# Source code for w3lib.http

    from __future__ import annotations

    from base64 import b64encode
    from collections.abc import Mapping, MutableMapping, Sequence
    from io import BytesIO
    from typing import Any, TypeAlias, overload

    from w3lib.util import to_bytes, to_unicode

    HeadersDictInput: TypeAlias = Mapping[bytes, Any | Sequence[bytes]]
    HeadersDictOutput: TypeAlias = MutableMapping[bytes, list[bytes]]

    @overload
    def headers_raw_to_dict(headers_raw: bytes) -> HeadersDictOutput: ...

    @overload
    def headers_raw_to_dict(headers_raw: None) -> None: ...

    def headers_raw_to_dict(headers_raw: bytes | None) -> HeadersDictOutput | None:
        r"""
        Convert raw headers (single multi-line bytestring)
        to a dictionary.

        For example:

        >>> import w3lib.http
        >>> w3lib.http.headers_raw_to_dict(b"Content-type: text/html\n\rAccept: gzip\n\n")   # doctest: +SKIP
        {'Content-type': ['text/html'], 'Accept': ['gzip']}

        Incorrect input:

        >>> w3lib.http.headers_raw_to_dict(b"Content-typt gzip\n\n")
        {}
        >>>

        Argument is ``None`` (return ``None``):

        >>> w3lib.http.headers_raw_to_dict(None)
        >>>

        """

        if headers_raw is None:
            return None

        if not headers_raw:
            return {}

        result_dict: HeadersDictOutput = {}

        for header in BytesIO(headers_raw):
            key, sep, value = header.partition(b":")
            if not sep:
                continue

            key, value = key.strip(), value.strip()

            if key in result_dict:
                result_dict[key].append(value)
            else:
                result_dict[key] = [value]

        return result_dict

    @overload
    def headers_dict_to_raw(headers_dict: HeadersDictInput) -> bytes: ...

    @overload
    def headers_dict_to_raw(headers_dict: None) -> None: ...

    def headers_dict_to_raw(headers_dict: HeadersDictInput | None) -> bytes | None:
        r"""
        Returns a raw HTTP headers representation of headers

        For example:

        >>> import w3lib.http
        >>> w3lib.http.headers_dict_to_raw({b'Content-type': b'text/html', b'Accept': b'gzip'}) # doctest: +SKIP
        'Content-type: text/html\\r\\nAccept: gzip'
        >>>

        Note that keys and values must be bytes.

        Argument is ``None`` (returns ``None``):

        >>> w3lib.http.headers_dict_to_raw(None)
        >>>

        """

        if headers_dict is None:
            return None

        if not headers_dict:
            return b""

        parts = bytearray()

        for key, value in headers_dict.items():
            if isinstance(value, bytes):
                if parts:
                    parts.extend(b"\r\n")
                parts.extend(key + b": " + value)

            elif isinstance(value, (list, tuple)):
                for v in value:
                    if parts:
                        parts.extend(b"\r\n")
                    parts.extend(key + b": " + v)

        return bytes(parts)

    def basic_auth_header(
        username: str | bytes, password: str | bytes, encoding: str = "ISO-8859-1"
    ) -> bytes:
        """
        Return an `Authorization` header field value for `HTTP Basic Access Authentication (RFC 2617)`_

        >>> import w3lib.http
        >>> w3lib.http.basic_auth_header('someuser', 'somepass')
        b'Basic c29tZXVzZXI6c29tZXBhc3M='

        .. _HTTP Basic Access Authentication (RFC 2617): http://www.ietf.org/rfc/rfc2617.txt

        """

        auth = f"{to_unicode(username)}:{to_unicode(password)}"
        # XXX: RFC 2617 doesn't define encoding, but ISO-8859-1
        # seems to be the most widely used encoding here. See also:
        # http://greenbytes.de/tech/webdav/draft-ietf-httpauth-basicauth-enc-latest.html
        return b"Basic " + b64encode(to_bytes(auth, encoding=encoding))