Method MaybeSetPeerAsAnnouncingHeaderAndIDs

src/net_processing.cpp:1284–1341

}

void PeerManagerImpl::MaybeSetPeerAsAnnouncingHeaderAndIDs(NodeId nodeid)
{
    AssertLockHeld(cs_main);

    // When in -blocksonly mode, never request high-bandwidth mode from peers. Our
    // mempool will not contain the transactions necessary to reconstruct the
    // compact block.
    if (m_opts.ignore_incoming_txs) return;

    CNodeState* nodestate = State(nodeid);
    PeerRef peer{GetPeerRef(nodeid)};
    if (!nodestate || !nodestate->m_provides_cmpctblocks) {
        // Don't request compact blocks if the peer has not signalled support
        return;
    }

    int num_outbound_hb_peers = 0;
    for (std::list<NodeId>::iterator it = lNodesAnnouncingHeaderAndIDs.begin(); it != lNodesAnnouncingHeaderAndIDs.end(); it++) {
        if (*it == nodeid) {
            lNodesAnnouncingHeaderAndIDs.erase(it);
            lNodesAnnouncingHeaderAndIDs.push_back(nodeid);
            return;
        }
        PeerRef peer_ref{GetPeerRef(*it)};
        if (peer_ref && !peer_ref->m_is_inbound) ++num_outbound_hb_peers;
    }
    if (peer && peer->m_is_inbound) {
        // If we're adding an inbound HB peer, make sure we're not removing
        // our last outbound HB peer in the process.
        if (lNodesAnnouncingHeaderAndIDs.size() >= 3 && num_outbound_hb_peers == 1) {
            PeerRef remove_peer{GetPeerRef(lNodesAnnouncingHeaderAndIDs.front())};
            if (remove_peer && !remove_peer->m_is_inbound) {
                // Put the HB outbound peer in the second slot, so that it
                // doesn't get removed.
                std::swap(lNodesAnnouncingHeaderAndIDs.front(), *std::next(lNodesAnnouncingHeaderAndIDs.begin()));
            }
        }
    }
    const bool nodeid_was_appended{m_connman.ForNode(nodeid, [this](CNode* pfrom) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
        AssertLockHeld(::cs_main);
        MakeAndPushMessage(*pfrom, NetMsgType::SENDCMPCT, /*high_bandwidth=*/true, /*version=*/CMPCTBLOCKS_VERSION);
        // save BIP152 bandwidth state: we select peer to be high-bandwidth
        pfrom->m_bip152_highbandwidth_to = true;
        lNodesAnnouncingHeaderAndIDs.push_back(pfrom->GetId());
        return true;
    })};
    if (nodeid_was_appended && lNodesAnnouncingHeaderAndIDs.size() > 3) {
        // As per BIP152, we only get 3 of our peers to announce
        // blocks using compact encodings.
        m_connman.ForNode(lNodesAnnouncingHeaderAndIDs.front(), [this](CNode* pnodeStop) {
            MakeAndPushMessage(*pnodeStop, NetMsgType::SENDCMPCT, /*high_bandwidth=*/false, /*version=*/CMPCTBLOCKS_VERSION);
            // save BIP152 bandwidth state: we select peer to be low-bandwidth
            pnodeStop->m_bip152_highbandwidth_to = false;
            return true;
        });
        lNodesAnnouncingHeaderAndIDs.pop_front();
    }
}