snap does not resume unfinished downloads

[Rolf Leggewie]

I am on bionic and just attempted to install skype on a flakey internet connection.

$ sudo snap install skype --classic

For some reason, the connection was always interrupted half-way through (well, that happens, I guess). What should not happen is for snap to restart the download from 0. It should pick up where it left off.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dan Watkins (oddbloke)]

Yep, I'm hitting a similar problem. I'm trying to install the spotify snap on a library wifi connection that only gives me ~250kB/s and it's going to take about a quarter hour. That makes using the connection for _anything else_ painful, but I can't interrupt the snap download without losing all the progress I've made.

[John Lenton (chipaca)]

Dan, if the download you are referring to is a refresh, note you can rate limit *auto*-refreshes (that is, non-interactive refreshes) via `snap system set refresh.rate-limit <some limit>`. For interactive refreshes and installs, you can replace them with a `snap download` followed by a `snap ack` and a `snap install`, and `snap download` will leave a .partial file if you interrupt it.

The problem with having snapd itself leave a partial file when the user has explicitly cancelled a manual install or refresh is that it's impossible to know when leaving the partial is the right thing to do. There are a couple of ideas going around as to how we _could_ make this better, but there's no solid way of doing it, they're both fiddly, and fall apart in some situations meaning there'd have to be a way of tuning the behaviour, which just makes the whole thing a mess.

[Daniel Manrique (roadmr)]

See https://forum.snapcraft.io/t/refreshing-downloading-a-snap-over-a-poor-connection/15350/5, looks like snapd is still not resuming downloads in situations where it should (unexpected connection interruptions).

[Svet Bajlekov (svetb)]

Just to follow up on my comments in the thread that @roadmr linked to, I can confirm that with 2.43.3, downloads resumption *is* possible using snap download, but does *not* currently appear to be implemented for snap refreshes (either automatic ones, or those triggered manually).

Looking at the codebase, I can see a few recent commits/PRs that appear to progress this, e.g.: https://github.com/snapcore/snapd/pull/8078, https://github.com/snapcore/snapd/pull/8119

Would be great to get an update on the current status and plan forward on this.

Thanks to all the developers (esp. @mvo) for the work clearly going into this!

[vr25 (vr25)]

I'm "using" the latest snapd (just checked for update before writing this).
The issue persists.
`snap install <package>` does not resume downloads, nor does `snap refresh` (including auto-refresh).
`snap download <package>` does resume downloads, but as far as I know, it won't download delta updates (sad).
I'm on a remote area and my internet connection is very unstable and slow (~64kB/s down, ~20ish kB/s up).
`apt` works fine, though.
Unfortunately, until this issue is fixed, I can't really use snaps.

[James (james-e-steward)]

I'm using an up to date Ubuntu 20.04 install and apt reports;
$ apt info snapd
Package: snapd
Version: 2.48.3+20.04

I'd like snap download to be able to resume a download even after I've manually killed it with Ctrl-c and then restart some time later.

I'm trying to install gimp, and the connection here is slow. A snap install has failed twice, and now I'm trying download.

I'd like to be able to stop and resume a download because at times I might start and then want to stop to use the internet connection for something else - without the added traffic of the download.

I agree with vr25.