FA-26401 / HTTP ranges / Open access
An encoded partial response carries its own representation validator · case 01
An encoded partial response carries its own representation validator.
ROOT CAUSE
The variant-etag-selection decision uses return tags["identity"].
VERIFIED REPAIR
Apply the bounded decision exactly: return tags[coding]
Unsuccessful approach: The partial repair uses return tags[coding] or tags["identity"], which still violates the stated contract.
Case contract
tags contains identity and gzip strings; return the selected tag, with no truthiness fallback for an intentionally empty opaque value.
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(coding, tags):
return tags["identity"]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('variant-etag-selection fixture 0', solve("gzip",{"identity":"i","gzip":"g"+str(N)}), "g"+str(N))
check('variant-etag-selection fixture 1', solve("gzip",{"identity":"i","gzip":""}), "")
check('variant-etag-selection fixture 2', solve("identity",{"identity":"i","gzip":"g"}), "i")
check('variant-etag-selection fixture 3', solve("gzip",{"identity":"same","gzip":"same"}), "same")
check('variant-etag-selection fixture 4', solve("identity",{"identity":"","gzip":"g"}), "")
check('variant-etag-selection fixture 5', solve("gzip",{"identity":"a","gzip":"b"}), "b")
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 |
|---|---|---|---|
| variant-etag-selection fixture 0 | i | g1 | Failed |
| variant-etag-selection fixture 1 | i | | Failed |
| variant-etag-selection fixture 2 | i | i | Passed |
| variant-etag-selection fixture 3 | same | same | Passed |
| variant-etag-selection fixture 4 | | | Passed |
| variant-etag-selection fixture 5 | a | b | Failed |
SHA-256 / 5b2052ff59aab6464b32b9fc0ef43f1af22a1956ca8b9b68e44f9414b0750a12
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(coding, tags):
return tags[coding] or tags["identity"]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('variant-etag-selection fixture 0', solve("gzip",{"identity":"i","gzip":"g"+str(N)}), "g"+str(N))
check('variant-etag-selection fixture 1', solve("gzip",{"identity":"i","gzip":""}), "")
check('variant-etag-selection fixture 2', solve("identity",{"identity":"i","gzip":"g"}), "i")
check('variant-etag-selection fixture 3', solve("gzip",{"identity":"same","gzip":"same"}), "same")
check('variant-etag-selection fixture 4', solve("identity",{"identity":"","gzip":"g"}), "")
check('variant-etag-selection fixture 5', solve("gzip",{"identity":"a","gzip":"b"}), "b")
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 |
|---|---|---|---|
| variant-etag-selection fixture 0 | g1 | g1 | Passed |
| variant-etag-selection fixture 1 | i | | Failed |
| variant-etag-selection fixture 2 | i | i | Passed |
| variant-etag-selection fixture 3 | same | same | Passed |
| variant-etag-selection fixture 4 | | | Passed |
| variant-etag-selection fixture 5 | b | b | Passed |
SHA-256 / 429a8b414bdc970ecb966ba8a2032bc62de1bb537e4a6591bf667acf73f3ea30
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(coding, tags):
return tags[coding]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('variant-etag-selection fixture 0', solve("gzip",{"identity":"i","gzip":"g"+str(N)}), "g"+str(N))
check('variant-etag-selection fixture 1', solve("gzip",{"identity":"i","gzip":""}), "")
check('variant-etag-selection fixture 2', solve("identity",{"identity":"i","gzip":"g"}), "i")
check('variant-etag-selection fixture 3', solve("gzip",{"identity":"same","gzip":"same"}), "same")
check('variant-etag-selection fixture 4', solve("identity",{"identity":"","gzip":"g"}), "")
check('variant-etag-selection fixture 5', solve("gzip",{"identity":"a","gzip":"b"}), "b")
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 |
|---|---|---|---|
| variant-etag-selection fixture 0 | g1 | g1 | Passed |
| variant-etag-selection fixture 1 | | | Passed |
| variant-etag-selection fixture 2 | i | i | Passed |
| variant-etag-selection fixture 3 | same | same | Passed |
| variant-etag-selection fixture 4 | | | Passed |
| variant-etag-selection fixture 5 | b | b | Passed |
SHA-256 / 14b6bbfcc278e4ba4659b48b7c38aeb3435ce986022e52902355a38c1931a385
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 2026-09-29T14:41:15.680587+00:00.
Case digest / 29803c1ccd9f7cf67a20d59a6208c38ee1e90aac1c05df8f14c4cdcafb045f93