authRTESFinalAssignment/lib/helpers.c

#include "helpers.h"

void set_timer_and_handler(void (*handler)(int), long int timer_interval) {
	struct itimerval interval_timer;
	struct sigaction signal_action;

	// Installs handler as the signal handler for SIGALRM
	memset(&signal_action, 0, sizeof(signal_action));
	signal_action.sa_handler = handler;
	if (sigaction(SIGALRM, &signal_action, NULL)) {
		perror("Couldn't install function handler for SIGALRM signals.");
		exit(EXIT_FAILURE);
	}

	// Sets an interval timer to deliver a SIGALRM signal every timer_interval seconds
	interval_timer.it_interval.tv_usec = 0;
	interval_timer.it_interval.tv_sec = timer_interval;
	interval_timer.it_value.tv_usec = 0;
	interval_timer.it_value.tv_sec = timer_interval;

	if (setitimer(ITIMER_REAL, &interval_timer, NULL) == -1) {
		perror("Couldn't set timer.");
		exit(EXIT_FAILURE);
	}
}

void enable_echo_broadcast(void) {
	if (system("echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts") < 0) {
		perror("Couldn't allow echo broadcasts.");
		exit(EXIT_FAILURE);
	}
}

/*
 * Function based on this snippet:
 * https://codereview.stackexchange.com/a/58107
*/
void search_for_neighbors(void) {
	// Broadcasts ping
	if (system("ping -b 10.255.255.255 -c 3 > /dev/null") < 0) {
		perror("Couldn't broadcast echo.");
		exit(EXIT_FAILURE);
	}

	// Reads the ARP file checking for connected devices
	FILE *arpCache = fopen(ARP_CACHE, "r");
	if (!arpCache) {
		perror("ARP Cache: Failed to open file \"" ARP_CACHE "\"");
		exit(EXIT_FAILURE);
	}

	// Ignores the first line, which contains the header
	char header[ARP_BUFFER_LEN];
	if (!fgets(header, sizeof(header), arpCache)) {
		perror("Couldn't read ARP file header.");
		exit(EXIT_FAILURE);
	}

	// Extracts IP addresses found in the file
	char ipAddr[ARP_BUFFER_LEN];
	int count = 0;
	while (1 == fscanf(arpCache, ARP_LINE_FORMAT, ipAddr)) {
		printf("%03d: [%s]\n", ++count, ipAddr);
	}

	fclose(arpCache);
}

/*
 * Function based on this example:
 * https://www.gnu.org/software/libc/manual/html_node/Inet-Example.html#Inet-Example
*/
int create_socket_and_listen(uint16_t port, uint8_t backlog_size) {
	int in_sock;
	struct sockaddr_in own_name;

	// Creates the socket
	in_sock = socket(PF_INET, SOCK_STREAM, 0);
	if (in_sock < 0) {
		perror("Couldn't create the socket.");
		exit(EXIT_FAILURE);
	}

	// Gives the socket a name
	own_name.sin_family = AF_INET;
	own_name.sin_port = htons(port);
	own_name.sin_addr.s_addr = htonl(INADDR_ANY);

	// Binds own address structure to socket
	if (bind(in_sock, (struct sockaddr *) &own_name, sizeof(own_name)) < 0) {
		perror("Couldn't bind the address structure to the socket.");
		exit(EXIT_FAILURE);
	}

	if (listen(in_sock, backlog_size) < 0) {
		perror("Couldn't listen for connections on the socket.");
		exit(EXIT_FAILURE);
	}

	return in_sock;
}

void send_message(const char *ipv4, uint16_t port, const char *message) {
	int out_sock;
	struct sockaddr_in peer_name;

	// Creates the socket
	out_sock = socket(PF_INET, SOCK_STREAM, 0);
	if (out_sock < 0) {
		perror("Couldn't create the socket.");
		exit(EXIT_FAILURE);
	}

	// Connects to the peer
	init_sockaddr(&peer_name, ipv4, port);
	if (connect(out_sock, (struct sockaddr *) &peer_name, sizeof(peer_name))) {
		printf("Couldn't connect to the peer.\n");
	} else {
		// Sends data to the peer
		write_to_peer(out_sock, message);
	}

	close(out_sock);
}

void accept_connection(int sock, struct sockaddr_in *peer_name, fd_set *active_fd_set) {
	size_t peer_name_size = sizeof((*peer_name));
	int comm_socket = accept(sock, (struct sockaddr *) peer_name, &peer_name_size);
	if (comm_socket < 0) {
		perror("Couldn't accept the connection.");
		exit(EXIT_FAILURE);
	}

	fprintf(stderr, "Connected to host %s, port %hd.\n",
		inet_ntoa((*peer_name).sin_addr), ntohs((*peer_name).sin_port));
	FD_SET(comm_socket, active_fd_set);
}

void write_to_peer(int file_desc, const char *message) {
	int num_bytes = write(file_desc, message, strlen(message) + 1);
	if (num_bytes < 0) {
		perror("Couldn't write to peer.");
		exit(EXIT_FAILURE);
	}
}

int read_from_peer(int file_des, uint16_t max_line) {
	char buffer[max_line];
	int num_bytes;

	num_bytes = read(file_des, buffer, sizeof(buffer));
	if (num_bytes < 0) {
		perror("Couldn't read from peer.");
		exit(EXIT_FAILURE);
	} else if (num_bytes == 0)
		// End-of-file
		return -1;
	else {
		fprintf(stderr, "Got message: `%s'\n", buffer);
		return 0;
	}
}

/*
 * Function based on this example:
 * https://www.gnu.org/software/libc/manual/html_node/Inet-Example.html#Inet-Example
*/
void init_sockaddr(struct sockaddr_in *peer_name, const char *ipv4, uint16_t port) {
	struct hostent *hostinfo;

	peer_name->sin_family = AF_INET;
	peer_name->sin_port = htons(port);
	hostinfo = gethostbyname(ipv4);
	if (hostinfo == NULL) {
		fprintf(stderr, "Unknown host %s.\n", ipv4);
		exit(EXIT_FAILURE);
	}
	peer_name->sin_addr = *(struct in_addr *) hostinfo->h_addr_list[0];
}