path: root/ipalib/frontend.py

# Authors:
#   Jason Gerard DeRose <jderose@redhat.com>
#
# Copyright (C) 2008  Red Hat
# see file 'COPYING' for use and warranty information
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

"""
Base classes for all front-end plugins.
"""

import re
import inspect
from base import lock, check_name, NameSpace
from plugable import Plugin, is_production_mode
from parameters import create_param, parse_param_spec, Param, Str, Flag, Password
from util import make_repr
from output import Output, Entry, ListOfEntries
from text import _, ngettext

from errors import ZeroArgumentError, MaxArgumentError, OverlapError, RequiresRoot, VersionError, RequirementError
from errors import InvocationError
from constants import TYPE_ERROR
from ipapython.version import API_VERSION
from distutils import version


RULE_FLAG = 'validation_rule'

def rule(obj):
    assert not hasattr(obj, RULE_FLAG)
    setattr(obj, RULE_FLAG, True)
    return obj

def is_rule(obj):
    return callable(obj) and getattr(obj, RULE_FLAG, False) is True


def entry_count(entry):
    """
    Return the number of entries in an entry. This is primarly for the
    failed output parameter so we don't print empty values.

    We also use this to determine if a non-zero return value is needed.
    """
    num_entries = 0
    for f in entry:
        if type(entry[f]) is dict:
            num_entries = num_entries + entry_count(entry[f])
        else:
            num_entries = num_entries + len(entry[f])

    return num_entries


class HasParam(Plugin):
    """
    Base class for plugins that have `Param` `NameSpace` attributes.

    Subclasses of `HasParam` will on one or more attributes store `NameSpace`
    instances containing zero or more `Param` instances.  These parameters might
    describe, for example, the arguments and options a command takes, or the
    attributes an LDAP entry can include, or whatever else the subclass sees
    fit.

    Although the interface a subclass must implement is very simple, it must
    conform to a specific naming convention: if you want a namespace
    ``SubClass.foo``, you must define a ``Subclass.takes_foo`` attribute and a
    ``SubCLass.get_foo()`` method, and you may optionally define a
    ``SubClass.check_foo()`` method.


    A quick big-picture example
    ===========================

    Say you want the ``options`` instance attribute on your subclass to be a
    `Param` `NameSpace`... then according to the enforced naming convention,
    your subclass must define a ``takes_options`` attribute and a
    ``get_options()`` method.  For example:

    >>> from ipalib import Str, Int
    >>> class Example(HasParam):
    ...
    ...     options = None  # This will be replaced with your namespace
    ...
    ...     takes_options = (Str('one'), Int('two'))
    ...
    ...     def get_options(self):
    ...         return self._get_param_iterable('options')
    ...
    >>> eg = Example()

    The ``Example.takes_options`` attribute is a ``tuple`` defining the
    parameters you want your ``Example.options`` namespace to contain.  Your
    ``Example.takes_options`` attribute will be accessed via
    `HasParam._get_param_iterable()`, which, among other things, enforces the
    ``('takes_' + name)`` naming convention.  For example:

    >>> eg._get_param_iterable('options')
    (Str('one'), Int('two'))

    The ``Example.get_options()`` method simply returns
    ``Example.takes_options`` by calling `HasParam._get_param_iterable()`.  Your
    ``Example.get_options()`` method will be called via
    `HasParam._filter_param_by_context()`, which, among other things, enforces
    the ``('get_' + name)`` naming convention.  For example:

    >>> list(eg._filter_param_by_context('options'))
    [Str('one'), Int('two')]

    At this point, the ``eg.options`` instance attribute is still ``None``:

    >>> eg.options is None
    True

    `HasParam._create_param_namespace()` will create the ``eg.options``
    namespace from the parameters yielded by
    `HasParam._filter_param_by_context()`.  For example:

    >>> eg._create_param_namespace('options')
    >>> eg.options
    NameSpace(<2 members>, sort=False)
    >>> list(eg.options)  # Like dict.__iter__()
    ['one', 'two']

    Your subclass can optionally define a ``check_options()`` method to perform
    sanity checks.  If it exists, the ``check_options()`` method is called by
    `HasParam._create_param_namespace()` with a single value, the `NameSpace`
    instance it created.  For example:

    >>> class Example2(Example):
    ...
    ...     def check_options(self, namespace):
    ...         for param in namespace():  # Like dict.itervalues()
    ...             if param.name == 'three':
    ...                 raise ValueError("I dislike the param 'three'")
    ...         print '  ** Looks good! **'  # Note output below
    ...
    >>> eg = Example2()
    >>> eg._create_param_namespace('options')
      ** Looks good! **
    >>> eg.options
    NameSpace(<2 members>, sort=False)

    However, if we subclass again and add a `Param` named ``'three'``:

    >>> class Example3(Example2):
    ...
    ...     takes_options = (Str('one'), Int('two'), Str('three'))
    ...
    >>> eg = Example3()
    >>> eg._create_param_namespace('options')
    Traceback (most recent call last):
      ...
    ValueError: I dislike the param 'three'
    >>> eg.options is None  # eg.options was not set
    True


    The Devil and the details
    =========================

    In the above example, ``takes_options`` is a ``tuple``, but it can also be
    a param spec (see `create_param()`), or a callable that returns an iterable
    containing one or more param spec.  Regardless of how ``takes_options`` is
    defined, `HasParam._get_param_iterable()` will return a uniform iterable,
    conveniently hiding the details.

