FA-26986 / HTTP ranges / Open access
Partial cache admission publishes complete requested fragments atomically: readers do not see an incomplete staged range generation · case 01
Partial cache admission publishes complete requested fragments atomically: readers do not see an incomplete staged range generation.
ROOT CAUSE
The partial-admission-transaction-read-isolation decision uses visible=dict(x[0]) pending=None reads=[] for event in x[1]: op=event[0] if op=='begin': if pending is not None: continue pending=[event[1],set(event[2]),{}] elif op=='put': if pending is None or event[1]!=pending[0]: continue at,char=event[2:] if at not in pending[1]: continue if at in pending[2] and pending[2][at]!=char: pending=None continue pending[2][at]=char elif op=='commit': if pending is None or event[1]!=pending[0]: continue if set(pending[2])!=pending[1]: continue visible=dict(pending[2]) pending=None elif op=='abort': if pending is not None and event[1]==pending[0]: pending=None elif op=='read': reads.append(sorted(pending[2].items()) if pending is not None else sorted(visible.items())) return [reads,sorted(visible.items()),pending[0] if pending is not None else None].
VERIFIED REPAIR
Apply the bounded decision exactly: visible=dict(x[0]) pending=None reads=[] for event in x[1]: op=event[0] if op=='begin': if pending is not None: continue pending=[event[1],set(event[2]),{}] elif op=='put': if pending is None or event[1]!=pending[0]: continue at,char=event[2:] if at not in pending[1]: continue if at in pending[2] and pending[2][at]!=char: pending=None continue pending[2][at]=char elif op=='commit': if pending is None or event[1]!=pending[0]: continue if set(pending[2])!=pending[1]: continue visible=dict(pending[2]) pending=None elif op=='abort': if pending is not None and event[1]==pending[0]: pending=None elif op=='read': reads.append(sorted(visible.items())) return [reads,sorted(visible.items()),pending[0] if pending is not None else None]
Unsuccessful approach: The partial repair uses visible=dict(x[0]) pending=None reads=[] for event in x[1]: op=event[0] if op=='begin': if pending is not None: continue pending=[event[1],set(event[2]),{}] elif op=='put': if pending is None or event[1]!=pending[0]: continue at,char=event[2:] if at not in pending[1]: continue if at in pending[2] and pending[2][at]!=char: pending=None continue pending[2][at]=char elif op=='commit': if pending is None or event[1]!=pending[0]: continue if set(pending[2])!=pending[1]: continue visible=dict(pending[2]) pending=None elif op=='abort': if pending is not None and event[1]==pending[0]: pending=None elif op=='read': reads.append(sorted((dict(visible,**{}) | pending[2]).items()) if pending is not None else sorted(visible.items())) return [reads,sorted(visible.items()),pending[0] if pending is not None else None], which still violates the stated contract.
Case contract
x is [old-visible-cells,events]. Events begin(id,expected-offsets), put(id,offset,char), commit(id), abort(id), read. One transaction at a time; unknown or mismatching ids ignored. A conflicting duplicate byte invalidates the active transaction. Commit succeeds only when every expected cell is present and replaces the old generation. Readers see committed cells sorted by offset. Return [read-snapshots,final-cells,pending-id].
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(x):
visible=dict(x[0])
pending=None
reads=[]
for event in x[1]:
op=event[0]
if op=='begin':
if pending is not None: continue
pending=[event[1],set(event[2]),{}]
elif op=='put':
if pending is None or event[1]!=pending[0]: continue
at,char=event[2:]
if at not in pending[1]: continue
if at in pending[2] and pending[2][at]!=char:
pending=None
continue
pending[2][at]=char
elif op=='commit':
if pending is None or event[1]!=pending[0]: continue
if set(pending[2])!=pending[1]: continue
visible=dict(pending[2])
pending=None
elif op=='abort':
if pending is not None and event[1]==pending[0]: pending=None
elif op=='read':
reads.append(sorted(pending[2].items()) if pending is not None else sorted(visible.items()))
return [reads,sorted(visible.items()),pending[0] if pending is not None else None]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('read-isolation fixture 0', json.loads(json.dumps(solve([[[0,'o'],[9,'z']],[['begin','a',[0,1]],['put','a',1,'b'],['read'],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[[0,'o'],[9,'z']],[[0,'a'],[1,'b']]],[[0,'a'],[1,'b']],None])))
