io-event-reactor

Node.js module for reacting to filesystem events by invoking plugins that match configurable evaluators.

• How it works
• Requirements
• Install
• Usage
• Plugins
• Monitor Plugins
• Reactor Plugins
• Unit tests

How it works

The basic concept is this; you have a monitor that listens for IO events for particular paths on the filesystem. As these IO events occur, they are passed on to one or more evaluators to decide whether or not the IoEvent should be reacted to by one or more configured reactors. The entire latter sequence is encapsulated in an IoReactor instance that manages the flow between the three described components.

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With this module, you construct and configure a single IoReactorService which can manage and contain one or more IoReactor instances, as many as you wish, providing for lots of flexibility for reacting to filesystem events.

When you configure the IoReactorService and its IoReactor instances, you specify which plugins you would like to use to fulfill the monitor and reactor roles. For evaluators you simply provide one or more functions which evaluate whether or not an IoEvent should be passed on to one or more reactors.

Requirements

• Node 4.4.5+

Install

npm install io-event-reactor

Usage

Usage is pretty straight forward, one of the better starting points to to review one of the following apps:

• io-event-reactor-integration-tests - simple low level app you can run
• io-overwatch - command line directory watching daemon

Below is an end-to-end simple sample:

1. mkdir myapp/
2. mkdir -p /tmp/myapp
3. npm install io-event-reactor
4. npm install io-event-reactor-plugin-chokidar
5. vi myapp.js

var IoReactorService = require("io-event-reactor");
var EvaluatorUtil = require('io-event-reactor/ioReactor').EvaluatorUtil;

// IoReactorService configuration
var config = {
  ioReactors: [
        {   id: "reactor1",
            monitor: {
                plugin: "io-event-reactor-plugin-chokidar",
                config: {
                    paths: "/tmp/myapp",
                    options: {
                        alwaysStat: false,
                        awaitWriteFinish: {
                            stabilityThreshold: 200,
                            pollInterval: 100
                        },
                        ignoreInitial:true
                    }
                }
            },

            /**
            *
            * evaluators - REQUIRED array[] of one or more config objects, each containing the following properties
            *   - evaluator: function(ioEventType, fullPath, optionalFsStats, optionalExtraInfo), if function returns 'true' all attached reactors will be invoked. If false, nothing will happen. See the 'Evaluators' class for methods that will generate an applicable function for simple use-cases.
            *   - reactors: array[] of reactor ids that should be invoked if the 'evaluator' function returns 'true'
            */
            evaluators: [
                {
                    // see ioReactor.js (EvaluatorUtil class) for some helper function generators for simple use cases
                    evaluator: EvaluatorUtil.regex(['add','change','unlink','unlinkDir','addDir'],'.*bitsofinfo.*','ig'),
                    reactors: ['code1']
                }
            ],

            reactors: [
                { id: "code1",
                  plugin: "./default_plugins/code/codeReactorPlugin",
                  config: {
                      codeFunction: function(ioEvent) {
                          return new Promise(function(resolve,reject){
                             console.log("I just reacted to an IoEvent! type: " +ioEvent.eventType + " file: " +ioEvent.fullPath);
                          });
                      }
                  }
                }
            ]
        }
   ]
};

// start the reactor
var reactor = new IoReactorService(config);

1. node myapp.js
2. In another shell: touch /tmp/myapp/bitsofinfo.txt
3. You should see output: I just reacted to an IoEvent! type: add file: /tmp/myapp/bitsofinfo.txt

For more info on configuration options see the JSDoc in ioReactorService.js and ioReactor.js

Plugin support

This module is extensible via plugin contracts for both monitors and reactors. You can pretty much customize it to integrate it with anything you want. See io-event-reactor-plugin-support for more details on creating plugins.

• io-event-reactor-plugin-support - Required module for developing any plugin

Monitor plugins

• io-event-reactor-plugin-chokidar - Monitor the filesystem for changes using Chokidar

Reactor plugins

Default Plugins

The plugins below are simple and just come with this module by default.

• code - Permits arbitrary execution of javascript, to use: ./default_plugins/code/codeReactorPlugin
• logger - Log reactions to monitored events, to use: ./default_plugins/logger/loggerReactorPlugin

External module plugins

• io-event-reactor-plugin-shell-exec - Exec shell commands via stateful-process-command-proxy
• io-event-reactor-plugin-mysql - Exec SQL against data in MySql via node-mysql

Unit tests

To run the unit tests go to the root of the project and run the following.

mocha test/all.js