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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
/// Lock used for synchronizing access to instance members.
private let nslock = NSLock()
/// Designated initializer
init(cacheFileURL: URL, prebundledCacheFileURL: URL) {
self.cacheFileURL = cacheFileURL
self.prebundledCacheFileURL = prebundledCacheFileURL
cachedAddresses = Self.defaultCachedAddresses
initializeStore()
}
func getCurrentEndpoint() -> AnyIPEndpoint {
nslock.lock()
defer { nslock.unlock() }
return cachedAddresses.endpoints.first!
}
func selectNextEndpoint(_ failedEndpoint: AnyIPEndpoint) -> AnyIPEndpoint {
nslock.lock()
defer { nslock.unlock() }
var currentEndpoint = cachedAddresses.endpoints.first!
guard failedEndpoint == currentEndpoint else {
return currentEndpoint
}
cachedAddresses.endpoints.removeFirst()
cachedAddresses.endpoints.append(failedEndpoint)
currentEndpoint = cachedAddresses.endpoints.first!
logger.debug("Failed to communicate using \(failedEndpoint). Next endpoint: \(currentEndpoint)")
do {
try writeToDisk()
} catch {
logger.error(
chainedError: AnyChainedError(error),
message: "Failed to write address cache after selecting next endpoint."
)
}
return currentEndpoint
}
func setEndpoints(_ endpoints: [AnyIPEndpoint]) throws {
nslock.lock()
defer { nslock.unlock() }
guard !endpoints.isEmpty else {
throw StoreError.emptyAddressList
}
if Set(cachedAddresses.endpoints) == Set(endpoints) {
cachedAddresses.updatedAt = Date()
} else {
// Shuffle new endpoints
var newEndpoints = endpoints.shuffled()
// Move current endpoint to the top of the list
let currentEndpoint = cachedAddresses.endpoints.first!
if let index = newEndpoints.firstIndex(of: currentEndpoint) {
newEndpoints.remove(at: index)
newEndpoints.insert(currentEndpoint, at: 0)
}
cachedAddresses = CachedAddresses(
updatedAt: Date(),
endpoints: newEndpoints
)
}
try writeToDisk()
}
func getLastUpdateDate() -> Date {
nslock.lock()
defer { nslock.unlock() }
return cachedAddresses.updatedAt
}
private func initializeStore() {
let readResult: ReadResult
do {
readResult = try readFromCacheLocationWithFallback()
} catch {
logger.error(
chainedError: AnyChainedError(error),
message: "Failed to read address cache. Fallback to default API endpoint."
)
cachedAddresses = Self.defaultCachedAddresses
logger.debug("Initialized cache with default API endpoint.")
return
}
guard !readResult.cachedAddresses.endpoints.isEmpty else {
logger.debug("Read empty cache from \(readResult.source). Fallback to default API endpoint.")
cachedAddresses = Self.defaultCachedAddresses
logger.debug("Initialized cache with default API endpoint.")
return
}
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.")
do {
try writeToDisk()
} catch {
logger.error(
chainedError: AnyChainedError(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).")
}
private func readFromCacheLocationWithFallback() throws -> ReadResult {
do {
return ReadResult(
cachedAddresses: try readFromCacheLocation(),
source: .disk
)
} catch {
logger.error(
chainedError: AnyChainedError(error),
message: "Failed to read address cache from disk. Fallback to pre-bundled cache."
)
}
return ReadResult(
cachedAddresses: try readFromBundle(),
source: .bundle
)
}
private func readFromCacheLocation() throws -> CachedAddresses {
do {
let data = try Data(contentsOf: cacheFileURL)
return try JSONDecoder().decode(CachedAddresses.self, from: data)
} catch let error as DecodingError {
throw StoreError.decodeCache(error)
} catch {
throw StoreError.readCache(error)
}
}
private func writeToDisk() throws {
let cacheDirectoryURL = cacheFileURL.deletingLastPathComponent()
try? FileManager.default.createDirectory(
at: cacheDirectoryURL,
withIntermediateDirectories: true,
attributes: nil
)
do {
let data = try JSONEncoder().encode(cachedAddresses)
try data.write(to: cacheFileURL, options: .atomic)
} catch let error as EncodingError {
throw StoreError.encodeCache(error)
} catch {
throw StoreError.writeCache(error)
}
}
private func readFromBundle() throws -> CachedAddresses {
do {
let data = try Data(contentsOf: prebundledCacheFileURL)
let endpoints = try JSONDecoder().decode([AnyIPEndpoint].self, from: data)
return CachedAddresses(
updatedAt: Date(timeIntervalSince1970: 0),
endpoints: endpoints
)
} catch let error as DecodingError {
throw StoreError.decodeCacheFromBundle(error)
} catch {
throw StoreError.decodeCacheFromBundle(error)
}
}
}
}
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