Use POSIX message queue for our IPC

Drop socket-based communication if favor of the POSIX message queue. The
main advantage of using this approach is code simplification and reduction
of the communication overhead - the network stack. Note, that we are using
a non-portable implementation which allows multiplexing, which means that
this code will not work in the Cygwin environment...

configure.ac

@@ -1,7 +1,7 @@
 # cmusfm - configure.ac
-# Copyright (c) 2014 Arkadiusz Bokowy
+# Copyright (c) 2014-2015 Arkadiusz Bokowy
 
-AC_INIT([cmusfm], [0.2.0], [[email protected]])
+AC_INIT([cmusfm], [0.2.5], [[email protected]])
 AC_CONFIG_HEADERS([config.h])
 AM_INIT_AUTOMAKE([foreign subdir-objects -Wall -Werror])
 
@@ -24,6 +24,14 @@ AC_CHECK_LIB(
 	[crypto], [MD5],
 	[], [AC_MSG_ERROR([crypto library not found])]
 )
+AC_CHECK_HEADERS(
+	[mqueue.h],
+	[], [AC_MSG_ERROR([mqueue.h header not found])]
+)
+AC_CHECK_LIB(
+	[rt], [mq_open],
+	[], [AC_MSG_ERROR([rt library not found])]
+)
 AC_CHECK_HEADERS(
 	[poll.h],
 	[], [AC_MSG_ERROR([poll.h header not found])]

src/cmusfm.h

@@ -26,8 +26,8 @@
 
 
 #define CONFIG_FNAME "cmusfm.conf"
-#define SOCKET_FNAME "cmusfm.socket"
 #define CACHE_FNAME  "cmusfm.cache"
+#define MQUEUE_NAME "cmusfm"
 
 
 /* time delay (in seconds) between login attempts to the Last.fm
@@ -40,7 +40,6 @@ extern unsigned char SC_api_key[16];
 extern unsigned char SC_secret[16];
 extern const char *cmusfm_cache_file;
 extern const char *cmusfm_config_file;
-extern const char *cmusfm_socket_file;
 extern struct cmusfm_config config;
 
 

src/main.c

@@ -184,7 +184,6 @@ int main(int argc, char *argv[]) {
 	/* setup global variables - file locations */
 	cmusfm_cache_file = get_cmusfm_cache_file();
 	cmusfm_config_file = get_cmusfm_config_file();
-	cmusfm_socket_file = get_cmusfm_socket_file();
 
 	if (argc == 2 && strcmp(argv[1], "init") == 0) {
 		cmusfm_initialization();

src/server.c

@@ -24,16 +24,16 @@
 
 #include "server.h"
 
+#include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>
+#include <mqueue.h>
 #include <poll.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
-#include <sys/socket.h>
-#include <sys/un.h>
 #if HAVE_SYS_INOTIFY_H
 #include <sys/inotify.h>
 #endif
@@ -47,6 +47,11 @@
 #endif
 
 
+/* Helper function for retrieving message queue name. */
+static char *get_mqueue_name(void) {
+	return "/" MQUEUE_NAME;
+}
+
 /* Helper function for artist name retrieval. */
 static char *get_record_artist(const struct cmusfm_data_record *r) {
 	return (char *)(r + 1);
@@ -96,7 +101,7 @@ static void set_trackinfo(scrobbler_trackinfo_t *sbt,
 static void cmusfm_server_process_data(scrobbler_session_t *sbs,
 		const struct cmusfm_data_record *record) {
 
-	static char saved_data[CMSOCKET_BUFFER_SIZE];
+	static char saved_data[MQUEUE_BUFFER_SIZE];
 	static char saved_is_radio = 0;
 	struct cmusfm_data_record *saved_record = (struct cmusfm_data_record *)saved_data;
 
@@ -256,23 +261,15 @@ static void cmusfm_server_process_data(scrobbler_session_t *sbs,
  * appropriately. */
 int cmusfm_server_check(void) {
 
-	struct sockaddr_un saddr;
-	int fd;
+	mqd_t mq;
 
-	memset(&saddr, 0, sizeof(saddr));
-	saddr.sun_family = AF_UNIX;
-	strcpy(saddr.sun_path, cmusfm_socket_file);
-
-	if ((fd = socket(PF_UNIX, SOCK_STREAM, 0)) == -1)
-		return -1;
-
-	/* check if behind the socket there is an active server instance */
-	if (connect(fd, (struct sockaddr *)(&saddr), sizeof(saddr)) == 0) {
-		close(fd);
+	if ((mq = mq_open(get_mqueue_name(), O_WRONLY)) != -1) {
+		mq_close(mq);
 		return 1;
 	}
 
-	return 0;
+	/* missing message queue is not an error here */
+	return errno == ENOENT ? 0 : -1;
 }
 
 /* server shutdown stuff */
@@ -287,10 +284,17 @@ static void cmusfm_server_stop(int sig) {
  * Upon error -1 is returned. */
 int cmusfm_server_start(void) {
 
-	char buffer[CMSOCKET_BUFFER_SIZE];
+	const char *mqueue_name = get_mqueue_name();
+	const struct mq_attr mqueue_attr = {
+		.mq_flags = O_NONBLOCK,
+		.mq_maxmsg = 10,
+		.mq_msgsize = MQUEUE_BUFFER_SIZE,
+		.mq_curmsgs = 0,
+	};
+
+	char buffer[mqueue_attr.mq_msgsize];
 	scrobbler_session_t *sbs;
 	struct sigaction sigact;
-	struct sockaddr_un saddr;
 	struct pollfd pfds[3];
 #if HAVE_SYS_INOTIFY_H
 	struct inotify_event inot_even;
@@ -301,16 +305,16 @@ int cmusfm_server_start(void) {
 
