I just followed an example how to make libcurl and libuv working together. I removed usage of global variables and tested the performance by downloading (not writing to disk) 4.4GB file. It works great. It is comparable to my experience with completion ports on Windows.
libcurl: 7.66.0 libuv: 1.33.1 url: http://saimei.ftp.acc.umu.se/debian-cd/current-live/amd64/iso-hybrid/debian-live-10.2.0-amd64-lxqt.iso code: 200 real 2m37,210s user 0m2,297s sys 0m6,527s
The source code of my playground: https://github.com/amacal/peak/tree/5810adf59a026fc5f630e57791fc463f0452701c