mirror of
https://github.com/swift-server/async-http-client.git
synced 2026-05-03 07:32:29 +00:00
jessezamora
0b6f957d33
Fixes #847. Motivation: On 32-bit systems, using .randomElement on a range larger than what can fit in Int32 (Int) causes a crash. After only 26 or 27 retries of a request using HTTPClient, the calculateBackoff method would run into this and crash consistently on an armv7 (32-bit) device. Modifications: A one-line fix to opt to using Int64.random on the same jitterRange instead of .randomElement, which works as expected without crashing on 32-bit systems. Result: The HTTPClient now works as expected and can perform as many retries as needed without crashing. I tested this on my armv7 board doing the retries, and ran up to several hundred repetitions after a few hours with no crashes as was happening before. @Lukasa
69 lines
2.6 KiB
Swift
69 lines
2.6 KiB
Swift
//===----------------------------------------------------------------------===//
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//
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// This source file is part of the AsyncHTTPClient open source project
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//
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// Copyright (c) 2021 Apple Inc. and the AsyncHTTPClient project authors
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// Licensed under Apache License v2.0
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//
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// See LICENSE.txt for license information
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// See CONTRIBUTORS.txt for the list of AsyncHTTPClient project authors
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//
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// SPDX-License-Identifier: Apache-2.0
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//
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//===----------------------------------------------------------------------===//
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import NIOCore
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#if canImport(Darwin)
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import func Darwin.pow
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#elseif canImport(Musl)
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import func Musl.pow
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#elseif canImport(Android)
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import func Android.pow
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#else
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import func Glibc.pow
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#endif
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extension HTTPConnectionPool {
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/// Calculates the delay for the next connection attempt after the given number of failed `attempts`.
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///
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/// Our backoff formula is: 100ms * 1.25^(attempts - 1) that is capped of at 1 minute.
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/// This means for:
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/// - 1 failed attempt : 100ms
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/// - 5 failed attempts: ~300ms
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/// - 10 failed attempts: ~930ms
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/// - 15 failed attempts: ~2.84s
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/// - 20 failed attempts: ~8.67s
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/// - 25 failed attempts: ~26s
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/// - 29 failed attempts: ~60s (max out)
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///
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/// - Parameter attempts: number of failed attempts in a row
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/// - Returns: time to wait until trying to establishing a new connection
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static func calculateBackoff(failedAttempt attempts: Int) -> TimeAmount {
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// Our backoff formula is: 100ms * 1.25^(attempts - 1) that is capped of at 1minute
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// This means for:
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// - 1 failed attempt : 100ms
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// - 5 failed attempts: ~300ms
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// - 10 failed attempts: ~930ms
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// - 15 failed attempts: ~2.84s
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// - 20 failed attempts: ~8.67s
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// - 25 failed attempts: ~26s
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// - 29 failed attempts: ~60s (max out)
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let start = Double(TimeAmount.milliseconds(100).nanoseconds)
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let backoffNanosecondsDouble = start * pow(1.25, Double(attempts - 1))
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// Cap to 60s _before_ we convert to Int64, to avoid trapping in the Int64 initializer.
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let backoffNanoseconds = Int64(min(backoffNanosecondsDouble, Double(TimeAmount.seconds(60).nanoseconds)))
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let backoff = TimeAmount.nanoseconds(backoffNanoseconds)
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// Calculate a 3% jitter range
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let jitterRange = (backoff.nanoseconds / 100) * 3
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// Pick a random element from the range +/- jitter range.
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let jitter: TimeAmount = .nanoseconds(Int64.random(in: -jitterRange...jitterRange))
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let jitteredBackoff = backoff + jitter
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return jitteredBackoff
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}
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}
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