FA-26411 / HTTP ranges / Open access

Range negotiation preserves preexisting Vary dimensions · case 01

Range negotiation preserves preexisting Vary dimensions.

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

ROOT CAUSE

The variant-vary-union decision uses return ["accept-encoding"] if selected_by_encoding else vary.

VERIFIED REPAIR

Apply the bounded decision exactly: return sorted(set(vary+(["accept-encoding"] if selected_by_encoding else [])))

Unsuccessful approach: The partial repair uses return sorted(vary+["accept-encoding"]) if selected_by_encoding else sorted(vary), which still violates the stated contract.

Case contract

Return sorted unique Vary names, adding accept-encoding when negotiated by encoding. Existing names are already lowercase.

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(vary, selected_by_encoding):
    return ["accept-encoding"] if selected_by_encoding else vary
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('variant-vary-union fixture 0', solve( ["accept-language"],True), ["accept-encoding","accept-language"])
check('variant-vary-union fixture 1', solve(["accept-encoding"],True), ["accept-encoding"])
check('variant-vary-union fixture 2', solve([],True), ["accept-encoding"])
check('variant-vary-union fixture 3', solve([],False), [])
check('variant-vary-union fixture 4', solve(["x-"+str(N)],False), ["x-"+str(N)])
check('variant-vary-union fixture 5', solve(["accept-language","accept-language"],False), ["accept-language"])
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
variant-vary-union fixture 0	`['accept-encoding']`	`['accept-encoding', 'accept-language']`	Failed
variant-vary-union fixture 1	`['accept-encoding']`	`['accept-encoding']`	Passed
variant-vary-union fixture 2	`['accept-encoding']`	`['accept-encoding']`	Passed
variant-vary-union fixture 3	`[]`	`[]`	Passed
variant-vary-union fixture 4	`['x-1']`	`['x-1']`	Passed
variant-vary-union fixture 5	`['accept-language', 'accept-language']`	`['accept-language']`	Failed

SHA-256 / 509ac6f44a4ae478665af300b6feeb3ae9c7dee7a3b3eb45562ba1d059c03d73

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(vary, selected_by_encoding):
    return sorted(vary+["accept-encoding"]) if selected_by_encoding else sorted(vary)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('variant-vary-union fixture 0', solve( ["accept-language"],True), ["accept-encoding","accept-language"])
check('variant-vary-union fixture 1', solve(["accept-encoding"],True), ["accept-encoding"])
check('variant-vary-union fixture 2', solve([],True), ["accept-encoding"])
check('variant-vary-union fixture 3', solve([],False), [])
check('variant-vary-union fixture 4', solve(["x-"+str(N)],False), ["x-"+str(N)])
check('variant-vary-union fixture 5', solve(["accept-language","accept-language"],False), ["accept-language"])
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
variant-vary-union fixture 0	`['accept-encoding', 'accept-language']`	`['accept-encoding', 'accept-language']`	Passed
variant-vary-union fixture 1	`['accept-encoding', 'accept-encoding']`	`['accept-encoding']`	Failed
variant-vary-union fixture 2	`['accept-encoding']`	`['accept-encoding']`	Passed
variant-vary-union fixture 3	`[]`	`[]`	Passed
variant-vary-union fixture 4	`['x-1']`	`['x-1']`	Passed
variant-vary-union fixture 5	`['accept-language', 'accept-language']`	`['accept-language']`	Failed

SHA-256 / 5423fbda7b286d8bc6b27c550ebb8f6b28b10e33f1c5bf5b75362b1c5824d0d1

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(vary, selected_by_encoding):
    return sorted(set(vary+(["accept-encoding"] if selected_by_encoding else [])))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('variant-vary-union fixture 0', solve( ["accept-language"],True), ["accept-encoding","accept-language"])
check('variant-vary-union fixture 1', solve(["accept-encoding"],True), ["accept-encoding"])
check('variant-vary-union fixture 2', solve([],True), ["accept-encoding"])
check('variant-vary-union fixture 3', solve([],False), [])
check('variant-vary-union fixture 4', solve(["x-"+str(N)],False), ["x-"+str(N)])
check('variant-vary-union fixture 5', solve(["accept-language","accept-language"],False), ["accept-language"])
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
variant-vary-union fixture 0	`['accept-encoding', 'accept-language']`	`['accept-encoding', 'accept-language']`	Passed
variant-vary-union fixture 1	`['accept-encoding']`	`['accept-encoding']`	Passed
variant-vary-union fixture 2	`['accept-encoding']`	`['accept-encoding']`	Passed
variant-vary-union fixture 3	`[]`	`[]`	Passed
variant-vary-union fixture 4	`['x-1']`	`['x-1']`	Passed
variant-vary-union fixture 5	`['accept-language']`	`['accept-language']`	Passed

SHA-256 / 4b01da1800e1c18b4b23acf0f9e20b3468f55e0574d29b5ddad599da7aaf3836

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 2026-09-29T14:41:15.694413+00:00.

Case digest / d046a6ccba26cee115859bdb5d48f5197194808d2c465571297632f1dfc74359