return correct post count if its out of sync

src/socket.io/topics.js

@@ -2,12 +2,14 @@
 
 var async = require('async');
 
+var db = require('../database');
 var topics = require('../topics');
 var posts = require('../posts');
 var websockets = require('./index');
 var user = require('../user');
 var meta = require('../meta');
 var apiController = require('../controllers/api');
+var privileges = require('../privileges');
 var socketHelpers = require('./helpers');
 
 var SocketTopics = module.exports;
@@ -62,7 +64,33 @@ function postTopic(socket, data, callback) {
 }
 
 SocketTopics.postcount = function (socket, tid, callback) {
-	topics.getTopicField(tid, 'postcount', callback);
+	async.waterfall([
+		function (next) {
+			privileges.topics.can('read', tid, socket.uid, next);
+		},
+		function (canRead, next) {
+			if (!canRead) {
+				return next(new Error('[[no-privileges]]'));
+			}
+
+			async.parallel({
+				replyCount: function (next) {
+					db.sortedSetCard('tid:' + tid + ':posts', next);
+				},
+				topicData: function (next) {
+					topics.getTopicFields(tid, ['mainPid', 'postcount'], next);
+				},
+			}, next);
+		},
+		function (results, next) {
+			if (results.topicData.mainPid && parseInt(results.topicData.postcount, 10) === parseInt(results.replyCount, 10) + 1) {
+				return next(null, results.topicData.postcount);
+			}
+			var postcount = results.replyCount + (results.topicData.mainPid ? 1 : 0);
+			topics.setTopicField(tid, 'postcount', postcount);
+			next(null, postcount);
+		},
+	], callback);
 };
 
 SocketTopics.bookmark = function (socket, data, callback) {