Reinstate preconfigured keepalives (nanocurrency#1854)

* Reinstate preconfigured keepalives

* Remove unused constants

* No need to insert preconfigured peers into container

* Remove unused param

nano/node/node.cpp

@@ -101,10 +101,10 @@ void nano::network::send_keepalive (nano::transport::channel const & channel_a)
 	channel_a.send (message);
 }
 
-void nano::node::keepalive (std::string const & address_a, uint16_t port_a, bool preconfigured_peer_a)
+void nano::node::keepalive (std::string const & address_a, uint16_t port_a)
 {
 	auto node_l (shared_from_this ());
-	network.resolver.async_resolve (boost::asio::ip::udp::resolver::query (address_a, std::to_string (port_a)), [node_l, address_a, port_a, preconfigured_peer_a](boost::system::error_code const & ec, boost::asio::ip::udp::resolver::iterator i_a) {
+	network.resolver.async_resolve (boost::asio::ip::udp::resolver::query (address_a, std::to_string (port_a)), [node_l, address_a, port_a](boost::system::error_code const & ec, boost::asio::ip::udp::resolver::iterator i_a) {
 		if (!ec)
 		{
 			for (auto i (i_a), n (boost::asio::ip::udp::resolver::iterator{}); i != n; ++i)
@@ -1597,7 +1597,7 @@ void nano::node::keepalive_preconfigured (std::vector<std::string> const & peers
 {
 	for (auto i (peers_a.begin ()), n (peers_a.end ()); i != n; ++i)
 	{
-		keepalive (*i, network_params.default_node_port, true);
+		keepalive (*i, network_params.default_node_port);
 	}
 }
 

nano/node/node.hpp

@@ -435,7 +435,7 @@ class node : public std::enable_shared_from_this<nano::node>
 		alarm.io_ctx.post (action_a);
 	}
 	bool copy_with_compaction (boost::filesystem::path const &);
-	void keepalive (std::string const &, uint16_t, bool = false);
+	void keepalive (std::string const &, uint16_t);
 	void start ();
 	void stop ();
 	std::shared_ptr<nano::node> shared ();

nano/node/repcrawler.cpp

@@ -36,8 +36,14 @@ void nano::rep_crawler::ongoing_crawl ()
 {
 	auto now (std::chrono::steady_clock::now ());
 	query (get_crawl_targets ());
+	auto sufficient_weight (total_weight_internal () > node.config.online_weight_minimum.number ());
+	// If online weight drops below minimum, reach out to preconfigured peers
+	if (!sufficient_weight)
+	{
+		node.keepalive_preconfigured (node.config.preconfigured_peers);
+	}
 	// Reduce crawl frequency when there's enough total peer weight
-	unsigned next_run_seconds = (total_weight_internal () > node.config.online_weight_minimum.number ()) ? 7 : 3;
+	unsigned next_run_seconds = sufficient_weight ? 7 : 3;
 	std::weak_ptr<nano::node> node_w (node.shared ());
 	node.alarm.add (now + std::chrono::seconds (next_run_seconds), [node_w, this]() {
 		if (auto node_l = node_w.lock ())