    The above example uses the simplest ``get_options()`` method possible, but
    you could instead implement a ``get_options()`` method that would, for
    example, produce (or withhold) certain parameters based on the whether
    certain plugins are loaded.

    Think of ``takes_options`` as declarative, a simple definition of *what*
    parameters should be included in the namespace.  You should only implement
    a ``takes_options()`` method if a `Param` must reference attributes on your
    plugin instance (for example, for validation rules); you should not use a
    ``takes_options()`` method to filter the parameters or add any other
    procedural behaviour.

    On the other hand, think of the ``get_options()`` method as imperative, a
    procedure for *how* the parameters should be created and filtered.  In the
    example above the *how* just returns the *what* unchanged, but arbitrary
    logic can be implemented in the ``get_options()`` method.  For example, you
    might filter certain parameters from ``takes_options`` base on some
    criteria, or you might insert additional parameters provided by other
    plugins.

    The typical use case for using ``get_options()`` this way is to procedurally
    generate the arguments and options for all the CRUD commands operating on a
    specific LDAP object: the `Object` plugin defines the possible LDAP entry
    attributes (as `Param`), and then the CRUD commands intelligently build
    their ``args`` and ``options`` namespaces based on which attribute is the
    primary key.  In this way new LDAP attributes (aka parameters) can be added
    to the single point of definition (the `Object` plugin), and all the
    corresponding CRUD commands pick up these new parameters without requiring
    modification.  For an example of how this is done, see the
    `ipalib.crud.Create` base class.

    However, there is one type of filtering you should not implement in your
    ``get_options()`` method, because it's already provided at a higher level:
    you should not filter parameters based on the value of ``api.env.context``
    nor (preferably) on any values in ``api.env``.
    `HasParam._filter_param_by_context()` already does this by calling
    `Param.use_in_context()` for each parameter.  Although the base
    `Param.use_in_context()` implementation makes a decision solely on the value
    of ``api.env.context``, subclasses can override this with implementations
    that consider arbitrary ``api.env`` values.
    """
    # HasParam is the base class for most frontend plugins, that make it to users
    # This flag indicates that the command should not be available in the cli
    NO_CLI = False

    def _get_param_iterable(self, name, verb='takes'):
        """
        Return an iterable of params defined by the attribute named ``name``.

        A sequence of params can be defined one of three ways: as a ``tuple``;
        as a callable that returns an iterable; or as a param spec (a `Param` or
        ``str`` instance).  This method returns a uniform iterable regardless of
        how the param sequence was defined.

        For example, when defined with a tuple:

        >>> class ByTuple(HasParam):
        ...     takes_args = (Param('foo'), Param('bar'))
        ...
        >>> by_tuple = ByTuple()
        >>> list(by_tuple._get_param_iterable('args'))
        [Param('foo'), Param('bar')]

        Or you can define your param sequence with a callable when you need to
        reference attributes on your plugin instance (for validation rules,
        etc.).  For example:

        >>> class ByCallable(HasParam):
        ...     def takes_args(self):
        ...         yield Param('foo', self.validate_foo)
        ...         yield Param('bar', self.validate_bar)
        ...
        ...     def validate_foo(self, _, value, **kw):
        ...         if value != 'Foo':
        ...             return _("must be 'Foo'")
        ...
        ...     def validate_bar(self, _, value, **kw):
        ...         if value != 'Bar':
        ...             return _("must be 'Bar'")
        ...
        >>> by_callable = ByCallable()
        >>> list(by_callable._get_param_iterable('args'))
        [Param('foo', validate_foo), Param('bar', validate_bar)]

        Lastly, as a convenience for when a param sequence contains a single
        param, your defining attribute may a param spec (either a `Param`
        or an ``str`` instance).  For example:

        >>> class BySpec(HasParam):
        ...     takes_args = Param('foo')
        ...     takes_options = 'bar?'
        ...
        >>> by_spec = BySpec()
        >>> list(by_spec._get_param_iterable('args'))
        [Param('foo')]
        >>> list(by_spec._get_param_iterable('options'))
        ['bar?']

        For information on how an ``str`` param spec is interpreted, see the
        `create_param()` and `parse_param_spec()` functions in the
        `ipalib.parameters` module.

        Also see `HasParam._filter_param_by_context()`.
        """
        src_name = verb + '_' + name
        src = getattr(self, src_name, None)
        if type(src) is tuple:
            return src
        if isinstance(src, (Param, str)):
            return (src,)
        if callable(src):
            return src()
        if src is None:
            return tuple()
        raise TypeError(
            '%s.%s must be a tuple, callable, or spec; got %r' % (
                self.name, src_name, src
            )
        )

    def _filter_param_by_context(self, name, env=None):
        """
        Filter params on attribute named ``name`` by environment ``env``.

