fix: request headers when a node falsely reports itself synchronized - #130
fix: request headers when a node falsely reports itself synchronized#130MathijsBok wants to merge 4 commits into
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A node whose header intake is blocked keeps a frozen fork detector, so computeNodeState derives hasLastBlock from probableHighestNonce and reports NsSynchronized while the chain moves on. syncBlock then returns early and the node stops asking for anything. shouldTryToRequestHeaders now derives the lag from the slot manager and the last committed block, which stays truthful in that state. This replaces a slot-index modulus trigger that could never fire there: isConsensusStuck uses the same lag threshold on SlotModulusTrigger (5), so every slot satisfying the old modulus of 20 also produced a forced-rollback ForkInfo that the isForcedRollBackOneBlock guard short-circuits on. Requesting on the slots in between is what keeps the fork detector out of that forced-rollback loop. isNodeSynchronized is deliberately untouched, since it gates consensus participation through initCurrentSlot. Also in this change: - Guard the same uint64 underflow in baseForkDetector.isConsensusStuck. There a wrapped lag clears the threshold and forces a rollback of a block that was just committed, which checkBlockBasicValidity makes reachable for a node whose clock trails its peers. - Warn once per slot when a node believes it is synchronized but has not committed a block for a while. It is the only signal this state emits, since MetricIsSyncing still reads 0 and GetNodeState still answers synchronized. Both operands are local, so a peer cannot drive it. - Log a dedicated debug line when a header is rejected specifically with ErrEpochNodesConfigDoesNotExist, naming the epoch actually looked up rather than the header's own epoch, which differ for an epoch-start header. - Use errors.Is for the ErrTimeIsOut comparison in doJobOnSyncBlockFail. Refs #90
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🔇 Additional comments (9)
WalkthroughThe PR replaces modulus-based sync detection with committed-block slot-lag detection, adds underflow guards and wrapped timeout handling, logs missing epoch configuration details during header verification, initializes warning sentinels, and adds regression coverage. It also removes the obsolete sync trigger constant. ChangesSynchronization and header verification
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🔵 Low · up to The change improves header re-request behavior and protects against lag-counter underflow, but the first checkpoint-ahead warning can still be suppressed when the local slot index is zero. This is a bounded diagnostic gap that is mergeable with explicit owner awareness or follow-up. Sequence Diagram(s)sequenceDiagram
participant NodeState as computeNodeState
participant BaseSync as baseSync
participant ForkDetector as baseForkDetector
participant HeaderSource as header recovery
NodeState->>BaseSync: pass synchronized-state result
BaseSync->>BaseSync: calculate committed-block slot lag
BaseSync->>ForkDetector: evaluate checkpoint-ahead state
ForkDetector-->>BaseSync: suppress false stall or report stall
BaseSync->>HeaderSource: request capped recovery headers
Possibly related issues
Suggested labels: 🚥 Pre-merge checks | ✅ 5 | ❌ 3❌ Failed checks (3 warnings)
✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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Review follow-up on the slot-lag gate. The "at most once per slot" bound the warning and the stuck-request goroutine rely on does not hold in import-db mode. GetNodeState answers NsNotSynchronized unconditionally while importing, so syncBlock never takes its early return, the defer clearing isNodeStateCalculated runs on every pass, and computeNodeState re-enters every sleepTime. Replaying historical blocks also produces an unbounded slot lag by construction, and there are no peers to request from, so the branch now returns early in that mode. Only the new branch is gated, leaving the pre-existing behaviour in import mode untouched. Also: - Note at syncBlock's early return that leaving isNodeStateCalculated set is what bounds the warning and the stuck-request path to once per slot, so a later cleanup that hoists the defer does not silently move both onto the 5 ms loop. - Make the emitted-fields subtest self-contained. It previously asserted on the buffer left behind by the two subtests above it, so it failed when run on its own and its field assertions could not distinguish which of the two lines carried which field. It now emits one rejection and asserts on that line. - Cover doJobOnSyncBlockFail, which held the only uncovered line of the previous commit. The table pins that a plain and a wrapped ErrTimeIsOut both decline to roll back while any other error does, which is exactly what the errors.Is change governs. Coverage of that function goes from 0 to 88.2 percent. - Cover the import-mode gate, including the counter-case that the same lag outside import mode still triggers a request. Refs #90
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Self-review notes
Recording what came out of my own review pass over this branch, so the reasoning behind a few non-obvious choices is on the record rather than only in my head. Everything actionable is already addressed in 8d4806c; the rest is rationale for reviewers.
