Listing 4. polling_server.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>
#include <signal.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <errno.h>
#include "utils.h"

#define MAX_BUFFERS (BACKLOG + 1) /* max clients + listener */

int main() {
  char buffer[BUFF_SIZE + 1];

  /* epoll structures */
  struct epoll_event event,     /* server2epoll */
    event_buffers[MAX_BUFFERS]; /* epoll2server */

  int epollfd = epoll_create(MAX_BUFFERS); /* arg just a hint */
  if (epollfd < 0) error_msg("Problem with epoll_create", true);

  struct sockaddr_in client_addr;
  socklen_t len = sizeof(struct sockaddr_in);

  int sock = create_server_socket(true); /* non-blocking */

  /* polling */
  event.events = EPOLLIN | EPOLLET; /* incoming, edge-triggered */
  event.data.fd = sock;             /* register listener */
  if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sock, &event) < 0)
    error_msg("Problem with epoll_ctl call", true);

  /* connections + requests */
  while (true) {
    /* event count */
    int n = epoll_wait(epollfd, event_buffers, MAX_BUFFERS, -1);
    if (n < 0) error_msg("Problem with epoll_wait call", true);

    /*
       -- If connection, add to polling: may be none or more
       -- If request, read and echo
    */
    int i;
    for (i = 0; i < n; i++) {
      /* listener? */
      if (event_buffers[i].data.fd == sock) {
        while (true) {
          socklen_t len = sizeof(client_addr);
          int client = accept(sock,
                              (struct sockaddr *) &client_addr,
                              &len);

          /* no client? */
          if (client < 0 && (EAGAIN == errno || EWOULDBLOCK == errno)) break;

          /* client */
          fcntl(client, F_SETFL, O_NONBLOCK); /* non-blocking */
          event.events = EPOLLIN | EPOLLET;   /* incoming,
                                                 edge-triggered */
          event.data.fd = client;
          if (epoll_ctl(epollfd, EPOLL_CTL_ADD, client, &event) < 0)
            error_msg("Problem with epoll_ctl ADD call", false);

          announce_client(&client_addr.sin_addr);
        }
      }
      /* request */
      else {
        bzero(buffer, sizeof(buffer));
        int bytes_read = recv(event_buffers[i].data.fd, buffer, sizeof(buffer), 0);

        /* echo request */
        if (bytes_read < 0) {
          char response[BUFF_SIZE * 2];
          bzero(response, sizeof(response));
          generate_echo_response(buffer, response);
          int bytes_written =
            send(event_buffers[i].data.fd, response, strlen(response), 0);
          if (bytes_written < 0) error_msg("Problem with send call", false);

          close(event_buffers[i].data.fd); /* epoll stops
                                              polling fd */
        }
      }
    }
  }

  return 0;
}