Snapcraft can be used to package and distribute Go applications in a way that enables convenient installation by users.
The process of creating a snap for a Go application builds on standard Go packaging tools, making it possible to adapt or integrate an application’s existing packaging into the snap building process.
Getting started
Snaps are defined in a single snapcraft.yaml file placed in a snap directory at the root of your project. This YAML file describes the application, its dependencies and how it should be built.
The following example shows the entire snapcraft.yaml file for the existing snap of the woke tool:
name: woke
summary: Detect non-inclusive language in your source code
description: |
Creating an inclusive work environment is imperative to a healthy,
supportive, and productive culture, and an environment where everyone
feels welcome and included. woke is a text file analysis tool that finds
places within your source code that contain non-inclusive language and
suggests replacing them with more inclusive alternatives.
adopt-info: woke
base: core22
confinement: devmode
plugs:
dot-config-woke:
interface: personal-files
read:
- $HOME/.config/woke.yaml
- $HOME/.config/woke.yml
- $HOME/.woke.yaml
- $HOME/.woke.yml
apps:
woke:
command: bin/woke
plugs:
- home
- dot-config-woke
- network
- removable-media
parts:
woke:
plugin: go
build-snaps: [go/latest/stable]
source: https://github.com/get-woke/woke
source-type: git
override-pull: |
snapcraftctl pull
snapcraftctl set-version \
"$(git describe --long --tags --always --match=v*.*.* | sed 's/v//')"
We’ll break this file down into its components in the following sections.
Metadata
The snapcraft.yaml file starts with a small amount of human-readable metadata, which is often already available in the project’s own packaging metadata or README. This data is used in the presentation of the application in the Snap Store.
name: woke
summary: Detect non-inclusive language in your source code
description: |
Creating an inclusive work environment is imperative to a healthy,
supportive, and productive culture, and an environment where everyone
feels welcome and included. woke is a text file analysis tool that finds
places within your source code that contain non-inclusive language and
suggests replacing them with more inclusive alternatives.
adopt-info: woke
The name must be unique in the Snap Store. A valid snap name consists of lowercase alphanumeric characters and hyphens. It can’t be all numbers and can’t start or end with a hyphen.
The summary cannot exceed 79 characters.
If your description is longer than 79 characters and needs to be spread across multiple lines, you can start the declaration with a pipe (|) and preserve the line breaks, or a greater-than sign (>), which concatenates the description into one unbroken line.
The adopt-info keyword is used to import metadata from other sources within the upstream project. This reduces redundancy and ensures consistency. Here, Snapcraft will look within the source repository defined in the woke part to find and adopt metadata such as version.
Base
The base keyword declares which base snap to use with the project. A base snap is a special kind of snap that provides a run-time environment alongside a minimal set of libraries that are common to most applications.
base: core22
In this example, core22 is used as the base for snap building, and is based on Ubuntu 22.04 LTS. See Base snaps for more details.
Security model
Snaps are containerised to ensure more predictable application behaviour and greater security. The general level of access a snap has to the user’s system depends on its level of confinement.
The next section of the snapcraft.yaml file describes the level of confinement applied to the running application:
confinement: devmode
When constructing a snap, we recommend that you begin with a more permissive confinement level. When you set a snap’s confinement to devmode (developer mode), it logs any confinement issues instead of actually confining the application. You can review the warnings by running journalctl -xe.
Because developer mode is only intended for development, snaps must be set to strict confinement before they can be published as stable in the Snap Store. Once an application is working well in developer mode, you can review confinement violations, add appropriate interfaces, and switch to strict confinement.
The previous example will also work if you change the confinement from devmode to strict, as you would before a release.
Parts
Parts define what sources are needed to build your application. Parts can be anything – programs, libraries, or other needed assets – but for this example, we only need to use one part for the woke source code:
parts:
woke:
plugin: go
build-snaps: [go/latest/stable]
source: https://github.com/get-woke/woke
source-type: git
override-pull: |
snapcraftctl pull
snapcraftctl set-version \
"$(git describe --long --tags --always --match=v*.*.* | sed 's/v//')"
The plugin keyword is used to select a language or technology-specific plugin that knows how to perform the build steps for the project. In this example, the go plugin is used to automate the build of this project using the version of Go on the host system.