        For example:

        >>> from ipalib.config import Env
        >>> class Example(HasParam):
        ...
        ...     takes_args = (
        ...         Str('foo_only', include=['foo']),
        ...         Str('not_bar', exclude=['bar']),
        ...         'both',
        ...     )
        ...
        ...     def get_args(self):
        ...         return self._get_param_iterable('args')
        ...
        ...
        >>> eg = Example()
        >>> foo = Env(context='foo')
        >>> bar = Env(context='bar')
        >>> another = Env(context='another')
        >>> (foo.context, bar.context, another.context)
        (u'foo', u'bar', u'another')
        >>> list(eg._filter_param_by_context('args', foo))
        [Str('foo_only', include=['foo']), Str('not_bar', exclude=['bar']), Str('both')]
        >>> list(eg._filter_param_by_context('args', bar))
        [Str('both')]
        >>> list(eg._filter_param_by_context('args', another))
        [Str('not_bar', exclude=['bar']), Str('both')]
        """
        env = getattr(self, 'env', env)
        get_name = 'get_' + name
        if not hasattr(self, get_name):
            raise NotImplementedError(
                '%s.%s()' % (self.name, get_name)
            )
        get = getattr(self, get_name)
        if not callable(get):
            raise TypeError(
                '%s.%s must be a callable; got %r' % (self.name, get_name, get)
            )
        for spec in get():
            param = create_param(spec)
            if env is None or param.use_in_context(env):
                if env is not None and not hasattr(param, 'env'):
                    # Force specified environment. The way it is done is violation of ReadOnly promise.
                    # Unfortunately, all alternatives are worse from both performance and code complexity
                    # points of view. See following threads on freeipa-devel@ for references:
                    # https://www.redhat.com/archives/freeipa-devel/2011-August/msg00000.html
                    # https://www.redhat.com/archives/freeipa-devel/2011-August/msg00011.html
                    object.__setattr__(param, 'env', env)
                yield param

    def _create_param_namespace(self, name, env=None):
        namespace = NameSpace(
            self._filter_param_by_context(name, env),
            sort=False
        )
        if not is_production_mode(self):
            check = getattr(self, 'check_' + name, None)
            if callable(check):
                check(namespace)
        setattr(self, name, namespace)


class Command(HasParam):
    """
    A public IPA atomic operation.

    All plugins that subclass from `Command` will be automatically available
    as a CLI command and as an XML-RPC method.

    Plugins that subclass from Command are registered in the ``api.Command``
    namespace. For example:

    >>> from ipalib import create_api
    >>> api = create_api()
    >>> class my_command(Command):
    ...     pass
    ...
    >>> api.register(my_command)
    >>> api.finalize()
    >>> list(api.Command)
    ['my_command']
    >>> api.Command.my_command # doctest:+ELLIPSIS
    ipalib.frontend.my_command()
    """

    finalize_early = False

    takes_options = tuple()
    takes_args = tuple()
    # Create stubs for attributes that are set in _on_finalize()
    args = Plugin.finalize_attr('args')
    options = Plugin.finalize_attr('options')
    params = Plugin.finalize_attr('params')
    obj = None

    use_output_validation = True
    output = Plugin.finalize_attr('output')
    has_output = ('result',)
    output_params = Plugin.finalize_attr('output_params')
    has_output_params = tuple()

    msg_summary = None
    msg_truncated = _('Results are truncated, try a more specific search')

    def __call__(self, *args, **options):
        """
        Perform validation and then execute the command.

        If not in a server context, the call will be forwarded over
        XML-RPC and the executed an the nearest IPA server.
        """
        self.ensure_finalized()
        params = self.args_options_2_params(*args, **options)
        self.debug(
            'raw: %s(%s)', self.name, ', '.join(self._repr_iter(**params))
        )
        while True:
            default = self.get_default(**params)
            if len(default) == 0:
                break
            params.update(default)
        params = self.normalize(**params)
        params = self.convert(**params)
        self.debug(
            '%s(%s)', self.name, ', '.join(self._repr_iter(**params))
        )
        if not self.api.env.in_server and 'version' not in params:
            params['version'] = API_VERSION
        self.validate(**params)
        if self.api.env.in_server:
            params = self.encode(**params)
        (args, options) = self.params_2_args_options(**params)
        ret = self.run(*args, **options)
        if (
            isinstance(ret, dict)
            and 'summary' in self.output
            and 'summary' not in ret
        ):
            if self.msg_summary:
                ret['summary'] = self.msg_summary % ret
            else:
                ret['summary'] = None
        if self.use_output_validation and (self.output or ret is not None):
            self.validate_output(ret)
        return ret

    def soft_validate(self, values):
        errors = dict()
        for p in self.params():
            try:
                value = values.get(p.name)
                values[p.name] = p(value, **values)
            except InvocationError, e:
                errors[p.name] = str(e)
        return dict(
            values=values,
            errors=errors,
        )

    def _repr_iter(self, **params):
        """
        Iterate through ``repr()`` of *safe* values of args and options.

