FA-27356 / HTTP ranges / Open access

A persisted partial-response cache record keeps byte coverage and revision metadata intact: coverage metadata is verified along with cached payload bytes · case 01

A persisted partial-response cache record keeps byte coverage and revision metadata intact: coverage metadata is verified along with cached payload bytes.

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ROOT CAUSE

The partial-cache-record-record-checksum decision uses wire=x if len(wire)<10 or any(not 0<=b<=255 for b in wire): return None if wire[:2]!=[82,71]: return None if wire[2]!=1: return None if wire[3]!=0: return None if False: return None generation=wire[4]256+wire[5] total=wire[6]256+wire[7] count=wire[8] pos=9 parts=[] owned=set() for _ in range(count): if pos+3>len(wire)-1: return None offset=wire[pos]*256+wire[pos+1] size=wire[pos+2] pos+=3 if pos+size>len(wire)-1 or offset+size>total: return None if any(i in owned for i in range(offset,offset+size)): return None owned.update(range(offset,offset+size)) parts.append([offset,''.join(chr(b) for b in wire[pos:pos+size])]) pos+=size if pos!=len(wire)-1: return None return [generation,total,parts].

VERIFIED REPAIR

Apply the bounded decision exactly: wire=x if len(wire)<10 or any(not 0<=b<=255 for b in wire): return None if wire[:2]!=[82,71]: return None if wire[2]!=1: return None if wire[3]!=0: return None if sum(wire[:-1])%256!=wire[-1]: return None generation=wire[4]*256+wire[5] total=wire[6]*256+wire[7] count=wire[8] pos=9 parts=[] owned=set() for _ in range(count): if pos+3>len(wire)-1: return None offset=wire[pos]*256+wire[pos+1] size=wire[pos+2] pos+=3 if pos+size>len(wire)-1 or offset+size>total: return None if any(i in owned for i in range(offset,offset+size)): return None owned.update(range(offset,offset+size)) parts.append([offset,''.join(chr(b) for b in wire[pos:pos+size])]) pos+=size if pos!=len(wire)-1: return None return [generation,total,parts]

Unsuccessful approach: The partial repair uses wire=x if len(wire)<10 or any(not 0<=b<=255 for b in wire): return None if wire[:2]!=[82,71]: return None if wire[2]!=1: return None if wire[3]!=0: return None if sum(wire[9:-1])%256!=wire[-1] and wire[8]>0: return None generation=wire[4]*256+wire[5] total=wire[6]*256+wire[7] count=wire[8] pos=9 parts=[] owned=set() for _ in range(count): if pos+3>len(wire)-1: return None offset=wire[pos]*256+wire[pos+1] size=wire[pos+2] pos+=3 if pos+size>len(wire)-1 or offset+size>total: return None if any(i in owned for i in range(offset,offset+size)): return None owned.update(range(offset,offset+size)) parts.append([offset,''.join(chr(b) for b in wire[pos:pos+size])]) pos+=size if pos!=len(wire)-1: return None return [generation,total,parts], which still violates the stated contract.

Case contract

Decode this stipulated local binary cache envelope: magic RG, version1, flags0, two-byte big-endian generation, two-byte big-endian complete length, one-byte fragment count, then fragments [two-byte big-endian offset,one-byte count,ASCII payload], followed by one checksum byte equal to sum of preceding bytes modulo256. Reject malformed envelopes, bytes outside0..255, trailing bytes, overlapping fragment ownership, or spans outside complete length. Return [generation,total,[[offset,payload],...]]. This is an invented bounded persistence format, not a public protocol.

