Socket Programing Example

8/13/2019 Socket Programing Example

1/19

TCP/IP socket programming in CThis is a quick tutorial on socket programming in clanguage on a Linux system.

"Linux" because the code snippets shown oer here will work only on a Linux

system and not on !indows. The windows api to socket programmingis called

winsock and we shall go through it in another tutorial.

ockets are the "irtual" endpoints o#

any kind o# network communications

done between $ hosts oer in a

network. %or example when you type

www.google.com in your web

browser& it opens a socket and

connects to google.com to #etch the

page and show it to you. ame with

any chat client like gtalk or skype.

'ny network communication goes

through a socket.

The socket api on linux is similar to

bsd/unix sockets #rom which it has

eoled. 'lthough oer time the api has become slightly di##erent at #ew places.

'nd now the newer o##icial standard is posix sockets apiwhich is same as bsd

sockets.

This tutorial assumes that you hae basic knowledge o# C and pointers. (ou willneed to hae gcc compilerinstalled on your Linux system. 'n I)* along with

gcc would be great. I would recommend geany as you can quickly edit and run

single #ile programs in it without much con#igurations. +n ubuntu you can do a

sudo apt,get install geany on the terminal.

'll along the tutorial there are code snippets to demonstrate some concepts. (ou

can run those code snippets in geany rightaway and test the results to better

understand the concepts.

Create a socketThis #irst thing to do is create a socket. The socket#unction does this.

-ere is a code sample 1234567

8910

#include#include

tmain(intargc , char*argv[]){ tsocket_desc; socket_desc socket!"_$%&' ( )*+,_)'-&" ( 0

1(socket_desc == -1) {
http://www.binarytides.com/winsock-socket-programming-tutorial/http://en.wikipedia.org/wiki/POSIXhttp://en.wikipedia.org/wiki/POSIXhttp://www.binarytides.com/winsock-socket-programming-tutorial/


2/19

1112131415

23 t1("Could not create socket"); 3etu3 0;

%unction socket0 creates a socket and returns a descriptor which can be used in

other #unctions. The aboe code will create a socket with #ollowing properties

'ddress %amily , '%1I2*T this is IP ersion 30Type , +C41T5*'6 this means connection oriented TCP protocol0Protocol , 7 8 or IPP5+T+1IP This is IP protocol9

2ext we shall try to connect to some serer using this socket.

!e can connect to www.google.com

Note

'part #rom +C41T5*'6 type o# sockets there is another type called

+C41):5'6 which indicates the UDP protocol. This type o# socket is non,connection socket. In this tutorial we shall stick to +C41T5*'6 or TCP sockets.

Connect socket to a server

!e connect to a remote serer on a certain port number. o we need $ things& ip

addressand port numberto connect to.

To connect to a remote serer we need to do a couple o# things. %irst is to create a

sockaddr1in structure with proper alues.

struct sockaddr1in serer;

-ae a look at the structure

12345678

910111213141516

// $4 "_$%&' socketsst3uctsockaddr_in sho3t sin_!amil; ## e$g$ %&_', %&_'+ unsined short sin_ort; ## e$g$ tons(./0) st3uctin_addr sin_addr; ## see struct in_addr, elo2 ch93 sin_3ero[4]; ## 3ero tis i! ou 2ant tost3uctin_addr unsined longs_addr; ## load 2it inet_ton()st3uctsockaddr unsined short sa_!amil; ## address !amil, %&_555 ch93 sa_data[1/]; ## 1/ tes o! rotocoladdress

The sockaddr1in has a member called sin1addr o# type in1addr which has a s1addr

which is nothing but a long. It contains the IP address in long #ormat.%unction inet_addris a ery handy #unction to conert an IP address to a long

#ormat. This is how you do it


3/19

1see.sin_dd.s_dd inet_dd!"6/$178$7.8$70");

o you need to know the IP address o# the remote serer you are connecting to.

-ere we used the ip address o# google.com as a sample. ' little later on we shall

see how to #ind out the ip address o# a gien domain name.

The last thing needed is the connect#unction. It needs a socket and a sockaddr

structure to connect to. -ere is a code sample.

