APPENDIX B: A Simple Server

/*

  Author : Ting-jen Yen (yentj@cs.nyu.edu)
  file name : server.c
  associated file: client.c

  Description : This is a simple iterative
		server that listens at port 1234.
		It will accept a number (unsigned, integer or
		float) from the client, and returns twice
		the number to the client. You can
		can access this server by running the client
		program (see file client.c), or just using
		"telnet" to connect to the server.

  Usage: Simply type "server" in the host machine to serve
		at default port 1234.  Otherwise type
		"server -p <port number>".

  How to compile :

  On Solaris 2 :

	% gcc -o server server.c -lsocket

  On SGI machies :

	% gcc -o server server.c


*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/errno.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <fcntl.h>
#include <string.h>
#include <signal.h>


int             server_sock, con_sock;
int             srv_port = 1234;
struct sockaddr_in source;

/* Close all sockets before the forced quit caused by
   signal */
void
signal_handler()
{
	close(con_sock);
	close(server_sock);

	exit(0);
}


/* When the state of a child process is changed, (for example,
   it is terminated, or ended by call exit(),) the server
   should call wait() to get the state. This will prevent
   the child process from becoming a zombie process when it has
   finished. */
void child_end()
{
  wait(NULL);
}

void
init_servconnection()
{
	struct sockaddr_in server;

	/* Creating socket */
	server_sock = socket(AF_INET, SOCK_STREAM, 0);
	if (server_sock < 0) {
		perror("socket");
		exit(1);
	}
	server.sin_family = AF_INET;
	server.sin_port = htons(srv_port);
	server.sin_addr.s_addr = INADDR_ANY;

/* bind the specified port to this socket */
	if (bind(server_sock, (struct sockaddr *) & server, sizeof(server))
		 < 0)
	{
		perror("bind socket");
		exit(1);
	}
/* listen for connection */
	if (listen(server_sock, 5) < 0) {
		perror("listen");
		exit(1);
	}
}

attenteconnection()
{
	int             lg, pid;

	lg = sizeof(struct sockaddr_in);

/* repeat until accept a successful connect */
	do
	  con_sock = accept(server_sock, (struct sockaddr *) & source, &lg);
	while (con_sock <= 0);

/* Fork a child process to serve the client */
	if ((pid = fork()) != 0)
	{
/* parent process can close the connect and quit */
	  close(con_sock);
	}
	else
	{
/* The child process will handle the client, and the quit when
   finished. */
		handle_req();
		exit(1);
	}
}

usage()
{
	fprintf(stderr, "usage homesrvd [-p port]\n");
	exit(1);
}

extern int errno;

/* handle_req() will get input from the client, parse
   it and write the result back to the client. In this
   case, it will accept a number, either integer or
   float-point value, and return twice the number.
   It will repeat until the input is string "quit".
*/
handle_req()
{
	char            buff[8192];
	int             lg, flag, srv1, is_float, result_i;
	char           *filename, *c, *p;
	struct stat     statres;
	char            req[1024];
	double		result_f;

        flag = 1;
	while (flag) {

/* Try to repeat until read something from the client,
   unless the connection is broken. */
	  do {
	  lg = read(con_sock, req, 1024);
	  if (lg == -1 && errno == EBADF)
	    goto error;
	  } while (lg <= 0);

/* Assume the input will be integer first. */
	  is_float = 0;

	  if (req[lg - 1] != '\n' || req[lg - 2] != '\r') {
		sprintf(req, "Error: Unknown input\r\n");
		write(con_sock, req, strlen(req));
		continue;
	  }

/* Get rid of the trailing new line character and
   carriage return character. */
	  req[lg - 2] = '\0';
/* Get the first part of the line only. (Separated by
   space.) */
	  c = strtok(req, " ");
/* Empty line */
	  if (c == NULL) {
		sprintf(req, "Error: Unknown input\r\n");
		write(con_sock, req, strlen(req));
		continue;
	  }
/* quit */
	  if (strncmp(c, "quit", 4) == 0)
	  {
		flag = 0;
		break;
	  }
/* Check every character to make sure the input is a number,
   determining it is an integer or not on the way. */
	  for (p = c; *p /* != NULL */ ; p ++)
	  {
	    if (!isdigit(*p))
	    {
	      if (*p != '.' || is_float)
	      {
/* If the character is not a digit, and not a decimal point,
   then it is not a number. If it is a decimal point, but
   there is already another one, then it is not a legal number.
*/
	        sprintf(req, "Error: Unknown input\r\n");
	        write(con_sock, req, strlen(req));
		is_float = -1;
	        break;
	      }
	      else
/* If we have one decimal point, then the number will not
   be an integer. */
	        is_float = 1;
	    }
	  }
	  if (is_float == 1)
	  {
/* A float-point number */
	    result_f = atof(c) * 2;
	    sprintf(req, "%f\r\n", result_f);
	    write(con_sock, req, strlen(req));
	  }
	  else if (is_float != -1)
	  {
/* An integer */
	    result_i = atoi(c) * 2;
	    sprintf(req, "%d\r\n", result_i);
	    write(con_sock, req, strlen(req));
	  }
	}

/* Some connection error happened, or quit the loop
   because receiving "quit"  from the client. Will
   close connection and exit this function. */
error:
	close(con_sock);
}

main(int argc,char **argv)
{
	int             lg;

/* Shift the parameter */
	argc--;
	argv++;
	while (argc > 0) {
		if (argv[0][0] != '-')
			usage();
		switch (argv[0][1]) {
		case 'p':
/* Set port number of the server */
			srv_port = atoi(argv[1]);
			argv += 2;
			argc -= 2;
			break;
		default:
			usage();
		}
	}

/* Intercept CHILD signal. This signal occurs when a child process
   changes its status. In this program, it usually means when
   a child process calls exit() to end itself. */
	sigset(SIGCHLD, child_end);

/* Intercept some signals which will end this process so
   we can close connection before quit it. */
	signal(SIGTERM, signal_handler);
	signal(SIGQUIT, signal_handler);
	signal(SIGINT, signal_handler);

/* Setup the socket and the port */
	init_servconnection();

/* Wait for connection */
	do {
		attenteconnection();
	} while (1);

}