closes #6875

src/controllers/authentication.js

@@ -164,6 +164,10 @@ authenticationController.registerComplete = function (req, res, next) {
 
 		var done = function (err, data) {
 			delete req.session.registration;
+			if (err) {
+				return res.redirect(nconf.get('relative_path') + '/?register=' + encodeURIComponent(err.message));
+			}
+
 			if (!err && data && data.message) {
 				return res.redirect(nconf.get('relative_path') + '/?register=' + encodeURIComponent(data.message));
 			}

src/user/approval.js

@@ -20,7 +20,7 @@ module.exports = function (User) {
 		userData.userslug = utils.slugify(userData.username);
 		async.waterfall([
 			function (next) {
-				User.isDataValid(userData, next);
+				canQueue(userData, next);
 			},
 			function (next) {
 				User.hashPassword(userData.password, next);
@@ -46,6 +46,31 @@ module.exports = function (User) {
 		], callback);
 	};
 
+	function canQueue(userData, callback) {
+		async.waterfall([
+			function (next) {
+				User.isDataValid(userData, next);
+			},
+			function (next) {
+				db.getSortedSetRange('registration:queue', 0, -1, next);
+			},
+			function (usernames, next) {
+				if (usernames.includes(userData.username)) {
+					return next(new Error('[[error:username-taken]]'));
+				}
+				const keys = usernames.filter(Boolean).map(username => 'registration:queue:name:' + username);
+				db.getObjectsFields(keys, ['email'], next);
+			},
+			function (data, next) {
+				const emails = data.map(data => data && data.email);
+				if (emails.includes(userData.email)) {
+					return next(new Error('[[error:email-taken]]'));
+				}
+				next();
+			},
+		], callback);
+	}
+
 	function sendNotificationToAdmins(username, callback) {
 		async.waterfall([
 			function (next) {