Improve Rojo sync reliability (#739)

Uses non-recursive main loop and avoids hanging promises

plugin/src/ApiContext.lua

@@ -11,13 +11,6 @@ local validateApiInfo = Types.ifEnabled(Types.ApiInfoResponse)
 local validateApiRead = Types.ifEnabled(Types.ApiReadResponse)
 local validateApiSubscribe = Types.ifEnabled(Types.ApiSubscribeResponse)
 
---[[
-	Returns a promise that will never resolve nor reject.
-]]
-local function hangingPromise()
-	return Promise.new(function() end)
-end
-
 local function rejectFailedRequests(response)
 	if response.code >= 400 then
 		local message = string.format("HTTP %s:\n%s", tostring(response.code), response.body)
@@ -212,12 +205,8 @@ function ApiContext:retrieveMessages()
 	local function sendRequest()
 		local request = Http.get(url)
 			:catch(function(err)
-				if err.type == Http.Error.Kind.Timeout then
-					if self.__connected then
-						return sendRequest()
-					else
-						return hangingPromise()
-					end
+				if err.type == Http.Error.Kind.Timeout and self.__connected then
+					return sendRequest()
 				end
 
 				return Promise.reject(err)

plugin/src/ServeSession.lua

@@ -299,27 +299,44 @@ function ServeSession:__initialSync(serverInfo)
 end
 
 function ServeSession:__mainSyncLoop()
-	return self.__apiContext:retrieveMessages()
-		:andThen(function(messages)
-			Log.trace("Serve session {} retrieved {} messages", tostring(self), #messages)
-
-			for _, message in ipairs(messages) do
-				local unappliedPatch = self.__reconciler:applyPatch(message)
-
-				if not PatchSet.isEmpty(unappliedPatch) then
-					Log.warn("Could not apply all changes requested by the Rojo server:\n{}",
-						PatchSet.humanSummary(self.__instanceMap, unappliedPatch))
-				end
-
-				if self.__patchAppliedCallback then
-					pcall(self.__patchAppliedCallback, message, unappliedPatch)
-				end
+	return Promise.new(function(resolve, reject)
+		while self.__status == Status.Connected do
+			local success, result = self.__apiContext:retrieveMessages()
+				:andThen(function(messages)
+					if self.__status == Status.Disconnected then
+						-- In the time it took to retrieve messages, we disconnected
+						-- so we just resolve immediately without patching anything
+						return
+					end
+
+					Log.trace("Serve session {} retrieved {} messages", tostring(self), #messages)
+
+					for _, message in messages do
+						local unappliedPatch = self.__reconciler:applyPatch(message)
+
+						if not PatchSet.isEmpty(unappliedPatch) then
+							Log.warn("Could not apply all changes requested by the Rojo server:\n{}",
+								PatchSet.humanSummary(self.__instanceMap, unappliedPatch))
+						end
+
+						if self.__patchAppliedCallback then
+							pcall(self.__patchAppliedCallback, message, unappliedPatch)
+						end
+					end
+				end):await()
+
+			if self.__status == Status.Disconnected then
+				-- If we are no longer connected after applying, we stop silently
+				-- without checking for errors as they are no longer relevant
+				break
+			elseif success == false then
+				reject(result)
 			end
+		end
 
-			if self.__status ~= Status.Disconnected then
-				return self:__mainSyncLoop()
-			end
-		end)
+		-- We are no longer connected, so we resolve the promise
+		resolve()
+	end)
 end
 
 function ServeSession:__stopInternal(err)