random tunnel reject when medium congestion

libi2pd/I2NPProtocol.cpp

@@ -396,8 +396,26 @@ namespace i2p
 					return false;
 				}	
 				uint8_t retCode = 0;
+				// decide if we should accept tunnel
+				bool accept = i2p::context.AcceptsTunnels ();
+				if (accept)
+				{
+					auto congestionLevel = i2p::context.GetCongestionLevel (false);
+					if (congestionLevel >= CONGESTION_LEVEL_MEDIUM)
+					{	
+						if (congestionLevel < CONGESTION_LEVEL_FULL)
+						{
+							// random reject depending on congestion level
+							int level = i2p::tunnel::tunnels.GetRng ()() % (CONGESTION_LEVEL_FULL - CONGESTION_LEVEL_MEDIUM) + CONGESTION_LEVEL_MEDIUM;
+							if (congestionLevel > level)
+								accept = false;
+						}	
+						else	
+							accept = false;
+					}	
+				}	
 				// replace record to reply
-				if (i2p::context.AcceptsTunnels () && i2p::context.GetCongestionLevel (false) < CONGESTION_LEVEL_FULL)
+				if (accept)
 				{
 					auto transitTunnel = i2p::tunnel::CreateTransitTunnel (
 							bufbe32toh (clearText + ECIES_BUILD_REQUEST_RECORD_RECEIVE_TUNNEL_OFFSET),

libi2pd/RouterContext.cpp

@@ -1489,7 +1489,7 @@ namespace i2p
 	void RouterContext::UpdateCongestion ()
 	{
 		auto c = i2p::data::RouterInfo::eLowCongestion;
-		if (!AcceptsTunnels () || !m_ShareRatio)
+		if (!AcceptsTunnels () || !m_ShareRatio || (m_Error == eRouterErrorSymmetricNAT && !SupportsV6 () && !SupportsMesh ()))                                        	
 			c = i2p::data::RouterInfo::eRejectAll;
 		else
 		{

libi2pd/Tunnel.cpp

@@ -350,7 +350,8 @@ namespace tunnel
 
 	Tunnels::Tunnels (): m_IsRunning (false), m_Thread (nullptr), m_MaxNumTransitTunnels (DEFAULT_MAX_NUM_TRANSIT_TUNNELS),
 		m_TotalNumSuccesiveTunnelCreations (0), m_TotalNumFailedTunnelCreations (0), // for normal average
-		m_TunnelCreationSuccessRate (TCSR_START_VALUE), m_TunnelCreationAttemptsNum(0)
+		m_TunnelCreationSuccessRate (TCSR_START_VALUE), m_TunnelCreationAttemptsNum(0),
+		m_Rng(i2p::util::GetMonotonicMicroseconds ()%1000000LL)
 	{
 	}
 

libi2pd/Tunnel.h

@@ -18,6 +18,7 @@
 #include <thread>
 #include <mutex>
 #include <memory>
+#include <random>
 #include "util.h"
 #include "Queue.h"
 #include "Crypto.h"
@@ -244,6 +245,8 @@ namespace tunnel
 			uint32_t GetMaxNumTransitTunnels () const { return m_MaxNumTransitTunnels; };
 			int GetCongestionLevel() const { return m_MaxNumTransitTunnels ? CONGESTION_LEVEL_FULL * m_TransitTunnels.size() / m_MaxNumTransitTunnels : CONGESTION_LEVEL_FULL; }
 
+			std::mt19937& GetRng () { return m_Rng; };
+			
 		private:
 
 			template<class TTunnel>
@@ -307,6 +310,7 @@ namespace tunnel
 			int m_TotalNumSuccesiveTunnelCreations, m_TotalNumFailedTunnelCreations;
 			double m_TunnelCreationSuccessRate;
 			int m_TunnelCreationAttemptsNum;
+			std::mt19937 m_Rng;
 
 		public: