i2pd/libi2pd/SSUData.cpp

/*
* Copyright (c) 2013-2021, The PurpleI2P Project
*
* This file is part of Purple i2pd project and licensed under BSD3
*
* See full license text in LICENSE file at top of project tree
*/

#include <stdlib.h>
#include "Log.h"
#include "Timestamp.h"
#include "NetDb.hpp"
#include "SSU.h"
#include "SSUData.h"

namespace i2p
{
namespace transport
{
	void IncompleteMessage::AttachNextFragment (const uint8_t * fragment, size_t fragmentSize)
	{
		if (msg->len + fragmentSize > msg->maxLen)
		{
			LogPrint (eLogWarning, "SSU: I2NP message size ", msg->maxLen, " is not enough");
			auto newMsg = NewI2NPMessage ();
			*newMsg = *msg;
			msg = newMsg;
		}
		if (msg->Concat (fragment, fragmentSize) < fragmentSize)
			LogPrint (eLogError, "SSU: I2NP buffer overflow ", msg->maxLen);
		nextFragmentNum++;
	}

	SSUData::SSUData (SSUSession& session):
		m_Session (session), m_ResendTimer (session.GetService ()),
		m_MaxPacketSize (session.IsV6 () ? SSU_V6_MAX_PACKET_SIZE : SSU_V4_MAX_PACKET_SIZE),
		m_PacketSize (m_MaxPacketSize), m_LastMessageReceivedTime (0)
	{
	}

	SSUData::~SSUData ()
	{
	}

	void SSUData::Start ()
	{
	}

	void SSUData::Stop ()
	{
		m_ResendTimer.cancel ();
		m_IncompleteMessages.clear ();
		m_SentMessages.clear ();
		m_ReceivedMessages.clear ();
	}

	void SSUData::AdjustPacketSize (std::shared_ptr<const i2p::data::RouterInfo> remoteRouter)
	{
		if (!remoteRouter) return;
		auto ssuAddress = remoteRouter->GetSSUAddress ();
		if (ssuAddress && ssuAddress->ssu->mtu)
		{
			if (m_Session.IsV6 ())
				m_PacketSize = ssuAddress->ssu->mtu - IPV6_HEADER_SIZE - UDP_HEADER_SIZE;
			else
				m_PacketSize = ssuAddress->ssu->mtu - IPV4_HEADER_SIZE - UDP_HEADER_SIZE;
			if (m_PacketSize > 0)
			{
				// make sure packet size multiple of 16
				m_PacketSize >>= 4;
				m_PacketSize <<= 4;
				if (m_PacketSize > m_MaxPacketSize) m_PacketSize = m_MaxPacketSize;
				LogPrint (eLogDebug, "SSU: MTU=", ssuAddress->ssu->mtu, " packet size=", m_PacketSize);
			}
			else
			{
				LogPrint (eLogWarning, "SSU: Unexpected MTU ", ssuAddress->ssu->mtu);
				m_PacketSize = m_MaxPacketSize;
			}
		}
	}

	void SSUData::UpdatePacketSize (const i2p::data::IdentHash& remoteIdent)
	{
		auto routerInfo = i2p::data::netdb.FindRouter (remoteIdent);
		if (routerInfo)
			AdjustPacketSize (routerInfo);
	}

	void SSUData::ProcessSentMessageAck (uint32_t msgID)
	{
		auto it = m_SentMessages.find (msgID);
		if (it != m_SentMessages.end ())
		{
			m_SentMessages.erase (it);
			if (m_SentMessages.empty ())
				m_ResendTimer.cancel ();
		}
	}

