FA-30711 / HTTP retries / Open access

Retry advice across wall and monotonic clocks: Duplicate advice violates retry transition semantics · case 01

Duplicate advice violates retry transition semantics

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Duplicate advice violates retry transition semantics

VERIFIED REPAIR

Restore the specified transition if len(advice)!=1:.

Unsuccessful approach: The attempted repair changes the faulty site to if len(advice)<1: but still violates a regression oracle.

Case contract

Controlled decoded Retry-After model. response(server Date or None,Age,received monotonic,local wall at receive) resets advice. delta(nonnegative seconds) or date(absolute seconds) records one advice; multiple advice values are rejected. For date, estimate server time as Date+Age, or local wall if Date absent. Project remaining server delay onto receive monotonic clock. advance moves monotonic time forward. schedule returns remaining wait or missing/ambiguous; no network requests or full header parsing.

Why this case matters

Offline deterministic model of HTTP request retries.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(events):
    server=None; age=0; received=0; wall=0; now=0; advice=[]; out=[]
    for e in events:
        if e[0]=='response':
            server=e[1]; age=e[2]; received=e[3]; wall=e[4]; now=received; advice=[]
        elif e[0] in ('delta','date'): advice.append((e[0],e[1]))
        elif e[0]=='advance': now=max(now,e[1])
        elif e[0]=='schedule':
            if not advice: out.append('missing'); continue
            if len(advice)>2: out.append('ambiguous'); continue
            kind,value=advice[0]
            if kind=='delta': due=received+value
            else:
                reference=server+age if server is not None else wall
                due=received+max(0,value-reference)
            out.append(max(0,due-now))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('response',100,0,N,200),('schedule',)]), ['missing'])
check('2', solve([('response',100,5,N,200),('date',110),('schedule',),('advance',N+2),('schedule',)]), [5,3])
check('3', solve([('response',None,99,N,200),('date',207),('schedule',)]), [7])
check('4', solve([('response',100,0,N,200),('delta',5),('advance',N+2),('schedule',),('advance',N),('schedule',)]), [3,3])
check('5', solve([('response',100,0,N,200),('delta',5),('delta',5),('schedule',),('response',100,0,N+1,200),('schedule',)]), ['ambiguous','missing'])
check('6', solve([('response',100,0,N,200),('date',90),('schedule',),('advance',N+10),('schedule',)]), [0,0])
check('7', solve([('response',100,13,N,200),('date',120),('schedule',)]), [7])
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
0	`[]`	`[]`	Passed
1	`['missing']`	`['missing']`	Passed
2	`[5, 3]`	`[5, 3]`	Passed
3	`[7]`	`[7]`	Passed
4	`[3, 3]`	`[3, 3]`	Passed
5	`[5, 'missing']`	`['ambiguous', 'missing']`	Failed
6	`[0, 0]`	`[0, 0]`	Passed
7	`[7]`	`[7]`	Passed

SHA-256 / 83b308958a05fb61d756ac9affe46d8cb0f494a192d5a70cb6c3d60cc764f0c7

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(events):
    server=None; age=0; received=0; wall=0; now=0; advice=[]; out=[]
    for e in events:
        if e[0]=='response':
            server=e[1]; age=e[2]; received=e[3]; wall=e[4]; now=received; advice=[]
        elif e[0] in ('delta','date'): advice.append((e[0],e[1]))
        elif e[0]=='advance': now=max(now,e[1])
        elif e[0]=='schedule':
            if not advice: out.append('missing'); continue
            if len(advice)<1: out.append('ambiguous'); continue
            kind,value=advice[0]
            if kind=='delta': due=received+value
            else:
                reference=server+age if server is not None else wall
                due=received+max(0,value-reference)
            out.append(max(0,due-now))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('response',100,0,N,200),('schedule',)]), ['missing'])
check('2', solve([('response',100,5,N,200),('date',110),('schedule',),('advance',N+2),('schedule',)]), [5,3])
check('3', solve([('response',None,99,N,200),('date',207),('schedule',)]), [7])
check('4', solve([('response',100,0,N,200),('delta',5),('advance',N+2),('schedule',),('advance',N),('schedule',)]), [3,3])
check('5', solve([('response',100,0,N,200),('delta',5),('delta',5),('schedule',),('response',100,0,N+1,200),('schedule',)]), ['ambiguous','missing'])
check('6', solve([('response',100,0,N,200),('date',90),('schedule',),('advance',N+10),('schedule',)]), [0,0])
check('7', solve([('response',100,13,N,200),('date',120),('schedule',)]), [7])
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
0	`[]`	`[]`	Passed
1	`['missing']`	`['missing']`	Passed
2	`[5, 3]`	`[5, 3]`	Passed
3	`[7]`	`[7]`	Passed
4	`[3, 3]`	`[3, 3]`	Passed
5	`[5, 'missing']`	`['ambiguous', 'missing']`	Failed
6	`[0, 0]`	`[0, 0]`	Passed
7	`[7]`	`[7]`	Passed

SHA-256 / 7f4d1ad4cc0ef1e91042cbee18af5e24fb72d5286e5734d8b5ef19fb4f775e06

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(events):
    server=None; age=0; received=0; wall=0; now=0; advice=[]; out=[]
    for e in events:
        if e[0]=='response':
            server=e[1]; age=e[2]; received=e[3]; wall=e[4]; now=received; advice=[]
        elif e[0] in ('delta','date'): advice.append((e[0],e[1]))
        elif e[0]=='advance': now=max(now,e[1])
        elif e[0]=='schedule':
            if not advice: out.append('missing'); continue
            if len(advice)!=1: out.append('ambiguous'); continue
            kind,value=advice[0]
            if kind=='delta': due=received+value
            else:
                reference=server+age if server is not None else wall
                due=received+max(0,value-reference)
            out.append(max(0,due-now))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('response',100,0,N,200),('schedule',)]), ['missing'])
check('2', solve([('response',100,5,N,200),('date',110),('schedule',),('advance',N+2),('schedule',)]), [5,3])
check('3', solve([('response',None,99,N,200),('date',207),('schedule',)]), [7])
check('4', solve([('response',100,0,N,200),('delta',5),('advance',N+2),('schedule',),('advance',N),('schedule',)]), [3,3])
check('5', solve([('response',100,0,N,200),('delta',5),('delta',5),('schedule',),('response',100,0,N+1,200),('schedule',)]), ['ambiguous','missing'])
check('6', solve([('response',100,0,N,200),('date',90),('schedule',),('advance',N+10),('schedule',)]), [0,0])
check('7', solve([('response',100,13,N,200),('date',120),('schedule',)]), [7])
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
0	`[]`	`[]`	Passed
1	`['missing']`	`['missing']`	Passed
2	`[5, 3]`	`[5, 3]`	Passed
3	`[7]`	`[7]`	Passed
4	`[3, 3]`	`[3, 3]`	Passed
5	`['ambiguous', 'missing']`	`['ambiguous', 'missing']`	Passed
6	`[0, 0]`	`[0, 0]`	Passed
7	`[7]`	`[7]`	Passed

SHA-256 / c5d80a71e09011e5b2da8d8167a3d9840c344a144bf963595ab2a32e4ff54905

Verification & scope

Stipulated bounded simulator, not a complete HTTP implementation or a standards conformance claim. 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 2026-09-29T14:41:55.380083+00:00.

Case digest / 07f11a5e32d8c4c8d3685f0bf325abea9ef609ce4623b4e586980899cc74c80f