AlistGo/alist · error

can not get captcha

Error message

can not get captcha

What it means

Thrown by Cloudreve doLogin when the site requires a captcha for login, the GET /site/captcha call technically succeeded, but the returned captcha string is empty. Without a captcha image the driver cannot OCR it, so login aborts before ever sending credentials.

Source

Thrown at drivers/cloudreve/util.go:127

		}
		if err.Error() != "CAPTCHA not match." {
			break
		}
	}
	return err
}

func (d *Cloudreve) doLogin(needCaptcha bool) error {
	var captchaCode string
	var err error
	if needCaptcha {
		var captcha string
		err = d.request(http.MethodGet, "/site/captcha", nil, &captcha)
		if err != nil {
			return err
		}
		if len(captcha) == 0 {
			return errors.New("can not get captcha")
		}
		i := strings.Index(captcha, ",")
		dec := base64.NewDecoder(base64.StdEncoding, strings.NewReader(captcha[i+1:]))
		vRes, err := base.RestyClient.R().SetMultipartField(
			"image", "validateCode.png", "image/png", dec).
			Post(setting.GetStr(conf.OcrApi))
		if err != nil {
			return err
		}
		if jsoniter.Get(vRes.Body(), "status").ToInt() != 200 {
			return errors.New("ocr error:" + jsoniter.Get(vRes.Body(), "msg").ToString())
		}
		captchaCode = jsoniter.Get(vRes.Body(), "result").ToString()
	}
	var resp Resp
	err = d.request(http.MethodPost, loginPath, func(req *resty.Request) {
		req.SetBody(base.Json{
			"username":    d.Addition.Username,

View on GitHub (pinned to 843d9dc814)

Solutions

  1. Retry the operation after a few seconds — captcha generation can be transiently unavailable or rate-limited.
  2. Disable login captcha in Cloudreve admin panel (Settings -> Login) if API mounting is intended, removing the dependency entirely.
  3. Verify GET /site/captcha directly with curl/cookies to confirm the server returns a non-empty base64 image.
  4. Upgrade the driver/repo — newer Cloudrebve builds tie captcha to a ticket; make sure your server and driver versions match.
Defensive patterns

Strategy: retry

Try / catch

for range 3 {
    err = d.doLogin(true)
    if err == nil || err.Error() != "can not get captcha" {
        break
    }
    time.Sleep(2 * time.Second) // captcha endpoint may be transiently empty
}

Prevention

When it happens

Trigger: Cloudreve has login captcha enabled; doLogin(needCaptcha=true) calls GET /site/captcha; the response decodes to an empty string (server-side captcha generation failure, rate limiting, or an error envelope that was silently unmarshalled to empty).

Common situations: Cloudrebve version change where /site/captcha only issues a captcha per session/ticket that was already consumed; login attempts hammered in a loop consuming the captcha; reverse proxy stripping the response; guest login forced by an unconfigured site.

Related errors

AI-assisted analysis of AlistGo/alist@843d9dc814 (2026-08-15). Data as JSON: /api/errors/75599767f95c5d94. Report an issue: GitHub.