Get the content length without storing the data locally

Question

I have a stream of data and want to hit a certain endpoint I don't want to store the data locally to find the content length as I need to pass the content length as the headers property. So what are possible ways to get the content length?

(readStream) => {
const requestOptions = {
      url: 'https://url.com',
      method: 'PUT',
      headers: {
        'Content-Type': 'application/octet-stream',
        'Content-Length': length,
      },
      body: readStream
    }
  request(requestOptions, function (error, response, body) {
    
  });
}