FA-7431 / DNS resolution / Open access

Dns edns fallback removes extension after format error only · case 01

Dns edns fallback removes extension after format error only.

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

ROOT CAUSE

The faulty implementation uses `edns` for the dns-edns-fallback-removes-extension-after-format-error-only decision.

VERIFIED REPAIR

Apply the explicit dns-edns-fallback-removes-extension-after-format-error-only contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `rcode == 1` and still violates a separate fixture.

Case contract

Bounded offline decision model: dns edns fallback removes extension after format error only. 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-edns-fallback-removes-extension-after-format-error-only 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(edns, rcode):
    return edns
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 1), True)", "check('fixture 2', solve(True, 3), False)", "check('fixture 3', solve(False, 1), False)", "check('fixture 4', solve(False, 0), 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 / 0b23aebb15cb884b98c6a31d3cedd8a3729c0fe678e35e44cc61a07567955e7d

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(edns, rcode):
    return rcode == 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 1), True)", "check('fixture 2', solve(True, 3), False)", "check('fixture 3', solve(False, 1), False)", "check('fixture 4', solve(False, 0), 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 / 308e2f6e3847f0d2265237cd9ceba807f9d03822ccb41facb6a1de1c982a0852

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(edns, rcode):
    return edns and rcode == 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(True, 1), True)", "check('fixture 2', solve(True, 3), False)", "check('fixture 3', solve(False, 1), False)", "check('fixture 4', solve(False, 0), 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 / bbea6ef6d4578a27ac1ca1c986647d3c37a2091b43fe2aa3c1e9bf0524509f54

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 2026-09-29T14:38:11.914640+00:00.

Case digest / 65cbfae0a29f330455b212d74a2612238ffc294369c1070577021210d563e353