send datetime block after approximately every 250 packets

libi2pd/SSU2Session.cpp

@@ -83,9 +83,9 @@ namespace transport
 		TransportSession (in_RemoteRouter, SSU2_CONNECT_TIMEOUT),
 		m_Server (server), m_Address (addr), m_RemoteTransports (0),
 		m_DestConnID (0), m_SourceConnID (0), m_State (eSSU2SessionStateUnknown),
-		m_SendPacketNum (0), m_ReceivePacketNum (0), m_IsDataReceived (false),
-		m_WindowSize (SSU2_MIN_WINDOW_SIZE), m_RTT (SSU2_RESEND_INTERVAL),
-		m_RTO (SSU2_RESEND_INTERVAL*SSU2_kAPPA), m_RelayTag (0),
+		m_SendPacketNum (0), m_ReceivePacketNum (0), m_LastDatetimeSentPacketNum (0),
+		m_IsDataReceived (false), m_WindowSize (SSU2_MIN_WINDOW_SIZE), 
+		m_RTT (SSU2_RESEND_INTERVAL), m_RTO (SSU2_RESEND_INTERVAL*SSU2_kAPPA), m_RelayTag (0),
 		m_ConnectTimer (server.GetService ()), m_TerminationReason (eSSU2TerminationReasonNormalClose),
 		m_MaxPayloadSize (SSU2_MIN_PACKET_SIZE - IPV6_HEADER_SIZE - UDP_HEADER_SIZE - 32) // min size
 	{
@@ -2806,7 +2806,16 @@ namespace transport
 	void SSU2Session::SendQuickAck ()
 	{
 		uint8_t payload[SSU2_MAX_PACKET_SIZE];
-		size_t payloadSize = CreateAckBlock (payload, m_MaxPayloadSize);
+		size_t payloadSize = 0;
+		if (m_SendPacketNum > m_LastDatetimeSentPacketNum + SSU2_SEND_DATETIME_NUM_PACKETS)
+		{	
+			payload[0] = eSSU2BlkDateTime;
+			htobe16buf (payload + 1, 4);
+			htobe32buf (payload + 3, (i2p::util::GetMillisecondsSinceEpoch () + 500)/1000);
+			payloadSize += 7;
+			m_LastDatetimeSentPacketNum = m_SendPacketNum;
+		}	
+		payloadSize += CreateAckBlock (payload + payloadSize, m_MaxPayloadSize - payloadSize);
 		payloadSize += CreatePaddingBlock (payload + payloadSize, m_MaxPayloadSize - payloadSize);
 		SendData (payload, payloadSize);
 	}

libi2pd/SSU2Session.h

@@ -52,6 +52,7 @@ namespace transport
 	const int SSU2_MAX_NUM_ACK_PACKETS = 510; // 2*255 ack + nack
 	const int SSU2_MAX_NUM_ACK_RANGES = 32; // to send
 	const uint8_t SSU2_MAX_NUM_FRAGMENTS = 64;
+	const int SSU2_SEND_DATETIME_NUM_PACKETS = 250;
 
 	// flags
 	const uint8_t SSU2_FLAG_IMMEDIATE_ACK_REQUESTED = 0x01;
@@ -344,7 +345,7 @@ namespace transport
 			uint64_t m_DestConnID, m_SourceConnID;
 			SSU2SessionState m_State;
 			uint8_t m_KeyDataSend[64], m_KeyDataReceive[64];
-			uint32_t m_SendPacketNum, m_ReceivePacketNum;
+			uint32_t m_SendPacketNum, m_ReceivePacketNum, m_LastDatetimeSentPacketNum;
 			std::set<uint32_t> m_OutOfSequencePackets; // packet nums > receive packet num
 			std::map<uint32_t, std::shared_ptr<SSU2SentPacket> > m_SentPackets; // packetNum -> packet
 			std::unordered_map<uint32_t, std::shared_ptr<SSU2IncompleteMessage> > m_IncompleteMessages; // msgID -> I2NP