Hello World in Rust

In this tutorial, you will learn how to generate, build, preview, configure, and publish a Rust-generated WebAssembly serverless function that parses Markdown for Cloudflare Workers.

​​ Before you start

All of the tutorials assume you have already completed the Get started guide, which gets you set up with a Cloudflare Workers account, and the Workers CLI tool, Wrangler Open external link .

​​ Init

Cloudflare’s command-line tool for managing Workers projects, Wrangler Open external link , supports various templates — pre-built collections of code that make it easy to get started writing Workers. You will use the rustwasm-worker template Open external link to start building your project.

In the command line, create your Workers project, cloning the rustwasm-worker-template Open external link URL and passing in a project name (for example, rustwasm-markdown-parser):

~ $ git clone https://github.com/cloudflare/rustwasm-worker-template/ rustwasm-markdown-parser

This command creates a directory called rustwasm-markdown-parser which you can now cd into.

Wrangler templates are git repositories. If you want to create your own templates, or use one from the Template Gallery, there is a variety of options to help you get started.

​​ Workers Playground

You can test how your Workers function will execute when it is deployed by using the dev command:

rustwasm-markdown-parser $ wrangler dev

Using the dev command will establish a connection between localhost and an global network server that operates your Worker in development.

​​ Building

Begin building your project by pulling in a dependency from the crates.io ecosystem called pulldown-cmark. Add the following content to your Cargo.toml file:

## Cargo.toml

[dependencies]
pulldown-cmark = "0.4.0"

Use the code in the string-to-string example from the pulldown-cmark GitHub repository. Change your src/lib.rs to look like this:

src/lib.rs
mod utils;

use cfg_if::cfg_if;
use wasm_bindgen::prelude::*;
use pulldown_cmark::{Parser, Options, html};

cfg_if! {
    // When the `wee_alloc` feature is enabled, use `wee_alloc` as the global
    // allocator.
    if #[cfg(feature = "wee_alloc")] {
        extern crate wee_alloc;
        #[global_allocator]
        static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;
    }
}

#[wasm_bindgen]
pub fn parse() -> String {
    let markdown_input: &str = "Hello world, this is a ~~complicated~~ *very simple* example.";
    println!("Parsing the following Markdown string:\n{}", markdown_input);

    // Set up options and parser. Strikethroughs are not part of the CommonMark standard
    // and we therefore must enable it explicitly.
    let mut options = Options::empty();
    options.insert(Options::ENABLE_STRIKETHROUGH);
    let parser = Parser::new_ext(markdown_input, options);

    // Write to String buffer.
    let mut html_output: String = String::with_capacity(markdown_input.len() * 3 / 2);
    html::push_html(&mut html_output, parser);

    // Check that the output is what you expected.
    let expected_html: &str = "<p>Hello world, this is a <del>complicated</del> <em>very simple</em> example.</p>\n";
    assert_eq!(expected_html, &html_output);

    format!("\nHTML output:\n{}", &html_output)
}

Update your worker/worker.js to use the new code:

addEventListener("fetch", (event) => {
  event.respondWith(handleRequest(event.request));
});

const { parse } = wasm_bindgen;
const instance = wasm_bindgen(wasm);

/**
 * Fetch and log a request
 * @param {Request} request
 */
async function handleRequest(request) {
  await instance;
  const output = parse();
  let res = new Response(output, { status: 200 });
  res.headers.set("Content-type", "text/html");
  return res;
}

If wrangler dev is running, you will see the output of your Rust program in your browser a few seconds after you save it in your editor. Wrangler watches your project for changes then compiles your Rust to WebAssembly and outputs compiler errors.

​​ Publish

You have completed writing a Cloudflare Workers function with Rust-generated Wasm.

Wrangler has built-in support for bundling, uploading, and releasing your Cloudflare Workers application. To do this, run wrangler publish, which will build and publish your code:

​​ Related resources

In this tutorial, you built and published a Rust-generated WebAssembly serverless function that parses Markdown. If you would like to review the full source code for this application, you can find it on GitHub Open external link .

If you enjoyed this tutorial, below you can find other tutorials for building on Cloudflare Workers:

• Build a JAMStack app
• Build a QR code generator

If you want to get started building your own projects, review the existing list of Quickstart templates.