Add incremental backoff to the filter/permchannels/xline_db modules.

Closes #1671.

docs/conf/modules.conf.example

@@ -1909,12 +1909,20 @@
 # 'saveperiod' determines how often to check if the database needs to be
 # saved to disk. Defaults to every five seconds.
 #
+# 'backoff' is the value to multiply the saveperiod by every time a save
+# fails. When the save succeeds the period will be reset.
+#
+# 'maxbackoff' is the maximum write period that should be allowed even
+# if incremental backoff is enabled.
+#
 # 'operonly' determines whether a server operator or services server is
 # needed to enable the permchannels mode. You should generally keep this
 # set to yes unless you know what you are doing.
 #<permchanneldb filename="permchannels.conf"
 #               listmodes="yes"
 #               saveperiod="5s"
+#               backoff="2"
+#               maxbackoff="5m"
 #               operonly="yes">
 #<include file="permchannels.conf" missingokay="yes">
 #
@@ -2658,7 +2666,10 @@
 
 # Specify the filename for the xline database and how often to check whether
 # the database needs to be saved here.
-#<xlinedb filename="xline.db" saveperiod="5s">
+#<xlinedb filename="xline.db"
+#         saveperiod="5s"
+#         backoff="2"
+#         maxbackoff="5m">
 
 #-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#-#
 #    ____                _   _____ _     _       ____  _ _   _        #

src/modules/m_filter.cpp

@@ -206,6 +206,9 @@ private:
 	bool dirty = false;
 	std::string filterconf;
 	Regex::Engine* factory;
+	unsigned long saveperiod;
+	unsigned long maxbackoff;
+	unsigned char backoff;
 	void FreeFilters();
 
 public:
@@ -238,6 +241,7 @@ public:
 	ModResult OnPreCommand(std::string& command, CommandBase::Params& parameters, LocalUser* user, bool validated) override;
 	void OnUnloadModule(Module* mod) override;
 	bool Tick() override;
+	bool WriteDatabase();
 	bool AppliesToMe(User* user, const FilterResult& filter, int flags);
 	void ReadFilters();
 	static bool StringToFilterAction(const std::string& str, FilterAction& fa);
@@ -645,7 +649,10 @@ void ModuleFilter::ReadConfig(ConfigStatus& status)
 	filterconf = tag->getString("filename");
 	if (!filterconf.empty())
 		filterconf = ServerInstance->Config->Paths.PrependConfig(filterconf);
-	SetInterval(tag->getDuration("saveperiod", 5));
+	saveperiod = tag->getDuration("saveperiod", 5);
+	backoff = tag->getNum<uint8_t>("backoff", 0);
+	maxbackoff = tag->getDuration("maxbackoff", saveperiod * 120, saveperiod);
+	SetInterval(saveperiod);
 
 	factory = RegexEngine ? (RegexEngine.operator->()) : nullptr;
 
@@ -934,9 +941,29 @@ void ModuleFilter::OnUnloadModule(Module* mod)
 
 bool ModuleFilter::Tick()
 {
-		if (!dirty) // No need to write.
-			return true;
+	if (dirty)
+	{
+		if (WriteDatabase())
+		{
+			// If we were previously unable to write but now can then reset the time interval.
+			if (GetInterval() != saveperiod)
+				SetInterval(saveperiod, false);
 
+			dirty = false;
+		}
+		else
+		{
+			// Back off a bit to avoid spamming opers.
+			if (backoff > 1)
+				SetInterval(std::min(GetInterval() * backoff, maxbackoff), false);
+			ServerInstance->Logs.Debug(MODNAME, "Trying again in {} seconds", GetInterval());
+		}
+	}
+	return true;
+};
+
+bool ModuleFilter::WriteDatabase()
+{
 		if (filterconf.empty()) // Nothing to write to.
 		{
 			dirty = false;
@@ -949,7 +976,7 @@ bool ModuleFilter::Tick()
 		{
 			ServerInstance->SNO.WriteToSnoMask('f', "Unable to save filters to \"{}\": {} ({})",
 					newfilterconf, strerror(errno), errno);
-			return true;
+			return false;
 		}
 
 		stream
@@ -977,7 +1004,7 @@ bool ModuleFilter::Tick()
 		{
 			ServerInstance->SNO.WriteToSnoMask('f', "Unable to save filters to \"{}\": {} ({})",
 				newfilterconf, strerror(errno), errno);
-			return true;
+			return false;
 		}
 		stream.close();
 
