FA-3656 / Binary formats / Open access

Varint continuation bits contribute to the value · case 01

Varint continuation bits contribute to the value.

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 exactly one complete unsigned little-endian base-128 varint, rejecting missing terminator or trailing bytes.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Decode exactly one complete unsigned little-endian base-128 varint, rejecting missing terminator or trailing bytes.

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

Case contract

Decode exactly one complete unsigned little-endian base-128 varint, rejecting missing terminator or trailing bytes.

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 sum(v<<(7*i) for i,v in enumerate(x))
    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([129, 1]), 129)
check('boundary 2', solve([128]), None)
check('boundary 3', solve([1, 0]), None)
check('boundary 4', solve([0]), 0)
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	`257`	`129`	Failed
boundary 2	`128`	`None`	Failed
boundary 3	`1`	`None`	Failed
boundary 4	`0`	`0`	Passed

SHA-256 / e9124b187154bb3e965a1bef3af532e1a4efabd56e298edb7a27c890874803bd

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 sum((v&127)<<(7*i) for i,v in enumerate(x))
    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([129, 1]), 129)
check('boundary 2', solve([128]), None)
check('boundary 3', solve([1, 0]), None)
check('boundary 4', solve([0]), 0)
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	`129`	`129`	Passed
boundary 2	`0`	`None`	Failed
boundary 3	`1`	`None`	Failed
boundary 4	`0`	`0`	Passed

SHA-256 / 76005923506954296201d27af9efc298a3405e66819d156364c5c7380d1151eb

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 not x or x[-1]&128 or any(not v&128 for v in x[:-1]) else sum((v&127)<<(7*i) for i,v in enumerate(x))
    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([129, 1]), 129)
check('boundary 2', solve([128]), None)
check('boundary 3', solve([1, 0]), None)
check('boundary 4', solve([0]), 0)
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	`129`	`129`	Passed
boundary 2	`None`	`None`	Passed
boundary 3	`None`	`None`	Passed
boundary 4	`0`	`0`	Passed

SHA-256 / 72335ada86c5ad89047c37a43e533efcc58d541e2c009566e8f9ab86c8385d2e

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 2026-09-29T14:37:29.116002+00:00.

Case digest / 953cb1801292d967f19f8fa96b5fbb29f475697fc1e968e2dcf8f05567f05e1d