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Introduction to the Runnable API

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.

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 Runnable interface

The first and most basic part of the Runnable API is the Runnable interface. Every Runnable you write will provide an instance of an object that conforms to this interface. It requires only one method: run.

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

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 various pages in this reference.

When handling HTTP requests, the input to the run method is the body of the request being handled. The other details of the request are available using the req namespace and will be discussed in the coming sections.

An example Runnable

Here is an example of a Runnable, written in Rust.

The subo CLI tool will automatically create new Runnables for you with the subo create runnable command.

use suborbital::runnable::*;
use suborbital::{req, util};

struct Foobar{}

impl Runnable for Foobar {
fn run(&self, _: Vec<u8>) -> Result<Vec<u8>, RunErr> {
let body = req::body_raw();
let body_string = util::to_string(body);

Ok(String::from(format!("hello {}", body_string)).as_bytes().to_vec())

// initialize the runner, do not edit below //
static RUNNABLE: &Foobar = &Foobar{};

pub extern fn init() {

This Runnable uses the req namespace to fetch the body of the HTTP request being handled, and then returns it.

To learn about all of the Runnable API namespaces, read on!