8 notes: 1 that changed behaviour, 3 that changed tests or comments, 4 recording why something is the way it is.
Legend: 🟡 changed behaviour | 💡 rationale or test change | 🟢 deliberate choice worth not undoing
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The core mechanism checks out and I want this fix in — verified the once-per-slot bound, the errors.Is behavior under the coordinator's %w wrapping, lock ordering, -race, and a clean trial merge against develop. I also traced the isConsensusStuck guard through history: it restores the pre-31c39abf4 signed-arithmetic semantics that the 2024 G115 overflow sweep accidentally inverted (the original int64 difference went negative when the checkpoint was ahead, correctly returning false; the unsigned conversion made it underflow and force a rollback of a just-committed block). So the guard is a regression fix, not new behavior — good catch.
Requesting two small changes before merge, plus one suggestion:
Required
-
Log inside both underflow guards. In
isConsensusStuck(baseForkDetector.gocurrentSlot < lastCheckpointSlotbranch) andslotsSinceLastCommittedBlock(baseSync.gosame condition), the guard returns silently. In the clock-trails-tip case (NTP step-back, VM resume), header intake is simultaneously blocked (checkBlockBasicValidityrejects at Debug,processReceivedHeaderskipsAddHeaderat Trace), the lag reads 0 so the new Warn atbaseSync.go:402can never fire, and the node sits frozen reportingNsSynchronizedwith zero diagnostic output — potentially for hours. Pre-PR the wrap at least produced visible rollback churn. Alog.Warnin each branch restores observability for the exact state this PR makes quiet. -
Move the new
log.Warnout of themutNodeStatecritical section.shouldTryToRequestHeaders(and its Warn atbaseSync.go:402) runs insidecomputeNodeState'smutNodeState.Lock(), which consensus contends on viaGetNodeState(worker.go:338,subslotStartSlot.go:103) — once per stall slot, consensus callers block behind log formatting inside a write lock. Moving the Warn intorequestHeadersIfSyncIsStuck(already a goroutine outside the lock, already recomputes the lag) preserves semantics and the once-per-slot bound, keeps the predicate side-effect-free, and drops the test-only need to stub the fork detector for the log call.
Suggested (one field solves two issues)
A lastStuckRequestSlot field checked in requestHeadersIfSyncIsStuck would:
- make the once-per-slot throttle self-enforcing — today it holds only because
syncBlock's early return sits above the defer that clearsisNodeStateCalculated, an invariant defended by comments in three places and pinned by no test; a future refactor hoisting the defer silently turns this into a request burst every 5ms loop iteration with all tests green; - allow cheap backoff: re-firing only every N slots (e.g. the old 20) after the first burst caps request amplification during a network-wide halt — currently every synced node emits up to 20 header requests every slot for the whole outage, and the requested-items TimeCache spans exactly one slot interval so it never dedups across slots.
Noted, out of scope for this PR (tickets)
- The false
NsSynchronizedreport itself is unchanged (the PR states this) — that's the klc-1920/klc-2389 branch's territory; the two are complementary and should be reconciled after this lands. - Rare stall variant: a header cached in the pool during a slot-skew window is never registered with the fork detector, and
requestHeadersskips pooled nonces — the burst can't recover that case. - The whole recovery relies on epoch-start headers verifying against epoch-1 (
headerSignatureVerify.go:105,:290, both TODO-marked). If that TODO is ever executed, issue #90 regresses with sync tests still green — worth an integration test pinning "a requested epoch-start header is verifiable while the new epoch's config is missing".
Optional cleanup
The saturating slot subtraction is hand-rolled in both new sites while tools.SafeSubUint64 exists (tools/computers.go:160); slotsSinceLastCommittedBlock re-derives the last-committed-slot that computeNodeState already computes inline. Fine to fold in if you're touching the files anyway.
Also a reminder: the ruleset requires all review threads resolved — the 8 open self-annotation threads will block merge until closed.