check('read-isolation fixture 1', json.loads(json.dumps(solve([[],[['begin','a',[0,1]],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('read-isolation fixture 2', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','wrong',0,'x'],['put','a',1,'y'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('read-isolation fixture 3', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',1,'b'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('read-isolation fixture 4', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'b'],['commit','a']]]))), json.loads(json.dumps([[],[],None])))
check('read-isolation fixture 5', json.loads(json.dumps(solve([[],[['begin','a',[0]],['begin','b',[]],['abort','b'],['put','a',0,'a'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('read-isolation fixture 6', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'a'],['commit','wrong'],['read'],['commit','a']]]))), json.loads(json.dumps([[[]],[[0,'a']],None])))
check('read-isolation fixture 7', json.loads(json.dumps(solve([[],[['begin','a',[]],['commit','a'],['begin','b',[N]],['put','b',N,'p'],['commit','b']]]))), json.loads(json.dumps([[],[[N,'p']],None])))
check('read-isolation fixture 8', json.loads(json.dumps(solve([[[0,'o']],[['begin','a',[0]],['put','a',0,'a'],['abort','a'],['read']]]))), json.loads(json.dumps([[[[0,'o']]],[[0,'o']],None])))
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 |
|---|---|---|---|
| read-isolation fixture 0 | [[[[1, 'b']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None] | [[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None] | Failed |
| read-isolation fixture 1 | [[[[0, 'a']]], [], 'a'] | [[[]], [], 'a'] | Failed |
| read-isolation fixture 2 | [[[]], [], 'a'] | [[[]], [], 'a'] | Passed |
| read-isolation fixture 3 | [[], [[0, 'a']], None] | [[], [[0, 'a']], None] | Passed |
| read-isolation fixture 4 | [[], [], None] | [[], [], None] | Passed |
| read-isolation fixture 5 | [[], [[0, 'a']], None] | [[], [[0, 'a']], None] | Passed |
| read-isolation fixture 6 | [[[[0, 'a']]], [[0, 'a']], None] | [[[]], [[0, 'a']], None] | Failed |
| read-isolation fixture 7 | [[], [[1, 'p']], None] | [[], [[1, 'p']], None] | Passed |
| read-isolation fixture 8 | [[[[0, 'o']]], [[0, 'o']], None] | [[[[0, 'o']]], [[0, 'o']], None] | Passed |
SHA-256 / a9f9300e5a742c963207919722d7b88b9477778ea4087945bb2ea31fa4f2e92d
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
visible=dict(x[0])
pending=None
reads=[]
for event in x[1]:
op=event[0]
if op=='begin':
if pending is not None: continue
pending=[event[1],set(event[2]),{}]
elif op=='put':
if pending is None or event[1]!=pending[0]: continue
at,char=event[2:]
if at not in pending[1]: continue
if at in pending[2] and pending[2][at]!=char:
pending=None
continue
pending[2][at]=char
elif op=='commit':
if pending is None or event[1]!=pending[0]: continue
if set(pending[2])!=pending[1]: continue
visible=dict(pending[2])
pending=None
elif op=='abort':
if pending is not None and event[1]==pending[0]: pending=None
elif op=='read':
reads.append(sorted((dict(visible,**{}) | pending[2]).items()) if pending is not None else sorted(visible.items()))
return [reads,sorted(visible.items()),pending[0] if pending is not None else None]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('read-isolation fixture 0', json.loads(json.dumps(solve([[[0,'o'],[9,'z']],[['begin','a',[0,1]],['put','a',1,'b'],['read'],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[[0,'o'],[9,'z']],[[0,'a'],[1,'b']]],[[0,'a'],[1,'b']],None])))
check('read-isolation fixture 1', json.loads(json.dumps(solve([[],[['begin','a',[0,1]],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('read-isolation fixture 2', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','wrong',0,'x'],['put','a',1,'y'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('read-isolation fixture 3', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',1,'b'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('read-isolation fixture 4', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'b'],['commit','a']]]))), json.loads(json.dumps([[],[],None])))
check('read-isolation fixture 5', json.loads(json.dumps(solve([[],[['begin','a',[0]],['begin','b',[]],['abort','b'],['put','a',0,'a'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('read-isolation fixture 6', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'a'],['commit','wrong'],['read'],['commit','a']]]))), json.loads(json.dumps([[[]],[[0,'a']],None])))
check('read-isolation fixture 7', json.loads(json.dumps(solve([[],[['begin','a',[]],['commit','a'],['begin','b',[N]],['put','b',N,'p'],['commit','b']]]))), json.loads(json.dumps([[],[[N,'p']],None])))
check('read-isolation fixture 8', json.loads(json.dumps(solve([[[0,'o']],[['begin','a',[0]],['put','a',0,'a'],['abort','a'],['read']]]))), json.loads(json.dumps([[[[0,'o']]],[[0,'o']],None])))
