4P14

Lab 2
Sockets




In this lab we will be looking at making multiple connections to a single server interface. Your goal in this lab will be to modify the client and server as appropriate so multiple clients can carry on concurrent conversations with a single server. You will need to install telnet if it is not already installed. Try the following:

    telnet localhost 80

If you get something like >telnet: command not found< then you must install it.

Installation can be accomplished with:

    yum install telnet -y

Try to telnet once again to confirm installation.

Your Lab instructor will now give you a crash course on Socket communications. Important information should be jotted down on the accompanying handout.

1)  Download and compile Multi_Socket.c example form the courses examples. Open a telnet session and telnet into the server from several clients concurrently. What did you see?







2) Consider the ability to echo back a conversation with a client. This we accomplished in lab 1. The server currently does the echo as part of its default response to the client. For the most part the clients you created in Lab 1 should be almost complete and be able to carry on a conversion with the server. Try this and show your lab leader it work.


3) On the server side, it would be nice to see which client requested an echo back. Thus, modify the server code to print out, which client requested a new connect and also every time an echo request was received (as part of the default behaviour from part 2). To do this you can use the getpeername() system call. An example of its usage is given below.  Try to connect to other lab servers, and have them connect to your. Be sure to disable the firewall to allow connections. Show your lab leader it works and enjoy your 4%.


In this example, getpeername returns the port and address of the peer program. 

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

f()
{
   int s;
   struct sockaddr_in peer;
   int peer_len;
   .
   .
   .
      /* We must put the length in a variable.              */
   peer_len = sizeof(peer);
      /* Ask getpeername to fill in peer's socket address.  */
   if (getpeername(s, &peer, &peer_len) == -1) {
      perror("getpeername() failed");
      return -1;
   }

      /* Print it. The IP address is often zero because     */
      /* sockets are seldom bound to a specific local       */
      /* interface.                                         */
   printf("Peer's IP address is: %s\n", inet_ntoa(peer.sin_addr));
   printf("Peer's port is: %d\n", (int) ntohs(peer.sin_port));
   .
   .
   .
}