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):
    wire=x
    if len(wire)<10 or any(not 0<=b<=255 for b in wire): return None
    if wire[:2]!=[82,71]: return None
    if wire[2]!=1: return None
    if wire[3]!=0: return None
    if False: return None
    generation=wire[4]*256+wire[5]
    total=wire[6]*256+wire[7]
    count=wire[8]
    pos=9
    parts=[]
    owned=set()
    for _ in range(count):
        if pos+3>len(wire)-1: return None
        offset=wire[pos]*256+wire[pos+1]
        size=wire[pos+2]
        pos+=3
        if pos+size>len(wire)-1 or offset+size>total: return None
        if any(i in owned for i in range(offset,offset+size)): return None
        owned.update(range(offset,offset+size))
        parts.append([offset,''.join(chr(b) for b in wire[pos:pos+size])])
        pos+=size
    if pos!=len(wire)-1: return None
    return [generation,total,parts]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('record-checksum fixture 0', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,1,N,1,2,2,0,0,2,97,98,1,0,2,99,100])))), json.loads(json.dumps([256+N,258,[[0,'ab'],[256,'cd']]])))
check('record-checksum fixture 1', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,0,0])))), json.loads(json.dumps([0,0,[]])))
check('record-checksum fixture 2', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,1,0,3,1,0,1,2,98,99])))), json.loads(json.dumps([1,3,[[1,'bc']]])))
check('record-checksum fixture 3', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,70,1,0,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 4', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,2,0,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 5', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,1,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 6', json.loads(json.dumps(solve([82,71,1,0,0,0,0,0,0,0]))), json.loads(json.dumps(None)))
check('record-checksum fixture 7', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,1,1,0,0,2,97,98])))), json.loads(json.dumps(None)))
check('record-checksum fixture 8', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,2,2,0,0,1,97,0,0,1,97])))), json.loads(json.dumps(None)))
check('record-checksum fixture 9', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,0,0,99])))), json.loads(json.dumps(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
record-checksum fixture 0	`[257, 258, [[0, 'ab'], [256, 'cd']]]`	`[257, 258, [[0, 'ab'], [256, 'cd']]]`	Passed
record-checksum fixture 1	`[0, 0, []]`	`[0, 0, []]`	Passed
record-checksum fixture 2	`[1, 3, [[1, 'bc']]]`	`[1, 3, [[1, 'bc']]]`	Passed
record-checksum fixture 3	`None`	`None`	Passed
record-checksum fixture 4	`None`	`None`	Passed
record-checksum fixture 5	`None`	`None`	Passed
record-checksum fixture 6	`[0, 0, []]`	`None`	Failed
record-checksum fixture 7	`None`	`None`	Passed
record-checksum fixture 8	`None`	`None`	Passed
record-checksum fixture 9	`None`	`None`	Passed

SHA-256 / 77abd07d8d7ba64d13c0bd1498b127a6e7f4d34d47fda8daaac5f7c0ad178de2

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    wire=x
    if len(wire)<10 or any(not 0<=b<=255 for b in wire): return None
    if wire[:2]!=[82,71]: return None
    if wire[2]!=1: return None
    if wire[3]!=0: return None
    if sum(wire[9:-1])%256!=wire[-1] and wire[8]>0: return None
    generation=wire[4]*256+wire[5]
    total=wire[6]*256+wire[7]
    count=wire[8]
    pos=9
    parts=[]
    owned=set()
    for _ in range(count):
        if pos+3>len(wire)-1: return None
        offset=wire[pos]*256+wire[pos+1]
        size=wire[pos+2]
        pos+=3
        if pos+size>len(wire)-1 or offset+size>total: return None
        if any(i in owned for i in range(offset,offset+size)): return None
        owned.update(range(offset,offset+size))
        parts.append([offset,''.join(chr(b) for b in wire[pos:pos+size])])
        pos+=size
    if pos!=len(wire)-1: return None
    return [generation,total,parts]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('record-checksum fixture 0', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,1,N,1,2,2,0,0,2,97,98,1,0,2,99,100])))), json.loads(json.dumps([256+N,258,[[0,'ab'],[256,'cd']]])))
check('record-checksum fixture 1', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,0,0])))), json.loads(json.dumps([0,0,[]])))
check('record-checksum fixture 2', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,1,0,3,1,0,1,2,98,99])))), json.loads(json.dumps([1,3,[[1,'bc']]])))
check('record-checksum fixture 3', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,70,1,0,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 4', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,2,0,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 5', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,1,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 6', json.loads(json.dumps(solve([82,71,1,0,0,0,0,0,0,0]))), json.loads(json.dumps(None)))
check('record-checksum fixture 7', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,1,1,0,0,2,97,98])))), json.loads(json.dumps(None)))
check('record-checksum fixture 8', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,2,2,0,0,1,97,0,0,1,97])))), json.loads(json.dumps(None)))
check('record-checksum fixture 9', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,0,0,99])))), json.loads(json.dumps(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
record-checksum fixture 0	`None`	`[257, 258, [[0, 'ab'], [256, 'cd']]]`	Failed
record-checksum fixture 1	`[0, 0, []]`	`[0, 0, []]`	Passed
record-checksum fixture 2	`None`	`[1, 3, [[1, 'bc']]]`	Failed
record-checksum fixture 3	`None`	`None`	Passed
record-checksum fixture 4	`None`	`None`	Passed
record-checksum fixture 5	`None`	`None`	Passed
record-checksum fixture 6	`[0, 0, []]`	`None`	Failed
record-checksum fixture 7	`None`	`None`	Passed
record-checksum fixture 8	`None`	`None`	Passed
record-checksum fixture 9	`None`	`None`	Passed

