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FA-27811 / HTTP ranges / Open access

An object store maps upload part numbers and byte ranges onto stored parts: a part begins at the sum of all earlier part sizes · case 01

An object store maps upload part numbers and byte ranges onto stored parts: a part begins at the sum of all earlier part sizes.

Verified by executionVariant 1 · 14 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The part-number-range-map-part-prefix-offset decision uses sizes=x['parts'] total=sum(sizes) starts=[] acc=0 for s in sizes: acc+=s starts.append(acc) q=x['query'] if q[0]=='part': n=q[1] if not 1<=n<=len(sizes) or sizes[n-1]==0: return [416,'bytes */%d'%total] a=starts[n-1] return [206,'bytes %d-%d/%d'%(a,a+sizes[n-1]-1,total)] a,b=q[1],q[2] if not 0<=a<=b<total: return [416,'bytes */%d'%total] out=[] for i,s in enumerate(sizes): lo=max(a,starts[i]) hi=min(b,starts[i]+s-1) if lo<=hi: out.append([i+1,lo-starts[i],hi-lo+1]) return [206,out].

THE FAILURE

The part-number-range-map-part-prefix-offset decision uses sizes=x['parts'] total=sum(sizes) starts=[] acc=0 for s in sizes: acc+=s starts.append(acc) q=x['query'] if q[0]=='part': n=q[1] if not 1<=n<=len(sizes) or sizes[n-1]==0: return [416,'bytes */%d'%total] a=starts[n-1] return [206,'bytes %d-%d/%d'%(a,a+sizes[n-1]-1,total)] a,b=q[1],q[2] if not 0<=a<=b<total: return [416,'bytes */%d'%total] out=[] for i,s in enumerate(sizes): lo=max(a,starts[i]) hi=min(b,starts[i]+s-1) if lo<=hi: out.append([i+1,lo-starts[i],hi-lo+1]) return [206,out].

Unsuccessful approach: The partial repair uses sizes=x['parts'] total=sum(sizes) starts=[] acc=0 for s in sizes: starts.append(acc) acc=s q=x['query'] if q[0]=='part': n=q[1] if not 1<=n<=len(sizes) or sizes[n-1]==0: return [416,'bytes */%d'%total] a=starts[n-1] return [206,'bytes %d-%d/%d'%(a,a+sizes[n-1]-1,total)] a,b=q[1],q[2] if not 0<=a<=b<total: return [416,'bytes */%d'%total] out=[] for i,s in enumerate(sizes): lo=max(a,starts[i]) hi=min(b,starts[i]+s-1) if lo<=hi: out.append([i+1,lo-starts[i],hi-lo+1]) return [206,out], which still violates the stated contract.

Case contract

x has stored part sizes in order and a query. ["part",n] (1-based) returns [206,bytes a-b/total] for that part, or [416,bytes */total] when n is outside 1..count or the part is empty. ["range",a,b] with inclusive bounds returns [416,bytes */total] unless 0<=a<=b<total; otherwise [206,rows] where each intersecting nonempty part yields [part-number,offset-within-part,count] in part order.

