udp-bind-twice.c

/*
 * Copyright (c) 2011, Ben Noordhuis <info@bnoordhuis.nl>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <errno.h>

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

#define assert_errno()          \
  do {                          \
    if (errno != 0) {           \
      fprintf(stderr,           \
              "%s:%d: %s\n",    \
              __FILE__,         \
              __LINE__,         \
              strerror(errno)); \
      abort();                  \
    }                           \
  }                             \
  while (0);

#define E(expr) (expr); assert_errno();

static int do_bind(int family) {
  struct sockaddr_storage storage;
  socklen_t socklen;
  int sockfd;

  assert(family == AF_INET || family == AF_INET6);

  E(sockfd = socket(family, SOCK_DGRAM, 0));
#if REUSEADDR
  {
    int yes = 1;
    E(setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof yes));
  }
#endif

  memset(&storage, 0, sizeof storage);
  if (family == AF_INET) {
    struct sockaddr_in *addr = (struct sockaddr_in *) &storage;
    addr->sin_family = family;
    addr->sin_addr.s_addr = INADDR_ANY;
    addr->sin_port = htons(12345);
    socklen = sizeof *addr;
  }
  else if (family == AF_INET6) {
    struct sockaddr_in6 *addr = (struct sockaddr_in6 *) &storage;
    addr->sin6_family = family;
    addr->sin6_addr = in6addr_any;
    addr->sin6_port = htons(12345);
    socklen = sizeof *addr;
  }
  else {
    assert(0 && "bad address family");
  }

  E(bind(sockfd, (struct sockaddr *) &storage, socklen));

  return sockfd;
}

int main(void) {
  do_bind(AF_INET);
  /*do_bind(AF_INET);*/
  sleep(1000);
  return 0;
}

Try running two separate instances of this compiled with -DREUSEADDR=1