d40844181a
For randomizing update check intervals and backoff delays to reduce chance of DoSing the server if lots of clients start together.
53 lines
1.6 KiB
Go
53 lines
1.6 KiB
Go
// Copyright 2017 CoreOS, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package client
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import (
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"math/rand"
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"time"
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)
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func init() {
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// Ensure seeding the prng is never forgotten, that would defeat
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// the whole point of using fuzzy timers to guard against a DoS.
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rand.Seed(time.Now().UnixNano())
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}
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// FuzzyDuration randomizes the duration d within the range specified
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// by fuzz. Specifically the value range is: [d-(fuzz/2), d+(fuzz/2)]
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// The result will never be negative.
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func FuzzyDuration(d, fuzz time.Duration) time.Duration {
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if fuzz < 0 {
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return d
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}
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// apply range [-fuzz/2, fuzz/2]
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d += time.Duration(rand.Int63n(int64(fuzz)+1) - (int64(fuzz) / 2))
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if d < 0 {
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return 0
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}
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return d
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}
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// FuzzyAfter waits for the fuzzy duration to elapse and then sends the
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// current time on the returned channel. See FuzzyDuration.
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func FuzzyAfter(d, fuzz time.Duration) <-chan time.Time {
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return time.After(FuzzyDuration(d, fuzz))
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}
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// FuzzySleep pauses the current goroutine for the fuzzy duration d.
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// See FuzzyDuration.
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func FuzzySleep(d, fuzz time.Duration) {
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time.Sleep(FuzzyDuration(d, fuzz))
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}
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