	void SSUData::ProcessAcks (uint8_t *& buf, uint8_t flag)
	{
		if (flag & DATA_FLAG_EXPLICIT_ACKS_INCLUDED)
		{
			// explicit ACKs
			uint8_t numAcks =*buf;
			buf++;
			for (int i = 0; i < numAcks; i++)
				ProcessSentMessageAck (bufbe32toh (buf+i*4));
			buf += numAcks*4;
		}
		if (flag & DATA_FLAG_ACK_BITFIELDS_INCLUDED)
		{
			// explicit ACK bitfields
			uint8_t numBitfields =*buf;
			buf++;
			for (int i = 0; i < numBitfields; i++)
			{
				uint32_t msgID = bufbe32toh (buf);
				buf += 4; // msgID
				auto it = m_SentMessages.find (msgID);
				// process individual Ack bitfields
				bool isNonLast = false;
				int fragment = 0;
				do
				{
					uint8_t bitfield = *buf;
					isNonLast = bitfield & 0x80;
					bitfield &= 0x7F; // clear MSB
					if (bitfield && it != m_SentMessages.end ())
					{
						int numSentFragments = it->second->fragments.size ();
						// process bits
						uint8_t mask = 0x01;
						for (int j = 0; j < 7; j++)
						{
							if (bitfield & mask)
							{
								if (fragment < numSentFragments)
									it->second->fragments[fragment] = nullptr;
							}
							fragment++;
							mask <<= 1;
						}
					}
					buf++;
				}
				while (isNonLast);
			}
		}
	}

	void SSUData::ProcessFragments (uint8_t * buf)
	{
		uint8_t numFragments = *buf; // number of fragments
		buf++;
		for (int i = 0; i < numFragments; i++)
		{
			uint32_t msgID = bufbe32toh (buf); // message ID
			buf += 4;
			uint8_t frag[4] = {0};
			memcpy (frag + 1, buf, 3);
			buf += 3;
			uint32_t fragmentInfo = bufbe32toh (frag); // fragment info
			uint16_t fragmentSize = fragmentInfo & 0x3FFF; // bits 0 - 13
			bool isLast = fragmentInfo & 0x010000; // bit 16
			uint8_t fragmentNum = fragmentInfo >> 17; // bits 23 - 17
			if (fragmentSize >= SSU_V4_MAX_PACKET_SIZE)
			{
				LogPrint (eLogError, "SSU: Fragment size ", fragmentSize, " exceeds max SSU packet size");
				return;
			}

			//  find message with msgID
			auto it = m_IncompleteMessages.find (msgID);
			if (it == m_IncompleteMessages.end ())
			{
				// create new message
				auto msg = (!fragmentNum && fragmentSize > 0 && buf[I2NP_SHORT_HEADER_TYPEID_OFFSET] == eI2NPTunnelData) ?
					NewI2NPTunnelMessage (true) : NewI2NPShortMessage ();
				msg->len -= I2NP_SHORT_HEADER_SIZE;
				it = m_IncompleteMessages.insert (std::make_pair (msgID,
					m_Session.GetServer ().GetIncompleteMessagesPool ().AcquireShared (msg))).first;
			}
			auto& incompleteMessage = it->second;
			// mark fragment as received
			if (fragmentNum < 64)
				incompleteMessage->receivedFragmentsBits |= (0x01 << fragmentNum);
			else
				LogPrint (eLogWarning, "SSU: Fragment number ", fragmentNum, " exceeds 64");
			