        This method uses `parameters.Param.safe_value()` to mask passwords when
        logging.  Logging the exact call is extremely useful, but we obviously
        don't want to log the cleartext password.

        For example:

        >>> class my_cmd(Command):
        ...     takes_args = ('login',)
        ...     takes_options=(Password('passwd'),)
        ...
        >>> c = my_cmd()
        >>> c.finalize()
        >>> list(c._repr_iter(login=u'Okay.', passwd=u'Private!'))
        ["u'Okay.'", "passwd=u'********'"]
        """
        for arg in self.args():         #pylint: disable=E1102
            value = params.get(arg.name, None)
            yield repr(arg.safe_value(value))
        for option in self.options():   #pylint: disable=E1102
            if option.name not in params:
                continue
            value = params[option.name]
            yield '%s=%r' % (option.name, option.safe_value(value))

    def args_options_2_params(self, *args, **options):
        """
        Merge (args, options) into params.
        """
        if self.max_args is not None and len(args) > self.max_args:
            if self.max_args == 0:
                raise ZeroArgumentError(name=self.name)
            raise MaxArgumentError(name=self.name, count=self.max_args)
        params = dict(self.__options_2_params(options))
        if len(args) > 0:
            arg_kw = dict(self.__args_2_params(args))
            intersection = set(arg_kw).intersection(params)
            if len(intersection) > 0:
                raise OverlapError(names=sorted(intersection))
            params.update(arg_kw)
        return params

    def __args_2_params(self, values):
        multivalue = False
        for (i, arg) in enumerate(self.args()): #pylint: disable=E1102
            assert not multivalue
            if len(values) > i:
                if arg.multivalue:
                    multivalue = True
                    if len(values) == i + 1 and type(values[i]) in (list, tuple):
                        yield (arg.name, values[i])
                    else:
                        yield (arg.name, values[i:])
                else:
                    yield (arg.name, values[i])
            else:
                break

    def __options_2_params(self, options):
        for name in self.params:
            if name in options:
                yield (name, options[name])

    def args_options_2_entry(self, *args, **options):
        """
        Creates a LDAP entry from attributes in args and options.
        """
        kw = self.args_options_2_params(*args, **options)
        return dict(self.__attributes_2_entry(kw))

    def __attributes_2_entry(self, kw):
        for name in self.params:
            if self.params[name].attribute and name in kw:
                value = kw[name]
                if isinstance(value, tuple):
                    yield (name, [v for v in value])
                else:
                    yield (name, kw[name])

    def params_2_args_options(self, **params):
        """
        Split params into (args, options).
        """
        args = tuple(params.get(name, None) for name in self.args)
        options = dict(self.__params_2_options(params))
        return (args, options)

    def __params_2_options(self, params):
        for name in self.options:
            if name in params:
                yield(name, params[name])

    def normalize(self, **kw):
        """
        Return a dictionary of normalized values.

        For example:

        >>> class my_command(Command):
        ...     takes_options = (
        ...         Param('first', normalizer=lambda value: value.lower()),
        ...         Param('last'),
        ...     )
        ...
        >>> c = my_command()
        >>> c.finalize()
        >>> c.normalize(first=u'JOHN', last=u'DOE')
        {'last': u'DOE', 'first': u'john'}
        """
        return dict(
            (k, self.params[k].normalize(v)) for (k, v) in kw.iteritems()
        )

    def convert(self, **kw):
        """
        Return a dictionary of values converted to correct type.

        >>> from ipalib import Int
        >>> class my_command(Command):
        ...     takes_args = (
        ...         Int('one'),
        ...         'two',
        ...     )
        ...
        >>> c = my_command()
        >>> c.finalize()
        >>> c.convert(one=1, two=2)
        {'two': u'2', 'one': 1}
        """
        return dict(
            (k, self.params[k].convert(v)) for (k, v) in kw.iteritems()
        )

    def encode(self, **kw):
        """
        Return a dictionary of encoded values.
        """
        return dict(
            (k, self.params[k].encode(v)) for (k, v) in kw.iteritems()
        )

    def __convert_iter(self, kw):
        for param in self.params():
            if kw.get(param.name, None) is None:
                continue

    def get_default(self, **kw):
        """
        Return a dictionary of defaults for all missing required values.

        For example:

        >>> from ipalib import Str
        >>> class my_command(Command):
        ...     takes_args = Str('color', default=u'Red')
        ...
        >>> c = my_command()
        >>> c.finalize()
        >>> c.get_default()
        {'color': u'Red'}
        >>> c.get_default(color=u'Yellow')
        {}
        """
        return dict(self.__get_default_iter(kw))

    def __get_default_iter(self, kw):
        """
        Generator method used by `Command.get_default`.
        """
        for param in self.params():
            if param.name in kw:
                continue
            if param.required or param.autofill:
                default = param.get_default(**kw)
                if default is not None:
                    yield (param.name, default)

    def validate(self, **kw):
        """
        Validate all values.

