#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/select.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>

/*
* In the included file  <netinet/in.h> a sockaddr_in is  defined as follows:
* struct sockaddr_in {
*      short   sin_family;
*      u_short sin_port;
*      struct in_addr sin_addr;
*      char    sin_zero[8];
* };
*
* This program  creates a datagram  socket, binds a name  to it,
  then reads * from the socket.
*/
int
main(void)
{
	  int sock, length, on, ret;
	  struct sockaddr_in name;
	  char buf[1024];
	  fd_set rdfds;

	  /* Create socket from which to read. */
	  sock = socket(AF_INET, SOCK_DGRAM, 0);
	  if (sock < 0) {
		 perror("opening datagram socket");
		 exit(1);
	  }
	  
	  on = 1;
	  ioctl(sock, FIONBIO, &on);
	  /* Create name with wildcards. */

	  name.sin_family = AF_INET;
	  name.sin_addr.s_addr = INADDR_ANY;
	  name.sin_port = 0;
	  if (bind(sock, (struct sockaddr *) &name, sizeof(name))) {
		 perror("binding datagram socket");
		 exit(1);
	  }
	  /* Find assigned port value and print it out. */
	  length = sizeof(name);
	  if (getsockname(sock, (struct sockaddr *) &name, &length)) {
		 perror("getting socket name");
		 exit(1);
	  }
	  printf("Socket has port #%d\n", ntohs(name.sin_port));
	  /* Read from the socket */
	  FD_ZERO(&rdfds);
	  FD_SET(sock, &rdfds);
	  ret = select(sock + 1, &rdfds, NULL, NULL, NULL);
	  if (ret == -1) {
		  err(1, "socket");
	  }
	  else if (ret == 0) {
		  fprintf(stderr, "unexpected timeout\n");
		  return 1;
	  }
	  else if (ret != 1) {
		  fprintf(stderr, "Unexpected ret from select: %d\n", ret);
		  return 1;
	  }
	  if (read(sock, buf, 1024) < 0)
		 perror("receiving datagram packet");
	  printf("-->%s\n", buf);
	  close(sock);
	  return 0;
}