Get the model assertion from the store automatically

[Barry Warsaw]

`snap known` provides a way to download a model assertion file from the store, so it might be kind of nice to provide a u-i cli interface for that. That would eliminate an out-of-band step where the user has to get their model assertion and then pass it to u-i cli.

E.g.

% snap known --remote model series=16 model=pc-amd64 brand-id=canonical

We'd have to figure out a nice way to structure the option, and provide some defaults, but it would help having to remember the magic `snap known` incantation.

[Steve Langasek (vorlon)]

I am unconvinced that this belongs in ubuntu-image. Model assertions may come from a number of different sources, including being locally generated by the developer; I don't think ubuntu-image should treat store-sourced model assertions specially.

[Barry Warsaw (barry)]

On Dec 16, 2016, at 03:33 PM, Steve Langasek wrote:

>I am unconvinced that this belongs in ubuntu-image. Model assertions
>may come from a number of different sources, including being locally
>generated by the developer; I don't think ubuntu-image should treat
>store-sourced model assertions specially.

It would just be an optional convenience. Of course you'd always be able to
specify a model assertion file on the cli. Anyway it was just a thought
springing out from conversations w/infinity.

[Steve Langasek (vorlon)]

On Fri, Dec 16, 2016 at 04:05:32PM -0000, Barry Warsaw wrote:
> On Dec 16, 2016, at 03:33 PM, Steve Langasek wrote:

> >I am unconvinced that this belongs in ubuntu-image. Model assertions
> >may come from a number of different sources, including being locally
> >generated by the developer; I don't think ubuntu-image should treat
> >store-sourced model assertions specially.

> It would just be an optional convenience. Of course you'd always be able to
> specify a model assertion file on the cli. Anyway it was just a thought
> springing out from conversations w/infinity.

I assume that's related to ubuntu-image autobuilding. I definitely don't
see any reason for ubuntu-image to wrap this, considering launchpad
autobuilds are going to need to support building for arbitrary models, which
means exposing the full array of options to 'snap known' through the
launchpad json. So passing this through ubuntu-image instead of directly to
'snap known' doesn't buy us anything.

[Łukasz Zemczak (sil2100)]

I think this is not a feature we'd want to directly support, so let me mark this Invalid.