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FA-76541 / Email MIME structure / Open access

Build a bounded MIME tree summary from parser events: skipped child counted · case 01

A container whose only child was skipped as too deep is additionally reported as an empty multipart.

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

ROOT CAUSE

The skipped child counted decision evaluates `if len(stack) + 1 > max_depth: errors.append('too-deep') skip = 1 continue if stack: stack[-1] += 1` where the contract requires `if stack: stack[-1] += 1 if len(stack) + 1 > max_depth: errors.append('too-deep') skip = 1 continue`.

VERIFIED REPAIR

Use `if stack: stack[-1] += 1 if len(stack) + 1 > max_depth: errors.append('too-deep') skip = 1 continue` for the skipped child counted decision and keep every other rule of the model unchanged.

Unsuccessful approach: Counting the child only when it is within the limit is the same omission in another form. The attempted `if stack and len(stack) < max_depth: stack[-1] += 1 if len(stack) + 1 > max_depth: errors.append('too-deep') skip = 1 continue` still disagrees with a fixture.

Case contract

events are ["open", type] (multipart start), ["leaf", type, size] and ["close"]. The root multipart has depth 1. An open that would exceed max_depth records "too-deep" and its whole subtree (including nested opens) is skipped, but it still counts as a child of its parent. A multipart closing with no children records "empty-multipart", a close with nothing open records "stray-close", and containers left open record "unclosed". Result {leaves, depth (maximum reached), errors}.

Why this case matters

Bounding MIME nesting protects mail parsers from resource exhaustion while keeping the reachable structure intact.

1 / The failure

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

N = 1
observations = []
def solve(events, max_depth):
    stack = []
    skip = 0
    leaves = 0
    depth = 0
    errors = []
    for ev in events:
        kind = ev[0]
        if skip:
            if kind == 'open':
                skip += 1
            elif kind == 'close':
                skip -= 1
            continue
        if kind == 'open':
            if len(stack) + 1 > max_depth:
                errors.append('too-deep')
                skip = 1
                continue
            if stack:
                stack[-1] += 1
            stack.append(0)
            depth = max(depth, len(stack))
        elif kind == 'leaf':
            leaves += 1
            if stack:
                stack[-1] += 1
        elif not stack:
            errors.append('stray-close')
        elif stack.pop() == 0:
            errors.append('empty-multipart')
    if stack:
        errors.append('unclosed')
    return {'leaves': leaves, 'depth': depth, 'errors': errors}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 1}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 4], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 1}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 1], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 1], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 2: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 2}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 5], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 2], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 2}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 2], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 2], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 3: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 3}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 6], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 3], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 3}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 3], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 3], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 4: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['leaf', 'image/png', 3], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 4}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 7], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 4], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2], ['leaf', 'text/plain', 3]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 4}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 4], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 4], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 5: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['leaf', 'image/png', 3], ['leaf', 'image/png', 4], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 5}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 8], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 5], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2], ['leaf', 'text/plain', 3], ['leaf', 'text/plain', 4]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 5}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 5], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
three levels with limit two{'depth': 2, 'errors': ['too-deep', 'empty-multipart'], 'leaves': 1}{'depth': 2, 'errors': ['too-deep'], 'leaves': 1}Failed
deep skipped subtree{'depth': 1, 'errors': ['too-deep'], 'leaves': 1}{'depth': 1, 'errors': ['too-deep'], 'leaves': 1}Passed
skipped child keeps parent non-empty{'depth': 1, 'errors': ['too-deep', 'empty-multipart'], 'leaves': 0}{'depth': 1, 'errors': ['too-deep'], 'leaves': 0}Failed
unterminated root{'depth': 1, 'errors': ['unclosed'], 'leaves': 1}{'depth': 1, 'errors': ['unclosed'], 'leaves': 1}Passed
deepest branch first{'depth': 3, 'errors': [], 'leaves': 2}{'depth': 3, 'errors': [], 'leaves': 2}Passed
stray close{'depth': 0, 'errors': ['stray-close'], 'leaves': 1}{'depth': 0, 'errors': ['stray-close'], 'leaves': 1}Passed
empty multipart{'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0}{'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0}Passed

SHA-256 / b821bbeaa1509a63d3518463afb53552bc5d23bbb6885e4da37d4886e40aa2ab

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(events, max_depth):
    stack = []
    skip = 0
    leaves = 0
    depth = 0
    errors = []
    for ev in events:
        kind = ev[0]
        if skip:
            if kind == 'open':
                skip += 1
            elif kind == 'close':
                skip -= 1
            continue
        if kind == 'open':
            if stack and len(stack) < max_depth:
                stack[-1] += 1
            if len(stack) + 1 > max_depth:
                errors.append('too-deep')
                skip = 1
                continue
            stack.append(0)
            depth = max(depth, len(stack))
        elif kind == 'leaf':
            leaves += 1
            if stack:
                stack[-1] += 1
        elif not stack:
            errors.append('stray-close')
        elif stack.pop() == 0:
            errors.append('empty-multipart')
    if stack:
        errors.append('unclosed')
    return {'leaves': leaves, 'depth': depth, 'errors': errors}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 1}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 4], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 1}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 1], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 1], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 2: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 2}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 5], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 2], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 2}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 2], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 2], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 3: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 3}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 6], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 3], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 3}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 3], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 3], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 4: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['leaf', 'image/png', 3], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 4}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 7], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 4], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2], ['leaf', 'text/plain', 3]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 4}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 4], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 4], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 5: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['leaf', 'image/png', 3], ['leaf', 'image/png', 4], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 5}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 8], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 5], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2], ['leaf', 'text/plain', 3], ['leaf', 'text/plain', 4]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 5}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 5], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
three levels with limit two{'depth': 2, 'errors': ['too-deep', 'empty-multipart'], 'leaves': 1}{'depth': 2, 'errors': ['too-deep'], 'leaves': 1}Failed
deep skipped subtree{'depth': 1, 'errors': ['too-deep'], 'leaves': 1}{'depth': 1, 'errors': ['too-deep'], 'leaves': 1}Passed
skipped child keeps parent non-empty{'depth': 1, 'errors': ['too-deep', 'empty-multipart'], 'leaves': 0}{'depth': 1, 'errors': ['too-deep'], 'leaves': 0}Failed
unterminated root{'depth': 1, 'errors': ['unclosed'], 'leaves': 1}{'depth': 1, 'errors': ['unclosed'], 'leaves': 1}Passed
deepest branch first{'depth': 3, 'errors': [], 'leaves': 2}{'depth': 3, 'errors': [], 'leaves': 2}Passed
stray close{'depth': 0, 'errors': ['stray-close'], 'leaves': 1}{'depth': 0, 'errors': ['stray-close'], 'leaves': 1}Passed
empty multipart{'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0}{'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0}Passed

SHA-256 / cc8523e0f9fda1633bffd45fc53536f3a9f8acf4400a2c301c0297a0edc7a11c

3 / The verified repair

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

N = 1
observations = []
def solve(events, max_depth):
    stack = []
    skip = 0
    leaves = 0
    depth = 0
    errors = []
    for ev in events:
        kind = ev[0]
        if skip:
            if kind == 'open':
                skip += 1
            elif kind == 'close':
                skip -= 1
            continue
        if kind == 'open':
            if stack:
                stack[-1] += 1
            if len(stack) + 1 > max_depth:
                errors.append('too-deep')
                skip = 1
                continue
            stack.append(0)
            depth = max(depth, len(stack))
        elif kind == 'leaf':
            leaves += 1
            if stack:
                stack[-1] += 1
        elif not stack:
            errors.append('stray-close')
        elif stack.pop() == 0:
            errors.append('empty-multipart')
    if stack:
        errors.append('unclosed')
    return {'leaves': leaves, 'depth': depth, 'errors': errors}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 1}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 4], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 1}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 1], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 1], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 2: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 2}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 5], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 2], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 2}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 2], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 2], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 3: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 3}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 6], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 3], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 3}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 3], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 3], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 4: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['leaf', 'image/png', 3], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 4}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 7], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 4], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2], ['leaf', 'text/plain', 3]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 4}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 4], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 4], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})], 5: [('three levels with limit two', ([['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close'], ['leaf', 'image/png', 0], ['leaf', 'image/png', 1], ['leaf', 'image/png', 2], ['leaf', 'image/png', 3], ['leaf', 'image/png', 4], ['close']], 2), {'depth': 2, 'errors': ['too-deep'], 'leaves': 5}), ('deep skipped subtree', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['leaf', 'text/plain', 2], ['close'], ['leaf', 'text/plain', 8], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 1}), ('skipped child keeps parent non-empty', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['leaf', 'text/plain', 5], ['close'], ['close']], 1), {'depth': 1, 'errors': ['too-deep'], 'leaves': 0}), ('unterminated root', ([['open', 'multipart/mixed'], ['leaf', 'text/plain', 0], ['leaf', 'text/plain', 1], ['leaf', 'text/plain', 2], ['leaf', 'text/plain', 3], ['leaf', 'text/plain', 4]], 3), {'depth': 1, 'errors': ['unclosed'], 'leaves': 5}), ('deepest branch first', ([['open', 'multipart/mixed'], ['open', 'multipart/mixed'], ['open', 'multipart/alternative'], ['leaf', 'text/plain', 1], ['close'], ['close'], ['open', 'multipart/related'], ['leaf', 'text/html', 5], ['close'], ['close']], 5), {'depth': 3, 'errors': [], 'leaves': 2}), ('stray close', ([['leaf', 'text/plain', 5], ['close']], 2), {'depth': 0, 'errors': ['stray-close'], 'leaves': 1}), ('empty multipart', ([['open', 'multipart/mixed'], ['close']], 2), {'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
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
three levels with limit two{'depth': 2, 'errors': ['too-deep'], 'leaves': 1}{'depth': 2, 'errors': ['too-deep'], 'leaves': 1}Passed
deep skipped subtree{'depth': 1, 'errors': ['too-deep'], 'leaves': 1}{'depth': 1, 'errors': ['too-deep'], 'leaves': 1}Passed
skipped child keeps parent non-empty{'depth': 1, 'errors': ['too-deep'], 'leaves': 0}{'depth': 1, 'errors': ['too-deep'], 'leaves': 0}Passed
unterminated root{'depth': 1, 'errors': ['unclosed'], 'leaves': 1}{'depth': 1, 'errors': ['unclosed'], 'leaves': 1}Passed
deepest branch first{'depth': 3, 'errors': [], 'leaves': 2}{'depth': 3, 'errors': [], 'leaves': 2}Passed
stray close{'depth': 0, 'errors': ['stray-close'], 'leaves': 1}{'depth': 0, 'errors': ['stray-close'], 'leaves': 1}Passed
empty multipart{'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0}{'depth': 1, 'errors': ['empty-multipart'], 'leaves': 0}Passed

SHA-256 / 3cfd44a122e85ff0428bcbb58adeea26488f54ea442855b83a0b4583647abd4a

Verification & scope

Stipulated offline model over pre-parsed MIME dictionaries; not a conforming MIME parser, generator or mail client. 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 2026-09-29T14:49:17.256925+00:00.

Case digest / e85773a6696cc7823e44b1bea496ee6b0ecb729b41a3c37bed8e543938b03b2d