{"abstract":"If unmodified since is ignored when if match present.","category":"HTTP caching","checks":4,"contract":"Given has_match, tag_ok, modified, since, if unmodified since is ignored when if match present. Return the protocol decision or transformed value; fields are validated and fixtures state boundary outcomes.","evaluation_group":"xh-if-unmodified-since-is-ignored-when-if-match-present","failed_approach":"The attempted repair uses `tag_ok if has_match else since is None or modified < since` and still violates a separate fixture.","family":"xh-if-unmodified-since-is-ignored-when-if-match-present","id":"FA-6811","implementations":{"attempt":{"sha256":"3bf9c6a11494c3d4ffde9ab973d75f86f42ff88fc5b508908e2ef4a4f8116245","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(has_match, tag_ok, modified, since):\n    return tag_ok if has_match else since is None or modified < since\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(True, True, 20, 10), True)\", \"check('fixture 2', solve(True, False, 0, 10), False)\", \"check('fixture 3', solve(False, False, 10, 10), True)\", \"check('fixture 4', solve(False, False, 20, None), True)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"58db0310e48c61cfcf5f704b6df71851850ed9463e371b6bb4a970c81c701634","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(has_match, tag_ok, modified, since):\n    return tag_ok and (since is None or modified <= since)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(True, True, 20, 10), True)\", \"check('fixture 2', solve(True, False, 0, 10), False)\", \"check('fixture 3', solve(False, False, 10, 10), True)\", \"check('fixture 4', solve(False, False, 20, None), True)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"c53acbfa3443f74b97f6b3320b9e089e4f966dfff580a089cb2e2d8c4d2cc193","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(has_match, tag_ok, modified, since):\n    return tag_ok if has_match else since is None or modified <= since\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(True, True, 20, 10), True)\", \"check('fixture 2', solve(True, False, 0, 10), False)\", \"check('fixture 3', solve(False, False, 10, 10), True)\", \"check('fixture 4', solve(False, False, 20, None), True)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"xh-if-unmodified-since-is-ignored-when-if-match-present","generated_at":"2026-09-29T14:38:05.487399+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic http caching model isolates the if-unmodified-since-is-ignored-when-if-match-present policy at a network component boundary.","repair":"Apply the explicit if-unmodified-since-is-ignored-when-if-match-present contract, including the tested boundary and negative cases.","root_cause":"The faulty implementation uses `tag_ok and (since is None or modified <= since)` for the if-unmodified-since-is-ignored-when-if-match-present decision.","sha256":"550925707ebdd026565c212dd62671a90f047262ad3d980dbd4b2fa633c35136","title":"If unmodified since is ignored when if match present · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":43.839,"exit_code":1,"observations":[{"actual":false,"check":"fixture 2","expected":false,"passed":true},{"actual":false,"check":"fixture 3","expected":true,"passed":false},{"actual":true,"check":"fixture 4","expected":true,"passed":true},{"actual":true,"check":"fixture 1","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":39.37,"exit_code":1,"observations":[{"actual":false,"check":"fixture 2","expected":false,"passed":true},{"actual":false,"check":"fixture 3","expected":true,"passed":false},{"actual":false,"check":"fixture 4","expected":true,"passed":false},{"actual":false,"check":"fixture 1","expected":true,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"fixture 1\", \"actual\": false, \"expected\": true, \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":73.871,"exit_code":0,"observations":[{"actual":false,"check":"fixture 2","expected":false,"passed":true},{"actual":true,"check":"fixture 3","expected":true,"passed":true},{"actual":true,"check":"fixture 4","expected":true,"passed":true},{"actual":true,"check":"fixture 1","expected":true,"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}