What peer messages mean

6501        }
6502
6503        // Check that outbound peers have reasonable chains
6504        // GetTime() is used by this anti-DoS logic so we can test this using mocktime
6505        ConsiderEviction(node, peer, GetTime<std::chrono::seconds>());
6506
6507        //
6508        // Message: getdata (blocks)
6509        //
6510        std::vector<CInv> vGetData;
6511        if (CanServeBlocks(peer) && ((sync_blocks_and_headers_from_peer && !IsLimitedPeer(peer)) || !m_chainman.IsInitialBlockDownload()) && state.vBlocksInFlight.size() < MAX_BLOCKS_IN_TRANSIT_PER_PEER) {
6512            std::vector<const CBlockIndex*> vToDownload;
6513            NodeId staller = -1;
6514            auto get_inflight_budget = [&state]() {
6515                return std::max(0, MAX_BLOCKS_IN_TRANSIT_PER_PEER - static_cast<int>(state.vBlocksInFlight.size()));
6516            };
6517
6518            // If there are multiple chainstates, download blocks for the
6519            // current chainstate first, to prioritize getting to network tip
6520            // before downloading historical blocks.
6521            FindNextBlocksToDownload(peer, get_inflight_budget(), vToDownload, staller);
6522            auto historical_blocks{m_chainman.GetHistoricalBlockRange()};
6523            if (historical_blocks && !IsLimitedPeer(peer)) {
6524                // If the first needed historical block is not an ancestor of the last,
6525                // we need to start requesting blocks from their last common ancestor.
6526                const CBlockIndex* from_tip = LastCommonAncestor(historical_blocks->first, historical_blocks->second);
6527                TryDownloadingHistoricalBlocks(
6528                    peer,
6529                    get_inflight_budget(),
6530                    vToDownload, from_tip, historical_blocks->second);
6531            }
6532            for (const CBlockIndex *pindex : vToDownload) {
6533                uint32_t nFetchFlags = GetFetchFlags(peer);
6534                vGetData.emplace_back(MSG_BLOCK | nFetchFlags, pindex->GetBlockHash());
6535                BlockRequested(node.GetId(), *pindex);
6536                LogDebug(BCLog::NET, "Requesting block %s (%d) peer=%d\n", pindex->GetBlockHash().ToString(),
6537                    pindex->nHeight, node.GetId());
6538            }
6539            if (state.vBlocksInFlight.empty() && staller != -1) {
6540                if (State(staller)->m_stalling_since == 0us) {
6541                    State(staller)->m_stalling_since = current_time;
6542                    LogDebug(BCLog::NET, "Stall started peer=%d\n", staller);
6543                }
6544            }
6545        }
6546
6547        //
6548        // Message: getdata (transactions)
6549        //
6550        {
6551            LOCK(m_tx_download_mutex);
6552            for (const GenTxid& gtxid : m_txdownloadman.GetRequestsToSend(node.GetId(), current_time)) {
6553                vGetData.emplace_back(gtxid.IsWtxid() ? MSG_WTX : (MSG_TX | GetFetchFlags(peer)), gtxid.ToUint256());
6554                if (vGetData.size() >= MAX_GETDATA_SZ) {
6555                    MakeAndPushMessage(node, NetMsgType::GETDATA, vGetData);
6556                    vGetData.clear();
6557                }
6558            }
6559        }
6560
6561        if (!vGetData.empty())
6562            MakeAndPushMessage(node, NetMsgType::GETDATA, vGetData);
6563    } // release cs_main
6564    MaybeSendFeefilter(node, peer, current_time);
6565    return true;
6566}
6567