Function BlockRequestAllowed

src/net_processing.cpp:834–841

To prevent fingerprinting attacks, only send blocks/headers outside of the active chain if they are no more than a month older (both in time, and in best equivalent proof of work) than the best header chain we know about and we fully-validated them at some point.

// best equivalent proof of work) than the best header chain we know about and
// we fully-validated them at some point.
static bool BlockRequestAllowed(const CBlockIndex* pindex, const Consensus::Params& consensusParams)
{
    AssertLockHeld(cs_main);
    if (chainActive.Contains(pindex)) return true;
    return pindex->IsValid(BLOCK_VALID_SCRIPTS) && (pindexBestHeader != nullptr) &&
        (pindexBestHeader->GetBlockTime() - pindex->GetBlockTime() < STALE_RELAY_AGE_LIMIT) &&
        (GetBlockProofEquivalentTime(*pindexBestHeader, *pindex, *pindexBestHeader, consensusParams) < STALE_RELAY_AGE_LIMIT);
}

PeerLogicValidation::PeerLogicValidation(CConnman* connmanIn, CScheduler &scheduler, bool enable_bip61)
    : connman(connmanIn), m_stale_tip_check_time(0), m_enable_bip61(enable_bip61) {