        If any value fails the validation, `ipalib.errors.ValidationError`
        (or a subclass thereof) will be raised.
        """
        for param in self.params():
            value = kw.get(param.name, None)
            param.validate(value, self.env.context, supplied=param.name in kw)

    def verify_client_version(self, client_version):
        """
        Compare the version the client provided to the version of the
        server.

        If the client major version does not match then return an error.
        If the client minor version is less than or equal to the server
        then let the request proceed.
        """
        server_ver = version.LooseVersion(API_VERSION)
        ver = version.LooseVersion(client_version)
        if len(ver.version) < 2:
            raise VersionError(cver=ver.version, sver=server_ver.version, server= self.env.xmlrpc_uri)
        client_major = ver.version[0]
        client_minor = ver.version[1]

        server_major = server_ver.version[0]
        server_minor = server_ver.version[1]

        if server_major != client_major:
            raise VersionError(cver=client_version, sver=API_VERSION, server=self.env.xmlrpc_uri)
        if client_minor > server_minor:
            raise VersionError(cver=client_version, sver=API_VERSION, server=self.env.xmlrpc_uri)

    def run(self, *args, **options):
        """
        Dispatch to `Command.execute` or `Command.forward`.

        If running in a server context, `Command.execute` is called and the
        actually work this command performs is executed locally.

        If running in a non-server context, `Command.forward` is called,
        which forwards this call over XML-RPC to the exact same command
        on the nearest IPA server and the actual work this command
        performs is executed remotely.
        """
        if self.api.env.in_server:
            if 'version' in options:
                self.verify_client_version(options['version'])
                del options['version']
            return self.execute(*args, **options)
        return self.forward(*args, **options)

    def execute(self, *args, **kw):
        """
        Perform the actual work this command does.

        This method should be implemented only against functionality
        in self.api.Backend.  For example, a hypothetical
        user_add.execute() might be implemented like this:

        >>> class user_add(Command):
        ...     def execute(self, **kw):
        ...         return self.api.Backend.ldap.add(**kw)
        ...
        """
        raise NotImplementedError('%s.execute()' % self.name)

    def forward(self, *args, **kw):
        """
        Forward call over XML-RPC to this same command on server.
        """
        return self.Backend.xmlclient.forward(self.name, *args, **kw)

    def _on_finalize(self):
        """
        Finalize plugin initialization.

        This method creates the ``args``, ``options``, and ``params``
        namespaces.  This is not done in `Command.__init__` because
        subclasses (like `crud.Add`) might need to access other plugins
        loaded in self.api to determine what their custom `Command.get_args`
        and `Command.get_options` methods should yield.
        """
        self._create_param_namespace('args')
        if len(self.args) == 0 or not self.args[-1].multivalue:
            self.max_args = len(self.args)
        else:
            self.max_args = None
        self._create_param_namespace('options')
        def get_key(p):
            if p.required:
                if p.sortorder < 0:
                    return p.sortorder
                if p.default_from is None:
                    return 0
                return 1
            return 2
        self.params = NameSpace(
            sorted(tuple(self.args()) + tuple(self.options()), key=get_key),    #pylint: disable=E1102
            sort=False
        )
        self.output = NameSpace(self._iter_output(), sort=False)
        self._create_param_namespace('output_params')
        super(Command, self)._on_finalize()

    def _iter_output(self):
        if type(self.has_output) is not tuple:
            raise TypeError('%s.has_output: need a %r; got a %r: %r' % (
                self.name, tuple, type(self.has_output), self.has_output)
            )
        for (i, o) in enumerate(self.has_output):
            if isinstance(o, str):
                o = Output(o)
            if not isinstance(o, Output):
                raise TypeError('%s.has_output[%d]: need a %r; got a %r: %r' % (
                    self.name, i, (str, Output), type(o), o)
                )
            yield o

    def get_args(self):
        """
        Iterate through parameters for ``Command.args`` namespace.

        This method gets called by `HasParam._create_param_namespace()`.

        Subclasses can override this to customize how the arguments are
        determined.  For an example of why this can be useful, see the
        `ipalib.crud.Create` subclass.
        """
        for arg in self._get_param_iterable('args'):
            yield arg

    def check_args(self, args):
        """
        Sanity test for args namespace.

        This method gets called by `HasParam._create_param_namespace()`.
        """
        optional = False
        multivalue = False
        for arg in args():
            if optional and arg.required:
                raise ValueError(
                    '%s: required argument after optional' % arg.name
                )
            if multivalue:
                raise ValueError(
                    '%s: only final argument can be multivalue' % arg.name
                )
            if not arg.required:
                optional = True
            if arg.multivalue:
                multivalue = True

    def get_options(self):
        """
        Iterate through parameters for ``Command.options`` namespace.

