rust - How can I read one character from stdin without having to hit enter?

Question

I want to run an executable that blocks on stdin and when a key is pressed that same character is printed immediately without Enter having to be pressed.

How can I read one character from stdin without having to hit Enter? I started with this example:

fn main() {
    println!("Type something!");

    let mut line = String::new();
    let input = std::io::stdin().read_line(&mut line).expect("Failed to read line");

    println!("{}", input);
}

I looked through the API and tried replacing read_line() with bytes(), but everything I try requires me to hit Enter before read occurs.

This question was asked for C/C++, but there seems to be no standard way to do it: Capture characters from standard input without waiting for enter to be pressed

It might not be doable in Rust considering it's not simple in C/C++.

Answer 1

While @Jon's solution using ncurses works, ncurses clears the screen by design. I came up with this solution that uses the termios crate for my little project to learn Rust. The idea is to modify ECHO and ICANON flags by accessing tcsetattr through termios bindings.

extern crate termios;
use std::io;
use std::io::Read;
use std::io::Write;
use termios::{Termios, TCSANOW, ECHO, ICANON, tcsetattr};

fn main() {
    let stdin = 0; // couldn't get std::os::unix::io::FromRawFd to work 
                   // on /dev/stdin or /dev/tty
    let termios = Termios::from_fd(stdin).unwrap();
    let mut new_termios = termios.clone();  // make a mutable copy of termios 
                                            // that we will modify
    new_termios.c_lflag &= !(ICANON | ECHO); // no echo and canonical mode
    tcsetattr(stdin, TCSANOW, &mut new_termios).unwrap();
    let stdout = io::stdout();
    let mut reader = io::stdin();
    let mut buffer = [0;1];  // read exactly one byte
    print!("Hit a key! ");
    stdout.lock().flush().unwrap();
    reader.read_exact(&mut buffer).unwrap();
    println!("You have hit: {:?}", buffer);
    tcsetattr(stdin, TCSANOW, & termios).unwrap();  // reset the stdin to 
                                                    // original termios data
}

One advantage of reading a single byte is capturing arrow keys, ctrl etc. Extended F-keys are not captured (although ncurses can capture these).

This solution is intended for UNIX-like platforms. I have no experience with Windows, but according to this forum perhaps something similar can be achieved using SetConsoleMode in Windows.