zookeeper "ruok" client, which properly reports errors, including the server address on connect.

ruok.rs

use std::io::prelude::*;
use std::net::TcpStream;

fn main() {
    let address = "192.168.0.109:9983";
    let mut stream = match TcpStream::connect(address) {
        Ok(s) => s,
        Err(e) => panic!("Cannot connect to {}: {}", address, e)
    };
    stream.write("ruok".as_bytes()).ok().expect("write failed");
    let mut buf = String::new();
    stream.read_to_string(&mut buf).ok().expect("read failed");
    println!("{}", buf);
}

This can hang up to a minute if the target is unreachable.
See http://stackoverflow.com/questions/30022084/how-do-i-set-connect-timeout-on-tcpstream