FAILURE MAP
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FA-27566 / HTTP ranges / Open access

A range-set guard limits amplification before serving resolved byte ranges: a contained range cannot shrink the coalesced end · case 01

A range-set guard limits amplification before serving resolved byte ranges: a contained range cannot shrink the coalesced end.

Verified by executionVariant 1 · 19 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The range-abuse-guard-merge-contained-end decision uses L=x['length'] rs=x['ranges'] if not rs: return ['full',None] if len(rs)>x['max_ranges']: return ['full',None] total=0 for a,b in rs: total+=b-a+1 if total>2*L: return ['full',None] if sum(1 for a,b in rs if b-a+1<x['min_span'])>x['max_tiny']: return ['full',None] order=sorted(rs) overlaps=0 end=-1 for a,b in order: if a<=end: overlaps+=1 end=max(end,b) if overlaps>x['max_overlaps']: return ['full',None] disorder=0 for i in range(1,len(rs)): if rs[i][0]<rs[i-1][0]: disorder+=1 if overlaps==0 and disorder<=x['max_disorder']: return ['ranges',[list(r) for r in rs]] merged=[] for lo,hi in order: if merged and lo<=merged[-1][1]+1: merged[-1][1]=hi else: merged.append([lo,hi]) return ['ranges',merged].

THE FAILURE

The range-abuse-guard-merge-contained-end decision uses L=x['length'] rs=x['ranges'] if not rs: return ['full',None] if len(rs)>x['max_ranges']: return ['full',None] total=0 for a,b in rs: total+=b-a+1 if total>2*L: return ['full',None] if sum(1 for a,b in rs if b-a+1<x['min_span'])>x['max_tiny']: return ['full',None] order=sorted(rs) overlaps=0 end=-1 for a,b in order: if a<=end: overlaps+=1 end=max(end,b) if overlaps>x['max_overlaps']: return ['full',None] disorder=0 for i in range(1,len(rs)): if rs[i][0]<rs[i-1][0]: disorder+=1 if overlaps==0 and disorder<=x['max_disorder']: return ['ranges',[list(r) for r in rs]] merged=[] for lo,hi in order: if merged and lo<=merged[-1][1]+1: merged[-1][1]=hi else: merged.append([lo,hi]) return ['ranges',merged].

Unsuccessful approach: The partial repair uses L=x['length'] rs=x['ranges'] if not rs: return ['full',None] if len(rs)>x['max_ranges']: return ['full',None] total=0 for a,b in rs: total+=b-a+1 if total>2*L: return ['full',None] if sum(1 for a,b in rs if b-a+1<x['min_span'])>x['max_tiny']: return ['full',None] order=sorted(rs) overlaps=0 end=-1 for a,b in order: if a<=end: overlaps+=1 end=max(end,b) if overlaps>x['max_overlaps']: return ['full',None] disorder=0 for i in range(1,len(rs)): if rs[i][0]<rs[i-1][0]: disorder+=1 if overlaps==0 and disorder<=x['max_disorder']: return ['ranges',[list(r) for r in rs]] merged=[] for lo,hi in order: if merged and lo<=merged[-1][1]+1: merged[-1][1]=max(merged[-1][0],hi) else: merged.append([lo,hi]) return ['ranges',merged], which still violates the stated contract.

Case contract

x holds a representation length, already resolved satisfiable inclusive ranges in request order, and local policy limits. Serve ["full",null] for an empty list, more than max_ranges members, requested byte sum above twice the length (duplicates count every time), more than max_tiny members shorter than min_span, or more than max_overlaps overlaps. Overlaps are counted by a sweep over start-sorted ranges against the running maximum end; adjacent ranges do not overlap. Inversions count request neighbors whose start decreases. Without overlaps and with inversions within max_disorder, return ["ranges",request-order ranges]; otherwise return ["ranges",start-sorted ranges with overlapping or adjacent members coalesced].

