Networks III: Homework

1. In the client code given below, identify the types of the following expressions
   1. p->h_addr_list[0]
   2. *ip
   3. &mysa
   4. mysa.sin_addr.s_addr
   5. (struct sockaddr*)&mysa
2. Identify the point in the client code below at which the socket is bound to a port number.
3. What sepcifies the hostname for the server we'll be connecting to?
4. What specifies the port number for the server we'll be connecting to?

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

int main(int argc, char **argv)
{
  // Print usage
  if (argc == 1) { fprintf(stderr,"usage: %s <hostname>!\n",argv[0]); exit(1); }

  // Set up socket
  int sfd = socket(AF_INET,SOCK_STREAM,0);
  if (sfd == -1) { fprintf(stderr,"Socket not created!\n"); exit(2); }

  // Get IP address from symbolic name
  struct hostent *p;
  p = gethostbyname(argv[1]);
  if (p == NULL) { fprintf(stderr,"Name not found!\n"); exit(1); }
  unsigned int *ip = (unsigned int*)(p->h_addr_list[0]);

  // Set up address structure
  struct sockaddr_in mysa;
  mysa.sin_family = AF_INET;
  mysa.sin_addr.s_addr = *ip;
  mysa.sin_port = htons(10000);

  // Connect!
  if (connect(sfd,(struct sockaddr*)&mysa,sizeof(mysa)) != 0)
  {
    fprintf(stderr,"Client could not connect!\n");
    exit(3);
  }

  // Communicate with server
  char inc, outc;
  while(scanf("%c",&inc) == 1)
  {
    write(sfd,&inc,1);
    read(sfd,&outc,1);
    printf("%c",outc);
  }
  close(sfd);

  return 0;
}