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FA-27036 / HTTP ranges / Open access

A client serializes a typed range request plan: byte-stable downloads request identity when configured · case 01

A client serializes a typed range request plan: byte-stable downloads request identity when configured.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The outbound-range-request-identity-negotiation decision uses members=[] for kind,a,b in x['selectors']: if kind=='closed': members.append(str(a)+'-'+str(b)) elif kind=='open': members.append(str(a)+'-') elif kind=='suffix': members.append('-'+str(a)) headers=[] if members: headers.append(['Range','bytes='+','.join(members)]) if x['validator'] is not None: kind,value=x['validator'] headers.append(['If-Range','"'+value+'"' if kind=='tag' else value]) if False: headers.append(['Accept-Encoding','identity']) return headers.

VERIFIED REPAIR

Apply the bounded decision exactly: members=[] for kind,a,b in x['selectors']: if kind=='closed': members.append(str(a)+'-'+str(b)) elif kind=='open': members.append(str(a)+'-') elif kind=='suffix': members.append('-'+str(a)) headers=[] if members: headers.append(['Range','bytes='+','.join(members)]) if x['validator'] is not None: kind,value=x['validator'] headers.append(['If-Range','"'+value+'"' if kind=='tag' else value]) if x['identity']: headers.append(['Accept-Encoding','identity']) return headers

Unsuccessful approach: The partial repair uses members=[] for kind,a,b in x['selectors']: if kind=='closed': members.append(str(a)+'-'+str(b)) elif kind=='open': members.append(str(a)+'-') elif kind=='suffix': members.append('-'+str(a)) headers=[] if members: headers.append(['Range','bytes='+','.join(members)]) if x['validator'] is not None: kind,value=x['validator'] headers.append(['If-Range','"'+value+'"' if kind=='tag' else value]) if x['identity'] and members: headers.append(['Accept-Encoding','identity']) return headers, which still violates the stated contract.

Case contract

Input x contains selectors [kind,a,b], validator [tag|date,value] or null, and accept encoding policy. Closed selectors serialize a-b, open selectors a-, suffix selectors -a, in input order. Empty selectors omit Range and If-Range. Tag validators are quoted opaque ASCII strings without quotes/backslashes; dates are already formatted and remain unquoted. Identity-only policy emits Accept-Encoding identity. Return ordered [header,value] pairs.

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):
    members=[]
    for kind,a,b in x['selectors']:
        if kind=='closed': members.append(str(a)+'-'+str(b))
        elif kind=='open': members.append(str(a)+'-')
        elif kind=='suffix': members.append('-'+str(a))
    headers=[]
    if members:
        headers.append(['Range','bytes='+','.join(members)])
        if x['validator'] is not None:
            kind,value=x['validator']
            headers.append(['If-Range','"'+value+'"' if kind=='tag' else value])
    if False: headers.append(['Accept-Encoding','identity'])
    return headers
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('identity-negotiation fixture 0', json.loads(json.dumps(solve({'selectors':[['closed',0,N],['suffix',2,None]],'validator':['tag','rev'],'identity':True}))), json.loads(json.dumps([['Range',"bytes=0-"+str(N)+",-2"],['If-Range','"rev"'],['Accept-Encoding','identity']])))
check('identity-negotiation fixture 1', json.loads(json.dumps(solve({'selectors':[['open',5,None]],'validator':['date','Mon, 01 Jan 2001 00:00:00 GMT'],'identity':False}))), json.loads(json.dumps([['Range','bytes=5-'],['If-Range','Mon, 01 Jan 2001 00:00:00 GMT']])))
check('identity-negotiation fixture 2', json.loads(json.dumps(solve({'selectors':[],'validator':['tag','rev'],'identity':False}))), json.loads(json.dumps([])))
check('identity-negotiation fixture 3', json.loads(json.dumps(solve({'selectors':[['closed',9,9],['closed',0,0]],'validator':None,'identity':False}))), json.loads(json.dumps([['Range','bytes=9-9,0-0']])))
check('identity-negotiation fixture 4', json.loads(json.dumps(solve({'selectors':[['suffix',0,None]],'validator':['tag',''],'identity':False}))), json.loads(json.dumps([['Range','bytes=-0'],['If-Range','""']])))
check('identity-negotiation fixture 5', json.loads(json.dumps(solve({'selectors':[],'validator':None,'identity':True}))), json.loads(json.dumps([['Accept-Encoding','identity']])))
check('identity-negotiation fixture 6', json.loads(json.dumps(solve({'selectors':[['open',0,None]],'validator':None,'identity':False}))), json.loads(json.dumps([['Range','bytes=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
identity-negotiation fixture 0[['Range', 'bytes=0-1,-2'], ['If-Range', '"rev"']][['Range', 'bytes=0-1,-2'], ['If-Range', '"rev"'], ['Accept-Encoding', 'identity']]Failed
identity-negotiation fixture 1[['Range', 'bytes=5-'], ['If-Range', 'Mon, 01 Jan 2001 00:00:00 GMT']][['Range', 'bytes=5-'], ['If-Range', 'Mon, 01 Jan 2001 00:00:00 GMT']]Passed
identity-negotiation fixture 2[][]Passed
identity-negotiation fixture 3[['Range', 'bytes=9-9,0-0']][['Range', 'bytes=9-9,0-0']]Passed
identity-negotiation fixture 4[['Range', 'bytes=-0'], ['If-Range', '""']][['Range', 'bytes=-0'], ['If-Range', '""']]Passed
identity-negotiation fixture 5[][['Accept-Encoding', 'identity']]Failed
identity-negotiation fixture 6[['Range', 'bytes=0-']][['Range', 'bytes=0-']]Passed

