Delay Dropbox polling by 5 seconds and dispatch only a single request

services/web/app/coffee/Features/Dropbox/DropboxWebhookController.coffee

@@ -10,6 +10,10 @@ module.exports = DropboxWebhookController =
 		logger.log dropbox_uids: dropbox_uids, "received webhook request from Dropbox"
 		if !dropbox_uids?
 			return res.send(400) # Bad Request
+			
+		# Do this in the background so as not to keep Dropbox waiting
 		DropboxWebhookHandler.pollDropboxUids dropbox_uids, (error) ->
-			return next(error) if error?
-			res.send(200)
+			if error?
+				logger.error err: error, dropbox_uids: dropbox_uids, "error in webhook"
+		
+		res.send(200)

services/web/app/coffee/Features/Dropbox/DropboxWebhookHandler.coffee

@@ -1,8 +1,13 @@
 logger = require("logger-sharelatex")
+settings = require("settings-sharelatex")
 async = require "async"
 User = require("../../models/User").User
 TpdsUpdateSender = require "../ThirdPartyDataStore/TpdsUpdateSender"
 
+redis = require('redis')
+rclient = redis.createClient(settings.redis.web.port, settings.redis.web.host)
+rclient.auth(settings.redis.web.password)
+
 module.exports = DropboxWebhookHandler =
 	pollDropboxUids: (dropbox_uids, callback = (error) ->) ->
 		jobs = []
@@ -13,13 +18,32 @@ module.exports = DropboxWebhookHandler =
 		async.series jobs, callback
 		
 	pollDropboxUid: (dropbox_uid, callback = (error) ->) ->
-		User.find {
-			"dropbox.access_token.uid": dropbox_uid.toString()
-			"features.dropbox": true
-		}, (error, users = []) ->
+		DropboxWebhookHandler._delayAndBatchPoll dropbox_uid, (error, shouldPoll) ->
 			return callback(error) if error?
-			user = users[0]
-			if !user?
-				logger.log dropbox_uid: dropbox_uid, "no sharelatex user found"
-				return callback()
-			TpdsUpdateSender.pollDropboxForUser user._id, callback
+			return callback() if !shouldPoll
+			User.find {
+				"dropbox.access_token.uid": dropbox_uid.toString()
+				"features.dropbox": true
+			}, (error, users = []) ->
+				return callback(error) if error?
+				user = users[0]
+				if !user?
+					logger.log dropbox_uid: dropbox_uid, "no sharelatex user found"
+					return callback()
+				TpdsUpdateSender.pollDropboxForUser user._id, callback
+		
+	POLL_DELAY_IN_MS: 5000 # 5 seconds
+	_delayAndBatchPoll: (dropbox_uid, callback = (error, shouldPoll) ->) ->
+		rclient.set(
+			"dropbox-poll-lock:#{dropbox_uid}", "LOCK",
+			"PX", DropboxWebhookHandler.POLL_DELAY_IN_MS,
+			"NX",
+		(error, gotLock) ->
+			return callback(error) if error?
+			if gotLock
+				setTimeout () ->
+					callback(null, true)
+				, DropboxWebhookHandler.POLL_DELAY_IN_MS
+			else
+				callback(null, false)
+		)