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# Licensed under the Apache License, Version 2.0 (the "License");
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#    http://www.apache.org/licenses/LICENSE-2.0
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from swift.common.utils import urlparse


def clean_acl(name, value):
    """
    Returns a cleaned ACL header value, validating that it meets the formatting
    requirements for standard Swift ACL strings.

    The ACL format is::

        [item[,item...]]

    Each item can be a group name to give access to or a referrer designation
    to grant or deny based on the HTTP Referer header.

    The referrer designation format is::

        .r:[-]value

    The ``.r`` can also be ``.ref``, ``.referer``, or ``.referrer``; though it
    will be shortened to just ``.r`` for decreased character count usage.

    The value can be ``*`` to specify any referrer host is allowed access, a
    specific host name like ``www.example.com``, or if it has a leading period
    ``.`` or leading ``*.`` it is a domain name specification, like
    ``.example.com`` or ``*.example.com``. The leading minus sign ``-``
    indicates referrer hosts that should be denied access.

    Referrer access is applied in the order they are specified. For example,
    .r:.example.com,.r:-thief.example.com would allow all hosts ending with
    .example.com except for the specific host thief.example.com.

    Example valid ACLs::

        .r:*
        .r:*,.r:-.thief.com
        .r:*,.r:.example.com,.r:-thief.example.com
        .r:*,.r:-.thief.com,bobs_account,sues_account:sue
        bobs_account,sues_account:sue

    Example invalid ACLs::

        .r:
        .r:-

    By default, allowing read access via .r will not allow listing objects in
    the container -- just retrieving objects from the container. To turn on
    listings, use the .rlistings directive.

    Also, .r designations aren't allowed in headers whose names include the
    word 'write'.

    ACLs that are "messy" will be cleaned up. Examples:

    ======================  ======================
    Original                Cleaned
    ----------------------  ----------------------
    ``bob, sue``            ``bob,sue``
    ``bob , sue``           ``bob,sue``
    ``bob,,,sue``           ``bob,sue``
    ``.referrer : *``       ``.r:*``
    ``.ref:*.example.com``  ``.r:.example.com``
    ``.r:*, .rlistings``    ``.r:*,.rlistings``
    ======================  ======================

    :param name: The name of the header being cleaned, such as X-Container-Read
                 or X-Container-Write.
    :param value: The value of the header being cleaned.
    :returns: The value, cleaned of extraneous formatting.
    :raises ValueError: If the value does not meet the ACL formatting
                        requirements; the error message will indicate why.
    """
    name = name.lower()
    values = []
    for raw_value in value.split(','):
        raw_value = raw_value.strip()
        if raw_value:
            if ':' not in raw_value:
                values.append(raw_value)
            else:
                first, second = (v.strip() for v in raw_value.split(':', 1))
                if not first or first[0] != '.':
                    values.append(raw_value)
                elif first in ('.r', '.ref', '.referer', '.referrer'):
                    if 'write' in name:
                        raise ValueError('Referrers not allowed in write ACL: '
                                         '%s' % repr(raw_value))
                    negate = False
                    if second and second[0] == '-':
                        negate = True
                        second = second[1:].strip()
                    if second and second != '*' and second[0] == '*':
                        second = second[1:].strip()
                    if not second or second == '.':
                        raise ValueError('No host/domain value after referrer '
                                         'designation in ACL: %s' %
                                         repr(raw_value))
                    values.append('.r:%s%s' % ('-' if negate else '', second))
                else:
                    raise ValueError('Unknown designator %s in ACL: %s' %
                                     (repr(first), repr(raw_value)))
    return ','.join(values)


def parse_acl(acl_string):
    """
    Parses a standard Swift ACL string into a referrers list and groups list.

    See :func:`clean_acl` for documentation of the standard Swift ACL format.

    :param acl_string: The standard Swift ACL string to parse.
    :returns: A tuple of (referrers, groups) where referrers is a list of
              referrer designations (without the leading .r:) and groups is a
              list of groups to allow access.
    """
    referrers = []
    groups = []
    if acl_string:
        for value in acl_string.split(','):
            if value.startswith('.r:'):
                referrers.append(value[len('.r:'):])
            else:
                groups.append(value)
    return referrers, groups


def referrer_allowed(referrer, referrer_acl):
    """
    Returns True if the referrer should be allowed based on the referrer_acl
    list (as returned by :func:`parse_acl`).

    See :func:`clean_acl` for documentation of the standard Swift ACL format.

    :param referrer: The value of the HTTP Referer header.
    :param referrer_acl: The list of referrer designations as returned by
                         :func:`parse_acl`.
    :returns: True if the referrer should be allowed; False if not.
    """
    allow = False
    if referrer_acl:
        rhost = urlparse(referrer or '').hostname or 'unknown'
        for mhost in referrer_acl:
            if mhost[0] == '-':
                mhost = mhost[1:]
                if mhost == rhost or (mhost[0] == '.' and
                                      rhost.endswith(mhost)):
                    allow = False
            elif mhost == '*' or mhost == rhost or \
                    (mhost[0] == '.' and rhost.endswith(mhost)):
                allow = True
    return allow