SHA-256 / edaa2b41847409d6670f1a9787a07107dd8e5c36e9b9c6f19c08c8c2b4743c49

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(x):
    wire=x
    if len(wire)<10 or any(not 0<=b<=255 for b in wire): return None
    if wire[:2]!=[82,71]: return None
    if wire[2]!=1: return None
    if wire[3]!=0: return None
    if sum(wire[:-1])%256!=wire[-1]: return None
    generation=wire[4]*256+wire[5]
    total=wire[6]*256+wire[7]
    count=wire[8]
    pos=9
    parts=[]
    owned=set()
    for _ in range(count):
        if pos+3>len(wire)-1: return None
        offset=wire[pos]*256+wire[pos+1]
        size=wire[pos+2]
        pos+=3
        if pos+size>len(wire)-1 or offset+size>total: return None
        if any(i in owned for i in range(offset,offset+size)): return None
        owned.update(range(offset,offset+size))
        parts.append([offset,''.join(chr(b) for b in wire[pos:pos+size])])
        pos+=size
    if pos!=len(wire)-1: return None
    return [generation,total,parts]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('record-checksum fixture 0', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,1,N,1,2,2,0,0,2,97,98,1,0,2,99,100])))), json.loads(json.dumps([256+N,258,[[0,'ab'],[256,'cd']]])))
check('record-checksum fixture 1', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,0,0])))), json.loads(json.dumps([0,0,[]])))
check('record-checksum fixture 2', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,1,0,3,1,0,1,2,98,99])))), json.loads(json.dumps([1,3,[[1,'bc']]])))
check('record-checksum fixture 3', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,70,1,0,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 4', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,2,0,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 5', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,1,0,0,0,0,0])))), json.loads(json.dumps(None)))
check('record-checksum fixture 6', json.loads(json.dumps(solve([82,71,1,0,0,0,0,0,0,0]))), json.loads(json.dumps(None)))
check('record-checksum fixture 7', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,1,1,0,0,2,97,98])))), json.loads(json.dumps(None)))
check('record-checksum fixture 8', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,2,2,0,0,1,97,0,0,1,97])))), json.loads(json.dumps(None)))
check('record-checksum fixture 9', json.loads(json.dumps(solve((lambda w:w+[sum(w)%256])([82,71,1,0,0,0,0,0,0,99])))), json.loads(json.dumps(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
record-checksum fixture 0	`[257, 258, [[0, 'ab'], [256, 'cd']]]`	`[257, 258, [[0, 'ab'], [256, 'cd']]]`	Passed
record-checksum fixture 1	`[0, 0, []]`	`[0, 0, []]`	Passed
record-checksum fixture 2	`[1, 3, [[1, 'bc']]]`	`[1, 3, [[1, 'bc']]]`	Passed
record-checksum fixture 3	`None`	`None`	Passed
record-checksum fixture 4	`None`	`None`	Passed
record-checksum fixture 5	`None`	`None`	Passed
record-checksum fixture 6	`None`	`None`	Passed
record-checksum fixture 7	`None`	`None`	Passed
record-checksum fixture 8	`None`	`None`	Passed
record-checksum fixture 9	`None`	`None`	Passed

SHA-256 / 326f6625aa96c31d6d2d42798179c0cd9f8d32cf625e70dce450a3c83f22ba3f

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 2026-09-29T14:41:24.403829+00:00.

Case digest / cd6f4b0b33a02ee4dfd5c505ed194b9f32203fa36fbf9a44b39870e04a48fca2