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pluginmgr(n)                                  Plugin management                                 pluginmgr(n)



____________________________________________________________________________________________________________

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 man-ager manager
       ager 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  object-Name objectName
              Name 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 com-mand command
              mand 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  vali-dated validated
       dated  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 attempt-ing attempting
              ing 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 com-plex complex
              plex checks on a loaded plugin package to validate it, which go beyond a simple list  of  pro-vided provided
              vided 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 avail-able available
              able 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 plug-in plugin
              in 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://source -
       forge.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)