FAILURE MAP
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FA-30601 / HTTP retries / Open access

Exactly one logical request completion: Begin result violates retry transition semantics · case 01

Begin result violates retry transition semantics

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

ROOT CAUSE

Begin result violates retry transition semantics

VERIFIED REPAIR

Restore the specified transition token=False; result=None; continue.

Unsuccessful approach: The attempted repair changes the faulty site to token=False; result=['cancelled',None]; 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=result; 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 or 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[['failure', 400], 2][['failure', 400], 2]Passed
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', 0], 0][['success', 1], 1]Failed
9[None, 1][None, 1]Passed
10[None, 1][None, 1]Passed
11[None, 0][None, 0]Passed

SHA-256 / 9a6ff4eea1e9ae66b55505dcc02a638d343c4e7f8bbc7fa20602da6a64426b5b

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=['cancelled',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 or 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[['cancelled', None], 0][['success', 1], 1]Failed
2[['cancelled', None], 0][['success', 1], 2]Failed
3[['failure', 400], 2][['failure', 400], 2]Passed
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[['cancelled', None], 0][['success', 1], 1]Failed
9[None, 1][None, 1]Passed
10[None, 1][None, 1]Passed
11[None, 0][None, 0]Passed

SHA-256 / 1c9efd235194d8c703413a3d63043a95bbcab00ece3ac1d1950bad43e8d307cf

3 / The verified repair

Exit 0
"""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 or 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[['failure', 400], 2][['failure', 400], 2]Passed
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 / 86ade7e878686193203b8b1bb9f1ed9316522aa24991ef6790fc52798a3aa5be

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 2026-09-29T14:41:54.446954+00:00.

Case digest / 98d39fbdb1fbaa05cb03d9f76be4cc8039d3cbe13e31e9681425c00510dcb549