feat(dns): Add flag to specify if we should prefer IPv4 over IPv6

src/dns.rs

@@ -15,10 +15,11 @@ use std::time::Duration;
 use tokio::net::{TcpStream, UdpSocket};
 use url::{Host, Url};
 
-// Interweave v4 and v6 addresses as per RFC8305.
+// Interleave v4 and v6 addresses as per RFC8305.
 // The first address is v6 if we have any v6 addresses.
-pub fn sort_socket_addrs(socket_addrs: &[SocketAddr]) -> impl Iterator<Item = &'_ SocketAddr> {
+#[inline]
-    let mut pick_v6 = false;
+fn sort_socket_addrs(socket_addrs: &[SocketAddr], prefer_ipv6: bool) -> impl Iterator<Item = &'_ SocketAddr> {
+    let mut pick_v6 = !prefer_ipv6;
     let mut v6 = socket_addrs.iter().filter(|s| matches!(s, SocketAddr::V6(_)));
     let mut v4 = socket_addrs.iter().filter(|s| matches!(s, SocketAddr::V4(_)));
     std::iter::from_fn(move || {
@@ -34,28 +35,39 @@ pub fn sort_socket_addrs(socket_addrs: &[SocketAddr]) -> impl Iterator<Item = &'
 #[derive(Clone)]
 pub enum DnsResolver {
     System,
-    TrustDns(AsyncResolver<GenericConnector<TokioRuntimeProviderWithSoMark>>),
+    TrustDns {
+        resolver: AsyncResolver<GenericConnector<TokioRuntimeProviderWithSoMark>>,
+        prefer_ipv6: bool,
+    },
 }
 
 impl DnsResolver {
     pub async fn lookup_host(&self, domain: &str, port: u16) -> anyhow::Result<Vec<SocketAddr>> {
         let addrs: Vec<SocketAddr> = match self {
             Self::System => tokio::net::lookup_host(format!("{}:{}", domain, port)).await?.collect(),
-            Self::TrustDns(dns_resolver) => dns_resolver
+            Self::TrustDns { resolver, prefer_ipv6 } => {
-                .lookup_ip(domain)
+                let addrs: Vec<_> = resolver
-                .await?
+                    .lookup_ip(domain)
-                .into_iter()
+                    .await?
-                .map(|ip| match ip {
+                    .into_iter()
-                    IpAddr::V4(ip) => SocketAddr::V4(SocketAddrV4::new(ip, port)),
+                    .map(|ip| match ip {
-                    IpAddr::V6(ip) => SocketAddr::V6(SocketAddrV6::new(ip, port, 0, 0)),
+                        IpAddr::V4(ip) => SocketAddr::V4(SocketAddrV4::new(ip, port)),
-                })
+                        IpAddr::V6(ip) => SocketAddr::V6(SocketAddrV6::new(ip, port, 0, 0)),
-                .collect(),
+                    })
+                    .collect();
+                sort_socket_addrs(&addrs, *prefer_ipv6).copied().collect()
+            }
         };
 
         Ok(addrs)
     }
 
-    pub fn new_from_urls(resolvers: &[Url], proxy: Option<Url>, so_mark: Option<u32>) -> anyhow::Result<Self> {
+    pub fn new_from_urls(
+        resolvers: &[Url],
+        proxy: Option<Url>,
+        so_mark: Option<u32>,
+        prefer_ipv6: bool,
+    ) -> anyhow::Result<Self> {
         if resolvers.is_empty() {
             // no dns resolver specified, fall-back to default one
             let Ok((cfg, mut opts)) = hickory_resolver::system_conf::read_system_conf() else {
@@ -63,7 +75,8 @@ impl DnsResolver {
                 return Ok(Self::System);
             };
 
-            opts.timeout = std::time::Duration::from_secs(1);
+            opts.ip_strategy = LookupIpStrategy::Ipv4AndIpv6;
+            opts.timeout = Duration::from_secs(1);
             // Windows end-up with too many dns resolvers, which causes a performance issue
             // https://github.com/hickory-dns/hickory-dns/issues/1968
             #[cfg(target_os = "windows")]
@@ -71,11 +84,14 @@ impl DnsResolver {
                 opts.cache_size = 1024;
                 opts.num_concurrent_reqs = cfg.name_servers().len();
             }
-            return Ok(Self::TrustDns(AsyncResolver::new(
+            return Ok(Self::TrustDns {
-                cfg,
+                resolver: AsyncResolver::new(
-                opts,
+                    cfg,
-                GenericConnector::new(TokioRuntimeProviderWithSoMark::new(proxy, so_mark)),
+                    opts,
-            )));
+                    GenericConnector::new(TokioRuntimeProviderWithSoMark::new(proxy, so_mark)),
+                ),
+                prefer_ipv6,
+            });
         };
 
