FA-7206 / Transport flow control / Open access
Send window is minimum of peer and congestion windows · case 01
Send window is minimum of peer and congestion windows.
ROOT CAUSE
The faulty implementation uses `max(0,max(peer,congestion)-flight)` for the send-window-is-minimum-of-peer-and-congestion-windows decision.
VERIFIED REPAIR
Apply the explicit send-window-is-minimum-of-peer-and-congestion-windows contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `min(peer,congestion)` and still violates a separate fixture.
Case contract
Bounded offline decision model: send window is minimum of peer and congestion windows. 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 send-window-is-minimum-of-peer-and-congestion-windows 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(peer, congestion, flight):
return max(0,max(peer,congestion)-flight)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 5, 2), 3)", "check('fixture 2', solve(3, 10, 4), 0)", "check('fixture 3', solve(10, 10, 0), 10)", "check('fixture 4', solve(0, 10, 0), 0)"]
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 | 6 | 0 | Failed |
| fixture 3 | 10 | 10 | Passed |
| fixture 4 | 10 | 0 | Failed |
| fixture 1 | 8 | 3 | Failed |
SHA-256 / 4ec5fe44e1434e5d02759bbfc19b3d6c90b2263ccaa9d28e3df6af680c32cfd4
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(peer, congestion, flight):
return min(peer,congestion)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 5, 2), 3)", "check('fixture 2', solve(3, 10, 4), 0)", "check('fixture 3', solve(10, 10, 0), 10)", "check('fixture 4', solve(0, 10, 0), 0)"]
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 | 3 | 0 | Failed |
| fixture 3 | 10 | 10 | Passed |
| fixture 4 | 0 | 0 | Passed |
| fixture 1 | 5 | 3 | Failed |
SHA-256 / 613125f8a16fe331a505e954b0795c0f0957e293e5e3dba33613488937322e98
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(peer, congestion, flight):
return max(0,min(peer,congestion)-flight)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 5, 2), 3)", "check('fixture 2', solve(3, 10, 4), 0)", "check('fixture 3', solve(10, 10, 0), 10)", "check('fixture 4', solve(0, 10, 0), 0)"]
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 | 0 | 0 | Passed |
| fixture 3 | 10 | 10 | Passed |
| fixture 4 | 0 | 0 | Passed |
| fixture 1 | 3 | 3 | Passed |
SHA-256 / e5c752f903245c17b2754a3a1330f2b92fc7fc81bae53665bb95c565deca2040
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 2026-09-29T14:38:09.396561+00:00.
Case digest / 1ecf385bef23756cd6f2237efea2c32d9eb6a2880f26db8e8f38609cee165d30