… burst cap Implements the changes requested in the PR #130 review, plus the throttle half of its suggestion. Both underflow guards now surface the clock-trails-tip state instead of going quiet. The fork detector guard warns through warnOnceCheckpointAheadOfSlotIndex, throttled to once per slot via lastCheckpointAheadWarnSlot because CheckFork runs on every 5 ms sync-loop iteration while the node is not synchronized. The bootstrapper helper logs the same condition at debug: it can run under mutNodeState, and the fork detector warning already fires in the same slot, so a second warn would double-log one condition. Both sites now use tools.SafeSubUint64 instead of hand-rolled comparisons. The guard itself restores the pre-31c39abf4 signed-arithmetic semantics that the G115 sweep inverted, per the review's history trace. The stall warning moved out of shouldTryToRequestHeaders, which runs inside computeNodeState's mutNodeState critical section that consensus contends on through GetNodeState, into the requestHeadersIfSyncIsStuck goroutine. The spawn site captures isNodeSynchronized as stalledWhileSynced; warning unconditionally in the goroutine would spam during ordinary catch-up, where it is spawned on every 5 ms pass. The predicate is side-effect-free again. requestHeadersIfSyncIsStuck now caps itself to one burst and one warning per slot through lastStuckRequestSlot, making the once-per-slot bound self-enforcing instead of an invariant carried by the position of a defer in syncBlock. The multi-slot backoff from the same suggestion is deliberately not included: it would re-slow the recovery this fix exists for, and the field makes it a one-line addition if testnet data shows the request cadence needs it. New tests pin the burst cap, the warn placement (fires with the flag, silent without it while the burst still fires, shares the cap), the checkpoint-ahead warn throttle in both directions, and the spawn-site wiring end to end through computeNodeState, which fails if the flag is hard-wired. Refs #90, follow-ups in #135 and #136.
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Both required changes are in as of a081057, plus the throttle half of the suggestion. Point by point, including where I deviated and why. Also: thanks for the Required 1: log inside both underflow guardsDone, with one deviation on level, stated openly so it is a decision and not an omission.
Your scenario is pinned by Required 2: move the warn out of the mutNodeState critical sectionDone, via a One nuance on top of your suggestion: warning unconditionally inside The independent pass over this increment caught that the spawn-site wiring itself was the one unpinned link (hard-wiring the argument to false kept every test green). Suggested:
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Actionable comments posted: 1
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Inline comments:
In `@core/process/sync/baseForkDetector.go`:
- Around line 650-653: Initialize lastCheckpointAheadWarnSlot to math.MinInt64
during baseForkDetector construction so a SlotManager.Index() value of 0 does
not suppress the first checkpoint-ahead warning. Add a regression test covering
SlotIndex == 0 and verifying the warning is emitted once.
🪄 Autofix
Fix all unresolved CodeRabbit comments on this PR:
- Push a commit to this branch (recommended)
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🧠 Learnings (2)
📚 Learning: 2026-04-21T20:12:22.959Z
Learnt from: phcarneirobc
Repo: klever-io/klever-go PR: 38
File: indexer/eventsProcessor.go:188-211
Timestamp: 2026-04-21T20:12:22.959Z
Learning: In Go structs that are JSON-marshaled, if a field is a `bool` and has the `json:"...,omitempty"` tag, then leaving that field at its zero value (`false`) is functionally equivalent (in the resulting JSON) to explicitly setting `Foundation: false`. Reviewers should not flag struct literals that omit such `bool` fields as an inconsistency; they will serialize identically because `omitempty` suppresses `false` values.
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📚 Learning: 2026-05-23T22:52:58.065Z
Learnt from: fbsobreira
Repo: klever-io/klever-go PR: 65
File: data/blockchain/blockchain.go:170-172
Timestamp: 2026-05-23T22:52:58.065Z
Learning: In Go, the pattern `append([]byte(nil), src...)` should be treated as preserving nil identity when `src` is a nil `[]byte`: spreading a nil slice contributes zero variadic arguments, so `append` performs no allocation and returns the original nil destination slice unchanged (i.e., result is nil, not an empty non-nil slice). Do not flag this as an incorrect empty-slice conversion; it intentionally maintains `nil`.
