example of libevent

libevent_example.c

/*
https://stackoverflow.com/questions/11990700/broken-pipe-epipe-on-connection-to-loopback-address/12068942#12068942
 */

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

/* Required by event.h. */
#include <sys/time.h>

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <err.h>

#include <assert.h>

#include <event2/event.h>
#include <event2/event_compat.h>

void on_connect(int sock, short ev, void *arg)
{
  assert(ev == EV_WRITE);
  printf("got writeable on: %d\n", sock);
  int optval = -1;
  socklen_t optlen = sizeof(optval);
  getsockopt(sock, SOL_SOCKET, SO_ERROR, &optval, &optlen);
  assert(optval == 0);
  printf("successfull asynchronous connect on: %d\n", sock);
  event_loopbreak();
}

void init_addr(struct sockaddr_in *addr, short port)
{
  memset(addr, '\0', sizeof(*addr));
  addr->sin_family = AF_INET;
  addr->sin_port = htons(port);
  addr->sin_addr.s_addr = htonl(INADDR_LOOPBACK);
}

void setup_accept(int sock)
{
  int one = 1;
  struct sockaddr_in addr;
  init_addr(&addr, 9876);
  setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
  bind(sock, (struct sockaddr *)&addr, sizeof(addr));
  listen(sock, 1);
}

int complete_accept(int sock)
{
  struct sockaddr_in addr;
  socklen_t addrlen = sizeof(addr);
  return accept(sock, (struct sockaddr *)&addr, &addrlen);
}

int try_connect(int sock)
{
  struct sockaddr_in addr;
  init_addr(&addr, 9876);
  return connect(sock, (struct sockaddr *)&addr, sizeof(addr));
}

int main(int argc, char *argv[])
{

  int accept_sock = socket(PF_INET, SOCK_STREAM, 0);
  setup_accept(accept_sock);

  int client_sock = socket(PF_INET, SOCK_STREAM, 0);
  fcntl(client_sock, F_SETFL, fcntl(client_sock, F_GETFL) | O_NONBLOCK);
  printf("trying first connect on: %d\n", client_sock);

  int r = try_connect(client_sock);
  assert(r < 0 && errno == EINPROGRESS);

  event_init();

  struct event_base *base = event_base_new();
  struct event *ev_connect;
  ev_connect = event_new(base, client_sock, EV_WRITE, on_connect, 0);
  event_add(ev_connect, 0);

  int new_sock = complete_accept(accept_sock);
  event_base_dispatch(base);
  
  return 0;
}