chenhg5/cc-connect · info

googlechat: upload: finalize multipart body: %w

Error message

googlechat: upload: finalize multipart body: %w

What it means

Returned by uploadAttachment when multipart.Writer.Close() fails while finalizing the multipart/related body. Close writes the terminating boundary; with an in-memory bytes.Buffer target this is practically unreachable with stock code. It propagates through postAttachment from SendImage/SendFile.

Source

Thrown at platform/googlechat/googlechat.go:474

	mw := multipart.NewWriter(buf)

	metaPart, err := mw.CreatePart(textproto.MIMEHeader{"Content-Type": {"application/json; charset=UTF-8"}})
	if err != nil {
		return "", fmt.Errorf("googlechat: upload: create metadata part: %w", err)
	}
	if err := json.NewEncoder(metaPart).Encode(map[string]string{"filename": filename}); err != nil {
		return "", fmt.Errorf("googlechat: upload: encode metadata: %w", err)
	}

	mediaPart, err := mw.CreatePart(textproto.MIMEHeader{"Content-Type": {mimeType}})
	if err != nil {
		return "", fmt.Errorf("googlechat: upload: create media part: %w", err)
	}
	if _, err := mediaPart.Write(data); err != nil {
		return "", fmt.Errorf("googlechat: upload: write media: %w", err)
	}
	if err := mw.Close(); err != nil {
		return "", fmt.Errorf("googlechat: upload: finalize multipart body: %w", err)
	}

	uploadURL := chatUploadBase + space + "/attachments:upload?uploadType=multipart"
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, uploadURL, buf)
	if err != nil {
		return "", fmt.Errorf("googlechat: upload: build request: %w", err)
	}
	req.Header.Set("Content-Type", "multipart/related; boundary="+mw.Boundary())

	resp, err := p.doRequest(req)
	if err != nil {
		return "", err
	}
	defer func() {
		if err := resp.Body.Close(); err != nil {
			slog.Warn("googlechat: close upload response body", "error", err)
		}
	}()

View on GitHub (pinned to 4000b2338a)

Solutions

1. Confirm unmodified library code; closing over a bytes.Buffer cannot fail.
2. If seen after local changes, ensure no calls after Close that mutate writer state.
3. Report a bug with the wrapped cause if reproducible on stock code.

if err := p.SendFile(ctx, target, file); err != nil {
    if strings.Contains(err.Error(), "finalize multipart body") {
        return fmt.Errorf("googlechat multipart finalize failure (library bug): %w", err)
    }
    return err
}

When it happens

Trigger: Calling SendImage()/SendFile(); mw.Close() returns an error during multipart body finalization — only possible with corrupted writer state or local modifications.

Common situations: Effectively never hit in production; would appear only if the multipart writer was misused in modified code (e.g. calls after Close that mutate writer state).

Related errors

• googlechat: upload: create metadata part: %w
• googlechat: upload: write media: %w
• googlechat: upload: encode metadata: %w
• googlechat: upload: create media part: %w
• create form file: %w

AI-assisted analysis of chenhg5/cc-connect@4000b2338a (2026-09-06). Data as JSON: /api/errors/5155cc8615da61f6. Report an issue: GitHub.