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FA-27521 / HTTP ranges / Open access

A zero-copy range sender accounts for partial progress reported with syscall errors: all promised bytes complete even if the same syscall reports would-block · case 01

A zero-copy range sender accounts for partial progress reported with syscall errors: all promised bytes complete even if the same syscall reports would-block.

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

ROOT CAUSE

The sendfile-range-events-completed-would-block decision uses offset=x['offset'] remaining=x['remaining'] state='running' opened=True out=[] for accepted,error in x['events']: if state in ('complete','aborted','truncated'): out.append([offset,remaining,state,opened]) continue if accepted<0 or accepted>remaining: state='aborted' opened=False out.append([offset,remaining,state,opened]) continue offset+=accepted remaining-=accepted if error=='fatal': state='aborted' elif remaining==0 and error=='none': state='complete' elif error=='again': state='blocked' elif error=='interrupt': state='running' elif accepted==0: state='truncated' else: state='running' opened=state not in ('complete','aborted','truncated') out.append([offset,remaining,state,opened]) return out.

THE FAILURE

The sendfile-range-events-completed-would-block decision uses offset=x['offset'] remaining=x['remaining'] state='running' opened=True out=[] for accepted,error in x['events']: if state in ('complete','aborted','truncated'): out.append([offset,remaining,state,opened]) continue if accepted<0 or accepted>remaining: state='aborted' opened=False out.append([offset,remaining,state,opened]) continue offset+=accepted remaining-=accepted if error=='fatal': state='aborted' elif remaining==0 and error=='none': state='complete' elif error=='again': state='blocked' elif error=='interrupt': state='running' elif accepted==0: state='truncated' else: state='running' opened=state not in ('complete','aborted','truncated') out.append([offset,remaining,state,opened]) return out.

Unsuccessful approach: The partial repair uses offset=x['offset'] remaining=x['remaining'] state='running' opened=True out=[] for accepted,error in x['events']: if state in ('complete','aborted','truncated'): out.append([offset,remaining,state,opened]) continue if accepted<0 or accepted>remaining: state='aborted' opened=False out.append([offset,remaining,state,opened]) continue offset+=accepted remaining-=accepted if error=='fatal': state='aborted' elif remaining==0 and error!='again': state='complete' elif error=='again': state='blocked' elif error=='interrupt': state='running' elif accepted==0: state='truncated' else: state='running' opened=state not in ('complete','aborted','truncated') out.append([offset,remaining,state,opened]) return out, which still violates the stated contract.

Case contract

x contains absolute offset, remaining promised bytes, and syscall events [accepted,error], where error is none,again,interrupt,fatal. Counts outside0..remaining abort without advancing. Valid accepted bytes advance even when again or interrupt accompanies them. Fatal errors abort; zero remaining completes; again blocks; interrupt reschedules; zero bytes with none truncates. Terminal states ignore later events. Return state snapshots [offset,remaining,state,handle-open] after each event.

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):
    offset=x['offset']
    remaining=x['remaining']
    state='running'
    opened=True
    out=[]
    for accepted,error in x['events']:
        if state in ('complete','aborted','truncated'):
            out.append([offset,remaining,state,opened])
            continue
        if accepted<0 or accepted>remaining:
            state='aborted'
            opened=False
            out.append([offset,remaining,state,opened])
            continue
        offset+=accepted
        remaining-=accepted
        if error=='fatal': state='aborted'
        elif remaining==0 and error=='none': state='complete'
        elif error=='again': state='blocked'
        elif error=='interrupt': state='running'
        elif accepted==0: state='truncated'
        else: state='running'
        opened=state not in ('complete','aborted','truncated')
        out.append([offset,remaining,state,opened])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('completed-would-block fixture 0', json.loads(json.dumps(solve({'offset':10,'remaining':5,'events':[[2,'interrupt'],[1,'again'],[2,'none']]}))), json.loads(json.dumps([[12,3,'running',True],[13,2,'blocked',True],[15,0,'complete',False]])))
check('completed-would-block fixture 1', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[0,'again'],[0,'interrupt'],[0,'none'],[1,'none']]}))), json.loads(json.dumps([[0,2,'blocked',True],[0,2,'running',True],[0,2,'truncated',False],[0,2,'truncated',False]])))
check('completed-would-block fixture 2', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[1,'fatal'],[1,'none']]}))), json.loads(json.dumps([[1,1,'aborted',False],[1,1,'aborted',False]])))
check('completed-would-block fixture 3', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[-1,'none']]}))), json.loads(json.dumps([[0,2,'aborted',False]])))
check('completed-would-block fixture 4', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[3,'none']]}))), json.loads(json.dumps([[0,2,'aborted',False]])))
check('completed-would-block fixture 5', json.loads(json.dumps(solve({'offset':N,'remaining':N,'events':[[N,'again'],[0,'fatal']]}))), json.loads(json.dumps([[2*N,0,'complete',False],[2*N,0,'complete',False]])))
check('completed-would-block fixture 6', json.loads(json.dumps(solve({'offset':0,'remaining':0,'events':[[0,'none']]}))), json.loads(json.dumps([[0,0,'complete',False]])))
check('completed-would-block fixture 7', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[2,'fatal']]}))), json.loads(json.dumps([[2,0,'aborted',False]])))
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
completed-would-block fixture 0[[12, 3, 'running', True], [13, 2, 'blocked', True], [15, 0, 'complete', False]][[12, 3, 'running', True], [13, 2, 'blocked', True], [15, 0, 'complete', False]]Passed
completed-would-block fixture 1[[0, 2, 'blocked', True], [0, 2, 'running', True], [0, 2, 'truncated', False], [0, 2, 'truncated', False]][[0, 2, 'blocked', True], [0, 2, 'running', True], [0, 2, 'truncated', False], [0, 2, 'truncated', False]]Passed
completed-would-block fixture 2[[1, 1, 'aborted', False], [1, 1, 'aborted', False]][[1, 1, 'aborted', False], [1, 1, 'aborted', False]]Passed
completed-would-block fixture 3[[0, 2, 'aborted', False]][[0, 2, 'aborted', False]]Passed
completed-would-block fixture 4[[0, 2, 'aborted', False]][[0, 2, 'aborted', False]]Passed
completed-would-block fixture 5[[2, 0, 'blocked', True], [2, 0, 'aborted', False]][[2, 0, 'complete', False], [2, 0, 'complete', False]]Failed
completed-would-block fixture 6[[0, 0, 'complete', False]][[0, 0, 'complete', False]]Passed
completed-would-block fixture 7[[2, 0, 'aborted', False]][[2, 0, 'aborted', False]]Passed

