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#include <netinet/in.h>
#include <poll.h>
#include <stdio.h>
#include <sys/socket.h>
#include <unistd.h>
// returns a socket file descriptor.
// if connection could not be established, -1 gets returned
int establish_connection(struct sockaddr_in addr) {
int sfd = socket(AF_INET, SOCK_STREAM, 0);
if (sfd == -1) {
perror("could not open socket");
return -1;
}
int opt = -1;
setsockopt(sfd, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
int bind_addr = bind(sfd, (struct sockaddr *)&addr, sizeof(addr));
if (bind_addr == -1) {
perror("could not bind socket");
close(sfd);
return -1;
}
int listen_addr = listen(sfd, 100);
if (listen_addr == -1) {
perror("could not listen");
close(sfd);
return -1;
}
return sfd;
}
// handles new telnet connections.
// returns 0 on success and -1 on failure.
int handle_new_connection(int sfd, struct pollfd *fds, nfds_t *nfds) {
int conn = accept(sfd, NULL, NULL);
if (conn == -1)
return -1;
fds[*nfds].fd = conn;
fds[*nfds].events = POLLIN;
(*nfds)++;
return 0;
}
// process message to all the connected clients.
// returns 0 on success and -1 on failure.
int process_message(struct pollfd *fds, nfds_t *nfds) {
for (nfds_t i = 1; i < *nfds; i++) {
/* if client has something to say */
if (fds[i].revents & POLLIN) {
char buffer[1024]; /* create a new empty buffer */
ssize_t message =
read(fds[i].fd, buffer,
sizeof(buffer)); /* read the message which the client sent */
/* if message of the client returns an error */
if (message <= 0) {
/* close the connection if client disappeared or disconnected */
close(fds[i].fd);
fds[i] = fds[*nfds - 1]; /* move back last slot */
(*nfds)--; /* size down the current array */
i--;
return -1;
} else {
/* send every message bytes to the other clients */
for (nfds_t j = 1; j < *nfds; j++) {
if (j != i) {
write(fds[j].fd, buffer, message);
}
}
}
}
}
return 0;
}
int main() {
struct sockaddr_in addr;
addr.sin_family = AF_INET; /* IPv4 */
addr.sin_port = htons(8000); /* Port */
addr.sin_addr.s_addr = INADDR_ANY; /* equals to 0.0.0.0 */
struct pollfd fds[256];
int sfd = establish_connection(addr);
if (sfd == -1) {
perror("could not establish connection");
return 1;
}
fds[0].fd = sfd; /* the listening socket */
fds[0].events = POLLIN; /* data to read */
nfds_t nfds = 1; /* 1 = listener alone, grows by 1 per connected client */
while (1) {
/* we start the polling here */
int ready =
poll(fds, nfds, -1); /* poll to accept many conn simultaneously */
if (ready == -1) {
perror("could not run poll");
return 1;
}
if (fds[0].revents & POLLIN) {
if (handle_new_connection(sfd, fds, &nfds) == -1) {
perror("could not accept connection");
continue;
}
}
if (process_message(fds, &nfds) == -1) {
perror("could not process message");
continue;
}
}
return 0;
}
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