From fc2dc9a0199bf1983673ead4adde19b6ec1c9dec Mon Sep 17 00:00:00 2001
From: orignal <i2porignal@yandex.ru>
Date: Sat, 12 Dec 2020 21:40:07 -0500
Subject: [PATCH] cumulative ACK bitfields

---
 libi2pd/SSUData.cpp | 35 +++++++++++++++++++----------------
 libi2pd/SSUData.h   |  6 ++++--
 2 files changed, 23 insertions(+), 18 deletions(-)

diff --git a/libi2pd/SSUData.cpp b/libi2pd/SSUData.cpp
index 4e0e712f..5458cc97 100644
--- a/libi2pd/SSUData.cpp
+++ b/libi2pd/SSUData.cpp
@@ -185,7 +185,12 @@ namespace transport
 					std::unique_ptr<IncompleteMessage>(new IncompleteMessage (msg)))).first;
 			}
 			std::unique_ptr<IncompleteMessage>& 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)
 			{
@@ -220,7 +225,7 @@ namespace transport
 					// missing fragment
 					LogPrint (eLogWarning, "SSU: Missing fragments from ", (int)incompleteMessage->nextFragmentNum, " to ", fragmentNum - 1, " of message ", msgID);
 					auto savedFragment = new Fragment (fragmentNum, buf, fragmentSize, isLast);
-					if (incompleteMessage->savedFragments.insert (std::unique_ptr<Fragment>(savedFragment)).second)
+					if (incompleteMessage->savedFragments.insert (std::unique_ptr<Fragment>(savedFragment)).second)	
 						incompleteMessage->lastFragmentInsertTime = i2p::util::GetSecondsSinceEpoch ();
 					else
 						LogPrint (eLogWarning, "SSU: Fragment ", (int)fragmentNum, " of message ", msgID, " already saved");
@@ -266,7 +271,7 @@ namespace transport
 				}
 			}
 			else
-				SendFragmentAck (msgID, fragmentNum);
+				SendFragmentAck (msgID, incompleteMessage->receivedFragmentsBits);
 			buf += fragmentSize;
 		}
 	}
@@ -394,13 +399,9 @@ namespace transport
 		m_Session.Send (buf, 48);
 	}
 
-	void SSUData::SendFragmentAck (uint32_t msgID, int fragmentNum)
+	void SSUData::SendFragmentAck (uint32_t msgID, uint64_t bits)
 	{
-		if (fragmentNum > 64)
-		{
-			LogPrint (eLogWarning, "SSU: Fragment number ", fragmentNum, " exceeds 64");
-			return;
-		}
+		if (!bits) return;
 		uint8_t buf[64 + 18] = {0};
 		uint8_t * payload = buf + sizeof (SSUHeader);
 		*payload = DATA_FLAG_ACK_BITFIELDS_INCLUDED; // flag
@@ -410,14 +411,16 @@ namespace transport
 		// one ack
 		*(uint32_t *)(payload) = htobe32 (msgID); // msgID
 		payload += 4;
-		div_t d = div (fragmentNum, 7);
-		memset (payload, 0x80, d.quot); // 0x80 means non-last
-		payload += d.quot;
-		*payload = 0x01 << d.rem; // set corresponding bit
-		payload++;
+		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
-
-		size_t len = d.quot < 4 ? 48 : 64; // 48 = 37 + 7 + 4 (3+1)
+		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);
diff --git a/libi2pd/SSUData.h b/libi2pd/SSUData.h
index 2e606053..902c009a 100644
--- a/libi2pd/SSUData.h
+++ b/libi2pd/SSUData.h
@@ -75,9 +75,11 @@ namespace transport
 		std::shared_ptr<I2NPMessage> msg;
 		int nextFragmentNum;
 		uint32_t lastFragmentInsertTime; // in seconds
+		uint64_t receivedFragmentsBits;
 		std::set<std::unique_ptr<Fragment>, FragmentCmp> savedFragments;
 
-		IncompleteMessage (std::shared_ptr<I2NPMessage> m): msg (m), nextFragmentNum (0), lastFragmentInsertTime (0) {};
+		IncompleteMessage (std::shared_ptr<I2NPMessage> m): msg (m), nextFragmentNum (0), 
+			lastFragmentInsertTime (0), receivedFragmentsBits (0) {};
 		void AttachNextFragment (const uint8_t * fragment, size_t fragmentSize);
 	};
 
@@ -109,7 +111,7 @@ namespace transport
 		private:
 
 			void SendMsgAck (uint32_t msgID);
-			void SendFragmentAck (uint32_t msgID, int fragmentNum);
+			void SendFragmentAck (uint32_t msgID, uint64_t bits);
 			void ProcessAcks (uint8_t *& buf, uint8_t flag);
 			void ProcessFragments (uint8_t * buf);
 			void ProcessSentMessageAck (uint32_t msgID);