			// handle current fragment
			if (fragmentNum == incompleteMessage->nextFragmentNum)
			{
				// expected fragment
				incompleteMessage->AttachNextFragment (buf, fragmentSize);
				if (!isLast && !incompleteMessage->savedFragments.empty ())
				{
					// try saved fragments
					for (auto it1 = incompleteMessage->savedFragments.begin (); it1 != incompleteMessage->savedFragments.end ();)
					{
						auto& savedFragment = *it1;
						if (savedFragment->fragmentNum == incompleteMessage->nextFragmentNum)
						{
							incompleteMessage->AttachNextFragment (savedFragment->buf, savedFragment->len);
							isLast = savedFragment->isLast;
							incompleteMessage->savedFragments.erase (it1++);
						}
						else
							break;
					}
					if (isLast)
						LogPrint (eLogDebug, "SSU: Message ", msgID, " complete");
				}
			}
			else
			{
				if (fragmentNum < incompleteMessage->nextFragmentNum)
					// duplicate fragment
					LogPrint (eLogWarning, "SSU: Duplicate fragment ", (int)fragmentNum, " of message ", msgID, ", ignored");
				else
				{
					// missing fragment
					LogPrint (eLogWarning, "SSU: Missing fragments from ", (int)incompleteMessage->nextFragmentNum, " to ", fragmentNum - 1, " of message ", msgID);
					auto savedFragment = m_Session.GetServer ().GetFragmentsPool ().AcquireShared (fragmentNum, buf, fragmentSize, isLast);
					if (incompleteMessage->savedFragments.insert (savedFragment).second)	
						incompleteMessage->lastFragmentInsertTime = i2p::util::GetSecondsSinceEpoch ();
					else
						LogPrint (eLogWarning, "SSU: Fragment ", (int)fragmentNum, " of message ", msgID, " already saved");
				}
				isLast = false;
			}

			if (isLast)
			{
				// delete incomplete message
				auto msg = incompleteMessage->msg;
				incompleteMessage->msg = nullptr;
				m_IncompleteMessages.erase (msgID);
				// process message
				SendMsgAck (msgID);
				msg->FromSSU (msgID);
				if (m_Session.GetState () == eSessionStateEstablished)
				{
					if (!m_ReceivedMessages.count (msgID))
					{
						m_LastMessageReceivedTime = i2p::util::GetSecondsSinceEpoch ();
						m_ReceivedMessages.emplace (msgID, m_LastMessageReceivedTime);
						if (!msg->IsExpired ())
						{
							m_Handler.PutNextMessage (std::move (msg));
						}
						else
							LogPrint (eLogDebug, "SSU: message expired");
					}
					else
						LogPrint (eLogWarning, "SSU: Message ", msgID, " already received");
				}
				else
				{
					// we expect DeliveryStatus
					if (msg->GetTypeID () == eI2NPDeliveryStatus)
					{
						LogPrint (eLogDebug, "SSU: session established");
						m_Session.Established ();
					}
					else
						LogPrint (eLogError, "SSU: unexpected message ", (int)msg->GetTypeID ());
				}
			}
			else
				SendFragmentAck (msgID, incompleteMessage->receivedFragmentsBits);
			buf += fragmentSize;
		}
	}

	void SSUData::FlushReceivedMessage ()
	{
		m_Handler.Flush ();
	}

	void SSUData::ProcessMessage (uint8_t * buf, size_t len)
	{
		//uint8_t * start = buf;
		uint8_t flag = *buf;
		buf++;
		LogPrint (eLogDebug, "SSU: Process data, flags=", (int)flag, ", len=", len);
		// process acks if presented
		if (flag & (DATA_FLAG_ACK_BITFIELDS_INCLUDED | DATA_FLAG_EXPLICIT_ACKS_INCLUDED))
			ProcessAcks (buf, flag);
		// extended data if presented
		if (flag & DATA_FLAG_EXTENDED_DATA_INCLUDED)
		{
			uint8_t extendedDataSize = *buf;
			buf++; // size
			LogPrint (eLogDebug, "SSU: extended data of ", extendedDataSize, " bytes present");
			buf += extendedDataSize;
		}
		// process data
		ProcessFragments (buf);
	}

	void SSUData::Send (std::shared_ptr<i2p::I2NPMessage> msg)
	{
		uint32_t msgID = msg->ToSSU ();
		if (m_SentMessages.find (msgID) != m_SentMessages.end())
		{
			LogPrint (eLogWarning, "SSU: message ", msgID, " already sent");
			return;
		}
		if (m_SentMessages.empty ()) // schedule resend at first message only
			ScheduleResend ();

