FAILURE MAP
← Case archive

FA-26606 / HTTP ranges / Open access

Failed absolute seek prevents a range read from the stale cursor · case 01

Failed absolute seek prevents a range read from the stale cursor.

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

ROOT CAUSE

The stream-seek-failure-stops-read decision uses return ["read",target,length].

VERIFIED REPAIR

Apply the bounded decision exactly: return ["read",target,length] if seek_ok else ["abort"]

Unsuccessful approach: The partial repair uses return ["read",target if seek_ok else 0,length], which still violates the stated contract.

Case contract

A failed seek yields only an abort operation. Successful seek schedules [read,target,length].

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(seek_ok, target, length):
    return ["read",target,length]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-seek-failure-stops-read fixture 0', solve(False,N,N), ["abort"])
check('stream-seek-failure-stops-read fixture 1', solve(False,0,N), ["abort"])
check('stream-seek-failure-stops-read fixture 2', solve(True,N,N), ["read",N,N])
check('stream-seek-failure-stops-read fixture 3', solve(True,0,0), ["read",0,0])
check('stream-seek-failure-stops-read fixture 4', solve(True,2*N,1), ["read",2*N,1])
check('stream-seek-failure-stops-read fixture 5', solve(False,N,0), ["abort"])
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 fixtureActualExpectedOutcome
stream-seek-failure-stops-read fixture 0['read', 1, 1]['abort']Failed
stream-seek-failure-stops-read fixture 1['read', 0, 1]['abort']Failed
stream-seek-failure-stops-read fixture 2['read', 1, 1]['read', 1, 1]Passed
stream-seek-failure-stops-read fixture 3['read', 0, 0]['read', 0, 0]Passed
stream-seek-failure-stops-read fixture 4['read', 2, 1]['read', 2, 1]Passed
stream-seek-failure-stops-read fixture 5['read', 1, 0]['abort']Failed

SHA-256 / 677883184c921c88a2316093c3ad5bf6dcbc1432a9731ba024f8e659f26953b3

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(seek_ok, target, length):
    return ["read",target if seek_ok else 0,length]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-seek-failure-stops-read fixture 0', solve(False,N,N), ["abort"])
check('stream-seek-failure-stops-read fixture 1', solve(False,0,N), ["abort"])
check('stream-seek-failure-stops-read fixture 2', solve(True,N,N), ["read",N,N])
check('stream-seek-failure-stops-read fixture 3', solve(True,0,0), ["read",0,0])
check('stream-seek-failure-stops-read fixture 4', solve(True,2*N,1), ["read",2*N,1])
check('stream-seek-failure-stops-read fixture 5', solve(False,N,0), ["abort"])
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 fixtureActualExpectedOutcome
stream-seek-failure-stops-read fixture 0['read', 0, 1]['abort']Failed
stream-seek-failure-stops-read fixture 1['read', 0, 1]['abort']Failed
stream-seek-failure-stops-read fixture 2['read', 1, 1]['read', 1, 1]Passed
stream-seek-failure-stops-read fixture 3['read', 0, 0]['read', 0, 0]Passed
stream-seek-failure-stops-read fixture 4['read', 2, 1]['read', 2, 1]Passed
stream-seek-failure-stops-read fixture 5['read', 0, 0]['abort']Failed

SHA-256 / 354efff5a742cc50d82acb39370324067a86df37f997930426a2afaf43dbb089

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(seek_ok, target, length):
    return ["read",target,length] if seek_ok else ["abort"]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-seek-failure-stops-read fixture 0', solve(False,N,N), ["abort"])
check('stream-seek-failure-stops-read fixture 1', solve(False,0,N), ["abort"])
check('stream-seek-failure-stops-read fixture 2', solve(True,N,N), ["read",N,N])
check('stream-seek-failure-stops-read fixture 3', solve(True,0,0), ["read",0,0])
check('stream-seek-failure-stops-read fixture 4', solve(True,2*N,1), ["read",2*N,1])
check('stream-seek-failure-stops-read fixture 5', solve(False,N,0), ["abort"])
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 fixtureActualExpectedOutcome
stream-seek-failure-stops-read fixture 0['abort']['abort']Passed
stream-seek-failure-stops-read fixture 1['abort']['abort']Passed
stream-seek-failure-stops-read fixture 2['read', 1, 1]['read', 1, 1]Passed
stream-seek-failure-stops-read fixture 3['read', 0, 0]['read', 0, 0]Passed
stream-seek-failure-stops-read fixture 4['read', 2, 1]['read', 2, 1]Passed
stream-seek-failure-stops-read fixture 5['abort']['abort']Passed

SHA-256 / 91fcc29971ee16c2144cfe0b7cf1111b43a460a20bc33ed8bdd152f8207957dc

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 2026-09-29T14:41:17.531036+00:00.

Case digest / 72210dba7e2d19d5dbdb7506cfca92998ddb1b2be868cea46a9833295b19b6ea