testepoll.c

/*
 * $ make testepoll CFLAGS="-Wall -Werror -ggdb3"
 *
 * One console:
 *
 *     $ nc -l 8000
 *
 * Other console:
 *
 *     $ ./testepoll
 *
 * Then when requested, kill the `nc`, check socket status
 *
 *     $ netstat -atnpl | grep 8000
 *
 * which should show `CLOSE_WAIT`, and press return in the `testepoll` console
 */

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

static int do_epoll(int epoll) {
        int rc = -1,
            i = 0;
        struct epoll_event events[2] = { 0 };

        rc = epoll_wait(epoll, events, sizeof(events) / sizeof(events[0]), -1);
        if(rc == -1) {
                return -1;
        }

        for(i = 0; i < rc; i++) {
                printf("event: %d, fd: %d\n", events[i].events, events[i].data.fd);
        }

        return 0;
}


int main(int argc, char **argv) {
        int epoll = -1,
            rc = 1,
            sock = -1,
            i = 0;
        struct addrinfo hints = { 0 },
                        *result = NULL,
                        *rp = NULL;
        struct epoll_event event = { 0 };
        char buf[16] = { 0 };

        memset(&hints, 0, sizeof(hints));
        hints.ai_family = AF_UNSPEC;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_flags = 0;
        hints.ai_protocol = 0;

        rc = getaddrinfo("localhost", "8000", &hints, &result);
        if(rc != 0) {
                fprintf(stderr, "getaddrinfo failed: %s\n", gai_strerror(rc));
                rc = 1;
                goto out;
        }

        for(rp = result; rp != NULL; rp = rp->ai_next) {
                sock = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
                if(sock < 0) {
                        perror("socket");
                        continue;
                }

                if(connect(sock, rp->ai_addr, rp->ai_addrlen) != -1) {
                        break;
                }
                else {
                        perror("connect");
                        close(sock);
                        sock = -1;
                }
        }

        if(sock < 0) {
                fprintf(stderr, "Unable to connect\n");
                goto out;
        }

        epoll = epoll_create1(EPOLL_CLOEXEC);
        if(epoll < 0) {
                perror("epoll_create");
                goto out;
        }

        event.events = EPOLLOUT;
        event.data.fd = sock;
        if(epoll_ctl(epoll, EPOLL_CTL_ADD, sock, &event) == -1) {
                perror("epoll_ctl");
                goto out;
        }

        rc = do_epoll(epoll);
        if(rc == -1) {
                perror("do_epoll");
                rc = 1;
                goto out;
        }

        printf("Kill server, check socket state, and press return");
        getchar();

        for(i = 0; i < 5; i++) {
                rc = do_epoll(epoll);
                if(rc == -1) {
                        perror("do_epoll");
                        rc = 1;
                        goto out;
                }
        }

        rc = write(sock, buf, sizeof(buf));
        if(rc < 0) {
                perror("write");
                rc = 1;
                goto out;
        }
        else if(rc == 0) {
                fprintf(stderr, "socket EOF\n");
        }
        else {
                printf("Wrote %d bytes\n", rc);
        }

        rc = 0;
out:
        if(epoll >= 0) {
                close(epoll);
                epoll = -1;
        }
        if(sock >= 0) {
                close(sock);
                sock = -1;
        }
        if(result != 0) {
                freeaddrinfo(result);
                result = NULL;
        }

        return rc;
}