FA-26766 / HTTP ranges / Open access
Download checkpoints advance only after durable writes · case 01
Download checkpoints advance only after durable writes.
ROOT CAUSE
The resume-checkpoint-after-fsync decision uses return written.
VERIFIED REPAIR
Apply the bounded decision exactly: return written if synced else checkpoint
Unsuccessful approach: The partial repair uses return checkpoint, which still violates the stated contract.
Case contract
Return durable checkpoint: synced writes advance to written; unsynced writes retain prior checkpoint. written>=checkpoint.
Why this case matters
Range responses combine representation identity, conditional requests, framing, and partial-object state.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(checkpoint, written, synced):
return written
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('resume-checkpoint-after-fsync fixture 0', solve(N,2*N,False), N)
check('resume-checkpoint-after-fsync fixture 1', solve(N,2*N,True), 2*N)
check('resume-checkpoint-after-fsync fixture 2', solve(0,0,False), 0)
check('resume-checkpoint-after-fsync fixture 3', solve(0,N,True), N)
check('resume-checkpoint-after-fsync fixture 4', solve(N,N,False), N)
check('resume-checkpoint-after-fsync fixture 5', solve(0,N,False), 0)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| resume-checkpoint-after-fsync fixture 0 | 2 | 1 | Failed |
| resume-checkpoint-after-fsync fixture 1 | 2 | 2 | Passed |
| resume-checkpoint-after-fsync fixture 2 | 0 | 0 | Passed |
| resume-checkpoint-after-fsync fixture 3 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 4 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 5 | 1 | 0 | Failed |
SHA-256 / c2c9d5785e8dc5e6ee25267cc3b2c33d500b35407addd85106854387a30e7600
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(checkpoint, written, synced):
return checkpoint
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('resume-checkpoint-after-fsync fixture 0', solve(N,2*N,False), N)
check('resume-checkpoint-after-fsync fixture 1', solve(N,2*N,True), 2*N)
check('resume-checkpoint-after-fsync fixture 2', solve(0,0,False), 0)
check('resume-checkpoint-after-fsync fixture 3', solve(0,N,True), N)
check('resume-checkpoint-after-fsync fixture 4', solve(N,N,False), N)
check('resume-checkpoint-after-fsync fixture 5', solve(0,N,False), 0)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| resume-checkpoint-after-fsync fixture 0 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 1 | 1 | 2 | Failed |
| resume-checkpoint-after-fsync fixture 2 | 0 | 0 | Passed |
| resume-checkpoint-after-fsync fixture 3 | 0 | 1 | Failed |
| resume-checkpoint-after-fsync fixture 4 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 5 | 0 | 0 | Passed |
SHA-256 / bf8412c87a2fba291dae872cd546f45c432b9a4e4167c431b34cfb9c1c97cf0a
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(checkpoint, written, synced):
return written if synced else checkpoint
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('resume-checkpoint-after-fsync fixture 0', solve(N,2*N,False), N)
check('resume-checkpoint-after-fsync fixture 1', solve(N,2*N,True), 2*N)
check('resume-checkpoint-after-fsync fixture 2', solve(0,0,False), 0)
check('resume-checkpoint-after-fsync fixture 3', solve(0,N,True), N)
check('resume-checkpoint-after-fsync fixture 4', solve(N,N,False), N)
check('resume-checkpoint-after-fsync fixture 5', solve(0,N,False), 0)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| resume-checkpoint-after-fsync fixture 0 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 1 | 2 | 2 | Passed |
| resume-checkpoint-after-fsync fixture 2 | 0 | 0 | Passed |
| resume-checkpoint-after-fsync fixture 3 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 4 | 1 | 1 | Passed |
| resume-checkpoint-after-fsync fixture 5 | 0 | 0 | Passed |
SHA-256 / 75955d7f2881ed1b0d8d1b4311ae5831c9b00b4a9169a57da9b9c2f87f972cf7
Verification & scope
Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:41:18.874548+00:00.
Case digest / 44b2ec7b5150fadd274b950db0880c94ab6995b1c7e82e6c4ae370b589f50a3b