114 lines
3.1 KiB
Go
114 lines
3.1 KiB
Go
package captcha
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import (
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"context"
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"crypto/rand"
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"encoding/base64"
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"errors"
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"fmt"
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"html"
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"math/big"
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"strings"
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"time"
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"github.com/redis/go-redis/v9"
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)
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var (
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ErrDependencyUnavailable = errors.New("captcha dependency unavailable")
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ErrInvalid = errors.New("captcha invalid")
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)
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type Item struct {
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CaptchaID string `json:"captcha_id"`
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Image string `json:"image"`
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ExpiresIn int64 `json:"expires_in"`
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}
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func Generate(ctx context.Context, redisClient *redis.Client, namespace string, ttl time.Duration) (*Item, error) {
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if redisClient == nil {
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return nil, ErrDependencyUnavailable
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}
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captchaID, err := randomToken(16)
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if err != nil {
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return nil, err
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}
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code, err := randomCaptchaCode(4)
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if err != nil {
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return nil, err
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}
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if err := redisClient.Set(ctx, key(namespace, captchaID), strings.ToUpper(code), ttl).Err(); err != nil {
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return nil, err
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}
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return &Item{
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CaptchaID: captchaID,
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Image: imageDataURL(code),
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ExpiresIn: int64(ttl.Seconds()),
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}, nil
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}
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func Verify(ctx context.Context, redisClient *redis.Client, namespace string, captchaID string, captchaCode string) error {
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if redisClient == nil {
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return ErrDependencyUnavailable
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}
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captchaID = strings.TrimSpace(captchaID)
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captchaCode = strings.TrimSpace(captchaCode)
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if captchaID == "" || captchaCode == "" {
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return ErrInvalid
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}
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redisKey := key(namespace, captchaID)
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stored, err := redisClient.Get(ctx, redisKey).Result()
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if errors.Is(err, redis.Nil) {
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return ErrInvalid
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}
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if err != nil {
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return err
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}
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_ = redisClient.Del(ctx, redisKey).Err()
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if strings.ToUpper(captchaCode) != stored {
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return ErrInvalid
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}
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return nil
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}
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func key(namespace string, id string) string {
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namespace = strings.Trim(strings.ToLower(strings.TrimSpace(namespace)), ":")
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if namespace == "" {
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namespace = "default"
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}
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return "captcha:" + namespace + ":" + id
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}
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func randomToken(length int) (string, error) {
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buf := make([]byte, length)
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if _, err := rand.Read(buf); err != nil {
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return "", err
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}
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return base64.RawURLEncoding.EncodeToString(buf), nil
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}
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func randomCaptchaCode(length int) (string, error) {
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const alphabet = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"
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result := make([]byte, length)
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for i := range result {
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n, err := rand.Int(rand.Reader, big.NewInt(int64(len(alphabet))))
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if err != nil {
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return "", err
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}
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result[i] = alphabet[n.Int64()]
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}
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return string(result), nil
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}
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func imageDataURL(code string) string {
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safeCode := html.EscapeString(strings.ToUpper(code))
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svg := fmt.Sprintf(`<svg xmlns="http://www.w3.org/2000/svg" width="132" height="44" viewBox="0 0 132 44">
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<rect width="132" height="44" rx="8" fill="#eef5f7"/>
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<path d="M8 32 C32 2, 62 52, 124 12" stroke="#0f766e" stroke-width="2" fill="none" opacity=".28"/>
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<path d="M10 13 C42 42, 86 0, 122 31" stroke="#2563eb" stroke-width="2" fill="none" opacity=".22"/>
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<text x="66" y="29" text-anchor="middle" font-family="Menlo,Consolas,monospace" font-size="24" font-weight="700" letter-spacing="4" fill="#111827">%s</text>
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</svg>`, safeCode)
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return "data:image/svg+xml;base64," + base64.StdEncoding.EncodeToString([]byte(svg))
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}
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