Merge bitcoin/bitcoin#22141: net processing: Remove hash and fValidatedHeaders from QueuedBlock

2f4ad6b7efa408b8a858e87499bf6cfcdf936d73 scripted-diff: rename MarkBlockAs functions (John Newbery)
2c45f832e87acd11fbd144cc0bb8e49816933c70 [net processing] Tidy up MarkBlockAsReceived() (John Newbery)
62993507336be06490b202b3955d4830a99e9e34 [net processing] Add IsBlockRequested() function (John Newbery)
4e90d2dd0e91e7eb560f2c1b430f13c7a047804f [net processing] Remove QueuedBlock.hash (John Newbery)
156a19ee6a22789adedcb6ab067c2eca2d3bfdfe scripted-diff: rename nPeersWithValidatedDownloads (John Newbery)
b03de9c7538d85b12929a62b9ec966fd3910e660 [net processing] Remove CNodeState.nBlocksInFlightValidHeaders (John Newbery)
b4e29f2436943c131dd25b123d13a25ce09bab58 [net processing] Remove QueuedBlock.fValidatedHeaders (John Newbery)
85e058b19145b5068f2f71a90c1182bf2a93c473 [net processing] Remove unnecessary hash arg from MarkBlockAsInFlight() (John Newbery)

Pull request description:

  The QueuedBlock struct contains a `fValidatedHeaders` field that indicates whether we have already validated a header for the requested block. Since headers-first syncing, we only request blocks where the header is already validated, so `fValidatedHeaders` is always true. Remove it and clean up the logic that uses that field.

  Likewise, QueuedBlock contains a `hash` field that is set to the block hash. Since headers-first syncing, we always have a CBlockIndex, which contains the block hash, so remove the redundant `hash` field.

  Tidy up the logic and rename functions to better indicate what they're doing.

ACKs for top commit:
  mjdietzx:
    crACK 2f4ad6b7efa408b8a858e87499bf6cfcdf936d73
  sipa:
    utACK 2f4ad6b7efa408b8a858e87499bf6cfcdf936d73
  MarcoFalke:
    review ACK 2f4ad6b7efa408b8a858e87499bf6cfcdf936d73 📊

Tree-SHA512: 3d31d2bcb4d35d0fdb7c1da624c2878203218026445e8f76c4a2df68cc7183ce0e7d0c47c7c0a3242e55efaca7c9f5532b683cf6ec7c03d23fa83764fdb82fd2

1 files changed, 68 insertions, 56 deletions

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 65224b4259..c5a389f228 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -159,10 +159,10 @@ static constexpr size_t MAX_ADDR_TO_SEND{1000};
 namespace {
 /** Blocks that are in flight, and that are in the queue to be downloaded. */
 struct QueuedBlock {
-    uint256 hash;
-    const CBlockIndex* pindex;                               //!< Optional.
-    bool fValidatedHeaders;                                  //!< Whether this block has validated headers at the time of request.
-    std::unique_ptr<PartiallyDownloadedBlock> partialBlock;  //!< Optional, used for CMPCTBLOCK downloads
+    /** BlockIndex. We must have this since we only request blocks when we've already validated the header. */
+    const CBlockIndex* pindex;
+    /** Optional, used for CMPCTBLOCK downloads */
+    std::unique_ptr<PartiallyDownloadedBlock> partialBlock;
 };
 
 /**
@@ -463,16 +463,20 @@ private:
     Mutex m_recent_confirmed_transactions_mutex;
     std::unique_ptr<CRollingBloomFilter> m_recent_confirmed_transactions GUARDED_BY(m_recent_confirmed_transactions_mutex);
 
