Epoll Example

epoll_server_example.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/epoll.h>
#include <errno.h>

#define MAXEVENTS 64

static int make_socket_non_blocking(int sfd)
{
    int flags, s;

    flags = fcntl(sfd, F_GETFL, 0);
    if(flags == -1)
    {
        perror("fcntl");
        return -1;
    }

    flags |= O_NONBLOCK;
    s = fcntl(sfd, F_SETFL, flags);
    if(s == -1)
    {
        perror("fcntl");
        return -1;
    }

    return 0;
}

static int create_and_bind(char *port)
{
    struct addrinfo hints;
    struct addrinfo *result, *rp;
    int s, sfd;

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;     /* Return IPv4 and IPv6 choices */
    hints.ai_socktype = SOCK_STREAM; /* We want a TCP socket */
    hints.ai_flags = AI_PASSIVE;     /* All interfaces */

    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 = rp->ai_next)
    {
        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)
        {
            /* We managed to bind successfully! */
            break;
        }
        close(sfd);
    }

    if(rp == NULL)
    {
        fprintf(stderr, "Could not bind\n");
        return -1;
    }
    freeaddrinfo(result);
    return sfd;
}

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 = create_and_bind(argv[1]);
    if(sfd == -1)
        abort();

    s = make_socket_non_blocking(sfd);
    if(s == -1)
        abort();

    s = listen(sfd, SOMAXCONN);
    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;
}