         // if one is specified as system, use the default one from libc
@@ -127,13 +143,16 @@ impl DnsResolver {
         }
 
         let mut opts = ResolverOpts::default();
-        opts.timeout = std::time::Duration::from_secs(1);
+        opts.timeout = Duration::from_secs(1);
         opts.ip_strategy = LookupIpStrategy::Ipv4AndIpv6;
-        Ok(Self::TrustDns(AsyncResolver::new(
+        Ok(Self::TrustDns {
-            cfg,
+            resolver: AsyncResolver::new(
-            opts,
+                cfg,
-            GenericConnector::new(TokioRuntimeProviderWithSoMark::new(proxy, so_mark)),
+                opts,
-        )))
+                GenericConnector::new(TokioRuntimeProviderWithSoMark::new(proxy, so_mark)),
+            ),
+            prefer_ipv6,
+        })
     }
 }
 
@@ -235,3 +254,29 @@ impl RuntimeProvider for TokioRuntimeProviderWithSoMark {
         Box::pin(socket)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::dns::sort_socket_addrs;
+    use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
+
+    #[test]
+    fn test_sort_socket_addrs() {
+        let addrs = [
+            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 1)),
+            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 2), 1)),
+            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 1), 1, 0, 0)),
+            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 3), 1)),
+            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 2), 1, 0, 0)),
+        ];
+        let expected = [
+            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 1), 1, 0, 0)),
+            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 1)),
+            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 2), 1, 0, 0)),
+            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 2), 1)),
+            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 3), 1)),
+        ];
+        let actual: Vec<_> = sort_socket_addrs(&addrs, true).copied().collect();
+        assert_eq!(expected, *actual);
+    }
+}

src/main.rs

@@ -258,6 +258,17 @@ struct Client {
     /// **WARN** On windows you may want to specify explicitly the DNS resolver to avoid excessive DNS queries
     #[arg(long, verbatim_doc_comment)]
     dns_resolver: Vec<Url>,
+
+    /// Enable if you prefer the dns resolver to prioritize IPv4 over IPv6
+    /// This is useful if you have a broken IPv6 connection, and want to avoid the delay of trying to connect to IPv6
+    /// If you don't have any IPv6 this does not change anything.
+    #[arg(
+        long,
+        default_value = "false",
+        env = "WSTUNNEL_DNS_PREFER_IPV4",
+        verbatim_doc_comment
+    )]
+    dns_resolver_prefer_ipv4: bool,
 }
 
 #[derive(clap::Args, Debug)]
@@ -295,6 +306,17 @@ struct Server {
     #[arg(long, verbatim_doc_comment)]
     dns_resolver: Vec<Url>,
 
+    /// Enable if you prefer the dns resolver to prioritize IPv4 over IPv6
+    /// This is useful if you have a broken IPv6 connection, and want to avoid the delay of trying to connect to IPv6
+    /// If you don't have any IPv6 this does not change anything.
+    #[arg(
+        long,
+        default_value = "false",
+        env = "WSTUNNEL_DNS_PREFER_IPV4",
+        verbatim_doc_comment
+    )]
+    dns_resolver_prefer_ipv4: bool,
+
     /// Server will only accept connection from the specified tunnel information.
     /// Can be specified multiple time
     /// Example: --restrict-to "google.com:443" --restrict-to "localhost:22"
@@ -755,8 +777,13 @@ impl WsClientConfig {
 #[tokio::main]
 async fn main() {
     let args = Wstunnel::parse();
-    let socket =  UdpSocket::bind(SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, 0, 0, 0)).await.unwrap();
+    let socket = UdpSocket::bind(SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, 0, 0, 0))
-    socket.connect("[2001:4810:0:3::78]:443".parse::<SocketAddr>().unwrap()).await.unwrap();
+        .await
+        .unwrap();
+    socket
+        .connect("[2001:4810:0:3::78]:443".parse::<SocketAddr>().unwrap())
+        .await
+        .unwrap();
 
     // Setup logging
     let mut env_filter = EnvFilter::builder().parse(&args.log_lvl).expect("Invalid log level");
@@ -902,8 +929,13 @@ async fn main() {
                 websocket_mask_frame: args.websocket_mask_frame,
                 cnx_pool: None,
                 tls_reloader: None,
-                dns_resolver: DnsResolver::new_from_urls(&args.dns_resolver, http_proxy.clone(), args.socket_so_mark)
+                dns_resolver: DnsResolver::new_from_urls(
-                    .expect("cannot create dns resolver"),
+                    &args.dns_resolver,
+                    http_proxy.clone(),
+                    args.socket_so_mark,
+                    !args.dns_resolver_prefer_ipv4,
+                )
+                .expect("cannot create dns resolver"),
                 http_proxy,
             };
 
