FA-6961 / Proxy forwarding / Open access
Forwarded chain appends current hop · case 01
Forwarded chain appends current hop.
ROOT CAUSE
The faulty implementation uses `[hop]+chain` for the forwarded-chain-appends-current-hop decision.
VERIFIED REPAIR
Apply the explicit forwarded-chain-appends-current-hop contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `[hop]` and still violates a separate fixture.
Case contract
Bounded offline decision model: forwarded chain appends current hop. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.
Why this case matters
This deterministic proxy forwarding model isolates the forwarded-chain-appends-current-hop 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(chain, hop):
return [hop]+chain
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['a'], 'b'), ['a', 'b'])", "check('fixture 2', solve([], 'a'), ['a'])", "check('fixture 3', solve(['a', 'b'], 'c'), ['a', 'b', 'c'])", "check('fixture 4', solve(['a'], 'a'), ['a', 'a'])"]
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 | ['a'] | ['a'] | Passed |
| fixture 3 | ['c', 'a', 'b'] | ['a', 'b', 'c'] | Failed |
| fixture 4 | ['a', 'a'] | ['a', 'a'] | Passed |
| fixture 1 | ['b', 'a'] | ['a', 'b'] | Failed |
SHA-256 / 8fd45df04fbb206db0c2761991144a41ee4f0867aa5674a71db668c90991aa94
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(chain, hop):
return [hop]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['a'], 'b'), ['a', 'b'])", "check('fixture 2', solve([], 'a'), ['a'])", "check('fixture 3', solve(['a', 'b'], 'c'), ['a', 'b', 'c'])", "check('fixture 4', solve(['a'], 'a'), ['a', 'a'])"]
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 | ['a'] | ['a'] | Passed |
| fixture 3 | ['c'] | ['a', 'b', 'c'] | Failed |
| fixture 4 | ['a'] | ['a', 'a'] | Failed |
| fixture 1 | ['b'] | ['a', 'b'] | Failed |
SHA-256 / d94e33500fab4199e08bed735131ea8be6fdc5f860a3b3cf360c6dd94a29323a
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(chain, hop):
return chain+[hop]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(['a'], 'b'), ['a', 'b'])", "check('fixture 2', solve([], 'a'), ['a'])", "check('fixture 3', solve(['a', 'b'], 'c'), ['a', 'b', 'c'])", "check('fixture 4', solve(['a'], 'a'), ['a', 'a'])"]
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 | ['a'] | ['a'] | Passed |
| fixture 3 | ['a', 'b', 'c'] | ['a', 'b', 'c'] | Passed |
| fixture 4 | ['a', 'a'] | ['a', 'a'] | Passed |
| fixture 1 | ['a', 'b'] | ['a', 'b'] | Passed |
SHA-256 / 7ee23c1d522acf0f547619f7ca84e8d1f0c4daeb96f88ecc7bed71793b40678c
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 2026-09-29T14:38:07.128698+00:00.
Case digest / 6010cb891432cd212d5363524f7d6ecaf746ca53c24bcf82e9e6313095b20a8a