/*******select.c*********/
/*******Using select() for I/O multiplexing */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
    /* port we're listening on */
#define PORT 2020
int
main (int argc, char *argv[])
{
  /* master file descriptor list */
  fd_set master;
  /* temp file descriptor list for select() */
  fd_set read_fds;
  /* server address */
  struct sockaddr_in serveraddr;
  /* client address */
  struct sockaddr_in clientaddr;
  /* maximum file descriptor number */
  int fdmax;
  /* listening socket descriptor */
  int listener;
  /* newly accept()ed socket descriptor */
  int newfd;
  /* buffer for client data */
  char buf[1024];
  int nbytes;
  socklen_t addrlen;
  int i, j;
  /* clear the master and temp sets */
  FD_ZERO (&master);
  FD_ZERO (&read_fds);
  /* get the listener */
  if ((listener = socket (AF_INET, SOCK_STREAM, 0)) == -1)
    {
      perror ("Server-socket() error");
      /*just exit */
      exit (1);
    }
  printf ("Server-socket() is OK...\n");
  /* bind */
  serveraddr.sin_family = AF_INET;
  serveraddr.sin_addr.s_addr = INADDR_ANY;
  serveraddr.sin_port = htons (PORT);
  memset (&(serveraddr.sin_zero), '\0', 8);
  if (bind (listener, (struct sockaddr *) &serveraddr, sizeof (serveraddr)) ==
      -1)
    {
      perror ("Server-bind() error");
      exit (1);
    }
  printf ("Server-bind() is OK...\n");
  /* listen */
  if (listen (listener, 10) == -1)
    {
      perror ("Server-listen() error");
      exit (1);
    }
  printf ("Server-listen() is OK...\n");
  /* add the listener to the master set */
  FD_SET (listener, &master);
  /* keep track of the biggest file descriptor */
  fdmax = listener;		/* so far, it's this one */
  /* loop */
  for (;;)
    {
      /* copy it */
      read_fds = master;
      if (select (fdmax + 1, &read_fds, NULL, NULL, NULL) == -1)
	{
	  perror ("Server-select() error");
	  exit (1);
	}
      printf ("Server-select() is OK...\n");
      /*run through the existing connections looking for data to be read */
      for (i = 0; i <= fdmax; i++)
	{
	  if (FD_ISSET (i, &read_fds))
	    {			/* we got one... */
	      if (i == listener)
		{
		  /* handle new connections */
		  addrlen = sizeof (clientaddr);
		  if ((newfd =
		       accept (listener, (struct sockaddr *) &clientaddr,
			       &addrlen)) == -1)
		    {
		      perror ("Server-accept() error");
		    }
		  else
		    {
		      printf ("Server-accept() is OK...\n");
		      FD_SET (newfd, &master);	/* add to master set */
		      if (newfd > fdmax)
			{	/* keep track of the maximum */
			  fdmax = newfd;
			}
		      printf ("%s: New connection from %s on socket %d\n",
			      argv[0], inet_ntoa (clientaddr.sin_addr),
			      newfd);
		    }
		}
	      else
		{
		  /* handle data from a client */
		  if ((nbytes = recv (i, buf, sizeof (buf), 0)) <= 0)
		    {
		      /* got error or connection closed by client */
		      if (nbytes == 0)
			/* connection closed */
			printf ("%s: socket %d hung up\n", argv[0], i);
		      else
			perror ("recv() error");
		      /* close it... */
		      close (i);
		      /* remove from master set */
		      FD_CLR (i, &master);
		    }
		  else
		    {
		      /* we got some data from a client */
		      for (j = 0; j <= fdmax; j++)
			{
			  /* send to everyone! */
			  if (FD_ISSET (j, &master))
			    {
			      /* except the listener and ourselves */
			      if (j != listener && j != i)
				{
				  if (send (j, buf, nbytes, 0) == -1)
				    perror ("send() error");
				}
			    }
			}
		    }
		}
	    }
	}
    }
  return 0;
}