Asserts whether all headers have been successfully parsed.
    Extracts encountered errors from the result of parsing headers.

    Only works on Python 3.

    :param headers: Headers to verify.
    :type headers: `httplib.HTTPMessage`.

    :raises urllib3.exceptions.HeaderParsingError:
        If parsing errors are found.

def assert_header_parsing(headers):
    """
    Asserts whether all headers have been successfully parsed.
    Extracts encountered errors from the result of parsing headers.

    Only works on Python 3.

    :param headers: Headers to verify.
    :type headers: `httplib.HTTPMessage`.

    :raises urllib3.exceptions.HeaderParsingError:
        If parsing errors are found.
    """

    # This will fail silently if we pass in the wrong kind of parameter.
    # To make debugging easier add an explicit check.
    if not isinstance(headers, httplib.HTTPMessage):
        raise TypeError('expected httplib.Message, got {0}.'.format(
            type(headers)))

    defects = getattr(headers, 'defects', None)
    get_payload = getattr(headers, 'get_payload', None)

    unparsed_data = None
    if get_payload:
        # get_payload is actually email.message.Message.get_payload;
        # we're only interested in the result if it's not a multipart message
        if not headers.is_multipart():
            payload = get_payload()

            if isinstance(payload, (bytes, str)):
                unparsed_data = payload

    if defects or unparsed_data:
        raise HeaderParsingError(defects=defects, unparsed_data=unparsed_data)