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 |
|---|---|---|---|
| read-isolation fixture 0 | [[[[0, 'o'], [1, 'b'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None] | [[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None] | Failed |
| read-isolation fixture 1 | [[[[0, 'a']]], [], 'a'] | [[[]], [], 'a'] | Failed |
| read-isolation fixture 2 | [[[]], [], 'a'] | [[[]], [], 'a'] | Passed |
| read-isolation fixture 3 | [[], [[0, 'a']], None] | [[], [[0, 'a']], None] | Passed |
| read-isolation fixture 4 | [[], [], None] | [[], [], None] | Passed |
| read-isolation fixture 5 | [[], [[0, 'a']], None] | [[], [[0, 'a']], None] | Passed |
| read-isolation fixture 6 | [[[[0, 'a']]], [[0, 'a']], None] | [[[]], [[0, 'a']], None] | Failed |
| read-isolation fixture 7 | [[], [[1, 'p']], None] | [[], [[1, 'p']], None] | Passed |
| read-isolation fixture 8 | [[[[0, 'o']]], [[0, 'o']], None] | [[[[0, 'o']]], [[0, 'o']], None] | Passed |
SHA-256 / 1c8663786afd3215b9ba5a4d0a0da2412a8b43a095772b6e764782a30824c706
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
visible=dict(x[0])
pending=None
reads=[]
for event in x[1]:
op=event[0]
if op=='begin':
if pending is not None: continue
pending=[event[1],set(event[2]),{}]
elif op=='put':
if pending is None or event[1]!=pending[0]: continue
at,char=event[2:]
if at not in pending[1]: continue
if at in pending[2] and pending[2][at]!=char:
pending=None
continue
pending[2][at]=char
elif op=='commit':
if pending is None or event[1]!=pending[0]: continue
if set(pending[2])!=pending[1]: continue
visible=dict(pending[2])
pending=None
elif op=='abort':
if pending is not None and event[1]==pending[0]: pending=None
elif op=='read':
reads.append(sorted(visible.items()))
return [reads,sorted(visible.items()),pending[0] if pending is not None else None]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('read-isolation fixture 0', json.loads(json.dumps(solve([[[0,'o'],[9,'z']],[['begin','a',[0,1]],['put','a',1,'b'],['read'],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[[0,'o'],[9,'z']],[[0,'a'],[1,'b']]],[[0,'a'],[1,'b']],None])))
check('read-isolation fixture 1', json.loads(json.dumps(solve([[],[['begin','a',[0,1]],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('read-isolation fixture 2', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','wrong',0,'x'],['put','a',1,'y'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('read-isolation fixture 3', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',1,'b'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('read-isolation fixture 4', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'b'],['commit','a']]]))), json.loads(json.dumps([[],[],None])))
check('read-isolation fixture 5', json.loads(json.dumps(solve([[],[['begin','a',[0]],['begin','b',[]],['abort','b'],['put','a',0,'a'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('read-isolation fixture 6', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'a'],['commit','wrong'],['read'],['commit','a']]]))), json.loads(json.dumps([[[]],[[0,'a']],None])))
check('read-isolation fixture 7', json.loads(json.dumps(solve([[],[['begin','a',[]],['commit','a'],['begin','b',[N]],['put','b',N,'p'],['commit','b']]]))), json.loads(json.dumps([[],[[N,'p']],None])))
check('read-isolation fixture 8', json.loads(json.dumps(solve([[[0,'o']],[['begin','a',[0]],['put','a',0,'a'],['abort','a'],['read']]]))), json.loads(json.dumps([[[[0,'o']]],[[0,'o']],None])))
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 |
|---|---|---|---|
| read-isolation fixture 0 | [[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None] | [[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None] | Passed |
| read-isolation fixture 1 | [[[]], [], 'a'] | [[[]], [], 'a'] | Passed |
| read-isolation fixture 2 | [[[]], [], 'a'] | [[[]], [], 'a'] | Passed |
| read-isolation fixture 3 | [[], [[0, 'a']], None] | [[], [[0, 'a']], None] | Passed |
| read-isolation fixture 4 | [[], [], None] | [[], [], None] | Passed |
| read-isolation fixture 5 | [[], [[0, 'a']], None] | [[], [[0, 'a']], None] | Passed |
| read-isolation fixture 6 | [[[]], [[0, 'a']], None] | [[[]], [[0, 'a']], None] | Passed |
| read-isolation fixture 7 | [[], [[1, 'p']], None] | [[], [[1, 'p']], None] | Passed |
| read-isolation fixture 8 | [[[[0, 'o']]], [[0, 'o']], None] | [[[[0, 'o']]], [[0, 'o']], None] | Passed |
SHA-256 / a0ad4a0493b8ad57f9ef96132d392c508a213a643e7a3a8ba977fd0811d5f625
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 2026-09-29T14:41:20.789414+00:00.
Case digest / c7fd591815595e029857486eef1a7aa7e3600625c729c484ce5a15ab44953634