FA-26831 / HTTP ranges / Open access

Preamble bytes before the first delimiter do not form a range part · case 01

Preamble bytes before the first delimiter do not form a range part.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The multipart-client-preamble-not-part decision uses return [preamble]+parts.

THE FAILURE

The multipart-client-preamble-not-part decision uses return [preamble]+parts.

Unsuccessful approach: The partial repair uses return [preamble]+parts if preamble else parts, which still violates the stated contract.

Case contract

Return only explicitly parsed part bodies; preamble is ignored even when nonempty.

Why this case matters

Range responses combine representation identity, conditional requests, framing, and partial-object state.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(preamble, parts):
    return [preamble]+parts
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('multipart-client-preamble-not-part fixture 0', solve("banner"*N,["p"]), ["p"])
check('multipart-client-preamble-not-part fixture 1', solve("",["p"]), ["p"])
check('multipart-client-preamble-not-part fixture 2', solve("banner",[]), [])
check('multipart-client-preamble-not-part fixture 3', solve("",[]), [])
check('multipart-client-preamble-not-part fixture 4', solve("x",["a","b"]), ["a","b"])
check('multipart-client-preamble-not-part fixture 5', solve("x",[""]), [""])
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
multipart-client-preamble-not-part fixture 0	`['banner', 'p']`	`['p']`	Failed
multipart-client-preamble-not-part fixture 1	`['', 'p']`	`['p']`	Failed
multipart-client-preamble-not-part fixture 2	`['banner']`	`[]`	Failed
multipart-client-preamble-not-part fixture 3	`['']`	`[]`	Failed
multipart-client-preamble-not-part fixture 4	`['x', 'a', 'b']`	`['a', 'b']`	Failed
multipart-client-preamble-not-part fixture 5	`['x', '']`	`['']`	Failed

SHA-256 / 084f5b6da971c02e7c866ea4b6c5a3016de0942358ec1309f4e82fd656ea2414

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(preamble, parts):
    return [preamble]+parts if preamble else parts
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('multipart-client-preamble-not-part fixture 0', solve("banner"*N,["p"]), ["p"])
check('multipart-client-preamble-not-part fixture 1', solve("",["p"]), ["p"])
check('multipart-client-preamble-not-part fixture 2', solve("banner",[]), [])
check('multipart-client-preamble-not-part fixture 3', solve("",[]), [])
check('multipart-client-preamble-not-part fixture 4', solve("x",["a","b"]), ["a","b"])
check('multipart-client-preamble-not-part fixture 5', solve("x",[""]), [""])
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
multipart-client-preamble-not-part fixture 0	`['banner', 'p']`	`['p']`	Failed
multipart-client-preamble-not-part fixture 1	`['p']`	`['p']`	Passed
multipart-client-preamble-not-part fixture 2	`['banner']`	`[]`	Failed
multipart-client-preamble-not-part fixture 3	`[]`	`[]`	Passed
multipart-client-preamble-not-part fixture 4	`['x', 'a', 'b']`	`['a', 'b']`	Failed
multipart-client-preamble-not-part fixture 5	`['x', '']`	`['']`	Failed

SHA-256 / 2ccebcd1b0c6df355b3f13a3923ee64b3a288bdcdc7e33220f06783f0ba89380

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 6 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. 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 2026-09-29T14:41:19.424107+00:00.

Case digest / ca1a951afb417c61980ac5aaff754604d27f46941ff3ce03d2205fa9aa5c2f70