FA-7381 / DNS resolution / Open access

Dns cname loop detection normalizes target identities · case 01

Dns cname loop detection normalizes target identities.

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

ROOT CAUSE

The faulty implementation uses `target in visited` for the dns-cname-loop-detection-normalizes-target-identities decision.

VERIFIED REPAIR

Apply the explicit dns-cname-loop-detection-normalizes-target-identities contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `target.lower() in {x.lower() for x in visited}` and still violates a separate fixture.

Case contract

Bounded offline decision model: dns cname loop detection normalizes target identities. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.

Why this case matters

This deterministic dns resolution model isolates the dns-cname-loop-detection-normalizes-target-identities 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(target, visited):
    return target in visited
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('A.', ['a']), True)", "check('fixture 2', solve('b', ['a']), False)", "check('fixture 3', solve('a', []), False)", "check('fixture 4', solve('A', ['a']), True)"]
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	`False`	`False`	Passed
fixture 3	`False`	`False`	Passed
fixture 4	`False`	`True`	Failed
fixture 1	`False`	`True`	Failed

SHA-256 / f1a5d22c5862f60c124a3004de86b91cc3cb3f9254f31215e74cf945c29008fd

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(target, visited):
    return target.lower() in {x.lower() for x in visited}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('A.', ['a']), True)", "check('fixture 2', solve('b', ['a']), False)", "check('fixture 3', solve('a', []), False)", "check('fixture 4', solve('A', ['a']), True)"]
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	`False`	`False`	Passed
fixture 3	`False`	`False`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`False`	`True`	Failed

SHA-256 / 864c88e4f50869e1429e7b1f44a2ba81ecdcf097452c3b5c51d265a97db2ea35

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(target, visited):
    return target.lower().rstrip(".") in {x.lower().rstrip(".") for x in visited}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('A.', ['a']), True)", "check('fixture 2', solve('b', ['a']), False)", "check('fixture 3', solve('a', []), False)", "check('fixture 4', solve('A', ['a']), True)"]
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	`False`	`False`	Passed
fixture 3	`False`	`False`	Passed
fixture 4	`True`	`True`	Passed
fixture 1	`True`	`True`	Passed

SHA-256 / eb7f4e216eb5afcd0c158b7dcf4de028e4549308396abf7362639ddf512a7f10

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 2026-09-29T14:38:11.422129+00:00.

Case digest / 54034517c705439083c5ab6ccbdfc321d96b714bea8b2b423df1bb75a6e0bd41