92 lines
2.6 KiB
Go
92 lines
2.6 KiB
Go
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// Copyright 2021 The Prometheus Authors
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// This code is partly borrowed from Caddy:
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// Copyright 2015 Matthew Holt and The Caddy Authors
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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 web
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import (
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weakrand "math/rand"
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"sync"
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"time"
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)
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var cacheSize = 100
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func init() {
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weakrand.Seed(time.Now().UnixNano())
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}
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type cache struct {
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cache map[string]bool
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mtx sync.Mutex
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}
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// newCache returns a cache that contains a mapping of plaintext passwords
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// to their hashes (with random eviction). This can greatly improve the
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// performance of traffic-heavy servers that use secure password hashing
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// algorithms, with the downside that plaintext passwords will be stored in
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// memory for a longer time (this should not be a problem as long as your
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// machine is not compromised, at which point all bets are off, since basicauth
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// necessitates plaintext passwords being received over the wire anyway).
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func newCache() *cache {
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return &cache{
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cache: make(map[string]bool),
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}
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}
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func (c *cache) get(key string) (bool, bool) {
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c.mtx.Lock()
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defer c.mtx.Unlock()
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v, ok := c.cache[key]
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return v, ok
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}
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func (c *cache) set(key string, value bool) {
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c.mtx.Lock()
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defer c.mtx.Unlock()
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c.makeRoom()
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c.cache[key] = value
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}
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func (c *cache) makeRoom() {
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if len(c.cache) < cacheSize {
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return
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}
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// We delete more than just 1 entry so that we don't have
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// to do this on every request; assuming the capacity of
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// the cache is on a long tail, we can save a lot of CPU
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// time by doing a whole bunch of deletions now and then
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// we won't have to do them again for a while.
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numToDelete := len(c.cache) / 10
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if numToDelete < 1 {
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numToDelete = 1
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}
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for deleted := 0; deleted <= numToDelete; deleted++ {
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// Go maps are "nondeterministic" not actually random,
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// so although we could just chop off the "front" of the
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// map with less code, this is a heavily skewed eviction
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// strategy; generating random numbers is cheap and
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// ensures a much better distribution.
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rnd := weakrand.Intn(len(c.cache))
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i := 0
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for key := range c.cache {
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if i == rnd {
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delete(c.cache, key)
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break
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}
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i++
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}
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}
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}
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