From f9d67b28eca2c692601ee4940ce4bc7488da2dae Mon Sep 17 00:00:00 2001
From: orignal <i2porignal@yandex.ru>
Date: Sat, 9 Apr 2022 19:56:57 -0400
Subject: [PATCH] handle fragmented SessionConfirmed

---
 libi2pd/SSU2.cpp | 27 +++++++++++++++++++++++++++
 libi2pd/SSU2.h   |  1 +
 2 files changed, 28 insertions(+)

diff --git a/libi2pd/SSU2.cpp b/libi2pd/SSU2.cpp
index 0ebbe3a6..c62945da 100644
--- a/libi2pd/SSU2.cpp
+++ b/libi2pd/SSU2.cpp
@@ -85,6 +85,7 @@ namespace transport
 		m_State = eSSU2SessionStateEstablished;
 		m_EphemeralKeys = nullptr;
 		m_NoiseState.reset (nullptr);
+		m_SessionConfirmedFragment1.reset (nullptr);
 		SetTerminationTimeout (SSU2_TERMINATION_TIMEOUT);
 		transports.PeerConnected (shared_from_this ());
 	}	
@@ -395,6 +396,7 @@ namespace transport
 		header.h.packetNum = 0;
 		header.h.type = eSSU2SessionConfirmed;
 		memset (header.h.flags, 0, 3);
+		header.h.flags[0] = 1; // frag, total fragments always 1
 		// payload
 		uint8_t  payload[SSU2_MTU];
 		size_t payloadSize = i2p::context.GetRouterInfo ().GetBufferLen ();
@@ -454,6 +456,31 @@ namespace transport
 			LogPrint (eLogWarning, "SSU2: Unexpected message type  ", (int)header.h.type);
 			return false;
 		}	
+		// check if fragmented
+		if ((header.h.flags[0] & 0x0F) > 1)
+		{
+			// fragmented
+			if (!(header.h.flags[0] & 0xF0))
+			{
+				// first fragment
+				m_SessionConfirmedFragment1.reset (new SentPacket);
+				m_SessionConfirmedFragment1->header = header;
+				memcpy (m_SessionConfirmedFragment1->payload, buf + 16, len - 16);
+				m_SessionConfirmedFragment1->payloadLen = len - 16;
+				return true; // wait for second fragment
+			}	
+			else
+			{
+				// second fragment
+				if (!m_SessionConfirmedFragment1) return false; // out of sequence
+				uint8_t fullMsg[2*SSU2_MTU];
+				header = m_SessionConfirmedFragment1->header;
+				memcpy (fullMsg + 16, m_SessionConfirmedFragment1->payload, m_SessionConfirmedFragment1->payloadLen);
+				memcpy (fullMsg + 16 + m_SessionConfirmedFragment1->payloadLen, buf + 16, len - 16);
+				buf = fullMsg;
+				len += m_SessionConfirmedFragment1->payloadLen;
+			}	
+		}	
 		// KDF for Session Confirmed part 1
 		m_NoiseState->MixHash (header.buf, 16); // h = SHA256(h || header) 
 		// decrypt part1
diff --git a/libi2pd/SSU2.h b/libi2pd/SSU2.h
index f0fd50c6..bfc1eaa0 100644
--- a/libi2pd/SSU2.h
+++ b/libi2pd/SSU2.h
@@ -191,6 +191,7 @@ namespace transport
 			SSU2Server& m_Server;
 			std::shared_ptr<i2p::crypto::X25519Keys> m_EphemeralKeys;
 			std::unique_ptr<i2p::crypto::NoiseSymmetricState> m_NoiseState;
+			std::unique_ptr<SentPacket> m_SessionConfirmedFragment1; // for Bob if applicable
 			std::shared_ptr<const i2p::data::RouterInfo::Address> m_Address;
 			boost::asio::ip::udp::endpoint m_RemoteEndpoint;
 			uint64_t m_DestConnID, m_SourceConnID;