pluginmgr(n)                   Plugin management                  pluginmgr(n)



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NAME
       pluginmgr - Manage a plugin

SYNOPSIS
       package require Tcl  8.4

       package require pluginmgr  ?0.3?

       ::pluginmgr objectName ?option value...?

       ::pluginmgr::paths objectName name...

       objectName method ?arg arg ...?

       objectName clone

       objectName configure

       objectName configure option

       objectName configure -option value...

       objectName cget -option

       objectName destroy

       objectName do arg...

       objectName interpreter

       objectName plugin

       objectName load string

       objectName unload

       objectName list

       objectName path path

       objectName paths

_________________________________________________________________

DESCRIPTION
       This package provides commands and objects for the generic management
       of plugins which can be loaded into an application.

       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

       [1]    How to translate a plugin name to the name of the package
              implementing it, and vice versa.

       [2]    The list of commands a plugin has to provide as API, and also of
              more complex checks as code.

       [3]    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:

              [1]    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.

              [2]    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.

              [3]    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.

              [4]    The directory "~/.name/plugin".

              [5]    The directory "~/.name/plugins".

                     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/plugin
                     path ~/.doctools/idx/plugin


   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:

              [1]    If the string contains the path to an existing file then
                     this file is taken as the implementation of the plugin.

              [2]    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.

              [3]    The load fails.

       The algorithm to validate and initialize the loaded code is:

              [1]    If the option -api is non-empty introspection commands
                     are used to ascertain that the plugin provides the listed
                     commands.

              [2]    If the option -check is non-empty the specified command
                     prefix is called.

              [3]    If either of the above fails the candidate plugin is
                     unloaded again

              [4]    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.

BUGS, IDEAS, FEEDBACK
       This document, and the package it describes, will undoubtedly contain
       bugs and other problems.  Please report such in the category pluginmgr
       of the Tcllib SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please also report
       any ideas for enhancements you may have for either package and/or
       documentation.

KEYWORDS
       plugin management, plugin search

CATEGORY
       Programming tools

COPYRIGHT
       Copyright (c) 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>




pluginmgr                             0.3                         pluginmgr(n)
