1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
use std::future::Future;
use std::net::{SocketAddr, SocketAddrV4, SocketAddrV6};
use std::time::Duration;
use tokio::io;
use tokio::net::{lookup_host, TcpStream, ToSocketAddrs};
fn partition<T: Iterator<Item = SocketAddr>>(
ips: T,
) -> (
impl Iterator<Item = SocketAddrV6>,
impl Iterator<Item = SocketAddrV4>,
) {
let (six, four): (Vec<SocketAddr>, Vec<SocketAddr>) =
ips.partition(|addr| matches!(addr, SocketAddr::V6(_)));
let six = six.into_iter().filter_map(|addr| match addr {
SocketAddr::V6(six) => Some(six),
SocketAddr::V4(_) => None,
});
let four = four.into_iter().filter_map(|addr| match addr {
SocketAddr::V4(four) => Some(four),
SocketAddr::V6(_) => None,
});
(six, four)
}
async fn connect_higher<I, F, T, L>(addr: T, lookup: L) -> io::Result<TcpStream>
where
I: Iterator<Item = SocketAddr>,
F: Future<Output = io::Result<I>>,
L: FnOnce(T) -> F,
{
let ips: I = lookup(addr).await?;
let (mut six, mut four) = partition(ips);
let (six, four) = match (six.next(), four.next()) {
(None, Some(addr)) => {
println!("only v4 address returned");
return TcpStream::connect(addr).await;
}
(Some(addr), None) => {
println!("only v6 address returned");
return TcpStream::connect(addr).await;
}
(Some(six), Some(four)) => (six, four),
(None, None) => return Err(io::ErrorKind::NotFound.into()),
};
let connect_six = TcpStream::connect(six);
tokio::pin!(connect_six);
let timeout = tokio::time::timeout(Duration::from_millis(250), &mut connect_six);
let err = match timeout.await {
Ok(Ok(stream)) => return Ok(stream),
Ok(Err(e)) => Some(e),
Err(_elapsed) => None,
};
tokio::select! {
biased;
stream = TcpStream::connect(four) => {
println!("successfully connected to v4");
return stream;
}
Ok(stream) = &mut connect_six, if err.is_none() => {
return Ok(stream);
}
}
}
pub async fn connect<T: ToSocketAddrs>(addr: T) -> io::Result<TcpStream> {
connect_higher(addr, lookup_host).await
}
#[cfg(test)]
mod tests {
use std::error::Error;
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio::net::TcpListener;
use super::*;
async fn echo(mut stream: TcpStream) -> io::Result<()> {
let mut buf = vec![0; 256].into_boxed_slice();
loop {
let n = stream.read(&mut buf[..]).await?;
stream.write_all(&buf[..n]).await?;
}
}
async fn server(listener: TcpListener) -> io::Result<()> {
loop {
let (stream, _) = listener.accept().await?;
tokio::spawn(echo(stream));
}
}
#[tokio::test]
async fn it_works() -> Result<(), Box<dyn Error + Send + Sync + 'static>> {
let (mut six, mut four) = lookup_host("localhost:80").await.map(partition)?;
if six.next().is_none() || four.next().is_none() {
Err("Both IPv6 and IPv4 need to be enabled on loopback interface")?
}
let listener_four = TcpListener::bind("127.0.0.1:0").await?;
let port = listener_four.local_addr()?.port();
let listener_six = TcpListener::bind(format!("[::1]:{}", port)).await?;
tokio::spawn(server(listener_four));
tokio::spawn(server(listener_six));
let mut stream = connect(format!("localhost:{}", port)).await?;
let expected = b"hallo";
stream.write_all(expected).await?;
let mut buf = vec![0; expected.len()].into_boxed_slice();
let n = stream.read_exact(&mut buf[..expected.len()]).await?;
assert_eq!(expected.len(), n);
assert_eq!(expected, &buf[..n]);
Ok(())
}
}