Add support for systemd watchdog.

This is a reworked version of
https://github.com/eclipse-mosquitto/mosquitto/pull/3158 by Gaël PORTAY.

ChangeLog.txt

@@ -77,7 +77,8 @@ Broker:
 - Add suport for PROXY protocol v1 and v2.
 - Log message if a client attempts to connect with TLS to a non-TLS listener.
 - Add `listener_allow_anonymous` option.
-- Add `listener_auto_id_prefix` ` option.
+- Add `listener_auto_id_prefix` option.
+- Add support for systemd watchdog.
 
 Plugins / plugin interface:
 - Add persist-sqlite plugin.

src/CMakeLists.txt

@@ -73,6 +73,7 @@ add_executable(mosquitto
 	../lib/tls_mosq.c
 	topic_tok.c
 	../lib/util_mosq.c ../lib/util_mosq.h
+	watchdog.c
 	websockets.c
 	will_delay.c
 	../lib/will_mosq.c ../lib/will_mosq.h

src/Makefile

@@ -109,6 +109,7 @@ OBJS=	mosquitto.o \
 		subs.o \
 		sys_tree.o \
 		topic_tok.o \
+		watchdog.o \
 		websockets.o \
 		will_delay.o \
 		xtreport.o

src/loop.c

@@ -170,6 +170,7 @@ int mosquitto_main_loop(struct mosquitto__listener_sock *listensock, int listens
 	int rc;
 
 
+	watchdog__init();
 #if defined(WITH_WEBSOCKETS) && WITH_WEBSOCKETS == WS_IS_LWS && LWS_LIBRARY_VERSION_NUMBER == 3002000
 	memset(&sul, 0, sizeof(struct lws_sorted_usec_list));
 #endif
@@ -194,6 +195,7 @@ int mosquitto_main_loop(struct mosquitto__listener_sock *listensock, int listens
 #endif
 
 		keepalive__check();
+		watchdog__check();
 
 #ifdef WITH_BRIDGE
 		bridge_check();

src/mosquitto_broker_internal.h

@@ -949,6 +949,12 @@ void service_run(char *name);
 DWORD WINAPI SigThreadProc(void* data);
 #endif
 
+/* ============================================================
+ * Watchdog
+ * ============================================================ */
+void watchdog__init(void);
+void watchdog__check(void);
+
 /* ============================================================
  * Websockets related functions
  * ============================================================ */

src/watchdog.c

@@ -0,0 +1,63 @@
+/*
+Copyright (c) 2009-2020 Roger Light <roger@atchoo.org>
+
+All rights reserved. This program and the accompanying materials
+are made available under the terms of the Eclipse Public License 2.0
+and Eclipse Distribution License v1.0 which accompany this distribution.
+
+The Eclipse Public License is available at
+   https://www.eclipse.org/legal/epl-2.0/
+and the Eclipse Distribution License is available at
+  http://www.eclipse.org/org/documents/edl-v10.php.
+
+SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
+
+Contributors:
+   Roger Light - initial implementation and documentation.
+   Tatsuzo Osawa - Add epoll.
+*/
+
+#include "config.h"
+
+#include <time.h>
+#include "mosquitto.h"
+
+#ifdef WITH_SYSTEMD
+#  include <systemd/sd-daemon.h>
+#endif
+
+#ifdef WITH_SYSTEMD
+static time_t next_ping = 0;
+static time_t ping_sec = 0;
+#endif
+
+void watchdog__init(void)
+{
+#ifdef WITH_SYSTEMD
+	char *watchdog_usec = getenv("WATCHDOG_USEC");
+	time_t next_ping = mosquitto_time();
+	time_t ping_sec = 0;
+
+	if(watchdog_usec){
+		char *endptr = NULL;
+		long usec = strtol(watchdog_usec, &endptr, 10);
+		if(watchdog_usec[0] != '\0' && endptr[0] == '\0' && usec > 0){
+			ping_sec = (usec / 1000000) / 2;
+		}
+		next_ping = mosquito_time();
+	}
+#endif
+}
+
+void watchdog__check(void)
+{
+#ifdef WITH_SYSTEMD
+	if(ping_sec){
+		time_t now = mosquitto_time();
+		if(now > next_ping){
+			sd_notify(0, "WATCHDOG=1");
+			next_ping = now + ping_sec;
+		}
+	}
+#endif
+}