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FA-26601 / HTTP ranges / Open access

Each multipart range begins with its own absolute seek · case 01

Each multipart range begins with its own absolute seek.

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

ROOT CAUSE

The stream-seek-before-read decision uses return [["read",length]].

VERIFIED REPAIR

Apply the bounded decision exactly: return ([] if current==target else [["seek",target]])+[["read",length]]

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

Case contract

Return ordered abstract I/O operations: seek target if cursor differs, then read length even for zero length; equal cursor avoids redundant seek.

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

SHA-256 / eeb6f52417abdb5b6e88ac905a74ec69651ece00c050bf6989dc20fac2c285dd

2 / The unsuccessful fix

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

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

SHA-256 / a8e740235c674195d14e53ecb6fca72c9d9956dcfbf96c4e5ee4e934f2195712

3 / The verified repair

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

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

SHA-256 / d619ac6f383ffa3a95569cae004dba8fe05e352a8be1ee62313191cfcceab558

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 2026-09-29T14:41:17.521120+00:00.

Case digest / a52e7a4b01a07e58cb970d5244bd2b2b26bc3f6c822879d8490d02e284a83ac9