Yes, it is such a shame that the almighty push to get users onto Galaxy made them withdraw GOG Downloader. That small, elegant, easy to use use little program did everything I needed with the minimum of fuss. Still, the plus side is that at least I'm now spending less money on games :D

Can you set it up to start downloading before you go to bed?
So when you wake up, the downloading will have finished.

I still wonder why do you have to turn off your PC, any specific reason, unless I missed it.

I only turn the PC off when outside is really bad weather, all those thunders and lightnings, I'm not taking any chance, and yes, I restart PC when there is some amount of decent updated to the PC, don't see a reason to turn it off.

If PC noice doesn't bother you leave download during the night, that's what I do, maybe download is a little better on my side, yet it is slow since I'm behind the walls and here you get crappy modem which signal is really weak to pass through walls, sometimes I get blazing speeds, sometimes I get disconnections a lot so I can't even use internet at all.

Range requests have been a thing since HTTP/1.1 (1997). There are twenty-year-old tools that can resume an interrupted download. Forcibly terminating a program does not corrupt the data it has written to files. The only problem is some programs that don't keep their files consistent (i.e. they write a corrupted file to begin with! and then expect to later be able to fix it without being interrupted in the middle). This is generally not a problem for simple file downloads since you're just appending data to the end of a file.

Besides, rebooting usually doesn't cause a forced termination. Programs are given a chance to exit cleanly and finish what they were doing.

And therein lies the worlds power shortage :o) I would always turn everything off all the time, power consumption for one, but also it allows the computer to cleanup and shut things down correctly. Also, you do t know what it’s doing whilst not live, don’t trust windows to not be communicating whilst in sleep or something. I know it’s not cool now, must have everything live all the time.
Yep, there are lots of posts trying to get it reinstated. You could try (If you can find it) a post from a user called Timboli who created some program to replicate downloaded. Can’t find it myself at the moment.

Found it:
https://www.gog.com/forum/general/gogplus_download_checker

the one from just prior to firefox switching how they did plugins a couple of years back. not sure on the actual version number, but will check later.

Certainly, but that doesn't account for things like one time authentication, handshakes, and other annoying factors.

I did not check in details how lgogdownloader does it, but of course any authentication process is done again on the download resuming. This is technically a new connection.

I guess it can use the size of the already partially downloaded file (and maybe some other informations) to skip what is already on disk and only download what should be appended to it. If you happen to know C++, the best way to understand how it really works is probably to have a look at its source code ;)

None of that matters. As long as you're able to start a download and the server supports range requests, you could move to Uganda, buy a new computer, drop your old interrupted download on it, create a new account on GOG, buy the game you already had, and resume that old download.

The whole point of the range header is that you can open a new connection and continue a download (and less commonly, seek in a media file). Historically, HTTP has very much been a one-connection per request kind of protocol (pipelining is supported in HTTP/1.1, but rarely used). There would be no point having such a header in the first place if you couldn't use it on a new connection.

Authentication is just cookies.

(I just tested this, started a download using wget and finished it on a different computer using curl) Exactly! This is how curl, wget, ftp, etc. work. And so does lgogdownloader: https://github.com/Sude-/lgogdownloader/blob/4997a455970f017b700267f4a514262d200cafcc/src/downloader.cpp#L1038

Thanks, I've been keeping my eye on Timboli's program and have high hopes that it will eventually do what I need.