FA-7291 / Transport flow control / Open access
Send buffer removes only cumulatively acknowledged segments · case 01
Send buffer removes only cumulatively acknowledged segments.
ROOT CAUSE
The faulty implementation uses `[(s,e) for s,e in segments if s > ack]` for the send-buffer-removes-only-cumulatively-acknowledged-segments decision.
VERIFIED REPAIR
Apply the explicit send-buffer-removes-only-cumulatively-acknowledged-segments contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `[(s,e) for s,e in segments if e >= ack]` and still violates a separate fixture.
Case contract
Bounded offline decision model: send buffer removes only cumulatively acknowledged segments. 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-buffer-removes-only-cumulatively-acknowledged-segments 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(segments, ack):
return [(s,e) for s,e in segments if s > ack]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve([(0, 5), (5, 10)], 5), [(5, 10)])", "check('fixture 2', solve([(0, 5)], 3), [(0, 5)])", "check('fixture 3', solve([], 0), [])", "check('fixture 4', solve([(0, 5)], 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 | [] | [[0, 5]] | Failed |
| fixture 3 | [] | [] | Passed |
| fixture 4 | [] | [] | Passed |
| fixture 1 | [] | [[5, 10]] | Failed |
SHA-256 / a73216f82b2b4cb078903662f1eee0468d2ab666a95813b7a93133260632ee87
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(segments, ack):
return [(s,e) for s,e in segments if e >= ack]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve([(0, 5), (5, 10)], 5), [(5, 10)])", "check('fixture 2', solve([(0, 5)], 3), [(0, 5)])", "check('fixture 3', solve([], 0), [])", "check('fixture 4', solve([(0, 5)], 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 | [[0, 5]] | [[0, 5]] | Passed |
| fixture 3 | [] | [] | Passed |
| fixture 4 | [[0, 5]] | [] | Failed |
| fixture 1 | [[0, 5], [5, 10]] | [[5, 10]] | Failed |
SHA-256 / b9d0cf4721a3f7180785573eaa1ad484650ea64c334c6af3eb010efbd2807659
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(segments, ack):
return [(s,e) for s,e in segments if e > ack]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve([(0, 5), (5, 10)], 5), [(5, 10)])", "check('fixture 2', solve([(0, 5)], 3), [(0, 5)])", "check('fixture 3', solve([], 0), [])", "check('fixture 4', solve([(0, 5)], 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 | [[0, 5]] | [[0, 5]] | Passed |
| fixture 3 | [] | [] | Passed |
| fixture 4 | [] | [] | Passed |
| fixture 1 | [[5, 10]] | [[5, 10]] | Passed |
SHA-256 / 239a1ad01e2382a9205c0791a256a607c534f5addd86d8885542f0d38805efa0
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 2026-09-29T14:38:10.350041+00:00.
Case digest / 3a28debbea1d208ebc5ada10b1ec3d125fc10c587cb551240d80d130bdd56706