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🔇 Additional comments (2)
core/process/sync/baseSync.go (1)
10-10: LGTM!Also applies to: 116-120, 348-348, 366-393, 406-420, 423-455, 615-615, 661-664
core/process/sync/baseSync_test.go (1)
64-85: LGTM!Also applies to: 218-272, 344-494
The zero value of lastCheckpointAheadWarnSlot equals slot index 0, so the first checkpoint-ahead warning there was swallowed (CodeRabbit). Writing the regression test surfaced that lastSlotWithForcedFork has the same collision one field over: its zero value makes isConsensusStuck treat the genesis slot as if a forced fork just happened and skip its entire body. Both now start at math.MinInt64, as does lastStuckRequestSlot in the bootstrapper for the same pattern. Pinned by TestMetaForkDetector_CheckpointAheadWarnsAtSlotIndexZero. Refs #90
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0 New Issues
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Live test results (KleverChain testnet, chain 109)Per the Slack thread and the review hold: this branch has now run on a live network. Setup: observer node on testnet (10-minute epochs, 150 slots x 4 s), image Six epoch boundaries, healthy operation900 API samples at 4 s intervals, 60 minutes, boundaries 79745 through 79751:
So on a healthy node: no regression, no request-cadence change, no log noise, and the issue #90 epoch-config window did not even open on any of the six boundaries. The epoch-start block commits and the new config is built before any new-epoch header reaches validation. Induced 16-slot stall (container pause)To exercise the recovery path live rather than only in unit tests:
Backoff decision, per the review threadData says no backoff, and the field stays as the hook: zero bursts across six healthy boundaries, and one single burst sufficing for a real 16-slot stall. There is no observed state in which re-firing every N slots would have reduced traffic, and the latency cost of backoff in the epoch-window case remains as described. If a future measurement shows sustained multi-slot bursting, it is a one-line addition on Honest limitationThe frozen-intake false-synchronized state itself (probable frozen while the chain moves, the exact #90 incident) is not reproducible on a healthy testnet node without an instrumented build, so that path is covered by the unit and wiring tests plus the mutation checks, not by this live run. The two adjacent gaps found during review are tracked in #135 and #136. The node has been reverted to the canonical run line (normal log view) after the measurement. |
2 participants
The problem
A node whose header intake is blocked keeps a frozen fork detector.
computeNodeStatederiveshasLastBlockfromprobableHighestNonce(core/process/sync/baseSync.go:304), and that counter only moves for headers that were accepted. So a node that is rejecting every incoming header sits at a stale nonce, computeshasLastBlock = true, reportsNsSynchronized, and writesMetricIsSyncing = 0.syncBlockthen returns early (:605-607) and the node stops asking for anything.Issue #90 reaches this through an epoch boundary:
nodesConfig[newEpoch]is only built when the epoch-start block commits, so until then every new-epoch header fails validation on all three intake paths (gossip, self-requested headers, and the consensus topic). But nothing about the mechanism is epoch-specific.What this changes
shouldTryToRequestHeadersnow derives the lag from the slot manager and the last committed block instead of from the fork detector, so it stays truthful in exactly that state.This replaces the previous
slotIndex % 20trigger rather than adding to it, and the reason matters. That trigger could never fire in this state:baseForkDetector.isConsensusStuck(:598-617) uses the same lag against the same threshold of 10 and fires onprocess.SlotModulusTrigger(5). Since 20 is a multiple of 5, every slot that satisfied the old modulus also produced a forced-rollbackForkInfo{IsDetected: true, Nonce: MaxUint64, Hash: nil}, which is exactly whatisForcedRollBackOneBlockmatches, andshouldTryToRequestHeadersshort-circuits on that guard before reaching the modulus.So the baseline behaviour was not a quiet idle. Every fifth slot the node ran
rollBackOneBlockForced, reverting state and dropping out of consensus for that slot. Requesting on the four slots in between is what keeps the fork detector out of that loop: once a requested header lands,isSyncing()turns true and the next stuck check stands down.SlotModulusTriggerWhenSyncIsStuckhad no other user and is removed, so nobody tunes a constant that does nothing.isNodeSynchronizedis deliberately untouched. It gates consensus participation throughinitCurrentSlot(core/consensus/slot/bls/subslotStartSlot.go:102-106), so making it slot-lag-aware would push every validator out of consensus during a genuine network-wide halt.Also in this change
A second, higher-impact underflow.
