Don't call sync functions inside async

Calling sync functions inside async can trigger the node max stack size.
Instead, build up our unique list of ids in advance, so we only call a
method in async for each user we actually need to look up, asynchronously.
Then use all the cached values synchronously afterwards.

services/web/app/coffee/Features/Chat/ChatController.coffee

@@ -34,32 +34,32 @@ module.exports = ChatController =
 				res.json messages
 
 	_injectUserInfoIntoThreads: (threads, callback = (error, threads) ->) ->
-		userCache = {}
-		getUserDetails = (user_id, callback = (error, user) ->) ->
-			return callback(null, userCache[user_id]) if userCache[user_id]?
-			UserInfoManager.getPersonalInfo user_id, (err, user) ->
-				return callback(error) if error?
-				user = UserInfoController.formatPersonalInfo user
-				userCache[user_id] = user
-				callback null, user
-		
-		jobs = []
+		# There will be a lot of repitition of user_ids, so first build a list
+		# of unique ones to perform db look ups on, then use these to populate the
+		# user fields
+		user_ids = {}
 		for thread_id, thread of threads
-			do (thread) ->
-				if thread.resolved
-					jobs.push (cb) ->
-						getUserDetails thread.resolved_by_user_id, (error, user) ->
-							cb(error) if error?
-							thread.resolved_by_user = user
-							cb()
-				for message in thread.messages
-					do (message) ->
-						jobs.push (cb) ->
-							getUserDetails message.user_id, (error, user) ->
-								cb(error) if error?
-								message.user = user
-								cb()
+			if thread.resolved
+				user_ids[thread.resolved_by_user_id] = true
+			for message in thread.messages
+				user_ids[message.user_id] = true
 		
+		jobs = []
+		users = {}
+		for user_id, _ of user_ids
+			do (user_id) ->
+				jobs.push (cb) ->
+					UserInfoManager.getPersonalInfo user_id, (err, user) ->
+						return cb(error) if error?
+						user = UserInfoController.formatPersonalInfo user
+						users[user_id] = user
+						cb()
+
 		async.series jobs, (error) ->
 			return callback(error) if error?
+			for thread_id, thread of threads
+				if thread.resolved
+					thread.resolved_by_user = users[thread.resolved_by_user_id]
+				for message in thread.messages
+					message.user = users[message.user_id]
 			return callback null, threads