		auto ret = m_SentMessages.emplace (msgID, m_Session.GetServer ().GetSentMessagesPool ().AcquireShared ());
		auto& sentMessage = ret.first->second;
		if (ret.second)
		{
			sentMessage->nextResendTime = i2p::util::GetSecondsSinceEpoch () + RESEND_INTERVAL;
			sentMessage->numResends = 0;
		}
		auto& fragments = sentMessage->fragments;
		size_t payloadSize = m_PacketSize - sizeof (SSUHeader) - 9; // 9  =  flag + #frg(1) + messageID(4) + frag info (3)
		size_t len = msg->GetLength ();
		uint8_t * msgBuf = msg->GetSSUHeader ();

		uint32_t fragmentNum = 0;
		while (len > 0 && fragmentNum <= 127)
		{
			auto fragment = m_Session.GetServer ().GetFragmentsPool ().AcquireShared ();
			fragment->fragmentNum = fragmentNum;
			uint8_t	* payload = fragment->buf + sizeof (SSUHeader);
			*payload = DATA_FLAG_WANT_REPLY; // for compatibility
			payload++;
			*payload = 1; // always 1 message fragment per message
			payload++;
			htobe32buf (payload, msgID);
			payload += 4;
			bool isLast = (len <= payloadSize) || fragmentNum == 127; // 127 fragments max
			size_t size = isLast ? len : payloadSize;
			uint32_t fragmentInfo = (fragmentNum << 17);
			if (isLast)
				fragmentInfo |= 0x010000;

			fragmentInfo |= size;
			fragmentInfo = htobe32 (fragmentInfo);
			memcpy (payload, (uint8_t *)(&fragmentInfo) + 1, 3);
			payload += 3;
			memcpy (payload, msgBuf, size);

			size += payload - fragment->buf;
			uint8_t rem = size & 0x0F;
			if (rem) // make sure 16 bytes boundary
			{	
				auto padding = 16 - rem;
				memset (fragment->buf + size, 0, padding);
				size += padding;
			}	
			fragment->len = size;
			fragments.push_back (fragment);

			// encrypt message with session key
			uint8_t buf[SSU_V4_MAX_PACKET_SIZE + 18];
			m_Session.FillHeaderAndEncrypt (PAYLOAD_TYPE_DATA, fragment->buf, size, buf);
			try
			{
				m_Session.Send (buf, size);
			}
			catch (boost::system::system_error& ec)
			{
				LogPrint (eLogWarning, "SSU: Can't send data fragment ", ec.what ());
			}
			if (!isLast)
			{
				len -= payloadSize;
				msgBuf += payloadSize;
			}
			else
				len = 0;
			fragmentNum++;
		}
	}

	void SSUData::SendMsgAck (uint32_t msgID)
	{
		uint8_t buf[48 + 18] = {0}; // actual length is 44 = 37 + 7 but pad it to multiple of 16
		uint8_t * payload = buf + sizeof (SSUHeader);
		*payload = DATA_FLAG_EXPLICIT_ACKS_INCLUDED; // flag
		payload++;
		*payload = 1; // number of ACKs
		payload++;
		htobe32buf (payload, msgID); // msgID
		payload += 4;
		*payload = 0; // number of fragments

		// encrypt message with session key
		m_Session.FillHeaderAndEncrypt (PAYLOAD_TYPE_DATA, buf, 48);
		m_Session.Send (buf, 48);
	}

