Why are some downloads able to be resumed while others not?

[fuzzybabybunny]

I've been in a few places where the wifi or cell reception cuts out from time to time. Some downloads simply fail and have to be restarted from scratch while other downloads simply resume where they left off.

I'm not sure why this happens. Surely it would be best to have all downloads have the capability to resume instead of having to restart over again? I don't know why this happens.

 

[Crusty]

It requires using the 'Range' HTTP header, where you can specify the range of bytes you want in the file.

As long as both the client and server support it there should be no problem, however there is no requirement to actually use it, so it could be disabled in your browser options.

 

[fuzzybabybunny]

I'm sure my browser supports it. Does that mean that they disabled it on the server side?

 

[Crusty]

I'm sure my browser supports it. Does that mean that they disabled it on the server side?

It's possible. It's also possible there's some sort of proxy/load balancer that is stripping the header out.

I believe this also happens if the server doesn't specify the 'Content-Length' header, making it so the client has no idea how many bytes there actually are.

You should be able to look at the headers involved with your requests using your browsers developer console to see if it is sending the 'Range' header. You should look for the 'Content-Range' header in the response from the server to see what it is doing with your 'Range' request.