tcp server using epoll gives non-socket error - c

Question

i am creating a simple tcp echo server in c using epoll. while compiling it gives error:
Socket operation on non-socket
why does it gives non-socket? i tried but couldn't get my head around it.
below is my code and here is the article that i am following
my code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <fcntl.h>
#include <sys/epoll.h>
#include <errno.h>
#include <unistd.h>
#define MAX_LISTEN_BACKLOG 1
#define BUFFER_SIZE 4096
int bind_and_create(char *port){
struct addrinfo hints;
struct addrinfo *result, *rp;
int s, sfd;
memset(&hints, 0, sizeof(struct addrinfo));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
s = getaddrinfo(NULL, port , &hints, &result);
if( s != 0 ){
fprintf(stderr,"getaddrinfo :%s\n",gai_strerror(s));
return -1;
}
for( rp = result; rp!= NULL; rp->ai_next){
int sfd = socket(rp->ai_family, rp->ai_socktype,rp->ai_protocol);
if ( sfd == -1)
continue;
s = bind(sfd, rp->ai_addr,rp->ai_addrlen);
if ( s == 0){
//succefull managed to bind socket
break;
}
close(sfd);
}
if ( rp == NULL){
fprintf(stderr,"could not bind");
}
freeaddrinfo(result);
return sfd;
}
int make_socket_non_blocking( int sfd ){
int flags , s;
flags = fcntl(sfd, F_GETFL, 0);
if (flags == -1){
perror("fnctl error");
return -1;
}
flags |= O_NONBLOCK;
s = fcntl(sfd,F_SETFL,flags);
if (s == -1){
perror("fnctl error");
return -1;
}
return 0;
}
#define MAXEVENTS 64
int main (int argc, char *argv[])
{
int sfd, s;
int efd;
struct epoll_event event;
struct epoll_event *events;
if (argc != 2)
{
fprintf (stderr, "Usage: %s [port]\n", argv[0]);
exit (EXIT_FAILURE);
}
sfd = bind_and_create (argv[1]);
if (sfd == -1)
abort ();
s = make_socket_non_blocking (sfd);
if (s == -1)
abort ();
s = listen (sfd, SOMAXCONN); // error is here but why????
if (s == -1)
{
perror ("listen");
abort ();
}
efd = epoll_create1 (0);
if (efd == -1)
{
perror ("epoll_create");
abort ();
}
event.data.fd = sfd;
event.events = EPOLLIN | EPOLLET;
s = epoll_ctl (efd, EPOLL_CTL_ADD, sfd, &event);
if (s == -1)
{
perror ("epoll_ctl");
abort ();
}
/* Buffer where events are returned */
events = calloc (MAXEVENTS, sizeof event);
/* The event loop */
while (1)
{
int n, i;
n = epoll_wait (efd, events, MAXEVENTS, -1);
for (i = 0; i < n; i++)
{
if ((events[i].events & EPOLLERR) ||
(events[i].events & EPOLLHUP) ||
(!(events[i].events & EPOLLIN)))
{
/* An error has occured on this fd, or the socket is not
ready for reading (why were we notified then?) */
fprintf (stderr, "epoll error\n");
close (events[i].data.fd);
continue;
}
else if (sfd == events[i].data.fd)
{
/* We have a notification on the listening socket, which
means one or more incoming connections. */
while (1)
{
struct sockaddr in_addr;
socklen_t in_len;
int infd;
char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
in_len = sizeof in_addr;
infd = accept (sfd, &in_addr, &in_len);
if (infd == -1)
{
if ((errno == EAGAIN) ||
(errno == EWOULDBLOCK))
{
/* We have processed all incoming
connections. */
break;
}
else
{
perror ("accept");
break;
}
}
s = getnameinfo (&in_addr, in_len,
hbuf, sizeof hbuf,
sbuf, sizeof sbuf,
NI_NUMERICHOST | NI_NUMERICSERV);
if (s == 0)
{
printf("Accepted connection on descriptor %d "
"(host=%s, port=%s)\n", infd, hbuf, sbuf);
}
/* Make the incoming socket non-blocking and add it to the
list of fds to monitor. */
s = make_socket_non_blocking (infd);
if (s == -1)
abort ();
event.data.fd = infd;
event.events = EPOLLIN | EPOLLET;
s = epoll_ctl (efd, EPOLL_CTL_ADD, infd, &event);
if (s == -1)
{
perror ("epoll_ctl");
abort ();
}
}
continue;
}
else
{
/* We have data on the fd waiting to be read. Read and
display it. We must read whatever data is available
completely, as we are running in edge-triggered mode
and won't get a notification again for the same
data. */
int done = 0;
while (1)
{
ssize_t count;
char buf[512];
count = read (events[i].data.fd, buf, sizeof buf);
if (count == -1)
{
/* If errno == EAGAIN, that means we have read all
data. So go back to the main loop. */
if (errno != EAGAIN)
{
perror ("read");
done = 1;
}
break;
}
else if (count == 0)
{
/* End of file. The remote has closed the
connection. */
done = 1;
break;
}
/* Write the buffer to standard output */
s = write (1, buf, count);
if (s == -1)
{
perror ("write");
abort ();
}
}
if (done)
{
printf ("Closed connection on descriptor %d\n",
events[i].data.fd);
/* Closing the descriptor will make epoll remove it
from the set of descriptors which are monitored. */
close (events[i].data.fd);
}
}
}
}
free (events);
close (sfd);
return EXIT_SUCCESS;
}

Answer 1

int bind_and_create(char *port){
...
int s, sfd; // <- one sfd
...
for( rp = result; rp!= NULL; rp->ai_next){ // <- rp->ai_next has no effect
int sfd = socket(...); // <-- two sfd
...
close(sfd); // <-- two sfd gone
}
...
return sfd; // <-- one sfd, still completely uninitialised
}
If you want to stop wasting your time on this, use -Wall or an equivalent compiler setting.