SHA-256 / 79f2d3431d44a56406253bd5664ee320f8c7dd5ff2706e9bb9aee2a65ee81dab

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    members=[]
    for kind,a,b in x['selectors']:
        if kind=='closed': members.append(str(a)+'-'+str(b))
        elif kind=='open': members.append(str(a)+'-')
        elif kind=='suffix': members.append('-'+str(a))
    headers=[]
    if members:
        headers.append(['Range','bytes='+','.join(members)])
        if x['validator'] is not None:
            kind,value=x['validator']
            headers.append(['If-Range','"'+value+'"' if kind=='tag' else value])
    if x['identity'] and members: headers.append(['Accept-Encoding','identity'])
    return headers
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('identity-negotiation fixture 0', json.loads(json.dumps(solve({'selectors':[['closed',0,N],['suffix',2,None]],'validator':['tag','rev'],'identity':True}))), json.loads(json.dumps([['Range',"bytes=0-"+str(N)+",-2"],['If-Range','"rev"'],['Accept-Encoding','identity']])))
check('identity-negotiation fixture 1', json.loads(json.dumps(solve({'selectors':[['open',5,None]],'validator':['date','Mon, 01 Jan 2001 00:00:00 GMT'],'identity':False}))), json.loads(json.dumps([['Range','bytes=5-'],['If-Range','Mon, 01 Jan 2001 00:00:00 GMT']])))
check('identity-negotiation fixture 2', json.loads(json.dumps(solve({'selectors':[],'validator':['tag','rev'],'identity':False}))), json.loads(json.dumps([])))
check('identity-negotiation fixture 3', json.loads(json.dumps(solve({'selectors':[['closed',9,9],['closed',0,0]],'validator':None,'identity':False}))), json.loads(json.dumps([['Range','bytes=9-9,0-0']])))
check('identity-negotiation fixture 4', json.loads(json.dumps(solve({'selectors':[['suffix',0,None]],'validator':['tag',''],'identity':False}))), json.loads(json.dumps([['Range','bytes=-0'],['If-Range','""']])))
check('identity-negotiation fixture 5', json.loads(json.dumps(solve({'selectors':[],'validator':None,'identity':True}))), json.loads(json.dumps([['Accept-Encoding','identity']])))
check('identity-negotiation fixture 6', json.loads(json.dumps(solve({'selectors':[['open',0,None]],'validator':None,'identity':False}))), json.loads(json.dumps([['Range','bytes=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
identity-negotiation fixture 0[['Range', 'bytes=0-1,-2'], ['If-Range', '"rev"'], ['Accept-Encoding', 'identity']][['Range', 'bytes=0-1,-2'], ['If-Range', '"rev"'], ['Accept-Encoding', 'identity']]Passed
identity-negotiation fixture 1[['Range', 'bytes=5-'], ['If-Range', 'Mon, 01 Jan 2001 00:00:00 GMT']][['Range', 'bytes=5-'], ['If-Range', 'Mon, 01 Jan 2001 00:00:00 GMT']]Passed
identity-negotiation fixture 2[][]Passed
identity-negotiation fixture 3[['Range', 'bytes=9-9,0-0']][['Range', 'bytes=9-9,0-0']]Passed
identity-negotiation fixture 4[['Range', 'bytes=-0'], ['If-Range', '""']][['Range', 'bytes=-0'], ['If-Range', '""']]Passed
identity-negotiation fixture 5[][['Accept-Encoding', 'identity']]Failed
identity-negotiation fixture 6[['Range', 'bytes=0-']][['Range', 'bytes=0-']]Passed