@@ -990,7 +1017,7 @@ bool ModuleFilter::Tick()
 		{
 			ServerInstance->SNO.WriteToSnoMask('f', "Unable to replace old filter config \"{}\" with \"{}\": {} ({})",
 				filterconf, newfilterconf, strerror(errno), errno);
-			return true;
+			return false;
 		}
 
 		dirty = false;

src/modules/m_permchannels.cpp

@@ -176,10 +176,15 @@ class ModulePermanentChannels final
 	, public Timer
 
 {
+private:
 	PermChannel p;
 	bool dirty = false;
 	bool loaded = false;
 	bool save_listmodes;
+	unsigned long saveperiod;
+	unsigned long maxbackoff;
+	unsigned char backoff;
+
 public:
 
 	ModulePermanentChannels()
@@ -195,7 +200,10 @@ public:
 		permchannelsconf = tag->getString("filename");
 		save_listmodes = tag->getBool("listmodes", true);
 		p.SetOperOnly(tag->getBool("operonly", true));
-		SetInterval(tag->getDuration("saveperiod", 5));
+		saveperiod = tag->getDuration("saveperiod", 5);
+		backoff = tag->getNum<uint8_t>("backoff", 0);
+		maxbackoff = tag->getDuration("maxbackoff", saveperiod * 120, saveperiod);
+		SetInterval(saveperiod);
 
 		if (!permchannelsconf.empty())
 			permchannelsconf = ServerInstance->Config->Paths.PrependConfig(permchannelsconf);
@@ -289,8 +297,23 @@ public:
 	bool Tick() override
 	{
 		if (dirty)
-			WriteDatabase(p, save_listmodes);
-		dirty = false;
+		{
+			if (WriteDatabase(p, save_listmodes))
+			{
+				// If we were previously unable to write but now can then reset the time interval.
+				if (GetInterval() != saveperiod)
+					SetInterval(saveperiod, false);
+
+				dirty = false;
+			}
+			else
+			{
+				// Back off a bit to avoid spamming opers.
+				if (backoff > 1)
+					SetInterval(std::min(GetInterval() * backoff, maxbackoff), false);
+				ServerInstance->Logs.Debug(MODNAME, "Trying again in {} seconds", GetInterval());
+			}
+		}
 		return true;
 	}
 

src/modules/m_xline_db.cpp

@@ -39,6 +39,9 @@ class ModuleXLineDB final
 private:
 	bool dirty;
 	std::string xlinedbpath;
+	unsigned long saveperiod;
+	unsigned long maxbackoff;
+	unsigned char backoff;
 
 public:
 	ModuleXLineDB()
@@ -57,7 +60,10 @@ public:
 		 */
 		const auto& Conf = ServerInstance->Config->ConfValue("xlinedb");
 		xlinedbpath = ServerInstance->Config->Paths.PrependData(Conf->getString("filename", "xline.db", 1));
-		SetInterval(Conf->getDuration("saveperiod", 5));
+		saveperiod = Conf->getDuration("saveperiod", 5);
+		backoff = Conf->getNum<uint8_t>("backoff", 0);
+		maxbackoff = Conf->getDuration("maxbackoff", saveperiod * 120, saveperiod);
+		SetInterval(saveperiod);
 
 		// Read xlines before attaching to events
 		ReadDatabase();
@@ -91,7 +97,20 @@ public:
 		if (dirty)
 		{
 			if (WriteDatabase())
+			{
+				// If we were previously unable to write but now can then reset the time interval.
+				if (GetInterval() != saveperiod)
+					SetInterval(saveperiod, false);
+
 				dirty = false;
+			}
+			else
+			{
+				// Back off a bit to avoid spamming opers.
+				if (backoff > 1)
+					SetInterval(std::min(GetInterval() * backoff, maxbackoff), false);
+				ServerInstance->Logs.Debug(MODNAME, "Trying again in {} seconds", GetInterval());
+			}
 		}
 		return true;
 	}