Where is the Source code of snaps?

Question

When I download open-source snaps on Ubuntu 20.10 I cannot find their source code, even though they are free.

Can anyone tell me where their source code is?

BTW, a program being free does not necessarily mean that it is open-source and vice versa. — BeastOfCaerbannog, Nov 27 '20 at 16:50

score 1 · Answer 1 · answered Nov 27 '20 at 16:43

To see the source code of a snap (that is how it was built), you can download the snap and inspect it.

For example, say you want to read the source code of gnome-system-monitor snap. You can download the snap in your current directory using:

sudo snap download gnome-system-monitor

This command will download two files, gnome-system-monitor_148.snap and gnome-system-monitor_148.assert (the number represents the snap's version and it can be different than 148).

Then, open Nautilus and go to the directory where the files are downloaded (it's the directory inside which you ran the above command). right-click the .snap file, select to open it with the Archive Manager and navigate in the snap directory in the Archive Manager window that opens. Finally double click the snapcraft.yaml and manifest.yaml to open them with your text editor. These files will show you how the snap package was built.

You can find some more info in this article: How to verify the source of a Snap package

22.04 doesn't give me the ability to look at that .snap file with "Archive manager". I can still check it with less ... since it's just text, but it's huge (at the one I'm looking at is some 130Mb). The apt-get source ... command is better. Snaps are not easy to work with... — Alexis Wilke, Jun 01 '23 at 18:10

score 0 · Answer 2 · answered Jun 01 '23 at 18:37

As mentioned by BeastOfCaerbannog, you can download the snap file like so:

mkdir <name>
cd <name>
snap download <name>

(Note: no need to use sudo ..., this is just a download in your current directory.)

The download saves two files in your current folder: a .assert and a .snap. The filename also includes a version.

The .snap file contains the actual binary snap, which includes a manifest with information about the source. That file is a compressed set of files found in a SquashFS file system. To see the list of files on newer systems, you can simply do:

less <name>_<version>.snap

That way you can verify that the files of interest exist.

To actually check the files, you need to mount the file system. mount does require sudo. I'm sure there are other ways to extract the data, but I find this one easy enough:

mkdir <name>.snap
sudo mount <name>_<version>.snap <name>.snap -t squashfs -o loop

Now all the files inside <name>.snap are accessible like any file on your disks (well, except that they are read-only). The manifest and snapcraft can be read like so:

less docker.snap/snap/manifest.yaml
less docker.snap/snap/snapcraft.yaml

It looks like the manifest has links to the git specifically used by this <name> project. That's where you would find the source.

For example, for docker, I found these:

source: https://github.com/moby/moby.git
source: https://github.com/containerd/containerd.git
source: https://github.com/opencontainers/runc.git
source: https://github.com/NVIDIA/nvidia-container-toolkit.git
source: https://github.com/NVIDIA/libnvidia-container.git
source: https://github.com/docker/libnetwork.git
source: https://github.com/krallin/tini.git
source: https://github.com/docker/cli.git
source: https://github.com/docker/buildx.git
source: https://github.com/docker/compose.git

Where is the Source code of snaps?

2 Answers2