ICS 451 Homework 1: UNIX Client and Server

Read the following Unix man pages: socket(2), bind(2), listen(2). accept(2), connect(2), fork(2).

1 Existing Unix clients

1.a Telnet

1. www.hawaii.edu
2. cs.stanford.edu
3. prep.ai.mit.edu
4. escher.uni-muenster.de

What happens if you attempt to connect to the daytime port of www.stanford.edu?

1.b Ping

Can you justify the round-trip times to each of these hosts by considering just the speed of light? Compare (approximate) distances to delays.

2 Writing a Unix client

2.a Compiling and running

Note that the program will not compile on uhunix, which does not have a C compiler. Send mail to sunx@hawaii.edu to obtain an account on the ICS Unix workstations, including your full name and the fact that you need an account for ICS 451.

Also note that you are welcome to do exercises 2 and 3 on winsock instead of Unix if you prefer. If you use winsock, you will have to figure out for yourself how to write a client and a server.

/* client.c: program to connect to server. */
/* compile with: gcc -o client client.c -lsocket -lnsl */

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

#define portnumber 4321
#define BUFSIZE 1000

#define error(s) { perror(s); exit(1); }

main ()
{
  int s;
  struct protoent * protocolentry;
  struct hostent * hostentry;
  struct sockaddr_in sin;
  struct sockaddr * sap = (struct sockaddr *) &sin;
  char buf[BUFSIZE];

  if ((protocolentry = getprotobyname("tcp")) == NULL)
    error("getprotobyname");
  if ((s = socket(AF_INET, SOCK_STREAM, protocolentry->p_proto)) < 0)
    error("socket");
  hostentry = gethostbyname("maru.ics.hawaii.edu");
  if ((hostentry == NULL) || (hostentry->h_addr_list == NULL))
    error("gethostbyname");
  bzero (&sin, sizeof (sin));
  sin.sin_family = AF_INET;
  bcopy(hostentry->h_addr_list[0], &(sin.sin_addr), hostentry->h_length);
  sin.sin_port = htons(portnumber);
  if (connect(s, sap, sizeof(sin)) < 0) error("connect");
  printf ("enter your e-mail address and your name: ");
  fgets (buf, BUFSIZE, stdin);
  if (write(s, buf, strlen(buf)) < 0) error("write");
  if (close(s) < 0) error("close");
}

2.b Reading data

2.c Change host and port

2.d Compute the time per connection

For all of exercise 2, the only thing you need to report is the total time and the time per connection from exercise 2.d.

3 Writing a Unix server

3.a Compiling and running

If you have trouble running the server, try using a different port number (someone else may be using the same port number as you).

Make sure you have killed your server when you are done. On the suns, use "ps -U yourlogin" to see what processes are still running.

/* server.c: program to accept input from clients. */
/* compile with: gcc -o server server.c -lsocket */

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

#define portnumber 4321
#define BUFSIZE 1000

#define error(s) { perror(s); exit(1); }

main ()
{
  int passive, session;
  struct sockaddr_in sin;
  struct sockaddr * sap = (struct sockaddr *) &sin;
  struct sigaction siga;
  int count, i = 0, pos = 0;
  char buf[BUFSIZE] = "";

  if ((passive = socket(AF_INET, SOCK_STREAM, 0)) < 0) error("socket");
  bzero (&sin, sizeof (sin));
  sin.sin_family = AF_INET;
  sin.sin_port = htons(portnumber);
  sin.sin_addr.s_addr = INADDR_ANY;
  if (bind(passive, sap, sizeof (sin)) != 0) error("bind");
  /* make sure child processes are really detached (see exit(2)) */
  signal(SIGCHLD, SIG_IGN);
  /* specify the maximum queue length */
  if(listen(passive, 5) < 0) error("listen");
  count = sizeof (sin);
  while ((session = accept(passive, sap, &count)) >= 0) {
    if (fork() == 0) {	/* child process */
      count = read(session, buf, BUFSIZE - 1);
      buf[count] = '\0';
      pos = count - 1;
      if (buf[pos] == '\n') pos--;
      for (i = 0; i <= pos; ) {   /* reverse string */
	int swap = buf[i];
	buf[i++] = buf[pos];
	buf[pos--] = swap;
      }
      if (write(session, buf, count) < 0) error("write");
      if (close(session) < 0) error("child close");
      exit(0);
    } else {			/* parent process */
      if (close(session) < 0) error("parent close");
    }
  }
}

3.b Bind

3.c Turn in

Computer Networks, ICS 451
Instructor: Edo Biagioni