don't request relay tag for every session if we have enough introducers

libi2pd/SSU2.h

@@ -72,6 +72,7 @@ namespace transport
 			bool IsSupported (const boost::asio::ip::address& addr) const;
 			uint16_t GetPort (bool v4) const;
 			std::mt19937& GetRng () { return m_Rng; }
+			bool IsMaxNumIntroducers (bool v4) const { return (v4 ? m_Introducers.size () : m_IntroducersV6.size ()) >= SSU2_MAX_NUM_INTRODUCERS; }
 			bool IsSyncClockFromPeers () const { return m_IsSyncClockFromPeers; };
 			void AdjustTimeOffset (int64_t offset, std::shared_ptr<const i2p::data::IdentityEx> from);
 

libi2pd/SSU2Session.cpp

@@ -679,12 +679,16 @@ namespace transport
 		htobe32buf (payload + 3, (ts + 500)/1000);
 		size_t payloadSize = 7;
 		if (GetRouterStatus () == eRouterStatusFirewalled && m_Address->IsIntroducer ())
+		{
+			if (!m_Server.IsMaxNumIntroducers (m_RemoteEndpoint.address ().is_v4 ()) ||
+			    m_Server.GetRng ()() & 0x01) // request tag with probability 1/2 if we have enough introducers
 			{	
 				// relay tag request
 				payload[payloadSize] = eSSU2BlkRelayTagRequest;
 				memset (payload + payloadSize + 1, 0, 2); // size = 0
 				payloadSize += 3;
 			}	
+		}
 		payloadSize += CreatePaddingBlock (payload + payloadSize, 40 - payloadSize, 1);
 		// KDF for session request
 		m_NoiseState->MixHash ({ {header.buf, 16}, {headerX, 16} }); // h = SHA256(h || header)