[net processing] Move hashContinue to net processing

Also rename to m_continuation_block to better communicate meaning.

Author: jnewbery

src/net.cpp

@@ -2955,7 +2955,6 @@ CNode::CNode(NodeId idIn, ServiceFlags nLocalServicesIn, int nMyStartingHeightIn
 {
     hSocket = hSocketIn;
     addrName = addrNameIn == "" ? addr.ToStringIPPort() : addrNameIn;
-    hashContinue = uint256();
     if (conn_type_in != ConnectionType::BLOCK_RELAY) {
         m_tx_relay = MakeUnique<TxRelay>();
     }

src/net.h

@@ -993,7 +993,6 @@ class CNode
     mapMsgCmdSize mapRecvBytesPerMsgCmd GUARDED_BY(cs_vRecv);
 
 public:
-    uint256 hashContinue;
     // We selected peer as (compact blocks) high-bandwidth peer (BIP152)
     std::atomic<bool> m_bip152_highbandwidth_to{false};
     // Peer selected us as (compact blocks) high-bandwidth peer (BIP152)

src/net_processing.cpp

@@ -1475,7 +1475,7 @@ static void RelayAddress(const CNode& originator,
     connman.ForEachNodeThen(std::move(sortfunc), std::move(pushfunc));
 }
 
-void static ProcessGetBlockData(CNode& pfrom, const CChainParams& chainparams, const CInv& inv, CConnman& connman)
+void static ProcessGetBlockData(CNode& pfrom, Peer& peer, const CChainParams& chainparams, const CInv& inv, CConnman& connman)
 {
     bool send = false;
     std::shared_ptr<const CBlock> a_recent_block;
@@ -1616,15 +1616,14 @@ void static ProcessGetBlockData(CNode& pfrom, const CChainParams& chainparams, c
         }
 
         // Trigger the peer node to send a getblocks request for the next batch of inventory
-        if (inv.hash == pfrom.hashContinue)
-        {
+        if (inv.hash == peer.m_continuation_block) {
             // Send immediately. This must send even if redundant,
             // and we want it right after the last block so they don't
             // wait for other stuff first.
             std::vector<CInv> vInv;
             vInv.push_back(CInv(MSG_BLOCK, ::ChainActive().Tip()->GetBlockHash()));
             connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::INV, vInv));
-            pfrom.hashContinue.SetNull();
+            peer.m_continuation_block.SetNull();
         }
     }
 }
@@ -1724,7 +1723,7 @@ void static ProcessGetData(CNode& pfrom, Peer& peer, const CChainParams& chainpa
     if (it != peer.m_getdata_requests.end() && !pfrom.fPauseSend) {
         const CInv &inv = *it++;
         if (inv.IsGenBlkMsg()) {
-            ProcessGetBlockData(pfrom, chainparams, inv, connman);
+            ProcessGetBlockData(pfrom, peer, chainparams, inv, connman);
         }
         // else: If the first item on the queue is an unknown type, we erase it
         // and continue processing the queue on the next call.
@@ -2805,7 +2804,7 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
                 // When this block is requested, we'll send an inv that'll
                 // trigger the peer to getblocks the next batch of inventory.
                 LogPrint(BCLog::NET, "  getblocks stopping at limit %d %s\n", pindex->nHeight, pindex->GetBlockHash().ToString());
-                pfrom.hashContinue = pindex->GetBlockHash();
+                peer->m_continuation_block = pindex->GetBlockHash();
                 break;
             }
         }

src/net_processing.h

@@ -76,6 +76,11 @@ struct Peer {
 
     /** This peer's reported block height when we connected */
     std::atomic<int> m_starting_height{-1};
+    /** The final block hash that we sent in an `inv` message to this peer.
+     * When the peer requests this block, we send an `inv` message to trigger
+     * the peer to request the next sequence of block hashes.
+     * Most peers use headers-first syncing, which doesn't use this mechanism */
+    uint256 m_continuation_block{};
 
     /** Set of txids to reconsider once their parent transactions have been accepted **/
     std::set<uint256> m_orphan_work_set GUARDED_BY(g_cs_orphans);