@@ -1324,8 +1356,13 @@ async fn main() {
                 timeout_connect: Duration::from_secs(10),
                 websocket_mask_frame: args.websocket_mask_frame,
                 tls: tls_config,
-                dns_resolver: DnsResolver::new_from_urls(&args.dns_resolver, None, args.socket_so_mark)
+                dns_resolver: DnsResolver::new_from_urls(
-                    .expect("Cannot create DNS resolver"),
+                    &args.dns_resolver,
+                    None,
+                    args.socket_so_mark,
+                    !args.dns_resolver_prefer_ipv4,
+                )
+                .expect("Cannot create DNS resolver"),
                 restriction_config: args.restrict_config,
             };
 

src/tcp.rs

@@ -2,7 +2,7 @@ use anyhow::{anyhow, Context};
 use std::{io, vec};
 use tokio::task::JoinSet;
 
-use crate::dns::{self, DnsResolver};
+use crate::dns::DnsResolver;
 use base64::Engine;
 use bytes::BytesMut;
 use log::warn;
@@ -73,14 +73,11 @@ pub async fn connect(
     let mut last_err = None;
     let mut join_set = JoinSet::new();
 
-    for (ix, addr) in dns::sort_socket_addrs(&socket_addrs).copied().enumerate() {
+    for (ix, addr) in socket_addrs.into_iter().enumerate() {
-        debug!("Connecting to {}", addr);
-
         let socket = match &addr {
             SocketAddr::V4(_) => TcpSocket::new_v4()?,
             SocketAddr::V6(_) => TcpSocket::new_v6()?,
         };
-
         configure_socket(socket2::SockRef::from(&socket), &so_mark)?;
 
         // Spawn the connection attempt in the join set.
@@ -90,6 +87,7 @@ pub async fn connect(
             if ix > 0 {
                 sleep(Duration::from_millis(250 * ix as u64)).await;
             }
+            debug!("Connecting to {}", addr);
             match timeout(connect_timeout, socket.connect(addr)).await {
                 Ok(Ok(s)) => Ok(Ok(s)),
                 Ok(Err(e)) => Ok(Err((addr, e))),
@@ -107,7 +105,7 @@ pub async fn connect(
         match res? {
             Ok(Ok(stream)) => {
                 // We've got a successful connection, so we can abort all other
-                // on-going attempts.
+                // ongoing attempts.
                 join_set.abort_all();
 
                 debug!(
@@ -227,7 +225,7 @@ pub async fn run_server(bind: SocketAddr, ip_transparent: bool) -> Result<TcpLis
 mod tests {
     use super::*;
     use futures_util::pin_mut;
-    use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr};
+    use std::net::SocketAddr;
     use testcontainers::core::WaitFor;
     use testcontainers::runners::AsyncRunner;
     use testcontainers::{ContainerAsync, Image, ImageArgs, RunnableImage};
@@ -259,26 +257,6 @@ mod tests {
         }
     }
 
-    #[test]
-    fn test_sort_socket_addrs() {
-        let addrs = [
-            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 1)),
-            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 2), 1)),
-            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 1), 1, 0, 0)),
-            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 3), 1)),
-            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 2), 1, 0, 0)),
-        ];
-        let expected = [
-            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 1), 1, 0, 0)),
-            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 1)),
-            SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(0, 0, 0, 0, 127, 0, 0, 2), 1, 0, 0)),
-            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 2), 1)),
-            SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 3), 1)),
-        ];
-        let actual: Vec<_> = dns::sort_socket_addrs(&addrs).copied().collect();
-        assert_eq!(expected, *actual);
-    }
-
     #[tokio::test]
     async fn test_proxy_connection() {
         let server_addr: SocketAddr = "[::1]:1236".parse().unwrap();

src/udp.rs

@@ -19,7 +19,7 @@ use tokio::io::{AsyncRead, AsyncWrite, ReadBuf};
 use tokio::net::UdpSocket;
 use tokio::sync::futures::Notified;
 
-use crate::dns::{self, DnsResolver};
+use crate::dns::DnsResolver;
 use tokio::sync::Notify;
 use tokio::time::{sleep, timeout, Interval};
 use tracing::{debug, error, info};
@@ -340,9 +340,7 @@ pub async fn connect(
     let mut last_err = None;
     let mut join_set = JoinSet::new();
 
-    for (ix, addr) in dns::sort_socket_addrs(&socket_addrs).copied().enumerate() {
+    for (ix, addr) in socket_addrs.into_iter().enumerate() {
-        debug!("connecting to {}", addr);
-
         let socket = match &addr {
             SocketAddr::V4(_) => UdpSocket::bind(SocketAddrV4::new(Ipv4Addr::UNSPECIFIED, 0)).await,
             SocketAddr::V6(_) => UdpSocket::bind(SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, 0, 0, 0)).await,
@@ -364,6 +362,7 @@ pub async fn connect(
                 sleep(Duration::from_millis(250 * ix as u64)).await;
             }
 
+            debug!("connecting to {}", addr);
             match timeout(connect_timeout, socket.connect(addr)).await {
                 Ok(Ok(())) => