Lec35) Socket Programming Part-2

Internet Domain UDP Sockets

Datagram sockets

unreliable , full duplex , packet oriented communication channel

unreliable means there is no sequence numbering

 

no connection establishment 

server has only one socket , no master socket like tcp , only has data socket

Connection-Orietned Datagram Sockets = but client can call connect method  , with this state you don't have to specify server address

 

Udp is good choice for streams of music and video wherer a mising note or frame may not even be noticed

 

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

int main(int argc, char** argv){
  if(argc != 3){printf("Must enter IP and port of echo server\n"); exit(1);}

//*** STEP-I:  Create a socket
   int sockfd = socket (PF_INET, SOCK_DGRAM, 0);

//*** STEP-II: Populate Socket's DS for remote IP and Port, and
//***          let the local IP and Port be selected by the OS itself
   struct sockaddr_in dest_addr;
   dest_addr.sin_family = AF_INET;    
   dest_addr.sin_port = htons(atoi(argv[2]));
   inet_aton(argv[1], &dest_addr.sin_addr);
   memset(&(dest_addr.sin_zero), '\0', sizeof dest_addr.sin_zero); 

//*** STEP-III: Connected UDP Socket
   connect(sockfd, (struct sockaddr*)& dest_addr, sizeof dest_addr);

//*** STEP-IV: Get a string from user and use write() to send that string
//***           to echo server and then read a message from server and display on stdout  
   char buff1[128],buff2[128] ;
   while(1){
      int n = read(0, buff1, sizeof buff1);   
      buff1[n] = '\0';
      write(sockfd, buff1, strlen(buff1));
      n = read(sockfd, buff2, strlen(buff1));
      buff2[n] = '\0';
      write(1, buff2, n);
   }
//*** STEP-IV:  Close socket
   close(sockfd);
   exit(0);
}

connected udp client , notice we are not using sendto or recvfrom.

need to change udp( /etc/xientd.d/echo) disable to no , default is yes, at server side