tcp_epoll_edge.c

#define _GNU_SOURCE
#define _POSIX_C_SOURCE 200809L
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <sys/epoll.h>

static int set_nonblock(int fd)
{
    int flags = fcntl(fd, F_GETFL, 0);
    if (flags < 0) return -1;
    if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) < 0) return -1;
    return 0;
}

int main(int argc, char **argv)
{
#if !defined(__linux__)
    fprintf(stderr, "tcp_epoll_edge is Linux-only\n");
    return 1;
#else
    int port = 12345;
    if (argc > 1) port = atoi(argv[1]);
    int srv = socket(AF_INET, SOCK_STREAM, 0);
    if (srv < 0) {
        perror("socket");
        return 1;
    }
    int opt = 1;
    setsockopt(srv, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof opt);
    struct sockaddr_in addr;
    memset(&addr, 0, sizeof addr);
    addr.sin_family = AF_INET;
    addr.sin_addr.s_addr = htonl(INADDR_ANY);
    addr.sin_port = htons(port);
    if (bind(srv, (struct sockaddr *)&addr, sizeof addr) < 0) {
        perror("bind");
        close(srv);
        return 1;
    }
    if (listen(srv, 128) < 0) {
        perror("listen");
        close(srv);
        return 1;
    }
    if (set_nonblock(srv) < 0) {
        perror("set_nonblock");
        close(srv);
        return 1;
    }
    int ep = epoll_create1(0);
    if (ep < 0) {
        perror("epoll_create1");
        close(srv);
        return 1;
    }
    struct epoll_event ev;
    ev.events = EPOLLIN | EPOLLET;
    ev.data.fd = srv;
    if (epoll_ctl(ep, EPOLL_CTL_ADD, srv, &ev) < 0) {
        perror("epoll_ctl");
        close(srv);
        close(ep);
        return 1;
    }
    printf("listening on port %d\n", port);
    struct epoll_event events[64];
    for (;;) {
        int n = epoll_wait(ep, events, 64, -1);
        if (n < 0) {
            if (errno == EINTR) continue;
            perror("epoll_wait");
            break;
        }
        for (int i = 0; i < n; i++) {
            int fd = events[i].data.fd;
            if (fd == srv) {
                for (;;) {
                    struct sockaddr_in caddr;
                    socklen_t clen = sizeof caddr;
                    int c = accept(srv, (struct sockaddr *)&caddr, &clen);
                    if (c < 0) {
                        if (errno == EAGAIN || errno == EWOULDBLOCK) break;
                        perror("accept");
                        break;
                    }
                    set_nonblock(c);
                    struct epoll_event cev;
                    cev.events = EPOLLIN | EPOLLET;
                    cev.data.fd = c;
                    epoll_ctl(ep, EPOLL_CTL_ADD, c, &cev);
                }
            } else {
                for (;;) {
                    char buf[4096];
                    ssize_t r = read(fd, buf, sizeof buf);
                    if (r == 0) {
                        close(fd);
                        epoll_ctl(ep, EPOLL_CTL_DEL, fd, NULL);
                        break;
                    } else if (r < 0) {
                        if (errno == EAGAIN || errno == EWOULDBLOCK) break;
                        perror("read");
                        close(fd);
                        epoll_ctl(ep, EPOLL_CTL_DEL, fd, NULL);
                        break;
                    } else {
                        write(fd, buf, r);
                    }
                }
            }
        }
    }
    close(srv);
    close(ep);
    return 0;
#endif
}