FA-3686 / Binary formats / Open access

An odd trailing byte is silently dropped from a word array · case 01

An odd trailing byte is silently dropped from a word array.

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

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Decode consecutive big-endian 16-bit words; reject odd byte length.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Decode consecutive big-endian 16-bit words; reject odd byte length.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Decode consecutive big-endian 16-bit words; reject odd byte length.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[i]*256+x[i+1] for i in range(0,len(x)-1,2)]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve([1]), None)
check('boundary 2', solve([0, 1, 0, 2]), [1, 2])
check('boundary 3', solve([]), [])
check('boundary 4', solve([255, 0]), [65280])
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
boundary 1	`[]`	`None`	Failed
boundary 2	`[1, 2]`	`[1, 2]`	Passed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[65280]`	`[65280]`	Passed

SHA-256 / ab3a6f4458a17ab355545e56111cde3e2d030707d45148dc576f17801fc603cf

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[i]+x[i+1]*256 for i in range(0,len(x)-1,2)]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve([1]), None)
check('boundary 2', solve([0, 1, 0, 2]), [1, 2])
check('boundary 3', solve([]), [])
check('boundary 4', solve([255, 0]), [65280])
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
boundary 1	`[]`	`None`	Failed
boundary 2	`[256, 512]`	`[1, 2]`	Failed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[255]`	`[65280]`	Failed

SHA-256 / ecc25e7977fc87786ad06595bf9dd8311e8dd912b1657f4765497a24ca4c74fa

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return None if len(x)%2 else [x[i]*256+x[i+1] for i in range(0,len(x),2)]
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve([1]), None)
check('boundary 2', solve([0, 1, 0, 2]), [1, 2])
check('boundary 3', solve([]), [])
check('boundary 4', solve([255, 0]), [65280])
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
boundary 1	`None`	`None`	Passed
boundary 2	`[1, 2]`	`[1, 2]`	Passed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[65280]`	`[65280]`	Passed

SHA-256 / 8c7a146fd2a0af4e8206037d802bbc345fdf3ff0cec90057cb07fe2072fd1a6d

Verification & scope

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 2026-09-29T14:37:29.511002+00:00.

Case digest / e7d25e0297204adb766c681a49d662880eafb4a42bf0b4ae45911bc2bbb4d9e9