FA-26801 / HTTP ranges / Open access
A longer boundary prefix is not mistaken for the chosen delimiter · case 01
A longer boundary prefix is not mistaken for the chosen delimiter.
ROOT CAUSE
The multipart-client-boundary-token-end decision uses return "part" if line.startswith("--"+boundary) else "payload".
VERIFIED REPAIR
Apply the bounded decision exactly: return "close" if line=="--"+boundary+"--" else ("part" if line=="--"+boundary else "payload")
Unsuccessful approach: The partial repair uses return "close" if line.endswith("--") else ("part" if line=="--"+boundary else "payload"), which still violates the stated contract.
Case contract
A delimiter line equals --boundary or --boundary--; lines are already stripped of CRLF. Return part, close, or payload.
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(line, boundary):
return "part" if line.startswith("--"+boundary) else "payload"
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('multipart-client-boundary-token-end fixture 0', solve("--b"+str(N)+"x","b"+str(N)), "payload")
check('multipart-client-boundary-token-end fixture 1', solve("unrelated--","b"), "payload")
check('multipart-client-boundary-token-end fixture 2', solve("--b--","b"), "close")
check('multipart-client-boundary-token-end fixture 3', solve("--b","b"), "part")
check('multipart-client-boundary-token-end fixture 4', solve("","b"), "payload")
check('multipart-client-boundary-token-end fixture 5', solve("--b-x","b"), "payload")
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-boundary-token-end fixture 0 | part | payload | Failed |
| multipart-client-boundary-token-end fixture 1 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 2 | part | close | Failed |
| multipart-client-boundary-token-end fixture 3 | part | part | Passed |
| multipart-client-boundary-token-end fixture 4 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 5 | part | payload | Failed |
SHA-256 / 352b7456195614d6a2db9bfb9cf80a9f95b3b285d944020bad944ba94fe0db10
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(line, boundary):
return "close" if line.endswith("--") else ("part" if line=="--"+boundary else "payload")
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('multipart-client-boundary-token-end fixture 0', solve("--b"+str(N)+"x","b"+str(N)), "payload")
check('multipart-client-boundary-token-end fixture 1', solve("unrelated--","b"), "payload")
check('multipart-client-boundary-token-end fixture 2', solve("--b--","b"), "close")
check('multipart-client-boundary-token-end fixture 3', solve("--b","b"), "part")
check('multipart-client-boundary-token-end fixture 4', solve("","b"), "payload")
check('multipart-client-boundary-token-end fixture 5', solve("--b-x","b"), "payload")
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-boundary-token-end fixture 0 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 1 | close | payload | Failed |
| multipart-client-boundary-token-end fixture 2 | close | close | Passed |
| multipart-client-boundary-token-end fixture 3 | part | part | Passed |
| multipart-client-boundary-token-end fixture 4 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 5 | payload | payload | Passed |
SHA-256 / 8720c05e4e1d92d1fbc2100fbaf96f4f91544aa966b0ef61486ff638b1ee11c9
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(line, boundary):
return "close" if line=="--"+boundary+"--" else ("part" if line=="--"+boundary else "payload")
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('multipart-client-boundary-token-end fixture 0', solve("--b"+str(N)+"x","b"+str(N)), "payload")
check('multipart-client-boundary-token-end fixture 1', solve("unrelated--","b"), "payload")
check('multipart-client-boundary-token-end fixture 2', solve("--b--","b"), "close")
check('multipart-client-boundary-token-end fixture 3', solve("--b","b"), "part")
check('multipart-client-boundary-token-end fixture 4', solve("","b"), "payload")
check('multipart-client-boundary-token-end fixture 5', solve("--b-x","b"), "payload")
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-boundary-token-end fixture 0 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 1 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 2 | close | close | Passed |
| multipart-client-boundary-token-end fixture 3 | part | part | Passed |
| multipart-client-boundary-token-end fixture 4 | payload | payload | Passed |
| multipart-client-boundary-token-end fixture 5 | payload | payload | Passed |
SHA-256 / 72bd7b2d6e3c9b9d87f4cca07a22c07cd8bafce2cc20f19b88d298e31b617af4
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 2026-09-29T14:41:19.323062+00:00.
Case digest / 51867721cd1f3370dd602086e6ab2bb6c1bf25c8f98e14c53a4ce3be0e65f2cd