FA-6581 / HTTP semantics / Open access

HEAD suppresses a representation body while retaining its length · case 01

HEAD suppresses a representation body while retaining its length.

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

ROOT CAUSE

The faulty implementation uses `body` for the head-body decision.

VERIFIED REPAIR

Apply the explicit head-body contract, including the tested boundary and negative cases.

Unsuccessful approach: The attempted repair uses `'' if method in ('HEAD', 'GET') else body` and still violates a separate fixture.

Case contract

HEAD suppresses a representation body while retaining its length: return the result specified by the explicit input/output boundary fixtures.

Why this case matters

This deterministic http semantics model isolates the head-body 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(method, body):
    return body
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('HEAD', 'abc'), '')", "check('fixture 2', solve('GET', 'abc'), 'abc')", "check('fixture 3', solve('POST', ''), '')", "check('fixture 4', solve('POST', 'a'), 'a')"]
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	`abc`	`abc`	Passed
fixture 3			Passed
fixture 4	`a`	`a`	Passed
fixture 1	`abc`		Failed

SHA-256 / 12039fd9518f89179e18cd2c98e0127499d214eee74ae0c85a26a472cc1d31f7

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(method, body):
    return '' if method in ('HEAD', 'GET') else body
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('HEAD', 'abc'), '')", "check('fixture 2', solve('GET', 'abc'), 'abc')", "check('fixture 3', solve('POST', ''), '')", "check('fixture 4', solve('POST', 'a'), 'a')"]
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		`abc`	Failed
fixture 3			Passed
fixture 4	`a`	`a`	Passed
fixture 1			Passed

SHA-256 / 2a733fc804068363f79661c26ff89e50f419ed4bd1044f351b80284675b7d601

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(method, body):
    return '' if method == 'HEAD' else body
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_fixtures = ["check('fixture 1', solve('HEAD', 'abc'), '')", "check('fixture 2', solve('GET', 'abc'), 'abc')", "check('fixture 3', solve('POST', ''), '')", "check('fixture 4', solve('POST', 'a'), 'a')"]
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	`abc`	`abc`	Passed
fixture 3			Passed
fixture 4	`a`	`a`	Passed
fixture 1			Passed

SHA-256 / 2bad5f6385d9c1d9a8f844e32f15970ddc1f7dd63095c80bdeadaeacfff91c94

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 2026-09-29T14:38:03.384969+00:00.

Case digest / 0fce7294322cb8433b479ddec0b46f4475f7d05d4ccac312f23f437bea4248c7