Added mongodb as document store adapter

lib/document_stores/mongodb.js

@@ -0,0 +1,94 @@
+const winston = require('winston');
+const mongodb = require('mongodb');
+
+const MongoDocumentStore = function (config){
+	this.expire = config.expire;
+	this.MongoClient = new mongodb.MongoClient(config.connectionUrl, config.clientOptions);
+};
+
+MongoDocumentStore.prototype.set = async function (key, data, callback, skipExpire){
+	winston.silly(`mongo set ${key}`);
+	const now = Math.floor(Date.now() / 1000);
+	const that = this;
+
+	this.safeConnect(async ( {error} = {} ) => {
+		if (error) return callback(false);
+
+		await this.MongoClient.db().collection('entries').updateOne(
+			{
+				'entry_id': key,
+				$or: [
+					{ expiration: -1 },
+					{ expiration: { $gt: now } }
+				]
+			},
+			{
+				$set: {
+					'entry_id': key,
+					value: data,
+					expiration: that.expire && !skipExpire ? that.expire + now : -1
+				}
+			},
+			{
+				upsert: true
+			}
+		).then((err, result) => {
+			return callback(true);
+		})
+		.catch((err, result) => {
+			winston.error('error updating mongodb document', { error: err });
+			return callback(false);
+		});
+	});
+};
+
+MongoDocumentStore.prototype.get = async function (key, callback, skipExpire){
+	winston.silly(`mongo get ${key}`);
+	const now = Math.floor(Date.now() / 1000);
+	const that = this;
+
+	this.safeConnect(async ( {error} = {} ) => {
+		if (error) return callback(false);
+
+		let document = await this.MongoClient.db().collection('entries').findOne({
+			'entry_id': key,
+			or: [
+				{ expiration: -1 },
+				{ expiration: { $gt: now } }
+			]
+		})
+		.catch(err => {
+			winston.error('error finding mongodb document', { error: err });
+			return callback(false);
+		});
+
+		callback(document ? document.value : false);
+
+		if (document && document.expiration != -1 && that.expire && !skipExpire){
+			await this.MongoClient.db().collection('entries').updateOne(
+				{ 'entry_id': key },
+				{ $set: { expiration: that.expire + now } }
+			).catch(err => {
+				return winston.warn('error extending expiry of mongodb document', { error: err });
+			});
+			winston.silly('extended expiry of mongodb document', { key: key, timestamp: that.expire + now })
+		}
+	});
+};
+
+MongoDocumentStore.prototype.safeConnect = function(cb){
+	//don't try connecting again if already connected
+	//https://jira.mongodb.org/browse/NODE-1868
+	if (this.MongoClient.isConnected()) return cb({error: null});
+	this.MongoClient.connect()
+		.then(client => {
+			winston.debug('connected to mongodb', { success: true });
+			cb({error: null});
+		})
+		.catch(err => {
+			winston.error('error connecting to mongodb', { error: err });
+			cb({error: err});
+		});
+};
+
+module.exports = MongoDocumentStore;