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: / lib / python3 / dist-packages / twisted /
Filename : plugin.py
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# -*- test-case-name: twisted.test.test_plugin -*-
# Copyright (c) 2005 Divmod, Inc.
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Plugin system for Twisted.

@author: Jp Calderone
@author: Glyph Lefkowitz
"""


import os
import pickle
import sys
import types
from typing import Iterable, Optional, Type, TypeVar

from zope.interface import Interface, providedBy

from twisted.python import log
from twisted.python.components import getAdapterFactory
from twisted.python.modules import getModule
from twisted.python.reflect import namedAny


class IPlugin(Interface):
    """
    Interface that must be implemented by all plugins.

    Only objects which implement this interface will be considered for return
    by C{getPlugins}.  To be useful, plugins should also implement some other
    application-specific interface.
    """


class CachedPlugin:
    def __init__(self, dropin, name, description, provided):
        self.dropin = dropin
        self.name = name
        self.description = description
        self.provided = provided
        self.dropin.plugins.append(self)

    def __repr__(self) -> str:
        return "<CachedPlugin {!r}/{!r} (provides {!r})>".format(
            self.name,
            self.dropin.moduleName,
            ", ".join([i.__name__ for i in self.provided]),
        )

    def load(self):
        return namedAny(self.dropin.moduleName + "." + self.name)

    def __conform__(self, interface, registry=None, default=None):
        for providedInterface in self.provided:
            if providedInterface.isOrExtends(interface):
                return self.load()
            if getAdapterFactory(providedInterface, interface, None) is not None:
                return interface(self.load(), default)
        return default

    # backwards compat HOORJ
    getComponent = __conform__


class CachedDropin:
    """
    A collection of L{CachedPlugin} instances from a particular module in a
    plugin package.

    @type moduleName: C{str}
    @ivar moduleName: The fully qualified name of the plugin module this
        represents.

    @type description: C{str} or L{None}
    @ivar description: A brief explanation of this collection of plugins
        (probably the plugin module's docstring).

    @type plugins: C{list}
    @ivar plugins: The L{CachedPlugin} instances which were loaded from this
        dropin.
    """

    def __init__(self, moduleName, description):
        self.moduleName = moduleName
        self.description = description
        self.plugins = []


def _generateCacheEntry(provider):
    dropin = CachedDropin(provider.__name__, provider.__doc__)
    for k, v in provider.__dict__.items():
        plugin = IPlugin(v, None)
        if plugin is not None:
            # Instantiated for its side-effects.
            CachedPlugin(dropin, k, v.__doc__, list(providedBy(plugin)))
    return dropin


try:
    fromkeys = dict.fromkeys
except AttributeError:

    def fromkeys(keys, value=None):
        d = {}
        for k in keys:
            d[k] = value
        return d


def getCache(module):
    """
    Compute all the possible loadable plugins, while loading as few as
    possible and hitting the filesystem as little as possible.

    @param module: a Python module object.  This represents a package to search
    for plugins.

    @return: a dictionary mapping module names to L{CachedDropin} instances.
    """
    allCachesCombined = {}
    mod = getModule(module.__name__)
    # don't want to walk deep, only immediate children.
    buckets = {}
    # Fill buckets with modules by related entry on the given package's
    # __path__.  There's an abstraction inversion going on here, because this
    # information is already represented internally in twisted.python.modules,
    # but it's simple enough that I'm willing to live with it.  If anyone else
    # wants to fix up this iteration so that it's one path segment at a time,
    # be my guest.  --glyph
    for plugmod in mod.iterModules():
        fpp = plugmod.filePath.parent()
        if fpp not in buckets:
            buckets[fpp] = []
        bucket = buckets[fpp]
        bucket.append(plugmod)
    for pseudoPackagePath, bucket in buckets.items():
        dropinPath = pseudoPackagePath.child("dropin.cache")
        try:
            lastCached = dropinPath.getModificationTime()
            with dropinPath.open("r") as f:
                dropinDotCache = pickle.load(f)
        except BaseException:
            dropinDotCache = {}
            lastCached = 0

        needsWrite = False
        existingKeys = {}
        for pluginModule in bucket:
            pluginKey = pluginModule.name.split(".")[-1]
            existingKeys[pluginKey] = True
            if (pluginKey not in dropinDotCache) or (
                pluginModule.filePath.getModificationTime() >= lastCached
            ):
                needsWrite = True
                try:
                    provider = pluginModule.load()
                except BaseException:
                    # dropinDotCache.pop(pluginKey, None)
                    log.err()
                else:
                    entry = _generateCacheEntry(provider)
                    dropinDotCache[pluginKey] = entry
        # Make sure that the cache doesn't contain any stale plugins.
        for pluginKey in list(dropinDotCache.keys()):
            if pluginKey not in existingKeys:
                del dropinDotCache[pluginKey]
                needsWrite = True
        if needsWrite:
            try:
                dropinPath.setContent(pickle.dumps(dropinDotCache))
            except OSError as e:
                log.msg(
                    format=(
                        "Unable to write to plugin cache %(path)s: error "
                        "number %(errno)d"
                    ),
                    path=dropinPath.path,
                    errno=e.errno,
                )
            except BaseException:
                log.err(None, "Unexpected error while writing cache file")
        allCachesCombined.update(dropinDotCache)
    return allCachesCombined


def _pluginsPackage() -> types.ModuleType:
    import twisted.plugins as package

    return package


_TInterface = TypeVar("_TInterface", bound=Interface)


def getPlugins(
    interface: Type[_TInterface], package: Optional[types.ModuleType] = None
) -> Iterable[_TInterface]:
    """
    Retrieve all plugins implementing the given interface beneath the given module.

    @param interface: An interface class.  Only plugins which implement this
    interface will be returned.

    @param package: A package beneath which plugins are installed.  For
    most uses, the default value is correct.

    @return: An iterator of plugins.
    """
    if package is None:
        package = _pluginsPackage()
    allDropins = getCache(package)
    for key, dropin in allDropins.items():
        for plugin in dropin.plugins:
            try:
                adapted = interface(plugin, None)
            except BaseException:
                log.err()
            else:
                if adapted is not None:
                    yield adapted


# Old, backwards compatible name.  Don't use this.
getPlugIns = getPlugins


def pluginPackagePaths(name):
    """
    Return a list of additional directories which should be searched for
    modules to be included as part of the named plugin package.

    @type name: C{str}
    @param name: The fully-qualified Python name of a plugin package, eg
        C{'twisted.plugins'}.

    @rtype: C{list} of C{str}
    @return: The absolute paths to other directories which may contain plugin
        modules for the named plugin package.
    """
    package = name.split(".")
    # Note that this may include directories which do not exist.  It may be
    # preferable to remove such directories at this point, rather than allow
    # them to be searched later on.
    #
    # Note as well that only '__init__.py' will be considered to make a
    # directory a package (and thus exclude it from this list).  This means
    # that if you create a master plugin package which has some other kind of
    # __init__ (eg, __init__.pyc) it will be incorrectly treated as a
    # supplementary plugin directory.
    return [
        os.path.abspath(os.path.join(x, *package))
        for x in sys.path
        if not os.path.exists(os.path.join(x, *package + ["__init__.py"]))
    ]


__all__ = ["getPlugins", "pluginPackagePaths"]