Added server status retrieval and implemented it on UI.

The player count on the landing page is now functional. If the server cannot be reached, the label and value will change to SERVER and OFFLINE, respectively. This behavior can be modified.

app/assets/js/serverstatus.js

@@ -0,0 +1,65 @@
+const net = require('net')
+
+/**
+ * Retrieves the status of a minecraft server.
+ * 
+ * @param {string} address The server address.
+ * @param {number} port Optional. The port of the server. Defaults to 25565.
+ * @returns {Promise.<Object>} A promise which resolves to an object containing
+ * status information.
+ */
+exports.getStatus = function(address, port = 25565){
+
+    if(port == null || port == ''){
+        port = 25565
+    }
+    if(typeof port === 'string'){
+        port = parseInt(port)
+    }
+
+    return new Promise((resolve, reject) => {
+        const socket = net.connect(port, address, () => {
+            let buff = new Buffer([0xFE, 0x01])
+            socket.write(buff)
+        })
+
+        socket.setTimeout(2500, () => {
+            socket.end()
+            reject({
+                code: 'ETIMEDOUT',
+                errno: 'ETIMEDOUT',
+                address,
+                port
+            })
+        })
+
+        socket.on('data', (data) => {
+            if(data != null && data != ''){
+                let server_info = data.toString().split('\x00\x00\x00')
+                const NUM_FIELDS = 6
+                if(server_info != null && server_info.length >= NUM_FIELDS){
+                    resolve({
+                        online: true,
+                        version: server_info[2].replace(/\u0000/g, ''),
+                        motd: server_info[3].replace(/\u0000/g, ''),
+                        onlinePlayers: server_info[4].replace(/\u0000/g, ''),
+                        maxPlayers: server_info[5].replace(/\u0000/g,'')
+                    })
+                } else {
+                    resolve({
+                        online: false
+                    })
+                }
+            }
+            socket.end()
+        })
+
+        socket.on('error', (err) => {
+            socket.destroy()
+            reject(err)
+            // ENOTFOUND = Unable to resolve.
+            // ECONNREFUSED = Unable to connect to port.
+        })
+    })
+
+}