/*
NAME:       UDP.ECHO.SERVER
SYNOPSIS:    UDPServer port_number
DESCRIPTION:    The program creates a datagram socket in the inet 
                domain, then receives messsages from client process 
                and echos it back to it.
*/

#include <stdio.h>
#include <errno.h>
#include <sys/time.h>
#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <sys/param.h>
#include <sys/socket.h>
#include <sys/file.h>
#include <stdlib.h>

#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>

#define MAXHOSTNAME 80
#define BUF_SIZE 500


void reusePort(int sock);

int main(int argc, char * argv[])
{
   struct addrinfo hints, *result, *rp;
   struct addrinfo hints_local, *result_local;
   int sfd, s;
   struct sockaddr_storage peer_addr;
   socklen_t peer_addr_len;
   ssize_t nread;
   char buffer[BUF_SIZE];
   char ThisHost[80];

   if (argc != 2) {
         fprintf(stderr, "Usage: %s port\n", argv[0]);
         exit(EXIT_FAILURE);
   }

   gethostname(ThisHost, MAXHOSTNAME);
    /*Obtain address(es) matching localhost/localport*/
    memset(&hints_local, 0, sizeof(hints_local));
    hints_local.ai_family = AF_INET; //IPv4
    hints_local.ai_socktype = SOCK_DGRAM; //UDP
    hints_local.ai_flags = AI_PASSIVE;

    if (getaddrinfo(ThisHost, argv[1], &hints_local, &result_local) != 0)
    {
        fprintf(stderr, "getaddrinfo error\n");
        exit(EXIT_FAILURE);
    }



    printf("----EchoServer running at host NAME: %s\n", ThisHost);
    printf("(EchoServer INET ADDRESS is: %s )\n", inet_ntoa(((struct sockaddr_in*)result_local->ai_addr)->sin_addr));
    printf("Server Port is: %s \n", argv[1]);

   memset(&hints, 0, sizeof(hints));

   hints.ai_family = AF_INET; //IPv4
   hints.ai_socktype = SOCK_DGRAM; //UDP
   hints.ai_flags = AI_PASSIVE; //For wildcard IP address


   if ((getaddrinfo(NULL, argv[1], &hints, &result)) != 0)
   {
      fprintf(stderr, "getaddrinfo error\n");
      exit(EXIT_FAILURE);
   }

   /* getaddrinfo() returns a list of address structures.
    Try each address until we successfully bind.
    If socket (or bind) fails, we (close the socket
    and) try the next address. */ 

   for (rp = result; rp != NULL; rp = rp->ai_next) {
      sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
      if (sfd == -1)
      continue;

      reusePort(sfd);

      if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
      break;                  /* Success */

      close(sfd);
   }

   freeaddrinfo(result);           /* No longer needed */

   if (rp == NULL) {               /* No address succeeded */
      fprintf(stderr, "Could not bind\n");
      exit(EXIT_FAILURE);
   }

   
   /* Read datagrams and echo them back to sender. */

   while (1)
   {
      peer_addr_len = sizeof(peer_addr);
      printf("\n...server is waiting...\n");
      nread = recvfrom(sfd, buffer, BUF_SIZE, 0, (struct sockaddr *)&peer_addr, &peer_addr_len);
      buffer[nread]='\0';
      if (nread == 1)
      {
         continue; //Ignore failed request
      }

      char host[NI_MAXHOST], service[NI_MAXSERV];

      s = getnameinfo((struct sockaddr *)&peer_addr, peer_addr_len, host, NI_MAXHOST, service, NI_MAXSERV, NI_NUMERICSERV);

      if (s == 0)
      {
         printf("Received: %s from %s:%s\n", buffer, host, service);
      }
      else
         fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));
      
      if (sendto(sfd, buffer, nread, 0, (struct sockaddr *)&peer_addr, peer_addr_len) != nread)
      {
         fprintf(stderr, "Error sending response\n");
      }
      
      

   }
   
}
void reusePort(int s)
{
  int one=1;
  
  if ( setsockopt(s,SOL_SOCKET,SO_REUSEADDR,(char *) &one,sizeof(one)) == -1 )
  {
    printf("error in setsockopt,SO_REUSEPORT \n");
    exit(-1);
  }
}