        This method gets called by `HasParam._create_param_namespace()`.

        For commands that return entries two special options are generated:
        --all   makes the command retrieve/display all attributes
        --raw   makes the command display attributes as they are stored

        Subclasses can override this to customize how the arguments are
        determined.  For an example of why this can be useful, see the
        `ipalib.crud.Create` subclass.
        """
        for option in self._get_param_iterable('options'):
            yield option
        for o in self.has_output:
            if isinstance(o, (Entry, ListOfEntries)):
                yield Flag('all',
                    cli_name='all',
                    doc=_('Retrieve and print all attributes from the server. Affects command output.'),
                    exclude='webui',
                    flags=['no_output'],
                )
                yield Flag('raw',
                    cli_name='raw',
                    doc=_('Print entries as stored on the server. Only affects output format.'),
                    exclude='webui',
                    flags=['no_output'],
                )
                yield Str('version?',
                    doc=_('Client version. Used to determine if server will accept request.'),
                    exclude='webui',
                    flags=['no_option', 'no_output'],
                )
                return

    def validate_output(self, output):
        """
        Validate the return value to make sure it meets the interface contract.
        """
        nice = '%s.validate_output()' % self.name
        if not isinstance(output, dict):
            raise TypeError('%s: need a %r; got a %r: %r' % (
                nice, dict, type(output), output)
            )
        if len(output) < len(self.output):
            missing = sorted(set(self.output).difference(output))
            raise ValueError('%s: missing keys %r in %r' % (
                nice, missing, output)
            )
        if len(output) > len(self.output):
            extra = sorted(set(output).difference(self.output))
            raise ValueError('%s: unexpected keys %r in %r' % (
                nice, extra, output)
            )
        for o in self.output():
            value = output[o.name]
            if not (o.type is None or isinstance(value, o.type)):
                raise TypeError('%s:\n  output[%r]: need %r; got %r: %r' % (
                    nice, o.name, o.type, type(value), value)
                )
            if callable(o.validate):
                o.validate(self, value)

    def get_output_params(self):
        for param in self._get_param_iterable('output_params', verb='has'):
            yield param
        if self.params is None:
            return
        for param in self.params():
            if 'no_output' in param.flags:
                continue
            yield param

    def output_for_cli(self, textui, output, *args, **options):
        """
        Generic output method. Prints values the output argument according
        to their type and self.output.

        Entry attributes are labeled and printed in the order specified in
        self.output_params. Attributes that aren't present in
        self.output_params are not printed unless the command was invokend
        with the --all option. Attribute labelling is disabled if the --raw
        option was given.

        Subclasses can override this method, if custom output is needed.
        """
        if not isinstance(output, dict):
            return

        rv = 0

        order = [p.name for p in self.output_params()]  #pylint: disable=E1102
        if options.get('all', False):
            order.insert(0, 'dn')
            print_all = True
        else:
            print_all = False

        if options.get('raw', False):
            labels = None
        else:
            labels = dict((p.name, unicode(p.label)) for p in self.output_params()) #pylint: disable=E1102
        flags = dict((p.name, p.flags) for p in self.output_params())   #pylint: disable=E1102

        for o in self.output:
            outp = self.output[o]
            if 'no_display' in outp.flags:
                continue
            result = output[o]

            if o.lower() == 'count' and result == 0:
                rv = 1
            elif o.lower() == 'failed':
                if entry_count(result) == 0:
                    # Don't display an empty failed list
                    continue
                else:
                    # Return an error to the shell
                    rv = 1
            if isinstance(outp, ListOfEntries):
                textui.print_entries(result, order, labels, flags, print_all)
            elif isinstance(result, (tuple, list)):
                textui.print_entries(result, order, labels, flags, print_all)
            elif isinstance(outp, Entry):
                textui.print_entry(result, order, labels, flags, print_all)
            elif isinstance(result, dict):
                textui.print_entry(result, order, labels, flags, print_all)
            elif isinstance(result, unicode):
                if o == 'summary':
                    textui.print_summary(result)
                else:
                    textui.print_indented(result)
            elif isinstance(result, bool):
                # the Delete commands return a boolean indicating
                # success or failure. Ignore these.
                pass
            elif isinstance(result, int):
                textui.print_count(result, '%s %%d' % unicode(self.output[o].doc))

        return rv

    # list of attributes we want exported to JSON
    json_friendly_attributes = (
        'name', 'takes_args', 'takes_options',
    )

    def __json__(self):
        json_dict = dict(
            (a, getattr(self, a)) for a in self.json_friendly_attributes
        )
        return json_dict

class LocalOrRemote(Command):
    """
    A command that is explicitly executed locally or remotely.

    This is for commands that makes sense to execute either locally or
    remotely to return a perhaps different result.  The best example of
    this is the `ipalib.plugins.f_misc.env` plugin which returns the
    key/value pairs describing the configuration state: it can be
    """

    takes_options = (
        Flag('server?',
            doc=_('Forward to server instead of running locally'),
        ),
    )

    def run(self, *args, **options):
        """
        Dispatch to forward() or execute() based on ``server`` option.

