main.c

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <assert.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/epoll.h>

#define MAXEVENTS 64

static int make_socket_non_blocking(int fd) {
  int result;

  int flags = fcntl(fd, F_GETFL, 0);
  assert(flags != -1);

  flags |= O_NONBLOCK;

  result = fcntl(fd, F_SETFL, flags);
  assert(result != -1);

  return 0;
}

static int create_server_socket(char* port) {
  struct addrinfo hints;
  struct addrinfo* addr;

  int server_fd;
  int result;

  memset(&hints, 0, sizeof(struct addrinfo));
  hints.ai_family = AF_UNSPEC; // IPv4 or IPv6
  hints.ai_socktype = SOCK_STREAM; // TCP
  hints.ai_flags = AI_PASSIVE;

  result = getaddrinfo(NULL, port, &hints, &addr);
  assert(result == 0);

  for (struct addrinfo* rp = addr; rp != NULL; rp->ai_next) {
    server_fd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);

    if (server_fd == -1)
      continue;

    result = bind(server_fd, rp->ai_addr, rp->ai_addrlen);

    if (result == 0)
      break;

    close(server_fd);
  }

  assert(addr != NULL);

  freeaddrinfo(addr);

  return server_fd;
}

int main (int argc, char* argv[]) {
  assert(argc == 2);

  int result;

  int server_fd = create_server_socket(argv[1]);
  assert(server_fd != -1);

  result = make_socket_non_blocking(server_fd);
  assert(result != -1);

  result = listen(server_fd, SOMAXCONN);
  assert(result != -1);

  int events_fd = epoll_create1(0);
  assert(events_fd != -1);

  struct epoll_event event;

  event.data.fd = server_fd;
  event.events = EPOLLIN | EPOLLET;

  result = epoll_ctl(events_fd, EPOLL_CTL_ADD, server_fd, &event);
  assert(result != -1);

  struct epoll_event* events = calloc(MAXEVENTS, sizeof(event));

  while (true) {
    int events_count = epoll_wait(events_fd, events, MAXEVENTS, -1);

    for (int i = 0; i < events_count; i++) {
      if ((events[i].events & EPOLLERR) ||
          (events[i].events & EPOLLHUP) ||
          (!(events[i].events & EPOLLIN))) {
        fprintf(stderr, "epoll error on %d\n", events[i].data.fd);
        close(events[i].data.fd);
        continue;
      } else
      // server events - new connections
      if (events[i].data.fd == server_fd) {
        while (true) {
          struct sockaddr incoming;
          socklen_t incoming_size = sizeof(incoming);
          int incoming_fd;
          char incoming_hostname[NI_MAXHOST], incoming_port[NI_MAXSERV];

          incoming_fd = accept(server_fd, &incoming, &incoming_size);

          if (incoming_fd == -1)
            break;

          result = getnameinfo(&incoming, incoming_size,
                               incoming_hostname, sizeof(incoming_hostname),
                               incoming_port, sizeof(incoming_size),
                               NI_NUMERICHOST | NI_NUMERICSERV);

          if (result == 0)
            fprintf(stdout, "new connection on %d from %s:%s\n", incoming_fd, incoming_hostname, incoming_port);

          result = make_socket_non_blocking(incoming_fd);
          assert(result != -1);

          event.data.fd = incoming_fd;
          event.events = EPOLLIN | EPOLLET;

          result = epoll_ctl(events_fd, EPOLL_CTL_ADD, incoming_fd, &event);
          assert(result != -1);
        }
      }
      else {
        int done = 0;

        while (true) {
          char buffer[512];

          ssize_t count = read(events[i].data.fd, buffer, sizeof(buffer));

          if (count == -1) {
            if (errno != EAGAIN) {
              fprintf(stdout, "done reading -1 from %d\n", events[i].data.fd);
              done = 1;
            }
            break;
          } else
          if (count == 0) {
            fprintf(stdout, "done reading 0 from %d\n", events[i].data.fd);
            done = 1;
            break;
          }

          if (buffer[0] != '.') {
            fprintf(stdout, "got data from %d - first %c (length %ld)\n", events[i].data.fd, buffer[0], count);
          }
        }

        if (done) {
          fprintf(stdout, "closing on %d\n", events[i].data.fd);
          close(events[i].data.fd);
        }
      }
    }
  }

  free(events);
  close(server_fd);

  return EXIT_SUCCESS;
}