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//
// RetryStrategy.swift
// MullvadREST
//
// Created by pronebird on 09/12/2021.
// Copyright © 2021 Mullvad VPN AB. All rights reserved.
//
import Foundation
import MullvadTypes
extension REST {
public struct RetryStrategy: Sendable {
public var maxRetryCount: Int
public var delay: RetryDelay
public var applyJitter: Bool
public init(maxRetryCount: Int, delay: RetryDelay, applyJitter: Bool) {
self.maxRetryCount = maxRetryCount
self.delay = delay
self.applyJitter = applyJitter
}
public func makeDelayIterator() -> AnyIterator<Duration> {
let inner = delay.makeIterator()
if applyJitter {
return switch delay {
case .never:
AnyIterator(inner)
case .constant:
AnyIterator(Jittered(inner))
case let .exponentialBackoff(_, _, maxDelay):
AnyIterator(Transformer(inner: Jittered(inner)) { nextValue in
guard let nextValue else { return maxDelay }
return nextValue >= maxDelay ? maxDelay : nextValue
})
}
} else {
return AnyIterator(inner)
}
}
/// Strategy configured to never retry.
public static let noRetry = RetryStrategy(
maxRetryCount: 0,
delay: .never,
applyJitter: false
)
/// Strategy configured with 2 retry attempts and exponential backoff.
public static let `default` = RetryStrategy(
maxRetryCount: 2,
delay: defaultRetryDelay,
applyJitter: true
)
/// Strategy configured with 10 retry attempts and exponential backoff.
public static let aggressive = RetryStrategy(
maxRetryCount: 10,
delay: defaultRetryDelay,
applyJitter: true
)
/// Default retry delay.
public static let defaultRetryDelay: RetryDelay = .exponentialBackoff(
initial: .seconds(2),
multiplier: 2,
maxDelay: .seconds(8)
)
public static let postQuantumKeyExchange = RetryStrategy(
maxRetryCount: 10,
delay: .exponentialBackoff(
initial: .seconds(10),
multiplier: UInt64(2),
maxDelay: .seconds(30)
),
applyJitter: true
)
public static let failedMigrationRecovery = RetryStrategy(
maxRetryCount: .max,
delay: .exponentialBackoff(
initial: .seconds(5),
multiplier: UInt64(1),
maxDelay: .minutes(1)
),
applyJitter: true
)
}
public enum RetryDelay: Equatable, Sendable {
/// Never wait to retry.
case never
/// Constant delay.
case constant(Duration)
/// Exponential backoff.
case exponentialBackoff(initial: Duration, multiplier: UInt64, maxDelay: Duration)
func makeIterator() -> AnyIterator<Duration> {
switch self {
case .never:
return AnyIterator {
nil
}
case let .constant(duration):
return AnyIterator {
duration
}
case let .exponentialBackoff(initial, multiplier, maxDelay):
return AnyIterator(ExponentialBackoff(
initial: initial,
multiplier: multiplier,
maxDelay: maxDelay
))
}
}
}
}
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