        When running in a client context, this command is executed remotely if
        ``options['server']`` is true; otherwise it is executed locally.

        When running in a server context, this command is always executed
        locally and the value of ``options['server']`` is ignored.
        """
        if options['server'] and not self.env.in_server:
            return self.forward(*args, **options)
        return self.execute(*args, **options)


class Local(Command):
    """
    A command that is explicitly executed locally.

    This is for commands that makes sense to execute only locally
    such as the help command.
    """

    def run(self, *args, **options):
        """
        Dispatch to forward() onlly.
        """
        return self.forward(*args, **options)


class Object(HasParam):
    finalize_early = False

    # Create stubs for attributes that are set in _on_finalize()
    backend = Plugin.finalize_attr('backend')
    methods = Plugin.finalize_attr('methods')
    properties = Plugin.finalize_attr('properties')
    params = Plugin.finalize_attr('params')
    primary_key = Plugin.finalize_attr('primary_key')
    params_minus_pk = Plugin.finalize_attr('params_minus_pk')

    # Can override in subclasses:
    backend_name = None
    takes_params = tuple()

    def _on_finalize(self):
        self.methods = NameSpace(
            self.__get_attrs('Method'), sort=False, name_attr='attr_name'
        )
        self.properties = NameSpace(
            self.__get_attrs('Property'), sort=False, name_attr='attr_name'
        )
        self._create_param_namespace('params')
        pkeys = filter(lambda p: p.primary_key, self.params())  #pylint: disable=E1102
        if len(pkeys) > 1:
            raise ValueError(
                '%s (Object) has multiple primary keys: %s' % (
                    self.name,
                    ', '.join(p.name for p in pkeys),
                )
            )
        if len(pkeys) == 1:
            self.primary_key = pkeys[0]
            self.params_minus_pk = NameSpace(
                filter(lambda p: not p.primary_key, self.params()), sort=False  #pylint: disable=E1102
            )
        else:
            self.primary_key = None
            self.params_minus_pk = self.params

        if 'Backend' in self.api and self.backend_name in self.api.Backend:
            self.backend = self.api.Backend[self.backend_name]

        super(Object, self)._on_finalize()

    def params_minus(self, *names):
        """
        Yield all Param whose name is not in ``names``.
        """
        if len(names) == 1 and not isinstance(names[0], (Param, str)):
            names = names[0]
        minus = frozenset(names)
        for param in self.params(): #pylint: disable=E1102
            if param.name in minus or param in minus:
                continue
            yield param

    def get_dn(self, *args, **kwargs):
        """
        Construct an LDAP DN.
        """
        raise NotImplementedError('%s.get_dn()' % self.name)

    def __get_attrs(self, name):
        if name not in self.api:
            return
        namespace = self.api[name]
        assert type(namespace) is NameSpace
        for plugin in namespace(): # Equivalent to dict.itervalues()
            if plugin.obj_name == self.name:
                yield plugin

    def get_params(self):
        """
        This method gets called by `HasParam._create_param_namespace()`.
        """
        props = self.properties.__todict__()
        for spec in self._get_param_iterable('params'):
            if type(spec) is str:
                key = spec.rstrip('?*+')
            else:
                assert isinstance(spec, Param)
                key = spec.name
            if key in props:
                yield props.pop(key).param
            else:
                yield create_param(spec)
        def get_key(p):
            if p.param.required:
                if p.param.default_from is None:
                    return 0
                return 1
            return 2
        for prop in sorted(props.itervalues(), key=get_key):
            yield prop.param


class Attribute(Plugin):
    """
    Base class implementing the attribute-to-object association.

    `Attribute` plugins are associated with an `Object` plugin to group
    a common set of commands that operate on a common set of parameters.

    The association between attribute and object is done using a simple
    naming convention: the first part of the plugin class name (up to the
    first underscore) is the object name, and rest is the attribute name,
    as this table shows:

    ===============  ===========  ==============
    Class name       Object name  Attribute name
    ===============  ===========  ==============
    noun_verb        noun         verb
    user_add         user         add
    user_first_name  user         first_name
    ===============  ===========  ==============

    For example:

    >>> class user_add(Attribute):
    ...     pass
    ...
    >>> instance = user_add()
    >>> instance.obj_name
    'user'
    >>> instance.attr_name
    'add'

    In practice the `Attribute` class is not used directly, but rather is
    only the base class for the `Method` and `Property` classes.  Also see
    the `Object` class.
    """
    finalize_early = False

    NAME_REGEX = re.compile(
        '^(?P<obj>[a-z][a-z0-9]+)_(?P<attr>[a-z][a-z0-9]+(?:_[a-z][a-z0-9]+)*)$'
    )

