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FA-27131 / HTTP ranges / Open access

A bounded Content-Range upload endpoint validates chunk admission: admitted upload chunks write at declared absolute offsets · case 01

A bounded Content-Range upload endpoint validates chunk admission: admitted upload chunks write at declared absolute offsets.

Verified by executionVariant 1 · 11 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The ranged-upload-admission-write-position decision uses cells=dict(x['cells']) r=x['request'] if r['method']!='PUT': return ['method',sorted(cells.items())] if r['session']!=x['session']: return ['session',sorted(cells.items())] if r['generation']!=x['generation']: return ['generation',sorted(cells.items())] if r['total']!=x['total']: return ['total',sorted(cells.items())] if r['total']>x['quota']: return ['quota',sorted(cells.items())] if r['start']<0 or r['stop']<r['start'] or r['stop']>r['total']: return ['bounds',sorted(cells.items())] if len(r['body'])!=r['stop']-r['start']: return ['length',sorted(cells.items())] if any(i in cells and cells[i]!=c for i,c in enumerate(r['body'],r['start'])): return ['conflict',sorted(cells.items())] for i,c in enumerate(r['body']): cells[i]=c complete=set(cells)==set(range(x['total'])) return ['complete' if complete else 'partial',sorted(cells.items())].

THE FAILURE

The ranged-upload-admission-write-position decision uses cells=dict(x['cells']) r=x['request'] if r['method']!='PUT': return ['method',sorted(cells.items())] if r['session']!=x['session']: return ['session',sorted(cells.items())] if r['generation']!=x['generation']: return ['generation',sorted(cells.items())] if r['total']!=x['total']: return ['total',sorted(cells.items())] if r['total']>x['quota']: return ['quota',sorted(cells.items())] if r['start']<0 or r['stop']<r['start'] or r['stop']>r['total']: return ['bounds',sorted(cells.items())] if len(r['body'])!=r['stop']-r['start']: return ['length',sorted(cells.items())] if any(i in cells and cells[i]!=c for i,c in enumerate(r['body'],r['start'])): return ['conflict',sorted(cells.items())] for i,c in enumerate(r['body']): cells[i]=c complete=set(cells)==set(range(x['total'])) return ['complete' if complete else 'partial',sorted(cells.items())].

Unsuccessful approach: The partial repair uses cells=dict(x['cells']) r=x['request'] if r['method']!='PUT': return ['method',sorted(cells.items())] if r['session']!=x['session']: return ['session',sorted(cells.items())] if r['generation']!=x['generation']: return ['generation',sorted(cells.items())] if r['total']!=x['total']: return ['total',sorted(cells.items())] if r['total']>x['quota']: return ['quota',sorted(cells.items())] if r['start']<0 or r['stop']<r['start'] or r['stop']>r['total']: return ['bounds',sorted(cells.items())] if len(r['body'])!=r['stop']-r['start']: return ['length',sorted(cells.items())] if any(i in cells and cells[i]!=c for i,c in enumerate(r['body'],r['start'])): return ['conflict',sorted(cells.items())] for i,c in enumerate(r['body'],len(cells)): cells[i]=c complete=set(cells)==set(range(x['total'])) return ['complete' if complete else 'partial',sorted(cells.items())], which still violates the stated contract.

Case contract

This stipulated endpoint accepts PUT chunks against an upload session. Inputs include session ID, generation, declared complete length, [start,stop) byte span, ASCII body, and known committed cells. Return a disposition and updated cells; malformed metadata never mutates stored bytes. Exact duplicate chunks are idempotent, contradicting overlap is conflict, and quota concerns the complete representation rather than chunk size.

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):
    cells=dict(x['cells'])
    r=x['request']
    if r['method']!='PUT': return ['method',sorted(cells.items())]
    if r['session']!=x['session']: return ['session',sorted(cells.items())]
    if r['generation']!=x['generation']: return ['generation',sorted(cells.items())]
    if r['total']!=x['total']: return ['total',sorted(cells.items())]
    if r['total']>x['quota']: return ['quota',sorted(cells.items())]
    if r['start']<0 or r['stop']<r['start'] or r['stop']>r['total']: return ['bounds',sorted(cells.items())]
    if len(r['body'])!=r['stop']-r['start']: return ['length',sorted(cells.items())]
    if any(i in cells and cells[i]!=c for i,c in enumerate(r['body'],r['start'])): return ['conflict',sorted(cells.items())]
    for i,c in enumerate(r['body']): cells[i]=c
    complete=set(cells)==set(range(x['total']))
    return ['complete' if complete else 'partial',sorted(cells.items())]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('write-position fixture 0', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':1,'stop':3,'body':'bc'}}))), json.loads(json.dumps(['complete',[[0,'a'],[1,'b'],[2,'c']]])))
check('write-position fixture 1', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'POST','session':'s','generation':2,'total':3,'start':1,'stop':2,'body':'b'}}))), json.loads(json.dumps(['method',[[0,'a']]])))
check('write-position fixture 2', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'other','generation':2,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['session',[]])))
check('write-position fixture 3', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':3,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['generation',[]])))
check('write-position fixture 4', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':4,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['total',[]])))
check('write-position fixture 5', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':2,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['quota',[]])))
check('write-position fixture 6', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':-1,'stop':0,'body':'a'}}))), json.loads(json.dumps(['bounds',[]])))
check('write-position fixture 7', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':1,'stop':3,'body':'b'}}))), json.loads(json.dumps(['length',[]])))
check('write-position fixture 8', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':0,'stop':1,'body':'x'}}))), json.loads(json.dumps(['conflict',[[0,'a']]])))
check('write-position fixture 9', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['partial',[[0,'a']]])))
check('write-position fixture 10', json.loads(json.dumps(solve({'session':'s','generation':2,'total':N,'quota':10,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':N,'start':0,'stop':N,'body':"p"*N}}))), json.loads(json.dumps(['complete',[[i,"p"] for i in range(N)]])))
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 fixtureActualExpectedOutcome
write-position fixture 0['partial', [[0, 'b'], [1, 'c']]]['complete', [[0, 'a'], [1, 'b'], [2, 'c']]]Failed
write-position fixture 1['method', [[0, 'a']]]['method', [[0, 'a']]]Passed
write-position fixture 2['session', []]['session', []]Passed
write-position fixture 3['generation', []]['generation', []]Passed
write-position fixture 4['total', []]['total', []]Passed
write-position fixture 5['quota', []]['quota', []]Passed
write-position fixture 6['bounds', []]['bounds', []]Passed
write-position fixture 7['length', []]['length', []]Passed
write-position fixture 8['conflict', [[0, 'a']]]['conflict', [[0, 'a']]]Passed
write-position fixture 9['partial', [[0, 'a']]]['partial', [[0, 'a']]]Passed
write-position fixture 10['complete', [[0, 'p']]]['complete', [[0, 'p']]]Passed

