FA-7211 / Transport flow control / Open access
Acknowledged byte count excludes already acknowledged prefix · case 01
Acknowledged byte count excludes already acknowledged prefix.
ROOT CAUSE
The faulty implementation uses `ack` for the acknowledged-byte-count-excludes-already-acknowledged-prefix decision.
VERIFIED REPAIR
Apply the explicit acknowledged-byte-count-excludes-already-acknowledged-prefix contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `max(0,ack-previous)` and still violates a separate fixture.
Case contract
Given ack, previous, sent, acknowledged byte count excludes already acknowledged prefix. Return the protocol decision or transformed value; fields are validated and fixtures state boundary outcomes.
Why this case matters
This deterministic transport flow control model isolates the acknowledged-byte-count-excludes-already-acknowledged-prefix 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(ack, previous, sent):
return ack
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 8, 12), 2)", "check('fixture 2', solve(7, 8, 12), 0)", "check('fixture 3', solve(13, 8, 12), None)", "check('fixture 4', solve(8, 8, 12), 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 | 7 | 0 | Failed |
| fixture 3 | 13 | None | Failed |
| fixture 4 | 8 | 0 | Failed |
| fixture 1 | 10 | 2 | Failed |
SHA-256 / 358c5a5324140fc76e0aef102d8e5842eff776e831b4832d7fbf06ff61edd39c
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(ack, previous, sent):
return max(0,ack-previous)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 8, 12), 2)", "check('fixture 2', solve(7, 8, 12), 0)", "check('fixture 3', solve(13, 8, 12), None)", "check('fixture 4', solve(8, 8, 12), 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 | 5 | None | Failed |
| fixture 4 | 0 | 0 | Passed |
| fixture 1 | 2 | 2 | Passed |
SHA-256 / 15aec4e6164efa855b27209449d5f31b48e04cd9e82373a27c7be7fa6305ed37
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(ack, previous, sent):
return None if ack > sent else max(0,ack-previous)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(10, 8, 12), 2)", "check('fixture 2', solve(7, 8, 12), 0)", "check('fixture 3', solve(13, 8, 12), None)", "check('fixture 4', solve(8, 8, 12), 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 | None | None | Passed |
| fixture 4 | 0 | 0 | Passed |
| fixture 1 | 2 | 2 | Passed |
SHA-256 / e3dd3c1012d6b0ae169aad3567a1ef5f2394bbf7ed9bedef80bbf1e1a76f4453
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 2026-09-29T14:38:09.412956+00:00.
Case digest / 22d392e51ad15b6d9e0480e9b32d39f2444e70c1bfda30fba0829e97bede2e9d