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//
// AddressCacheStore.swift
// MullvadVPN
//
// Created by pronebird on 08/12/2021.
// Copyright © 2021 Mullvad VPN AB. All rights reserved.
//
import Foundation
import Logging
extension AddressCache {
struct CachedAddresses: Codable {
/// Date when the cached addresses were last updated.
var updatedAt: Date
/// API endpoints.
var endpoints: [AnyIPEndpoint]
}
enum CacheSource: CustomStringConvertible {
/// Cache file originates from disk location.
case disk
/// Cache file originates from application bundle.
case bundle
var description: String {
switch self {
case .disk:
return "disk"
case .bundle:
return "bundle"
}
}
}
struct ReadResult {
var cachedAddresses: CachedAddresses
var source: CacheSource
}
class Store {
static let shared: Store = {
let cacheFilename = "api-ip-address.json"
let cacheDirectoryURL = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
let cacheFileURL = cacheDirectoryURL.appendingPathComponent(cacheFilename, isDirectory: false)
let prebundledCacheFileURL = Bundle.main.url(forResource: cacheFilename, withExtension: nil)!
return Store(
cacheFileURL: cacheFileURL,
prebundledCacheFileURL: prebundledCacheFileURL
)
}()
static var defaultCachedAddresses: CachedAddresses {
return CachedAddresses(
updatedAt: Date(timeIntervalSince1970: 0),
endpoints: [
ApplicationConfiguration.defaultAPIEndpoint
]
)
}
/// Logger.
private let logger = Logger(label: "AddressCache.Store")
/// Memory cache.
private var cachedAddresses: CachedAddresses
/// Cache file location.
private let cacheFileURL: URL
/// The location of pre-bundled address cache file.
private let prebundledCacheFileURL: URL
/// Queue used for synchronizing access to instance members.
private let stateQueue = DispatchQueue(label: "AddressCacheStoreQueue")
/// Designated initializer
init(cacheFileURL: URL, prebundledCacheFileURL: URL) {
self.cacheFileURL = cacheFileURL
self.prebundledCacheFileURL = prebundledCacheFileURL
self.cachedAddresses = Self.defaultCachedAddresses
switch readFromCacheLocationWithFallback() {
case .success(let readResult):
if readResult.cachedAddresses.endpoints.isEmpty {
logger.debug("Read empty cache from \(readResult.source). Fallback to default API endpoint.")
cachedAddresses = Self.defaultCachedAddresses
logger.debug("Initialized cache with default API endpoint.")
} else {
switch readResult.source {
case .disk:
cachedAddresses = readResult.cachedAddresses
case .bundle:
var addresses = readResult.cachedAddresses
addresses.endpoints.shuffle()
cachedAddresses = addresses
logger.debug("Persist address list read from bundle.")
if case .failure(let error) = self.writeToDisk() {
logger.error(chainedError: error, message: "Failed to persist address cache after reading it from bundle.")
}
}
logger.debug("Initialized cache from \(readResult.source) with \(cachedAddresses.endpoints.count) endpoint(s).")
}
case .failure(let error):
logger.error(chainedError: error, message: "Failed to read address cache. Fallback to default API endpoint.")
cachedAddresses = Self.defaultCachedAddresses
logger.debug("Initialized cache with default API endpoint.")
}
}
func getCurrentEndpoint(_ completionHandler: @escaping (AnyIPEndpoint) -> Void) {
stateQueue.async {
let currentEndpoint = self.cachedAddresses.endpoints.first!
completionHandler(currentEndpoint)
}
}
func selectNextEndpoint(_ failedEndpoint: AnyIPEndpoint, completionHandler: @escaping (AnyIPEndpoint) -> Void) {
stateQueue.async {
var currentEndpoint = self.cachedAddresses.endpoints.first!
if failedEndpoint == currentEndpoint {
self.cachedAddresses.endpoints.removeFirst()
self.cachedAddresses.endpoints.append(failedEndpoint)
currentEndpoint = self.cachedAddresses.endpoints.first!
self.logger.debug("Failed to communicate using \(failedEndpoint). Next endpoint: \(currentEndpoint)")
if case .failure(let error) = self.writeToDisk() {
self.logger.error(chainedError: error, message: "Failed to write address cache after selecting next endpoint.")
}
}
completionHandler(currentEndpoint)
}
}
func setEndpoints(_ endpoints: [AnyIPEndpoint], completionHandler: @escaping (AddressCache.StoreError?) -> Void) {
stateQueue.async {
guard !endpoints.isEmpty else {
completionHandler(.emptyAddressList)
return
}
if Set(self.cachedAddresses.endpoints) == Set(endpoints) {
self.cachedAddresses.updatedAt = Date()
} else {
// Shuffle new endpoints
var newEndpoints = endpoints.shuffled()
// Move current endpoint to the top of the list
let currentEndpoint = self.cachedAddresses.endpoints.first!
if let index = newEndpoints.firstIndex(of: currentEndpoint) {
newEndpoints.remove(at: index)
newEndpoints.insert(currentEndpoint, at: 0)
}
self.cachedAddresses = CachedAddresses(
updatedAt: Date(),
endpoints: newEndpoints
)
}
let writeResult = self.writeToDisk()
completionHandler(writeResult.error)
}
}
func getLastUpdateDate(_ completionHandler: @escaping (Date) -> Void) {
stateQueue.async {
completionHandler(self.cachedAddresses.updatedAt)
}
}
func getLastUpdateDateAndWait() -> Date {
return stateQueue.sync {
return self.cachedAddresses.updatedAt
}
}
private func readFromCacheLocationWithFallback() -> Result<ReadResult, AddressCache.StoreError> {
return readFromCacheLocation()
.map { addresses in
return ReadResult(
cachedAddresses: addresses,
source: .disk
)
}
.flatMapError { error in
logger.error(chainedError: error, message: "Failed to read address cache from disk. Fallback to pre-bundled cache.")
return readFromBundle().map { cachedAddresses in
return ReadResult(
cachedAddresses: cachedAddresses,
source: .bundle
)
}
}
}
private func readFromCacheLocation() -> Result<CachedAddresses, AddressCache.StoreError> {
return Result { try Data(contentsOf: cacheFileURL) }
.mapError { error in
return .readCache(error)
}
.flatMap { data in
return Result { try JSONDecoder().decode(CachedAddresses.self, from: data) }
.mapError { error in
return .decodeCache(error)
}
}
}
private func writeToDisk() -> Result<(), AddressCache.StoreError> {
let cacheDirectoryURL = cacheFileURL.deletingLastPathComponent()
try? FileManager.default.createDirectory(
at: cacheDirectoryURL,
withIntermediateDirectories: true,
attributes: nil
)
return Result { try JSONEncoder().encode(cachedAddresses) }
.mapError { error in
return .encodeCache(error)
}
.flatMap { data in
return Result { try data.write(to: cacheFileURL, options: .atomic) }
.mapError { error in
return .writeCache(error)
}
}
}
private func readFromBundle() -> Result<CachedAddresses, AddressCache.StoreError> {
return Result { try Data(contentsOf: prebundledCacheFileURL) }
.mapError { error in
return .readCacheFromBundle(error)
}
.flatMap { data in
return Result { try JSONDecoder().decode([AnyIPEndpoint].self, from: data) }
.mapError { error in
return .decodeCacheFromBundle(error)
}
.map { endpoints in
return CachedAddresses(
updatedAt: Date(timeIntervalSince1970: 0),
endpoints: endpoints
)
}
}
}
}
}
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