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//
// AddressCache.swift
// MullvadREST
//
// Created by pronebird on 08/12/2021.
// Copyright © 2021 Mullvad VPN AB. All rights reserved.
//
import Foundation
import MullvadLogging
import MullvadTypes
extension REST {
public final class AddressCache {
/// Logger.
private let logger = Logger(label: "AddressCache")
/// Memory cache.
private var cachedAddresses: CachedAddresses = defaultCachedAddresses
/// Cache file location.
private let cacheFileURL: URL
/// Lock used for synchronizing access to instance members.
private let cacheLock = NSLock()
/// Whether address cache can be written to.
private let canWriteToCache: Bool
/// The name of the cache file on disk
internal static let cacheFileName = "api-ip-address.json"
/// The default set of endpoints to use as a fallback mechanism
private static let defaultCachedAddresses = CachedAddresses(
updatedAt: Date(timeIntervalSince1970: 0),
endpoints: [REST.defaultAPIEndpoint]
)
// MARK: -
// MARK: Public API
/// Designated initializer.
public init(canWriteToCache: Bool, cacheFolder: URL) {
let cacheFileURL = cacheFolder.appendingPathComponent(
Self.cacheFileName,
isDirectory: false
)
self.cacheFileURL = cacheFileURL
self.canWriteToCache = canWriteToCache
initCache()
}
/// Returns the latest available endpoint
///
/// When running from the Network Extension, this method will read from the cache before returning.
/// - Returns: The latest available endpoint, or a default endpoint if no endpoints are available
public func getCurrentEndpoint() -> AnyIPEndpoint {
cacheLock.lock()
defer { cacheLock.unlock() }
var currentEndpoint = cachedAddresses.endpoints.first ?? REST.defaultAPIEndpoint
// Reload from disk cache when in the Network Extension as there is no `AddressCacheTracker` running
// there
if canWriteToCache == false {
do {
cachedAddresses = try readFromCache()
if let firstEndpoint = cachedAddresses.endpoints.first {
currentEndpoint = firstEndpoint
}
} catch {
logger.error(error: error)
}
}
return currentEndpoint
}
public func selectNextEndpoint(_ failedEndpoint: AnyIPEndpoint) -> AnyIPEndpoint {
// This function currently acts as a convoluted no-op. It will be soon deleted.
return getCurrentEndpoint()
}
/// Updates the available endpoints to use
///
/// Only the first available endpoint is kept, the rest are discarded.
/// This method will only modify the on disk cache when running from the UI process.
/// - Parameter endpoints: The new endpoints to use for API requests
public func setEndpoints(_ endpoints: [AnyIPEndpoint]) {
cacheLock.lock()
defer { cacheLock.unlock() }
guard let firstEndpoint = endpoints.first else { return }
if Set(cachedAddresses.endpoints) == Set(endpoints) {
cachedAddresses.updatedAt = Date()
} else {
cachedAddresses = CachedAddresses(
updatedAt: Date(),
endpoints: [firstEndpoint]
)
}
if canWriteToCache {
do {
try writeToCache()
} catch {
logger.error(
error: error,
message: "Failed to write address cache after setting new endpoints."
)
}
}
}
/// The `Date` when the cache was last updated at
///
/// - Returns: The `Date` when the cache was last updated at
public func getLastUpdateDate() -> Date {
cacheLock.lock()
defer { cacheLock.unlock() }
return cachedAddresses.updatedAt
}
// MARK: - Private API
/// Initializes the cache by reading the a cached file from disk
///
/// If no cache file is present, a default API endpoint will be selected instead
private func initCache() {
// The first time the application is ran, this statement will fail as there is no cache. This is fine.
// The cache will be filled when either `getCurrentEndpoint` or `setEndpoints()` are called.
do {
cachedAddresses = try readFromCache()
} catch {
logger.debug("Initialized cache with default API endpoint.")
cachedAddresses = Self.defaultCachedAddresses
}
}
/// Reads the cache file from disk
///
/// - Returns: A list of cached API endpoints in a `CachedAddresses` form
private func readFromCache() throws -> CachedAddresses {
let fileCoordinator = NSFileCoordinator(filePresenter: nil)
let result = try fileCoordinator
.coordinate(readingItemAt: cacheFileURL, options: [.withoutChanges]) { file in
let data = try Data(contentsOf: file)
let cachedAddresses = try JSONDecoder().decode(CachedAddresses.self, from: data)
if cachedAddresses.endpoints.isEmpty {
throw EmptyCacheError()
}
return cachedAddresses
}
return result
}
/// Writes the cache file to the disk
private func writeToCache() throws {
precondition(canWriteToCache == true)
let fileCoordinator = NSFileCoordinator(filePresenter: nil)
try fileCoordinator.coordinate(writingItemAt: cacheFileURL, options: [.forReplacing]) { file in
let data = try JSONEncoder().encode(self.cachedAddresses)
try data.write(to: file)
}
}
}
struct CachedAddresses: Codable {
/// Date when the cached addresses were last updated.
var updatedAt: Date
/// API endpoints.
var endpoints: [AnyIPEndpoint]
}
struct EmptyCacheError: LocalizedError {
var errorDescription: String? {
return "Address cache file does not contain any API addresses."
}
}
}
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