chenhg5/cc-connect · error

empty url

Error message

empty url

What it means

downloadAttachment refuses to issue an HTTP GET when the supplied URL is the empty string. The URL is normally a pre-signed CDN link taken from a MAX message payload; an empty value means the payload never contained one.

Source

Thrown at platform/max/max.go:1184

				return sub
			}
		}
	}
	if filename != "" {
		if i := strings.LastIndex(filename, "."); i >= 0 && i < len(filename)-1 {
			return strings.ToLower(filename[i+1:])
		}
	}
	return "ogg"
}

// downloadAttachment GETs an arbitrary URL (typically a pre-signed CDN link
// from MAX), capping the response at maxAttachmentBytes. The URLs MAX serves
// for image/file payloads are already authenticated, so no bot token is
// attached to the request.
func (p *Platform) downloadAttachment(ctx context.Context, url string) ([]byte, string, error) {
	if url == "" {
		return nil, "", fmt.Errorf("empty url")
	}
	dlCtx, cancel := context.WithTimeout(ctx, attachmentDownloadTO)
	defer cancel()
	req, err := http.NewRequestWithContext(dlCtx, http.MethodGet, url, nil)
	if err != nil {
		return nil, "", err
	}
	resp, err := p.client.Do(req)
	if err != nil {
		return nil, "", err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, "", fmt.Errorf("HTTP %d", resp.StatusCode)
	}
	data, err := io.ReadAll(io.LimitReader(resp.Body, maxAttachmentBytes+1))
	if err != nil {
		return nil, "", err

View on GitHub (pinned to 4000b2338a)

Solutions

1. Check url != "" (or validate the attachment object) before calling downloadAttachment
2. Use resolveMediaURL for video/audio attachments that only provide a token
3. Log the raw attachment JSON when the URL is missing to identify the message type
4. Skip or placeholder the attachment in the outgoing message instead of failing

Example fix

// before
data, ct, err := p.downloadAttachment(ctx, att.URL)
// after
if att.URL == "" {
	return skipAttachment(att)
}
data, ct, err := p.downloadAttachment(ctx, att.URL)

if url == "" { return skipOrPlaceholder(attachment) }

When it happens

Trigger: A MAX image/file message arrives whose attachment object has an empty url field and the platform calls downloadAttachment with that value directly.

Common situations: Processing message types that carry attachments without download URLs (e.g. stickers, voice handled via tokens instead of URLs); MAX API change removing the url field; upstream sender sending malformed attachments.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• %s is not an image (detected mime: %s)
• %s is not %s media (detected mime: %s)
• attachment %s exceeds size limit (%d MB)
• empty token
• max: send message: attachment not ready after %d retries

AI-assisted analysis of chenhg5/cc-connect@4000b2338a (2026-09-06). Data as JSON: /api/errors/53b3fe4fe5e1a221. Report an issue: GitHub.