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//
// NetworkOperation.swift
// MullvadVPN
//
// Created by pronebird on 08/12/2021.
// Copyright © 2021 Mullvad VPN AB. All rights reserved.
//
import Foundation
import Logging
extension REST {
enum RetryAction {
/// Retry request using next endpoint.
case useNextEndpoint
/// Retry request using current endpoint.
case useCurrentEndpoint
/// Fail immediately.
case failImmediately
}
class NetworkOperation<Success>: AsyncOperation {
typealias CompletionHandler = (Result<Success, REST.Error>) -> Void
typealias Generator = (AnyIPEndpoint, @escaping CompletionHandler) -> Result<URLSessionTask, REST.Error>
private let networkTaskGenerator: Generator
private let addressCacheStore: AddressCache.Store
private var completionHandler: CompletionHandler?
private var sessionTask: URLSessionTask?
private let retryStrategy: RetryStrategy
private var retryTimer: DispatchSourceTimer?
private var retryCount = 0
private let logger = Logger(label: "REST.NetworkOperation")
private let loggerMetadata: Logger.Metadata = ["requestID": .string(UUID().uuidString)]
init(networkTaskGenerator: @escaping Generator, addressCacheStore: AddressCache.Store, retryStrategy: RetryStrategy, completionHandler: @escaping CompletionHandler) {
self.networkTaskGenerator = networkTaskGenerator
self.addressCacheStore = addressCacheStore
self.retryStrategy = retryStrategy
self.completionHandler = completionHandler
}
override func cancel() {
DispatchQueue.main.async {
super.cancel()
// Cancel pending retry
self.retryTimer?.cancel()
// Cancel active network task
self.sessionTask?.cancel()
}
}
override func main() {
DispatchQueue.main.async {
// Finish immediately if operation was cancelled before execution
guard !self.isCancelled else {
self.finish(with: .failure(Self.cancellationError))
return
}
// Get current endpoint
self.addressCacheStore.getCurrentEndpoint { endpoint in
DispatchQueue.main.async {
self.sendRequest(endpoint: endpoint) { [weak self] result in
self?.finish(with: result)
}
}
}
}
}
private func sendRequest(endpoint: AnyIPEndpoint, completionHandler: @escaping CompletionHandler) {
// Handle operation cancellation
guard !isCancelled else {
completionHandler(.failure(Self.cancellationError))
return
}
// Create network task and execute it
let taskResult = networkTaskGenerator(endpoint) { [weak self] result in
DispatchQueue.main.async {
self?.handleResponse(endpoint: endpoint, result: result, completionHandler: completionHandler)
}
}
switch taskResult {
case .success(let dataTask):
logger.debug("Executing request using \(endpoint)", metadata: loggerMetadata)
sessionTask = dataTask
dataTask.resume()
case .failure(let error):
logger.error(chainedError: error, message: "Failed to create data task", metadata: loggerMetadata)
completionHandler(.failure(error))
}
}
private func handleResponse(endpoint: AnyIPEndpoint, result: Result<Success, REST.Error>, completionHandler: @escaping CompletionHandler) {
guard case .failure(let error) = result else {
completionHandler(result)
return
}
logger.debug("Failed to perform request to \(endpoint)", metadata: self.loggerMetadata)
switch Self.evaluateError(error) {
case .useNextEndpoint:
// Pick next endpoint in the event of network error
addressCacheStore.selectNextEndpoint(endpoint) { nextEndpoint in
DispatchQueue.main.async {
self.retryRequest(endpoint: nextEndpoint, previousResult: result, completionHandler: completionHandler)
}
}
case .useCurrentEndpoint:
// Retry request using the same endpoint otherwise
retryRequest(endpoint: endpoint, previousResult: result, completionHandler: completionHandler)
case .failImmediately:
// Fail immediately in case of other errors, like server errors
completionHandler(result)
}
}
private func retryRequest(endpoint: AnyIPEndpoint, previousResult: Result<Success, REST.Error>, completionHandler: @escaping CompletionHandler) {
// Handle operation cancellation
guard !isCancelled else {
completionHandler(.failure(Self.cancellationError))
return
}
// Increment retry count
retryCount += 1
// Check if retry count is not exceeded.
guard retryCount < retryStrategy.maxRetryCount else {
logger.debug("Ran out of retry attempts (\(retryStrategy.maxRetryCount))", metadata: loggerMetadata)
completionHandler(previousResult)
return
}
// Retry immediatly if retry delay is set to .never
guard retryStrategy.retryDelay != .never else {
sendRequest(endpoint: endpoint, completionHandler: completionHandler)
return
}
// Create timer to delay retry
retryTimer = DispatchSource.makeTimerSource(queue: .main)
retryTimer?.setEventHandler { [weak self] in
self?.sendRequest(endpoint: endpoint, completionHandler: completionHandler)
}
retryTimer?.setCancelHandler {
completionHandler(.failure(Self.cancellationError))
}
retryTimer?.schedule(wallDeadline: .now() + retryStrategy.retryDelay)
retryTimer?.activate()
}
private func finish(with result: Result<Success, REST.Error>) {
completionHandler?(result)
completionHandler = nil
finish()
}
private static func evaluateError(_ error: REST.Error) -> RetryAction {
guard case .network(let networkError) = error else {
return .failImmediately
}
switch networkError.code {
case .cancelled:
return .failImmediately
case .notConnectedToInternet, .internationalRoamingOff, .callIsActive:
return .useCurrentEndpoint
default:
return .useNextEndpoint
}
}
private static var cancellationError: REST.Error {
return .network(URLError(.cancelled))
}
}
}
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