/* receiver for internet datagram demo */
/* modification 9/20/93 with Louis Sanchez's bug fix */

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

#define ENDPACKET "end"

/************************************************************
printsockaddr prints the contents of a sockaddr_in structure when
called with a pointer to such a structure.
************************************************************/


void printsockaddr(struct sockaddr_in *arg)
{
   struct hostent *hp;
   printf("  sockaddr_in: ");
   printf("Domain=%d, ", arg->sin_family);
   hp=gethostbyaddr((const char *)&(arg->sin_addr), sizeof(arg->sin_addr), AF_INET);
   printf("Hostname=%s, ", hp->h_name);
   printf("Port=%d, ", ntohs(arg->sin_port));
   printf("Address=%s,\n", inet_ntoa(arg->sin_addr));
}

getline(s, lim)                                                        
char s[];                                                              
int lim;                                                               
{                                                                      
        int c, i;                                                      
                                                                       
        for (i=0; i<lim-1 && (c=getchar()) != EOF && c != '\n' ; ++i)  
                s[i] = c;                                              
        if (c == '\n') {                                               
                s[i]= c;                                               
                i++;                                                   
        }                                                              
        s[i]= '\0';                                                    
        return(i);                                                     
}                                                                     


help_msg()
{
   printf("format: idgr -[d]\n");
   printf("        option: d set debug mode\n");
}

main(argc, argv)
int argc;
char *argv[];
{
   int sock; 
   struct sockaddr_in from;
   int n, i;
   char toBuf[2048];
   char fromBuf[2048];
   int length;
   int flag = 1;
   extern char *optarg;
   extern int   optind;
   int option_exist = 0;
   int debug = 0;
        int c;

   /* process command line args */
   while ((c=getopt(argc,argv,"d")) != EOF)
   {
      option_exist = 1;
      switch(c)
      {
      case 'd':
         debug = 1;
         if (debug)
            printf("turn on debug mode.\n");
         break;

      case '?':
         help_msg();
         exit (1);
      default:
         fprintf (stderr, "unrecognized arg >%s<\n", optarg);
         help_msg();
         exit (1);
      }
   }


   /* create socket */
   sock = socket(AF_INET, SOCK_DGRAM, 0);
   if (sock < 0) {
      perror("opening datagram socket");
      exit(1);
   }
   /* create name structure with wildcard using INADDR_ANY */
   from.sin_family = AF_INET;
   from.sin_addr.s_addr = INADDR_ANY;
   from.sin_port = 0;  
   /* port no. < 1024 IPPORT_RESERVED is for privillege process */
   /* here just initialized it, it will be assigned value after call */
   /* getsockname() */
   if (bind(sock, &from, sizeof(struct sockaddr_in))) {
      perror("binding name to datagram socket");
      exit(1);
   }
   length = sizeof(from);
   if (getsockname(sock, &from, &length)) {
      perror("getting socket name");
      exit(1);
   }
   /* Find assigned port value and print out. */
   printf("socket has port #%d\n", ntohs(from.sin_port));

   /* receive message */
   while (flag) {
      n = recvfrom(sock, fromBuf, sizeof(fromBuf), 0, &from, &length);
      if (n < 0) perror("receiving datagram message");
      fromBuf[n] = 0; /* null terminate */
      if (debug) {
         printf("The no. of bytes received=%d\n", n);
         printf("received msg=");
         for (i=0; i<n; i++) {
            if ((i+1)%80 == 0) printf("\n");
            else printf("%c", fromBuf[i]);
         }
         printf("rcvd from");
         printsockaddr(&from);
      }

		printf("What is your reply?");
		if ((n=getline(toBuf, 1024)) <= 0)
			break;
      /* use the returned sender's socket address in the from structure to
              send the reply message */
      if (sendto(sock, toBuf, strlen(toBuf), 0, &from, sizeof(from)) < 0) 
         perror("sending datagram message");
   }
   close(sock);
}