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//
// AddressCacheTracker.swift
// MullvadVPN
//
// Created by pronebird on 08/12/2021.
// Copyright © 2021 Mullvad VPN AB. All rights reserved.
//
import UIKit
import BackgroundTasks
import Logging
extension AddressCache {
class Tracker {
/// Update interval (in seconds).
private static let updateInterval: TimeInterval = 60 * 60 * 24
/// Retry interval (in seconds).
private static let retryInterval: TimeInterval = 60 * 15
/// Logger.
private let logger = Logger(label: "AddressCache.Tracker")
/// REST client
private let restClient: REST.Client
/// Store.
private let store: AddressCache.Store
/// A flag that indicates whether periodic updates are running
private var isPeriodicUpdatesEnabled = false
/// The date of last failed attempt.
private var lastFailureAttemptDate: Date?
/// Timer used for scheduling periodic updates.
private var timer: DispatchSourceTimer?
/// Operation queue.
private let operationQueue: OperationQueue = {
let operationQueue = OperationQueue()
operationQueue.maxConcurrentOperationCount = 1
return operationQueue
}()
/// Queue used for synchronizing access to instance members.
private let stateQueue = DispatchQueue(label: "AddressCache.Tracker.stateQueue")
/// Designated initializer
init(restClient: REST.Client, store: AddressCache.Store) {
self.restClient = restClient
self.store = store
}
func startPeriodicUpdates() {
stateQueue.async {
guard !self.isPeriodicUpdatesEnabled else {
return
}
self.logger.debug("Start periodic address cache updates")
self.isPeriodicUpdatesEnabled = true
let scheduleDate = self.nextScheduleDate()
self.logger.debug("Schedule address cache update on \(scheduleDate.logFormatDate())")
self.scheduleEndpointsUpdate(startTime: .now() + scheduleDate.timeIntervalSinceNow)
}
}
func stopPeriodicUpdates() {
stateQueue.async {
guard self.isPeriodicUpdatesEnabled else { return }
self.logger.debug("Stop periodic address cache updates")
self.isPeriodicUpdatesEnabled = false
self.timer?.cancel()
self.timer = nil
}
}
func updateEndpoints(completionHandler: ((_ result: CacheUpdateResult) -> Void)? = nil) -> AnyCancellable {
let operation = UpdateAddressCacheOperation(
queue: stateQueue,
restClient: restClient,
store: store,
updateInterval: Self.updateInterval,
completionHandler: { [weak self] result in
self?.handleCacheUpdateResult(result)
completionHandler?(result)
}
)
let backgroundTaskIdentifier = UIApplication.shared.beginBackgroundTask(withName: "AddressCache.Tracker.updateEndpoints") {
operation.cancel()
}
operation.completionBlock = {
UIApplication.shared.endBackgroundTask(backgroundTaskIdentifier)
}
operationQueue.addOperation(operation)
return AnyCancellable {
operation.cancel()
}
}
private func scheduleEndpointsUpdate(startTime: DispatchWallTime) {
let newTimer = DispatchSource.makeTimerSource()
newTimer.setEventHandler { [weak self] in
self?.handleTimer()
}
newTimer.schedule(wallDeadline: startTime)
newTimer.activate()
timer?.cancel()
timer = newTimer
}
private func handleTimer() {
_ = updateEndpoints { result in
guard self.isPeriodicUpdatesEnabled else { return }
let scheduleDate = self.nextScheduleDate()
self.logger.debug("Schedule next address cache update on \(scheduleDate.logFormatDate())")
self.scheduleEndpointsUpdate(startTime: .now() + scheduleDate.timeIntervalSinceNow)
}
}
private func nextScheduleDate() -> Date {
if let lastFailureAttemptDate = lastFailureAttemptDate {
return Date(timeInterval: Self.retryInterval, since: lastFailureAttemptDate)
} else {
let updatedAt = store.getLastUpdateDateAndWait()
return Date(timeInterval: Self.updateInterval, since: updatedAt)
}
}
private func handleCacheUpdateResult(_ result: AddressCache.CacheUpdateResult) {
switch result {
case .success:
logger.debug("Finished updating address cache")
lastFailureAttemptDate = nil
case .failure(let error):
logger.error(chainedError: AnyChainedError(error), message: "Failed to update address cache")
lastFailureAttemptDate = Date()
case .throttled:
logger.debug("Address cache update was throttled")
lastFailureAttemptDate = nil
case .cancelled:
logger.debug("Address cache update was cancelled")
lastFailureAttemptDate = Date()
}
}
}
}
// MARK: - Background tasks
@available(iOS 13.0, *)
extension AddressCache.Tracker {
/// Register background task with scheduler.
func registerBackgroundTask() {
let taskIdentifier = ApplicationConfiguration.addressCacheUpdateTaskIdentifier
let isRegistered = BGTaskScheduler.shared.register(forTaskWithIdentifier: taskIdentifier, using: nil) { task in
self.handleBackgroundTask(task as! BGProcessingTask)
}
if isRegistered {
logger.debug("Registered address cache update task")
} else {
logger.error("Failed to register address cache update task")
}
}
/// Create and submit task request to scheduler.
func scheduleBackgroundTask() throws {
let beginDate = nextScheduleDate()
logger.debug("Schedule address cache update task on \(beginDate.logFormatDate())")
let taskIdentifier = ApplicationConfiguration.addressCacheUpdateTaskIdentifier
let request = BGProcessingTaskRequest(identifier: taskIdentifier)
request.earliestBeginDate = beginDate
request.requiresNetworkConnectivity = true
return try BGTaskScheduler.shared.submit(request)
}
/// Background task handler.
private func handleBackgroundTask(_ task: BGProcessingTask) {
logger.debug("Start address cache update task")
let cancellable = updateEndpoints { result in
do {
// Schedule next background task
try self.scheduleBackgroundTask()
} catch {
self.logger.error(chainedError: AnyChainedError(error), message: "Failed to schedule next address cache update task")
}
task.setTaskCompleted(success: result.isTaskCompleted)
}
task.expirationHandler = {
cancellable.cancel()
}
}
}
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