Is there a standard way of discarding input in Rust?

Question

Reading input from stdin in Rust is pretty straightforward:

use std::io;

let mut some_string = String::new();
let _ = io::stdin().read_line(&mut some_string);

but sometimes you might want to just discard it without acknowledging it anywhere or procuring a buffer, like:

println!("Press Enter to close");
io::stdin().discard_input(); // discard_input() doesn't exist

It could read any number of characters until encountering \n, ignore it all and return nothing or io::Result. Is there a standard way of doing it or do I have to implement it myself? I traced the implementation of read_line to read_until implemented by BufRead, but I'm not sure if it's a good idea to start from there.

Answer 1

You can implement .discard_until_newline() on stdin for example like this:

This should be a correct and efficient implementation (using a buffer to read, but not copying the read parts anywhere). It could be much simpler if you don't anticipate any long lines and just read a byte at a time, of course.

use std::io::Stdin;
use std::io;
use std::io::prelude::*;

pub trait DiscardUntil {
    fn discard_until_newline(&mut self) -> Result<(), io::Error>;
}

impl DiscardUntil for Stdin {
    fn discard_until_newline(&mut self) -> Result<(), io::Error> {
        let mut buffered = self.lock();
        loop {
            let (consume, done) = {
                let data = try!(buffered.fill_buf());
                if data.is_empty() {
                    (0, true)
                } else if let Some(newline_pos) = data.iter().position(|b| *b == b'\n') {
                    (newline_pos + 1, true)
                } else {
                    (data.len(), false)
                }
            };
            buffered.consume(consume);
            if done {
                break;
            }
        }
        Ok(())
    }
}

fn main() {
    println!("hi");
    io::stdin().discard_until_newline().unwrap();
    println!("again");
    io::stdin().discard_until_newline().unwrap();
    println!("goodbye");
}