send response to recived datagram from ECIESX25519AEADRatchet session

libi2pd/Datagram.cpp

@@ -247,6 +247,8 @@ namespace datagram
 		auto path = GetSharedRoutingPath();
 		if(path)
 			path->updateTime = i2p::util::GetSecondsSinceEpoch ();
+		if (m_RoutingSession && m_RoutingSession->IsRatchets ())
+			SendMsg (nullptr); // send empty message in case if we have some data to send
 	}
 
 	std::shared_ptr<i2p::garlic::GarlicRoutingPath> DatagramSession::GetSharedRoutingPath ()
@@ -352,14 +354,14 @@ namespace datagram
 
 	void DatagramSession::HandleSend(std::shared_ptr<I2NPMessage> msg)
 	{
-	  m_SendQueue.push_back(msg);
+		if (msg || m_SendQueue.empty ())
+			m_SendQueue.push_back(msg);
 		// flush queue right away if full
 		if(m_SendQueue.size() >= DATAGRAM_SEND_QUEUE_MAX_SIZE) FlushSendQueue();
 	}
 
 	void DatagramSession::FlushSendQueue ()
 	{
-
 		std::vector<i2p::tunnel::TunnelMessageBlock> send;
 		auto routingPath = GetSharedRoutingPath();
 		// if we don't have a routing path we will drop all queued messages
@@ -368,7 +370,8 @@ namespace datagram
 			for (const auto & msg : m_SendQueue)
 			{
 				auto m = m_RoutingSession->WrapSingleMessage(msg);
-				send.push_back(i2p::tunnel::TunnelMessageBlock{i2p::tunnel::eDeliveryTypeTunnel,routingPath->remoteLease->tunnelGateway, routingPath->remoteLease->tunnelID, m});
+				if (m)
+					send.push_back(i2p::tunnel::TunnelMessageBlock{i2p::tunnel::eDeliveryTypeTunnel,routingPath->remoteLease->tunnelGateway, routingPath->remoteLease->tunnelID, m});
 			}
 			routingPath->outboundTunnel->SendTunnelDataMsg(send);
 		}

libi2pd/ECIESX25519AEADRatchetSession.cpp

@@ -641,6 +641,7 @@ namespace garlic
     { 
         auto payload = CreatePayload (msg, m_State != eSessionStateEstablished);  
         size_t len = payload.size ();
+		if (!len) return nullptr;
 		auto m = NewI2NPMessage (len + 100); // 96 + 4
 		m->Align (12); // in order to get buf aligned to 16 (12 + 4)
 		uint8_t * buf = m->GetPayload () + 4; // 4 bytes for length
@@ -708,11 +709,14 @@ namespace garlic
 		{
 			payloadLen += 6;
 			if (m_NextSendRatchet->newKey) payloadLen += 32;
+		}
+		uint8_t paddingSize = 0;
+		if (payloadLen)
+		{	
+		    RAND_bytes (&paddingSize, 1);
+		    paddingSize &= 0x0F; paddingSize++; // 1 - 16
+		    payloadLen += paddingSize + 3;   
 		}	
-        uint8_t paddingSize;
-        RAND_bytes (&paddingSize, 1);
-        paddingSize &= 0x0F; paddingSize++; // 1 - 16
-        payloadLen += paddingSize + 3;                 
         std::vector<uint8_t> v(payloadLen);
         size_t offset = 0;
         // DateTime
@@ -785,9 +789,12 @@ namespace garlic
 			}	
 		}	
         // padding
-        v[offset] = eECIESx25519BlkPadding; offset++; 
-        htobe16buf (v.data () + offset, paddingSize); offset += 2;
-        memset (v.data () + offset, 0, paddingSize); offset += paddingSize; 
+		if (paddingSize)
+		{                
+		    v[offset] = eECIESx25519BlkPadding; offset++; 
+		    htobe16buf (v.data () + offset, paddingSize); offset += 2;
+		    memset (v.data () + offset, 0, paddingSize); offset += paddingSize;
+		}	
         return v;
     }