FA-6916 / Content negotiation / Open access

Wildcard vary absorbs other vary fields · case 01

Wildcard vary absorbs other vary fields.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The faulty implementation uses `fields` for the wildcard-vary-absorbs-other-vary-fields decision.

VERIFIED REPAIR

Apply the explicit wildcard-vary-absorbs-other-vary-fields contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `['*'] if fields else []` and still violates a separate fixture.

Case contract

Bounded offline decision model: wildcard vary absorbs other vary fields. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.

Why this case matters

This deterministic content negotiation model isolates the wildcard-vary-absorbs-other-vary-fields policy at a network component boundary.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(fields):
    return fields
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['accept', '*']), ['*'])", "check('fixture 2', solve(['accept']), ['accept'])", "check('fixture 3', solve([]), [])", "check('fixture 4', solve(['*']), ['*'])"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
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
fixture 2	`['accept']`	`['accept']`	Passed
fixture 3	`[]`	`[]`	Passed
fixture 4	`['*']`	`['*']`	Passed
fixture 1	`['accept', '*']`	`['*']`	Failed

SHA-256 / 038797f8a7ea0e9478488ec8cd028f6f4d5b53bcbd39465c0d737ead1c8c1b38

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(fields):
    return ['*'] if fields else []
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['accept', '*']), ['*'])", "check('fixture 2', solve(['accept']), ['accept'])", "check('fixture 3', solve([]), [])", "check('fixture 4', solve(['*']), ['*'])"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
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
fixture 2	`['*']`	`['accept']`	Failed
fixture 3	`[]`	`[]`	Passed
fixture 4	`['*']`	`['*']`	Passed
fixture 1	`['*']`	`['*']`	Passed

SHA-256 / 009e2bd7d66785699caf71789dbdd13d8ac316ef54707a009b29c4d2822e22d2

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import ipaddress
import re
from urllib.parse import urlsplit, urljoin
N = 1
observations = []
def solve(fields):
    return ['*'] if '*' in fields else fields
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['accept', '*']), ['*'])", "check('fixture 2', solve(['accept']), ['accept'])", "check('fixture 3', solve([]), [])", "check('fixture 4', solve(['*']), ['*'])"]
for _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:
    exec(_line)
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
fixture 2	`['accept']`	`['accept']`	Passed
fixture 3	`[]`	`[]`	Passed
fixture 4	`['*']`	`['*']`	Passed
fixture 1	`['*']`	`['*']`	Passed

SHA-256 / 7d747032d78277a6f8c0c22d137d3ae8b7baf1efa3538bf6b6ed48443e5fba3d

Verification & scope

Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. 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 2026-09-29T14:38:06.440994+00:00.

Case digest / 52bfe002d9e94332a222a95c5b6aa7e342237eb2c3e735463238eb0f3e609a2c