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(x):
    L=x['length']
    rs=x['ranges']
    if not rs: return ['full',None]
    if len(rs)>x['max_ranges']: return ['full',None]
    total=0
    for a,b in rs:
        total+=b-a+1
    if total>2*L: return ['full',None]
    if sum(1 for a,b in rs if b-a+1<x['min_span'])>x['max_tiny']: return ['full',None]
    order=sorted(rs)
    overlaps=0
    end=-1
    for a,b in order:
        if a<=end: overlaps+=1
        end=max(end,b)
    if overlaps>x['max_overlaps']: return ['full',None]
    disorder=0
    for i in range(1,len(rs)):
        if rs[i][0]<rs[i-1][0]: disorder+=1
    if overlaps==0 and disorder<=x['max_disorder']: return ['ranges',[list(r) for r in rs]]
    merged=[]
    for lo,hi in order:
        if merged and lo<=merged[-1][1]+1:
            merged[-1][1]=hi
        else:
            merged.append([lo,hi])
    return ['ranges',merged]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('merge-contained-end fixture 0', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 1', json.loads(json.dumps(solve({'length':0,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 2', json.loads(json.dumps(solve({'length':10,'max_disorder':1,'max_overlaps':5,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[0,9],[0,9]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 3', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[20,29]]}))), json.loads(json.dumps(['ranges',[[0,9],[20,29]]])))
check('merge-contained-end fixture 4', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[50,59],[0,9]]}))), json.loads(json.dumps(['ranges',[[50,59],[0,9]]])))
check('merge-contained-end fixture 5', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[50,59],[20,29],[0,9]]}))), json.loads(json.dumps(['ranges',[[0,9],[20,29],[50,59]]])))
check('merge-contained-end fixture 6', json.loads(json.dumps(solve({'length':100,'max_disorder':0,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[10,19],[30,39],[20,29]]}))), json.loads(json.dumps(['ranges',[[10,39]]])))
check('merge-contained-end fixture 7', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[50,59],[20,29],[30,39]]}))), json.loads(json.dumps(['ranges',[[50,59],[20,29],[30,39]]])))
check('merge-contained-end fixture 8', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[5,14]]}))), json.loads(json.dumps(['ranges',[[0,14]]])))
check('merge-contained-end fixture 9', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,20],[5,9]]}))), json.loads(json.dumps(['ranges',[[0,20]]])))
check('merge-contained-end fixture 10', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[1,9],[2,9],[3,9]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 11', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':1,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[20,29],[0,5],[40,49],[30,35]]}))), json.loads(json.dumps(['ranges',[[0,5],[20,35],[40,49]]])))
check('merge-contained-end fixture 12', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':1,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,50],[10,20],[30,40]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 13', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':1,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[10,19],[20,29]]}))), json.loads(json.dumps(['ranges',[[0,9],[10,19],[20,29]]])))
check('merge-contained-end fixture 14', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':0,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[9,19]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 15', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':1,'min_span':4,'ranges':[[0,0],[10,10],[20,29]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 16', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,1],[10,11],[20,21],[30,31],[40,41],[50,51],[60,61],[70,71],[80,81]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 17', json.loads(json.dumps(solve({'length':10*N,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,N-1],[N,2*N-1]]}))), json.loads(json.dumps(['ranges',[[0,N-1],[N,2*N-1]]])))
check('merge-contained-end fixture 18', json.loads(json.dumps(solve({'length':5*N+1,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,5*N],[0,5*N]]}))), json.loads(json.dumps(['ranges',[[0,5*N]]])))
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
merge-contained-end fixture 0['full', None]['full', None]Passed
merge-contained-end fixture 1['full', None]['full', None]Passed
merge-contained-end fixture 2['full', None]['full', None]Passed
merge-contained-end fixture 3['ranges', [[0, 9], [20, 29]]]['ranges', [[0, 9], [20, 29]]]Passed
merge-contained-end fixture 4['ranges', [[50, 59], [0, 9]]]['ranges', [[50, 59], [0, 9]]]Passed
merge-contained-end fixture 5['ranges', [[0, 9], [20, 29], [50, 59]]]['ranges', [[0, 9], [20, 29], [50, 59]]]Passed
merge-contained-end fixture 6['ranges', [[10, 39]]]['ranges', [[10, 39]]]Passed
merge-contained-end fixture 7['ranges', [[50, 59], [20, 29], [30, 39]]]['ranges', [[50, 59], [20, 29], [30, 39]]]Passed
merge-contained-end fixture 8['ranges', [[0, 14]]]['ranges', [[0, 14]]]Passed
merge-contained-end fixture 9['ranges', [[0, 9]]]['ranges', [[0, 20]]]Failed
merge-contained-end fixture 10['full', None]['full', None]Passed
merge-contained-end fixture 11['ranges', [[0, 5], [20, 35], [40, 49]]]['ranges', [[0, 5], [20, 35], [40, 49]]]Passed
merge-contained-end fixture 12['full', None]['full', None]Passed
merge-contained-end fixture 13['ranges', [[0, 9], [10, 19], [20, 29]]]['ranges', [[0, 9], [10, 19], [20, 29]]]Passed
merge-contained-end fixture 14['full', None]['full', None]Passed
merge-contained-end fixture 15['full', None]['full', None]Passed
merge-contained-end fixture 16['full', None]['full', None]Passed
merge-contained-end fixture 17['ranges', [[0, 0], [1, 1]]]['ranges', [[0, 0], [1, 1]]]Passed
merge-contained-end fixture 18['ranges', [[0, 5]]]['ranges', [[0, 5]]]Passed

