What causes "%s is not an image (detected mime: %s)" in chenhg5/cc-connect?

Pass an actual image (png, jpeg, gif, webp, ...) via --image.

%s is not an image (detected mime: %s)

Error message

%s is not an image (detected mime: %s)

What it means

loadImageAttachments sniffs each file's MIME type via readAttachment and only accepts types starting with "image/". A file whose detected content type is not an image (e.g. text/plain, application/pdf) produces "%s is not an image (detected mime: %s)". Detection is content-based, so a wrong extension does not bypass the check.

Source

Thrown at cmd/cc-connect/send.go:226

	req.Audios = audioFiles
	req.Videos = videoFiles

	if req.Message == "" && req.TTSText == "" && len(req.Images) == 0 && len(req.Files) == 0 && len(req.Audios) == 0 && len(req.Videos) == 0 {
		return req, "", fmt.Errorf("message, tts text, or attachment is required")
	}

	return req, dataDir, nil
}

func loadImageAttachments(paths []string, maxSize int64) ([]core.ImageAttachment, error) {
	images := make([]core.ImageAttachment, 0, len(paths))
	for _, path := range paths {
		data, fileName, mimeType, err := readAttachment(path, maxSize)
		if err != nil {
			return nil, err
		}
		if !strings.HasPrefix(mimeType, "image/") {
			return nil, fmt.Errorf("%s is not an image (detected mime: %s)", path, mimeType)
		}
		images = append(images, core.ImageAttachment{MimeType: mimeType, Data: data, FileName: fileName})
	}
	return images, nil
}

func loadFileAttachments(paths []string, maxSize int64) ([]core.FileAttachment, error) {
	files := make([]core.FileAttachment, 0, len(paths))
	for _, path := range paths {
		data, fileName, mimeType, err := readAttachment(path, maxSize)
		if err != nil {
			return nil, err
		}
		files = append(files, core.FileAttachment{MimeType: mimeType, Data: data, FileName: fileName})
	}
	return files, nil
}

View on GitHub (pinned to 4000b2338a)

Solutions

Pass an actual image (png, jpeg, gif, webp, ...) via --image.
For non-image documents use --file instead of --image.
Run `file <path>` to check the detected MIME type before sending.
Re-export/re-download the image if it was saved as text/HTML by mistake.

Example fix

// before
cc-connect send --image ./report.pdf
// after
cc-connect send --file ./report.pdf
// or a real image:
cc-connect send --image ./chart.png

Defensive patterns

Strategy: validation

Validate before calling

file --brief --mime-type "$IMG" | grep -q '^image/' || { echo "$IMG is not an image"; exit 1; }
cc-connect send --image "$IMG"

Try / catch

out, err := cmd.CombinedOutput()
if err != nil && strings.Contains(string(out), "is not an image") {
    log.Printf("use --file for non-image attachments: %v", err)
}

Prevention

Detect the real MIME type (file --brief --mime-type) before passing --image.
Use --file for PDFs, text, and other documents.
Beware of HTML error pages saved with image extensions.
Content sniffing decides, not the file extension.

When it happens

Trigger: `cc-connect send --image notes.txt` (detected text/plain); passing a PDF, JSON, or renamed binary as --image; an HTML error page saved as .png (detected text/html).

Common situations: Wrong path/variable pointing at a non-image file; expecting --image to accept PDFs (use --file instead); a failed download left an HTML/text blob with an image extension.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of chenhg5/cc-connect@4000b2338a (2026-09-06). Data as JSON: /api/errors/87c111714c04e1cc. Report an issue: GitHub.