/* svudp.c  Server code, UDP, from Padovano, "Networking Applications
            on Unix System V Release 4", Prentice-Hall, page 514 ..
	    (with minor modification to allow system selected port)
	    This program is called as follows
	         svudp &
	    and it will print out a port number. svudp when queried
	    by a client with a user name, say fowler, reports to the
	    client if fowler is or not logged on this machine.
 */

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

/* #define SERV_PORT 2345 */

#define MAXNAME 1024

main() 
{
  int dg_fd;                          /* file descriptor into UDP */
  struct sockaddr_in myaddr;          /* the addr of this service */
  int len;                            /* length of address        */
  char buff[MAXNAME];                 /* buffer to hold datagram  */
  char reply;                         /* response to the client   */
  struct sockaddr_in client_addr;     /* the addr of client       */

  char cmd[BUFSIZ];                   /* Variables used to figure */
  char junkbuf[BUFSIZ];               /* if user is logged onto   */
  FILE *fp;                           /* the system               */

  /* Open a socket into UDP/IP */

  if ((dg_fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
    perror("socket failed");
    exit(1);
  }

  /* Set up our address */

  bzero((char *)&myaddr, sizeof(myaddr));
  myaddr.sin_family = AF_INET;
  myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  myaddr.sin_port = 0; /*htons(SERV_PORT);*/

  /* Bind to the address of this service */

  if (bind(dg_fd, (struct sockaddr *) &myaddr, sizeof(myaddr)) < 0) {
    perror("bind failed");
    exit(1);
  }

  /* Print port number */
  len = sizeof(myaddr);
  if (getsockname(dg_fd, (struct sockaddr *)&myaddr, &len) < 0) {
    perror("Error getting socketname \n");
    exit(1);
  }
  printf("Socket port #%d\n", ntohs(myaddr.sin_port));
  

  /* Loop continuously, processing datagrams. */

  len = sizeof(struct sockaddr);
  while (1) {
    if(recvfrom(dg_fd, buff, MAXNAME, 0, &client_addr, &len) < 0) {
      perror("could not read datagram");
      continue;
    }

    sprintf(cmd, "who | grep '^%s '", buff);
    if ((fp = popen(cmd, "r")) == NULL ||
	fgets(junkbuf, BUFSIZ, fp) == NULL) {
      reply = 'n';
    } else {
      reply = 'y';
    }
    if (sendto(dg_fd, &reply, 1, 0, &client_addr, len) < 0) {
      perror("continue not send datagram!");
      continue;
    }
  }
}