Improve WebSocketServer Error Handling (#6230)

* Improve WebSocketServer Error Handling

Closes: https://github.com/parse-community/parse-server/issues/6173

Prevents an unhandled server rejection.

Includes an example for LiveQuery test and closing the proper connections.

Improve live query monitoring

* fix tests

spec/ParseLiveQuery.spec.js

@@ -0,0 +1,35 @@
+'use strict';
+
+describe('ParseLiveQuery', function() {
+  it('can subscribe to query', async done => {
+    await reconfigureServer({
+      liveQuery: {
+        classNames: ['TestObject'],
+      },
+      startLiveQueryServer: true,
+      verbose: false,
+      silent: true,
+    });
+    const object = new TestObject();
+    await object.save();
+
+    const query = new Parse.Query(TestObject);
+    query.equalTo('objectId', object.id);
+    const subscription = await query.subscribe();
+    subscription.on('update', async object => {
+      expect(object.get('foo')).toBe('bar');
+      done();
+    });
+    object.set({ foo: 'bar' });
+    await object.save();
+  });
+
+  afterEach(async function(done) {
+    const client = await Parse.CoreManager.getLiveQueryController().getDefaultLiveQueryClient();
+    client.close();
+    // Wait for live query client to disconnect
+    setTimeout(() => {
+      done();
+    }, 1000);
+  });
+});

spec/ParseWebSocketServer.spec.js

@@ -39,6 +39,45 @@ describe('ParseWebSocketServer', function() {
     }, 10);
   });
 
+  it('can handle error event', async () => {
+    jasmine.restoreLibrary('ws', 'Server');
+    const WebSocketServer = require('ws').Server;
+    let wssError;
+    class WSSAdapter {
+      constructor(options) {
+        this.options = options;
+      }
+      onListen() {}
+      onConnection() {}
+      onError() {}
+      start() {
+        const wss = new WebSocketServer({ server: this.options.server });
+        wss.on('listening', this.onListen);
+        wss.on('connection', this.onConnection);
+        wss.on('error', error => {
+          wssError = error;
+          this.onError(error);
+        });
+        this.wss = wss;
+      }
+    }
+
+    const server = await reconfigureServer({
+      liveQuery: {
+        classNames: ['TestObject'],
+      },
+      liveQueryServerOptions: {
+        wssAdapter: WSSAdapter,
+      },
+      startLiveQueryServer: true,
+      verbose: false,
+      silent: true,
+    });
+    const wssAdapter = server.liveQueryServer.parseWebSocketServer.server;
+    wssAdapter.wss.emit('error', 'Invalid Packet');
+    expect(wssError).toBe('Invalid Packet');
+  });
+
   afterEach(function() {
     jasmine.restoreLibrary('ws', 'Server');
   });