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):
    sizes=x['parts']
    total=sum(sizes)
    starts=[]
    acc=0
    for s in sizes:
        acc+=s
        starts.append(acc)
    q=x['query']
    if q[0]=='part':
        n=q[1]
        if not 1<=n<=len(sizes) or sizes[n-1]==0: return [416,'bytes */%d'%total]
        a=starts[n-1]
        return [206,'bytes %d-%d/%d'%(a,a+sizes[n-1]-1,total)]
    a,b=q[1],q[2]
    if not 0<=a<=b<total: return [416,'bytes */%d'%total]
    out=[]
    for i,s in enumerate(sizes):
        lo=max(a,starts[i])
        hi=min(b,starts[i]+s-1)
        if lo<=hi: out.append([i+1,lo-starts[i],hi-lo+1])
    return [206,out]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('part-prefix-offset fixture 0', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',2]}))), json.loads(json.dumps([206,'bytes 5-7/12'])))
check('part-prefix-offset fixture 1', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',3]}))), json.loads(json.dumps([206,'bytes 8-11/12'])))
check('part-prefix-offset fixture 2', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',0]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 3', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',-1]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 4', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',4]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 5', json.loads(json.dumps(solve({'parts':[5,0,4],'query':['part',2]}))), json.loads(json.dumps([416,'bytes */9'])))
check('part-prefix-offset fixture 6', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',3,9]}))), json.loads(json.dumps([206,[[1,3,2],[2,0,3],[3,0,2]]])))
check('part-prefix-offset fixture 7', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',4,5]}))), json.loads(json.dumps([206,[[1,4,1],[2,0,1]]])))
check('part-prefix-offset fixture 8', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',5,7]}))), json.loads(json.dumps([206,[[2,0,3]]])))
check('part-prefix-offset fixture 9', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',0,12]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 10', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',0,11]}))), json.loads(json.dumps([206,[[1,0,5],[2,0,3],[3,0,4]]])))
check('part-prefix-offset fixture 11', json.loads(json.dumps(solve({'parts':[5,0,4],'query':['range',4,5]}))), json.loads(json.dumps([206,[[1,4,1],[3,0,1]]])))
check('part-prefix-offset fixture 12', json.loads(json.dumps(solve({'parts':[],'query':['part',1]}))), json.loads(json.dumps([416,'bytes */0'])))
check('part-prefix-offset fixture 13', json.loads(json.dumps(solve({'parts':[N,N],'query':['part',2]}))), json.loads(json.dumps([206,"bytes %d-%d/%d"%(N,2*N-1,2*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
part-prefix-offset fixture 0[206, 'bytes 8-10/12'][206, 'bytes 5-7/12']Failed
part-prefix-offset fixture 1[206, 'bytes 12-15/12'][206, 'bytes 8-11/12']Failed
part-prefix-offset fixture 2[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 3[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 4[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 5[416, 'bytes */9'][416, 'bytes */9']Passed
part-prefix-offset fixture 6[206, [[1, 0, 5], [2, 0, 2]]][206, [[1, 3, 2], [2, 0, 3], [3, 0, 2]]]Failed
part-prefix-offset fixture 7[206, [[1, 0, 1]]][206, [[1, 4, 1], [2, 0, 1]]]Failed
part-prefix-offset fixture 8[206, [[1, 0, 3]]][206, [[2, 0, 3]]]Failed
part-prefix-offset fixture 9[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 10[206, [[1, 0, 5], [2, 0, 3]]][206, [[1, 0, 5], [2, 0, 3], [3, 0, 4]]]Failed
part-prefix-offset fixture 11[206, [[1, 0, 1]]][206, [[1, 4, 1], [3, 0, 1]]]Failed
part-prefix-offset fixture 12[416, 'bytes */0'][416, 'bytes */0']Passed
part-prefix-offset fixture 13[206, 'bytes 2-2/2'][206, 'bytes 1-1/2']Failed

