Add support for MySQL/MariaDB databases #1817

This commit adds support for monitoring MySQL and MariaDB database
servers. The mysql2 package was choosen over mysql as it provides a
promise wrapper and is reportedly faster than the original mysql package
whilst still maintaining the same API.

Signed-off-by: Matthew Nickson <mnickson@sidingsmedia.com>

server/util-server.js

@@ -13,6 +13,7 @@ const { badgeConstants } = require("./config");
 const mssql = require("mssql");
 const { Client } = require("pg");
 const postgresConParse = require("pg-connection-string").parse;
+const mysql = require("mysql2/promise");
 const { NtlmClient } = require("axios-ntlm");
 const { Settings } = require("./settings");
 const radiusClient = require("node-radius-client");
@@ -291,6 +292,28 @@ exports.postgresQuery = function (connectionString, query) {
     });
 };
 
+/**
+ * Run a query on MySQL/MariaDB
+ * @param {string} connectionString The database connection string
+ * @param {string} query The query to validate the database with
+ * @returns {Promise<(string[]|Object[]|Object)>}
+ */
+exports.mysqlQuery = function (connectionString, query) {
+    return new Promise((resolve, reject) => {
+        return mysql.createConnection(connectionString)
+            .then(connection => {
+                connection.connect();
+                return connection.query(query);
+            })
+            .then(res => {
+                resolve(res);
+            })
+            .catch(err => {
+                reject(err);
+            });
+    });
+};
+
 exports.radius = function (
     hostname,
     username,