#define _XOPEN_SOURCE   500
#define __EXTENSIONS__

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/signal.h>
#include <sys/socket.h>
#include <sys/filio.h>
/*
#include <netinet/sctp.h>
*/


int
main(int argc, char **argv)
{
  int echo_s;
  struct sockaddr_in laddr;
  int ret;
  struct msghdr mhdr;
  struct iovec iov;
  char data[8192];
  char cdata[sizeof (struct sockaddr_in) + sizeof (struct cmsghdr)];
  struct cmsghdr *cmsg;
  struct sockaddr_in from;
  struct sockaddr_in toaddr;
  socklen_t fromlen = sizeof (struct sockaddr_in);
  fd_set  rset;
  int i;
  struct in_addr        ip_addr;       
  char   str[32];



  struct cmsghdr  *cmptr;


  if (argc < 2) {
    printf("usage: udpServerDaddr <local_port>\n");
    exit(0);
  }

  echo_s = socket(AF_INET, SOCK_DGRAM, 0);

  bzero(&laddr, sizeof (laddr));
  laddr.sin_family = AF_INET;
  laddr.sin_port = htons(atoi(argv[1]));
  if (bind(echo_s, (struct sockaddr *)&laddr, sizeof (laddr)) < 0) {
    perror("bind error");
    exit(1);
  }

  i = 1;
  setsockopt(echo_s, SOL_SOCKET, SO_REUSEADDR, &i, sizeof (i));
  i = 1;
  if (setsockopt(echo_s, IPPROTO_IP, IP_RECVDSTADDR, (char *) &i, sizeof(i)) < 0)
    perror("IP_RECVDSTADDR setsockopt error");

  FD_ZERO(&rset);

  while (1) {
    FD_SET(echo_s, &rset);
    select(5, &rset, NULL, NULL, NULL);
    if (FD_ISSET(echo_s, &rset) ) {
      bzero(cdata, sizeof (cdata));
      bzero(&mhdr, sizeof (mhdr));
      mhdr.msg_name = &from;
      mhdr.msg_namelen = fromlen;
      mhdr.msg_iov = &iov;
      mhdr.msg_iovlen = 1;
      mhdr.msg_control = cdata;
      mhdr.msg_controllen = sizeof (cdata);
      iov.iov_base = data;
      iov.iov_len = sizeof (data);
      cmsg = (struct cmsghdr *)cdata;

      if ((ret = recvmsg(echo_s, &mhdr, MSG_DONTWAIT)) < 0) {
        perror("recvmsg()");
      }
      /* recv address info */

      for (cmptr = CMSG_FIRSTHDR(&mhdr); cmptr != NULL;
          cmptr = CMSG_NXTHDR(&mhdr, cmptr)) {

        if (cmptr->cmsg_level == IPPROTO_IP &&
            cmptr->cmsg_type == IP_RECVDSTADDR) {

          memcpy(&ip_addr, CMSG_DATA(cmptr), sizeof(struct in_addr));

          printf("udp message sent  to: %s\n", inet_ntop(AF_INET, &ip_addr, str, sizeof(str)));



        }
      }
      /* end of recv adddress info */
      /* echo back */
      iov.iov_len = ret;
      toaddr.sin_family = AF_INET;
      toaddr.sin_addr =  ip_addr;
      toaddr.sin_port = laddr.sin_port;

      mhdr.msg_name = &toaddr;

      if (sendmsg(echo_s, &mhdr, MSG_DONTWAIT) < 0) {
        perror("sendmsg()");
      }
      printf("received:");
      fflush(stdout);
      write(1, data, ret);
    }
  }
}