add latency requirement option

Tunnel.h

@@ -79,6 +79,22 @@ namespace tunnel
 		eTunnelStateExpiring
 	};	
 
+	/** @brief for storing latency history */
+	struct TunnelLatency
+	{
+		typedef uint64_t Sample;
+		typedef uint64_t Latency;
+
+		
+		void AddSample(Sample s);
+		bool HasSamples() const;
+		Latency GetMeanLatency() const;
+
+		Latency m_latency = 0;
+		std::size_t m_samples = 0;
+		
+	};
+	
 	class OutboundTunnel;
 	class InboundTunnel;
 	class Tunnel: public TunnelBase
@@ -118,6 +134,14 @@ namespace tunnel
 			void SendTunnelDataMsg (std::shared_ptr<i2p::I2NPMessage> msg);
 			void EncryptTunnelMsg (std::shared_ptr<const I2NPMessage> in, std::shared_ptr<I2NPMessage> out); 
 
+		/** @brief add latency sample */
+		void AddLatencySample(const uint64_t ms) { m_Latency.AddSample(ms); }
+		/** @brief get this tunnel's estimated latency */
+		uint64_t GetMeanLatency() const { return m_Latency.GetMeanLatency(); }
+		/** @breif return true if this tunnel's latency fits in range [lowerbound, upperbound] */
+		bool LatencyFitsRange(uint64_t lowerbound, uint64_t upperbound) const;
+		
+		bool LatencyIsKnown() const { return m_Latency.HasSamples(); }
 		protected:
 
 			void PrintHops (std::stringstream& s) const;
@@ -129,6 +153,7 @@ namespace tunnel
 			std::shared_ptr<TunnelPool> m_Pool; // pool, tunnel belongs to, or null
 			TunnelState m_State;
 			bool m_IsRecreated;
+		TunnelLatency m_Latency;
 	};	
 
 	class OutboundTunnel: public Tunnel