webmentions_ssg/url_security.py


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import ipaddress
from urllib.parse import urlsplit

import dns.exception
import dns.resolver


class AddressResolutionError(Exception):
    pass


def is_public_url(url: str) -> bool:
    hostname = urlsplit(url).hostname

    if hostname is None:
        raise ValueError("No hostname was specified")

    try:
        answers = dns.resolver.resolve_name(hostname)
    except dns.exception.DNSException as exc:
        raise AddressResolutionError(
            f"Could not resolve hostname {hostname!r}"
        ) from exc
    else:
        for address in answers.addresses():
            if not ipaddress.ip_address(address).is_global:
                return False

        return True


def is_http_url(url: str) -> bool:
    """Return whether a URL is an absolute HTTP or HTTPS URL."""
    try:
        parsed = urlsplit(url)
    except ValueError:
        return False

    return parsed.scheme.lower() in {"http", "https"} and parsed.hostname is not None