Im%ortant &!nction'(ocket)*

This function is called by both T!P server and client process to create an empty socket.

Einclude =sys/socket.h>

int socket $int family int type int protocol%5

family* specifies the protocol family and is one of the constants below*

+ami,- Decri%tion

)'4#NBT #Pv8 protocols

)'4#NBTA #PvA protocols

)'4FO!)F 1ni" domain protocols

)'4GO1TB Gouting sockets

)'4HBI Hey sockets

type* indicates communications semantics

SO!H4STGB)J @ stream socket

SO!H42KG)J @ datagram socketSO!H4G)W @ raw socket

protocol* set to L e"cept for raw sockets.

Geturns on success* socket descriptor $a small nonnegative integer% on error* @+

2( .in$)*

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The bind function assigns a local protocol address to a socket. The protocol address is the

combination of either a ?@bit #PM8 address or a +C@bit #PMA address along with a +A@bit T!P

or 12P port number.


int bind$int sockfd const struct sockaddr 6myaddr socklen4t addrlen%5

sockfd* a socket descriptor returned by the socket function.

6myaddr* a pointer to a protocol@specific address.

addrlen* the si(e of the socket address structure.

Geturns on success* L on error* @+

/( connect)*

The connect function is used by a T!P client to establish a connection with a T!P server.


int connect$int sockfd const struct sockaddr 6servaddr socklen4t addrlen%5

sockfd* a socket descriptor returned by the socket function

6servaddr* a pointer to a socket address structure

addrlen* the si(e of the socket address structure


#( ,iten)*

The listen function is called only by a T!P server to converts an unconnected socket into a

passive socket indicating that kernel should accept incoming connection reuests directed to its

socket.

Einclude=sys/socket.h>int listen $int sockfd int backlog%5


backlog* ma"imum number of connections that the kernel should ueue for this socket.


0( acce%t)*

The accept function is called by the T!P server to return the ne"t completed connection from the

front of the completed connection ueue.

Einclude=sys/socket.h>int accept $int sockfd struct sockaddr 6cliaddr socklen4t 6addrlen%5

sockfd* This is the same socket descriptor as in listen call.

6cliaddr* used to return the protocol address of the connected peer process

6addrlen* length of the address.

Geturns on success* a new $connected%socket descriptor on error*@+

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1( c,oe)*

The close function is used to close a socket and terminate a T!P connection.

Einclude =unistd.h>

int close $int sockfd%5

sockfd* This socket descriptor is no longer useable.


( rea$)*

The read function is used to receive data from the specified socket.

Einclude =unistd.h>

ssi(e4t read$int sockfd const void 6 buf si(e4t nbytes%5


buf* buffer to store the data.

nbytes* si(e of the buffer

Geturns* number of bytes read if OHL on BO' @+ on error

3( write)*

The write function is used to send the data through the specified socket.

Einclude =unistd.h>

ssi(e4t write$int sockfd const void 6 buf si(e4t nbytes%5


buf* buffer to store the data.

nbytes* si(e of the buffer

Geturns* number of bytes written if OHL on BO' @+ on error

4( en$to)*

This function is similar to the write function but additional arguments are reuired.

Einclude=sys/socket.h>

ssi(e4t sendto$int sockfd const void 6buff si(e4t nbyte int flag

const struct sockaddr 6to socklen4t addrlen%5

sockfd D socket descriptor

6buff D pointer to buffer to write from.

nbytes D number of bytes to write.to D socket address structure containing the protocol address of where the data is to be sent.

addrlen D si(e of the socket address structure

Geturns* number of bytes read or written if OH@+ on error

'5( rec"&rom)*

This function is similar to the read function but additional arguments are reuired.

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ssi(e4t recvfrom$int sockfd void 6buff si(e4t nbyte int flag

struct sockaddr 6from socklen4t 6addrlen%5

sockfd D socket descriptor

6buff D pointer to buffer to read.nbytes D number of bytes to read.

addrlen D si(e of the socket address structure

from @ socket address structure of who sent the datagram.

Geturns* number of bytes read or written if OH@+ on error

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EOF notifcation

data ( reply)

data ( request)

Connection establishment

blocks until connection rom client

process request

TCP Client

TCP Server

socket()

socket()

bind()

listen()

accept()

read()write()

read()

write()

read()

close()

close()

conect()

Socket &!nction &or connection6oriente$ comm!nication

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UDP Client

UDP Server

Blocks until datagram receied rom a client

!rocess request

"ata (reply)

"ata (request)

close()

recrom()

sendto()

sendto()

recrom()

bind()

socket()

socket()

Socket &!nction &or connection6,e comm!nication

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Program to create a ocket

/6 B"@+ Program To !reate a Socket 6/

Einclude =stdio.h> /6 NBB2B2 B)2BG '#FBS 6/

Einclude =stdlib.h>

Einclude =unistd.h>


Einclude=netinet/in.h>

Einclude=arpa/inet.h>

int main$%

3

int sockfd+sockfd5 /6 sokcet file descriptors 6/

sockfd+socket$)'4#NBTSO!H4STGB)JL%5 /6 socket system call 6/

sockfdsocket$P'4#NBTSO!H42KG)JL%5

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if$sockfd+@+% /6 error checking 6/

