FAILURE MAP
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FA-26546 / HTTP ranges / Open access

Read-ahead respects both stream credit and remaining range bytes · case 01

Read-ahead respects both stream credit and remaining range bytes.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The stream-credit-backpressure decision uses return min(remaining,block).

VERIFIED REPAIR

Apply the bounded decision exactly: return min(credit,remaining,block)

Unsuccessful approach: The partial repair uses return min(credit,block), which still violates the stated contract.

Case contract

Return the next permitted read size min(credit,remaining,block), all nonnegative.

Why this case matters

Range responses combine representation identity, conditional requests, framing, and partial-object state.

1 / The failure

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

N = 1
observations = []
def solve(credit, remaining, block):
    return min(remaining,block)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-credit-backpressure fixture 0', solve(N,3*N,2*N), N)
check('stream-credit-backpressure fixture 1', solve(3*N,N,2*N), N)
check('stream-credit-backpressure fixture 2', solve(3*N,3*N,N), N)
check('stream-credit-backpressure fixture 3', solve(0,N,N), 0)
check('stream-credit-backpressure fixture 4', solve(N,0,N), 0)
check('stream-credit-backpressure fixture 5', solve(N,N,0), 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
stream-credit-backpressure fixture 021Failed
stream-credit-backpressure fixture 111Passed
stream-credit-backpressure fixture 211Passed
stream-credit-backpressure fixture 310Failed
stream-credit-backpressure fixture 400Passed
stream-credit-backpressure fixture 500Passed

SHA-256 / 96ecf23cff8166c2e4ba7c9b24f8811a955be4f56dac9341721bca1d7f008e57

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(credit, remaining, block):
    return min(credit,block)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-credit-backpressure fixture 0', solve(N,3*N,2*N), N)
check('stream-credit-backpressure fixture 1', solve(3*N,N,2*N), N)
check('stream-credit-backpressure fixture 2', solve(3*N,3*N,N), N)
check('stream-credit-backpressure fixture 3', solve(0,N,N), 0)
check('stream-credit-backpressure fixture 4', solve(N,0,N), 0)
check('stream-credit-backpressure fixture 5', solve(N,N,0), 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
stream-credit-backpressure fixture 011Passed
stream-credit-backpressure fixture 121Failed
stream-credit-backpressure fixture 211Passed
stream-credit-backpressure fixture 300Passed
stream-credit-backpressure fixture 410Failed
stream-credit-backpressure fixture 500Passed

SHA-256 / 4df796570e880002c6a8c630a5c32f7aad72f22216e217966880476e69df531c

3 / The verified repair

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

N = 1
observations = []
def solve(credit, remaining, block):
    return min(credit,remaining,block)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-credit-backpressure fixture 0', solve(N,3*N,2*N), N)
check('stream-credit-backpressure fixture 1', solve(3*N,N,2*N), N)
check('stream-credit-backpressure fixture 2', solve(3*N,3*N,N), N)
check('stream-credit-backpressure fixture 3', solve(0,N,N), 0)
check('stream-credit-backpressure fixture 4', solve(N,0,N), 0)
check('stream-credit-backpressure fixture 5', solve(N,N,0), 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
stream-credit-backpressure fixture 011Passed
stream-credit-backpressure fixture 111Passed
stream-credit-backpressure fixture 211Passed
stream-credit-backpressure fixture 300Passed
stream-credit-backpressure fixture 400Passed
stream-credit-backpressure fixture 500Passed

SHA-256 / aac95db9276c126a0af01a12671d5066fa354d4840c30b5c698a5457a7338ab1

Verification & scope

Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. 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 2026-09-29T14:41:16.933155+00:00.

Case digest / 51e03d29d174928f3ad7168adf3be07e4e066d1c832dec4e3d29b5f7d9869caa