tftptest.c

this gives details of the network programming

/* The beginnings of a tftp client (enough to use for grading P3) */

#include <stdio.h>      /* standard C i/o facilities */
#include <stdlib.h>     /* needed for atoi() */
#include <unistd.h>  	/* defines STDIN_FILENO, system calls,etc */
#include <sys/types.h>  /* system data type definitions */
#include <sys/socket.h> /* socket specific definitions */
#include <netinet/in.h> /* INET constants and stuff */
#include <arpa/inet.h>  /* IP address conversion stuff */
#include <netdb.h>	/* gethostbyname */

void tests(int,struct sockaddr_in *, int subtest);

/* client program:

   The following must passed in on the command line:
      hostname of the server (argv[1])
      port number of the server (argv[2])
*/



int main( int argc, char **argv ) {
  int sk, subtest;
  struct sockaddr_in server;
  struct hostent *hp;


  /* Make sure we have the right number of command line args */

  if (argc < 3 || argc > 4) {
    printf ("Usage: %s <server name> <port number> [sub-test number (0/1/2/3)]\n",argv[0]);
    exit(0);
  }

  /* create a socket 
     IP protocol family (PF_INET) 
     UDP (SOCK_DGRAM)
  */
  
  if ((sk = socket( PF_INET, SOCK_DGRAM, 0 )) < 0)
    {
      printf("Problem creating socket\n");
      exit(1);
    }

  /* now create a sockaddr that will be used to contact the server 

     fill in an address structure that will be used to specify
     the address of the server we want to connect to

     address family is IP  (AF_INET)

     server IP address is found by calling gethostbyname with the
     name of the server (entered on the command line)

     server port number is argv[2] (entered on the command line)
  */

  server.sin_family = AF_INET;
  if ((hp = gethostbyname(argv[1]))==0) {
    printf("Invalid or unknown host\n");
    exit(1);
  }

  /* copy the IP address into the sockaddr 
     It is already in network byte order 
  */

  memcpy( &server.sin_addr.s_addr, hp->h_addr, hp->h_length);

  /* establish the server port number - we must use network byte order! */
  server.sin_port = htons(atoi(argv[2]));

  subtest = argc == 3 ? 0 : atoi(argv[3]);

  if (subtest < 0 || subtest > 3) {
    printf ("Usage: %s <server name> <port number> [sub-test number (0/1/2/3)]\n",argv[0]);
    exit(0);
  }

  tests(sk,&server,subtest);
  return(0);
}