allow execution of on_unknown_torrent method in the absence of active…

… torrents

include/libtorrent/aux_/session_impl.hpp

@@ -349,7 +349,8 @@ namespace aux {
 				plugins_all_idx = 0, // to store all plugins
 				plugins_optimistic_unchoke_idx = 1, // optimistic_unchoke_feature
 				plugins_tick_idx = 2, // tick_feature
-				plugins_dht_request_idx = 3 // dht_request_feature
+				plugins_dht_request_idx = 3, // dht_request_feature
+				plugins_unknown_torrent_idx = 4 // unknown_torrent_feature
 			};
 
 			template <typename Fun, typename... Args>

include/libtorrent/extensions.hpp

@@ -211,6 +211,10 @@ TORRENT_VERSION_NAMESPACE_3
 		// called
 		static constexpr feature_flags_t alert_feature = 4_bit;
 
+		// include this bit if your plugin needs to have on_unknown_torrent()
+		// called even if there is no active torrent in the session
+		static constexpr feature_flags_t unknown_torrent_feature = 5_bit;
+
 		// This function is expected to return a bitmask indicating which features
 		// this plugin implements. Some callbacks on this object may not be called
 		// unless the corresponding feature flag is returned here. Note that

src/session_impl.cpp

@@ -992,6 +992,8 @@ bool ssl_server_name_callback(ssl::stream_handle_type stream_handle, std::string
 			m_ses_extensions[plugins_tick_idx].push_back(ext);
 		if (features & plugin::dht_request_feature)
 			m_ses_extensions[plugins_dht_request_idx].push_back(ext);
+		if (features & plugin::unknown_torrent_feature)
+			m_ses_extensions[plugins_unknown_torrent_idx].push_back(ext);
 		if (features & plugin::alert_feature)
 			m_alerts.add_extension(ext);
 		session_handle h(shared_from_this());
@@ -3086,7 +3088,7 @@ namespace {
 
 		// check if we have any active torrents
 		// if we don't reject the connection
-		if (m_torrents.empty())
+		if (m_torrents.empty() && m_ses_extensions[plugins_unknown_torrent_idx].empty())
 		{
 #ifndef TORRENT_DISABLE_LOGGING
 			session_log("<== INCOMING CONNECTION [ rejected, there are no torrents ]");
@@ -3140,7 +3142,7 @@ namespace {
 		// the setting to start up queued torrents when they
 		// get an incoming connection is enabled, we cannot
 		// perform this check.
-		if (!m_settings.get_bool(settings_pack::incoming_starts_queued_torrents))
+		if (!m_settings.get_bool(settings_pack::incoming_starts_queued_torrents) || m_ses_extensions[plugins_unknown_torrent_idx].empty())
 		{
 			bool has_active_torrent = std::any_of(m_torrents.begin(), m_torrents.end()
 				, [](std::shared_ptr<torrent> const& i)