FA-7301 / Transport flow control / Open access
Sack reports out of order blocks without changing cumulative ack · case 01
Sack reports out of order blocks without changing cumulative ack.
ROOT CAUSE
The faulty implementation uses `blocks` for the sack-reports-out-of-order-blocks-without-changing-cumulative-ack decision.
VERIFIED REPAIR
Apply the explicit sack-reports-out-of-order-blocks-without-changing-cumulative-ack contract, including the tested boundary and negative cases.
Unsuccessful approach: The attempted repair uses `[(s,e) for s,e in blocks if e > next_]` and still violates a separate fixture.
Case contract
Bounded offline decision model: sack reports out of order blocks without changing cumulative ack. 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 sack-reports-out-of-order-blocks-without-changing-cumulative-ack 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(blocks, next_):
return blocks
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve([(0, 5), (8, 10)], 5), [(8, 10)])", "check('fixture 2', solve([(3, 8)], 5), [])", "check('fixture 3', solve([], 5), [])", "check('fixture 4', solve([(9, 10)], 5), [(9, 10)])"]
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, 8]] | [] | Failed |
| fixture 3 | [] | [] | Passed |
| fixture 4 | [[9, 10]] | [[9, 10]] | Passed |
| fixture 1 | [[0, 5], [8, 10]] | [[8, 10]] | Failed |
SHA-256 / f54bebb0a7575c6cbf95a0285e9eb6a4e2ed11c4883a18988228d7b1cb07e6a4
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(blocks, next_):
return [(s,e) for s,e in blocks if e > next_]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve([(0, 5), (8, 10)], 5), [(8, 10)])", "check('fixture 2', solve([(3, 8)], 5), [])", "check('fixture 3', solve([], 5), [])", "check('fixture 4', solve([(9, 10)], 5), [(9, 10)])"]
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, 8]] | [] | Failed |
| fixture 3 | [] | [] | Passed |
| fixture 4 | [[9, 10]] | [[9, 10]] | Passed |
| fixture 1 | [[8, 10]] | [[8, 10]] | Passed |
SHA-256 / 7123099455b09234be11deeaa4f2aa2321fbb04a100a62981f1e79a52c32524c
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(blocks, next_):
return [(s,e) for s,e in blocks if s > next_]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve([(0, 5), (8, 10)], 5), [(8, 10)])", "check('fixture 2', solve([(3, 8)], 5), [])", "check('fixture 3', solve([], 5), [])", "check('fixture 4', solve([(9, 10)], 5), [(9, 10)])"]
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 | [] | [] | Passed |
| fixture 3 | [] | [] | Passed |
| fixture 4 | [[9, 10]] | [[9, 10]] | Passed |
| fixture 1 | [[8, 10]] | [[8, 10]] | Passed |
SHA-256 / fc333ee01f792b9e8393b465eeb927c12fba1aca89048e3307e3f957a5b8abf8
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 2026-09-29T14:38:10.453232+00:00.
Case digest / faff9a156f3e3e2da19537c4bd10c152919fcb8b9e85766dfb4c51364e720637