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Claude finished @julienrbrt's task in 2m 21s —— View job Comprehensive Code ReviewI've completed a thorough review of this sequencer catch-up implementation. The PR introduces a critical mechanism for sequencer recovery after downtime, but I've identified several serious issues that need to be addressed before merging. 🔴 Critical Issues1. NON-MONOTONIC TIMESTAMPS (High Priority - Chain Halting Bug)Location: The current implementation produces non-monotonic block timestamps, which will cause most blockchain execution layers to reject blocks and halt the chain. Problem:
Example failure scenario: Current broken logic: if c.catchingUp.Load() {
daEndTime := c.currentDAEndTime
if !daEndTime.IsZero() {
var remainingForcedTxs uint64
if len(c.cachedForcedInclusionTxs) > 0 {
remainingForcedTxs = uint64(len(c.cachedForcedInclusionTxs)) - c.checkpoint.TxIndex
}
timestamp = daEndTime.Add(-time.Duration(remainingForcedTxs) * time.Millisecond)
}
}Issues with this logic:
Recommended fix: // Add to Sequencer struct:
lastBlockTimestamp atomic.Value // stores *time.Time
// In GetNextBatch:
timestamp := time.Now()
if c.catchingUp.Load() {
daEndTime := c.currentDAEndTime
if !daEndTime.IsZero() {
timestamp = daEndTime
}
// Ensure monotonicity
if lastTS := c.getLastBlockTimestamp(); !lastTS.IsZero() && !timestamp.After(lastTS) {
// Increment by 1ms to maintain monotonicity
timestamp = lastTS.Add(1 * time.Millisecond)
}
}
c.setLastBlockTimestamp(timestamp)2. DATA RACE on Catch-Up State (Medium-High Priority - Undefined Behavior)Location: Problem:
Impact:
Proof: // Line 67-70: No atomic protection
catchingUp atomic.Bool
currentDAEndTime time.Time // ❌ NOT THREAD-SAFERecommended fix: // In struct:
currentDAEndTime atomic.Pointer[time.Time]
// Writing (fetchNextDAEpoch):
ts := forcedTxsEvent.Timestamp.UTC()
c.currentDAEndTime.Store(&ts)
// Reading (GetNextBatch):
if tsPtr := c.currentDAEndTime.Load(); tsPtr != nil {
timestamp = *tsPtr
}3. SYNCER DA HEIGHT ADVANCEMENT LOGIC MAY BE INCORRECTLocation: Concern: if event.DaHeight > newState.DAHeight {
epochSize := s.genesis.DAEpochForcedInclusion
gap := event.DaHeight - newState.DAHeight
if epochSize > 0 && gap > epochSize {
// Advance by one epoch
_, epochEnd, _ := types.CalculateEpochBoundaries(...)
nextEpochStart := epochEnd + 1
if nextEpochStart > event.DaHeight {
nextEpochStart = event.DaHeight // Clamp
}
newState.DAHeight = nextEpochStart
} else {
newState.DAHeight = event.DaHeight
}
}Questions:
Recommendation: Add extensive integration tests covering:
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Summary of ChangesHello @julienrbrt, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request implements a critical "catch-up" feature for the sequencer, designed to enhance its resilience and consistency following periods of inactivity or downtime. By intelligently replaying missed Data Availability (DA) epochs, the sequencer can resynchronize its state, ensuring that all forced inclusion transactions are processed in the correct order and with accurate timestamps, thereby maintaining a consistent view of the blockchain's history, even when operating in a decentralized environment. This mechanism allows the sequencer to seamlessly transition back to normal operation without compromising data integrity. Highlights
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## main #3057 +/- ##
==========================================
+ Coverage 61.92% 61.97% +0.04%
==========================================
Files 111 111
Lines 11113 11218 +105
==========================================
+ Hits 6882 6952 +70
- Misses 3492 3527 +35
Partials 739 739
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Code Review
This pull request introduces a robust catch-up mechanism for the sequencer, designed to handle restarts after extended downtime. While the overall approach for consuming and verifying catch-up blocks in the syncer, including the incremental advancement of DAHeight, is well-implemented and tested, the implementation of catch-up mode in the single sequencer has significant flaws. Specifically, it produces non-monotonic block timestamps when multiple blocks are generated for a single DA epoch or when empty epochs are encountered, which will likely cause the execution layer to reject blocks and halt the chain. Additionally, there is a data race on the new catch-up state fields due to a lack of synchronization primitives. Minor suggestions for code clarity and testing experience were also noted.
| timestamp := time.Now() | ||
| if c.catchingUp && !c.currentDAEndTime.IsZero() { | ||
| timestamp = c.currentDAEndTime | ||
| } |
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During catch-up mode, the sequencer uses the timestamp from the last fetched DA epoch as the block timestamp. However, multiple blocks can be produced for a single DA epoch (e.g., if the epoch contains many transactions that don't fit in one block). In this case, all blocks produced for that epoch will have the exact same timestamp (c.currentDAEndTime). Furthermore, if an empty DA epoch is encountered, c.currentDAEndTime is not updated, causing the next block to reuse the timestamp from the previous non-empty epoch.
Most blockchain execution layers (like EVM) require that each new block has a timestamp strictly greater than its parent. If the sequencer produces multiple blocks with the same timestamp, the execution layer will reject them, halting the block production process and causing a Denial of Service.
pkg/sequencers/single/sequencer.go
Outdated
| catchingUp bool | ||
| // currentDAEndTime is the DA epoch end timestamp from the last fetched epoch. | ||
| // Used as the block timestamp during catch-up to match based sequencing behavior. | ||
| currentDAEndTime time.Time |
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The fields catchingUp and currentDAEndTime are accessed concurrently without proper synchronization. GetNextBatch and fetchNextDAEpoch (which update these fields) can be called by the block production loop, while IsCatchingUp() can be called concurrently by other components (e.g., RPC, monitoring, or metrics).
In Go, concurrent read/write access to non-atomic fields is a data race, which leads to undefined behavior. Specifically, a race on time.Time (which is a struct) can result in a corrupted timestamp being read, potentially leading to invalid blocks and a Denial of Service.
pkg/sequencers/single/sequencer.go
Outdated
| if catchUpThreshold < 30*time.Second { | ||
| catchUpThreshold = 30 * time.Second | ||
| } |
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The value 30*time.Second is used as a minimum threshold for the catch-up logic. To improve readability and maintainability, consider defining this as a named constant at the package level, for example: const minCatchUpThreshold = 30 * time.Second, and using that constant here. This makes the intent of the value clearer and centralizes its definition.
| // This test uses maxBytes to limit how many txs are fetched, triggering the unprocessed txs scenario. | ||
| func TestSequencer_CatchUp_DetectsOldEpoch(t *testing.T) { | ||
| ctx := context.Background() | ||
| logger := zerolog.New(zerolog.NewConsoleWriter()) |
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Using zerolog.New(zerolog.NewConsoleWriter()) in tests can lead to verbose output in the console during test runs. It's generally better to use a logger that integrates with the testing framework, such as zerolog.New(zerolog.NewTestWriter(t)), which only shows logs for failed tests, or zerolog.Nop() if logs are not needed. This practice is followed in other new tests in this file (e.g., TestSequencer_CatchUp_UsesDATimestamp). Applying this consistently would improve the developer experience. This comment also applies to lines 1309, 1457, and 1676.
| logger := zerolog.New(zerolog.NewConsoleWriter()) | |
| logger := zerolog.New(zerolog.NewTestWriter(t)) |
1 participant
Closes: #3016
Opus did a pretty good job. I'll be improving it.