Node example with Realm and Express/Winston to demonstrate interprocess communication.

examples/Node-Interprocess/README.md

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+# Realm-JS Interprocess Example
+Small example of interprocess support with Realm and Node.js
+
+The example makes use of [Winston](https://github.com/winstonjs/winston), a 
+logging library, and includes `winston-realm.js` which defines a custom transport
+utilizing Realm for storage. The main file, `index.js` is a basic 
+[Express](https://github.com/expressjs/express) app. The app listens on port 
+3000 and responds with "Hello World!" at the base path `/` and logs at `info` 
+"Handled Hello World" to Winston. At any other path it returns a `404` error and 
+logs an error message to Winston with URL in question.
+
+Since the log messages are being stored in a Realm (`winston.realm`), we can 
+listen for changes on another process. The `listener.js` is a small example of 
+this. When running, this listens to the `winston.realm` for changes and writes 
+to the console the latest error level log message.
+
+To test:
+
+1. `npm install`
+2. `node .` to run the Express app
+3. In another process: `node listener.js`
+4. Go to `http://localhost:3000/whatever` to see error message across processes

examples/Node-Interprocess/index.js

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+var express = require('express'),
+    util = require('util'),
+    winston = require('winston');
+    RealmWinston = require('./winston-realm').Realm;
+
+var app = express();
+
+// Use custom Winston transport: RealmWinston
+// Writes log data to winston.realm
+winston.add(RealmWinston, {});
+
+app.get('/', function (req, res) {
+  res.send('Hello World!');
+  winston.info('Handled Hello World');
+});
+
+app.use(function (req, res, next) {
+  res.status(404).send('Sorry can not find that!');
+  winston.error('404 Error at: ' + req.url);
+})
+
+app.listen(3000, function () {
+  console.log('Example app listening on port 3000!');
+});
+

examples/Node-Interprocess/listener.js

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+'use strict';
+
+var Realm = require('realm');
+
+let winstonRealm = new Realm({
+  path: 'winston.realm'
+});
+
+// Register listener to print out log messages at error level
+winstonRealm.objects('Log').filtered('level = "error"').addListener((logs, changes) => {
+  changes.insertions.map((index) => {
+    let log = logs[index];
+    console.log(log.message);
+  })
+});
+

examples/Node-Interprocess/package.json

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+{
+  "name": "winston-realm-test",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "dependencies": {
+    "express": "^4.14.0",
+    "winston": "^2.3.0"
+  },
+  "devDependencies": {},
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "author": "",
+  "license": "ISC"
+}
+

examples/Node-Interprocess/winston-realm.js

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+'use strict';
+
+var util = require('util'),
+    winston = require('winston'),
+    Realm = require('realm');
+
+var RealmLogger = exports.Realm = function (options) {
+  winston.Transport.call(this, options);
+
+  //
+  // Configure the Realm`
+  //
+  let LogSchema = {
+    name: 'Log',
+    properties: {
+        level: 'string',
+        message: 'string',
+        timestamp: 'date',
+    }
+  };
+  
+  this.realm = new Realm({
+    path: 'winston.realm',
+    schema: [LogSchema]
+  });
+};
+
+//
+// Inherit from `winston.Transport` so you can take advantage
+// of the base functionality and `.handleExceptions()`.
+//
+util.inherits(RealmLogger, winston.Transport);
+
+//
+// Expose the name of this Transport on the prototype
+//
+RealmLogger.prototype.name = 'realm';
+
+//
+// Define a getter so that `winston.transports.Realm`
+// is available and thus backwards compatible.
+//
+winston.transports.Realm = RealmLogger;
+
+//
+// ### function log (level, msg, [meta], callback)
+// #### @level {string} Level at which to log the message.
+// #### @msg {string} Message to log
+// #### @meta {Object} **Optional** Additional metadata to attach
+// #### @callback {function} Continuation to respond to when complete.
+// Core logging method exposed to Winston. Metadata is optional.
+//
+RealmLogger.prototype.log = function (level, msg, meta, callback) {
+  let ts = new Date();
+  
+  this.realm.write(() => {
+    this.realm.create('Log', {level: level, message: msg, timestamp: ts});
+  });
+
+  callback(null, true);
+};
+