simple_server.c

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

#define PORT    5555
#define MAXMSG  512

int make_socket(uint16_t port) {
	struct sockaddr_in name;

	/* Create the socket. */
	int sock = socket(PF_INET, SOCK_STREAM, 0);
	if (sock < 0) {
		perror ("socket");
		exit (EXIT_FAILURE);
	}

	/* Give the socket a name. */
	name.sin_family = AF_INET;
	name.sin_port = htons(port);
	name.sin_addr.s_addr = htonl (INADDR_ANY);
	if (bind(sock, (struct sockaddr *) &name, sizeof(name)) < 0) {
		perror("bind");
		exit (EXIT_FAILURE);
	}

	return sock;
}


int read_from_client (int filedes) {
	char buffer[MAXMSG];
	int nbytes;

	nbytes = read (filedes, buffer, MAXMSG);
	if (nbytes < 0) {
		/* Read error. */
		perror ("read");
		exit (EXIT_FAILURE);
	} else if (nbytes == 0) {
		/* End-of-file. */
		return -1;
	} else {
		/* Data read. */
		printf("%s\n", buffer);
		return 0;
	}
}

int main (void) {
	fd_set active_fd_set, read_fd_set;
	int i;
	struct sockaddr_in clientname;
	/* size_t size; */
	socklen_t size;

	/* Create the socket and set it up to accept connections. */
	int sock = make_socket (PORT);
	if (listen (sock, 1) < 0) {
		perror ("listen");
		exit (EXIT_FAILURE);
	}

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

	while (1) {
		/* Block until input 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 the sockets with input pending. */
		for (i = 0; i < FD_SETSIZE; ++i) {
			if (FD_ISSET (i, &read_fd_set)) {
				if (i == sock) {
					/* Connection request on original socket. */
					int new;
					/* size = sizeof (clientname); */
					size = sizeof(clientname);
					new = accept (sock, (struct sockaddr *) &clientname, &size);
					if (new < 0) {
						perror ("accept");
						exit (EXIT_FAILURE);
					}
					printf("server: connect from host: %s, port:%hd.\n", inet_ntoa(clientname.sin_addr), ntohs(clientname.sin_port));
					FD_SET (new, &active_fd_set);
				} else {
					/* Data arriving on an already-connected socket. */
					if (read_from_client (i) < 0) {
						close (i);
						FD_CLR (i, &active_fd_set);
					}
				}
			}
		}
	}
}