From 678a1ae0fb6d893709e413bda01476ab3c695d28 Mon Sep 17 00:00:00 2001
From: orignal <i2porignal@yandex.ru>
Date: Sat, 9 Apr 2022 11:42:34 -0400
Subject: [PATCH] send fragmented messages

---
 libi2pd/SSU2.cpp | 66 +++++++++++++++++++++++++++++++++++++++++++++++-
 libi2pd/SSU2.h   |  3 +++
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/libi2pd/SSU2.cpp b/libi2pd/SSU2.cpp
index 433a3afb..0ebbe3a6 100644
--- a/libi2pd/SSU2.cpp
+++ b/libi2pd/SSU2.cpp
@@ -123,7 +123,10 @@ namespace transport
 					payloadSize += CreateI2NPBlock (payload + payloadSize, SSU2_MAX_PAYLOAD_SIZE - payloadSize, std::move (msg));
 				}	
 				else if (len > SSU2_MAX_PAYLOAD_SIZE - 32) // message too long
-					m_SendQueue.pop_front ();  // drop it. TODO: fragmentation
+				{	
+					m_SendQueue.pop_front ();
+					SendFragmentedMessage (msg);
+				}	
 				else
 				{
 					// send right a way
@@ -147,6 +150,31 @@ namespace transport
 		}	
 	}	
 
+	void SSU2Session::SendFragmentedMessage (std::shared_ptr<I2NPMessage> msg)
+	{
+		uint32_t msgID;
+		memcpy (&msgID, msg->GetHeader () + I2NP_HEADER_MSGID_OFFSET, 4);
+		uint8_t payload[SSU2_MAX_PAYLOAD_SIZE];
+		size_t payloadSize = 0;
+		payloadSize += CreateAckBlock (payload + payloadSize, SSU2_MAX_PAYLOAD_SIZE - payloadSize);
+		auto size = CreateFirstFragmentBlock (payload + payloadSize, SSU2_MAX_PAYLOAD_SIZE - 32 - payloadSize, msg);
+		if (!size) return;
+		payloadSize += size;
+		payloadSize += CreatePaddingBlock (payload + payloadSize, SSU2_MAX_PAYLOAD_SIZE - payloadSize);	
+		auto firstPacket = SendData (payload, payloadSize);
+		if (firstPacket)
+			m_SentPackets.emplace (firstPacket->packetNum, firstPacket);
+		uint8_t fragmentNum = 0;
+		while (msg->offset < msg->len)
+		{
+			payloadSize += CreateFollowOnFragmentBlock (payload + payloadSize, SSU2_MAX_PAYLOAD_SIZE - payloadSize - 16, msg, fragmentNum, msgID);
+			payloadSize += CreatePaddingBlock (payload + payloadSize, SSU2_MAX_PAYLOAD_SIZE - payloadSize);	
+			auto followonPacket = SendData (payload, payloadSize);
+			if (followonPacket)
+				m_SentPackets.emplace (followonPacket->packetNum, followonPacket);
+		}	
+	}	
+		
 	void SSU2Session::Resend (uint64_t ts)
 	{
 		if (m_SendQueue.empty ()) return;
@@ -1038,6 +1066,42 @@ namespace transport
 		memcpy (buf + 3, msgBuf, msgLen);
 		return msgLen + 3;
 	}	
+
+	size_t SSU2Session::CreateFirstFragmentBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage> msg)
+	{
+		if (len < 12) return 0;
+		msg->ToNTCP2 ();
+		auto msgBuf = msg->GetNTCP2Header ();
+		auto msgLen = msg->GetNTCP2Length ();
+		if (msgLen + 3 <= len) return 0;
+		msgLen = len - 3;
+		buf[0] = eSSU2BlkFirstFragment;
+		htobe16buf (buf + 1, msgLen); // size
+		memcpy (buf + 3, msgBuf, msgLen);
+		msg->offset = (msgBuf - buf) + msgLen;
+		return msgLen + 3;
+	}	
+
+	size_t SSU2Session::CreateFollowOnFragmentBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage> msg, uint8_t& fragmentNum, uint32_t msgID)
+	{	
+		if (len < 8) return 0; 
+		bool isLast = true;
+		auto msgLen = msg->len - msg->offset;
+		if (msgLen + 8 > len) 
+		{
+			msgLen = len - 8;
+			isLast = false;
+		}	
+		buf[0] = eSSU2BlkFollowOnFragment;
+		htobe16buf (buf + 1, msgLen); // size
+		fragmentNum++;
+		buf[3] = fragmentNum << 1;
+		if (isLast) buf[3] |= 0x01;
+		memcpy (buf + 4, &msgID, 4);
+		memcpy (buf + 8, msg->buf + msg->offset, msgLen);
+		msg->offset += msgLen;
+		return msgLen + 8;
+	}
 		
 	std::shared_ptr<const i2p::data::RouterInfo> SSU2Session::ExtractRouterInfo (const uint8_t * buf, size_t size)
 	{
diff --git a/libi2pd/SSU2.h b/libi2pd/SSU2.h
index f9d0f848..f0fd50c6 100644
--- a/libi2pd/SSU2.h
+++ b/libi2pd/SSU2.h
@@ -153,6 +153,7 @@ namespace transport
 			void Established ();
 			void PostI2NPMessages (std::vector<std::shared_ptr<I2NPMessage> > msgs);
 			void SendQueue ();
+			void SendFragmentedMessage (std::shared_ptr<I2NPMessage> msg);
 			
 			void ProcessSessionRequest (Header& header, uint8_t * buf, size_t len);
 			void ProcessTokenRequest (Header& header, uint8_t * buf, size_t len);
@@ -182,6 +183,8 @@ namespace transport
 			size_t CreateAckBlock (uint8_t * buf, size_t len);
 			size_t CreatePaddingBlock (uint8_t * buf, size_t len, size_t minSize = 0);
 			size_t CreateI2NPBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage>&& msg);
+			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);
 			
 		private: