Christian Krakau-Louis
204 lines
6.4 KiB
Python
204 lines
6.4 KiB
Python
"""BIMI DNS posture checks for monitored domains."""
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from __future__ import annotations
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import json
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from dataclasses import asdict, dataclass, field
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from datetime import datetime, timedelta, timezone
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from typing import List, Optional, Tuple
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from urllib.parse import urlparse
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from sqlalchemy.exc import IntegrityError
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from sqlalchemy.orm import Session
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from app.models.dns_cache import DNSCache
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from app.services.dns_cache import DEFAULT_DNS_CACHE_TTL_SECONDS
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from app.services.dns_resolver import BaseDNSProvider
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_CACHE_KEY_PREFIX = "bimi-v1"
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@dataclass
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class BIMIResult:
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"""Operator-facing BIMI posture evidence."""
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status: str = "fail"
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selector: str = "default"
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query_name: str = ""
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dns_record: Optional[str] = None
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logo_url: Optional[str] = None
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certificate_url: Optional[str] = None
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evidence_url: Optional[str] = None
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errors: List[str] = field(default_factory=list)
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warnings: List[str] = field(default_factory=list)
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def _utcnow_naive() -> datetime:
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return datetime.now(timezone.utc).replace(tzinfo=None)
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def _is_fresh(row: DNSCache, ttl_seconds: int, now: datetime) -> bool:
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return row.checked_at >= now - timedelta(seconds=ttl_seconds)
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def _result_from_json(value: str) -> BIMIResult:
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data = json.loads(value)
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return BIMIResult(
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status=str(data.get("status") or "fail"),
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selector=str(data.get("selector") or "default"),
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query_name=str(data.get("query_name") or ""),
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dns_record=data.get("dns_record"),
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logo_url=data.get("logo_url"),
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certificate_url=data.get("certificate_url"),
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evidence_url=data.get("evidence_url"),
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errors=list(data.get("errors") or []),
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warnings=list(data.get("warnings") or []),
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)
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def _https_url(value: Optional[str]) -> bool:
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if not value:
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return False
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parsed = urlparse(value)
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return parsed.scheme == "https" and bool(parsed.netloc)
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def _tags(record: str) -> dict[str, str]:
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return {
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part.split("=", 1)[0].strip().lower(): part.split("=", 1)[1].strip()
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for part in record.split(";")
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if "=" in part
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}
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def parse_bimi_record(records: List[str]) -> Tuple[Optional[BIMIResult], List[str], List[str]]:
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"""Parse BIMI TXT records into a normalized result, warnings, and errors."""
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bimi_records = [record for record in records if record.lower().startswith("v=bimi1")]
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if not bimi_records:
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return None, [], ["No BIMI TXT record was found at the selector."]
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warnings: List[str] = []
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errors: List[str] = []
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if len(bimi_records) > 1:
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warnings.append("Multiple BIMI TXT records were found; publish exactly one.")
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record = bimi_records[0]
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tags = _tags(record)
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logo_url = tags.get("l")
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certificate_url = tags.get("a")
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if tags.get("v", "").lower() != "bimi1":
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errors.append("The BIMI TXT record must start with v=BIMI1.")
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if not logo_url:
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errors.append("The BIMI TXT record must include an l= HTTPS SVG logo URL.")
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elif not _https_url(logo_url):
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errors.append("The BIMI logo URL must use HTTPS.")
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elif not urlparse(logo_url).path.lower().endswith(".svg"):
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warnings.append("The BIMI logo URL should point to an SVG file.")
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if certificate_url and not _https_url(certificate_url):
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errors.append("The BIMI certificate URL must use HTTPS when present.")
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elif not certificate_url:
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warnings.append("No BIMI certificate URL is published; some mailbox providers require one.")
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result = BIMIResult(
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status="pass" if not errors else "fail",
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dns_record=record,
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logo_url=logo_url,
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certificate_url=certificate_url,
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evidence_url=logo_url,
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errors=errors,
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warnings=warnings,
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)
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return result, warnings, errors
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async def check_bimi(
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domain: str,
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provider: BaseDNSProvider,
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*,
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selector: str = "default",
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) -> BIMIResult:
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"""Resolve and validate the BIMI TXT record for a domain selector."""
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normalized_selector = (selector or "default").strip().lower()
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query_name = f"{normalized_selector}._bimi.{domain}"
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result = BIMIResult(selector=normalized_selector, query_name=query_name)
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try:
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records = await provider.lookup_txt(query_name)
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except LookupError as exc:
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result.errors.append(f"BIMI DNS lookup failed: {exc}")
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return result
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parsed, warnings, errors = parse_bimi_record(records)
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if parsed is None:
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result.errors.extend(errors)
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return result
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parsed.selector = normalized_selector
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parsed.query_name = query_name
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parsed.warnings = warnings
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parsed.errors = errors
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return parsed
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async def check_bimi_cached(
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db: Session,
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provider: BaseDNSProvider,
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domain: str,
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*,
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selector: str = "default",
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ttl_seconds: int = DEFAULT_DNS_CACHE_TTL_SECONDS,
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refresh: bool = False,
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) -> Tuple[BIMIResult, bool, datetime]:
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"""Resolve BIMI posture, reusing the shared DNS cache semantics."""
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normalized_selector = (selector or "default").strip().lower()
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cache_key = f"{_CACHE_KEY_PREFIX}:{normalized_selector}"
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now = _utcnow_naive()
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provider_name = f"{provider.__class__.__name__}:bimi"
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row = (
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db.query(DNSCache)
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.filter(
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DNSCache.domain == domain,
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DNSCache.provider == provider_name,
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DNSCache.selectors_key == cache_key,
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)
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.first()
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)
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if row and not refresh and _is_fresh(row, ttl_seconds, now):
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return _result_from_json(row.result_json), True, row.checked_at
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result = await check_bimi(domain, provider, selector=normalized_selector)
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payload = json.dumps(asdict(result), sort_keys=True, separators=(",", ":"))
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if row is None:
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row = DNSCache(
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domain=domain,
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provider=provider_name,
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selectors_key=cache_key,
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result_json=payload,
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checked_at=now,
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)
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db.add(row)
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else:
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row.result_json = payload
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row.checked_at = now
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try:
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db.commit()
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except IntegrityError:
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db.rollback()
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row = (
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db.query(DNSCache)
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.filter(
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DNSCache.domain == domain,
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DNSCache.provider == provider_name,
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DNSCache.selectors_key == cache_key,
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)
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.first()
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)
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if row is None:
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raise
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row.result_json = payload
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row.checked_at = now
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db.commit()
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db.refresh(row)
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return result, False, row.checked_at
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