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FA-30071 / HTTP retries / Open access

File-backed request replay integrity: Read bound violates retry transition semantics · case 01

Read bound violates retry transition semantics

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

ROOT CAUSE

Read bound violates retry transition semantics

VERIFIED REPAIR

Restore the specified transition min(e[1],max(0,snapshot[1]-cursor)).

Unsuccessful approach: The attempted repair changes the faulty site to min(e[1],snapshot[1]) but still violates a regression oracle.

Case contract

open(file identity,size,mtime,offset) snapshots file metadata and starting byte. inspect(current identity,size,mtime) records current metadata. read(count) advances bounded cursor only while valid. retry compares all snapshot metadata before rewinding; any mismatch permanently invalidates this body. close invalidates. New open resets validity. Return read byte counts and retry dispositions.

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):
    snapshot=None; current=None; origin=0; cursor=0; valid=False; out=[]
    for e in events:
        if e[0]=='open':
            snapshot=tuple(e[1:4]); current=snapshot
            origin=e[4]; cursor=origin
            valid=True
        elif e[0]=='inspect': current=tuple(e[1:4])
        elif e[0]=='close': valid=False
        elif e[0]=='read':
            if not valid: out.append('invalid'); continue
            amount=e[1]
            cursor+=amount
            out.append(amount)
        elif e[0]=='retry':
            if not valid: out.append('invalid'); continue
            if current!=snapshot:
                valid=False; out.append('changed'); continue
            cursor=origin
            out.append('rewound')
    return [out,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [[],0])
check('1', solve([('open','a',N+5,1,2),('read',2),('read',N+9),('read',1),('retry',),('read',1)]), [[2,N+1,0,'rewound',1],3])
check('2', solve([('open','a',5,1,0),('inspect','b',5,1),('retry',),('read',1)]), [['changed','invalid'],0])
check('3', solve([('open','a',5,1,0),('inspect','a',6,1),('retry',),('retry',)]), [['changed','invalid'],0])
check('4', solve([('open','a',5,1,0),('inspect','a',5,2),('retry',),('inspect','a',5,1),('retry',)]), [['changed','invalid'],0])
check('5', solve([('open','a',0,1,0),('read',1),('retry',),('close',),('read',1),('retry',)]), [[0,'rewound','invalid','invalid'],0])
check('6', solve([('open','a',N+3,1,1),('close',),('open','b',2,2,1),('read',1)]), [[1],2])
check('7', solve([('open','a',N+3,1,1),('inspect','a',N+3,1),('retry',),('close',),('read',1),('retry',)]), [['rewound','invalid','invalid'],1])
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[[], 0][[], 0]Passed
1[[2, 10, 1, 'rewound', 1], 3][[2, 2, 0, 'rewound', 1], 3]Failed
2[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
3[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
4[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
5[[1, 'rewound', 'invalid', 'invalid'], 0][[0, 'rewound', 'invalid', 'invalid'], 0]Failed
6[[1], 2][[1], 2]Passed
7[['rewound', 'invalid', 'invalid'], 1][['rewound', 'invalid', 'invalid'], 1]Passed

