eplugin

This library intends to provide a simple way to manage plugins for an Erlang application, right now the abstraction is very simple and high level but it is quite flexible.

usage

Simply start the application, there is only one configuration variable at the moment named plugin_dir which as the name suggests specifies where the plugins are discovered. It defaults to "plugins".

apply/2

This function can be used to call all the functions that were registered to a certain callback, with the args given as seconds argument.

eplugin:apply(my_fancy_callback, [1, 2, 3]).

call/1+

This function is a simplification of apply with a fixed number of arguments, this way it gets around using erlang:apply internally.

eplugin:apply(my_fancy_callback, [1, 2, 3]) =:= eplugin:call(my_fancy_callback, 1, 2, 3).

fold/2

This function folds an argument through all callbacks. The first argument is the name the second the Acc0 for the fold.

test_apply/1+

Threads through the callbacks as long as true is returned, if anything else is returned execution is terminated and this value returned.

test_apply/2 test/1+

Threads through the callbacks as long as true is returned, if anything else is returned execution is terminated and this value returned.

Naming is according to apply and call.

callbacks/1

The basis for apply, this function returns all modules and functions registered for a certain callback. It returns: [{Module, Function}]

eplugin:callbacks(my_fancy_callback).
%% -> [{some_module, some_function}, {some_other_module, some_function}]

config/1

Fetches the custom plugin Config. This is holding plugin internal information as well as some used by eplugin.project-fifo.net

eplugin:config(my_fancy_callback).
%% -> {ok, Config}

plugins/0

This function lists all installed plugins.

enable/1 --------˘ Enables a plugin.

disable/1

disables a plugin.

is_enabled/1

Returns true if a plugin is enabled (aka has any callbacks registered).

register/4 /5

Registers a callback.

Writing plugins

A plugin is a directory with a plugin.conf file and one or more .erl files so the plugin directory could look like:

-plugins
 -plug1
  -plugin.conf
  -plug1_test.erl
  -plug1_test2.erl
 -plug2
  -plugin.conf
  -plug2_test.erl

Please be aware that module names need to be unique!

The plugin.conf is a simple file with the following syntax:

{PluginName,
 [{Module, [{Callback, Function}|{Callback, Function, CallbackOptions}]}],
 OptionPlist}.

CallbackOptions has the following possible values

• priority - the priority for execution order, highest priority first, default is 0

OptionsPlist has the following reserved options:

• disabled - this plugin will not load.
• dependencies - a list of dependencies.¯
• provides - a list of dependencies the plugin provides.
• add path - relative pathes to be added to the loadpath. Callbacks =========

notation

callbacks are noted as <callback name>(arguments) so eplugin:init(Config) means the callback eplugin:init is called with 1 argument - Config.

internal callbacks¯¯

eplugin provides the following callbacks itself:

• eplugin:enable(Config) - this is called before a module gets enabled.
• eplugin:disable(Config) - this gets called after a module gets disabled.
• eplugin:enable_plugin(Plugin) - this gets called whenever a plugin is enabled.
• eplugin:disable_plugin(Plugin) - this gets called whenever a plugin is disabled.