tokio/tokio-tcp/tests/tcp_peek.rs

#![deny(warnings, rust_2018_idioms)]
#![feature(async_await)]

use std::thread;
use std::{convert::TryInto, io::Write, net};
use tokio::io::AsyncReadExt;
use tokio::net::TcpStream;
use tokio_test::assert_ok;

#[tokio::test]
async fn peek() {
    let listener = net::TcpListener::bind("127.0.0.1:0").unwrap();
    let addr = listener.local_addr().unwrap();
    let t = thread::spawn(move || assert_ok!(listener.accept()).0);

    let left = net::TcpStream::connect(&addr).unwrap();
    let mut right = t.join().unwrap();
    right.write(&[1, 2, 3, 4]).unwrap();

    let mut left: TcpStream = left.try_into().unwrap();
    let mut buf = [0u8; 16];
    let n = assert_ok!(left.peek(&mut buf).await);
    assert_eq!([1, 2, 3, 4], buf[..n]);

    let n = assert_ok!(left.read(&mut buf).await);
    assert_eq!([1, 2, 3, 4], buf[..n]);
}