From 4634bff9f0d4f49d46bd21cf71f8592c361f274a Mon Sep 17 00:00:00 2001
From: orignal <i2porignal@yandex.ru>
Date: Sat, 3 Sep 2022 15:38:52 -0400
Subject: [PATCH] limit number of resent packets. Resend interval variance

---
 libi2pd/SSU2.cpp        | 14 ++++++++++----
 libi2pd/SSU2.h          |  7 +++++--
 libi2pd/SSU2Session.cpp | 10 ++++++----
 libi2pd/SSU2Session.h   |  2 +-
 4 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/libi2pd/SSU2.cpp b/libi2pd/SSU2.cpp
index 019fffca..156bc2b0 100644
--- a/libi2pd/SSU2.cpp
+++ b/libi2pd/SSU2.cpp
@@ -86,6 +86,7 @@ namespace transport
 			if (found)
 				m_ReceiveService.Start ();
 			ScheduleTermination ();
+			ScheduleResend (false);
 		}
 	}
 
@@ -749,9 +750,10 @@ namespace transport
 		}
 	}
 
-	void SSU2Server::ScheduleResend ()
+	void SSU2Server::ScheduleResend (bool more)
 	{
-		m_ResendTimer.expires_from_now (boost::posix_time::milliseconds(SSU2_RESEND_CHECK_TIMEOUT));
+		m_ResendTimer.expires_from_now (boost::posix_time::milliseconds (more ? SSU2_RESEND_CHECK_MORE_TIMEOUT : 
+			(SSU2_RESEND_CHECK_TIMEOUT + rand () % SSU2_RESEND_CHECK_TIMEOUT_VARIANCE)));
 		m_ResendTimer.async_wait (std::bind (&SSU2Server::HandleResendTimer,
 			this, std::placeholders::_1));
 	}
@@ -760,12 +762,16 @@ namespace transport
 	{
 		if (ecode != boost::asio::error::operation_aborted)
 		{
+			size_t resentPacketsNum = 0;
 			auto ts = i2p::util::GetMillisecondsSinceEpoch ();
 			for (auto it: m_Sessions)
-				it.second->Resend (ts);
+			{	
+				resentPacketsNum += it.second->Resend (ts);
+				if (resentPacketsNum > SSU2_MAX_RESEND_PACKETS) break;
+			}	
 			for (auto it: m_PendingOutgoingSessions)
 				it.second->Resend (ts);
-			ScheduleResend ();
+			ScheduleResend (resentPacketsNum > SSU2_MAX_RESEND_PACKETS);
 		}
 	}
 
diff --git a/libi2pd/SSU2.h b/libi2pd/SSU2.h
index 8ad64692..27af6bf8 100644
--- a/libi2pd/SSU2.h
+++ b/libi2pd/SSU2.h
@@ -18,7 +18,10 @@ namespace i2p
 namespace transport
 {
 	const int SSU2_TERMINATION_CHECK_TIMEOUT = 30; // in seconds
-	const int SSU2_RESEND_CHECK_TIMEOUT = 500; // in milliseconds
+	const int SSU2_RESEND_CHECK_TIMEOUT = 400; // in milliseconds
+	const int SSU2_RESEND_CHECK_TIMEOUT_VARIANCE = 100; // in milliseconds
+	const int SSU2_RESEND_CHECK_MORE_TIMEOUT = 10; // in milliseconds
+	const size_t SSU2_MAX_RESEND_PACKETS = 128; // packets to resend at the time
 	const size_t SSU2_SOCKET_RECEIVE_BUFFER_SIZE = 0x1FFFF; // 128K
 	const size_t SSU2_SOCKET_SEND_BUFFER_SIZE = 0x1FFFF; // 128K
 	const size_t SSU2_MAX_NUM_INTRODUCERS = 3;
@@ -104,7 +107,7 @@ namespace transport
 			void ScheduleTermination ();
 			void HandleTerminationTimer (const boost::system::error_code& ecode);
 
-			void ScheduleResend ();
+			void ScheduleResend (bool more);
 			void HandleResendTimer (const boost::system::error_code& ecode);
 
 			void ConnectThroughIntroducer (std::shared_ptr<SSU2Session> session);
diff --git a/libi2pd/SSU2Session.cpp b/libi2pd/SSU2Session.cpp
index 2a6ef162..5053dc94 100644
--- a/libi2pd/SSU2Session.cpp
+++ b/libi2pd/SSU2Session.cpp
@@ -434,7 +434,7 @@ namespace transport
 		return ackBlockSent;
 	}
 
-	void SSU2Session::Resend (uint64_t ts)
+	size_t SSU2Session::Resend (uint64_t ts)
 	{
 		// resend handshake packet
 		if (m_SentHandshakePacket && ts >= m_SentHandshakePacket->sendTime + SSU2_HANDSHAKE_RESEND_INTERVAL)
@@ -442,10 +442,10 @@ namespace transport
 			LogPrint (eLogDebug, "SSU2: Resending ", (int)m_State);
 			ResendHandshakePacket ();
 			m_SentHandshakePacket->sendTime = ts;
-			return;
+			return 0;
 		}	
 		// resend data packets
-		if (m_SentPackets.empty ()) return;
+		if (m_SentPackets.empty ()) return 0;
 		std::map<uint32_t, std::shared_ptr<SSU2SentPacket> > resentPackets;
 		for (auto it = m_SentPackets.begin (); it != m_SentPackets.end (); )
 			if (ts >= it->second->sendTime + it->second->numResends*m_RTO)
@@ -456,7 +456,7 @@ namespace transport
 					m_SentPackets.clear ();
 					m_SendQueue.clear ();
 					RequestTermination (eSSU2TerminationReasonTimeout);
-					return;
+					return resentPackets.size ();
 				}	
 				else
 				{
@@ -478,7 +478,9 @@ namespace transport
 #endif
 			m_WindowSize >>= 1; // /2
 			if (m_WindowSize < SSU2_MIN_WINDOW_SIZE) m_WindowSize = SSU2_MIN_WINDOW_SIZE;
+			return resentPackets.size ();
 		}
+		return 0;
 	}
 
 	void SSU2Session::ResendHandshakePacket ()
diff --git a/libi2pd/SSU2Session.h b/libi2pd/SSU2Session.h
index 1e2644ab..72211bf6 100644
--- a/libi2pd/SSU2Session.h
+++ b/libi2pd/SSU2Session.h
@@ -243,7 +243,7 @@ namespace transport
 			void SendLocalRouterInfo (bool update) override;
 			void SendI2NPMessages (const std::vector<std::shared_ptr<I2NPMessage> >& msgs) override;
 			uint32_t GetRelayTag () const override { return m_RelayTag; };
-			void Resend (uint64_t ts);
+			size_t Resend (uint64_t ts); // return number or resent packets
 			bool IsEstablished () const { return m_State == eSSU2SessionStateEstablished; };
 			uint64_t GetConnID () const { return m_SourceConnID; };
 			SSU2SessionState GetState () const { return m_State; };