plainbox.impl.secure.plugins – interface for accessing extension points

This module contains plugin interface for plainbox. Plugins are based on pkg_resources entry points feature. Any python package can advertise the existence of entry points associated with a given namespace. Any other package can query a given namespace and enumerate a sequence of entry points.

Each entry point has a name and importable identifier. The identifier can be imported using the load() method. A loaded entry point is exposed as an instance of PlugIn. A high-level collection of plugins (that may eventually also query alternate backends) is offered by PlugInCollection.

Using PlugInCollection.load() one can load all plugins from a particular namespace and work with them using provided utility methods such as PlugInCollection.get_by_name() or PlugInCollection.get_all_names()

The set of loaded plugins can be overridden by mock/patching PlugInCollection._get_entry_points(). This is especially useful for testing in isolation from whatever entry points may exist in the system.

class plainbox.impl.secure.plugins.FsPlugInCollection(dir_list, ext, recursive=False, load=False, wrapper=<class 'plainbox.impl.secure.plugins.PlugIn'>, *wrapper_args, **wrapper_kwargs)[source]

Bases: plainbox.impl.secure.plugins.PlugInCollectionBase

Collection of plug-ins based on filesystem entries

Instantiate with dir_list and ext, call load() and then access any of the loaded plug-ins using the API offered. All loaded plugin information files are wrapped by a plug-in container. By default that is PlugIn but it may be adjusted if required.

The name of each plugin is the base name of the plugin file, the object of each plugin is the text read from the plugin file.

discovery_time

Time, in fractional seconds, that was required to discover all objects.

This time is separate from the load and wrap time of all each individual plug-in. Typically this is either a fixed cost or a predictable cost related to traversing the file system.

fake_plugins(plugins, problem_list=None)

Context manager for using fake list of plugins

Parameters:
  • plugins – list of PlugIn-alike objects
  • problem_list – list of problems (exceptions)

The provided list of plugins overrides any previously loaded plugins and prevent loading any other, real, plugins. After the context manager exits the previous state is restored.

get_all_items()

Get a list of all the pairs of plugin name and plugin

Returns:a list of tuples (plugin.plugin_name, plugin)
get_all_names()

Get a list of all the plug-in names

Returns:a list of plugin names
get_all_plugin_objects()

Get an list of plug-in objects

get_all_plugins()

Get a list of all the plug-ins

Returns:a list of plugin objects
get_by_name(name)

Get the specified plug-in (by name)

Parameters:name – name of the plugin to locate
Returns:PlugIn like object associated with the name
Raises:KeyError – if the specified name cannot be found
get_total_time() → float

Get the sum of load and wrap time of each plugin object

Returns:The total number of fractional seconds of wall-clock time spent by loading this collection. This value doesn’t include some small overhead of this class but is representative of the load times of pluggable code.
load()[source]

Load all plug-ins.

This method loads all plug-ins from the search directories (as defined by the path attribute). Missing directories are silently ignored.

problem_list

List of problems encountered while loading plugins

wrap_and_add_plugin(plugin_name, plugin_obj, plugin_load_time)

Internal method of PlugInCollectionBase.

Parameters:
  • plugin_name – plugin name, some arbitrary string
  • plugin_obj – plugin object, some arbitrary object.
  • plugin_load_time – number of seconds it took to load this plugin

This method prepares a wrapper (PlugIn subclass instance) for the specified plugin name/object by attempting to instantiate the wrapper class. If a PlugInError exception is raised then it is added to the problem_list and the corresponding plugin is not added to the collection of plugins.

class plainbox.impl.secure.plugins.IPlugIn[source]

Bases: object

Piece of code loaded at runtime, one of many for a given extension point

plugin_load_time

time, in fractional seconds, that was needed to load the plugin

plugin_name

name of the plugin, may not be unique

plugin_object

external object

plugin_wrap_time

time, in fractional seconds, that was needed to wrap the plugin

Note

The difference between plugin_wrap_time and plugin_load_time depends on context. In practical terms the sum of the two is interesting for analysis but in some cases having access to both may be important.

class plainbox.impl.secure.plugins.IPlugInCollection[source]

Bases: object

A collection of IPlugIn objects.

discovery_time

Time, in fractional seconds, that was used to discover all objects.

