Go applications

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 folder 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 an existing project, Woke:

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.
version: git
grade: stable
base: core20

confinement: devmode

apps:
  woke:
    command: bin/woke
    plugs:
      - home
parts:
  woke:
    plugin: go
    source-type: git
    source: https://github.com/get-woke/woke

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.md file. 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.
version: git

The name must be unique in the Snap Store. Valid snap names consist of lower-case alphanumeric characters and hyphens. They cannot be all numbers and they also cannot start or end with a hyphen.

By specifying git for the version, the current git tag or commit will be used as the version string. Versions carry no semantic meaning in snaps.

The summary can not exceed 79 characters. You can use a chevron ‘>’ in the description key to declare a multi-line description.

Base

The base keyword declares which :term: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: core20

In this example, core20 is used as the base for snap building, and is based on Ubuntu 20.04 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 :term:confinement applied to the running application:

confinement: devmode

It is best to start creating a snap with a confinement level that provides warnings for confinement issues instead of strictly applying confinement. This is done by specifying the devmode (developer mode) confinement value. When a snap is in devmode, runtime confinement violations will be allowed but reported. These can be reviewed by running journalctl -xe.

Because devmode 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 devmode, you can review confinement violations, add appropriate interfaces, and switch to strict confinement.

The above 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
    source-type: git
    source: https://github.com/get-woke/woke

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 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.

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. This 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 Metadata above), 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 was defined in the Security model section above, can be changed through a set of :term:interfaces. In this example, the plugs keyword is used to specify 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 above repository), you can build the snap by simply executing the snapcraft command in the project directory:

$ snapcraft
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

Removing the snap is simple too:

$ 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” as part of the account creation process. 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 turn on automatic builds so any further commits automatically get released to edge, without requiring you to manually build locally.

Congratulations! 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.

Last updated a month ago.

Help improve this document in the forum.