networking - 确定数据是否在 TcpStream 上可用

Question

我有一个 std::net::TcpStream。我想确定是否有数据可供读取而无需实际读取。

我能在 TcpStream 上找到的唯一相关 API 是 read

does not provide any guarantees about whether it blocks waiting for data

对于这个问题，这听起来并不令人鼓舞。

A related question似乎下降到文件描述符和 read(2) 以强制进行非阻塞读取。但是，我无法弄清楚如何使用 read(2) 在不实际阅读的情况下查看 fd。

我想这是 select(2) 的工作，但是为 C 参数构造 fd_set 似乎相当棘手。肯定没有 Rust 类型，而且还不清楚我将如何发明一个。

Answer 1

I suppose this is a job for select(2), but constructing the fd_sets for the C arguments seems rather hairy.

我想 poll(2) 应该更方便。例如:

#![feature(std_misc, net, libc, os, io)]

extern crate libc;
use libc::{c_int, c_uint, c_short};
use std::thread::spawn;
use std::net::{TcpListener, TcpStream};
use std::os;
use std::io::Read;
use std::os::unix::AsRawFd;

#[repr(C)]
struct pollfd {
    fd: c_int,
    events: c_short,
    revents: c_short,
}

extern { fn poll(fds: *mut pollfd, nfds: c_uint, timeout: c_int) -> c_int; }

const POLLIN: c_short = 1;

fn handle_client(mut stream: TcpStream) {
    let mut fdset = pollfd { fd: stream.as_raw_fd(), events: POLLIN, revents: 0, };
    loop {
        match unsafe { poll(&mut fdset as *mut _, 1, -1) } {
            ret if ret < 0 => panic!("poll error: {}", os::last_os_error()),
            ret if ret > 0 && fdset.events == fdset.revents => {
                let mut byte: &mut [u8] = &mut [0];
                match stream.read(&mut byte).unwrap() {
                    0 => break,
                    1 => println!("A byte read: {}", byte[0]),
                    _ => unreachable!(),
                }
            },
            _ => break,
        }
    }
}

fn main() {
    let listener = TcpListener::bind("127.0.0.1:9999").unwrap();
    for stream in listener.incoming() {
        match stream {
            Ok(stream) => { spawn(move || handle_client(stream)); },
            Err(e) => panic!("connection error: {}", e),
        }
    }
}