123456789

10111213141516171819

2021222324252627282930

#include#include#include //inet_dd tmain(intargc , char*argv[]){ tsocket_desc; st3uctsockaddr_in server;

//+ete socket socket_desc socket!"_$%&' ( )*+,_)'-&" ( 0 1(socket_desc == -1) { 23 t1("Could not create socket");

see.sin_dd.s_dd inet_dd!"6/$178$7.8$70"); see.sin_:ily "_$%&' see.sin_ot htons! 80

//+onnect to e:ote see 1(connect(socket_desc , (structsockaddr *)9server ,sizeof(server)) : 0) { 2uts("connect error"); 3etu3 1; 2uts("Connected"); 3etu3 0;

It cannot be any simpler. It creates a socket and then connects. I# you run the

program it should show Connected.

Try connecting to a port di##erent #rom port


4/19

streams each haing communication o# its own. Think o# this as a pipe which is not

inter#ered by other data.

+ther sockets like =)P & IC6P & '5P dont hae a concept o# "connection". These

are non,connection based communication. !hich means you keep sending or

receiing packets #rom anybody and eerybody.

Send data over socket

%unction sendwill simply send data. It needs the socket descriptor & the data to

send and its si>e.

-ere is a ery simple example o# sending some data to google.com ip 1234

567891011121314

1516171819202122232425

2627282930313233343536373839

#include#include //stlen#include#include //inet_dd

tmain(intargc , char*argv[]){ tsocket_desc; st3uctsockaddr_in server; ch93*message;



//+onnect to e:ote see 1(connect(socket_desc , (structsockaddr *)9server ,sizeof(server)) : 0)

{ 2uts("connect error"); 3etu3 1; 2uts("Connectedn");

//)end so:e dt :esse "#1$1rnrn"; 1( send(socket_desc , message , strlen(message) , 0) : 0) { 2uts("?end !ailed"); 3etu3 1;


5/19

404142

2uts("@ata ?endn"); 3etu3 0;

In the aboe example & we #irst connect to an ip address and then send the string

message ":*T / -TTP/?.?@r@n@r@n" to it.

The message is actually a http command to #etch the mainpage o# a website.

2ow that we hae send some data & its time to receie a reply #rom the serer. o

lets do it.

Note

!hen sending data to a socket you are basically writing data to that socket. This is

similar to writing data to a #ile. -ence you can also use the 2rite#unction to send

data to a socket. Later in this tutorial we shall use write #unction to send data.

Receive data on socket%unction recvis used to receie data on a socket. In the #ollowing example we

shall send the same message as the last example and receie a reply #rom the

serer.12345678910111213141516

1718192021222324252627

282930

#include#include //stlen#include#include //inet_dd tmain(intargc , char*argv[]){ tsocket_desc; st3uctsockaddr_in server; ch93*message , server_rel[7000];



//+onnect to e:ote see 1(connect(socket_desc , (structsockaddr *)9server ,sizeof(server)) : 0) { 2uts("connect error"); 3etu3 1;


6/19

31323334353637383940414243444546

47484950

2uts("Connectedn");

//)end so:e dt :esse "#1$1rnrn"; 1( send(socket_desc , message , strlen(message) , 0) : 0) {

2uts("?end !ailed"); 3etu3 1; 2uts("@ata ?endn");

//-eceie ely o: the see 1( recv(socket_desc, server_rel , 7000 , 0) : 0) { 2uts("recv !ailed"); 2uts("Ael receivedn"); 2uts(server_rel); 3etu3 0;

-ere is the output o# the aboe code

+onnected

;t )end

-ely eceied

''/1.1 302 ound

=oction htt//.oole.co.in/

+che?+ontol ite

+ontent?'ye te@t/ht:l chsetA'?8

)et?+ookie-&$;0edd21160dB2190'1324644706=1324644706)C6h;+9cDE&o_o e@ies)un( 22?;ec?2013 125146 E' th/ do:in.oole.co:

;te i( 23 ;ec 2011 125146 E'

)ee s

+ontent?=enth 221

F?F))?otection 1 :odeBlock

F?:e?*tions )"&*-$E$%


7/19

.


8/19

3456789

{ ch93*_name; #* B!!icial name o! ost$ *# ch93**_aliases; #* %lias list$ *# t_addrte; #* ost address te$ *# t_lengt; #* engt o! address$ *# ch93**_addr_list; #* ist o! addresses !rom nameserver$ *#

The _addr_listhas the IP addresses. o now lets hae some code to use them.

