DownloadFile is not able to use content-length header

[henryju]

Contrary to the documentation, it seems you are always forced to manually pass the file length. The code trying to read the Content-Length header is not working. My little understanding (and after lot of debugging) is that fetch is doing a "cors" mode request, and Content-Length is not whitelisted in this mode.

[damieng]

Yes, it looks like the server needs to send an extra header to enable this;

Access-Control-Expose-Headers "content-length"

I'll add that to the docs - I don't see a way to avoid it unfortunately.