miniupnpd: default NOTIFY interval of 900s minus a random value

fixes #698

As advised in UDA:
  Due to the unreliable nature of UDP, devices SHOULD send the entire set
  of discovery messages more than once with some delay between sets e.g. a
  few hundred milliseconds. To avoid network congestion discovery messages
  SHOULD NOT be sent more than three times. In addition, the device MUST
  re-send its advertisements periodically prior to expiration of the duration
  specified in the CACHE-CONTROL header field; it is RECOMMENDED that such
  refreshing of advertisements be done at a randomly-distributed interval
  of less than one-half of the advertisement expiration time.

(CACHE-CONTROL value is minimum 1800 seconds, so the interval should be
less than 900s

miniupnpd/Changelog.txt

@@ -1,5 +1,8 @@
 $Id: Changelog.txt,v 1.515 2024/03/19 23:40:30 nanard Exp $
 
+2024/06/09:
+  default NOTIFY interval of 900s minus a random value
+
 2024/04/29:
   ipv6: prefer globally routable addresses
 

miniupnpd/miniupnpd.c

@@ -303,6 +303,14 @@ tomato_helper(void)
 #endif  /* 1 (tomato) */
 #endif	/* TOMATO */
 
+static int gen_current_notify_interval(int notify_interval) {
+	/* if possible, remove a random number of seconds between 1 and 64 */
+	if (notify_interval > 65)
+		return notify_interval - 1 - (random() & 0x3f);
+	else
+		return notify_interval;
+}
+
 /* OpenAndConfHTTPSocket() :
  * setup the socket used to handle incoming HTTP connections. */
 static int
@@ -896,7 +904,7 @@ struct runtime_vars {
 #ifdef ENABLE_HTTPS
 	int https_port;	/* HTTPS Port */
 #endif
-	int notify_interval;	/* seconds between SSDP announces */
+	int notify_interval;	/* seconds between SSDP announces. Should be >= 900s */
 	/* unused rules cleaning related variables : */
 	int clean_ruleset_threshold;	/* threshold for removing unused rules */
 	int clean_ruleset_interval;		/* (minimum) interval between checks. 0=disabled */
@@ -1220,7 +1228,7 @@ init(int argc, char * * argv, struct runtime_vars * v)
 #ifdef ENABLE_HTTPS
 	v->https_port = -1;
 #endif
-	v->notify_interval = 30;	/* seconds between SSDP announces */
+	v->notify_interval = 900;	/* seconds between SSDP announces */
 	v->clean_ruleset_threshold = 20;
 	v->clean_ruleset_interval = 0;	/* interval between ruleset check. 0=disabled */
 #ifndef DISABLE_CONFIG_FILE
@@ -2147,6 +2155,7 @@ main(int argc, char * * argv)
 	fd_set readset;	/* for select() */
 	fd_set writeset;
 	struct timeval timeout, timeofday, lasttimeofday = {0, 0};
+	int current_notify_interval;	/* with random variation */
 	int max_fd = -1;
 #ifdef USE_MINIUPNPDCTL
 	int sctl = -1;
@@ -2233,6 +2242,7 @@ main(int argc, char * * argv)
 	memset(&v, 0, sizeof(v));
 	if(init(argc, argv, &v) != 0)
 		return 1;
+	current_notify_interval = gen_current_notify_interval(v.notify_interval);
 #ifdef ENABLE_HTTPS
 	if(init_ssl() < 0)
 		return 1;
@@ -2658,13 +2668,13 @@ main(int argc, char * * argv)
 		if(upnp_gettimeofday(&timeofday) < 0)
 		{
 			syslog(LOG_ERR, "gettimeofday(): %m");
-			timeout.tv_sec = v.notify_interval;
+			timeout.tv_sec = current_notify_interval;
 			timeout.tv_usec = 0;
 		}
 		else
 		{
 			/* the comparaison is not very precise but who cares ? */
-			if(timeofday.tv_sec >= (lasttimeofday.tv_sec + v.notify_interval))
+			if(timeofday.tv_sec >= (lasttimeofday.tv_sec + current_notify_interval))
 			{
 				if (GETFLAG(ENABLEUPNPMASK))
 					SendSSDPNotifies2(snotify,
@@ -2673,13 +2683,14 @@ main(int argc, char * * argv)
 					              (unsigned short)v.https_port,
 #endif
 				                  v.notify_interval << 1);
+				current_notify_interval = gen_current_notify_interval(v.notify_interval);
 				memcpy(&lasttimeofday, &timeofday, sizeof(struct timeval));
-				timeout.tv_sec = v.notify_interval;
+				timeout.tv_sec = current_notify_interval;
 				timeout.tv_usec = 0;
 			}
 			else
 			{
-				timeout.tv_sec = lasttimeofday.tv_sec + v.notify_interval
+				timeout.tv_sec = lasttimeofday.tv_sec + current_notify_interval
 				                 - timeofday.tv_sec;
 				if(timeofday.tv_usec > lasttimeofday.tv_usec)
 				{

miniupnpd/miniupnpd.conf

@@ -133,9 +133,9 @@
 # Report system uptime instead of daemon uptime
 system_uptime=yes
 
-# Notify interval in seconds. default is 30 seconds.
+# Notify interval in seconds. default is 900 seconds.
-#notify_interval=240
+# As advised in the standard, announcement have a lifetime double of this value.
-notify_interval=60
+notify_interval=900
 
 # Unused rules cleaning.
 # never remove any rule before this threshold for the number