    # Create stubs for attributes that are set in _on_finalize()
    __obj = Plugin.finalize_attr('_Attribute__obj')

    def __init__(self):
        m = self.NAME_REGEX.match(type(self).__name__)
        assert m
        self.__obj_name = m.group('obj')
        self.__attr_name = m.group('attr')
        super(Attribute, self).__init__()

    def __get_obj_name(self):
        return self.__obj_name
    obj_name = property(__get_obj_name)

    def __get_attr_name(self):
        return self.__attr_name
    attr_name = property(__get_attr_name)

    def __get_obj(self):
        """
        Returns the obj instance this attribute is associated with, or None
        if no association has been set.
        """
        return self.__obj
    obj = property(__get_obj)

    def _on_finalize(self):
        self.__obj = self.api.Object[self.obj_name]
        super(Attribute, self)._on_finalize()


class Method(Attribute, Command):
    """
    A command with an associated object.

    A `Method` plugin must have a corresponding `Object` plugin.  The
    association between object and method is done through a simple naming
    convention: the first part of the method name (up to the first under
    score) is the object name, as the examples in this table show:

    =============  ===========  ==============
    Method name    Object name  Attribute name
    =============  ===========  ==============
    user_add       user         add
    noun_verb      noun         verb
    door_open_now  door         open_now
    =============  ===========  ==============

    There are three different places a method can be accessed.  For example,
    say you created a `Method` plugin and its corresponding `Object` plugin
    like this:

    >>> from ipalib import create_api
    >>> api = create_api()
    >>> class user_add(Method):
    ...     def run(self):
    ...             return dict(result='Added the user!')
    ...
    >>> class user(Object):
    ...     pass
    ...
    >>> api.register(user_add)
    >>> api.register(user)
    >>> api.finalize()

    First, the ``user_add`` plugin can be accessed through the ``api.Method``
    namespace:

    >>> list(api.Method)
    ['user_add']
    >>> api.Method.user_add() # Will call user_add.run()
    {'result': 'Added the user!'}

    Second, because `Method` is a subclass of `Command`, the ``user_add``
    plugin can also be accessed through the ``api.Command`` namespace:

    >>> list(api.Command)
    ['user_add']
    >>> api.Command.user_add() # Will call user_add.run()
    {'result': 'Added the user!'}

    And third, ``user_add`` can be accessed as an attribute on the ``user``
    `Object`:

    >>> list(api.Object)
    ['user']
    >>> list(api.Object.user.methods)
    ['add']
    >>> api.Object.user.methods.add() # Will call user_add.run()
    {'result': 'Added the user!'}

    The `Attribute` base class implements the naming convention for the
    attribute-to-object association.  Also see the `Object` and the
    `Property` classes.
    """
    extra_options_first = False
    extra_args_first = False

    def __init__(self):
        super(Method, self).__init__()

    def get_output_params(self):
        for param in self.obj.params():
            if 'no_output' in param.flags:
                continue
            yield param
        for param in self.params():
            if param.name not in list(self.obj.params):
                if 'no_output' in param.flags:
                    continue
                yield param
        for param in self._get_param_iterable('output_params', verb='has'):
            yield param


class Property(Attribute):
    klass = Str
    default = None
    default_from = None
    normalizer = None

    def __init__(self):
        super(Property, self).__init__()
        # FIXME: This is a hack till Param.label is updated to require a
        # LazyText instance:
        self.label = None
        self.rules = tuple(
            sorted(self.__rules_iter(), key=lambda f: getattr(f, '__name__'))
        )
        self.kwargs = tuple(
            sorted(self.__kw_iter(), key=lambda keyvalue: keyvalue[0])
        )
        kw = dict(self.kwargs)
        self.param = self.klass(self.attr_name, *self.rules, **kw)

    def __kw_iter(self):
        for (key, kind, default) in self.klass.kwargs:
            if getattr(self, key, None) is not None:
                yield (key, getattr(self, key))

    def __rules_iter(self):
        """
        Iterates through the attributes in this instance to retrieve the
        methods implementing validation rules.
        """
        for name in dir(self.__class__):
            if name.startswith('_'):
                continue
            base_attr = getattr(self.__class__, name)
            if is_rule(base_attr):
                attr = getattr(self, name)
                if is_rule(attr):
                    yield attr

class Updater(Method):
    """
    An LDAP update with an associated object (always update).

    All plugins that subclass from `Updater` will be automatically available
    as a server update function.

    Plugins that subclass from Updater are registered in the ``api.Updater``
    namespace. For example:

    >>> from ipalib import create_api
    >>> api = create_api()
    >>> class my(Object):
    ...     pass
    ...
    >>> api.register(my)
    >>> class my_update(Updater):
    ...     pass
    ...
    >>> api.register(my_update)
    >>> api.finalize()
    >>> list(api.Updater)
    ['my_update']
    >>> api.Updater.my_update # doctest:+ELLIPSIS
    ipalib.frontend.my_update()
    """
    def __init__(self):
        super(Updater, self).__init__()

    def __call__(self, **options):
        self.debug(
            'raw: %s', self.name
        )

        return self.execute(**options)