chenhg5/cc-connect · info

googlechat: upload: encode metadata: %w

Error message

googlechat: upload: encode metadata: %w

What it means

Returned by uploadAttachment when json.Encoder.Encode fails while serializing the {"filename": ...} metadata map into the multipart metadata part. Because the encoder writes to an in-memory bytes.Buffer, Encode can only fail if the part writer is broken; with a plain map[string]string this is practically unreachable. It propagates through postAttachment from SendImage/SendFile.

Source

Thrown at platform/googlechat/googlechat.go:463

	return p.post(ctx, rctx, content)
}

func (p *Platform) Send(ctx context.Context, rctx any, content string) error {
	return p.post(ctx, rctx, content)
}

// uploadAttachment uploads raw bytes to the Chat media endpoint using a
// multipart/related request and returns the attachmentDataRef resource name.
func (p *Platform) uploadAttachment(ctx context.Context, space, filename, mimeType string, data []byte) (string, error) {
	buf := bytes.NewBuffer(make([]byte, 0, 256+len(data)))
	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)
	}

View on GitHub (pinned to 4000b2338a)

Solutions

1. Confirm you are running unmodified library code; the payload is a trivial map.
2. If seen after local changes, check that the metadata part writer is not already closed or broken.
3. Check the error chain (%w) for the underlying cause and report a bug if it occurs on stock code.

if err := p.SendImage(ctx, target, path); err != nil {
    if strings.Contains(err.Error(), "encode metadata") {
        return fmt.Errorf("googlechat upload metadata failure: %w", err)
    }
    return err
}

When it happens

Trigger: Calling SendImage()/SendFile(); during uploadAttachment the json.NewEncoder(metaPart).Encode(map[string]string{"filename": filename}) call returns an error — only possible if the underlying multipart part write fails.

Common situations: Effectively never hit in production with stock code; may appear if the multipart writer or buffer was modified or data was corrupted upstream.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• googlechat: upload: create metadata part: %w
• googlechat: upload: create media part: %w
• googlechat: upload: write media: %w
• googlechat: upload: finalize multipart body: %w
• googlechat: upload: decode response: %w

AI-assisted analysis of chenhg5/cc-connect@4000b2338a (2026-09-06). Data as JSON: /api/errors/144985abe7b55fad. Report an issue: GitHub.