Get current tabstop

tabstop.rs

use std::io;

mod term {
    use termios;

    /// echo off. Return old termios state.
    pub fn echo_off() -> termios::Termios {
        let oldstat = termios::Termios::from_fd(0).unwrap();
        let mut termstat = oldstat;
        termstat.c_lflag &= !(termios::ICANON | termios::ECHO);
        termios::tcsetattr(0, termios::TCSANOW, &termstat).unwrap();
        oldstat
    }

    /// echo on. Pass old termios state.
    pub fn echo_on(termstat: &termios::Termios) {
        termios::tcsetattr(0, termios::TCSANOW, &termstat).unwrap();
    }
}

mod csi {
    use std::io::{self, Read, Write};

    // avoid zero
    fn _nz(n: u32) -> u32 {
        if n == 0 {
            1
        } else {
            n
        }
    }

    /// CHA: cursor horizontal absolute
    pub fn cha(w: &mut Write, n: u32) {
        write!(w, "{}", format!("\x1b[{}G", _nz(n))).unwrap();
    }

    /// DSR: device status report
    /// return (row, col)
    pub fn dsr(w: &mut Write) -> Option<(u32, u32)> {
        let oldstat: Box<termios::Termios> = Box::new(super::term::echo_off());
        write!(w, "\x1b[6n").unwrap();;
        w.flush().unwrap();
        let (mut row, mut col, mut tmp) = (0u32, 0u32, 0u32);
        let s = io::stdin();
        // => "[${row};${col}R"
        for b in s.lock().bytes().filter_map(|v| v.ok()) {
            match b {
                // '0' ... '9'
                0x30...0x39 => {
                    tmp = tmp * 10 + u32::from(b - 0x30);
                }
                // ';'
                0x3b => {
                    row = tmp;
                    tmp = 0;
                }
                // 'R'
                0x52 => {
                    col = tmp;
                    break;
                }
                _ => {}
            }
        }
        super::term::echo_on(&*oldstat);
        Some((row, col))
    }
}

// print current tabstop
fn main() {
    let mut w = io::stdout();
    csi::cha(&mut w, 1);
    let base = csi::dsr(&mut w).unwrap().1;
    print!("\t");
    let tab = csi::dsr(&mut w).unwrap().1;
    csi::cha(&mut w, 1);
    println!("tabstop={}", tab - base);
}

$ tabs 2
$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tabstop`
tabstop=2
$ tabs 4
$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tabstop`
tabstop=4
$ tabs 8
$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tabstop`
tabstop=8
$ tabs 16
$ cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/tabstop`
tabstop=16