# Source code for scrapy.spidermiddlewares.referer

    """
    RefererMiddleware: populates Request referer field, based on the Response which
    originated it.
    """

    from __future__ import annotations

    import warnings
    from abc import ABC, abstractmethod
    from typing import TYPE_CHECKING, cast
    from urllib.parse import urlparse

    from w3lib.url import safe_url_string

    from scrapy import Spider, signals
    from scrapy.exceptions import NotConfigured
    from scrapy.http import Request, Response
    from scrapy.spidermiddlewares.base import BaseSpiderMiddleware
    from scrapy.utils.misc import load_object
    from scrapy.utils.python import to_unicode
    from scrapy.utils.url import strip_url

    if TYPE_CHECKING:
        # typing.Self requires Python 3.11
        from typing_extensions import Self

        from scrapy.crawler import Crawler
        from scrapy.settings import BaseSettings

    LOCAL_SCHEMES: tuple[str, ...] = (
        "about",
        "blob",
        "data",
        "filesystem",
    )

    POLICY_NO_REFERRER = "no-referrer"
    POLICY_NO_REFERRER_WHEN_DOWNGRADE = "no-referrer-when-downgrade"
    POLICY_SAME_ORIGIN = "same-origin"
    POLICY_ORIGIN = "origin"
    POLICY_STRICT_ORIGIN = "strict-origin"
    POLICY_ORIGIN_WHEN_CROSS_ORIGIN = "origin-when-cross-origin"
    POLICY_STRICT_ORIGIN_WHEN_CROSS_ORIGIN = "strict-origin-when-cross-origin"
    POLICY_UNSAFE_URL = "unsafe-url"
    POLICY_SCRAPY_DEFAULT = "scrapy-default"

    class ReferrerPolicy(ABC):
        """Abstract base class for referrer policies."""

        NOREFERRER_SCHEMES: tuple[str, ...] = LOCAL_SCHEMES
        name: str

        @abstractmethod
        def referrer(self, response_url: str, request_url: str) -> str | None:
            raise NotImplementedError

        def stripped_referrer(self, url: str) -> str | None:
            if urlparse(url).scheme not in self.NOREFERRER_SCHEMES:
                return self.strip_url(url)
            return None

        def origin_referrer(self, url: str) -> str | None:
            if urlparse(url).scheme not in self.NOREFERRER_SCHEMES:
                return self.origin(url)
            return None

        def strip_url(self, url: str, origin_only: bool = False) -> str | None:
            """
            https://www.w3.org/TR/referrer-policy/#strip-url

            If url is null, return no referrer.
            If url's scheme is a local scheme, then return no referrer.
            Set url's username to the empty string.
            Set url's password to null.
            Set url's fragment to null.
            If the origin-only flag is true, then:
                Set url's path to null.
                Set url's query to null.
            Return url.
            """
            if not url:
                return None
            return strip_url(
                url,
                strip_credentials=True,
                strip_fragment=True,
                strip_default_port=True,
                origin_only=origin_only,
            )

        def origin(self, url: str) -> str | None:
            """Return serialized origin (scheme, host, path) for a request or response URL."""
            return self.strip_url(url, origin_only=True)

        def potentially_trustworthy(self, url: str) -> bool:
            # Note: this does not follow https://w3c.github.io/webappsec-secure-contexts/#is-url-trustworthy
            parsed_url = urlparse(url)
            if parsed_url.scheme in ("data",):
                return False
            return self.tls_protected(url)

        def tls_protected(self, url: str) -> bool:
            return urlparse(url).scheme in ("https", "ftps")

    class NoReferrerPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-no-referrer

        The simplest policy is "no-referrer", which specifies that no referrer information
        is to be sent along with requests made from a particular request client to any origin.
        The header will be omitted entirely.
        """

        name: str = POLICY_NO_REFERRER

        def referrer(self, response_url: str, request_url: str) -> str | None:
            return None

    class NoReferrerWhenDowngradePolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-no-referrer-when-downgrade

        The "no-referrer-when-downgrade" policy sends a full URL along with requests
        from a TLS-protected environment settings object to a potentially trustworthy URL,
        and requests from clients which are not TLS-protected to any origin.

        Requests from TLS-protected clients to non-potentially trustworthy URLs,
        on the other hand, will contain no referrer information.
        A Referer HTTP header will not be sent.

