Scala Native and Nix - a match made in heaven??

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Jakub Kozłowski | WSUG | 11.12.2024 Scala Native & Nix A match made in heaven?? https://linktr.ee/kubukoz

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Story time

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I once made a REPL for managing my Spotify playlists • f: fast forward • m: move to "good" • d: remove from "pending" • (and some more)

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But it had problems. • had to keep the terminal tab open nearby • switching to/from it took time and I used it tens/hundreds of times throughout the day • the work fl ow in general could use improvement

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No content

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I decided to get rid of the keyboard • Using the HID API, read a DualSense's output • Decode with scodec • Map to button presses and commands • Pipe to the Spotify REPL

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HID on the JVM: hidapi + hid4java • hidapi: C library for HID access, abstracting away OS di ff erences • hid4java: JNA-based Java library wrapping hidapi

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Problem solved? • I don't always have a free USB port • Feels odd to keep this running on my work computer all the time • (and there's overhead) • But I had one of these! Not quite...

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JVM on RPi Zero 2 😒 • slow startup (3s to run hello world, 11s on the dualshock4s CLI) • poor performance • JNA / native library shenanigans at runtime • surely there's a better way

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Onto Scala Native

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Scala Native Alternative target for Scala • Supports all Scala language features • Compiles using LLVM • Runs without a JVM • Relatively easy to set up nowadays

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Let's use hidapi on Native! • Get headers • Generate bindings • Get hidapi binary • Compile & link • Run

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Headers

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Bindings https://sn-bindgen.indoorvivants.com/ (this is easier in sbt)

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Get hidapi binary • Use a package manager like brew, vcpkg... • Or compile from source

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Compilation & linking This part gets tricky Where they are What libraries to link with

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Running :shipit:

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Running... on RPi

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Scala Native The downsides... • Portability :( • Native dependencies :( • Linking times (getting better) • Scala library availability :/

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Cross-compilation of native programs • generally possible • crazy di ff i cult • I will not get into it during this talk • ...but I did once manage to cross- compile to a 32-bit bare-metal console: https://youtu.be/paHZkg8Py1U https://clang.llvm.org/docs/CrossCompilation.html

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What now? • you know exactly what comes now ❆

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Nix

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What is Nix? • A package manager, build system, deployment tool... • Purely functional, immutable packages... • Built and installed in isolation...

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What does Nix buy us?

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Nixpkgs The world's largest package repository (according to Repology)

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Remote builds ... https://nixbuild.net

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Transparent caching fi rst run A: 21.337s fi rst run B: 23.391s second run A: 0.226s Works remotely too! https://zero-to-nix.com/concepts/caching/ https://www.cachix.org/

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nix copy Copy a Nix path and all its dependencies

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Scala Native build with Nix ...with native dependencies 1. SN con fi g (linux has hidapi-hidraw & hidapi-libusb variants)

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2. Bindgen con fi g Headers provided by Nix sn-bindgen binary provided by Nix Scala Native build with Nix ...with native dependencies

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3. Nix environment Scala Native build with Nix ...with native dependencies fl ake.nix

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4. Nix derivation Scala Native build with Nix ...with native dependencies Changes whenever you update sbt libs/plugins Makes hidapi appear on the link path How to build the app Putting the app in the special path at $out sbt-derivation / Nix shenanigans ;) from sbt-derivation

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Bonus: development shell + + =

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Caveats • Nix documentation is scattered around the Internet • It's much better today, and improving! https://nix.dev • Complexity, usability issues • Dated syntax • Disk usage can go high (use GC!) • Caches can sometimes take more time to download than a fresh build would • ...

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Is this for me? • I don't know, consider alternatives too • Find your level of Nix (dis)comfort (nix builds? shells? home-manager? NixOS?)

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How to get started? -https://zero-to-nix.com/start/ -https://nix.dev/ -https://nixos.org/guides/nix-pills/ -https://github.com/zaninime/sbt-derivation More about Scala + Nix: https://speakerdeck.com/kubukoz/nix-for-scala-folks

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Links • Slides/contact/YouTube: https://linktr.ee/kubukoz • Sample repo: https://github.com/kubukoz/talks/tree/main/scala-native-and-nix • Nix/NixOS: https://nixos.org/ • Nixpkgs Search: https://search.nixos.org/packages https://linktr.ee/kubukoz