minicrossterm/docs/mdbook/src/input.md

Crossterm provides a way to work with the terminal input. We will not cover the basic usage but instead asynchronous and synchronous reading of input. Please check out these examples for reading a line or a character from the user.

Differences Synchronous and Asynchronous

Crossterm provides two ways to read user input, synchronous and asynchronous.

Synchronous reading

Read the input synchronously from the user, the reads performed will be blocking calls. Using synchronous over asynchronous reading has the benefit that it is using fewer resources than the asynchronous because background thread and queues are left away.

You can get an synchronous event reader by calling: TerminalInput::read_sync.

Asynchronous reading

Read the input asynchronously, input events are gathered on the background and will be queued for you to read. Using asynchronous reading has the benefit that input events are queued until you read them. You can poll for occurred events, and the reads won't block your program.

You can get an synchronous event reader by calling: TerminalInput::read_async, TerminalInput::read_async_until.

Technical details

On UNIX systems crossterm reads from the TTY, on Windows, it uses ReadConsoleInputW. For asynchronous reading, a background thread will be fired up to read input events, occurred events will be queued on an MPSC-channel, and the user can iterate over those events.

The terminal has to be in raw mode, raw mode prevents the input of the user to be displayed on the terminal screen, see screen for more info.

Example

In the following example, we will create a small program that will listen for mouse and keyboard input. On the press of the 'escape' key, the program will be stopped.

So let's start by setting up the basics.

use std::{thread, time::Duration};
use crossterm::{input, InputEvent, KeyEvent};

fn main() {
    println!("Press 'ESC' to quit.");

    /* next code here */
}

Next, we need to put the terminal into raw mode. We do this because we don't want the user input to be printed to the terminal screen.

// enable raw mode
let screen = RawScreen::into_raw_mode();

// create a input from our screen
let input = input();

/* next code here */

Now that we constructed a TerminalInput instance we can go ahead an start the reading. Do this by calling input.read_async(), which returns an AsyncReader. This is an iterator over the input events that you could as any other iterator.

let mut async_stdin = input.read_async();

loop {
    if let Some(key_event) = async_stdin.next() {
        /* next code here */
    }
    thread::sleep(Duration::from_millis(50));
}

The AsyncReader iterator will return None when nothing is there to read, Some(InputEvent) if there are events to read. I use a thread delay to prevent spamming the iterator.

Next up we can start pattern matching to see if there are input events we'd like to catch. In our case, we want to catch the Escape Key.

 match key_event {
    InputEvent::Keyboard(event) => match event {
        KeyEvent::Esc => {
            println!("Program closing ...");
            break
        }
        _ => println!("Key {:?} was pressed!", event)
    }
    InputEvent::Mouse(event) => { /* Mouse Event */ }
    _ => { }
}

As you see, we check if the KeyEvent::Esc was pressed, if that's true we stop the program by breaking out of the loop.

final code

use std::{thread, time::Duration};
use crossterm::{input, InputEvent, KeyEvent};

fn main() {
    println!("Press 'ESC' to quit.");

    // enable raw mode
    let screen = RawScreen::into_raw_mode();

    // create a input from our screen.
    let input = input();

    // create async reader
    let mut async_stdin = input.read_async();

    loop {
        // try to get the next input event.
        if let Some(key_event) = async_stdin.next() {
            match key_event {
                InputEvent::Keyboard(event) => match event {
                    KeyEvent::Esc => {
                        println!("Program closing ...");
                        break
                    }
                    _ => println!("Key {:?} was pressed!", event)
                }
                InputEvent::Mouse(event) => { /* Mouse Event */ }
                _ => { }
            }
        }
        thread::sleep(Duration::from_millis(50));
    }
} // <=== background reader will be disposed when dropped.s

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More robust and complete examples on all input aspects like mouse, keys could be found here.