10 Domain Sockets

int socketpair(int domain, int type, int protocol, int sv[2]);

socketpair(AF_UNIX, SOCK_STREAM, 0, fd)

int main(int argc, char **argv) {
	int num_to_recv = atoi(argv[1]);
	int fd;
	
	struct sockaddr_un  un,  clnt_un;  // UDP socket structure
	socklen_t           len, clnt_len;
		
	char *name = "serv-dom-sock";
	
	// create a UNIX domain DATAGRAM socket
	fd = socket(AF_UNIX, SOCK_DGRAM, 0))

	// remove the server domain socket file if exists already
	unlink(name);
	
	// Boiler plate: prepare the server domain socket address structure
	memset(&un, 0, sizeof(un));
	un.sun_family = AF_UNIX;
	strcpy(un.sun_path, name);
	len = offsetof(struct sockaddr_un, sun_path) + strlen(name);
	
	// bind the server domain socket name to the descriptor
	bind(fd, (struct sockaddr *)&un, len) 

	
	char *buf = malloc(num_to_recv + 1);
	char reply[100];
	int i = 0, n;
	
	for (;;) {
		memset(buf, 0, num_to_recv + 1);
		clnt_len = sizeof(clnt_un);
		// recvfrom gives client address structure to &clnt_un
		n = recvfrom(fd, buf, num_to_recv, 0,
					 (struct sockaddr *) &clnt_un, &clnt_len);

		fprintf(stderr, "\"%s\" received from ", buf);
		write(STDERR_FILENO, clnt_un.sun_path,
				clnt_len - offsetof(struct sockaddr_un, sun_path));
		fprintf(stderr, " (clnt_len:%d), ", clnt_len);

		// sends back to client
		snprintf(reply, sizeof(reply), "[%d](%s)", ++i, buf);
		n = sendto(fd, reply, strlen(reply), 0, 
				   (struct sockaddr *) &clnt_un, clnt_len);
		fprintf(stderr, "sent back %d bytes: %s\n", n, reply);
	}
	
	// Clean up
	fprintf(stderr, "Server shutting down\n");
	free(buf);
	close(fd);
	unlink(name);
}

static void die(const char *m) { perror(m); exit(1); }
	
int main(int argc, char **argv)
{
	const char *msg = argv[1];
	int num_repeat = atoi(argv[2]);
	
	int fd;
	socklen_t my_len;
	struct sockaddr_un my_un;
	
	char my_name[sizeof(my_un.sun_path)];
	snprintf(my_name, sizeof(my_name), "clnt-dom-sock.%d", getpid());
	
	// create a UNIX domain datagram socket
	if ((fd = socket(AF_UNIX, SOCK_DGRAM, 0)) < 0)
		die("socket failed");
	
	// fill in my own domain socket address structure
	memset(&my_un, 0, sizeof(my_un));
	my_un.sun_family = AF_UNIX;
	strcpy(my_un.sun_path, my_name);
	my_len = offsetof(struct sockaddr_un, sun_path) + strlen(my_name);
	
	// bind my own domain sock name to the descriptor
	if (bind(fd, (struct sockaddr *)&my_un, my_len) < 0) 
		die("bind failed");
	
	socklen_t serv_len;
	struct sockaddr_un serv_un;
	char *serv_name = "serv-dom-sock";
	assert(strlen(serv_name) < sizeof(serv_un.sun_path));
	
	// fill in the server's domain socket address structure
	memset(&serv_un, 0, sizeof(serv_un));
	serv_un.sun_family = AF_UNIX;
	strcpy(serv_un.sun_path, serv_name);
	serv_len = offsetof(struct sockaddr_un, sun_path) + strlen(serv_name);
	
	int i, n;
	
	// send messages
	for (i = 0; i < num_repeat; i++) {
		n = sendto(fd, msg, strlen(msg), 0,
				   (struct sockaddr *) &serv_un, serv_len);
		fprintf(stderr, "[%d] sent %d bytes: \"%s\"\n", i+1, n, msg);
	}
	
	// receive replies
	char reply[100];
	for (i = 0; i < num_repeat; i++) {
		memset(reply, 0, sizeof(reply));
		// since bind() called, know address
		n = recvfrom(fd, reply, sizeof(reply), 0, NULL, NULL);
		fprintf(stderr, "%d bytes received: \"%s\"\n", n, reply);
	}
	
	// clean up
	close(fd);
	unlink(my_name);
}