Method UpdatePeerStateForReceivedHeaders

src/net_processing.cpp:2938–2987

* Given receipt of headers from a peer ending in last_header, along with * whether that header was new and whether the headers message was full, * update the state we keep for the peer. */

 * update the state we keep for the peer.
 */
void PeerManagerImpl::UpdatePeerStateForReceivedHeaders(CNode& pfrom, Peer& peer,
        const CBlockIndex& last_header, bool received_new_header, bool may_have_more_headers)
{
    LOCK(cs_main);
    CNodeState *nodestate = State(pfrom.GetId());

    UpdateBlockAvailability(pfrom.GetId(), last_header.GetBlockHash());

    // From here, pindexBestKnownBlock should be guaranteed to be non-null,
    // because it is set in UpdateBlockAvailability. Some nullptr checks
    // are still present, however, as belt-and-suspenders.

    if (received_new_header && last_header.nChainWork > m_chainman.ActiveChain().Tip()->nChainWork) {
        nodestate->m_last_block_announcement = GetTime();
    }

    // If we're in IBD, we want outbound peers that will serve us a useful
    // chain. Disconnect peers that are on chains with insufficient work.
    if (m_chainman.IsInitialBlockDownload() && !may_have_more_headers) {
        // If the peer has no more headers to give us, then we know we have
        // their tip.
        if (nodestate->pindexBestKnownBlock && nodestate->pindexBestKnownBlock->nChainWork < m_chainman.MinimumChainWork()) {
            // This peer has too little work on their headers chain to help
            // us sync -- disconnect if it is an outbound disconnection
            // candidate.
            // Note: We compare their tip to the minimum chain work (rather than
            // m_chainman.ActiveChain().Tip()) because we won't start block download
            // until we have a headers chain that has at least
            // the minimum chain work, even if a peer has a chain past our tip,
            // as an anti-DoS measure.
            if (pfrom.IsOutboundOrBlockRelayConn()) {
                LogInfo("outbound peer headers chain has insufficient work, %s", pfrom.DisconnectMsg());
                pfrom.fDisconnect = true;
            }
        }
    }

    // If this is an outbound full-relay peer, check to see if we should protect
    // it from the bad/lagging chain logic.
    // Note that outbound block-relay peers are excluded from this protection, and
    // thus always subject to eviction under the bad/lagging chain logic.
    // See ChainSyncTimeoutState.
    if (!pfrom.fDisconnect && pfrom.IsFullOutboundConn() && nodestate->pindexBestKnownBlock != nullptr) {
        if (m_outbound_peers_with_protect_from_disconnect < MAX_OUTBOUND_PEERS_TO_PROTECT_FROM_DISCONNECT && nodestate->pindexBestKnownBlock->nChainWork >= m_chainman.ActiveChain().Tip()->nChainWork && !nodestate->m_chain_sync.m_protect) {
            LogDebug(BCLog::NET, "Protecting outbound peer=%d from eviction\n", pfrom.GetId());
            nodestate->m_chain_sync.m_protect = true;
            ++m_outbound_peers_with_protect_from_disconnect;
        }
    }
}

void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
                                            std::vector<CBlockHeader>&& headers,