This time is separate from the load and wrap time of all each individual plug-in. Typically this is either a fixed cost or a predictable cost related to traversing the file system.

fake_plugins(plugins, problem_list=None)[source]

Context manager for using fake list of plugins

Parameters:
  • plugins – list of PlugIn-alike objects
  • problem_list – list of problems (exceptions)

The provided list of plugins and exceptions overrides any previously loaded plugins and prevent loading any other, real, plugins. After the context manager exits the previous state is restored.

get_all_items()[source]

Get an iterator to a sequence of (name, plug-in)

get_all_names()[source]

Get an iterator to a sequence of plug-in names

get_all_plugin_objects()[source]

Get an list of plug-in objects

This is a shortcut that gives fastest access to a list of IPlugIn.plugin_object of each loaded plugin.

get_all_plugins()[source]

Get an iterator to a sequence plug-ins

get_by_name(name)[source]

Get the specified plug-in (by name)

get_total_time() → float[source]

Get the cost to prepare everything required by this collection

Returns:The total number of fractional seconds of wall-clock time spent on discovering, loading and wrapping each object now contained in this collection.
load()[source]

Load all plug-ins.

This method loads all plug-ins from the specified name-space. It may perform a lot of IO so it’s somewhat slow / expensive on a cold disk cache.

problem_list

List of problems encountered while loading plugins

class plainbox.impl.secure.plugins.LazyFileContent(name)[source]

Bases: object

Support class for FsPlugInCollection’s subclasses that behaves like a string of text loaded from a file. The actual text is loaded on demand, the first time it is needed.

The actual methods implemented here are just enough to work for loading a provider. Since __getattr__() is implemented the class should be pretty versatile but your millage may vary.

class plainbox.impl.secure.plugins.LazyFsPlugInCollection(dir_list, ext, recursive=False, load=False, wrapper=<class 'plainbox.impl.secure.plugins.PlugIn'>, *wrapper_args, **wrapper_kwargs)[source]

Bases: plainbox.impl.secure.plugins.FsPlugInCollection

Collection of plug-ins based on filesystem entries

Instantiate with dir_list and ext, call load() and then access any of the loaded plug-ins using the API offered. All loaded plugin information files are wrapped by a plug-in container. By default that is PlugIn but it may be adjusted if required.

The name of each plugin is the base name of the plugin file, the object of each plugin is a handle that can be used to optionally load the content of the file.

discovery_time

Time, in fractional seconds, that was required to discover all objects.

This time is separate from the load and wrap time of all each individual plug-in. Typically this is either a fixed cost or a predictable cost related to traversing the file system.

fake_plugins(plugins, problem_list=None)

Context manager for using fake list of plugins

Parameters:
  • plugins – list of PlugIn-alike objects
  • problem_list – list of problems (exceptions)

The provided list of plugins overrides any previously loaded plugins and prevent loading any other, real, plugins. After the context manager exits the previous state is restored.

get_all_items()

Get a list of all the pairs of plugin name and plugin

Returns:a list of tuples (plugin.plugin_name, plugin)
get_all_names()

Get a list of all the plug-in names

Returns:a list of plugin names
get_all_plugin_objects()

Get an list of plug-in objects

get_all_plugins()

Get a list of all the plug-ins

Returns:a list of plugin objects
get_by_name(name)

Get the specified plug-in (by name)

Parameters:name – name of the plugin to locate
Returns:PlugIn like object associated with the name
Raises:KeyError – if the specified name cannot be found
get_total_time() → float

Get the sum of load and wrap time of each plugin object

Returns:The total number of fractional seconds of wall-clock time spent by loading this collection. This value doesn’t include some small overhead of this class but is representative of the load times of pluggable code.
load()

Load all plug-ins.

This method loads all plug-ins from the search directories (as defined by the path attribute). Missing directories are silently ignored.

problem_list

List of problems encountered while loading plugins

wrap_and_add_plugin(plugin_name, plugin_obj, plugin_load_time)

Internal method of PlugInCollectionBase.