 	/* setup poll structure for data reading */
 	pfds[0].events = POLLIN;  /* server */
-	pfds[1].events = POLLIN;  /* client */
+	pfds[1].events = POLLIN;  /* not used */
 	pfds[2].events = POLLIN;  /* inotify */
 	pfds[1].fd = -1;
 	pfds[2].fd = -1;
 
-	memset(&saddr, 0, sizeof(saddr));
-	saddr.sun_family = AF_UNIX;
-	strcpy(saddr.sun_path, cmusfm_socket_file);
-	if ((pfds[0].fd = socket(PF_UNIX, SOCK_STREAM, 0)) == -1)
+	if ((pfds[0].fd = mq_open(mqueue_name,
+					O_CREAT | O_EXCL | O_RDONLY, 0600, &mqueue_attr)) == -1) {
+		perror("error: create message queue");
 		return -1;
+	}
 
 	/* initialize scrobbling library */
 	sbs = scrobbler_initialize(SC_api_key, SC_secret);
@@ -328,12 +332,6 @@ int cmusfm_server_start(void) {
 	sigaction(SIGTERM, &sigact, NULL);
 	sigaction(SIGINT, &sigact, NULL);
 
-	/* create server communication socket */
-	unlink(saddr.sun_path);
-	if (bind(pfds[0].fd, (struct sockaddr *)(&saddr), sizeof(saddr)) == -1 ||
-			listen(pfds[0].fd, 2) == -1)
-		goto return_failure;
-
 #if HAVE_SYS_INOTIFY_H
 	/* initialize inode notification to watch changes in the config file */
 	pfds[2].fd = inotify_init();
@@ -347,14 +345,7 @@ int cmusfm_server_start(void) {
 			break;  /* signal interruption */
 
 		if (pfds[0].revents & POLLIN) {
-			pfds[1].fd = accept(pfds[0].fd, NULL, NULL);
-			debug("new client accepted: %d", pfds[1].fd);
-		}
-
-		if (pfds[1].revents & POLLIN && pfds[1].fd != -1) {
-			read(pfds[1].fd, buffer, sizeof(buffer));
-			close(pfds[1].fd);
-			pfds[1].fd = -1;
+			mq_receive(pfds[0].fd, buffer, sizeof(buffer), NULL);
 			cmusfm_server_process_data(sbs, (struct cmusfm_data_record *)buffer);
 		}
 
@@ -385,20 +376,19 @@ int cmusfm_server_start(void) {
 	cmusfm_notify_free();
 #endif
 	scrobbler_free(sbs);
-	close(pfds[0].fd);
-	unlink(saddr.sun_path);
+	mq_close(pfds[0].fd);
+	mq_unlink(mqueue_name);
 
 	return retval;
 }
 
 /* Send track info to server instance. */
 int cmusfm_server_send_track(struct cmtrack_info *tinfo) {
 
-	char buffer[CMSOCKET_BUFFER_SIZE];
+	char buffer[MQUEUE_BUFFER_SIZE];
 	struct cmusfm_data_record *record = (struct cmusfm_data_record *)buffer;
 	struct format_match *match, *matches;
-	struct sockaddr_un saddr;
-	int sock;
+	mqd_t mq;
 
 	/* helper accessors for dynamic fields */
 	char *artist = &buffer[sizeof(*record)];
@@ -482,25 +472,15 @@ int cmusfm_server_send_track(struct cmtrack_info *tinfo) {
 	record->checksum1 = make_record_checksum1(record);
 	record->checksum2 = make_record_checksum2(record);
 
-	/* connect to the communication socket */
-	memset(&saddr, 0, sizeof(saddr));
-	strcpy(saddr.sun_path, cmusfm_socket_file);
-	saddr.sun_family = AF_UNIX;
-	sock = socket(PF_UNIX, SOCK_STREAM, 0);
-	if (connect(sock, (struct sockaddr *)(&saddr), sizeof(saddr)) == -1) {
-		close(sock);
+	if ((mq = mq_open(get_mqueue_name(), O_WRONLY)) == -1) {
+		perror("error: open message queue");
 		return -1;
 	}
 
 	debug("record length: %ld", sizeof(struct cmusfm_data_record) +
 			record->off_title + record->off_location + strlen(location) + 1);
-	write(sock, buffer, sizeof(struct cmusfm_data_record) +
-			record->off_title + record->off_location + strlen(location) + 1);
-
-	return close(sock);
-}
+	mq_send(mq, buffer, sizeof(struct cmusfm_data_record) +
+			record->off_title + record->off_location + strlen(location) + 1, 0);
 
-/* Helper function for retrieving cmusfm server socket file. */
-char *get_cmusfm_socket_file(void) {
-	return get_cmus_home_file(SOCKET_FNAME);
+	return mq_close(mq);
 }

src/server.h

@@ -24,8 +24,8 @@
 #include "cmusfm.h"
 
 
-/* communication socket buffer size */
-#define CMSOCKET_BUFFER_SIZE 1024
+/* message size for message queue */
+#define MQUEUE_BUFFER_SIZE 512
 
 /* shoutcast/stream flag for the status field */
 #define CMSTATUS_SHOUTCASTMASK 0xF0
@@ -58,7 +58,6 @@ struct cmusfm_data_record {
 };
 
 
-char *get_cmusfm_socket_file(void);
 int cmusfm_server_check(void);
 int cmusfm_server_start(void);
 int cmusfm_server_send_track(struct cmtrack_info *tinfo);