#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>

#define PORT 1200
#define MAXMSGLENGTH 12

int
main (void)
{
		int sock; /* server socket, which accepts new connections */
		fd_set active_fd_set, read_fd_set; /* sets of serving socket descriptors */
		int i;
		struct sockaddr_in clientname, server;
		size_t size;

		/* Create the socket and set it up to accept connections */
		sock = socket(PF_INET, SOCK_STREAM, 0);
		if (sock < 0) {
				perror("socket");
				exit(EXIT_FAILURE);
		}

		/* Give the socket a name */
		server.sin_family = AF_INET;
		server.sin_port = htons(PORT);
		server.sin_addr.s_addr = htonl(INADDR_ANY);

		if (bind(sock, (struct sockaddr *) &server, sizeof(server)) < 0) {
				perror("bind");
				exit(EXIT_FAILURE);
		}

		if (listen(sock, 10) < 0) {
				perror("listen");
				exit(EXIT_FAILURE);
		}

		/* Initialize the set of active sockets */
		FD_ZERO (&active_fd_set);
		FD_SET (sock, &active_fd_set);

		/* going into server main loop */
		while (1) {
				/* Block until unput arrives on one or more active sockets */
				read_fd_set = active_fd_set;
				if (select (FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0) {
						perror ("select");
						exit (EXIT_FAILURE);
				}

				/* Service all sockets with input pending */
				for (i = 0; i < FD_SETSIZE; ++i) {
						if (i == sock) {
								/* Connection on server socket - new connection request */
								int new;
								size = sizeof (clientname);
								new = accept(sock, (struct sockaddr *) &clientname, &size);
								if (new < 0) {
										perror ("accept");
										exit (EXIT_FAILURE);
								}

								fprintf (stderr, "connect from host %s, port %hd.\n",
									inet_ntoa (clientname.sin_addr),
									ntohs(clientname.sin_port));
								FD_SET (new, &active_fd_set);
						}
						else {
								if (read_from_client (i) < 0) {
										close (i);
										FD_CLR (i, &active_fd_set);
								}
						}
				}
		}
}

int
read_from_client (int fd)
{
		char buffer[MAXMSGLENGTH];
		int nbytes;

		nbytes = read (fd, buffer, MAXMSGLENGTH);
		if (nbytes < 0) {
				perror("read");
				exit(EXIT_FAILURE);
		}
		else if (nbytes == 0) {
				return -1;
		}
		else {
				fprintf (stderr, "got message from %d client: `%s'\n", fd, buffer);
				return 0;
		}
}