Async Counter App

In the previous counter app, we had a purely sequential blocking application. There are times when you may be interested in running IO operations or compute asynchronously.

For this tutorial, we will build a single file version of an async TUI using tokio. This tutorial section is a simplified version of the ratatui-async-template project.

Installation

Here’s an example of the Cargo.toml file required for this tutorial:

[package]
name = "ratatui-counter-async-app"
version = "0.1.0"
edition = "2021"

[dependencies]
color-eyre = "0.6.2"
crossterm = { version = "0.27.0", features = ["event-stream"] }
ratatui = "0.24.0"
tokio = { version = "1.32.0", features = ["full"] }
tokio-util = "0.7.9"
futures = "0.3.28"

cargo add ratatui crossterm color-eyre tokio tokio-util futures --features tokio/full,crossterm/event-stream

Setup

Let’s take the single file multiple function example from the counter app from earlier:

// Hover on this codeblock and click "Show hidden lines" in the top right to see the full code
use color_eyre::eyre::Result;
use crossterm::{
  event::{self, Event::Key, KeyCode::Char},
  execute,
  terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use ratatui::{
  prelude::{CrosstermBackend, Terminal},
  widgets::Paragraph,
};

pub type Frame<'a> = ratatui::Frame<'a, CrosstermBackend<std::io::Stderr>>;

fn startup() -> Result<()> {
  enable_raw_mode()?;
  execute!(std::io::stderr(), EnterAlternateScreen)?;
  Ok(())
}

fn shutdown() -> Result<()> {
  execute!(std::io::stderr(), LeaveAlternateScreen)?;
  disable_raw_mode()?;
  Ok(())
}

// App state
struct App {
  counter: i64,
  should_quit: bool,
}

// App ui render function
fn ui(app: &App, f: &mut Frame<'_>) {
  f.render_widget(Paragraph::new(format!("Counter: {}", app.counter)), f.size());
}

// App update function
fn update(app: &mut App) -> Result<()> {
  if event::poll(std::time::Duration::from_millis(250))? {
    if let Key(key) = event::read()? {
      if key.kind == event::KeyEventKind::Press {
        match key.code {
          Char('j') => app.counter += 1,
          Char('k') => app.counter -= 1,
          Char('q') => app.should_quit = true,
          _ => {},
        }
      }
    }
  }
  Ok(())
}

fn run() -> Result<()> {
  // ratatui terminal
  let mut t = Terminal::new(CrosstermBackend::new(std::io::stderr()))?;

  // application state
  let mut app = App { counter: 0, should_quit: false };

  loop {
    // application update
    update(&mut app)?;

    // application render
    t.draw(|f| {
      ui(&app, f);
    })?;

    // application exit
    if app.should_quit {
      break;
    }
  }

  Ok(())
}

fn main() -> Result<()> {
  // setup terminal
  startup()?;

  let result = run();

  // teardown terminal before unwrapping Result of app run
  shutdown()?;

  result?;

  Ok(())
}

Tokio is an asynchronous runtime for the Rust programming language. It provides the building blocks needed for writing network applications. We recommend you read the Tokio documentation to learn more.

For the setup for this section of the tutorial, we are going to make just one change. We are going to make our main function a tokio entry point.

// Hover on this codeblock and click "Show hidden lines" in the top right to see the full code
use color_eyre::eyre::Result;
use crossterm::{
  event::{self, Event::Key, KeyCode::Char},
  execute,
  terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen},
};
use ratatui::{
  prelude::{CrosstermBackend, Terminal},
  widgets::Paragraph,
};

pub type Frame<'a> = ratatui::Frame<'a, CrosstermBackend<std::io::Stderr>>;

fn startup() -> Result<()> {
  enable_raw_mode()?;
  execute!(std::io::stderr(), EnterAlternateScreen)?;
  Ok(())
}

fn shutdown() -> Result<()> {
  execute!(std::io::stderr(), LeaveAlternateScreen)?;
  disable_raw_mode()?;
  Ok(())
}

// App state
struct App {
  counter: i64,
  should_quit: bool,
}

// App ui render function
fn ui(app: &App, f: &mut Frame<'_>) {
  f.render_widget(Paragraph::new(format!("Counter: {}", app.counter)), f.size());
}

// App update function
fn update(app: &mut App) -> Result<()> {
  if event::poll(std::time::Duration::from_millis(250))? {
    if let Key(key) = event::read()? {
      if key.kind == event::KeyEventKind::Press {
        match key.code {
          Char('j') => app.counter += 1,
          Char('k') => app.counter -= 1,
          Char('q') => app.should_quit = true,
          _ => {},
        }
      }
    }
  }
  Ok(())
}

fn run() -> Result<()> {
  // ratatui terminal
  let mut t = Terminal::new(CrosstermBackend::new(std::io::stderr()))?;

  // application state
  let mut app = App { counter: 0, should_quit: false };

  loop {
    // application update
    update(&mut app)?;

    // application render
    t.draw(|f| {
      ui(&app, f);
    })?;

    // application exit
    if app.should_quit {
      break;
    }
  }

  Ok(())
}

#[tokio::main]
async fn main() -> Result<()> {
  // setup terminal
  startup()?;

  let result = run();

  // teardown terminal before unwrapping Result of app run
  shutdown()?;

  result?;

  Ok(())
}

Adding this #[tokio::main] macro allows us to spawn tokio tasks within main. At the moment, there are no async functions other than main and we are not using .await anywhere yet. We will change that in the following sections. But first, we let us introduce the Action enum.