FA-7376 / DNS resolution / Open access

Dns cname target is followed until requested type is reached · case 01

Dns cname target is followed until requested type is reached.

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

ROOT CAUSE

The faulty implementation uses `is_alias` for the dns-cname-target-is-followed-until-requested-type-is-reached decision.

VERIFIED REPAIR

Apply the explicit dns-cname-target-is-followed-until-requested-type-is-reached contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `requested_type != "CNAME"` and still violates a separate fixture.

Case contract

Bounded offline decision model: dns cname target is followed until requested type is reached. 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-target-is-followed-until-requested-type-is-reached 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(is_alias, requested_type):
    return is_alias
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 'A'), True)", "check('fixture 2', solve(True, 'CNAME'), False)", "check('fixture 3', solve(False, 'A'), False)", "check('fixture 4', solve(False, 'CNAME'), False)"]
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	`True`	`False`	Failed
fixture 3	`False`	`False`	Passed
fixture 4	`False`	`False`	Passed
fixture 1	`True`	`True`	Passed

SHA-256 / 161e6a24ef9b32f4f4bc92aab659608692f4accd3a7db98952ac865c790b8277

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(is_alias, requested_type):
    return requested_type != "CNAME"
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 'A'), True)", "check('fixture 2', solve(True, 'CNAME'), False)", "check('fixture 3', solve(False, 'A'), False)", "check('fixture 4', solve(False, 'CNAME'), False)"]
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	`True`	`False`	Failed
fixture 4	`False`	`False`	Passed
fixture 1	`True`	`True`	Passed

SHA-256 / 1bcfb8a96e4cb24525ea22c954afb79d8c2473143f073c58975fb77e8f595c65

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(is_alias, requested_type):
    return is_alias and requested_type != "CNAME"
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 'A'), True)", "check('fixture 2', solve(True, 'CNAME'), False)", "check('fixture 3', solve(False, 'A'), False)", "check('fixture 4', solve(False, 'CNAME'), False)"]
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`	`False`	Passed
fixture 1	`True`	`True`	Passed

SHA-256 / d782ca4aba30e56a28865a99f8a7238a0a8a982aae06195955da11d3972989b6

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 2026-09-29T14:38:11.402501+00:00.

Case digest / 7e6363e67f3f6b792a14f311c82c46bbe4986976fa6d59d08f0968b973ef623f