freeipa/ipalib/plugable.py

443 lines
11 KiB
Python

# 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; version 2 only
#
# 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, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
"""
Base classes for plug-in architecture and generative API.
"""
import re
import inspect
import errors
def to_cli(name):
"""
Takes a Python identifier and transforms it into form suitable for the
Command Line Interface.
"""
assert isinstance(name, str)
return name.replace('_', '-')
def from_cli(cli_name):
"""
Takes a string from the Command Line Interface and transforms it into a
Python identifier.
"""
assert isinstance(cli_name, basestring)
return cli_name.replace('-', '_')
def check_identifier(name):
"""
Raises errors.NameSpaceError if `name` is not a valid Python identifier
suitable for use in a NameSpace.
"""
regex = r'^[a-z][_a-z0-9]*[a-z0-9]$'
if re.match(regex, name) is None:
raise errors.NameSpaceError(name, regex)
class Plugin(object):
"""
Base class for all plugins.
"""
__api = None
def __get_api(self):
"""
Returns the plugable.API instance passed to Plugin.finalize(), or
or returns None if finalize() has not yet been called.
"""
return self.__api
api = property(__get_api)
def finalize(self, api):
"""
After all the plugins are instantiated, the plugable.API calls this
method, passing itself as the only argument. This is where plugins
should check that other plugins they depend upon have actually be
loaded.
"""
assert self.__api is None, 'finalize() can only be called once'
assert api is not None, 'finalize() argument cannot be None'
self.__api = api
def __get_name(self):
"""
Returns the class name of this instance.
"""
return self.__class__.__name__
name = property(__get_name)
def __repr__(self):
"""
Returns a fully qualified <module><name> representation of the class.
"""
return '%s.%s' % (
self.__class__.__module__,
self.__class__.__name__
)
class ReadOnly(object):
"""
Base class for classes with read-only attributes.
"""
__slots__ = tuple()
def __setattr__(self, name, value):
"""
This raises an AttributeError anytime an attempt is made to set an
attribute.
"""
raise AttributeError('read-only: cannot set %s.%s' %
(self.__class__.__name__, name)
)
def __delattr__(self, name):
"""
This raises an AttributeError anytime an attempt is made to delete an
attribute.
"""
raise AttributeError('read-only: cannot del %s.%s' %
(self.__class__.__name__, name)
)
class Proxy(ReadOnly):
"""
Used to only export certain attributes into the generative API.
Subclasses must list names of attributes to be proxied in the __slots__
class attribute.
"""
__slots__ = (
'__obj',
'name',
)
def __init__(self, obj, proxy_name=None):
"""
Proxy attributes on `obj`.
"""
if proxy_name is None:
proxy_name = obj.__class__.__name__
check_identifier(proxy_name)
object.__setattr__(self, '_Proxy__obj', obj)
object.__setattr__(self, 'name', proxy_name)
for name in self.__slots__:
attr = getattr(obj, name)
if callable(attr):
object.__setattr__(self, name, attr)
def __repr__(self):
return '%s(%r)' % (self.__class__.__name__, self.__obj)
def __str__(self):
return to_cli(self.name)
def _clone(self, new_name):
return self.__class__(self.__obj, proxy_name=new_name)
def __getattr__(self, name):
if name in self.__slots__:
return getattr(self.__obj, name)
raise AttributeError('attribute %r not in %s.__slots__' % (
name,
self.__class__.__name__
)
)
class Proxy2(ReadOnly):
__slots__ = (
'base',
'name',
'__target',
)
def __init__(self, base, target, name_attr='name'):
if not inspect.isclass(base):
raise TypeError('arg1 must be a class, got %r' % base)
if not isinstance(target, base):
raise ValueError('arg2 must be instance of arg1, got %r' % target)
object.__setattr__(self, 'base', base)
object.__setattr__(self, '_Proxy2__target', target)
# Check base.public
assert type(self.base.public) is frozenset
# Check name
object.__setattr__(self, 'name', getattr(target, name_attr))
check_identifier(self.name)
def __iter__(self):
for name in sorted(self.base.public):
yield name
def __getitem__(self, key):
if key in self.base.public:
return getattr(self.__target, key)
raise KeyError('no proxy attribute %r' % key)
def __getattr__(self, name):
if name in self.base.public:
return getattr(self.__target, name)
raise AttributeError('no proxy attribute %r' % name)
def __call__(self, *args, **kw):
return self['__call__'](*args, **kw)
class NameSpace2(ReadOnly):
"""
A read-only namespace of (key, value) pairs that can be accessed
both as instance attributes and as dictionary items.
"""
def __init__(self, proxies):
"""
NameSpace2
"""
object.__setattr__(self, '_NameSpace2__proxies', tuple(proxies))
object.__setattr__(self, '_NameSpace2__d', dict())
for proxy in self.__proxies:
assert isinstance(proxy, Proxy2)
assert proxy.name not in self.__d
self.__d[proxy.name] = proxy
assert not hasattr(self, proxy.name)
object.__setattr__(self, proxy.name, proxy)
def __iter__(self):
"""
Iterates through the proxies in this NameSpace in the same order they
were passed in the contructor.