1234567

8910111213141516171819202122232425262728

2930313233

#include //int#include //stcy#include#include //hostent#include tmain(intargc , char*argv[]){ ch93*ostname = "222$google$com"; ch93i[100]; st3uctostent *e; st3uctin_addr **addr_list; ti; 1( (e = getostname( ostname ) ) == D)

{ //ethostByn:e iled heo!"getostname");

3etu3 1;

//+st the h_dd_list to in_dd ( since h_dd_list lsohs the i ddess in lon o:t only dd_list !structin_addr **) e-E_addr_list; 1o3(i = 0; addr_list[i] F= D; iGG)

{ //-etun the ist one st3c2y(i , inet_ntoa(*addr_list[i]) ); 23 t1("Hs resolved to I Hs", ostname , i); 3etu3 0;

+utput o# the code would look like

.oole.co: esoled to 74.125.235.20

o the aboe code can be used to #ind the ip address o# any domain name. Then

the ip address can be used to make a connection using a socket.

%unction inet_ntoawill conert an IP address in long #ormat to dotted #ormat. This

is Dust the opposite o# inet_addr.


9/19

o #ar we hae see some important structures that are used. Lets reise them

?. sockaddr_in, Connection in#ormation. =sed by connect & send & rec etc.

$. in_addr, Ip address in long #ormat

. sockaddr

3. ostent, The ip addresses o# a hostname. =sed by gethostbyname

In the next part we shall look into creating serers using socket. erers are the

opposite o# clients& that instead o# connecting out to others& they wait #or incoming

connections.

ocket serer+4 now onto serer things. ocket serers operate in the #ollowing manner

?. +pen a socket$. Eind to a addressand port0.

. Listen #or incoming connections.3. 'ccept connectionsF. 5ead/end

!e hae already learnt how to open a socket. o the next thing would be to bind it.

!ind socket to a port

The bind #unction can be used to bind a socket to a particular "address and port"

combination. It needs a sockaddr1in structure similar to connect #unction.

12345678910

1112131415161718192021

tsocket_desc;st3uctsockaddr_in server;//+ete socketsocket_desc socket!"_$%&' ( )*+,_)'-&" ( 01(socket_desc == -1){ 23 t1("Could not create socket");//ee the sockdd_in stuctue

see.sin_:ily "_$%&'see.sin_dd.s_dd $%";;-_"%Jsee.sin_ot htons! 8888 //Iind1( ind(socket_desc,(structsockaddr *)9server ,sizeof(server)) : 0){ 2uts("ind !ailed");

2uts("ind done");2ow that bind is done& its time to make the socket listen to connections. !e bind asocket to a particular IP address and a certain port number. Ey doing this we


10/19

ensure that all incoming data which is directed towards this port number is

receied by this application.

This makes it obious that you cannot hae $ sockets bound to the same port.

Listen for incoming connections on te socket

'#ter binding a socket to a port the next thing we need to do is listen #or

connections. %or this we need to put the socket in listening mode.

%unction listenis used to put the socket in listening mode. Gust add the #ollowing

line a#ter bind.12//=istenlisten!socket_desc ( 3

Thats all. 2ow comes the main part o# accepting new connections.

"ccept connection%unction accetis used #or this. -ere is the code12345678

910111213141516171819

20212223242526272829

303132

#include#include#include //inet_dd tmain(intargc , char*argv[]){ tsocket_desc , ne2_socket , c; st3uctsockaddr_in server , client;


//ee the sockdd_in stuctue see.sin_:ily "_$%&' see.sin_dd.s_dd $%";;-_"%J

see.sin_ot htons! 8888

//Iind 1( ind(socket_desc,(structsockaddr *)9server ,sizeof(server)) : 0) { 2uts("ind !ailed"); 2uts("ind done");

//=isten listen!socket_desc ( 3


11/19

3334353637

38394041424344

//"ccet nd inco:in connection 2uts("Jaiting !or incoming connections$$$"); c sizeof(structsockaddr_in); ne_socket ccet!socket_desc( !structsockaddr *)9client,(socklen_t*)9c); 1(ne2_socket:0) { 2e33o3("accet !ailed"); 2uts("Connection acceted"); 3etu3 0;

