The Runnables that you write for your Atmo application are compiled to WebAssembly, and are run in a controlled sandbox. The Runnable API is the set of capabilities Atmo grants to the sandbox which can be used to build your application's logic.

When a Runnable is handling a particular request, Atmo binds that request to the module while it's being run. The Runnable API allows your code to access everything about the request, and also gives you the ability to access the "outside world" by giving functions for HTTP requests, accessing static files, logging, and more. This section describes all of the capabilities available via the Runnable API and how to use them in Rust and Swift Runnable code.

The Runnable API is provided via a library for each of the supported languages, and simply needs to be imported to turn your module into a Runnable. subo will configure all of this on your behalf.

The first and most basic part of the Runnable API is the Runnable interface (also known as a Rust trait or Swift protocol). Every Runnable you write will provide an instance of an object that conforms to this interface. It is very simple, and only requires on method, run.

The Rust Runnable API crate is considered stable

In Rust:

pub trait Runnable {
fn run(&self, input: Vec<u8>) -> Option<Vec<u8>>;

The Swift Runnable API library is still considered experimental

And in Swift:

public protocol Runnable {
func run(input: String) -> String

Your Runnable object will be created automatically by subo when you use the create runnable command. All you need to do is write your logic within the run method, and Atmo will handle executing it.

There are several namespaces available in the Runnable API, each are discussed in the following pages.

When handling an HTTP request, the input to the run method will be a summary of the request being handled, not the request itself. The full details of the request are available using the req namespace, which will be discussed next.