To avoid the implementation of yet another system to locate Tcl code the system provides by this package is built on top of the regular package management system. Each plugin is considered as a package and a simple invokation of package require is enough to locate and load it, if it exists. The only time we will need additional paths is when a plugin manager is part of a wrapped application and has to be able to search for plugins existing outside of that application. For this situation the package provides a command to create a general set of such paths based on names for the plugin manager and/or application in question.

The main contribution of this package is a generic framework which allows the easy declaration of

How to translate a plugin name to the name of the package implementing it, and vice versa.
The list of commands a plugin has to provide as API, and also of more complex checks as code.
The list of commands expected by the plugin from the environment.

This then allows the easy generation of plugin managers customized to particular types of plugins for an application.

It should be noted that all plugin code is considered untrusted and will always be executed within a safe interpreter. The interpreter is enabled enough to allow plugins the loading of all additional packages they may need.

PUBLIC API

PACKAGE COMMANDS

::pluginmgr objectName ?option value...?

This command creates a new plugin manager object with an associated Tcl command whose name is objectName. This object command is explained in full detail in the sections OBJECT COMMAND and OBJECT METHODS. The object command will be created under the current namespace if the objectName is not fully qualified, and in the specified namespace otherwise.

The options and their values coming after the name of the object are used to set the initial configuration of the mamager object, specifying the applicable plugins and their API.

::pluginmgr::paths objectName name...

This utility command adds a set of paths to the specified object, based on the given names. It will search for:

The environment variable name_PLUGINS. Its contents will be interpreted as a list of package paths. The entries have to be separated by either : (unix) or ; (windows).

The name will be converted to upper-case letters.
The registry entry "HKEY_LOCAL_MACHINE\SOFTWARE\name\PLUGINS". Its contents will be interpreted as a list of package paths. The entries have to be separated by ;. This item is considered only when on Windows (tm).

The casing of letters is not changed.
The registry entry "HKEY_CURRENT_USER\SOFTWARE\name\PLUGINS". Its contents will be interpreted as a list of package paths. The entries have to be separated by ;. This item is considered only when on Windows (tm).

The casing of letters is not changed.
The directory "~/.name/plugin".

The casing of letters is not changed.

and add all the paths found that way to the list of package paths maintained by the object.

If name is namespaced each item in the list will be repeated per prefix of name, with conversion of :-sequences into the proper separator (underscore for environment variables, backslash for registry entries, and / for directories).

Examples:

    ::pluginmgr::paths ::obj docidx

    => env  DOCIDX_PLUGINS
       reg  HKEY_LOCAL_MACHINE\SOFTWARE\docidx\PLUGINS
       reg  HKEY_CURRENT_USER\SOFTWARE\docidx\PLUGINS
       path ~/.docidx/plugins

    ::pluginmgr::paths ::obj doctools::idx

    => env  DOCTOOLS_PLUGINS
       env  DOCTOOLS_IDX_PLUGINS
       reg  HKEY_LOCAL_MACHINE\SOFTWARE\doctools\PLUGINS
       reg  HKEY_LOCAL_MACHINE\SOFTWARE\doctools\idx\PLUGINS
       reg  HKEY_CURRENT_USER\SOFTWARE\doctools\PLUGINS
       reg  HKEY_CURRENT_USER\SOFTWARE\doctools\idx\PLUGINS
       path ~/.doctools/plugins
       path ~/.doctools/idx/plugins

OBJECT COMMAND

All commands created by the command ::pluginmgr (See section PACKAGE COMMANDS) have the following general form and may be used to invoke various operations on their plugin manager object.

objectName method ?arg arg ...?: The method method and its arg'uments determine the exact behavior of the command. See section OBJECT METHODS for the detailed specifications.

OBJECT METHODS

objectName clone

This method creates a new plugin management object and returns the associated object command. The generated object is a clone of the object the method was invoked on. I.e. the new object will have the same configuration as the current object. With regard to state, if the current object has a plugin loaded then this plugin and all associated state is moved to the generated clone and the current object is reset into the base state (no plugin loaded). In this manner a configured plugin manager is also a factory for loaded plugins.

objectName configure

The method returns a list of all known options and their current values when called without any arguments.

objectName configure option

The method behaves like the method cget when called with a single argument and returns the value of the option specified by said argument.

objectName configure -option value...

