Class confinement for Python snaps

[Didier Roche]

Le 10/03/2017 à 16:14, Barry Warsaw a écrit :
> I'm converting ubuntu-image from a devmode snap to a classic snap, but I'm
> running into some problems.  ubuntu-image is a Python 3 application, and I'm
> using snapcraft 2.27.1+17.4 on Zesty.
>
> The first problem I'm having is I think directly related to LP: #1670749.

Hey Barry,
Note as well that I opened 
https://bugs.launchpad.net/snapcraft/+bug/1670388 against the snapcraft 
project a couple of days ago.
I think snapcraft should at least fail the build to warn you about this.

Cheers,
Didier

>    I
> ended up reopening this because while Corey found that he ultimately only
> needed to set the $PATH environment variable, I still also had to $PYTHONPATH
> and I had to make sure the snap versions come before the system versions:
>
> environment:
>    PATH: $SNAP/bin/:$PATH
>    PYTHONPATH: $SNAP/lib/python3.5/site-packages:$PYTHONPATH
>
> This gets me pretty close, but then I run into my second problem which is that
> we depend on pyparted, in Ubuntu as python3-pyparted.  This package contains
> both Python source and an extension module and to further complicate things,
> its tarball is only released on GitHub, not on PyPI, so adding it to
> python-packages in the ubuntu-image part doesn't work.  Further, it doesn't
> help to add python3-parted to stage-packages because it appears that with
> classic confinement, none of those Python packages end up in the snap.
>
> I tried to add a scriptlet to copy things over, but that also fails.  E.g.:
>
> parts:
>    ubuntu-image:
>      plugin: python
>      source: https://github.com/CanonicalLtd/ubuntu-image.git
>      source-type: git
>      python-packages:
>        - PyYAML
>        - attrs
>        - voluptuous
>      prime:
>        - bin/ubuntu-image
>        - usr
>        - lib
>        - sbin
>      stage-packages:
>        - e2fsprogs
>        - mtools
>        - python3-debian
>        - python3-parted
>        - util-linux
>      install: |
>        cp -a ../install/usr/lib/python3/dist-packages/parted ../stage/lib/python3.5/site-packages
>        cp -a ../install/usr/lib/python3/dist-packages/pyparted-*.egg-info ../stage/lib/python3.5/site-packages
>
> $ snapcraft
> ...
> /home/barry/projects/ubuntu/allsnappy/ubuntu-image/parts/ubuntu-image/build
> cp: cannot create directory '../stage/lib/python3.5/site-packages': No such file or directory
> cp: cannot create regular file '../stage/lib/python3.5/site-packages': No such file or directory
> Command '['/bin/sh', '/tmp/tmpfeczxcco', '/tmp/tmp2__1bdau']' returned non-zero exit status 1
>
> This happens because ./stage/ is empty at the point that the install scriptlet
> is run.
>
> I can think of a couple of approaches that might be useful.
>
> * Allow python-packages specifications to pip install from repositories other
>    than PyPI.
>
> * Allow python-packages to come from git and/or https URLs (I tried this and
>    it didn't work).
>
> * Integrate dirtbike and wheels into the Python parts building phases.
>    (dirtbike is a tool that Debian/Ubuntu uses in very limited cases to turn
>    installed distro packages into .whl files.)
>
> * Provide a scriptlet hook that runs after the normal part installation step.
>
> My current WIP snapcraft.yaml file is here:
>
> https://github.com/CanonicalLtd/ubuntu-image/blob/lp1638645/snapcraft.yaml
>
> I'm going to keep trying a few things, but any suggestions are welcome.  I'm
> happy to file bugs as needed.
>
> Cheers,
> -Barry
>
>