/*****************************************************************************
 *** Demo program explaining the client-server model                       ***
 *** This is the server program                                            ***
 *** Written by Abhijit Das, CSE, IIT Kharagpur                            ***
 *** Last modified: October 13, 2006                                       ***
 *****************************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <netinet/in.h>

/* Global constants */
#define SERVICE_PORT 41041
#define Q_SIZE 5
#define MAX_LEN 1024

/* Function prototypes */
int startServer ( );
void clientTalk ( int );
void serverLoop ( int );
int wordCount ( char * );

/* Start the server: socket(), bind() and listen() */
int startServer ()
{
   int sfd;                    /* for listening to port PORT_NUMBER */
   struct sockaddr_in saddr;   /* address of server */
   int status;

   /* Request for a socket descriptor */
   sfd = socket(AF_INET, SOCK_STREAM, 0);
   if (sfd == -1) {
      fprintf(stderr, "*** Server error: unable to get socket descriptor\n");
      exit(1);
   }

   /* Set the fields of server's internet address structure */
   saddr.sin_family = AF_INET;            /* Default value for most applications */
   saddr.sin_port = htons(SERVICE_PORT);  /* Service port in network byte order */
   saddr.sin_addr.s_addr = INADDR_ANY;    /* Server's local address: 0.0.0.0 (htons not necessary) */
   bzero(&(saddr.sin_zero),8);            /* zero the rest of the structure */

   /* Bind the socket to SERVICE_PORT for listening */
   status = bind(sfd, (struct sockaddr *)&saddr, sizeof(struct sockaddr));
   if (status == -1) {
      fprintf(stderr, "*** Server error: unable to bind to port %d\n", SERVICE_PORT);
      exit(2);
   }

   /* Now listen to the service port */
   status = listen(sfd,Q_SIZE);
   if (status == -1) {
      fprintf(stderr, "*** Server error: unable to listen\n");
      exit(3);
   }

   fprintf(stderr, "+++ Server successfully started, listening to port %hd\n", SERVICE_PORT);
   return sfd;
}

/* Accept connections from clients, spawn a child process for each request */
void serverLoop ( int sfd )
{
   int cfd;                    /* for communication with clients */
   struct sockaddr_in caddr;   /* address of client */
   int size;

   while (1) {
      /* accept connection from clients */
      cfd = accept(sfd, (struct sockaddr *)&caddr, &size);
      if (cfd == -1) {
         fprintf(stderr, "*** Server error: unable to accept request\n");
         continue;
      }
      fprintf(stderr, "+++ Connected with %s\n", inet_ntoa(caddr.sin_addr));

      /* fork a child to process request from client */
      if (!fork()) {
         clientTalk(cfd);
         fprintf(stderr, "+++ Closed connection with %s\n", inet_ntoa(caddr.sin_addr));
         close(cfd);
         exit(0);
      }

      /* parent (server) does not talk with clients */
      close(cfd);

      /* parent waits for termination of child processes */
      while (waitpid(-1,NULL,WNOHANG) > 0);
   }
}

/* Interaction of the child process with the client */
void clientTalk ( int cfd )
{
   int status;
   int nbytes;
   int wc;
   char buffer[MAX_LEN];

   /* Send greetings to client */
   status = send(cfd, "!!! Welcome to server.\n!!! Enter a sentence : ", 46, 0);
   if (status == -1) {
      fprintf(stderr, "*** Server error: unable to send\n");
      return;
   }

   /* Receive response from server */
   nbytes = recv(cfd, buffer, MAX_LEN-1, 0);
   if (nbytes == -1) {
      fprintf(stderr, "*** Server error: unable to receive\n");
      return;
   }
   buffer[nbytes] = '\0';
   fprintf(stderr, "+++ Received sentence from client:\n");
   fprintf(stderr, "+++ \t\"%s\"\n", buffer);

   /* Process response and send output to server */
   wc = wordCount(buffer);
   sprintf(buffer, "!!! Number of words: %d\n", wc);
   send(cfd, buffer, strlen(buffer), 0);
   if (status == -1) {
      fprintf(stderr, "*** Server error: unable to send\n");
      return;
   }

   /* Wind up */
   status = send(cfd, "!!! Tschus!\n", 12, 0);
   if (status == -1) {
      fprintf(stderr, "*** Server error: unable to send\n");
      return;
   }
}

/* Auxiliary routine used by clientTalk() */
int wordCount ( char *str )
{
   int wc = 0, i;

   while (1) {
      while ((*str == ' ') || (*str == '\t')) ++str;
      if (*str == '\0') break;
      ++wc;
      while ((*str != ' ') && (*str != '\t') && (*str != '\0')) ++str;
   }
   return wc;
}

int main ()
{
   int sfd;

   sfd = startServer();
   serverLoop(sfd);
}

/*** End of server.c ***/