Respond to path challenge. Correct termination reason for duplicated session

libi2pd/SSU2.cpp

@@ -292,7 +292,7 @@ namespace transport
 					// session already exists
 					LogPrint (eLogWarning, "SSU2: Session to ", ident->GetIdentHash ().ToBase64 (), " already exists");
 					// terminate existing
-					GetService ().post (std::bind (&SSU2Session::RequestTermination, ret.first->second, eSSU2TerminationReasonTerminationReceived));
+					GetService ().post (std::bind (&SSU2Session::RequestTermination, ret.first->second, eSSU2TerminationReasonReplacedByNewSession));
 					// update session
 					ret.first->second = session;
 				}

libi2pd/SSU2Session.cpp

@@ -1403,8 +1403,11 @@ namespace transport
 					break;
 				}
 				case eSSU2BlkPathChallenge:
+					LogPrint (eLogDebug, "SSU2: Path challenge");
+					SendPathResponse (buf + offset, size);
 				break;
 				case eSSU2BlkPathResponse:
+					LogPrint (eLogDebug, "SSU2: Path response");
 				break;
 				case eSSU2BlkFirstPacketNumber:
 				break;
@@ -2440,6 +2443,19 @@ namespace transport
 		payloadSize += CreatePaddingBlock (payload + payloadSize, 32 - payloadSize);
 		SendData (payload, payloadSize);
 	}
+
+	void SSU2Session::SendPathResponse (const uint8_t * data, size_t len)
+	{
+		if (len < 8 || len > m_MaxPayloadSize - 3)
+		{
+			LogPrint (eLogWarning, "SSU2: Incorrect data size for path response ", len);
+			return;
+		}	
+		uint8_t payload[SSU2_MAX_PACKET_SIZE];
+		payload[0] = eSSU2BlkPathResponse;
+		htobe16buf (payload + 1, len);
+		SendData (payload, len + 3);
+	}	
 		
 	void SSU2Session::CleanUp (uint64_t ts)
 	{

libi2pd/SSU2Session.h

@@ -150,7 +150,8 @@ namespace transport
 		eSSU2TerminationReasonBadToken = 18,
 		eSSU2TerminationReasonConnectionLimits = 19,
 		eSSU2TerminationReasonIncompatibleVersion = 20,
-		eSSU2TerminationReasonWrongNetID = 21
+		eSSU2TerminationReasonWrongNetID = 21,
+		eSSU2TerminationReasonReplacedByNewSession = 22
 	};	
 	
 	struct SSU2IncompleteMessage
@@ -272,6 +273,7 @@ namespace transport
 			void SendTermination ();
 			void SendHolePunch (uint32_t nonce, const boost::asio::ip::udp::endpoint& ep, const uint8_t * introKey, uint64_t token);
 			void SendPeerTest (uint8_t msg, const uint8_t * signedData, size_t signedDataLen, const uint8_t * introKey); // PeerTest message 
+			void SendPathResponse (const uint8_t * data, size_t len);
 			
 			void HandlePayload (const uint8_t * buf, size_t len);
 			void HandleAck (const uint8_t * buf, size_t len);