read_password.rs

use std::borrow::Cow::{self, Borrowed, Owned};

use rustyline::config::Configurer;
use rustyline::highlight::{CmdKind, Highlighter};
use rustyline::{ColorMode, Editor, Result};
use rustyline::{Completer, Helper, Hinter, Validator};

#[derive(Completer, Helper, Hinter, Validator)]
struct MaskingHighlighter {
    masking: bool,
}

impl Highlighter for MaskingHighlighter {
    fn highlight<'l>(&self, line: &'l str, _pos: usize) -> Cow<'l, str> {
        use unicode_width::UnicodeWidthStr;
        if self.masking {
            Owned(" ".repeat(line.width()))
        } else {
            Borrowed(line)
        }
    }

    fn highlight_char(&self, _line: &str, _pos: usize, kind: CmdKind) -> bool {
        match kind {
            CmdKind::MoveCursor => false,
            _ => self.masking,
        }
    }
}

fn main() -> Result<()> {
    env_logger::init();
    println!("This is just a hack. Reading passwords securely requires more than that.");
    let h = MaskingHighlighter { masking: false };
    let mut rl = Editor::new()?;
    rl.set_helper(Some(h));

    let username = rl.readline("Username:")?;
    println!("Username: {username}");

    rl.helper_mut().expect("No helper").masking = true;
    rl.set_color_mode(ColorMode::Forced); // force masking
    rl.set_auto_add_history(false); // make sure password is not added to history
    let mut guard = rl.set_cursor_visibility(false)?;
    let passwd = rl.readline("Password:")?;
    guard.take();
    println!("Secret: {passwd}");
    Ok(())
}