allow false as beforePing callback result to ignore pings and terminate the connection (#986)

docs/API.md

@@ -15,6 +15,7 @@ automatically logged in and validated against mojang's auth.
  * beforePing : allow customisation of the answer to ping the server does. 
  It takes a function with argument response and client, response is the default json response, and client is client who sent a ping.
  It can take as third argument a callback. If the callback is passed, the function should pass its result to the callback, if not it should return.
+ If the result is `false` instead of a response object then the connection is terminated and no ping is returned to the client.
  * beforeLogin : allow customisation of client before the `success` packet is sent.
  It takes a function with argument client and should be synchronous for the server to wait for completion before continuing execution.
  * motd : default to "A Minecraft server"

src/server/ping.js

@@ -41,7 +41,11 @@ module.exports = function (client, server, { beforePing = null, version, fallbac
 
     function answerToPing (err, response) {
       if (err) return
-      client.write('server_info', { response: JSON.stringify(response) })
+      if (response === false) {
+        client.socket.destroy()
+      } else {
+        client.write('server_info', { response: JSON.stringify(response) })
+      }
     }
 
     if (beforePing) {