Avoid extra reconstruction request that returns 416#778
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assafvayner wants to merge 3 commits intomainfrom
Open
Avoid extra reconstruction request that returns 416#778assafvayner wants to merge 3 commits intomainfrom
assafvayner wants to merge 3 commits intomainfrom
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Prefetch tasks are spawned eagerly (at least two in new()), but later tasks don't check whether an earlier task has already discovered the true end of file. This causes the last prefetch to always send an HTTP request that gets a 416 Range Not Satisfiable response. Add a check at the start of each spawned prefetch task: before calling retrieve_file_term_block, read the known_final_byte_position atomic. If a previously completed task has updated it and this task's range starts at or past that position, short-circuit with Ok(None).
hoytak
reviewed
Apr 6, 2026
| // making this request unnecessary. This avoids sending a request that would | ||
| // return a 416 Range Not Satisfiable. | ||
| if prefetch_block_range.start >= known_final_byte_position.load(Ordering::Relaxed) { | ||
| known_final_byte_position.fetch_min(prefetch_block_range.start, Ordering::Relaxed); |
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I think this line is a no-op -- this only triggers if prefetch_block_range.start is already >= known_final_byte_position, which means known_final_byte_position is already at the min of the two.
hoytak
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Apr 6, 2026
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hoytak
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LGTM, with a minor correction.
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Summary
new()), but later tasks don't check whether an earlier task has already discovered the true end of fileknown_final_byte_positionatomic at the start of each spawned task, and short-circuit if a previous task has already found the file endTest plan
Note
Low Risk
Low risk: small change to prefetch task scheduling that only short-circuits requests once EOF is already known, plus lockfile version bumps.
Overview
Avoids sending redundant reconstruction range requests that would return
416 Range Not Satisfiableby having each spawned prefetch task checkknown_final_byte_positionand exit early when the requested start is already past the discovered EOF.Also bumps
xet-*crate versions from1.4.0to1.5.0in the WASMCargo.lock.Reviewed by Cursor Bugbot for commit 9ff4ed6. Bugbot is set up for automated code reviews on this repo. Configure here.