如何在 Rust 中广播 UDP 数据报并接收响应？

Question

我正在尝试在 Rust 中实现 VXI11 协议（与示波器、电源等仪器进行通信），并且我成功发送了广播 UDP 消息，但没有收到响应。这是我用来设置 UDP 套接字的代码：

    let socket:UdpSocket = UdpSocket::bind("0.0.0.0:0")?;
    socket.set_read_timeout(Some(Duration::new(5, 0)))?;
    socket.set_broadcast(true)?;
    socket.connect(("255.255.255.255", port))?;
    println!("Connected on port {}", port);
    println!("Broadcast: {:?}", socket.broadcast());
    println!("Timeout: {:?}", socket.read_timeout());

我还在绑定调用中尝试过“255.255.255.255:0”和“192.168.2.255:0”，但没有成功。这是我用来接收响应的代码。

    let call:Vec<u8> = self.packer.get_buf()?;
    println!("Sending call, {} bytes", call.len());
    match self.socket.send(&call) {
        Ok(n) => {
            if n != call.len() {
                return Err(Error::new(ErrorKind::Other, "Sent the wrong number of bytes"))
            }
            else {
                // Do nothing because we sent the number of bytes we expected to send
            }
        },
        Err(e) => return Err(e),
    }

    println!("Awaiting responses...");   // self.recv_buff is a [u8; 8092]
    while let Ok((n, addr)) = self.socket.recv_from(&mut self.recv_buff) {
        println!("{} bytes response from {:?}", n, addr);
        // Remaining code not directly relevant to the question
    }

这是 STDOUT 输出：

Connected on port 111
Broadcast: Ok(true)
Timeout: Ok(Some(5s))
Sending call, 56 bytes
Awaiting responses...

我还知道远程主机正在响应，因为我可以在 tcpdump 中看到它。然而，Rust 代码只是没有收到响应。任何人都知道为什么会这样？

$ sudo tcpdump 'udp port 111'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on wlo1, link-type EN10MB (Ethernet), capture size 262144 bytes
11:00:54.094534 IP deathStar.51499 > 255.255.255.255.sunrpc: UDP, length 56
11:00:54.100199 IP 192.168.2.4.sunrpc > deathStar.51499: UDP, length 28
11:00:54.100755 IP 192.168.2.3.sunrpc > deathStar.51499: UDP, length 28

Answer 1

TL;DR删除UdpSocket::connect呼叫，然后重试。然后它就会起作用。

看起来这UdpSocket::connect是根本原因。根据文档，UdpSocket::connect如果套接字必须处理来自具体远程地址的数据，则应使用。如果不知道远程地址，那么您可以connect完全避免呼叫。如果没有connect调用，套接字将从任何远程地址接收数据。

let socket:UdpSocket = UdpSocket::bind("0.0.0.0:0")?;
socket.set_read_timeout(Some(Duration::new(5, 0)))?;
socket.set_broadcast(true)?;
println!("Connected on port {}", port);
println!("Broadcast: {:?}", socket.broadcast());
println!("Timeout: {:?}", socket.read_timeout());

let call:Vec<u8> = self.packer.get_buf()?;
println!("Sending call, {} bytes", call.len());
match self.socket.send(&call) {
    Ok(n) => {
        if n != call.len() {
            return Err(Error::new(ErrorKind::Other, "Sent the wrong number of bytes"))
        }
        else {
            // Do nothing because we sent the number of bytes we expected to send
        }
    },
    Err(e) => return Err(e),
}

println!("Awaiting responses...");   // self.recv_buff is a [u8; 8092]
while let Ok((n, addr)) = self.socket.recv_from(&mut self.recv_buff) {
    println!("{} bytes response from {:?}", n, addr);
    // Remaining code not directly relevant to the question
}