Program output

5un the program. It should show

Bind done

Litin o inco:in connections...

o now this program is waiting #or incoming connections on port


12/19

!e can simply use the 2rite#unction to write something to the socket o# the

incoming connection and the client should see it. -ere is an example 1234567891011121314

1516171819202122232425

262728293031323334353637383940414243444546

474849

#include#include //stlen#include#include //inet_dd#include //ite tmain(intargc , char*argv[]){ tsocket_desc , ne2_socket , c; st3uctsockaddr_in server , client; ch93*message;

//+ete socket socket_desc socket!"_$%&' ( )*+,_)'-&" ( 0

1(socket_desc == -1) { 23 t1("Could not create socket");

//ee the sockdd_in stuctue see.sin_:ily "_$%&' see.sin_dd.s_dd $%";;-_"%J see.sin_ot htons! 8888

//Iind

1( ind(socket_desc,(structsockaddr *)9server ,sizeof(server)) : 0) { 2uts("ind !ailed"); 3etu3 1; 2uts("ind done");


//"ccet nd inco:in connection 2uts("Jaiting !or incoming connections$$$"); c sizeof(structsockaddr_in); ne_socket ccet!socket_desc( !structsockaddr *)9client,(socklen_t*)9c); 1(ne2_socket:0) { 2e33o3("accet !ailed"); 3etu3 1;

2uts("Connection acceted");


13/19

50515253

//-ely to the client :esse "ello Client , ' ave received our connection$Kut ' ave to go no2, en"; ite!ne_socket ( :esse ( strlen(message)); 3etu3 0;

5un the aboe code in ? terminal. 'nd connect to this serer using telnet #rom

another terminal and you should see this

M telnet loclhost 8888

'yin 127.0.0.1...

+onnected to loclhost.

&sce chcte is NOPN.

ello +lient ( $ he eceied you connection. Iut $ he to o no( Bye

+onnection closed By oein host.o the clienttelnet0 receied a reply #rom serer.

!e can see that the connection is closed immediately a#ter that simply because

the serer program ends a#ter accepting and sending reply. ' serer like

www.google.com is always up to accept incoming connections.

It means that a serer is supposed to be running all the time. '#terall its a serer

meant to sere. o we need to keep our serer 5=22I2: non,stop. The simplest

way to do this is to put the accetin a loop so that it can receie incoming

connections all the time.

Live Server

o a lie serer will be alie #or all time. Lets code this up

123456

78910111213141516

171819

#include#include //stlen#include#include //inet_dd#include //ite tmain(intargc , char*argv[]){ tsocket_desc , ne2_socket , c; st3uctsockaddr_in server , client; ch93*message;

//+ete socket socket_desc socket!"_$%&' ( )*+,_)'-&" ( 0 1(socket_desc == -1) {

23 t1("Could not create socket");


14/19

202122232425262728293031323334

3536373839404142434445

46474849505152535455


//Iind

1( ind(socket_desc,(structsockaddr *)9server ,sizeof(server)) : 0) { 2uts("ind !ailed"); 3etu3 1; 2uts("ind done");


//"ccet nd inco:in connection 2uts("Jaiting !or incoming connections$$$"); c sizeof(structsockaddr_in); >h le( (ne2_socket = accet(socket_desc, (structsockaddr*)9client, (socklen_t*)9c)) ) { 2uts("Connection acceted");

//-ely to the client :esse "ello Client , ' ave received our

connection$ Kut ' ave to go no2, en"; ite!ne_socket ( :esse ( strlen(message)); 1(ne2_socket:0) { 2e33o3("accet !ailed"); 3etu3 1; 3etu3 0;

!e haent done a lot there. Gust the accept was put in a loop.

2ow run the program in ? terminal & and open other terminals. %rom each o# the

terminal do a telnet to the serer port.

*ach o# the telnet terminal would show

M telnet loclhost 8888

'yin 127.0.0.1...


&sce chcte is NOPN.

ello +lient ( $ he eceied you connection. Iut $ he to o no( Bye


15/19

'nd the serer terminal would show

Bind done

Litin o inco:in connections...

+onnection cceted

+onnection cceted

+onnection cceted

o now the serer is running nonstop and the telnet terminals are also connected

nonstop. 2ow close the serer program.

'll telnet terminals would show "Connection closed by #oreign host."

