justcaptcha/pkg/captcha/db.go

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package captcha
import (
"crypto/sha256"
"encoding/base64"
"errors"
"image"
"strconv"
"sync"
"time"
)
var errorNotFound = errors.New("captcha not found")
var defaultExpiredScanInterval = 60 * time.Second
type ID string
// NewID generates an ID as a sha256 hash of additionalData, current time
// and answer encoded with base64 in raw URL variant.
func NewID(additionalData string, answer Answer) ID {
idHash := sha256.New()
idHash.Write([]byte(additionalData))
idHash.Write([]byte(strconv.FormatInt(time.Now().UnixMicro(), 16)))
idHash.Write([]byte(answer))
return ID(base64.RawURLEncoding.EncodeToString(idHash.Sum(nil)))
}
type CaptchaDB interface {
New(data string, captcha Captcha) (Captcha, ID)
GetExpiry() time.Duration
Image(id ID, style string) (*image.Image, error)
Solve(id ID, answer Answer) (bool, error)
IsSolved(id ID) (bool, error)
cleanExpired()
}
type InMemoryCaptchaDB struct {
sync.Mutex
db map[ID]Captcha
expireIn time.Duration
expireScanInterval time.Duration
}
func NewInMemoryCaptchaDB(expire time.Duration) *InMemoryCaptchaDB {
db := &InMemoryCaptchaDB{
db: make(map[ID]Captcha),
expireIn: expire}
if expire < defaultExpiredScanInterval {
db.expireScanInterval = expire
} else {
db.expireScanInterval = defaultExpiredScanInterval
}
db.cleanExpired()
return db
}
// New accepts an Captcha instance, generates an ID and store it in a database.
// `data` string is an additional random data used to generate an ID,
// e.g. IP-address.
func (cdb *InMemoryCaptchaDB) New(data string, captcha Captcha) (Captcha, ID) {
id := NewID(data, captcha.GetAnswer())
cdb.Lock()
cdb.db[id] = captcha
cdb.Unlock()
return captcha, id
}
// cleanExpired starts a goroutine that deletes expired CAPTCHAs.
func (cdb *InMemoryCaptchaDB) cleanExpired() {
go func() {
for {
sleepFor := cdb.expireScanInterval - (time.Duration(time.Now().Second()) % cdb.expireScanInterval)
time.Sleep(sleepFor)
cdb.Lock()
for id, captcha := range cdb.db {
if time.Since(captcha.Expiry()) >= cdb.expireIn {
delete(cdb.db, id)
}
}
cdb.Unlock()
}
}()
}
// GetExpiry returns time for how long captcha will last.
func (cdb *InMemoryCaptchaDB) GetExpiry() time.Duration {
return cdb.expireIn
}
// Image returns image for a captcha.
func (cdb *InMemoryCaptchaDB) Image(id ID, style string) (*image.Image, error) {
cdb.Lock()
defer cdb.Unlock()
if c, ok := cdb.db[id]; ok {
return c.Image(style), nil
}
return nil, errorNotFound
}
// Solve compares given answer with a stored one and if failed
// deletes a captcha from database.
func (cdb *InMemoryCaptchaDB) Solve(id ID, answer Answer) (bool, error) {
cdb.Lock()
defer cdb.Unlock()
if c, ok := cdb.db[id]; ok {
ok = c.Solve(answer)
if !ok {
delete(cdb.db, id)
}
return ok, nil
}
return false, errorNotFound
}
// IsSolved checks if captcha was solved and removes it
// from a database.
func (cdb *InMemoryCaptchaDB) IsSolved(id ID) (bool, error) {
cdb.Lock()
defer cdb.Unlock()
if c, ok := cdb.db[id]; ok {
ok = c.IsSolved()
delete(cdb.db, id)
return ok, nil
}
return false, errorNotFound
}