FA-26501 / HTTP ranges / Open access

Missing cached bytes remain unavailable instead of becoming zero bytes · case 01

Missing cached bytes remain unavailable instead of becoming zero bytes.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The cache-holes-not-zero-filled decision uses return "".join(cells.get(i,"\x00") for i in offsets).

VERIFIED REPAIR

Apply the bounded decision exactly: return "".join(cells[i] for i in offsets) if all(i in cells for i in offsets) else None

Unsuccessful approach: The partial repair uses return "".join(cells[i] for i in offsets if i in cells), which still violates the stated contract.

Case contract

cells maps integer offsets to one-character strings. Return the requested bytes only if every requested offset exists, else None; empty request returns empty.

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(cells, offsets):
    return "".join(cells.get(i,"\x00") for i in offsets)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('cache-holes-not-zero-filled fixture 0', solve( {N:"a"},[N,N+1]), None)
check('cache-holes-not-zero-filled fixture 1', solve({},[N]), None)
check('cache-holes-not-zero-filled fixture 2', solve({N:"a"},[N]), "a")
check('cache-holes-not-zero-filled fixture 3', solve({},[]), "")
check('cache-holes-not-zero-filled fixture 4', solve({0:"\x00"},[0]), "\x00")
check('cache-holes-not-zero-filled fixture 5', solve({0:"a",1:"b"},[1,0]), "ba")
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
cache-holes-not-zero-filled fixture 0	`a`	`None`	Failed
cache-holes-not-zero-filled fixture 1		`None`	Failed
cache-holes-not-zero-filled fixture 2	`a`	`a`	Passed
cache-holes-not-zero-filled fixture 3			Passed
cache-holes-not-zero-filled fixture 4			Passed
cache-holes-not-zero-filled fixture 5	`ba`	`ba`	Passed

SHA-256 / a603738a5299e68647a9b4fdfced5d9ddeb0b318acb415d4ed518225eaee81f2

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(cells, offsets):
    return "".join(cells[i] for i in offsets if i in cells)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('cache-holes-not-zero-filled fixture 0', solve( {N:"a"},[N,N+1]), None)
check('cache-holes-not-zero-filled fixture 1', solve({},[N]), None)
check('cache-holes-not-zero-filled fixture 2', solve({N:"a"},[N]), "a")
check('cache-holes-not-zero-filled fixture 3', solve({},[]), "")
check('cache-holes-not-zero-filled fixture 4', solve({0:"\x00"},[0]), "\x00")
check('cache-holes-not-zero-filled fixture 5', solve({0:"a",1:"b"},[1,0]), "ba")
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
cache-holes-not-zero-filled fixture 0	`a`	`None`	Failed
cache-holes-not-zero-filled fixture 1		`None`	Failed
cache-holes-not-zero-filled fixture 2	`a`	`a`	Passed
cache-holes-not-zero-filled fixture 3			Passed
cache-holes-not-zero-filled fixture 4			Passed
cache-holes-not-zero-filled fixture 5	`ba`	`ba`	Passed

SHA-256 / cf6b4e7754eaf10106f94368d08aaae4826c7bd26fddf3710497a6235b2eb68b

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(cells, offsets):
    return "".join(cells[i] for i in offsets) if all(i in cells for i in offsets) else None
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('cache-holes-not-zero-filled fixture 0', solve( {N:"a"},[N,N+1]), None)
check('cache-holes-not-zero-filled fixture 1', solve({},[N]), None)
check('cache-holes-not-zero-filled fixture 2', solve({N:"a"},[N]), "a")
check('cache-holes-not-zero-filled fixture 3', solve({},[]), "")
check('cache-holes-not-zero-filled fixture 4', solve({0:"\x00"},[0]), "\x00")
check('cache-holes-not-zero-filled fixture 5', solve({0:"a",1:"b"},[1,0]), "ba")
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
cache-holes-not-zero-filled fixture 0	`None`	`None`	Passed
cache-holes-not-zero-filled fixture 1	`None`	`None`	Passed
cache-holes-not-zero-filled fixture 2	`a`	`a`	Passed
cache-holes-not-zero-filled fixture 3			Passed
cache-holes-not-zero-filled fixture 4			Passed
cache-holes-not-zero-filled fixture 5	`ba`	`ba`	Passed

SHA-256 / f17e80453e211a552ad0b171a54cd4b8cc1504c917a0fa8598c077932398ca2d

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 2026-09-29T14:41:16.557200+00:00.

Case digest / 5f993e3e5373d7da4e92058450572af048875c6e29d28f99086205393c412c4b