fix(auth): prevent stalling on authentication when connected

ReplicaSet was storing the authentication call in the disconnectHandler
when it didn't need to, leading to auth stalling. From now on, will
only store handlers if ReplSet is not actually connected.

NODE-1402

lib/topologies/replset.js

@@ -1413,7 +1413,7 @@ ReplSet.prototype.auth = function(mechanism, db) {
 
   // Topology is not connected, save the call in the provided store to be
   // Executed at some point when the handler deems it's reconnected
-  if (self.s.disconnectHandler != null) {
+  if (!this.isConnected() && self.s.disconnectHandler != null) {
     if (!self.s.replicaSetState.hasPrimary() && !self.s.options.secondaryOnlyConnectionAllowed) {
       return self.s.disconnectHandler.add('auth', db, allArgs, {}, callback);
     } else if (

test/tests/unit/replset/auth_tests.js

@@ -0,0 +1,67 @@
+'use strict';
+
+const ReplSet = require('../../../../lib/topologies/replset');
+const mock = require('mongodb-mock-server');
+const ReplSetFixture = require('../common').ReplSetFixture;
+const ReadPreference = require('../../../../lib/topologies/read_preference');
+
+describe('Auth (ReplSet)', function() {
+  let test;
+  before(() => (test = new ReplSetFixture()));
+  afterEach(() => mock.cleanup());
+  beforeEach(() => test.setup());
+
+  // mock ops store from node-mongodb-native
+  const mockDisconnectHandler = {
+    add: () => {},
+    execute: () => {},
+    flush: () => {}
+  };
+
+  it('should not stall on authentication when you are connected', function(done) {
+    let finish = err => {
+      finish = () => {};
+      done(err);
+    };
+
+    test.primaryServer.setMessageHandler(request => {
+      const doc = request.document;
+      if (doc.ismaster) {
+        setTimeout(() => request.reply(test.primaryStates[0]));
+      } else if (doc.saslStart) {
+        finish();
+      }
+    });
+
+    test.firstSecondaryServer.setMessageHandler(request => {
+      const doc = request.document;
+      if (doc.ismaster) {
+        setTimeout(() => request.reply(test.firstSecondaryStates[0]), 2000);
+      } else if (doc.saslStart) {
+        finish();
+      }
+    });
+
+    const replSet = new ReplSet(
+      [test.primaryServer.address(), test.firstSecondaryServer.address()],
+      {
+        setName: 'rs',
+        haInterval: 10000,
+        connectionTimeout: 3000,
+        disconnectHandler: mockDisconnectHandler,
+        secondaryOnlyConnectionAllowed: true,
+        size: 1
+      }
+    );
+
+    replSet.once('error', finish);
+    replSet.once('connect', () => replSet.auth('default', 'db', 'user', 'pencil', () => {}));
+    replSet.connect({
+      readPreference: new ReadPreference('primary'),
+      checkServerIdentity: true,
+      rejectUnauthorized: true
+    });
+
+    setTimeout(() => finish('replicaset stalled when attempting to authenticate'), 5000);
+  });
+});