You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/serenity/examples/e01_basic_ping_bot/src
    
    the code of the file until where you have to start completion: use std::env;

use serenity::async_trait;
use serenity::model::channel::Message;
use serenity::model::gateway::Ready;
use serenity::prelude::*;

struct Handler;

#[async_trait]
impl EventHandler for Handler {
    // Set a handler for the `message` event. This is called whenever a new message is received.
    //
    // Event handlers are dispatched through a threadpool, and so multiple events can be
    // dispatched simultaneously.
    async fn message(&self, ctx: Context, msg: Message) {
        if msg.content == "!ping" {
            // Sending a message can fail, due to a network error, an authe
    
async fn main() {
    // Configure the client with your Discord bot token in 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. This will automatically prepend
    // your bot token with "Bot ", which is a requirement by Discord for bot users.
    let mut client =
        Client::builder(&token, intents).event_handler(Handler).await.expect("Err creating client");

    // Finally, start a single shard, and start listening to events.
    //
    // Shards will automatically attempt to reconnect, and will perform exponential backoff until
    // it reconnects.
    if let Err(why) = client.start().await {
        println!("Client error: {why:?}");
    }
}