Notes

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define PORT 4950 /*port we are listening on*/
#define BUFFER 1024 /*buffer size used*/

void send_to_everyone(int j, int i, int fd, int no_bytes, char *reply, fd_set *master)/*sending received data to everyone*/
{
if (FD_ISSET(j, master)){ /*sends message to everyone */
if (j != fd && j != i) { /*except the server and the client which sent data*/
if (send(j, reply, no_bytes, 0) == -1) {/*sending message to rest all clients*/
printf("error in the clientn");
}
}
}
}

void send_and_recv(int i, fd_set *master, int fd, int maximumfd)
{
int no_bytes, j;
char reply[BUFFER], buf[BUFFER]; /*buffer for client data*/

if ((no_bytes = recv(i, reply, BUFFER, 0)) <= 0) { /*number of bytes received*/
if (no_bytes == 0) {
printf("socket %d closed its connectionn", i);
}else {
printf("there is some error in the client");
}
close(i);
FD_CLR(i, master);
}else {

for(j = 0; j <= maximumfd; j++){ /*if there a data from any client*/
send_to_everyone(j, i, fd, no_bytes, reply, master );/*send it to everyone*/
}
}
}

void connection_accept(fd_set *master, int *maximumfd, int fd, struct sockaddr_in *client_addr)
{
socklen_t addrlen; /*handles upcoming connection*/
int newconn; /*newly accepted socket file descriptor*/

addrlen = sizeof(struct sockaddr_in);
if((newconn = accept(fd, (struct sockaddr *)client_addr, &addrlen)) == -1) { /*accepting the connection from client*/
printf("accept");
exit(1);
}else {
FD_SET(newconn, master);
if(newconn > *maximumfd){ /*keeping track of maximum*/
*maximumfd = newconn;
}
printf("n");
printf("New connection from Clientn");
printf("client address:%sn",inet_ntoa(client_addr->sin_addr));
printf("Client port:%dn",ntohs(client_addr->sin_port));
}
}

void connect_request(int *fd, struct sockaddr_in *server_addr)
{
int x = 1; /*for setsockopt*/

if ((*fd = socket(AF_INET, SOCK_STREAM, 0)) == -1) { /*creating socket file descriptor*/
printf("socket not opened");
exit(1);
}

server_addr->sin_family = AF_INET; /*Initialize the environment for sockaddr structure*/
server_addr->sin_port = htons(PORT);
server_addr->sin_addr.s_addr = INADDR_ANY;
memset(server_addr->sin_zero, '', sizeof server_addr->sin_zero);

if (setsockopt(*fd, SOL_SOCKET, SO_REUSEADDR, &x, sizeof(int)) == -1) { /*To reuse the same address*/
printf("setsockopt not ok");
exit(1);
}

if (bind(*fd, (struct sockaddr *)server_addr, sizeof(struct sockaddr)) == -1) { /*Binding socket to the port*/
printf("Unable to bind");
exit(1);
}
if (listen(*fd, 10) == -1) { /*Server listening at defined port*/
printf("listen error");
exit(1);
}
printf("TCP server is waiting for client");
fflush(stdout);
}
int main()
{
fd_set master; /*master file descriptor set*/
fd_set read_fds; /*list of file descriptors for select*/
int maximumfd, i; /*maximum file descriptor number*/
int fd= 0; /*listening socket descriptor*/
struct sockaddr_in server_addr, client_addr; /*server and client address*/

FD_ZERO(&master); /*clears master set*/
FD_ZERO(&read_fds); /*clears select file descriptor*/
connect_request(&fd, &server_addr); /*connection establishment*/
FD_SET(fd, &master); /*Adding socket file descriptor to the master set*/

maximumfd = fd; /*keeping track of maximum file descriptor*/
for(;;){
read_fds = master;
if(select(maximumfd+1, &read_fds, NULL, NULL, NULL) == -1){ /*To see how many file descriptors are ready for read*/
printf("None of them are readyn");
exit(4);
}

for (i = 0; i <= maximumfd; i++){ /*Run through the existing connection*/
if (FD_ISSET(i, &read_fds)){ /*Looking for data to be read*/
if (i == fd)
connection_accept(&master, &maximumfd, fd, &client_addr); /*accept the connection from requested client*/
else
send_and_recv(i, &master, fd, maximumfd); /*broadcast the message recived*/
}
}
}
return 0;
}