main: improve api socket bind

If the grout process is launched a second time, then socket api bind() failed
and the process unlink socket file before exiting, making the first running
process unreachable.

If the grout process crash, it won't remove api socket file, and the next
invocation will fail at socket api bind().

Change api_socket_start() to check, if bind() fails, whether there's a
listening process behind the scene:

* If there is, exit without removing socket api file
* If there is not, then remove file and resume bind.

Signed-off-by: Olivier Gournet <[email protected]>

Author: ogournet

Diff for: main/api.c

@@ -206,6 +206,7 @@ int api_socket_start(struct event_base *base) {
 		struct sockaddr_un un;
 		struct sockaddr a;
 	} addr;
+	int ret;
 	int fd;
 
 	fd = socket(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0);
@@ -215,7 +216,24 @@ int api_socket_start(struct event_base *base) {
 	addr.un.sun_family = AF_UNIX;
 	memccpy(addr.un.sun_path, path, 0, sizeof(addr.un.sun_path) - 1);
 
-	if (bind(fd, &addr.a, sizeof(addr.un)) < 0) {
+	ret = bind(fd, &addr.a, sizeof(addr.un));
+	if (ret < 0 && errno == EADDRINUSE) {
+		// unix socket file exists, check if there is a process
+		// listening on the other side.
+		ret = connect(fd, &addr.a, sizeof(addr.un));
+		if (ret == 0) {
+			LOG(ERR, "grout already running on API socket %s, exiting", path);
+			close(fd);
+			return errno_set(EADDRINUSE);
+		}
+		if (ret < 0 && errno != ECONNREFUSED)
+			return errno_log(errno, "connect");
+		// remove socket file, and try to bind again
+		if (unlink(addr.un.sun_path) < 0)
+			return errno_log(errno, "unlink");
+		ret = bind(fd, &addr.a, sizeof(addr.un));
+	}
+	if (ret < 0) {
 		close(fd);
 		return errno_log(errno, "bind");
 	}

Diff for: main/main.c

@@ -211,7 +211,8 @@ int main(int argc, char **argv) {
 		modules_fini(ev_base);
 		event_base_free(ev_base);
 	}
-	unlink(args.api_sock_path);
+	if (err != EADDRINUSE)
+		unlink(args.api_sock_path);
 	libevent_global_shutdown();
 dpdk_stop:
 	dpdk_fini();