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// Copyright 2011 Dmitry Chestnykh. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.
package captcha
import (
"container/list"
"sync"
"time"
)
// An object implementing Store interface can be registered with SetCustomStore
// function to handle storage and retrieval of captcha ids and solutions for
// them, replacing the default memory store.
//
// It is the responsibility of an object to delete expired and used captchas
// when necessary (for example, the default memory store collects them in Set
// method after the certain amount of captchas has been stored.)
type Store interface {
// Set sets the digits for the captcha id.
Set(id string, digits []byte)
// Get returns stored digits for the captcha id. Clear indicates
// whether the captcha must be deleted from the store.
Get(id string, reset bool) (digits []byte)
}
// expValue stores timestamp and id of captchas. It is used in the list inside
// memoryStore for indexing generated captchas by timestamp to enable garbage
// collection of expired captchas.
type idByTimeValue struct {
timestamp time.Time
id string
}
// memoryStore is an internal store for captcha ids and their values.
type memoryStore struct {
sync.RWMutex
digitsByID map[string][]byte
idByTime *list.List
// Number of items stored since last collection.
numStored int
// Number of saved items that triggers collection.
collectNum int
// Expiration time of captchas.
expiration time.Duration
}
// NewMemoryStore returns a new standard memory store for captchas with the
// given collection threshold and expiration time (duration). The returned
// store must be registered with SetCustomStore to replace the default one.
func NewMemoryStore(collectNum int, expiration time.Duration) Store {
s := new(memoryStore)
s.digitsByID = make(map[string][]byte)
s.idByTime = list.New()
s.collectNum = collectNum
s.expiration = expiration
return s
}
func (s *memoryStore) Set(id string, digits []byte) {
s.Lock()
s.digitsByID[id] = digits
s.idByTime.PushBack(idByTimeValue{time.Now(), id})
s.numStored++
if s.numStored <= s.collectNum {
s.Unlock()
return
}
s.Unlock()
go s.collect()
}
func (s *memoryStore) Get(id string, reset bool) (digits []byte) {
if !reset {
// When we don't need to clear captcha, acquire read lock.
s.RLock()
defer s.RUnlock()
} else {
s.Lock()
defer s.Unlock()
}
digits, ok := s.digitsByID[id]
if !ok {
return
}
if reset {
delete(s.digitsByID, id)
// XXX(dchest) Index (s.idByTime) will be cleaned when
// collecting expired captchas. Can't clean it here, because
// we don't store reference to expValue in the map.
// Maybe store it?
}
return
}
func (s *memoryStore) collect() {
now := time.Now()
s.Lock()
defer s.Unlock()
s.numStored = 0
for e := s.idByTime.Front(); e != nil; {
ev, ok := e.Value.(idByTimeValue)
if !ok {
return
}
if ev.timestamp.Add(s.expiration).Before(now) {
delete(s.digitsByID, ev.id)
next := e.Next()
s.idByTime.Remove(e)
e = next
} else {
return
}
}
}
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