        This is a user agent's default behavior, if no policy is otherwise specified.
        """

        name: str = POLICY_NO_REFERRER_WHEN_DOWNGRADE

        def referrer(self, response_url: str, request_url: str) -> str | None:
            if not self.tls_protected(response_url) or self.tls_protected(request_url):
                return self.stripped_referrer(response_url)
            return None

    class SameOriginPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-same-origin

        The "same-origin" policy specifies that a full URL, stripped for use as a referrer,
        is sent as referrer information when making same-origin requests from a particular request client.

        Cross-origin requests, on the other hand, will contain no referrer information.
        A Referer HTTP header will not be sent.
        """

        name: str = POLICY_SAME_ORIGIN

        def referrer(self, response_url: str, request_url: str) -> str | None:
            if self.origin(response_url) == self.origin(request_url):
                return self.stripped_referrer(response_url)
            return None

    class OriginPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-origin

        The "origin" policy specifies that only the ASCII serialization
        of the origin of the request client is sent as referrer information
        when making both same-origin requests and cross-origin requests
        from a particular request client.
        """

        name: str = POLICY_ORIGIN

        def referrer(self, response_url: str, request_url: str) -> str | None:
            return self.origin_referrer(response_url)

    class StrictOriginPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-strict-origin

        The "strict-origin" policy sends the ASCII serialization
        of the origin of the request client when making requests:
        - from a TLS-protected environment settings object to a potentially trustworthy URL, and
        - from non-TLS-protected environment settings objects to any origin.

        Requests from TLS-protected request clients to non- potentially trustworthy URLs,
        on the other hand, will contain no referrer information.
        A Referer HTTP header will not be sent.
        """

        name: str = POLICY_STRICT_ORIGIN

        def referrer(self, response_url: str, request_url: str) -> str | None:
            if (
                self.tls_protected(response_url)
                and self.potentially_trustworthy(request_url)
            ) or not self.tls_protected(response_url):
                return self.origin_referrer(response_url)
            return None

    class OriginWhenCrossOriginPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-origin-when-cross-origin

        The "origin-when-cross-origin" policy specifies that a full URL,
        stripped for use as a referrer, is sent as referrer information
        when making same-origin requests from a particular request client,
        and only the ASCII serialization of the origin of the request client
        is sent as referrer information when making cross-origin requests
        from a particular request client.
        """

        name: str = POLICY_ORIGIN_WHEN_CROSS_ORIGIN

        def referrer(self, response_url: str, request_url: str) -> str | None:
            origin = self.origin(response_url)
            if origin == self.origin(request_url):
                return self.stripped_referrer(response_url)
            return origin

    class StrictOriginWhenCrossOriginPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-strict-origin-when-cross-origin

        The "strict-origin-when-cross-origin" policy specifies that a full URL,
        stripped for use as a referrer, is sent as referrer information
        when making same-origin requests from a particular request client,
        and only the ASCII serialization of the origin of the request client
        when making cross-origin requests:

        - from a TLS-protected environment settings object to a potentially trustworthy URL, and
        - from non-TLS-protected environment settings objects to any origin.

        Requests from TLS-protected clients to non- potentially trustworthy URLs,
        on the other hand, will contain no referrer information.
        A Referer HTTP header will not be sent.
        """

        name: str = POLICY_STRICT_ORIGIN_WHEN_CROSS_ORIGIN

        def referrer(self, response_url: str, request_url: str) -> str | None:
            origin = self.origin(response_url)
            if origin == self.origin(request_url):
                return self.stripped_referrer(response_url)
            if (
                self.tls_protected(response_url)
                and self.potentially_trustworthy(request_url)
            ) or not self.tls_protected(response_url):
                return self.origin_referrer(response_url)
            return None

    class UnsafeUrlPolicy(ReferrerPolicy):
        """
        https://www.w3.org/TR/referrer-policy/#referrer-policy-unsafe-url

        The "unsafe-url" policy specifies that a full URL, stripped for use as a referrer,
        is sent along with both cross-origin requests
        and same-origin requests made from a particular request client.

