Kobo Now Supports Applications

Cobalt is a comprehensive, open-source ecosystem designed to bring application functionality to Kobo e-readers. It consists of a dedicated launcher, a verified App Store, a Rust-based SDK, and a secure runtime environment that isolates every application within its own unprivileged process.

Once installed, the management of apps—including installation, updates, and removal—is handled directly on the device via Wi-Fi.

Disclaimer: This project is not affiliated with Rakuten Kobo.

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🛠️ Technical Architecture

Every application is deployed as a static ARM binary. To ensure system stability and security, these binaries run as unprivileged processes on the device's stock hardware.

Security & Distribution

The App Store manages the lifecycle of these binaries over Wi-Fi. Before any application is permitted to launch, the system performs a strict signature verification.

The verification logic can be represented as: $\text{Launch} \iff (\text{Binary} \in \text{Catalog}) \land (\text{Signature} = \text{Valid})$

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📱 The App Ecosystem

The platform distinguishes between "Platform" apps (shipped with the install) and "Store" apps (versioned independently).

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💻 Developer Guide

Developers implement the KoboApp trait to define their application. The runtime manages the heavy lifting: layout, e-ink refresh cycles, navigation, and the app lifecycle.

Capabilities & Constraints

Access to the following is capability-gated:

• Network $\rightarrow$ Storage $\rightarrow$ Audio $\rightarrow$ Frontlight $\rightarrow$ Wi-Fi

If a request is denied, the runtime returns a value that the app must handle gracefully.

Development Workflow

Example Implementation

To get started, use the CLI: kobo new my-app $\rightarrow$ cd my-app $\rightarrow$ kobo dev

use kobo_sdk::{ ActionId, Context, KoboApp, ScreenBuilder };

#[derive(Default)]
struct Hello { taps: u32 }

impl KoboApp for Hello {
    fn on_start(mut self, ctx: mut Context) {
        self.show(ctx);
    }

    fn on_action(mut self, ctx: mut Context, a: ActionId) {
        if a == kobo_sdk::action_id("tap") {
            self.taps += 1;
        }
        self.show(ctx);
    }
}

impl Hello {
    fn show(self, ctx: mut Context) {
        let screen = ScreenBuilder::new("hello")
            .top_bar("Hello")
            .heading(format!("{} taps", self.taps))
            .button("tap", "Tap me")
            .build();
        ctx.set_screen(screen);
    }
}

fn main() {
    let app = Hello::default();
    let _ = kobo_sdk::run("hello", app);
}

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🚀 Installation & Deployment

Setup Checklist

• Clone the repository: git clone https://github.com/BandarLabs/Cobalt.git
• Enter directory: cd Cobalt
• Add ARM target: rustup target add armv7-unknown-linux-musleabihf
• Execute setup: cargo run -p kobo-cli -- setup
• Restart device and launch Cobalt from the menu.

Detailed recovery steps are available in docs/INSTALL.md.

Publishing Apps

1. Add the app as a workspace package in apps/app-id/.
2. Register the app in apps/catalog.json.
3. Implement unit and layout tests; verify in browser/runtime simulators.
4. Merge the PR $\rightarrow$ the automated workflow signs and publishes the app.

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⚠️ Safety and Compatibility

Install on any Kobo model $\rightarrow$ Only install on models with a reviewed, hardware-tested profile.

• Hardware Safety: Device writes are restricted to exact hardware/firmware matches. A reboot will always return the device to the stock reader state.
• Risk: The initial installation modifies the user storage partition and is provided without warranty.
• Updates: The Cobalt platform updates via Settings on a separate channel from the App Store. All transactions are recovery-safe; interrupted updates will not brick the device.