Packaging Rust Binaries

I spent a bit of time recently working on getting Launchpad to build my Rust binary into something that could be easily installed. To make this search easier, I made a minimal rust project that was basically ‘Hello World’, but using the log crate; I called the project rust-hello. After considering what my goals were, I knew that I had a couple of options:

1. I could build a PPA
   • apt install rust-hello after adding my PPA
2. I could use Canonical’s new cross-distro packaging system Snappy
   • snap install rust-hello immediately after build

Building a source package on Launchpad for a PPA means packaging dependencies into additional PPAs, and then depending on those, up to the root of the rustc dependency. This would mean that, for a crate merely requiring the log crate, I’d have to depend on the rustc available in the repositories (version 1.6.0) and manage my own log crate package (as well as its dependencies, recursively) before I can build my own package.

Snappy, on the other hand, meant adding a snapcraft.yaml file to my repository and typing snapcraft cleanbuild. The snapcraft.yaml is a relatively simple file for a Rust project:

name: rust-hello # you probably want to 'snapcraft register <name>'
version: '0.1' # just for humans, typically '1.2+git' or '1.3.2'
summary: Prove cross platform rust snaps # 79 char long summary
description: |
  This is a snap to validate a Rust project building cross architecture
grade: stable # must be 'stable' to release into candidate/stable channels
confinement: strict # use 'strict' once you have the right plugs and slots

parts:
  hello-rust:
    # See 'snapcraft plugins'
    plugin: x-rust
    source: .
apps:
  hello:
command: hello

Snappy is supported on Launchpad, which means that I was able to build a snappy package on Launchpad with specific hardware targets following the guide at kyrofa’s blog.

Initially, this failed because Launchpad builders for snappy don’t have internet access during the build phase, only during the pull phase, which meant that I had to make a few modifications to add a custom plugin. At the same time, I’ve opened a Pull Request against Snapcraft to make the rust plugin work on Launchpad. This let me build rust-hello for all of the Ubuntu supported architectures with a git push :-D

If you want to see if it worked and you’re on Xenial (16.04) or newer, you can run snap search rust-hello to see it, or run sudo snap install rust-hello to install the snap. After installing, rust-hello will be available at /snap/bin/rust-hello.hello and can be run directly. To make your app available at /snap/bin/$NAME, you should make sure that the app_name and snap name defined in snapcraft.yaml match. For example:

name: rust-hello # you probably want to 'snapcraft register <name>'
...
apps:
  rust-hello:
    command: hello

The code used to build this snap is available on Launchpad or Github.