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Move enough-headers check up, rejecting excess headers when received.

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This commit is contained in:
Glenn Willen 2022-12-06 17:17:32 -08:00
parent 394e59d38d
commit fba37b74b4
1 changed files with 25 additions and 21 deletions
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46
src/net_processing.cpp
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@ -2007,6 +2007,28 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
return;
}
// If we are already too far ahead of where we want to be on headers, discard
// the received headers. We can still get ahead by up to a single maximum-sized
// headers message here, but never further, so that's fine.
if (pindexBestHeader) {
uint64_t headers_ahead = pindexBestHeader->nHeight - m_chainman.ActiveHeight();
bool too_far_ahead = fTrimHeaders && (headers_ahead >= nHeaderDownloadBuffer);
if (too_far_ahead) {
LogPrint(BCLog::NET, "Discarding received headers and pausing header sync from peer=%d, because we are too far ahead of block sync (%d > %d, %d new headers received)\n", pfrom.GetId(), pindexBestHeader->nHeight, m_chainman.ActiveHeight(), nCount);
LOCK(cs_main);
CNodeState *nodestate = State(pfrom.GetId());
if (nodestate->fSyncStarted) {
// Cancel sync from this node, so we don't penalize it later.
// This will cause us to automatically start syncing from a different node (or restart syncing from the same node) later,
// if we still need to sync headers.
nSyncStarted--;
nodestate->fSyncStarted = false;
nodestate->m_headers_sync_timeout = 0us;
}
return;
}
}
bool received_new_header = false;
const CBlockIndex *pindexLast = nullptr;
{
@ -2084,17 +2106,11 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
nodestate->m_last_block_announcement = GetTime();
}
uint64_t headers_ahead = pindexLast->nHeight - m_chainman.ActiveHeight();
bool got_enough_headers = fTrimHeaders && (headers_ahead >= nHeaderDownloadBuffer);
// If a peer gives us as many headers as possible, this is implicitly a signal that the
// peer has more headers to send us. In Bitcoin Core, the node always asks for more
// headers at this point. Our logic is slightly more complex, because:
// (1) There is an apparent bug in the Bitcoin Core state machine here, where we can
// end up downloading headers from lots of peers at the same time by accident, which we
// work around rather than truly fix;
// (2) For various reasons we may want to avoid letting the header downloads get "too
// far ahead" of block downloads, so we may pause syncing for that reasons.
// headers at this point. Our logic is slightly more complex, to work around an apparent
// bug in the Bitcoin Core state machine, where we can end up downloading headers from
/// lots of peers at the same time by accident.
if (nCount == MAX_HEADERS_RESULTS) {
if (all_duplicate && !nodestate->fSyncStarted) {
// In this case two things are true:
@ -2106,18 +2122,6 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, const Peer& peer,
// In this case the right thing to do is simply stop syncing headers from this
// peer; it's redundant. Here we do nothing; since we don't ask the peer for
// more headers, it will stop sending them.
} else if (got_enough_headers) {
// If we're trying to save memory on headers, and we've already got plenty of headers,
// pause until we're ready for more.
LogPrint(BCLog::NET, "Pausing header sync from peer=%d, because the last one was too far ahead of block sync (%d >> %d)\n", pfrom.GetId(), pindexLast->nHeight, m_chainman.ActiveHeight());
if (nodestate->fSyncStarted) {
// Cancel sync from this node, so we don't penalize it later.
// This will cause us to automatically start syncing from a different node (or restart syncing from the same node) later,
// if we still need to sync headers.
nSyncStarted--;
nodestate->fSyncStarted = false;
nodestate->m_headers_sync_timeout = 0us;
}
} else {
// TODO: optimize: if pindexLast is an ancestor of m_chainman.ActiveChain().Tip or pindexBestHeader, continue
// from there instead.