FAILURE MAP
← Case archive

FA-27021 / HTTP ranges / Open access

A client serializes a typed range request plan: an empty selector plan emits no conditional range field · case 01

A client serializes a typed range request plan: an empty selector plan emits no conditional range field.

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

ROOT CAUSE

The outbound-range-request-empty-request 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 or x['validator'] is not None: 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.

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 or x['identity']: 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, 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 or x['validator'] is not None:
        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('empty-request 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('empty-request 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('empty-request fixture 2', json.loads(json.dumps(solve({'selectors':[],'validator':['tag','rev'],'identity':False}))), json.loads(json.dumps([])))
check('empty-request 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('empty-request 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('empty-request fixture 5', json.loads(json.dumps(solve({'selectors':[],'validator':None,'identity':True}))), json.loads(json.dumps([['Accept-Encoding','identity']])))
check('empty-request 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
empty-request 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
empty-request 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
empty-request fixture 2[['Range', 'bytes='], ['If-Range', '"rev"']][]Failed
empty-request fixture 3[['Range', 'bytes=9-9,0-0']][['Range', 'bytes=9-9,0-0']]Passed
empty-request fixture 4[['Range', 'bytes=-0'], ['If-Range', '""']][['Range', 'bytes=-0'], ['If-Range', '""']]Passed
empty-request fixture 5[['Accept-Encoding', 'identity']][['Accept-Encoding', 'identity']]Passed
empty-request fixture 6[['Range', 'bytes=0-']][['Range', 'bytes=0-']]Passed

SHA-256 / c5db87c1e22c4ca354d85af6bfb9089dcd20fa40cf7205f532af3b6a7a0e83db

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 or x['identity']:
        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('empty-request 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('empty-request 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('empty-request fixture 2', json.loads(json.dumps(solve({'selectors':[],'validator':['tag','rev'],'identity':False}))), json.loads(json.dumps([])))
check('empty-request 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('empty-request 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('empty-request fixture 5', json.loads(json.dumps(solve({'selectors':[],'validator':None,'identity':True}))), json.loads(json.dumps([['Accept-Encoding','identity']])))
check('empty-request 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
empty-request 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
empty-request 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
empty-request fixture 2[][]Passed
empty-request fixture 3[['Range', 'bytes=9-9,0-0']][['Range', 'bytes=9-9,0-0']]Passed
empty-request fixture 4[['Range', 'bytes=-0'], ['If-Range', '""']][['Range', 'bytes=-0'], ['If-Range', '""']]Passed
empty-request fixture 5[['Range', 'bytes='], ['Accept-Encoding', 'identity']][['Accept-Encoding', 'identity']]Failed
empty-request fixture 6[['Range', 'bytes=0-']][['Range', 'bytes=0-']]Passed

SHA-256 / ff165e69213c1331f9358e063e051d360177ec988e93b9db5eeb1c47831d8627

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('empty-request 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('empty-request 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('empty-request fixture 2', json.loads(json.dumps(solve({'selectors':[],'validator':['tag','rev'],'identity':False}))), json.loads(json.dumps([])))
check('empty-request 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('empty-request 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('empty-request fixture 5', json.loads(json.dumps(solve({'selectors':[],'validator':None,'identity':True}))), json.loads(json.dumps([['Accept-Encoding','identity']])))
check('empty-request 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
empty-request 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
empty-request 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
empty-request fixture 2[][]Passed
empty-request fixture 3[['Range', 'bytes=9-9,0-0']][['Range', 'bytes=9-9,0-0']]Passed
empty-request fixture 4[['Range', 'bytes=-0'], ['If-Range', '""']][['Range', 'bytes=-0'], ['If-Range', '""']]Passed
empty-request fixture 5[['Accept-Encoding', 'identity']][['Accept-Encoding', 'identity']]Passed
empty-request fixture 6[['Range', 'bytes=0-']][['Range', 'bytes=0-']]Passed

SHA-256 / 60c1fb8823187c93cef5ff25779efacc8b7bfa2266dad4ccb8c093a6a50c5144

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 2026-09-29T14:41:21.376529+00:00.

Case digest / d17fe0c54a4da8cebc8a6d5b315b534d024cf2625208c5898a615c52e913665e