code: func NewSentMessage(params *MessageParams) (*sentMessage, error) {
  	const payloadSizeFieldMaxSize = 4
  	msg := sentMessage{}
  	msg.Raw = make([]byte, 1,
  		flagsLength+payloadSizeFieldMaxSize+len(params.Payload)+len(params.Padding)+signatureLength+padSizeLimit)
  	msg.Raw[0] = 0 // set all the flags to zero
  	msg.addPayloadSizeField(params.Payload)
  	msg.Raw = append(msg.Raw, params.Payload...)
  	err := msg.appendPadding(params)
  	return &msg, err
  }
docs: // NewSentMessage creates and initializes a non-signed, non-encrypted Whisper message.