isConsensusStuckhad the identical unguardedSafeI64ToU64(Index()) - lastCheckpoint().slot. There a wrapped lag does not merely waste a header request: it clears the threshold and forces a rollback of a block that was just committed.checkBlockBasicValiditydeliberately accepts headers one slot ahead of the local index, so a node whose clock trails its peers reaches this without any peer misbehaving.A warning at default log level. Everything about this state was previously invisible:
MetricIsSyncingreads 0,GetNodeStateanswers synchronized, and both relevant log lines are debug while the node default is info. A node that stalls and simply receives nothing produced no signal at all. The new line fires at most once per slot and both its operands are local (own slot index, own last committed block), so a peer cannot drive it.A dedicated debug line for the epoch-config rejection, from both verification entry points in
core/process/headerCheck. It stays at debug on purpose: an unauthenticated peer can reach that path with a header carrying an arbitrary epoch, becauseisEpochCorrectadmits anyepoch >= trigger.Epoch(). It names the epoch actually looked up as well as the header's own epoch, which differ for an epoch-start header, so it cannot send an operator to the wrong configuration. The header hash is deliberately absent: it is not computed at that point, and computing one would put a marshal plus a hash on an attacker-drivable path.errors.Isfor theErrTimeIsOutcomparison indoJobOnSyncBlockFail, whicherrorlintflags and which fails on wrapped errors.What this does not do
It does not remove the false
NsSynchronizedreport. During the window the node still advertises synchronized andMetricIsSyncingstill reads 0; only the request path and the new warning react. Detection latency is unchanged at 11 slots (~44 s atslotInterval: 4000); what changes is that past that threshold the node reacts on the next slot rather than on the next multiple of 20, and that it no longer sits in the forced-rollback loop while waiting.It also does not change
isConsensusStuck's semantics beyond the underflow guard. During a genuine network-wide halt the forced-rollback loop still runs. Whether that is correct is an open question that needs the measurement the new diagnostics provide, not a guess.Tests
Every production change is pinned by a test that fails without it, verified by reverting each change in a scratch copy:
TestShouldTryToRequestHeaders_SyncedNodeReactsToSlotLagOnEverySlotsweeps slot indices 1 to 40. Without the change it fails on 28 of them (11-19 and 21-39), the ones the old modulus missed.TestShouldTryToRequestHeaders_GuardsShortCircuitBeforeSlotLagpins thatBeforeGenesisand both forced-rollback guards still run first, using a lag of 100 so a regression cannot hide.TestSlotsSinceLastCommittedBlockcovers the current-header path, the genesis fallback, and the underflow guard.TestRequestHeadersIfSyncIsStuckpins the burst formula operators see in the logs:min(MaxHeadersToRequestInAdvance, lag-1)starting at the nonce after the last committed block, the cap at 20, and that the underflow guard prevents a burst for nonces that cannot exist.TestMetaForkDetector_CheckForkNoForcedRollBackWhenCheckpointIsAheadOfSlotIndexand its counterpart...StillDetectsStuckConsensusWhenCheckpointIsBehindcover both directions of the fork-detector guard, so it cannot silently disable the mechanism.TestHeaderSigVerifier_EpochNodesConfigMissingIsSurfacedIntactasserts the sentinel survives both entry points (the consensus worker's blacklist suppression keys off it) and, through a log observer, that the line is actually emitted, carries the fields needed to measure the window, names the previous epoch for an epoch-start header, and stays silent for an unrelated error.Verification
gofmtclean,go build ./...clean,go vetclean,golangci-lintreports 0 issues on both touched packages,go test -racegreen on both, andgo test ./core/... ./sharding/...is 75 ok with no failures.Changed-line coverage:
shouldTryToRequestHeaders,slotsSinceLastCommittedBlockandlogIfEpochConfigMissingat 100%, and the new fork-detector guard covered in both directions. One new line is uncovered, theerrors.Isfix indoJobOnSyncBlockFail, a function at 0% coverage whose fixture is disproportionate to a one-line lint fix.Two pre-existing conditions worth knowing, neither caused here:
golangci-lintcannot run with the repo's own config because.golangci.ymlsetsmodules-download-mode: vendorand there is novendor/tree, so--modules-download-mode=modwas used; and CI runs the lint step asgolangci-lint run ... || true(#94), so it cannot fail the build.Refs #90
Summary
ErrTimeIsOuterrors witherrors.Is.SlotModulusTriggerWhenSyncIsStuckconstant.Impact