set 'content-length' and 'transfer-encoding:gzip' for 'pm2 serve'

What's going wrong?

I need to download and show loading progress with javascript on web page, but when I'm serving with pm2 serve, there is no way to get the total size of a file downloaded with XmlHttpRequest.

How could we reproduce this issue?

1. serve some files with pm2 serve
2. in js file:

let xhr = new XMLHttpRequest();

xhr.open('GET', url, true);

xhr.responseType = responseType || 'blob';

xhr.onprogress = function(p) {

  let contentLength = xhr.getResponseHeader('x-decompressed-content-length')

  let contentLength2 = xhr.getResponseHeader('Content-Length')

  console.warn(p.loaded, p.total, p.lengthComputable, contentLength, contentLength2)

};

xhr.send(null);

3. after funning the js above, the progress info will be logged, and only p.loaded is available so there is no way to calculate the percentage of the loading progress. And by looking into the network tab of the devtool, it can be seen the 'transfer-encoding' is 'chunked' and the 'content-length' is not set.

Supporting information

# Run the following commands
$ pm2 report

Start with the pm2 serve command and its static-file response path, then reproduce the XMLHttpRequest case described in the issue and inspect the response headers. Done means served files expose a usable total size through Content-Length or the intended decompressed-length header instead of only chunked transfer encoding.