	void SSUData::SendFragmentAck (uint32_t msgID, uint64_t bits)
	{
		if (!bits) return;
		uint8_t buf[64 + 18] = {0};
		uint8_t * payload = buf + sizeof (SSUHeader);
		*payload = DATA_FLAG_ACK_BITFIELDS_INCLUDED; // flag
		payload++;
		*payload = 1; // number of ACK bitfields
		payload++;
		// one ack
		*(uint32_t *)(payload) = htobe32 (msgID); // msgID
		payload += 4;
		size_t len = 0; 
		while (bits)
		{
			*payload = (bits & 0x7F); // next 7 bits
			bits >>= 7;
			if (bits) *payload &= 0x80; // 0x80 means non-last
			payload++; len++;
		}	
		*payload = 0; // number of fragments
		len = (len <= 4) ? 48 : 64; // 48 = 37 + 7 + 4
		// encrypt message with session key
		m_Session.FillHeaderAndEncrypt (PAYLOAD_TYPE_DATA, buf, len);
		m_Session.Send (buf, len);
	}

	void SSUData::ScheduleResend()
	{
		m_ResendTimer.cancel ();
		m_ResendTimer.expires_from_now (boost::posix_time::seconds(RESEND_INTERVAL));
		auto s = m_Session.shared_from_this();
		m_ResendTimer.async_wait ([s](const boost::system::error_code& ecode)
			{ s->m_Data.HandleResendTimer (ecode); });
	}

	void SSUData::HandleResendTimer (const boost::system::error_code& ecode)
	{
		if (ecode != boost::asio::error::operation_aborted)
		{
			uint8_t buf[SSU_V4_MAX_PACKET_SIZE + 18];
			uint32_t ts = i2p::util::GetSecondsSinceEpoch ();
			int numResent = 0;
			for (auto it = m_SentMessages.begin (); it != m_SentMessages.end ();)
			{
				if (ts >= it->second->nextResendTime)
				{
					if (it->second->numResends < MAX_NUM_RESENDS)
					{
						for (auto& f: it->second->fragments)
							if (f)
							{
								try
								{					
									m_Session.FillHeaderAndEncrypt (PAYLOAD_TYPE_DATA, f->buf, f->len, buf);
									m_Session.Send (buf, f->len); // resend
									numResent++;
								}
								catch (boost::system::system_error& ec)
								{
									LogPrint (eLogWarning, "SSU: Can't resend message ", it->first, " data fragment: ", ec.what ());
								}
							}

						it->second->numResends++;
						it->second->nextResendTime += it->second->numResends*RESEND_INTERVAL;
						++it;
					}
					else
					{
						LogPrint (eLogInfo, "SSU: message ", it->first, " has not been ACKed after ", MAX_NUM_RESENDS, " attempts, deleted");
						it = m_SentMessages.erase (it);
					}
				}
				else
					++it;
			}
			if (m_SentMessages.empty ()) return; // nothing to resend
			if (numResent < MAX_OUTGOING_WINDOW_SIZE)
				ScheduleResend ();
			else
			{
				LogPrint (eLogError, "SSU: resend window exceeds max size. Session terminated");
				m_Session.Close ();
			}
		}
	}

	void SSUData::CleanUp (uint64_t ts)
	{
		for (auto it = m_IncompleteMessages.begin (); it != m_IncompleteMessages.end ();)
		{
			if (ts > it->second->lastFragmentInsertTime + INCOMPLETE_MESSAGES_CLEANUP_TIMEOUT)
			{
				LogPrint (eLogWarning, "SSU: message ", it->first, " was not completed in ", INCOMPLETE_MESSAGES_CLEANUP_TIMEOUT, " seconds, deleted");
				it = m_IncompleteMessages.erase (it);
			}
			else
				++it;
		}
	
		if (m_ReceivedMessages.size () > MAX_NUM_RECEIVED_MESSAGES || ts > m_LastMessageReceivedTime + DECAY_INTERVAL)
			// decay
			m_ReceivedMessages.clear ();
		else
		{
			// delete old received messages	
			for (auto it = m_ReceivedMessages.begin (); it != m_ReceivedMessages.end ();)
			{
				if (ts > it->second + RECEIVED_MESSAGES_CLEANUP_TIMEOUT)
					it = m_ReceivedMessages.erase (it);
				else
					++it;
			}		
		}		
	}	
}
}