Work on p2p socket communication, Stylistic changes

lib/helpers.c

@@ -1,56 +1,179 @@
 #include "helpers.h"
 
-int create_socket(uint16_t port) {
-	int sock;
-	struct sockaddr_in socket_name;
+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
-	sock = socket (PF_INET, SOCK_STREAM, 0); //TODO: check if PF_INET is the right one
-	if (sock < 0) {
+	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
-	socket_name.sin_family = AF_INET;
-	socket_name.sin_port = htons(port);
-	socket_name.sin_addr.s_addr = htonl(INADDR_ANY);
+	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(sock, (struct sockaddr *) &socket_name, sizeof(socket_name)) < 0) {
+	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);
 	}
 
-	return sock;
+	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_client(int file_des, uint16_t max_line) {
+int read_from_peer(int file_des, uint16_t max_line) {
 	char buffer[max_line];
-	int nbytes;
+	int num_bytes;
 
-	nbytes = read(file_des, buffer, sizeof(buffer));
-	if (nbytes < 0) {
-		perror("Couldn't read from client.");
+	num_bytes = read(file_des, buffer, sizeof(buffer));
+	if (num_bytes < 0) {
+		perror("Couldn't read from peer.");
 		exit(EXIT_FAILURE);
-	} else if (nbytes == 0)
+	} else if (num_bytes == 0)
 		// End-of-file
 		return -1;
 	else {
-		fprintf(stderr, "Server: got message: `%s'\n", buffer);
+		fprintf(stderr, "Got message: `%s'\n", buffer);
 		return 0;
 	}
 }
 
-void init_sockaddr(struct sockaddr_in *name, const char *hostname, uint16_t port) {
+/*
+ * 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;
 
-	name->sin_family = AF_INET;
-	name->sin_port = htons(port);
-	hostinfo = gethostbyname(hostname);
+	peer_name->sin_family = AF_INET;
+	peer_name->sin_port = htons(port);
+	hostinfo = gethostbyname(ipv4);
 	if (hostinfo == NULL) {
-		fprintf(stderr, "Unknown host %s.\n", hostname);
+		fprintf(stderr, "Unknown host %s.\n", ipv4);
 		exit(EXIT_FAILURE);
 	}
-	name->sin_addr = *(struct in_addr *) hostinfo->h_addr_list[0];
+	peer_name->sin_addr = *(struct in_addr *) hostinfo->h_addr_list[0];
 }

lib/helpers.h

@@ -11,10 +11,37 @@
 #include <netdb.h>
 #include <arpa/inet.h>
 #include <sys/select.h>
+#include <sys/time.h>
+#include <signal.h>
+#include <string.h>
 
-int create_socket(uint16_t port);
+// Macros to turn a numeric macro into a string literal
+#define xstr(s) str(s)
+#define str(s) #s
 
-int read_from_client(int file_des, uint16_t max_line);
+// Neighbor discovery related definitions
+#define ARP_CACHE "/proc/net/arp"
+#define ARP_STRING_LEN 1023
+#define ARP_BUFFER_LEN (ARP_STRING_LEN + 1)
+
+// Format for fscanf() to read the 1st field of ARP
+#define ARP_LINE_FORMAT "%" xstr(ARP_STRING_LEN) "s %*s %*s %*s %*s %*s"
+
+void set_timer_and_handler(void (*handler)(int), long int timer_interval);
+
+void enable_echo_broadcast(void);
+
+void search_for_neighbors(void);
+
+int create_socket_and_listen(uint16_t port, uint8_t backlog_size);
+
+void send_message(const char *ipv4, uint16_t port, const char *message);
+
+void accept_connection(int sock, struct sockaddr_in *client_name, fd_set *active_fd_set);
+
+void write_to_peer(int filedes, const char *message);
+
+int read_from_peer(int file_des, uint16_t max_line);
 
 void init_sockaddr(struct sockaddr_in *name, const char *hostname, uint16_t port);
 

src/zaqar.c

@@ -2,154 +2,75 @@
 
 #define MESSAGE "You got mail!!! xo xo xo"
 
-volatile sig_atomic_t out_flag = false;
-
-void write_to_server(int filedes) {
-	int nbytes;
-
-	nbytes = write(filedes, MESSAGE, strlen(MESSAGE) + 1);
-	if (nbytes < 0) {
-		perror("write");
-		exit(EXIT_FAILURE);
-	}
-}
-
-void handle_alarm(int sig) {
-	if (sig == SIGALRM) {
-		out_flag = true;
-
-		int sock;
-		struct sockaddr_in servername;
-
-		printf("GOT_CL1\n");
-
-		/* Create the socket. */
-		sock = socket (PF_INET, SOCK_STREAM, 0);
-		if (sock < 0) {
-			perror("socket (client)");
-			exit(EXIT_FAILURE);
-		}
-
-		/* Connect to the server. */
-		init_sockaddr (&servername, "10.0.88.79", PORT);
-		if (connect(sock, (struct sockaddr *) &servername, sizeof (servername))) {
-			printf("GOT_CL2\n");
-			//perror("connect (client)");
-			//exit(EXIT_FAILURE);
-		} else {
-			printf("GOT_CL3\n");
-			/* Send data to the server. */
-			write_to_server(sock);
-		}
-
-		//close (sock);
-	}
-}
+volatile sig_atomic_t sigalrm_flag = false;
 
 int main(void) {
-	int sock;
+	int in_sock;
 	fd_set active_fd_set, read_fd_set;
-	struct sockaddr_in client_name;
-	size_t size;
-
-	alarm(0);
-	//signal(SIGALRM, handle_alarm);
-
-	struct itimerval new;
-
-	new.it_interval.tv_usec = 0;
-	new.it_interval.tv_sec = 8;
-	new.it_value.tv_usec = 0;
-	new.it_value.tv_sec = 8;
+	struct sockaddr_in peer_name;
 
