Add beforeLogin function option on server (PrismarineJS#871)

* Add `beforeLogin` event on server

* optional function passin instead of emitted event

* Add documentation and bump version

* undo release push

* add test for `beforeLogin`

Author: rob9315

docs/API.md

@@ -15,6 +15,8 @@ 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.
+ * 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"
  * maxPlayers : default to 20
  * keepAlive : send keep alive packets : default to true

src/index.d.ts

@@ -82,6 +82,7 @@ declare module 'minecraft-protocol' {
 		port?: number
 		version?: string
 		beforePing?: (response: any, client: Client, callback?: (result: any) => any) => any
+		beforeLogin?: (client: Client) => void
 		errorHandler?: (client: Client, error: Error) => void
 		agent?: Agent
 	}

src/server/login.js

@@ -109,6 +109,7 @@ module.exports = function (client, server, options) {
     if (onlineMode === false || isException) {
       client.uuid = nameToMcOfflineUUID(client.username)
     }
+    options.beforeLogin?.(client)
     if (client.protocolVersion >= 27) { // 14w28a (27) added whole-protocol compression (http://wiki.vg/Protocol_History#14w28a), earlier versions per-packet compressed TODO: refactor into minecraft-data
       client.write('compress', { threshold: 256 }) // Default threshold is 256
       client.compressionThreshold = 256

test/serverTest.js

@@ -191,6 +191,32 @@ for (const supportedVersion of mc.supportedVersions) {
       })
       server.on('close', done)
     })
+    it('clients can be changed by beforeLogin', function (done) {
+      const notchUUID = '069a79f4-44e9-4726-a5be-fca90e38aaf5'
+      const server = mc.createServer({
+        'online-mode': false,
+        version: version.minecraftVersion,
+        port: PORT,
+        beforeLogin: (client) => {
+          client.uuid = notchUUID
+        }
+      })
+      server.on('listening', function () {
+        const client = mc.createClient({
+          username: 'notNotch',
+          host: '127.0.0.1',
+          version: version.minecraftVersion,
+          port: PORT
+        })
+        client.on('packet', (data, {name})=>{
+          if (name === 'success') {
+            assert.strictEqual(data.uuid, notchUUID, 'UUID')
+            server.close()
+          }
+        })
+      })
+      server.on('close', done)
+    })
     it('clients can log in and chat', function (done) {
       const server = mc.createServer({
         'online-mode': false,