From e2a1b6d7e510657ace55fe8639fd28904afb9c3a Mon Sep 17 00:00:00 2001
From: orignal <i2porignal@yandex.ru>
Date: Thu, 13 Aug 2026 21:29:48 -0400
Subject: [PATCH] try to request block from piece requested by another
 connection if no other pieces available

---
 libi2pd_client/Torrents.cpp | 35 ++++++++++++++++++++++++-----------
 libi2pd_client/Torrents.h   |  3 ++-
 2 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/libi2pd_client/Torrents.cpp b/libi2pd_client/Torrents.cpp
index 27a0f77c..b1cb4e7a 100644
--- a/libi2pd_client/Torrents.cpp
+++ b/libi2pd_client/Torrents.cpp
@@ -507,7 +507,7 @@ namespace torrents
 		return complete;
 	}
 
-	std::tuple<uint32_t, uint32_t, uint32_t> Torrent::GetNextBlockToRequest (std::shared_ptr<PeerConnection> conn)
+	std::tuple<uint32_t, uint32_t, uint32_t> Torrent::GetNextBlockToRequest (std::shared_ptr<PeerConnection> conn, bool skipRequested)
 	{
 		if (conn)
 		{
@@ -530,7 +530,7 @@ namespace torrents
 			uint32_t ind = 0;
 			for (auto& it: m_Pieces)
 			{
-				if (!it.IsComplete () && conn->IsPieceAvailable (ind) && !it.IsRequested ())
+				if (!it.IsComplete () && conn->IsPieceAvailable (ind) && (!skipRequested || !it.IsRequested ()))
 					sortedByNumPeers.emplace (ind, it.GetNumPeers ());
 				ind++;
 			}
@@ -1279,21 +1279,34 @@ namespace torrents
 	bool PeerConnection::RequestNextBlock ()
 	{
 		if (!m_Torrent) return false;
-		auto [index, offset, len] = m_Torrent->GetNextBlockToRequest (shared_from_this ());
+		auto [index, offset, len] = m_Torrent->GetNextBlockToRequest (shared_from_this (), true); // skip already requested pieces
 		if (len > 0)
+			RequestNextBlock (index, offset, len);
+		else
 		{
-			m_LastRequestedPieceIndex = index;
-			SendRequestMsg (index, offset, len);
-			m_NumRequests++;
-		}
-		else if (m_LastRequestedPieceIndex >= 0)
-		{
-			m_LastRequestedPieceIndex = -1; // no request
-			SendNotinterestedMsg ();
+			// try to get block from requested by another connection piece
+			auto [index1, offset1, len1] = m_Torrent->GetNextBlockToRequest (shared_from_this (), false);
+			if (len1 > 0)
+			{
+				len = len1;
+				RequestNextBlock (index1, offset1, len1);
+			}
+			else if (m_LastRequestedPieceIndex >= 0)
+			{
+				m_LastRequestedPieceIndex = -1; // no request
+				SendNotinterestedMsg ();
+			}
 		}
 		return len > 0;
 	}
 
+	void PeerConnection::RequestNextBlock (uint32_t index, uint32_t offset, uint32_t len)
+	{
+		m_LastRequestedPieceIndex = index;
+		SendRequestMsg (index, offset, len);
+		m_NumRequests++;
+	}
+
 	void PeerConnection::RequestNextBlocks ()
 	{
 		if (m_IsChoked || !m_Torrent || m_Torrent->IsComplete ()) return;
diff --git a/libi2pd_client/Torrents.h b/libi2pd_client/Torrents.h
index 0be21183..c9bf1e90 100644
--- a/libi2pd_client/Torrents.h
+++ b/libi2pd_client/Torrents.h
@@ -168,7 +168,7 @@ namespace torrents
 			std::pair<std::vector<uint8_t>, bool> CreateBitfield () const; // (bitfield, empty)
 			bool ApplyBitfield (const std::vector<uint8_t>& bitfield); // return true if complete
 			const std::unordered_set<i2p::data::IdentHash>&  GetPeers () const { return m_Peers; }
-			std::tuple<uint32_t, uint32_t, uint32_t> GetNextBlockToRequest (std::shared_ptr<PeerConnection> conn); // return (index, offset, len)
+			std::tuple<uint32_t, uint32_t, uint32_t> GetNextBlockToRequest (std::shared_ptr<PeerConnection> conn, bool skipRequested = true); // return (index, offset, len)
 			std::vector<PieceFileFragment> GetPieceFileFragments (int index) const;
 			bool UpdateStatus (uint64_t ts); // return true if complete
 
@@ -265,6 +265,7 @@ namespace torrents
 			void HandleChokeMsg ();
 
 			bool RequestNextBlock ();
+			void RequestNextBlock (uint32_t index, uint32_t offset, uint32_t len);
 			void RequestNextBlocks ();
 
 			bool SendRequestedBlock (const RequestedBlock& requestedBlock);