send relay response

libi2pd/SSU2.cpp

@@ -1045,6 +1045,12 @@ namespace transport
 	void SSU2Session::HandleRelayIntro (const uint8_t * buf, size_t len)
 	{
 		// we are Charlie
+		auto r = i2p::data::netdb.FindRouter (buf + 1); // Alice
+		if (!r)
+		{
+			LogPrint (eLogError, "SSU2: RelayIntro unknown router to introduce"); 
+			return;
+		}	
 		SignedData s;
 		s.Insert ((const uint8_t *)"RelayRequestData", 16); // prologue
 		s.Insert (GetRemoteIdentity ()->GetIdentHash (), 32); // bhash
@@ -1052,14 +1058,19 @@ namespace transport
 		s.Insert (buf + 33, 14); // nonce, relay tag, timestamp, ver, asz
 		uint8_t asz = buf[46];
 		s.Insert (buf + 47, asz); // Alice Port, Alice IP 
-		if (!s.Verify (GetRemoteIdentity (), buf + 47 + asz))
+		if (!s.Verify (r->GetIdentity (), buf + 47 + asz))
 		{
 			LogPrint (eLogWarning, "SSU2: RelayIntro signature verification failed");
 			return; // TODO: send relay response
 		}	
 
-		// TODO: send RelayResponse to Bob
+		// send relay response to Bob
+		uint8_t payload[SSU2_MTU];
+		size_t payloadSize = CreateRelayResponseBlock (payload, SSU2_MTU, bufbe32toh (buf + 33), bufbe32toh (buf + 37));
+		payloadSize += CreatePaddingBlock (payload + payloadSize, SSU2_MTU - payloadSize);
+		SendData (payload, payloadSize);
 
+		// send HolePunch
 		boost::asio::ip::udp::endpoint ep;
 		if (ExtractEndpoint (buf + 47, asz, ep))
 			m_Server.SendHolePunch (ep);
@@ -1089,21 +1100,20 @@ namespace transport
 		return true;
 	}
 
-	size_t SSU2Session::CreateAddressBlock (const boost::asio::ip::udp::endpoint& ep, uint8_t * buf, size_t len)
+	size_t SSU2Session::CreateEndpoint (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& ep)
 	{
-		if (len < 9) return 0;
-		buf[0] = eSSU2BlkAddress;
-		htobe16buf (buf + 3, ep.port ());
+		if (len < 6) return 0;
+		htobe16buf (buf, ep.port ());
 		size_t size = 0;
 		if (ep.address ().is_v4 ())
 		{
-			memcpy (buf + 5, ep.address ().to_v4 ().to_bytes ().data (), 4);
+			memcpy (buf + 2, ep.address ().to_v4 ().to_bytes ().data (), 4);
 			size = 6;
 		}	
 		else if (ep.address ().is_v6 ())
 		{
-			if (len < 21) return 0;
-			memcpy (buf + 5, ep.address ().to_v6 ().to_bytes ().data (), 16);
+			if (len < 18) return 0;
+			memcpy (buf + 2, ep.address ().to_v6 ().to_bytes ().data (), 16);
 			size = 18;
 		}	
 		else
@@ -1111,6 +1121,15 @@ namespace transport
 			LogPrint (eLogWarning, "SSU2: Wrong address type ", ep.address ().to_string ());
 			return 0;
 		}
+		return size;
+	}	
+		
+	size_t SSU2Session::CreateAddressBlock (const boost::asio::ip::udp::endpoint& ep, uint8_t * buf, size_t len)
+	{
+		if (len < 9) return 0;
+		buf[0] = eSSU2BlkAddress;
+		size_t size = CreateEndpoint (buf + 3, len - 3, ep);
+		if (!size) return 0;
 		htobe16buf (buf + 1, size);
 		return size + 3;	
 	}	
@@ -1241,6 +1260,29 @@ namespace transport
 		return payloadSize + 3;
 	}	
 
+	size_t SSU2Session::CreateRelayResponseBlock (uint8_t * buf, size_t len, uint32_t nonce, uint32_t relayTag)
+	{
+		buf[0] = eSSU2BlkRelayResponse;
+		buf[3] = 0; // flag
+		buf[4] = 0;  // code, accept
+		htobe32buf (buf + 5, nonce); // nonce
+		htobe32buf (buf + 9, relayTag); // relayTag
+		htobe32buf (buf + 13, i2p::util::GetSecondsSinceEpoch ()); // timestamp
+		buf[17] = 2; // ver
+		size_t csz = CreateEndpoint (buf + 19, len - 19, boost::asio::ip::udp::endpoint (m_Address->host, m_Address->port));
+		if (!csz) return 0;
+		buf[18] = csz; // csz
+		// signature
+		SignedData s;
+		s.Insert ((const uint8_t *)"RelayAgreementOK", 16); // prologue
+		s.Insert (GetRemoteIdentity ()->GetIdentHash (), 32); // bhash
+		s.Insert (buf + 9, 10 + csz); // relay tag, timestamp, ver, csz and Charlie's endpoint
+		s.Sign (i2p::context.GetPrivateKeys (), buf + 19 + csz);
+		size_t payloadSize = 16 + csz + i2p::context.GetIdentity ()->GetSignatureLen ();
+		htobe16buf (buf + 1, payloadSize); // size
+		return payloadSize + 3;
+	}	
+		
 	std::shared_ptr<const i2p::data::RouterInfo> SSU2Session::ExtractRouterInfo (const uint8_t * buf, size_t size)
 	{
 		if (size < 2) return nullptr;

libi2pd/SSU2.h

@@ -179,6 +179,7 @@ namespace transport
 			void HandleAck (const uint8_t * buf, size_t len);
 			void HandleAckRange (uint32_t firstPacketNum, uint32_t lastPacketNum);
 			bool ExtractEndpoint (const uint8_t * buf, size_t size, boost::asio::ip::udp::endpoint& ep);
+			size_t CreateEndpoint (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& ep);
 			std::shared_ptr<const i2p::data::RouterInfo> ExtractRouterInfo (const uint8_t * buf, size_t size);
 			void CreateNonce (uint64_t seqn, uint8_t * nonce);
 			bool UpdateReceivePacketNum (uint32_t packetNum); // for Ack, returns false if duplicate
@@ -195,6 +196,7 @@ namespace transport
 			size_t CreateFirstFragmentBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage> msg);
 			size_t CreateFollowOnFragmentBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage> msg, uint8_t& fragmentNum, uint32_t msgID);
 			size_t CreateRelayIntroBlock (uint8_t * buf, size_t len, const uint8_t * introData, size_t introDataLen);
+			size_t CreateRelayResponseBlock (uint8_t * buf, size_t len, uint32_t nonce, uint32_t relayTag); // Charlie
 			
 		private: