fix setup of DHT logic in session_impl::init (#1830)

fix setup of DHT logic in session_impl::init

include/libtorrent/aux_/session_impl.hpp

@@ -737,6 +737,7 @@ namespace libtorrent
 			peer_class_pool m_classes;
 
 			void init(std::shared_ptr<settings_pack> pack);
+			void init_dht();
 
 			void submit_disk_jobs();
 

src/session_impl.cpp

@@ -630,10 +630,45 @@ namespace aux {
 		update_upnp();
 		update_natpmp();
 		update_lsd();
-		update_dht();
 		update_peer_fingerprint();
-		update_dht_bootstrap_nodes();
-		update_dht_announce_interval();
+
+		init_dht();
+	}
+
+	void session_impl::init_dht()
+	{
+		// the need of this elaborated logic is because if the value
+		// of settings_pack::dht_bootstrap_nodes is not the default,
+		// then update_dht_bootstrap_nodes is called. For this reason,
+		// three different cases should be considered.
+		// 1-) dht_bootstrap_nodes setting not touched
+		// 2-) dht_bootstrap_nodes changed but not empty
+		// 3-) dht_bootstrap_nodes set to empty ("")
+		// TODO: find a solution and refactor to avoid potentially stalling
+		// for minutes due to the name resolution
+
+#ifndef TORRENT_DISABLE_DHT
+		if (m_outstanding_router_lookups == 0)
+		{
+			// this can happens because either the setting value was untouched
+			// or the value in the initial settings is empty
+			if (m_settings.get_str(settings_pack::dht_bootstrap_nodes).empty())
+			{
+				// case 3)
+				update_dht();
+				update_dht_announce_interval();
+			}
+			else
+			{
+				// case 1)
+				// eventually update_dht() is called when all resolves are done
+				update_dht_bootstrap_nodes();
+			}
+		}
+		// else is case 2)
+		// in this case the call to update_dht_bootstrap_nodes() by the apply settings
+		// will eventually call update_dht() when all resolves are done
+#endif
 	}
 
 	void session_impl::async_resolve(std::string const& host, int flags

test/test_session.cpp

@@ -394,3 +394,73 @@ TORRENT_TEST(save_state_peer_id)
 	TEST_CHECK(pid3[5] == 'r');
 }
 
+TORRENT_TEST(init_dht)
+{
+	auto count_dht_inits = [](session& ses)
+	{
+		int count = 0;
+		int num = 70; // this number is adjusted per version, an estimate
+		time_point const end_time = clock_type::now() + seconds(15);
+		while (true)
+		{
+			time_point const now = clock_type::now();
+			if (now > end_time) return count;
+
+			ses.wait_for_alert(end_time - now);
+			std::vector<alert*> alerts;
+			ses.pop_alerts(&alerts);
+			for (auto a : alerts)
+			{
+				std::printf("%d: [%s] %s\n", num, a->what(), a->message().c_str());
+				if (a->type() == log_alert::alert_type)
+				{
+					std::string const msg = a->message();
+					if (msg.find("about to start DHT") != std::string::npos)
+						count++;
+				}
+				num--;
+			}
+			if (num <= 0) return count;
+		}
+		return count;
+	};
+
+	{
+		settings_pack p = settings();
+		p.set_bool(settings_pack::enable_dht, true);
+		p.set_int(settings_pack::alert_mask, alert::all_categories);
+		// default value
+		p.set_str(settings_pack::dht_bootstrap_nodes, "dht.libtorrent.org:25401");
+
+		lt::session s(p);
+
+		int const count = count_dht_inits(s);
+		TEST_EQUAL(count, 1);
+	}
+
+	{
+		settings_pack p = settings();
+		p.set_bool(settings_pack::enable_dht, true);
+		p.set_int(settings_pack::alert_mask, alert::all_categories);
+		// no default value
+		p.set_str(settings_pack::dht_bootstrap_nodes, "test.libtorrent.org:25401:8888");
+
+		lt::session s(p);
+
+		int const count = count_dht_inits(s);
+		TEST_EQUAL(count, 1);
+	}
+
+	{
+		settings_pack p = settings();
+		p.set_bool(settings_pack::enable_dht, true);
+		p.set_int(settings_pack::alert_mask, alert::all_categories);
+		// empty value
+		p.set_str(settings_pack::dht_bootstrap_nodes, "");
+
+		lt::session s(p);
+
+		int const count = count_dht_inits(s);
+		TEST_EQUAL(count, 1);
+	}
+}