-    /* Returns a bool indicating whether we requested this block.
-     * Also used if a block was /not/ received and timed out or started with another peer
+    /** Have we requested this block from a peer */
+    bool IsBlockRequested(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+
+    /** Remove this block from our tracked requested blocks. Called if:
+     *  - the block has been recieved from a peer
+     *  - the request for the block has timed out
      */
-    bool MarkBlockAsReceived(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    void RemoveBlockRequest(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     /* Mark a block as in flight
      * Returns false, still setting pit, if the block was already in flight from the same peer
      * pit will only be valid as long as the same cs_main lock is being held
      */
-    bool MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, const CBlockIndex* pindex = nullptr, std::list<QueuedBlock>::iterator** pit = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    bool BlockRequested(NodeId nodeid, const CBlockIndex* pindex, std::list<QueuedBlock>::iterator** pit = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     bool TipMayBeStale() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
@@ -512,7 +516,7 @@ private:
     std::list<NodeId> lNodesAnnouncingHeaderAndIDs GUARDED_BY(cs_main);
 
     /** Number of peers from which we're downloading blocks. */
-    int nPeersWithValidatedDownloads GUARDED_BY(cs_main) = 0;
+    int m_peers_downloading_from GUARDED_BY(cs_main) = 0;
 
     /** Storage for orphan information */
     TxOrphanage m_orphanage;
@@ -627,7 +631,6 @@ struct CNodeState {
     //! When the first entry in vBlocksInFlight started downloading. Don't care when vBlocksInFlight is empty.
     std::chrono::microseconds m_downloading_since{0us};
     int nBlocksInFlight{0};
-    int nBlocksInFlightValidHeaders{0};
     //! Whether we consider this a preferred download peer.
     bool fPreferredDownload{false};
     //! Whether this peer wants invs or headers (when possible) for block announcements.
@@ -758,32 +761,43 @@ static void UpdatePreferredDownload(const CNode& node, CNodeState* state) EXCLUS
     nPreferredDownload += state->fPreferredDownload;
 }
 
-bool PeerManagerImpl::MarkBlockAsReceived(const uint256& hash)
+bool PeerManagerImpl::IsBlockRequested(const uint256& hash)
 {
-    std::map<uint256, std::pair<NodeId, std::list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
-    if (itInFlight != mapBlocksInFlight.end()) {
-        CNodeState *state = State(itInFlight->second.first);
-        assert(state != nullptr);
-        state->nBlocksInFlightValidHeaders -= itInFlight->second.second->fValidatedHeaders;
-        if (state->nBlocksInFlightValidHeaders == 0 && itInFlight->second.second->fValidatedHeaders) {
-            // Last validated block on the queue was received.
-            nPeersWithValidatedDownloads--;
-        }
-        if (state->vBlocksInFlight.begin() == itInFlight->second.second) {
-            // First block on the queue was received, update the start download time for the next one
-            state->m_downloading_since = std::max(state->m_downloading_since, GetTime<std::chrono::microseconds>());
-        }
-        state->vBlocksInFlight.erase(itInFlight->second.second);
-        state->nBlocksInFlight--;
-        state->m_stalling_since = 0us;
-        mapBlocksInFlight.erase(itInFlight);
-        return true;
+    return mapBlocksInFlight.find(hash) != mapBlocksInFlight.end();
+}
+
+void PeerManagerImpl::RemoveBlockRequest(const uint256& hash)
+{
+    auto it = mapBlocksInFlight.find(hash);
+    if (it == mapBlocksInFlight.end()) {
+        // Block was not requested
+        return;
     }
-    return false;
+
+    auto [node_id, list_it] = it->second;
+    CNodeState *state = State(node_id);
+    assert(state != nullptr);
+
+    if (state->vBlocksInFlight.begin() == list_it) {
+        // First block on the queue was received, update the start download time for the next one
+        state->m_downloading_since = std::max(state->m_downloading_since, GetTime<std::chrono::microseconds>());
+    }
+    state->vBlocksInFlight.erase(list_it);
+
+    state->nBlocksInFlight--;
+    if (state->nBlocksInFlight == 0) {
+        // Last validated block on the queue was received.
+        m_peers_downloading_from--;
+    }
+    state->m_stalling_since = 0us;
+    mapBlocksInFlight.erase(it);
 }
 
