switch to single get/set method for getProjectDocs

if project state hasn't changed, return the docs. Otherwise set the hash
and return a 409 Conflict response.

services/document-updater/app/coffee/Errors.coffee

@@ -12,7 +12,14 @@ OpRangeNotAvailableError = (message) ->
 	return error
 OpRangeNotAvailableError.prototype.__proto__ = Error.prototype
 
+ProjectStateChangedError = (message) ->
+	error = new Error(message)
+	error.name = "ProjectStateChangedError"
+	error.__proto__ = ProjectStateChangedError.prototype
+	return error
+ProjectStateChangedError.prototype.__proto__ = Error.prototype
+
 module.exports = Errors =
 	NotFoundError: NotFoundError
 	OpRangeNotAvailableError: OpRangeNotAvailableError
-
+	ProjectStateChangedError: ProjectStateChangedError

services/document-updater/app/coffee/HttpController.coffee

@@ -39,6 +39,7 @@ module.exports = HttpController =
 
 	getProjectDocs: (req, res, next = (error) ->) ->
 		project_id = req.params.project_id
+		projectStateHash = req.query?.state
 		# exclude is string of existing docs "id:version,id:version,..."
 		excludeItems = req.query?.exclude?.split(',') or []
 		logger.log project_id: project_id, exclude: excludeItems, "getting docs via http"
@@ -47,10 +48,14 @@ module.exports = HttpController =
 		for item in excludeItems
 			[id,version] = item?.split(':')
 			excludeVersions[id] = version
-		logger.log {project_id: project_id, excludeVersions: excludeVersions}, "excluding versions"
-		ProjectManager.getProjectDocs project_id, excludeVersions, (error, result) ->
+		logger.log {project_id: project_id, projectStateHash: projectStateHash, excludeVersions: excludeVersions}, "excluding versions"
+		ProjectManager.getProjectDocs project_id, projectStateHash, excludeVersions, (error, result) ->
 			timer.done()
-			return next(error) if error?
+			if error instanceof Errors.ProjectStateChangedError
+				res.send 409 # conflict
+			else if error?
+				return next(error)
+			else
 				logger.log project_id: project_id, result: ("#{doc._id}:#{doc.rev}" for doc in result), "got docs via http"
 				res.send result
 

services/document-updater/app/coffee/ProjectManager.coffee

@@ -3,6 +3,7 @@ DocumentManager = require "./DocumentManager"
 async = require "async"
 logger = require "logger-sharelatex"
 Metrics = require "./Metrics"
+Errors = require "./Errors"
 
 module.exports = ProjectManager =
 	flushProjectWithLocks: (project_id, _callback = (error) ->) ->
@@ -57,12 +58,17 @@ module.exports = ProjectManager =
 				else
 					callback(null)
 
-	getProjectDocs: (project_id, excludeVersions = {}, _callback = (error) ->) ->
+	getProjectDocs: (project_id, projectStateHash, excludeVersions = {}, _callback = (error) ->) ->
 		timer = new Metrics.Timer("projectManager.getProjectDocs")
 		callback = (args...) ->
 			timer.done()
 			_callback(args...)
 
+		RedisManager.checkOrSetProjectState project_id, projectStateHash, (error, projectStateChanged) ->
+			return callback(error) if error?
+			# we can't return docs if project structure has changed
+			return callback Errors.ProjectStateChangedError("project state changed") if projectStateChanged
+			# project structure hasn't changed, return doc content from redis
 			RedisManager.getDocIdsInProject project_id, (error, doc_ids) ->
 				return callback(error) if error?
 				jobs = []

services/document-updater/app/coffee/RedisManager.coffee

@@ -90,10 +90,22 @@ module.exports = RedisManager =
 			return callback(error) if error?
 			multi = rclient.multi()
 			multi.srem keys.docsInProject(project_id:project_id), doc_id
-			if keys.clsiState?
-				multi.del keys.clsiState(project_id:project_id)
+			if keys.projectState?
+				multi.del keys.projectState(project_id:project_id)
 			multi.exec callback
 
+	checkOrSetProjectState: (project_id, newState, callback = (error, stateChanged) ->) ->
+		if keys.projectState?
+			multi = rclient.multi()
+			multi.getset keys.projectState(project_id:project_id), newState
+			multi.expire keys.projectState(project_id:project_id), 30 * minutes
+			multi.exec (error, response) ->
+				return callback(error) if error?
+				logger.log project_id: project_id, newState:newState, oldState: response[0], "checking project state"
+				callback(null, response[0] isnt newState)
+		else
+			callback(null,true)
+
 	getDoc : (project_id, doc_id, callback = (error, lines, version, ranges) ->)->
 		timer = new metrics.Timer("redis.get-doc")
 		multi = rclient.multi()