Parameters:
  • plugin_name – plugin name, some arbitrary string
  • plugin_obj – plugin object, some arbitrary object.
  • plugin_load_time – number of seconds it took to load this plugin

This method prepares a wrapper (PlugIn subclass instance) for the specified plugin name/object by attempting to instantiate the wrapper class. If a PlugInError exception is raised then it is added to the problem_list and the corresponding plugin is not added to the collection of plugins.

class plainbox.impl.secure.plugins.LazyPlugInCollection(mapping, load=False, wrapper=<class 'plainbox.impl.secure.plugins.PlugIn'>, *wrapper_args, **wrapper_kwargs)[source]

Bases: plainbox.impl.secure.plugins.PlugInCollectionBase

Collection of plug-ins based on a mapping of imported objects

All loaded plugin information files are wrapped by a plug-in container. By default that is PlugIn but it may be adjusted if required.

discover()[source]
discovery_time

Time, in fractional seconds, that was required to discover all objects.

This time is separate from the load and wrap time of all each individual plug-in. Typically this is either a fixed cost or a predictable cost related to traversing the file system.

Note

This overridden version can be called at any time, unlike the base class implementation. Before all discovery is done, it simply returns zero.

do_discover()[source]
do_load_one(name, discovery_data)[source]
fake_plugins(plugins, problem_list=None)[source]
get_all_items()

Get a list of all the pairs of plugin name and plugin

Returns:a list of tuples (plugin.plugin_name, plugin)
get_all_names()[source]

Get a list of all the plug-in names

Returns:a list of plugin names
get_all_plugin_objects()

Get an list of plug-in objects

get_all_plugins()

Get a list of all the plug-ins

Returns:a list of plugin objects
get_by_name(name)[source]

Get the specified plug-in (by name)

Parameters:name – name of the plugin to locate
Returns:PlugIn like object associated with the name
Raises:KeyError – if the specified name cannot be found
get_total_time() → float

Get the sum of load and wrap time of each plugin object

Returns:The total number of fractional seconds of wall-clock time spent by loading this collection. This value doesn’t include some small overhead of this class but is representative of the load times of pluggable code.
load()[source]
load_one(name, discovery_data)[source]
problem_list

List of problems encountered while loading plugins

wrap_and_add_plugin(plugin_name, plugin_obj, plugin_load_time)

Internal method of PlugInCollectionBase.

Parameters:
  • plugin_name – plugin name, some arbitrary string
  • plugin_obj – plugin object, some arbitrary object.
  • plugin_load_time – number of seconds it took to load this plugin

This method prepares a wrapper (PlugIn subclass instance) for the specified plugin name/object by attempting to instantiate the wrapper class. If a PlugInError exception is raised then it is added to the problem_list and the corresponding plugin is not added to the collection of plugins.

class plainbox.impl.secure.plugins.PkgResourcesPlugInCollection(namespace, load=False, wrapper=<class 'plainbox.impl.secure.plugins.PlugIn'>, *wrapper_args, **wrapper_kwargs)[source]

Bases: plainbox.impl.secure.plugins.PlugInCollectionBase

Collection of plug-ins based on pkg_resources

Instantiate with namespace, call load() and then access any of the loaded plug-ins using the API offered. All loaded objects are wrapped by a plug-in container. By default that is PlugIn but it may be adjusted if required.

discovery_time

Time, in fractional seconds, that was required to discover all objects.

This time is separate from the load and wrap time of all each individual plug-in. Typically this is either a fixed cost or a predictable cost related to traversing the file system.

fake_plugins(plugins, problem_list=None)

Context manager for using fake list of plugins

Parameters:
  • plugins – list of PlugIn-alike objects
  • problem_list – list of problems (exceptions)

The provided list of plugins overrides any previously loaded plugins and prevent loading any other, real, plugins. After the context manager exits the previous state is restored.

get_all_items()

Get a list of all the pairs of plugin name and plugin

Returns:a list of tuples (plugin.plugin_name, plugin)
get_all_names()

Get a list of all the plug-in names

Returns:a list of plugin names
get_all_plugin_objects()

Get an list of plug-in objects

get_all_plugins()

Get a list of all the plug-ins

Returns:a list of plugin objects
get_by_name(name)

Get the specified plug-in (by name)

Parameters:name – name of the plugin to locate
Returns:PlugIn like object associated with the name
Raises:KeyError – if the specified name cannot be found
get_total_time() → float

Get the sum of load and wrap time of each plugin object

Returns:The total number of fractional seconds of wall-clock time spent by loading this collection. This value doesn’t include some small overhead of this class but is representative of the load times of pluggable code.
load()[source]

Load all plug-ins.