SHA-256 / 329e8ffb9adcb44fb1af9f629bcf1fa6df36c049b5877e1bbd611c653a6d2d70

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    L=x['length']
    rs=x['ranges']
    if not rs: return ['full',None]
    if len(rs)>x['max_ranges']: return ['full',None]
    total=0
    for a,b in rs:
        total+=b-a+1
    if total>2*L: return ['full',None]
    if sum(1 for a,b in rs if b-a+1<x['min_span'])>x['max_tiny']: return ['full',None]
    order=sorted(rs)
    overlaps=0
    end=-1
    for a,b in order:
        if a<=end: overlaps+=1
        end=max(end,b)
    if overlaps>x['max_overlaps']: return ['full',None]
    disorder=0
    for i in range(1,len(rs)):
        if rs[i][0]<rs[i-1][0]: disorder+=1
    if overlaps==0 and disorder<=x['max_disorder']: return ['ranges',[list(r) for r in rs]]
    merged=[]
    for lo,hi in order:
        if merged and lo<=merged[-1][1]+1:
            merged[-1][1]=max(merged[-1][0],hi)
        else:
            merged.append([lo,hi])
    return ['ranges',merged]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('merge-contained-end fixture 0', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 1', json.loads(json.dumps(solve({'length':0,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 2', json.loads(json.dumps(solve({'length':10,'max_disorder':1,'max_overlaps':5,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[0,9],[0,9]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 3', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[20,29]]}))), json.loads(json.dumps(['ranges',[[0,9],[20,29]]])))
check('merge-contained-end fixture 4', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[50,59],[0,9]]}))), json.loads(json.dumps(['ranges',[[50,59],[0,9]]])))
check('merge-contained-end fixture 5', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[50,59],[20,29],[0,9]]}))), json.loads(json.dumps(['ranges',[[0,9],[20,29],[50,59]]])))
check('merge-contained-end fixture 6', json.loads(json.dumps(solve({'length':100,'max_disorder':0,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[10,19],[30,39],[20,29]]}))), json.loads(json.dumps(['ranges',[[10,39]]])))
check('merge-contained-end fixture 7', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[50,59],[20,29],[30,39]]}))), json.loads(json.dumps(['ranges',[[50,59],[20,29],[30,39]]])))
check('merge-contained-end fixture 8', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[5,14]]}))), json.loads(json.dumps(['ranges',[[0,14]]])))
check('merge-contained-end fixture 9', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,20],[5,9]]}))), json.loads(json.dumps(['ranges',[[0,20]]])))
check('merge-contained-end fixture 10', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[1,9],[2,9],[3,9]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 11', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':1,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[20,29],[0,5],[40,49],[30,35]]}))), json.loads(json.dumps(['ranges',[[0,5],[20,35],[40,49]]])))
check('merge-contained-end fixture 12', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':1,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,50],[10,20],[30,40]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 13', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':1,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[10,19],[20,29]]}))), json.loads(json.dumps(['ranges',[[0,9],[10,19],[20,29]]])))
