FA-26541 / HTTP ranges / Open access

A short socket write preserves the unsent byte suffix · case 01

A short socket write preserves the unsent byte suffix.

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

ROOT CAUSE

The stream-short-write-resume decision uses return "".

VERIFIED REPAIR

Apply the bounded decision exactly: return pending[accepted:]

Unsuccessful approach: The partial repair uses return pending[accepted:] if accepted else "", which still violates the stated contract.

Case contract

accepted is a valid integer count in [0,len(pending)]. Return remaining ASCII bytes after only that count was accepted.

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(pending, accepted):
    return ""
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-short-write-resume fixture 0', solve("abc"*N,N), ("abc"*N)[N:])
check('stream-short-write-resume fixture 1', solve("abc",0), "abc")
check('stream-short-write-resume fixture 2', solve("abc",3), "")
check('stream-short-write-resume fixture 3', solve("",0), "")
check('stream-short-write-resume fixture 4', solve("x",1), "")
check('stream-short-write-resume fixture 5', solve("abcd",2), "cd")
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	Expected	Outcome
stream-short-write-resume fixture 0	`bc`	Failed
stream-short-write-resume fixture 1	`abc`	Failed
stream-short-write-resume fixture 2		Passed
stream-short-write-resume fixture 3		Passed
stream-short-write-resume fixture 4		Passed
stream-short-write-resume fixture 5	`cd`	Failed

SHA-256 / ac514114da33c57d75bbcc39cb766855c161633fb347374642b2f9d6f31b55d4

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(pending, accepted):
    return pending[accepted:] if accepted else ""
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-short-write-resume fixture 0', solve("abc"*N,N), ("abc"*N)[N:])
check('stream-short-write-resume fixture 1', solve("abc",0), "abc")
check('stream-short-write-resume fixture 2', solve("abc",3), "")
check('stream-short-write-resume fixture 3', solve("",0), "")
check('stream-short-write-resume fixture 4', solve("x",1), "")
check('stream-short-write-resume fixture 5', solve("abcd",2), "cd")
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
stream-short-write-resume fixture 0	`bc`	`bc`	Passed
stream-short-write-resume fixture 1		`abc`	Failed
stream-short-write-resume fixture 2			Passed
stream-short-write-resume fixture 3			Passed
stream-short-write-resume fixture 4			Passed
stream-short-write-resume fixture 5	`cd`	`cd`	Passed

SHA-256 / 0ffbb15fa5decfa725df4625dfda456573706d080929989de4f2f2d6e358a286

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(pending, accepted):
    return pending[accepted:]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-short-write-resume fixture 0', solve("abc"*N,N), ("abc"*N)[N:])
check('stream-short-write-resume fixture 1', solve("abc",0), "abc")
check('stream-short-write-resume fixture 2', solve("abc",3), "")
check('stream-short-write-resume fixture 3', solve("",0), "")
check('stream-short-write-resume fixture 4', solve("x",1), "")
check('stream-short-write-resume fixture 5', solve("abcd",2), "cd")
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
stream-short-write-resume fixture 0	`bc`	`bc`	Passed
stream-short-write-resume fixture 1	`abc`	`abc`	Passed
stream-short-write-resume fixture 2			Passed
stream-short-write-resume fixture 3			Passed
stream-short-write-resume fixture 4			Passed
stream-short-write-resume fixture 5	`cd`	`cd`	Passed

SHA-256 / 42ec9089dbdbbeed4054a6707c507e83a0923e608d31aaeb4fc1f19146e2fced

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 2026-09-29T14:41:16.906514+00:00.

Case digest / 0b90ec7cf24c4f3309f96c453b19fc5aba14ad858a9a6a95fc616d799f205387