"""
for proxy in self.__proxies:
yield proxy
def __len__(self):
"""
Returns number of proxies in this NameSpace.
"""
return len(self.__proxies)
def __contains__(self, key):
"""
Returns True if a proxy named `key` is in this NameSpace.
"""
return key in self.__d
def __getitem__(self, key):
"""
Returns proxy named `key`; otherwise raises KeyError.
"""
if key in self.__d:
return self.__d[key]
raise KeyError('NameSpace has no item for key %r' % key)
def __repr__(self):
return '%s(<%d proxies>)' % (self.__class__.__name__, len(self))
class NameSpace(ReadOnly):
"""
A read-only namespace of (key, value) pairs that can be accessed
both as instance attributes and as dictionary items.
"""
def __init__(self, items):
"""
`items` should be an iterable providing the members of this
NameSpace.
"""
object.__setattr__(self, '_NameSpace__items', tuple(items))
# dict mapping Python name to item:
object.__setattr__(self, '_NameSpace__pname', {})
# dict mapping human-readibly name to item:
object.__setattr__(self, '_NameSpace__hname', {})
for item in self.__items:
object.__setattr__(self, item.name, item)
for (key, d) in [
(item.name, self.__pname),
(str(item), self.__hname),
]:
assert key not in d
d[key] = item
def __iter__(self):
"""
Iterates through the items in this NameSpace in the same order they
were passed in the contructor.
"""
for item in self.__items:
yield item
def __len__(self):
"""
Returns number of items in this NameSpace.
"""
return len(self.__items)
def __contains__(self, key):
"""
Returns True if an item with pname or hname `key` is in this
NameSpace.
"""
return (key in self.__pname) or (key in self.__hname)
def __getitem__(self, key):
"""
Returns item with pname or hname `key`; otherwise raises KeyError.
"""
if key in self.__pname:
return self.__pname[key]
if key in self.__hname:
return self.__hname[key]
raise KeyError('NameSpace has no item for key %r' % key)
def __repr__(self):
return '%s(<%d proxies>)' % (self.__class__.__name__, len(self))
class Registrar(object):
def __init__(self, *allowed):
"""
`*allowed` is a list of the base classes plugins can be subclassed
from.
"""
self.__allowed = frozenset(allowed)
self.__d = {}
self.__registered = set()
assert len(self.__allowed) == len(allowed)
for base in self.__allowed:
assert inspect.isclass(base)
assert base.__name__ not in self.__d
self.__d[base.__name__] = {}
def __findbase(self, cls):
"""
If `cls` is a subclass of a base in self.__allowed, returns that
base; otherwise raises SubclassError.
"""
assert inspect.isclass(cls)
found = False
for base in self.__allowed:
if issubclass(cls, base):
found = True
yield base
if not found:
raise errors.SubclassError(cls, self.__allowed)
def __call__(self, cls, override=False):
"""
Register the plugin `cls`.
"""
if not inspect.isclass(cls):
raise TypeError('plugin must be a class: %r' % cls)
# Raise DuplicateError if this exact class was already registered:
if cls in self.__registered:
raise errors.DuplicateError(cls)
# Find the base class or raise SubclassError:
for base in self.__findbase(cls):
sub_d = self.__d[base.__name__]
# Check override:
if cls.__name__ in sub_d:
# Must use override=True to override:
if not override:
raise errors.OverrideError(base, cls)
else:
# There was nothing already registered to override:
if override:
raise errors.MissingOverrideError(base, cls)
# The plugin is okay, add to sub_d:
sub_d[cls.__name__] = cls
# The plugin is okay, add to __registered:
self.__registered.add(cls)
def __getitem__(self, item):
"""
Returns a copy of the namespace dict of the base class named `name`.
"""
if inspect.isclass(item):
if item not in self.__allowed:
raise KeyError(repr(item))
key = item.__name__
else:
key = item
return dict(self.__d[key])
def __contains__(self, item):
"""
Returns True if a base class named `name` is in this Registrar.
"""
if inspect.isclass(item):
return item in self.__allowed
return item in self.__d
def __iter__(self):
"""
Iterates through a (base, registered_plugins) tuple for each allowed
base.
"""
for base in self.__allowed:
sub_d = self.__d[base.__name__]
yield (base, tuple(sub_d[k] for k in sorted(sub_d)))
class API(ReadOnly):
def __init__(self, *allowed):
keys = tuple(b.__name__ for b in allowed)
object.__setattr__(self, '_API__keys', keys)
object.__setattr__(self, 'register', Registrar(*allowed))
object.__setattr__(self, '_API__plugins', [])
def __call__(self):
"""
Finalize the registration, instantiate the plugins.
"""
for (base, plugins) in self.register:
ns = NameSpace(self.__plugin_iter(base, plugins))
assert not hasattr(self, base.__name__)
object.__setattr__(self, base.__name__, ns)
for plugin in self.__plugins:
plugin.finalize(self)
assert plugin.api is self
def __plugin_iter(self, base, plugins):
assert issubclass(base.proxy, Proxy)
for cls in plugins:
plugin = cls()
self.__plugins.append(plugin)
yield base.proxy(plugin)
def __iter__(self):
for key in self.__keys:
yield key