don't delete unreachable routers if no transports

libi2pd/NetDb.cpp

@@ -638,6 +638,7 @@ namespace data
 		if (checkForExpiration && uptime > i2p::transport::SSU2_TO_INTRODUCER_SESSION_DURATION) // 1 hour
 			expirationTimeout = i2p::context.IsFloodfill () ? NETDB_FLOODFILL_EXPIRATION_TIMEOUT*1000LL :
 				NETDB_MIN_EXPIRATION_TIMEOUT*1000LL + (NETDB_MAX_EXPIRATION_TIMEOUT - NETDB_MIN_EXPIRATION_TIMEOUT)*1000LL*NETDB_MIN_ROUTERS/total;
+		bool isOffline = checkForExpiration && i2p::transport::transports.GetNumPeers () < NETDB_MIN_TRANSPORTS; // enough routers and uptime, but no tranports
 			
 		std::list<std::pair<std::string, std::shared_ptr<RouterInfo::Buffer> > > saveToDisk;
 		std::list<std::string> removeFromDisk;	
@@ -672,7 +673,7 @@ namespace data
 			if (r->GetProfile ()->IsUnreachable ())
 				r->SetUnreachable (true);
 			// make router reachable back if too few routers or floodfills
-			if (r->IsUnreachable () && (total - deletedCount < NETDB_MIN_ROUTERS || isLowRate ||
+			if (r->IsUnreachable () && (total - deletedCount < NETDB_MIN_ROUTERS || isLowRate || isOffline ||
 				(r->IsFloodfill () && totalFloodfills - deletedFloodfillsCount < NETDB_MIN_FLOODFILLS)))
 				r->SetUnreachable (false);
 			if (!r->IsUnreachable ())

libi2pd/NetDb.hpp

@@ -39,6 +39,7 @@ namespace data
 {
 	const int NETDB_MIN_ROUTERS = 90;
 	const int NETDB_MIN_FLOODFILLS = 5;
+	const int NETDB_MIN_TRANSPORTS = 10 ; // otherwise assume offline
 	const int NETDB_NUM_FLOODFILLS_THRESHOLD = 1200;
 	const int NETDB_NUM_ROUTERS_THRESHOLD = 4*NETDB_NUM_FLOODFILLS_THRESHOLD;
 	const int NETDB_TUNNEL_CREATION_RATE_THRESHOLD = 10; // in %