This method loads all plug-ins from the specified name-space. It may perform a lot of IO so it’s somewhat slow / expensive on a cold disk cache.

Note

this method queries pkg-resources only once.

problem_list

List of problems encountered while loading plugins

wrap_and_add_plugin(plugin_name, plugin_obj, plugin_load_time)

Internal method of PlugInCollectionBase.

Parameters:
  • plugin_name – plugin name, some arbitrary string
  • plugin_obj – plugin object, some arbitrary object.
  • plugin_load_time – number of seconds it took to load this plugin

This method prepares a wrapper (PlugIn subclass instance) for the specified plugin name/object by attempting to instantiate the wrapper class. If a PlugInError exception is raised then it is added to the problem_list and the corresponding plugin is not added to the collection of plugins.

class plainbox.impl.secure.plugins.PlugIn(name: str, obj: object, load_time: float = 0, wrap_time: float = 0)[source]

Bases: plainbox.impl.secure.plugins.IPlugIn

Simple plug-in that does not offer any guarantees beyond knowing it’s name and some arbitrary external object.

plugin_load_time

time, in fractional seconds, that was needed to load the plugin

plugin_name

plugin name, arbitrary string

plugin_object

plugin object, arbitrary object

plugin_wrap_time

time, in fractional seconds, that was needed to wrap the plugin

class plainbox.impl.secure.plugins.PlugInCollectionBase(load=False, wrapper=<class 'plainbox.impl.secure.plugins.PlugIn'>, *wrapper_args, **wrapper_kwargs)[source]

Bases: plainbox.impl.secure.plugins.IPlugInCollection

Base class that shares some of the implementation with the other PlugInCollection implemenetations.

discovery_time

Time, in fractional seconds, that was required to discover all objects.

This time is separate from the load and wrap time of all each individual plug-in. Typically this is either a fixed cost or a predictable cost related to traversing the file system.

fake_plugins(plugins, problem_list=None)[source]

Context manager for using fake list of plugins

Parameters:
  • plugins – list of PlugIn-alike objects
  • problem_list – list of problems (exceptions)

The provided list of plugins overrides any previously loaded plugins and prevent loading any other, real, plugins. After the context manager exits the previous state is restored.

get_all_items()[source]

Get a list of all the pairs of plugin name and plugin

Returns:a list of tuples (plugin.plugin_name, plugin)
get_all_names()[source]

Get a list of all the plug-in names

Returns:a list of plugin names
get_all_plugin_objects()[source]

Get an list of plug-in objects

get_all_plugins()[source]

Get a list of all the plug-ins

Returns:a list of plugin objects
get_by_name(name)[source]

Get the specified plug-in (by name)

Parameters:name – name of the plugin to locate
Returns:PlugIn like object associated with the name
Raises:KeyError – if the specified name cannot be found
get_total_time() → float[source]

Get the sum of load and wrap time of each plugin object

Returns:The total number of fractional seconds of wall-clock time spent by loading this collection. This value doesn’t include some small overhead of this class but is representative of the load times of pluggable code.
load()

Load all plug-ins.

This method loads all plug-ins from the specified name-space. It may perform a lot of IO so it’s somewhat slow / expensive on a cold disk cache.

problem_list

List of problems encountered while loading plugins

wrap_and_add_plugin(plugin_name, plugin_obj, plugin_load_time)[source]

Internal method of PlugInCollectionBase.

Parameters:
  • plugin_name – plugin name, some arbitrary string
  • plugin_obj – plugin object, some arbitrary object.
  • plugin_load_time – number of seconds it took to load this plugin

This method prepares a wrapper (PlugIn subclass instance) for the specified plugin name/object by attempting to instantiate the wrapper class. If a PlugInError exception is raised then it is added to the problem_list and the corresponding plugin is not added to the collection of plugins.

exception plainbox.impl.secure.plugins.PlugInError[source]

Bases: Exception

Exception that may be raised by PlugIn.__init__() to signal it cannot be fully loaded and should not be added to any collection.

args
with_traceback()

Exception.with_traceback(tb) – set self.__traceback__ to tb and return self.

plainbox.impl.secure.plugins.now() → float[source]

Get the current “time”.

Returns:A fractional number of seconds since some undefined base event.

This methods returns the current “time” that is useful for measuring plug-in loading time. The return value is meaningless but delta between two values is a fractional number of seconds between the two corresponding events.

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