The build-snaps keyword specifies a list of snaps that should be available during the build process. Here, using go/latest/stable ensures that the latest stable version of the Go snap is available for building the snap package.
The source keyword points to the source code of the project, which can be a local directory or remote Git repository. In this case, it refers to the main project repository.
The source-type keyword indicates that the source is a git repository.
The override-pull keyword in the snapcraft.yaml file allows you to customise the actions taken during the pull step of the build process. The pull step is responsible for fetching the source code from the repository specified in the source keyword. By default, Snapcraft handles this step automatically, but override-pull lets you define your own commands to extend or replace this behaviour. See Override build steps for more details.
Apps
Apps are the commands and services that the snap provides to users. Each key under apps is the name of a command or service that should be made available on users’ systems.
apps:
woke:
command: bin/woke
plugs:
- home
The command specifies the path to the binary to be run. The path is resolved relative to the root of the snap contents.
If the command name matches the name of the snap specified in the top-level name keyword (see the Metadata section), the binary file will be given the same name as the snap, as in this example. If the names differ, the binary file name will be prefixed with the snap name to avoid naming conflicts between installed snaps. An example of this would be woke.some-command.
The confinement of the snap, which we defined in the Security model section, can be changed through a set of interfaces. In this example, the plugs keyword specifies the interfaces that the snap needs to access.
Building the snap
You can download the example repository with the following command:
git clone https://github.com/degville/woke-snap
After you have created the snapcraft.yaml file (which already exists in the sample repository), you can build the snap by running the snapcraft command without arguments in the project directory:
snapcraft
A successful build output will look similar to the following:
Launching a container.
Waiting for container to be ready
[...]
Pulling woke
+ snapcraftctl pull
Cloning into '/root/parts/woke/src'...
remote: Enumerating objects: 2723, done.
remote: Counting objects: 100% (939/939), done.
remote: Compressing objects: 100% (401/401), done.
remote: Total 2723 (delta 697), reused 635 (delta 522), pack-reused 1784
Receiving objects: 100% (2723/2723), 22.33 MiB | 2.88 MiB/s, done.
Resolving deltas: 100% (1574/1574), done.
Building woke
+ snapcraftctl build
+ go mod download
+ go install -p 8 -ldflags -linkmode=external ./...
Staging woke
+ snapcraftctl stage
Priming woke
+ snapcraftctl prime
Determining the version from the project repo (version: git).
The version has been set to '0+git.f23bb0a-dirty'
Snapping |
Snapped woke_0+git.f23bb0a-dirty_multi.snap
The resulting snap can be installed locally. This requires the --dangerous flag because the snap is not signed by the Snap Store. The --devmode flag acknowledges that you are installing an unconfined application:
sudo snap install woke_*.snap --devmode --dangerous
You can then try it out:
woke -h
When you’re done testing, you can remove the snap:
sudo snap remove woke
Publishing your snap
To share your snaps, you need to publish them in the Snap Store. First, create an account on the dashboard. Here you can customise how your snaps are presented, review your uploads, and control publishing.
You’ll need to choose a unique developer namespace during account creation. This name will be visible by users and associated with your published snaps.
Make sure the snapcraft command is authenticated using the email address attached to your Snap Store account:
snapcraft login
Reserve a name for your snap
You can publish your own version of a snap, provided you do so under a name you have rights to. You can register a name on dashboard.snapcraft.io, or by running the following command:
snapcraft register mygosnap
Be sure to update the name in your snapcraft.yaml to match this registered name, then run snapcraft again.
Upload your snap
Use snapcraft to push the snap to the Snap Store.
snapcraft upload --release=edge mygosnap_*.snap
If you’re happy with the result, you can commit the snapcraft.yaml to your GitHub repo and optionally enable building directly from GitHub so that any further commits automatically get released to edge, without requiring you to manually build locally.
You’ve just built and published your first Go snap. For a more in-depth overview of the snap building process, see Creating a snap.