-	if (setitimer (ITIMER_REAL, &new, NULL) == -1) {
-		perror("Couldn't set timer.");
-		exit(EXIT_FAILURE);
-	}
-
-	sigset_t mask;
-	int sfd;
-	struct signalfd_siginfo fdsi;
+	// Sets a timer and handler to produce interrupts for sending messages
+	set_timer_and_handler(handle_alarm, TIMER_INTERVAL);
 
-	sigemptyset(&mask);
-	sigaddset(&mask, SIGALRM);
-	/*if (sigprocmask(SIGALRM, &mask, NULL) == -1)
-		perror("sigprocmask");*/
+	// Searches network for neighbors
+	enable_echo_broadcast();
+	search_for_neighbors();
 
-	sfd = signalfd(-1, &mask, 0);
-	if (sfd == -1)
-		perror("signalfd");
-
-	// Creates the socket and sets it up to accept connections
-	sock = create_socket(PORT);
-	if (listen(sock, BACKLOG_SIZE) < 0) {
-		perror("Couldn't listen for connections on the socket.");
-		exit(EXIT_FAILURE);
-	}
+	// Creates a socket and sets it up to accept connections
+	in_sock = create_socket_and_listen(PORT, BACKLOG_SIZE);
 
-	printf("GOT_SV1\n");
 	// Initializes the set of active sockets
 	// Clears the descriptor set
 	FD_ZERO(&active_fd_set);
 	// Sets socket in active readset
-	FD_SET(sock, &active_fd_set);
-	FD_SET(sfd, &active_fd_set);
+	FD_SET(in_sock, &active_fd_set);
 
 	while (1) {
-		printf("GOT_SV2\n");
+		if (sigalrm_flag) {
+			// It's time to send a message!
+			send_message("10.0.82.61", PORT, MESSAGE);
+
+			sigalrm_flag = false;
+		}
+
 		// Shallow copies the readset
 		read_fd_set = active_fd_set;
 
 		// Blocks until input arrives on one or more active sockets
 		if (select(FD_SETSIZE, &read_fd_set, NULL, NULL, NULL) < 0) {
-			if (out_flag) {
-				printf("GOT_SV2.1\n");
-				out_flag = false;
+			// Handles the wake-up from alarm signal interrupts
+			if (sigalrm_flag) {
 				continue;
 			}
-			printf("GOT_SV2.2\n");
+
 			perror("Couldn't initiate synchronous I/O multiplexing.");
 			exit(EXIT_FAILURE);
 		}
 
 		// Services all the sockets with input pending
-		for (int i = 0; i < FD_SETSIZE; ++i) { //TODO: is this needed?
+		for (int i = 0; i < FD_SETSIZE; ++i) {
 			if (FD_ISSET(i, &read_fd_set)) {
-				printf("GOT_SV3\n");
-				if (i == sock) {
+				if (i == in_sock) {
 					// Connection request on original socket
-					size = sizeof(client_name);
-					int new = accept(sock, (struct sockaddr *) &client_name, &size);
-					if (new < 0) {
-						perror("Couldn't accept the connection.");
-						exit(EXIT_FAILURE);
-					}
-
-					fprintf(stderr, "Server: connect from host %s, port %hd.\n",
-						inet_ntoa(client_name.sin_addr), ntohs(client_name.sin_port));
-					FD_SET(new, &active_fd_set);
-				} else if (i == sfd) {
-					ssize_t s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo));
-					if (s != sizeof(struct signalfd_siginfo))
-						perror("read");
-
-					if (fdsi.ssi_signo == SIGALRM) {
-						printf("Got SIGALRM\n");
-						handle_alarm(SIGALRM);
-					} else {
-						printf("Read unexpected signal\n");
-					}
+					accept_connection(in_sock, &peer_name, &active_fd_set);
 				} else { 
 					// Data arriving on an already-connected socket
-					if (read_from_client(i, MAXLINE) < 0) {
+					if (read_from_peer(i, MAXLINE) < 0) {
 						close(i);
 						FD_CLR(i, &active_fd_set);
 					}
 				}
 			}
 		}
-		printf("GOT_SV4\n");
 	}
 
 	return 0;
 }
+
+void handle_alarm(int sig) {
+	if (sig != SIGALRM) {
+		return;
+	} else {
+		sigalrm_flag = true;
+	}
+}

src/zaqar.h

@@ -2,8 +2,6 @@
 #define ZAQAR_H_
 
 #include <stdbool.h>
-#include <signal.h>
-#include <string.h>
 #include <stdio.h>
 #include <errno.h>
 #include <stdlib.h>
@@ -14,14 +12,16 @@
 #include <netdb.h>
 #include <arpa/inet.h>
 #include <sys/select.h>
-#include <sys/time.h>
 
 #include <sys/signalfd.h>
 
 #include "helpers.h"
 
+#define TIMER_INTERVAL 10
 #define PORT 5000
 #define MAXLINE 1024
 #define BACKLOG_SIZE 2
 
+void handle_alarm(int sig);
+
 #endif //ZAQAR_H_