-bool PeerManagerImpl::MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, const CBlockIndex* pindex, std::list<QueuedBlock>::iterator** pit)
+bool PeerManagerImpl::BlockRequested(NodeId nodeid, const CBlockIndex* pindex, std::list<QueuedBlock>::iterator** pit)
 {
+    assert(pindex);
+    const uint256& hash{pindex->GetBlockHash()};
+
     CNodeState *state = State(nodeid);
     assert(state != nullptr);
 
@@ -797,18 +811,15 @@ bool PeerManagerImpl::MarkBlockAsInFlight(NodeId nodeid, const uint256& hash, co
     }
 
     // Make sure it's not listed somewhere already.
-    MarkBlockAsReceived(hash);
+    RemoveBlockRequest(hash);
 
     std::list<QueuedBlock>::iterator it = state->vBlocksInFlight.insert(state->vBlocksInFlight.end(),
-            {hash, pindex, pindex != nullptr, std::unique_ptr<PartiallyDownloadedBlock>(pit ? new PartiallyDownloadedBlock(&m_mempool) : nullptr)});
+            {pindex, std::unique_ptr<PartiallyDownloadedBlock>(pit ? new PartiallyDownloadedBlock(&m_mempool) : nullptr)});
     state->nBlocksInFlight++;
-    state->nBlocksInFlightValidHeaders += it->fValidatedHeaders;
     if (state->nBlocksInFlight == 1) {
         // We're starting a block download (batch) from this peer.
         state->m_downloading_since = GetTime<std::chrono::microseconds>();
-    }
-    if (state->nBlocksInFlightValidHeaders == 1 && pindex != nullptr) {
-        nPeersWithValidatedDownloads++;
+        m_peers_downloading_from++;
     }
     itInFlight = mapBlocksInFlight.insert(std::make_pair(hash, std::make_pair(nodeid, it))).first;
     if (pit)
@@ -978,7 +989,7 @@ void PeerManagerImpl::FindNextBlocksToDownload(NodeId nodeid, unsigned int count
             if (pindex->nStatus & BLOCK_HAVE_DATA || m_chainman.ActiveChain().Contains(pindex)) {
                 if (pindex->HaveTxsDownloaded())
                     state->pindexLastCommonBlock = pindex;
-            } else if (mapBlocksInFlight.count(pindex->GetBlockHash()) == 0) {
+            } else if (!IsBlockRequested(pindex->GetBlockHash())) {
                 // The block is not already downloaded, and not yet in flight.
                 if (pindex->nHeight > nWindowEnd) {
                     // We reached the end of the window.
@@ -1129,13 +1140,13 @@ void PeerManagerImpl::FinalizeNode(const CNode& node)
         nSyncStarted--;
 
