KUAL Hello World in Rust

Background

This is a tutorial to create a simple script that will show a “Hello World” message. This will be an extension within KUAL, so it’ll need some additional configuration.

Configuration

Here we are creating some boilerplate for KUAL to recognise our app

config.xml

<extension>
    <information>
        <name>KindleApp</name>
		<version>0.1.0</version>
		<author>Me</author>
		<id>KindleApp</id>
    </information>
    <menus>
        <menu type="json" dynamic="true">menu.json</menu>
    </menus>
</extension>

menu.json

{
    "items": [
        {
            "name": "Hello World",
            "priority": -999,
            "action": "kindleapp/target/arm-unknown-linux-musleabi/release/kindleapp",
            "exitmenu": true
        }
    ]
}

Rust Binary

Now lets create our rust binary that we want to run on the kindle.

cargo new kindleapp && cd kindleapp

src/main.rs

use std::process::Command;

fn main() {
    Command::new("eips").arg("1").arg("1").arg("\"Hello World\"").output().ok();
}

Make sure you have docker installed, running, and your account is added to the docker group, and then install Cross

Add the arm target to rust

rustup target add arm-unknown-linux-musleabi

Finally compile for the kindle

RUSTFLAGS="-C target-feature=+crt-static" cross --target arm-unknown-linux-musleabi --release

Final check

.
├── kindleapp/
│   ├── src/
│   │   └── main.rs
│   ├── target/
│   ├── .gitignore
│   ├── Cargo.lock
│   └── cargo.toml
├── config.xml
└── menu.json

Moving to the kindle

For the sake of simplicity, we are going to do a very bad thing and move everything to the kindle within a single folder to extensions.

This is the programming equivalent of taking a jet to the kitchen. When you eventually commit to creating a kindle app, I strongly recommend you to single out the rust binary kindleapp/target/arm-unknown-linux-musleabi/release/kindleapp outside of the rust folder, something like:

.
├── kindleapp
├── config.xml
└── menu.json

to avoid having to transfer literal gigabytes in dependencies; make sure to change the path in menu.json to just kindleapp! For such a small project this doesnt matter as it currently should be ~10mb, but it will later bite you in the butt if you are not careful.

At the end, it should look like this on the kindle:

/
├── ...
└── extensions/
    └── kindleapp/
        ├── config.xml
        ├── menu.json
        └── kindleapp/
            └── ...

Starting

Eject, then on the kindle go to KUAL -> “Hello World” and you should see a message show in the top left corner if successful.

Closing Notes

Make sure to remove the rust dependencies (see note above) when you start writing more complex scripts.