code: func upload(data []byte, endpoint string) (string, error) {
  	swarm := client.NewClient(endpoint)
  	f := &client.File{
  		ReadCloser: ioutil.NopCloser(bytes.NewReader(data)),
  		ManifestEntry: api.ManifestEntry{
  			ContentType: "text/plain",
  			Mode:        0660,
  			Size:        int64(len(data)),
  		},
  	}
  
  	// upload data to bzz:// and retrieve the content-addressed manifest hash, hex-encoded.
  	return swarm.Upload(f, "", false)
  }
docs: // upload an arbitrary byte as a plaintext file  to `endpoint` using the api client