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FA-7266 / Transport flow control / Open access

Retransmission timeout doubles with upper cap · case 01

Retransmission timeout doubles with upper cap.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The faulty implementation uses `2*rto` for the retransmission-timeout-doubles-with-upper-cap decision.

VERIFIED REPAIR

Apply the explicit retransmission-timeout-doubles-with-upper-cap contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `max(2*rto,cap)` and still violates a separate fixture.

Case contract

Bounded offline decision model: retransmission timeout doubles with upper cap. 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 retransmission-timeout-doubles-with-upper-cap 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(rto, cap):
    return 2*rto
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(8, 10), 10)", "check('fixture 2', solve(2, 10), 4)", "check('fixture 3', solve(0, 10), 0)", "check('fixture 4', solve(5, 10), 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 fixtureActualExpectedOutcome
fixture 244Passed
fixture 300Passed
fixture 41010Passed
fixture 11610Failed

SHA-256 / 0b7f1110ca09af5dd1ef5d4a2580b280751ab2859e3898eb78c32e0aeb2657c6

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(rto, cap):
    return max(2*rto,cap)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(8, 10), 10)", "check('fixture 2', solve(2, 10), 4)", "check('fixture 3', solve(0, 10), 0)", "check('fixture 4', solve(5, 10), 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 fixtureActualExpectedOutcome
fixture 2104Failed
fixture 3100Failed
fixture 41010Passed
fixture 11610Failed

SHA-256 / f28603eb4453caf30cbfd47163d60be8c30b105b5f603c15d05a3da9eab3d3cf

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(rto, cap):
    return min(2*rto,cap)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve(8, 10), 10)", "check('fixture 2', solve(2, 10), 4)", "check('fixture 3', solve(0, 10), 0)", "check('fixture 4', solve(5, 10), 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 fixtureActualExpectedOutcome
fixture 244Passed
fixture 300Passed
fixture 41010Passed
fixture 11010Passed

SHA-256 / 10442c42b909f53efedc5f531d753c395339659e15317fc4ff04b512b69db8a4

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 2026-09-29T14:38:09.942197+00:00.

Case digest / bdc295f6e0efad20f4bffee6b9154118c3073c33aeb07913f256e63be4e2a815