SHA-256 / 38133ca6d51e830f2f0a141da64169485f057e7425dd1537d5049b1f8f63c0f9

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    offset=x['offset']
    remaining=x['remaining']
    state='running'
    opened=True
    out=[]
    for accepted,error in x['events']:
        if state in ('complete','aborted','truncated'):
            out.append([offset,remaining,state,opened])
            continue
        if accepted<0 or accepted>remaining:
            state='aborted'
            opened=False
            out.append([offset,remaining,state,opened])
            continue
        offset+=accepted
        remaining-=accepted
        if error=='fatal': state='aborted'
        elif remaining==0 and error!='again': state='complete'
        elif error=='again': state='blocked'
        elif error=='interrupt': state='running'
        elif accepted==0: state='truncated'
        else: state='running'
        opened=state not in ('complete','aborted','truncated')
        out.append([offset,remaining,state,opened])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('completed-would-block fixture 0', json.loads(json.dumps(solve({'offset':10,'remaining':5,'events':[[2,'interrupt'],[1,'again'],[2,'none']]}))), json.loads(json.dumps([[12,3,'running',True],[13,2,'blocked',True],[15,0,'complete',False]])))
check('completed-would-block fixture 1', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[0,'again'],[0,'interrupt'],[0,'none'],[1,'none']]}))), json.loads(json.dumps([[0,2,'blocked',True],[0,2,'running',True],[0,2,'truncated',False],[0,2,'truncated',False]])))
check('completed-would-block fixture 2', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[1,'fatal'],[1,'none']]}))), json.loads(json.dumps([[1,1,'aborted',False],[1,1,'aborted',False]])))
check('completed-would-block fixture 3', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[-1,'none']]}))), json.loads(json.dumps([[0,2,'aborted',False]])))
check('completed-would-block fixture 4', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[3,'none']]}))), json.loads(json.dumps([[0,2,'aborted',False]])))
check('completed-would-block fixture 5', json.loads(json.dumps(solve({'offset':N,'remaining':N,'events':[[N,'again'],[0,'fatal']]}))), json.loads(json.dumps([[2*N,0,'complete',False],[2*N,0,'complete',False]])))
check('completed-would-block fixture 6', json.loads(json.dumps(solve({'offset':0,'remaining':0,'events':[[0,'none']]}))), json.loads(json.dumps([[0,0,'complete',False]])))
check('completed-would-block fixture 7', json.loads(json.dumps(solve({'offset':0,'remaining':2,'events':[[2,'fatal']]}))), json.loads(json.dumps([[2,0,'aborted',False]])))
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
completed-would-block fixture 0[[12, 3, 'running', True], [13, 2, 'blocked', True], [15, 0, 'complete', False]][[12, 3, 'running', True], [13, 2, 'blocked', True], [15, 0, 'complete', False]]Passed
completed-would-block fixture 1[[0, 2, 'blocked', True], [0, 2, 'running', True], [0, 2, 'truncated', False], [0, 2, 'truncated', False]][[0, 2, 'blocked', True], [0, 2, 'running', True], [0, 2, 'truncated', False], [0, 2, 'truncated', False]]Passed
completed-would-block fixture 2[[1, 1, 'aborted', False], [1, 1, 'aborted', False]][[1, 1, 'aborted', False], [1, 1, 'aborted', False]]Passed
completed-would-block fixture 3[[0, 2, 'aborted', False]][[0, 2, 'aborted', False]]Passed
completed-would-block fixture 4[[0, 2, 'aborted', False]][[0, 2, 'aborted', False]]Passed
completed-would-block fixture 5[[2, 0, 'blocked', True], [2, 0, 'aborted', False]][[2, 0, 'complete', False], [2, 0, 'complete', False]]Failed
completed-would-block fixture 6[[0, 0, 'complete', False]][[0, 0, 'complete', False]]Passed
completed-would-block fixture 7[[2, 0, 'aborted', False]][[2, 0, 'aborted', False]]Passed

SHA-256 / 1970479d30e7155b903853be1e044ef180d26dd812f1110c7ee5b46cfc7f5fd2

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 8 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 2026-09-29T14:41:25.798697+00:00.

Case digest / 6f80a11e019287e3ed51e5e98097386dcbe9b4d5c2379d19e4e7c26b4de08ae8