The method reconfigures the specified options of the object, setting them to the associated values, when called with an even number of arguments, at least two.

The legal options are described in the section OBJECT CONFIGURATION.

objectName cget -option

This method expects a legal configuration option as argument and will return the current value of that option for the object the method was invoked for.

The legal configuration options are described in section OBJECT CONFIGURATION.

objectName destroy

This method destroys the object it is invoked for.

objectName do arg...

This method interprets its list of arguments as the words of a command and invokes this command in the execution context of the plugin. The result of the invoked command is made the result of the method. The call will fail with an error if no valid plugin has been loaded into the manager object.

objectName interpreter

This method returns the handle of the safe interpreter the current plugin is loaded into. An empty string as return value signals that the manager currently has no valid plugin loaded.

objectName plugin

This method returns the name of the plugin currently loaded. An empty string as return value signals that the manager currently has no valid plugin loaded.

objectName load string

This method loads, validates, and initializes a named plugin into the manager object.

The algorithm to locate and load the plugin employed is:

If the string contains the path to an existing file then this file is taken as the implementation of the plugin.
Otherwise the plugin name is translated into a package name via the value of the option -pattern and then loaded through the regular package management.
The load fails.

The algorithm to validate and initialize the loaded code is:

If the option -api is non-empty introspection commands are used to ascertain that the plugin provides the listed commands.
If the option -check is non-empty the specified command prefix is called.
If either of the above fails the candidate plugin is unloaded again
Otherwise all the commands specified via the option -cmds are installed in the plugin.

A previously loaded plugin is discarded, but only if the new plugin was found and sucessfully validated and initialized. Note that there will be no intereference between old and new plugin as both will be put into separate safe interpreters.

objectName unload

This method unloads the currently loaded plugin. It returns the empty string. The call will be silently ignored if no plugin is loaded at all.

objectName list

This method uses the contents of the option -pattern to find all packages which can be plugins under the purview of this manager object. It translates their names into plugin names and returns a list containing them.

objectName path path

This methods adds the specified path to the list of additional package paths to look at when searching for a plugin. It returns the empty string. Duplicate paths are ignored, i.e. each path is added only once. Paths are made absolute, but are not normalized.

objectName paths

This method returns a list containing all additional paths which have been added to the plugin manager object since its creation.

OBJECT CONFIGURATION

All plugin manager objects understand the following configuration options:

-pattern string: The value of this option is a glob pattern which has to contain exactly one '*'-operator. All packages whose names match this pattern are the plugins recognized by the manager object. And vice versa, the replacement of the '*'-operator with a plugin name will yield the name of the package implementing that plugin.

This option has no default, except if option -name was set. It has to be set before attempting to load a plugin, either directly, or through option -name.
-api list: The value of this option is a list of command names, and any plugin loaded has to provide these commands. Names which are not fully qualified are considered to be rooted in the global namespace. If empty no expectations are made on the plugin. The default value is the empty list.
-check cmdprefix: The value of this option is interpreted as a command prefix. Its purpose is to perform complex checks on a loaded plugin package to validate it, which go beyond a simple list of provided commands.

It is called with the manager object command as the only argument and has to return a boolean value. A value of true will be interpreted to mean that the candidate plugin passed the test. The call will happen if and only if the candidate plugin already passed the basic API check specified through the option -api.

The default value is the empty list, which causes the manager object to suppress the call and to assume the candidate plugin passes.
-cmds dict: The value of this option is a dictionary. It specifies the commands which will be made available to the plugin (as keys), and the trusted commands in the environment which implement them (as values). The trusted commands will be executed in the interpreter specified by the option -cmdip. The default value is the empty dictionary.
-cmdip ipspec: The value of this option is the path of the interpreter where the trusted commands given to the plugin will be executed in. The default is the empty string, referring to the current interpreter.
-setup cmdprefix: The value of this option is interpreted as a command prefix.

It is called whenever a new safe interpreter for a plugin has been created, but before a plugin is loaded. It is provided with the manager object command and the interpreter handle as its only arguments. Any return value will be ignored.

Its purpose is give a user of the plugin management the ability to define commands, packages, etc. a chosen plugin may need while being loaded.

plugin(n) 1.1 "Plugin management"

Copyright © 2006 for compilation: ActiveState