Tencent/WeKnora · error

invalid image content type: %s

Error message

invalid image content type: %s

What it means

For image attachments small enough for direct vision input, the service sniffs the content with http.DetectContentType; if the detected media type does not start with "image/", the bytes are not a valid image and this error is returned instead of building a data URL.

Source

Thrown at internal/im/service.go:666

			result, err = nil, nil
		}
	}
	if result == nil && docparser.IsSimpleFormat(attachment.FileType) {
		result, err = (&docparser.SimpleFormatReader{}).Read(attachmentCtx, request)
	} else if result == nil && !isImage && s.documentReader != nil {
		result, err = s.documentReader.Read(attachmentCtx, request)
	}
	if err != nil {
		logger.Warnf(ctx, "[IM] attachment parsing failed, continuing with attachment metadata: %v", err)
	}
	if result != nil {
		applyIMAttachmentTruncation(result.MarkdownContent, &attachment)
	}
	var imageURLs []string
	if isImage && len(content) <= maxIMVisionAttachmentBytes {
		mediaType := http.DetectContentType(content)
		if !strings.HasPrefix(mediaType, "image/") {
			return nil, nil, nil, fmt.Errorf("invalid image content type: %s", mediaType)
		}
		imageURLs = []string{"data:" + mediaType + ";base64," + base64.StdEncoding.EncodeToString(content)}
	} else if isImage {
		logger.Warnf(ctx, "[IM] image is too large for direct vision input: size=%d limit=%d", len(content), maxIMVisionAttachmentBytes)
	}
	return types.MessageAttachments{attachment}, imageURLs, &imDownloadedAttachment{fileName: fileName, content: content}, nil
}

func applyIMAttachmentTruncation(content string, attachment *types.MessageAttachment) {
	attachment.LineCount = strings.Count(content, "\n") + 1

	limited := truncateUTF8ByBytes(content, maxIMAttachmentContentBytes)
	lines := strings.SplitN(limited, "\n", maxIMAttachmentLines+1)
	if len(lines) > maxIMAttachmentLines {
		limited = strings.Join(lines[:maxIMAttachmentLines], "\n")
	}

	attachment.Content = limited

View on GitHub (pinned to 988cbb0330)

Solutions

1. Verify the file is a real image and resend it
2. Re-download the source — the original fetch may have returned an error page
3. Convert the file to png/jpg before sending, or send it as a document rather than an image

head := content[:min(512, len(content))]
if !strings.HasPrefix(http.DetectContentType(head), "image/") {
    return errors.New("not a valid image")
}

func isImageBytes(b []byte) bool {
    return strings.HasPrefix(http.DetectContentType(b), "image/")
}

When it happens

Trigger: A message typed as image (or an image-like extension such as png/jpg) whose downloaded bytes are not actually an image — DetectContentType returns e.g. text/plain or application/octet-stream.

Common situations: Renamed files (a .png that is actually text/HTML); an HTML error page saved as an image URL; corrupted or truncated uploads; SVG or exotic formats DetectContentType classifies as text.

Related errors

• non-image content type: %s
• cannot run workspace script %q for skill %q: no installed sk
• invite code has expired
• join request not found
• failed to retrieve: %s

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/3fe1e100bfb0b249. Report an issue: GitHub.