Discord Bot - Rust

Preface

Rust is a compiled, strongly and statically typed general purpose programming language. Compared to Python, Rust applications must be compiled for each operating system and architecture combination, and all variables defined should have a single type.

To learn more about Rust, read "The Book", or follow a more interactive learning guide with example code and output.

Getting Started

What to expect in this section:

1. Installing Rust and Cargo
2. Setting up a Rust project
3. Installing needed dependencies (also known as "crates")

To get started, install Rust and Cargo (the package manager for Rust) using rustup.

Once installed, create a new project by using Cargo.

cargo init ping-pong-rs

Running cargo init ping-pong-rs will create a folder named ping-pong-rs with the basic structure of a Rust project.

Next, we need to install some dependencies (crates). For this tutorial, we'll be using serenity to interact with Discord, tokio with the "full" feature to manage asynchronous behavior, and dotenvy to read your Discord bot token from a file.

To install these crates, use need to use Cargo again.

cargo add dotenvy tokio serenity -F tokio/full

Once you have the crates installed, you are now ready to code!

Writing the Discord Bot

What to expect in this section:

1. Creating an example ping-pong bot
2. Building and testing your Discord bot on your machine

We'll be using a modified version of serenity's sample ping-pong bot. Open the main.rs file located in the src folder and paste the following code inside of it:

use std::env;

use dotenvy::dotenv;
use serenity::async_trait;
use serenity::model::channel::Message;
use serenity::prelude::*;

struct Handler;

#[async_trait]
impl EventHandler for Handler {
    async fn message(&self, ctx: Context, msg: Message) {
        if msg.content == "!ping" {
            if let Err(why) = msg.channel_id.say(&ctx.http, "Pong!").await {
                println!("Error sending message: {why:?}");
            }
        }
    }
}

#[tokio::main]
async fn main() {
    // Load all variables from a local environment variable file
    dotenv().expect("Expected a .env file to be created");

    // Login with a bot token from the environment
    let token = env::var("DISCORD_TOKEN").expect("Expected a token in the environment");

    // Set gateway intents, which decides what events the bot will be notified about
    let intents = GatewayIntents::GUILD_MESSAGES
        | GatewayIntents::DIRECT_MESSAGES
        | GatewayIntents::MESSAGE_CONTENT;

    // Create a new instance of the Client, logging in as a bot.
    let mut client = Client::builder(&token, intents)
        .event_handler(Handler)
        .await
        .expect("Err creating client");

    println!("Starting bot");

    // Start listening for events by starting a single shard
    if let Err(why) = client.start().await {
        println!("Client error: {why:?}");
    }
}

Next, you'll need to copy your Discord bot token into a file named .env. This file should be located in the same place as the src folder, NOT inside of it.

The environment file should contain your token:

DISCORD_TOKEN=your_discord_bot_token

Finally, you are now ready to run your bot locally to test it out!

cargo run

The run command will build and run your bot locally. Remember, Rust is a compiled language. This means that your bot must be compiled before it can be run, this can take around a minute.

lucas@fozziebear:~/heliohost/ping-pong-rs$ cargo run
   Compiling proc-macro2 v1.0.106
   Compiling quote v1.0.44
   .
   .
   .
   Compiling hyper-rustls v0.27.7
   Compiling reqwest v0.12.28
   Compiling ping-pong-rs v0.1.0 (/home/lucas/heliohost/ping-pong-rs)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 41.00s
     Running `target/debug/ping-pong-rs`
Starting bot

You should see the message Starting bot at the end if everything compiled successfully.

Once your project is up and running, return to Discord and type !ping in the channel your bot is located in and see it return your message!

Building your Discord Bot for HelioHost

What to expect in this section:

1. How to build the correct file to work in HelioHost

Rust applications must be built to run on the machine that you want to run your application on. In simple terms, this means that to run a Rust Discord bot on HelioHost, you should build a Linux x86_64 application.

For users that are writing code on a Windows machine (this does not include WSL2), or a MacOS machine, you will need to cross compile to the correct architecture.

Building a release binary on the same architecture and host

If you are on a system that matches the HelioHost machines (Linux x86_64), then you do not need to cross compile. Simply running a normal release build is enough.

cargo build --release

This will build the final file under target/release/ping-pong-rs.

Building a release binary on a different host

If you are on a system that does not match the HelioHost machines (Linux x86_64), then you do not need to cross compile. This includes Windows, MacOS, or Linux ARM machines.

The most straightforward way to do this is by using cross] to build your application inside of a Docker container.

To get started, install Docker. This is most commonly done by installing Docker Desktop for those using Windows or MacOS.

Once you have Docker installed and running, install cross by using Cargo.

cargo install cross --git https://github.com/cross-rs/cross

After cross has completed building and installing, create a release build for the Linux x86_64 architecture using the tool.

cross build --target x86_64-unknown-linux-gnu --release

This will build the final file under target/x86_64-unknown-linux-gnu/release/ping-pong-rs.