3

printf$QSocket+ not !reatedRnQ%5

:

else

3

printf$QSocket+ !reated and Rt Socket+ 'ile 2escriptor value is d RnQsockfd+%5

if$sockfd@+%

3

printf$Qsocket creation errorQ%5

:

else

3

printf$QSocket created and Rt socket descriptor value is dRnQsockfd%5

:

::

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O!t%!t:

Socket ' &i,e $ecri%tion "a,!e i /

Socket # &i,e $ecri%tion "a,!e i #

Program to 7in$ a ocket

/6 B"@ Program to -ind a Socket 6/

Einclude=stdio.h>


Einclude=arpa/inet.h>

Einclude=netinet/in.h>

Edefine POGTNO LLL /6 Type definition of a Port number 6/

int main$%

3

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int sockfdiPOGTNO5

struct sockaddr4in myaddr5 /6 -uiltin structure for internet address 6/

if$$sockfdsocket$)'4#NBTSO!H4STGB)JL%%@+%

3printf$QSocket !reation BrrorRnQ%5:

myaddr.sin4family)'4#NBT5 /6 Structure variable definition 6/

myaddr.sin4porthtons$POGTNO%5

myaddr.sin4addr.s4addr#N)22G4)NI5

memset$&$myaddr.sin4(ero%RLC%5 /6 fills with constant byte to remaining space 6/

/6 socket -inding process and error checking 6/

if$bind$sockfd$struct sockaddr 6%&myaddrsi(eof$struct sockaddr%%U@+%

3

printf$Q Socket is -inded at port dRnQi%5

:

else

3

printf$Q-inding BrrorRnQ%5

:

:

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OUTPUT:

SOCKET IS 7INDED AT PORT 2555

Program to im%,ement ,iten)* -tem ca,,

/6 B"@? Program to implement F#STBN system call 6/

Einclude =stdio.h> /6 These are the usual header files 6/

Einclude =sys/types.h>

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Einclude =netinet/in.h>

Edefine POGT ?VVL /6)ssigning Port number 6/

Edefine -)!HFOK + /6 Number of allowed connections 6/

main$%

3

int fd5 /6 file descriptors 6/

struct sockaddr4in server5 /6 servers address information 6/

struct sockaddr4in client5 /6 clients address information 6/

int sin4si(e5

int "5

if $$fdsocket$)'4#NBT SO!H4STGB)J L%% @+ %3 /6 calls socket$% 6/

printf$Qsocket$% errorRnQ%5

e"it$@+%5

:

server.sin4family )'4#NBT5

server.sin4port htons$POGT%5 /6 Gemember htons$% from Q!onversionsQ section % 6/

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server.sin4addr.s4addr #N)22G4)NI5 /6 #N)22G4)NI puts your #P address

automatically 6/

b(ero$&$server.sin4(ero%C%5 /6 (ero the rest of the structure 6/

if$bind$fd$struct sockaddr6%&serversi(eof$struct sockaddr%%@+% /6 calls bind$% 6/

3 printf$Qbind$% errorRnQ%5

e"it$@+%5

:

"listen$fd-)!HFOK% 5 /6 calls listen$% 6/

if$"@+%

3

printf$Qlisten$% errorRnQ%5

e"it$@+%5

:

else

3

printf$Server is in listening mode Rn %5

:

close$fd%5 /6 close fd 6/

:

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OUTPUT:

Ser"er i in ,itening mo$e(

Program &or acce%t)* -tem ca,,

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/6 B"@? Program to implement )!!BPT system calls 6/

Einclude =stdio.h> /6 These are the usual header files 6/

Einclude =sys/types.h>


Einclude =netinet/in.h>

Edefine POGT ?VVL /6 )ssigning Port numbers 6/

Edefine -)!HFOK /6 Number of allowed connections 6/

main$%

3

int fd fd5 /6 file descriptors 6/

struct sockaddr4in server5 /6 servers address information 6/

struct sockaddr4in client5 /6 clients address information 6/

int sin4si(e5

if $$fdsocket$)'4#NBT SO!H4STGB)J L%% @+ % /6 calls socket$% 6/

3

printf$Qsocket$% errorRnQ%5

e"it$@+%5

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3

sin4si(esi(eof$struct sockaddr4in%5

if $$fd accept$fd$struct sockaddr 6%&client&sin4si(e%%@+%3 /6 calls accept$% 6/

printf$Qaccept$% errorRnQ%5

e"it$@+%5

:

else

printf$Q Server is in accept mode Q%5

printf$QIou got a connection from sRnQinet4ntoa$client.sin4addr% %5 /6 prints clients #P 6/

close$fd%5 /6 close fd 6/

:

:

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OUTPUT:

cc("8k!mar

(9a(o!t7in$)*error

Re!,t:

Thus the basics of socket with e"ample peograms are studied.

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