SHA-256 / 1c470cfcdfe536e77d3291975c2c3e7dc948b26641f9d6d69df8113b15d40b5e

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(events):
    snapshot=None; current=None; origin=0; cursor=0; valid=False; out=[]
    for e in events:
        if e[0]=='open':
            snapshot=tuple(e[1:4]); current=snapshot
            origin=e[4]; cursor=origin
            valid=True
        elif e[0]=='inspect': current=tuple(e[1:4])
        elif e[0]=='close': valid=False
        elif e[0]=='read':
            if not valid: out.append('invalid'); continue
            amount=min(e[1],snapshot[1])
            cursor+=amount
            out.append(amount)
        elif e[0]=='retry':
            if not valid: out.append('invalid'); continue
            if current!=snapshot:
                valid=False; out.append('changed'); continue
            cursor=origin
            out.append('rewound')
    return [out,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [[],0])
check('1', solve([('open','a',N+5,1,2),('read',2),('read',N+9),('read',1),('retry',),('read',1)]), [[2,N+1,0,'rewound',1],3])
check('2', solve([('open','a',5,1,0),('inspect','b',5,1),('retry',),('read',1)]), [['changed','invalid'],0])
check('3', solve([('open','a',5,1,0),('inspect','a',6,1),('retry',),('retry',)]), [['changed','invalid'],0])
check('4', solve([('open','a',5,1,0),('inspect','a',5,2),('retry',),('inspect','a',5,1),('retry',)]), [['changed','invalid'],0])
check('5', solve([('open','a',0,1,0),('read',1),('retry',),('close',),('read',1),('retry',)]), [[0,'rewound','invalid','invalid'],0])
check('6', solve([('open','a',N+3,1,1),('close',),('open','b',2,2,1),('read',1)]), [[1],2])
check('7', solve([('open','a',N+3,1,1),('inspect','a',N+3,1),('retry',),('close',),('read',1),('retry',)]), [['rewound','invalid','invalid'],1])
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[[], 0][[], 0]Passed
1[[2, 6, 1, 'rewound', 1], 3][[2, 2, 0, 'rewound', 1], 3]Failed
2[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
3[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
4[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
5[[0, 'rewound', 'invalid', 'invalid'], 0][[0, 'rewound', 'invalid', 'invalid'], 0]Passed
6[[1], 2][[1], 2]Passed
7[['rewound', 'invalid', 'invalid'], 1][['rewound', 'invalid', 'invalid'], 1]Passed

SHA-256 / fc890dc92898c29508d0d59a98aeb91d3eccc4ecbb828ee258ae06ac450c4d21

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(events):
    snapshot=None; current=None; origin=0; cursor=0; valid=False; out=[]
    for e in events:
        if e[0]=='open':
            snapshot=tuple(e[1:4]); current=snapshot
            origin=e[4]; cursor=origin
            valid=True
        elif e[0]=='inspect': current=tuple(e[1:4])
        elif e[0]=='close': valid=False
        elif e[0]=='read':
            if not valid: out.append('invalid'); continue
            amount=min(e[1],max(0,snapshot[1]-cursor))
            cursor+=amount
            out.append(amount)
        elif e[0]=='retry':
            if not valid: out.append('invalid'); continue
            if current!=snapshot:
                valid=False; out.append('changed'); continue
            cursor=origin
            out.append('rewound')
    return [out,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [[],0])
check('1', solve([('open','a',N+5,1,2),('read',2),('read',N+9),('read',1),('retry',),('read',1)]), [[2,N+1,0,'rewound',1],3])
check('2', solve([('open','a',5,1,0),('inspect','b',5,1),('retry',),('read',1)]), [['changed','invalid'],0])
check('3', solve([('open','a',5,1,0),('inspect','a',6,1),('retry',),('retry',)]), [['changed','invalid'],0])
check('4', solve([('open','a',5,1,0),('inspect','a',5,2),('retry',),('inspect','a',5,1),('retry',)]), [['changed','invalid'],0])
check('5', solve([('open','a',0,1,0),('read',1),('retry',),('close',),('read',1),('retry',)]), [[0,'rewound','invalid','invalid'],0])
check('6', solve([('open','a',N+3,1,1),('close',),('open','b',2,2,1),('read',1)]), [[1],2])
check('7', solve([('open','a',N+3,1,1),('inspect','a',N+3,1),('retry',),('close',),('read',1),('retry',)]), [['rewound','invalid','invalid'],1])
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[[], 0][[], 0]Passed
1[[2, 2, 0, 'rewound', 1], 3][[2, 2, 0, 'rewound', 1], 3]Passed
2[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
3[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
4[['changed', 'invalid'], 0][['changed', 'invalid'], 0]Passed
5[[0, 'rewound', 'invalid', 'invalid'], 0][[0, 'rewound', 'invalid', 'invalid'], 0]Passed
6[[1], 2][[1], 2]Passed
7[['rewound', 'invalid', 'invalid'], 1][['rewound', 'invalid', 'invalid'], 1]Passed

SHA-256 / dfb4b951db5e073350bfb8a305973ea669079245a6119c1a30c4f3597818385d

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 2026-09-29T14:41:49.271303+00:00.

Case digest / e714b6c95448c2351a9c3f7c4e4080b22cd7977d7ddab7c8d2cd010142014977