        Note: The policy's name doesn't lie; it is unsafe.
        This policy will leak origins and paths from TLS-protected resources
        to insecure origins.
        Carefully consider the impact of setting such a policy for potentially sensitive documents.
        """

        name: str = POLICY_UNSAFE_URL

        def referrer(self, response_url: str, request_url: str) -> str | None:
            return self.stripped_referrer(response_url)

    class DefaultReferrerPolicy(NoReferrerWhenDowngradePolicy):
        """
        A variant of "no-referrer-when-downgrade",
        with the addition that "Referer" is not sent if the parent request was
        using ``file://`` or ``s3://`` scheme.
        """

        NOREFERRER_SCHEMES: tuple[str, ...] = (*LOCAL_SCHEMES, "file", "s3")
        name: str = POLICY_SCRAPY_DEFAULT

    _policy_classes: dict[str, type[ReferrerPolicy]] = {
        p.name: p
        for p in (
            NoReferrerPolicy,
            NoReferrerWhenDowngradePolicy,
            SameOriginPolicy,
            OriginPolicy,
            StrictOriginPolicy,
            OriginWhenCrossOriginPolicy,
            StrictOriginWhenCrossOriginPolicy,
            UnsafeUrlPolicy,
            DefaultReferrerPolicy,
        )
    }

    # Reference: https://www.w3.org/TR/referrer-policy/#referrer-policy-empty-string
    _policy_classes[""] = NoReferrerWhenDowngradePolicy

    def _load_policy_class(
        policy: str, warning_only: bool = False
    ) -> type[ReferrerPolicy] | None:
        """
        Expect a string for the path to the policy class,
        otherwise try to interpret the string as a standard value
        from https://www.w3.org/TR/referrer-policy/#referrer-policies
        """
        try:
            return cast("type[ReferrerPolicy]", load_object(policy))
        except ValueError:
            tokens = [token.strip() for token in policy.lower().split(",")]
            # https://www.w3.org/TR/referrer-policy/#parse-referrer-policy-from-header
            for token in tokens[::-1]:
                if token in _policy_classes:
                    return _policy_classes[token]

            msg = f"Could not load referrer policy {policy!r}"
            if not warning_only:
                raise RuntimeError(msg)
            warnings.warn(msg, RuntimeWarning)
            return None

    class RefererMiddleware(BaseSpiderMiddleware):
        def __init__(self, settings: BaseSettings | None = None):  # pylint: disable=super-init-not-called
            self.default_policy: type[ReferrerPolicy] = DefaultReferrerPolicy
            if settings is not None:
                settings_policy = _load_policy_class(settings.get("REFERRER_POLICY"))
                assert settings_policy
                self.default_policy = settings_policy

        @classmethod
        def from_crawler(cls, crawler: Crawler) -> Self:
            if not crawler.settings.getbool("REFERER_ENABLED"):
                raise NotConfigured
            mw = cls(crawler.settings)

            # Note: this hook is a bit of a hack to intercept redirections
            crawler.signals.connect(mw.request_scheduled, signal=signals.request_scheduled)

            return mw

        def policy(self, resp_or_url: Response | str, request: Request) -> ReferrerPolicy:
            """
            Determine Referrer-Policy to use from a parent Response (or URL),
            and a Request to be sent.

            - if a valid policy is set in Request meta, it is used.
            - if the policy is set in meta but is wrong (e.g. a typo error),
              the policy from settings is used
            - if the policy is not set in Request meta,
              but there is a Referrer-policy header in the parent response,
              it is used if valid
            - otherwise, the policy from settings is used.
            """
            policy_name = request.meta.get("referrer_policy")
            if policy_name is None and isinstance(resp_or_url, Response):
                policy_header = resp_or_url.headers.get("Referrer-Policy")
                if policy_header is not None:
                    policy_name = to_unicode(policy_header.decode("latin1"))
            if policy_name is None:
                return self.default_policy()

            cls = _load_policy_class(policy_name, warning_only=True)
            return cls() if cls else self.default_policy()

        def get_processed_request(
            self, request: Request, response: Response | None
        ) -> Request | None:
            if response is None:
                # start requests
                return request
            referrer = self.policy(response, request).referrer(response.url, request.url)
            if referrer is not None:
                request.headers.setdefault("Referer", referrer)
            return request

        def request_scheduled(self, request: Request, spider: Spider) -> None:
            # check redirected request to patch "Referer" header if necessary
            redirected_urls = request.meta.get("redirect_urls", [])
            if redirected_urls:
                request_referrer = request.headers.get("Referer")
                # we don't patch the referrer value if there is none
                if request_referrer is not None:
                    # the request's referrer header value acts as a surrogate
                    # for the parent response URL
                    #
                    # Note: if the 3xx response contained a Referrer-Policy header,
                    #       the information is not available using this hook
                    parent_url = safe_url_string(request_referrer)
                    policy_referrer = self.policy(parent_url, request).referrer(
                        parent_url, request.url
                    )
                    if policy_referrer != request_referrer.decode("latin1"):
                        if policy_referrer is None:
                            request.headers.pop("Referer")
                        else:
                            request.headers["Referer"] = policy_referrer