     for (const QueuedBlock& entry : state->vBlocksInFlight) {
-        mapBlocksInFlight.erase(entry.hash);
+        mapBlocksInFlight.erase(entry.pindex->GetBlockHash());
     }
     WITH_LOCK(g_cs_orphans, m_orphanage.EraseForPeer(nodeid));
     m_txrequest.DisconnectedPeer(nodeid);
     nPreferredDownload -= state->fPreferredDownload;
-    nPeersWithValidatedDownloads -= (state->nBlocksInFlightValidHeaders != 0);
-    assert(nPeersWithValidatedDownloads >= 0);
+    m_peers_downloading_from -= (state->nBlocksInFlight != 0);
+    assert(m_peers_downloading_from >= 0);
     m_outbound_peers_with_protect_from_disconnect -= state->m_chain_sync.m_protect;
     assert(m_outbound_peers_with_protect_from_disconnect >= 0);
     m_wtxid_relay_peers -= state->m_wtxid_relay;
@@ -1147,7 +1158,7 @@ void PeerManagerImpl::FinalizeNode(const CNode& node)
         // Do a consistency check after the last peer is removed.
         assert(mapBlocksInFlight.empty());
         assert(nPreferredDownload == 0);
-        assert(nPeersWithValidatedDownloads == 0);
+        assert(m_peers_downloading_from == 0);
         assert(m_outbound_peers_with_protect_from_disconnect == 0);
         assert(m_wtxid_relay_peers == 0);
         assert(m_txrequest.Size() == 0);
@@ -2056,7 +2067,7 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
             // Calculate all the blocks we'd need to switch to pindexLast, up to a limit.
             while (pindexWalk && !m_chainman.ActiveChain().Contains(pindexWalk) && vToFetch.size() <= MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
                 if (!(pindexWalk->nStatus & BLOCK_HAVE_DATA) &&
-                        !mapBlocksInFlight.count(pindexWalk->GetBlockHash()) &&
+                        !IsBlockRequested(pindexWalk->GetBlockHash()) &&
                         (!IsWitnessEnabled(pindexWalk->pprev, m_chainparams.GetConsensus()) || State(pfrom.GetId())->fHaveWitness)) {
                     // We don't have this block, and it's not yet in flight.
                     vToFetch.push_back(pindexWalk);
@@ -2081,7 +2092,7 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
                     }
                     uint32_t nFetchFlags = GetFetchFlags(pfrom);
                     vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
-                    MarkBlockAsInFlight(pfrom.GetId(), pindex->GetBlockHash(), pindex);
+                    BlockRequested(pfrom.GetId(), pindex);
                     LogPrint(BCLog::NET, "Requesting block %s from  peer=%d\n",
                             pindex->GetBlockHash().ToString(), pfrom.GetId());
                 }
@@ -2827,7 +2838,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 LogPrint(BCLog::NET, "got inv: %s  %s peer=%d\n", inv.ToString(), fAlreadyHave ? "have" : "new", pfrom.GetId());
 
