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//! Asynchronous DNS resolver
#![macro_use]
pub use self::resolver::{DnsResolve, DnsResolver};
#[cfg(feature = "hickory-dns")]
mod hickory_dns_resolver;
mod resolver;
/// Helper macro for resolving host and then process each addresses
#[macro_export]
macro_rules! lookup_then {
($context:expr_2021, $addr:expr_2021, $port:expr_2021, |$resolved_addr:ident| $body:block) => {{
use std::net::SocketAddr;
let ipv6_first = $context.ipv6_first();
let mut v4_addrs = Vec::new();
let mut v6_addrs = Vec::new();
for addr in $context.dns_resolve($addr, $port).await? {
match addr {
SocketAddr::V4(..) => v4_addrs.push(addr),
SocketAddr::V6(..) => v6_addrs.push(addr),
}
}
let has_v4 = !v4_addrs.is_empty();
let has_v6 = !v6_addrs.is_empty();
assert!(has_v4 || has_v6, "resolved empty address");
if !has_v4 && has_v6 {
lookup_then!(RESOLVE @ v6_addrs, $resolved_addr, $body)
} else if has_v4 && !has_v6 {
lookup_then!(RESOLVE @ v4_addrs, $resolved_addr, $body)
} else {
if ipv6_first {
match lookup_then!(RESOLVE @ v6_addrs, $resolved_addr, $body) {
Ok(r) => Ok(r),
Err(_v6_err) => lookup_then!(RESOLVE @ v4_addrs, $resolved_addr, $body),
}
} else {
match lookup_then!(RESOLVE @ v4_addrs, $resolved_addr, $body) {
Ok(r) => Ok(r),
Err(_v4_err) => lookup_then!(RESOLVE @ v6_addrs, $resolved_addr, $body),
}
}
}
}};
(RESOLVE @ $addrs:expr_2021, $resolved_addr:ident, $body:block) => {{
let mut result = None;
for $resolved_addr in $addrs {
match $body {
Ok(r) => {
result = Some(Ok(($resolved_addr, r)));
break;
}
Err(err) => {
result = Some(Err(err));
}
}
}
result.expect("resolved empty address")
}};
}
#[macro_export]
macro_rules! lookup_then_connect {
($context:expr_2021, $addr:expr_2021, $port:expr_2021, |$resolved_addr:ident| $body:block) => {{
use futures::future::{self, Either};
use log::trace;
use std::{net::SocketAddr, time::Duration};
use tokio::time;
let ipv6_first = $context.ipv6_first();
let mut v4_addrs = Vec::new();
let mut v6_addrs = Vec::new();
for addr in $context.dns_resolve($addr, $port).await? {
match addr {
SocketAddr::V4(..) => v4_addrs.push(addr),
SocketAddr::V6(..) => v6_addrs.push(addr),
}
}
let has_v4 = !v4_addrs.is_empty();
let has_v6 = !v6_addrs.is_empty();
assert!(has_v4 || has_v6, "resolved empty address");
// Happy Eyeballs, RFC6555, RFC8305
//
// RFC6555 gives an example that Chrome and Firefox uses 300ms
const FIXED_DELAY: Duration = Duration::from_millis(300);
// Connects every addresses synchronously.
// TODO: Try another address after FIXED_DELAY if one of the IPs is unreachable.
//
// This would require `future::select_ok`, which will require futures to be `Unpin`
// (boxed future, excessive memory allocation).
let connect_v4 = async {
// use futures::FutureExt;
//
// let mut vfut = Vec::new();
//
// let mut delay = Duration::from_millis(0);
//
// for $resolved_addr in v4_addrs {
// vfut.push(
// async move {
// if delay != Duration::from_millis(0) {
// time::sleep(delay).await;
// }
//
// trace!("trying connect {}:{} {}", $addr, $port, $resolved_addr);
//
// match $body {
// Ok(r) => Ok(($resolved_addr, r)),
// Err(err) => Err(err),
// }
// }
// .boxed(),
// );
//
// delay += FIXED_DELAY;
// }
//
// match future::select_ok(vfut).await {
// Ok((r, _)) => Ok(r),
// Err(err) => Err(err),
// }
let mut result = None;
for $resolved_addr in v4_addrs {
trace!("trying connect {}:{} {}", $addr, $port, $resolved_addr);
match $body {
Ok(r) => {
trace!("connected {}:{} {}", $addr, $port, $resolved_addr);
result = Some(Ok(($resolved_addr, r)));
break;
}
Err(err) => {
result = Some(Err(err));
}
}
}
result.expect("impossible")
};
let connect_v6 = async {
let mut result = None;
for $resolved_addr in v6_addrs {
trace!("trying connect {}:{} {}", $addr, $port, $resolved_addr);
match $body {
Ok(r) => {
trace!("connected {}:{} {}", $addr, $port, $resolved_addr);
result = Some(Ok(($resolved_addr, r)));
break;
}
Err(err) => {
result = Some(Err(err));
}
}
}
result.expect("impossible")
};
if has_v4 && !has_v6 {
connect_v4.await
} else if !has_v4 && has_v6 {
connect_v6.await
} else {
if ipv6_first {
let v4_fut = async move {
time::sleep(FIXED_DELAY).await;
connect_v4.await
};
let v6_fut = connect_v6;
tokio::pin!(v4_fut);
tokio::pin!(v6_fut);
match future::select(v4_fut, v6_fut).await {
Either::Left((v4_res, v6_fut)) => match v4_res {
Ok(res) => Ok(res),
Err(_v4_err) => v6_fut.await,
},
Either::Right((v6_res, v4_fut)) => match v6_res {
Ok(res) => Ok(res),
Err(_v6_err) => v4_fut.await,
},
}
} else {
let v6_fut = async move {
time::sleep(FIXED_DELAY).await;
connect_v6.await
};
let v4_fut = connect_v4;
tokio::pin!(v4_fut);
tokio::pin!(v6_fut);
match future::select(v4_fut, v6_fut).await {
Either::Left((v4_res, v6_fut)) => match v4_res {
Ok(res) => Ok(res),
Err(_v4_err) => v6_fut.await,
},
Either::Right((v6_res, v4_fut)) => match v6_res {
Ok(res) => Ok(res),
Err(_v6_err) => v4_fut.await,
},
}
}
}
}};
}