FAILURE MAP
← Case archive

FA-30621 / HTTP retries / Open access

Exactly one logical request completion: Response active violates retry transition semantics · case 01

Response active violates retry transition semantics

Verified by executionVariant 1 · 12 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Response active violates retry transition semantics

THE FAILURE

Response active violates retry transition semantics

Unsuccessful approach: The attempted repair changes the faulty site to if not active and e[1]!=generation: continue but still violates a regression oracle.

Case contract

begin resets generation and final result. launch creates next active generation; response(generation,status,payload) accepts only current active attempt. A 2xx result completes immediately, retryable statuses 429/503 leave logical request pending with a retry token, other statuses terminally fail. retry consumes token to launch next attempt. cancel wins if no final result. Once final, every later event except begin is ignored. Return result and number of attempts launched.

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):
    generation=0; active=False; token=False; result=None
    for e in events:
        if e[0]=='begin': generation=0; active=False; token=False; result=None; continue
        if result is not None: continue
        if e[0]=='launch':
            if active or generation!=0: continue
            generation+=1; active=True
        elif e[0]=='response':
            if e[1]!=generation: continue
            active=False
            if 200<=e[2]<300: result=['success',e[3]]
            elif e[2] in (429,503): token=True
            else: result=['failure',e[2]]
        elif e[0]=='retry':
            if not token or active: continue
            token=False; generation+=1; active=True
        elif e[0]=='cancel':
            result=['cancelled',None]; active=False; token=False
    return [result,generation]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [None,0])
check('1', solve([('begin',),('launch',),('response',1,200,N),('cancel',),('launch',)]), [['success',N],1])
check('2', solve([('begin',),('launch',),('response',1,503,0),('launch',),('retry',),('response',1,200,0),('response',3,200,0),('response',2,204,N)]), [['success',N],2])
check('3', solve([('launch',),('response',1,429,0),('response',1,200,N),('retry',),('response',2,400,N),('cancel',)]), [['failure',400],2])
check('4', solve([('launch',),('cancel',),('response',1,200,N),('retry',)]), [['cancelled',None],1])
check('5', solve([('retry',),('launch',),('response',1,300,N)]), [['failure',300],1])
check('6', solve([('launch',),('response',1,199,N)]), [['failure',199],1])
check('7', solve([('launch',),('response',1,500,N)]), [['failure',500],1])
check('8', solve([('launch',),('response',1,200,0),('begin',),('launch',),('response',1,201,N)]), [['success',N],1])
check('9', solve([('launch',),('response',1,503,N),('launch',)]), [None,1])
check('10', solve([('launch',),('launch',)]), [None,1])
check('11', solve([('retry',)]), [None,0])
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
0[None, 0][None, 0]Passed
1[['success', 1], 1][['success', 1], 1]Passed
2[['success', 1], 2][['success', 1], 2]Passed
3[['success', 1], 1][['failure', 400], 2]Failed
4[['cancelled', None], 1][['cancelled', None], 1]Passed
5[['failure', 300], 1][['failure', 300], 1]Passed
6[['failure', 199], 1][['failure', 199], 1]Passed
7[['failure', 500], 1][['failure', 500], 1]Passed
8[['success', 1], 1][['success', 1], 1]Passed
9[None, 1][None, 1]Passed
10[None, 1][None, 1]Passed
11[None, 0][None, 0]Passed

SHA-256 / 4d781e30854e86bbadf910caf21e188ca013828d5e5a9ea86f68082a9367b636

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(events):
    generation=0; active=False; token=False; result=None
    for e in events:
        if e[0]=='begin': generation=0; active=False; token=False; result=None; continue
        if result is not None: continue
        if e[0]=='launch':
            if active or generation!=0: continue
            generation+=1; active=True
        elif e[0]=='response':
            if not active and e[1]!=generation: continue
            active=False
            if 200<=e[2]<300: result=['success',e[3]]
            elif e[2] in (429,503): token=True
            else: result=['failure',e[2]]
        elif e[0]=='retry':
            if not token or active: continue
            token=False; generation+=1; active=True
        elif e[0]=='cancel':
            result=['cancelled',None]; active=False; token=False
    return [result,generation]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [None,0])
check('1', solve([('begin',),('launch',),('response',1,200,N),('cancel',),('launch',)]), [['success',N],1])
check('2', solve([('begin',),('launch',),('response',1,503,0),('launch',),('retry',),('response',1,200,0),('response',3,200,0),('response',2,204,N)]), [['success',N],2])
check('3', solve([('launch',),('response',1,429,0),('response',1,200,N),('retry',),('response',2,400,N),('cancel',)]), [['failure',400],2])
check('4', solve([('launch',),('cancel',),('response',1,200,N),('retry',)]), [['cancelled',None],1])
check('5', solve([('retry',),('launch',),('response',1,300,N)]), [['failure',300],1])
check('6', solve([('launch',),('response',1,199,N)]), [['failure',199],1])
check('7', solve([('launch',),('response',1,500,N)]), [['failure',500],1])
check('8', solve([('launch',),('response',1,200,0),('begin',),('launch',),('response',1,201,N)]), [['success',N],1])
check('9', solve([('launch',),('response',1,503,N),('launch',)]), [None,1])
check('10', solve([('launch',),('launch',)]), [None,1])
check('11', solve([('retry',)]), [None,0])
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
0[None, 0][None, 0]Passed
1[['success', 1], 1][['success', 1], 1]Passed
2[['success', 0], 2][['success', 1], 2]Failed
3[['success', 1], 1][['failure', 400], 2]Failed
4[['cancelled', None], 1][['cancelled', None], 1]Passed
5[['failure', 300], 1][['failure', 300], 1]Passed
6[['failure', 199], 1][['failure', 199], 1]Passed
7[['failure', 500], 1][['failure', 500], 1]Passed
8[['success', 1], 1][['success', 1], 1]Passed
9[None, 1][None, 1]Passed
10[None, 1][None, 1]Passed
11[None, 0][None, 0]Passed

SHA-256 / 5c88fa26580e022b6b8c67323bb2e58d957bb17fa2704d6abc1ddc5db3a7791a

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 12 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Sign in to the archive ↗

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 2026-09-29T14:41:55.079047+00:00.

Case digest / 3a0b672fbb1d82278e91aa0aa0ae892945aeacfca2ad966a22bfb5c47f56b13f