FA-7296 / Transport flow control / Open access
Out of order receive does not advance cumulative ack over gap · case 01
Out of order receive does not advance cumulative ack over gap.
ROOT CAUSE
The faulty implementation uses `max(next_,end)` for the out-of-order-receive-does-not-advance-cumulative-ack-over-gap decision.
VERIFIED REPAIR
Apply the explicit out-of-order-receive-does-not-advance-cumulative-ack-over-gap contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `end if start == next_ else next_` and still violates a separate fixture.
Case contract
Bounded offline decision model: out of order receive does not advance cumulative ack over gap. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.
Why this case matters
This deterministic transport flow control model isolates the out-of-order-receive-does-not-advance-cumulative-ack-over-gap 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(next_, start, end):
return max(next_,end)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(5, 8, 10), 5)", "check('fixture 2', solve(5, 3, 8), 8)", "check('fixture 3', solve(5, 5, 8), 8)", "check('fixture 4', solve(5, 0, 3), 5)"]
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 | 8 | 8 | Passed |
| fixture 3 | 8 | 8 | Passed |
| fixture 4 | 5 | 5 | Passed |
| fixture 1 | 10 | 5 | Failed |
SHA-256 / fc2fde3815c58935ef8ec64dd459845fb6d981416eef357f08068227dee30a75
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(next_, start, end):
return end if start == next_ else next_
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(5, 8, 10), 5)", "check('fixture 2', solve(5, 3, 8), 8)", "check('fixture 3', solve(5, 5, 8), 8)", "check('fixture 4', solve(5, 0, 3), 5)"]
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 | 5 | 8 | Failed |
| fixture 3 | 8 | 8 | Passed |
| fixture 4 | 5 | 5 | Passed |
| fixture 1 | 5 | 5 | Passed |
SHA-256 / 1f0adf17caa3014233cf34bda74ec9d4035a79410ca9e70456e5391613717dc8
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(next_, start, end):
return end if start <= next_ < end else next_
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(5, 8, 10), 5)", "check('fixture 2', solve(5, 3, 8), 8)", "check('fixture 3', solve(5, 5, 8), 8)", "check('fixture 4', solve(5, 0, 3), 5)"]
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 | 8 | 8 | Passed |
| fixture 3 | 8 | 8 | Passed |
| fixture 4 | 5 | 5 | Passed |
| fixture 1 | 5 | 5 | Passed |
SHA-256 / d2ef6d80944f57c2b2bc18a43f173ed2db3d185f66913e753e1c05f6c1a44298
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 2026-09-29T14:38:10.408451+00:00.
Case digest / 5dd6de1a4a7b6647ac23bdbd84e85bfc553edba5222997d4f650c7d4263f2d61