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//
// StoreTransactionLog.swift
// MullvadVPN
//
// Created by pronebird on 26/10/2023.
// Copyright © 2025 Mullvad VPN AB. All rights reserved.
//
import Foundation
import MullvadLogging
/// Transaction log responsible for storing and querying processed transactions.
///
/// This class is thread safe.
final class StoreTransactionLog: @unchecked Sendable {
private let logger = Logger(label: "StoreTransactionLog")
private var transactionIdentifiers: Set<String> = []
private let stateLock = NSLock()
/// The location of the transaction log file on disk.
let fileURL: URL
/// Default location for the transaction log.
static var defaultFileURL: URL {
let directories = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)
let location = directories.first?.appendingPathComponent("transaction.log", isDirectory: false)
return location!
}
/// Default transaction log.
static let `default` = StoreTransactionLog(fileURL: defaultFileURL)
/// Initialize the new transaction log.
///
/// - Warning: Panics on attempt to initialize with a non-file URL.
///
/// - Parameter fileURL: a file URL to the transaction log file within the local filesystem.
init(fileURL: URL) {
precondition(fileURL.isFileURL, "Only local filesystem URLs are accepted.")
self.fileURL = fileURL
}
/// Check if transaction log contains the transaction identifier.
///
/// - Parameter transactionIdentifier: a transaction identifier.
/// - Returns: `true` if transaction log contains such transaction identifier, otherwise `false`.
func contains(transactionIdentifier: String) -> Bool {
stateLock.withLock {
transactionIdentifiers.contains(transactionIdentifier)
}
}
/// Add transaction identifier into transaction log.
///
/// Automatically persists the transaction log for new transaction identifiers. Returns immediately If the transaction identifier is already present in the
/// transaction log.
///
/// - Parameter transactionIdentifier: a transaction identifier.
func add(transactionIdentifier: String) {
stateLock.withLock {
guard !transactionIdentifiers.contains(transactionIdentifier) else { return }
transactionIdentifiers.insert(transactionIdentifier)
persist()
}
}
/// Read transaction log from file.
func read() {
stateLock.withLock {
do {
let serializedString = try String(contentsOf: fileURL)
transactionIdentifiers = deserialize(from: serializedString)
} catch {
switch error {
case CocoaError.fileReadNoSuchFile, CocoaError.fileNoSuchFile:
// Ignore errors pointing at missing transaction log file.
break
default:
logger.error(error: error, message: "Failed to load transaction log from disk.")
}
}
}
}
/// Persist the transaction identifiers on disk.
/// Creates the cache directory if it doesn't exist yet.
private func persist() {
let serializedData = serialize()
do {
try persistInner(serializedString: serializedData)
} catch CocoaError.fileNoSuchFile {
createDirectoryAndPersist(serializedString: serializedData)
} catch {
logger.error(error: error, message: "Failed to persist transaction log.")
}
}
/// Create the cache directory, then write the transaction log.
/// - Parameter serializedString: serialized transaction log.
private func createDirectoryAndPersist(serializedString: String) {
do {
try FileManager.default.createDirectory(
at: fileURL.deletingLastPathComponent(),
withIntermediateDirectories: true
)
} catch {
logger.error(
error: error,
message: "Failed to create a directory for transaction log. Trying to persist once again."
)
}
do {
try persistInner(serializedString: serializedString)
} catch {
logger.error(error: error, message: "Failed to persist transaction log.")
}
}
/// Serialize transaction log into a string.
/// - Returns: string that contains a serialized transaction log.
private func serialize() -> String {
transactionIdentifiers.joined(separator: "\n")
}
/// Deserialize transaction log from a string.
/// - Parameter serializedString: serialized string representation of a transaction log.
/// - Returns: a set of transaction identifiers.
private func deserialize(from serializedString: String) -> Set<String> {
let transactionIdentifiers = serializedString.split { $0.isNewline }
.map { String($0) }
return Set(transactionIdentifiers)
}
/// Write a list of transaction identifiers on disk.
///
/// Transaction identifiers are stored as one per line.
/// Always ensures to exclude the transaction log file from backups after writing contents on disk.
/// - Parameter serializedString: serialized transaction log
private func persistInner(serializedString: String) throws {
try serializedString.write(to: fileURL, atomically: true, encoding: .utf8)
excludeFromBackups()
}
/// Exclude transaction log file from backups.
private func excludeFromBackups() {
do {
var resourceValues = URLResourceValues()
resourceValues.isExcludedFromBackup = true
var mutableFileURL = fileURL
try mutableFileURL.setResourceValues(resourceValues)
} catch {
logger.error(error: error, message: "Failed to exclude transaction log from backups.")
}
}
}
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