SHA-256 / a6d249126574ecbfa6935268b513c7cfa072ae53f70876d2fd3ea289cf72e291

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    sizes=x['parts']
    total=sum(sizes)
    starts=[]
    acc=0
    for s in sizes:
        starts.append(acc)
        acc=s
    q=x['query']
    if q[0]=='part':
        n=q[1]
        if not 1<=n<=len(sizes) or sizes[n-1]==0: return [416,'bytes */%d'%total]
        a=starts[n-1]
        return [206,'bytes %d-%d/%d'%(a,a+sizes[n-1]-1,total)]
    a,b=q[1],q[2]
    if not 0<=a<=b<total: return [416,'bytes */%d'%total]
    out=[]
    for i,s in enumerate(sizes):
        lo=max(a,starts[i])
        hi=min(b,starts[i]+s-1)
        if lo<=hi: out.append([i+1,lo-starts[i],hi-lo+1])
    return [206,out]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('part-prefix-offset fixture 0', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',2]}))), json.loads(json.dumps([206,'bytes 5-7/12'])))
check('part-prefix-offset fixture 1', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',3]}))), json.loads(json.dumps([206,'bytes 8-11/12'])))
check('part-prefix-offset fixture 2', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',0]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 3', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',-1]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 4', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['part',4]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 5', json.loads(json.dumps(solve({'parts':[5,0,4],'query':['part',2]}))), json.loads(json.dumps([416,'bytes */9'])))
check('part-prefix-offset fixture 6', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',3,9]}))), json.loads(json.dumps([206,[[1,3,2],[2,0,3],[3,0,2]]])))
check('part-prefix-offset fixture 7', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',4,5]}))), json.loads(json.dumps([206,[[1,4,1],[2,0,1]]])))
check('part-prefix-offset fixture 8', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',5,7]}))), json.loads(json.dumps([206,[[2,0,3]]])))
check('part-prefix-offset fixture 9', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',0,12]}))), json.loads(json.dumps([416,'bytes */12'])))
check('part-prefix-offset fixture 10', json.loads(json.dumps(solve({'parts':[5,3,4],'query':['range',0,11]}))), json.loads(json.dumps([206,[[1,0,5],[2,0,3],[3,0,4]]])))
check('part-prefix-offset fixture 11', json.loads(json.dumps(solve({'parts':[5,0,4],'query':['range',4,5]}))), json.loads(json.dumps([206,[[1,4,1],[3,0,1]]])))
check('part-prefix-offset fixture 12', json.loads(json.dumps(solve({'parts':[],'query':['part',1]}))), json.loads(json.dumps([416,'bytes */0'])))
check('part-prefix-offset fixture 13', json.loads(json.dumps(solve({'parts':[N,N],'query':['part',2]}))), json.loads(json.dumps([206,"bytes %d-%d/%d"%(N,2*N-1,2*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
part-prefix-offset fixture 0[206, 'bytes 5-7/12'][206, 'bytes 5-7/12']Passed
part-prefix-offset fixture 1[206, 'bytes 3-6/12'][206, 'bytes 8-11/12']Failed
part-prefix-offset fixture 2[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 3[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 4[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 5[416, 'bytes */9'][416, 'bytes */9']Passed
part-prefix-offset fixture 6[206, [[1, 3, 2], [2, 0, 3], [3, 0, 4]]][206, [[1, 3, 2], [2, 0, 3], [3, 0, 2]]]Failed
part-prefix-offset fixture 7[206, [[1, 4, 1], [2, 0, 1], [3, 1, 2]]][206, [[1, 4, 1], [2, 0, 1]]]Failed
part-prefix-offset fixture 8[206, [[2, 0, 3], [3, 2, 2]]][206, [[2, 0, 3]]]Failed
part-prefix-offset fixture 9[416, 'bytes */12'][416, 'bytes */12']Passed
part-prefix-offset fixture 10[206, [[1, 0, 5], [2, 0, 3], [3, 0, 4]]][206, [[1, 0, 5], [2, 0, 3], [3, 0, 4]]]Passed
part-prefix-offset fixture 11[206, [[1, 4, 1]]][206, [[1, 4, 1], [3, 0, 1]]]Failed
part-prefix-offset fixture 12[416, 'bytes */0'][416, 'bytes */0']Passed
part-prefix-offset fixture 13[206, 'bytes 1-1/2'][206, 'bytes 1-1/2']Passed

SHA-256 / 132094d4e208e0f49b73b1f0551ed49324a7f280161770c9e6d31e88f3ee598b

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 14 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 2026-09-29T14:41:28.383274+00:00.

Case digest / 52f86495a0196eb255477837b359695c2ee9b57c8298467eb8972402a43dc0fc