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eth/downloader: stop snap sync when the result queue closes empty - #2477
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Amirhosein wants to merge 1 commit into
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Amirhosein wants to merge 1 commit into
Amirhosein wants to merge 1 commit into
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When the result queue closes before a pivot block is committed or held (oldPivot == nil), Results(true) returns an empty slice. Previously, the loop proceeded to evaluate results[len(results)-1].Header, causing an index out of range [-1] panic. Cancel state sync and return early when results is empty and oldPivot is nil: if sync.Cancel() returns a non-cancellation error (e.g. from closeOnErr), surface that error; otherwise return errCanceled so callers can surface fetcher errors.
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Summary
Fixes an
index out of range [-1]panic inprocessSnapSyncContentwhen the result queue closes before a pivot block has been committed or held (oldPivot == nil).When
queue.Close()is called whilepivotHeaderis still uncommitted andcancelChis open:d.queue.Results(true)unblocks and returns an empty slice ([]*fetchResult{}).latest := results[len(results)-1].Header, indexing into-1and panicking.With this change, when
len(results) == 0andoldPivot == nil:sync.Cancel()is invoked. If state sync failed for a real reason (e.g. queue closed bycloseOnErr), that underlying non-cancellation error is returned.errCanceledis returned so that caller routines (such asspawnSync) can prioritize fetcher errors (such aserrNoPeers).Note: This PR addresses observation A reported in #2441 (the empty results queue panic during snap sync). Protocol receipt size limits (>10 MiB) are out of scope.
Executed tests
TestProcessSnapSyncContentEmptyQueuecovering:BareQueueShutdown: clean queue closure with healthy state sync returnserrCanceled.StateSyncFailure: queue closure triggered by a state sync failure returns the underlying error.CommittedWithEmptyQueue: empty queue when already committed preserves the normal exit path.go test -v -race ./eth/downloader -run TestProcessSnapSyncContentEmptyQueue(passed, 0 race warnings).go test -short ./eth/downloader(all passed).Rollout notes
Non-breaking bug fix, backwards-compatible, not consensus-affecting.