                 UpdateBlockAvailability(pfrom.GetId(), inv.hash);
-                if (!fAlreadyHave && !fImporting && !fReindex && !mapBlocksInFlight.count(inv.hash)) {
+                if (!fAlreadyHave && !fImporting && !fReindex && !IsBlockRequested(inv.hash)) {
                     // Headers-first is the primary method of announcement on
                     // the network. If a node fell back to sending blocks by inv,
                     // it's probably for a re-org. The final block hash
@@ -3384,7 +3395,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             if ((!fAlreadyInFlight && nodestate->nBlocksInFlight < MAX_BLOCKS_IN_TRANSIT_PER_PEER) ||
                  (fAlreadyInFlight && blockInFlightIt->second.first == pfrom.GetId())) {
                 std::list<QueuedBlock>::iterator* queuedBlockIt = nullptr;
-                if (!MarkBlockAsInFlight(pfrom.GetId(), pindex->GetBlockHash(), pindex, &queuedBlockIt)) {
+                if (!BlockRequested(pfrom.GetId(), pindex, &queuedBlockIt)) {
                     if (!(*queuedBlockIt)->partialBlock)
                         (*queuedBlockIt)->partialBlock.reset(new PartiallyDownloadedBlock(&m_mempool));
                     else {
@@ -3397,7 +3408,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 PartiallyDownloadedBlock& partialBlock = *(*queuedBlockIt)->partialBlock;
                 ReadStatus status = partialBlock.InitData(cmpctblock, vExtraTxnForCompact);
                 if (status == READ_STATUS_INVALID) {
-                    MarkBlockAsReceived(pindex->GetBlockHash()); // Reset in-flight state in case Misbehaving does not result in a disconnect
+                    RemoveBlockRequest(pindex->GetBlockHash()); // Reset in-flight state in case Misbehaving does not result in a disconnect
                     Misbehaving(pfrom.GetId(), 100, "invalid compact block");
                     return;
                 } else if (status == READ_STATUS_FAILED) {
@@ -3492,7 +3503,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 // process from some other peer.  We do this after calling
                 // ProcessNewBlock so that a malleated cmpctblock announcement
                 // can't be used to interfere with block relay.
-                MarkBlockAsReceived(pblock->GetHash());
+                RemoveBlockRequest(pblock->GetHash());
             }
         }
         return;
@@ -3524,7 +3535,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             PartiallyDownloadedBlock& partialBlock = *it->second.second->partialBlock;
             ReadStatus status = partialBlock.FillBlock(*pblock, resp.txn);
             if (status == READ_STATUS_INVALID) {
-                MarkBlockAsReceived(resp.blockhash); // Reset in-flight state in case Misbehaving does not result in a disconnect
+                RemoveBlockRequest(resp.blockhash); // Reset in-flight state in case Misbehaving does not result in a disconnect
                 Misbehaving(pfrom.GetId(), 100, "invalid compact block/non-matching block transactions");
                 return;
             } else if (status == READ_STATUS_FAILED) {
@@ -3550,7 +3561,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 // though the block was successfully read, and rely on the
                 // handling in ProcessNewBlock to ensure the block index is
                 // updated, etc.
-                MarkBlockAsReceived(resp.blockhash); // it is now an empty pointer
+                RemoveBlockRequest(resp.blockhash); // it is now an empty pointer
                 fBlockRead = true;
                 // mapBlockSource is used for potentially punishing peers and
                 // updating which peers send us compact blocks, so the race
@@ -3615,9 +3626,10 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
         const uint256 hash(pblock->GetHash());
         {
             LOCK(cs_main);
-            // Also always process if we requested the block explicitly, as we may
-            // need it even though it is not a candidate for a new best tip.
-            forceProcessing |= MarkBlockAsReceived(hash);
+            // Always process the block if we requested it, since we may
+            // need it even when it's not a candidate for a new best tip.
+            forceProcessing = IsBlockRequested(hash);
+            RemoveBlockRequest(hash);
             // mapBlockSource is only used for punishing peers and setting
             // which peers send us compact blocks, so the race between here and
             // cs_main in ProcessNewBlock is fine.
@@ -4712,9 +4724,9 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
         // to unreasonably increase our timeout.
         if (state.vBlocksInFlight.size() > 0) {
             QueuedBlock &queuedBlock = state.vBlocksInFlight.front();
-            int nOtherPeersWithValidatedDownloads = nPeersWithValidatedDownloads - (state.nBlocksInFlightValidHeaders > 0);
+            int nOtherPeersWithValidatedDownloads = m_peers_downloading_from - 1;
             if (current_time > state.m_downloading_since + std::chrono::seconds{consensusParams.nPowTargetSpacing} * (BLOCK_DOWNLOAD_TIMEOUT_BASE + BLOCK_DOWNLOAD_TIMEOUT_PER_PEER * nOtherPeersWithValidatedDownloads)) {
-                LogPrintf("Timeout downloading block %s from peer=%d, disconnecting\n", queuedBlock.hash.ToString(), pto->GetId());
+                LogPrintf("Timeout downloading block %s from peer=%d, disconnecting\n", queuedBlock.pindex->GetBlockHash().ToString(), pto->GetId());
                 pto->fDisconnect = true;
                 return true;
             }
@@ -4767,7 +4779,7 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
             for (const CBlockIndex *pindex : vToDownload) {
                 uint32_t nFetchFlags = GetFetchFlags(*pto);
                 vGetData.push_back(CInv(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash()));
-                MarkBlockAsInFlight(pto->GetId(), pindex->GetBlockHash(), pindex);
+                BlockRequested(pto->GetId(), pindex);
                 LogPrint(BCLog::NET, "Requesting block %s (%d) peer=%d\n", pindex->GetBlockHash().ToString(),
                     pindex->nHeight, pto->GetId());
             }