:ood so #ar. Eut still there is not e##ectie communication between the serer and

the client.

The serer program accepts connections in a loop and Dust send them a reply& a#ter

that it does nothing with them. 'lso it is not able to handle more than ? connection

at a time. o now its time to handle the connections & and handle multiple

connections together.

#andle multiple socket connections $it treads

To handle eery connection we need a separate handling code to run along with

the main serer accepting connections.

+ne way to achiee this is using threads. The main serer program accepts a

connection and creates a new thread to handle communication #or the connection&

and then the serer goes back to accept more connections.

+n Linux threading can be done with the pthread posix threads0 library. It would

be good to read some small tutorial about it i# you dont know anything about it.

-oweer the usage is not ery complicated.

!e shall now use threads to create handlers #or each connection the serer

accepts. Lets do it pal.

12345678910111213

141516

#include#include //stlen#include //stlen#include#include //inet_dd#include //ite#include //o thedin ( link ith lthed6o d*connection_andler(void*); tmain(intargc , char*argv[]){

tsocket_desc , ne2_socket , c , *ne2_sock; st3uctsockaddr_in server , client; ch93*message;


16/19

171819202122

232425262728293031323334353637383940414243

4445464748495051525354

5556575859606162636465666768

//+ete socket

socket_desc socket!"_$%&' ( )*+,_)'-&" ( 0 1(socket_desc == -1) { 23 t1("Could not create socket");


//Iind 1( ind(socket_desc,(structsockaddr *)9server ,sizeof(server)) : 0) { 2uts("ind !ailed"); 3etu3 1; 2uts("ind done");


//"ccet nd inco:in connection 2uts("Jaiting !or incoming connections$$$"); c sizeof(structsockaddr_in); >h le( (ne2_socket = accet(socket_desc, (structsockaddr*)9client, (socklen_t*)9c)) ) { 2uts("Connection acceted");

//-ely to the client :esse "ello Client , ' ave received ourconnection$ %nd no2 ' 2ill assign a andler !or oun"; ite!ne_socket ( :esse ( strlen(message));

thed_t snie_thed ne_sock malloc(1); Kne_sock ne_socket 1( tread_create( 9sni!!er_tread , D ,connection_andler , (void*) ne2_sock) : 0) { 2e33o3("could not create tread"); 3etu3 1;

//%o Qoin the thed ( so tht e dont te:inte Beoethe thed //thed_Qoin! snie_thed ( %A==


17/19

6970717273747576777879808182

8384858687888990919293

94959697

2uts("andler assigned"); 1(ne2_socket:0) { 2e33o3("accet !ailed"); 3etu3 1; 3etu3 0;/KK 'his ill hndle connection o ech clientK K/6o d*connection_andler(void*socket_desc){ //Eet the socket descito tsock = *(int*)socket_desc; ch93*message;

//)end so:e :esses to the client :esse "


18/19

+ne way to do this is by making the connection handler wait #or some message

#rom a client as long as the client is connected. I# the client disconnects & the

connection handler ends.

o the connection handler can be rewritten like this

12345678910

111213141516171819202122232425262728293031

3233343536373839

/KK 'his ill hndle connection o ech clientK K/6o d*connection_andler(void*socket_desc){ //Eet the socket descito tsock = *(int*)socket_desc; tread_si3e; ch93*message , client_message[7000];

//)end so:e :esses to the client

:esse "


19/19


&sce chcte is NOPN.

ello +lient ( $ he eceied you connection. "nd no $ ill ssin hndle o you

EeetinsR $ : you connection hndle

%o tye so:ethin nd i shll eet ht you tyeello

ello

o e you

o e you

$ : ine

$ : ine

o now we hae a serer thats communicatie. Thats use#ul now.

Linking te ptread library

!hen compiling programs that use the pthread library you need to link the library.

This is done like this

M cc o:.c ?lthed

Conclusion

Ey now you must hae learned the basics o# socket programming in C. (ou can

try out some experiments like writing a chat client or something similar.

I# you think that the tutorial needs some addons or improements or any o# thecode snippets aboe dont work then #eel #ree to make a comment below so that it

gets #ixed.

Date post:	04-Jun-2018
Category:	Documents
Upload:	vinodmca
View:	223 times
Download:	0 times

Socket Programing Example

Documents