SHA-256 / 79d7044a65f6763bb84e6d89134df1bb45263f5f5e79360f20a59f6aa045ef95

3 / The verified repair

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

N = 1
observations = []
def solve(x):
    members=[]
    for kind,a,b in x['selectors']:
        if kind=='closed': members.append(str(a)+'-'+str(b))
        elif kind=='open': members.append(str(a)+'-')
        elif kind=='suffix': members.append('-'+str(a))
    headers=[]
    if members:
        headers.append(['Range','bytes='+','.join(members)])
        if x['validator'] is not None:
            kind,value=x['validator']
            headers.append(['If-Range','"'+value+'"' if kind=='tag' else value])
    if x['identity']: headers.append(['Accept-Encoding','identity'])
    return headers
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('identity-negotiation fixture 0', json.loads(json.dumps(solve({'selectors':[['closed',0,N],['suffix',2,None]],'validator':['tag','rev'],'identity':True}))), json.loads(json.dumps([['Range',"bytes=0-"+str(N)+",-2"],['If-Range','"rev"'],['Accept-Encoding','identity']])))
check('identity-negotiation fixture 1', json.loads(json.dumps(solve({'selectors':[['open',5,None]],'validator':['date','Mon, 01 Jan 2001 00:00:00 GMT'],'identity':False}))), json.loads(json.dumps([['Range','bytes=5-'],['If-Range','Mon, 01 Jan 2001 00:00:00 GMT']])))
check('identity-negotiation fixture 2', json.loads(json.dumps(solve({'selectors':[],'validator':['tag','rev'],'identity':False}))), json.loads(json.dumps([])))
check('identity-negotiation fixture 3', json.loads(json.dumps(solve({'selectors':[['closed',9,9],['closed',0,0]],'validator':None,'identity':False}))), json.loads(json.dumps([['Range','bytes=9-9,0-0']])))
check('identity-negotiation fixture 4', json.loads(json.dumps(solve({'selectors':[['suffix',0,None]],'validator':['tag',''],'identity':False}))), json.loads(json.dumps([['Range','bytes=-0'],['If-Range','""']])))
check('identity-negotiation fixture 5', json.loads(json.dumps(solve({'selectors':[],'validator':None,'identity':True}))), json.loads(json.dumps([['Accept-Encoding','identity']])))
check('identity-negotiation fixture 6', json.loads(json.dumps(solve({'selectors':[['open',0,None]],'validator':None,'identity':False}))), json.loads(json.dumps([['Range','bytes=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
identity-negotiation fixture 0[['Range', 'bytes=0-1,-2'], ['If-Range', '"rev"'], ['Accept-Encoding', 'identity']][['Range', 'bytes=0-1,-2'], ['If-Range', '"rev"'], ['Accept-Encoding', 'identity']]Passed
identity-negotiation fixture 1[['Range', 'bytes=5-'], ['If-Range', 'Mon, 01 Jan 2001 00:00:00 GMT']][['Range', 'bytes=5-'], ['If-Range', 'Mon, 01 Jan 2001 00:00:00 GMT']]Passed
identity-negotiation fixture 2[][]Passed
identity-negotiation fixture 3[['Range', 'bytes=9-9,0-0']][['Range', 'bytes=9-9,0-0']]Passed
identity-negotiation fixture 4[['Range', 'bytes=-0'], ['If-Range', '""']][['Range', 'bytes=-0'], ['If-Range', '""']]Passed
identity-negotiation fixture 5[['Accept-Encoding', 'identity']][['Accept-Encoding', 'identity']]Passed
identity-negotiation fixture 6[['Range', 'bytes=0-']][['Range', 'bytes=0-']]Passed

SHA-256 / f456a47f11adc089b129373d5ea28346ef3b3548d41caa911c2b7ec9ed8173d5

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 2026-09-29T14:41:21.417619+00:00.

Case digest / f22c80894350688e0b6e4897cf9b6ae7c8a9ad1bc24685b3045927809b8efc86