check('merge-contained-end fixture 14', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':0,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,9],[9,19]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 15', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':1,'min_span':4,'ranges':[[0,0],[10,10],[20,29]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 16', json.loads(json.dumps(solve({'length':100,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,1],[10,11],[20,21],[30,31],[40,41],[50,51],[60,61],[70,71],[80,81]]}))), json.loads(json.dumps(['full',None])))
check('merge-contained-end fixture 17', json.loads(json.dumps(solve({'length':10*N,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,N-1],[N,2*N-1]]}))), json.loads(json.dumps(['ranges',[[0,N-1],[N,2*N-1]]])))
check('merge-contained-end fixture 18', json.loads(json.dumps(solve({'length':5*N+1,'max_disorder':1,'max_overlaps':2,'max_ranges':8,'max_tiny':8,'min_span':1,'ranges':[[0,5*N],[0,5*N]]}))), json.loads(json.dumps(['ranges',[[0,5*N]]])))
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
merge-contained-end fixture 0['full', None]['full', None]Passed
merge-contained-end fixture 1['full', None]['full', None]Passed
merge-contained-end fixture 2['full', None]['full', None]Passed
merge-contained-end fixture 3['ranges', [[0, 9], [20, 29]]]['ranges', [[0, 9], [20, 29]]]Passed
merge-contained-end fixture 4['ranges', [[50, 59], [0, 9]]]['ranges', [[50, 59], [0, 9]]]Passed
merge-contained-end fixture 5['ranges', [[0, 9], [20, 29], [50, 59]]]['ranges', [[0, 9], [20, 29], [50, 59]]]Passed
merge-contained-end fixture 6['ranges', [[10, 39]]]['ranges', [[10, 39]]]Passed
merge-contained-end fixture 7['ranges', [[50, 59], [20, 29], [30, 39]]]['ranges', [[50, 59], [20, 29], [30, 39]]]Passed
merge-contained-end fixture 8['ranges', [[0, 14]]]['ranges', [[0, 14]]]Passed
merge-contained-end fixture 9['ranges', [[0, 9]]]['ranges', [[0, 20]]]Failed
merge-contained-end fixture 10['full', None]['full', None]Passed
merge-contained-end fixture 11['ranges', [[0, 5], [20, 35], [40, 49]]]['ranges', [[0, 5], [20, 35], [40, 49]]]Passed
merge-contained-end fixture 12['full', None]['full', None]Passed
merge-contained-end fixture 13['ranges', [[0, 9], [10, 19], [20, 29]]]['ranges', [[0, 9], [10, 19], [20, 29]]]Passed
merge-contained-end fixture 14['full', None]['full', None]Passed
merge-contained-end fixture 15['full', None]['full', None]Passed
merge-contained-end fixture 16['full', None]['full', None]Passed
merge-contained-end fixture 17['ranges', [[0, 0], [1, 1]]]['ranges', [[0, 0], [1, 1]]]Passed
merge-contained-end fixture 18['ranges', [[0, 5]]]['ranges', [[0, 5]]]Passed

SHA-256 / be419c612c7bcebffe2d1239a95b3800f77b3a67e41e5ddc232fcb9d8318b8d4

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 19 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.

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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 2026-09-29T14:41:26.269427+00:00.

Case digest / 243553e0f3867040fac32f83eb8653b573d2ae4bcb48b59c3a3b116a6ffb7951