SHA-256 / bbc9741ce7ff5b3b8069185ef4e29761c392879497fc5299418b42ec98ae4353

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    cells=dict(x['cells'])
    r=x['request']
    if r['method']!='PUT': return ['method',sorted(cells.items())]
    if r['session']!=x['session']: return ['session',sorted(cells.items())]
    if r['generation']!=x['generation']: return ['generation',sorted(cells.items())]
    if r['total']!=x['total']: return ['total',sorted(cells.items())]
    if r['total']>x['quota']: return ['quota',sorted(cells.items())]
    if r['start']<0 or r['stop']<r['start'] or r['stop']>r['total']: return ['bounds',sorted(cells.items())]
    if len(r['body'])!=r['stop']-r['start']: return ['length',sorted(cells.items())]
    if any(i in cells and cells[i]!=c for i,c in enumerate(r['body'],r['start'])): return ['conflict',sorted(cells.items())]
    for i,c in enumerate(r['body'],len(cells)): cells[i]=c
    complete=set(cells)==set(range(x['total']))
    return ['complete' if complete else 'partial',sorted(cells.items())]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('write-position fixture 0', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':1,'stop':3,'body':'bc'}}))), json.loads(json.dumps(['complete',[[0,'a'],[1,'b'],[2,'c']]])))
check('write-position fixture 1', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'POST','session':'s','generation':2,'total':3,'start':1,'stop':2,'body':'b'}}))), json.loads(json.dumps(['method',[[0,'a']]])))
check('write-position fixture 2', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'other','generation':2,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['session',[]])))
check('write-position fixture 3', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':3,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['generation',[]])))
check('write-position fixture 4', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':4,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['total',[]])))
check('write-position fixture 5', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':2,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['quota',[]])))
check('write-position fixture 6', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':-1,'stop':0,'body':'a'}}))), json.loads(json.dumps(['bounds',[]])))
check('write-position fixture 7', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':1,'stop':3,'body':'b'}}))), json.loads(json.dumps(['length',[]])))
check('write-position fixture 8', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':0,'stop':1,'body':'x'}}))), json.loads(json.dumps(['conflict',[[0,'a']]])))
check('write-position fixture 9', json.loads(json.dumps(solve({'session':'s','generation':2,'total':3,'quota':5,'cells':[[0,'a']],'request':{'method':'PUT','session':'s','generation':2,'total':3,'start':0,'stop':1,'body':'a'}}))), json.loads(json.dumps(['partial',[[0,'a']]])))
check('write-position fixture 10', json.loads(json.dumps(solve({'session':'s','generation':2,'total':N,'quota':10,'cells':[],'request':{'method':'PUT','session':'s','generation':2,'total':N,'start':0,'stop':N,'body':"p"*N}}))), json.loads(json.dumps(['complete',[[i,"p"] for i in range(N)]])))
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 fixtureActualExpectedOutcome
write-position fixture 0['complete', [[0, 'a'], [1, 'b'], [2, 'c']]]['complete', [[0, 'a'], [1, 'b'], [2, 'c']]]Passed
write-position fixture 1['method', [[0, 'a']]]['method', [[0, 'a']]]Passed
write-position fixture 2['session', []]['session', []]Passed
write-position fixture 3['generation', []]['generation', []]Passed
write-position fixture 4['total', []]['total', []]Passed
write-position fixture 5['quota', []]['quota', []]Passed
write-position fixture 6['bounds', []]['bounds', []]Passed
write-position fixture 7['length', []]['length', []]Passed
write-position fixture 8['conflict', [[0, 'a']]]['conflict', [[0, 'a']]]Passed
write-position fixture 9['partial', [[0, 'a'], [1, 'a']]]['partial', [[0, 'a']]]Failed
write-position fixture 10['complete', [[0, 'p']]]['complete', [[0, 'p']]]Passed

SHA-256 / 124715602657d0ce3f2ff61cfa700715faeb555a70b9ab551c70184ef41fbb53

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 11 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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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 2026-09-29T14:41:22.364580+00:00.

Case digest / bf9b0acb880343f9cf0435e1a959800c62d0ead3d84292bc3f7728991b441203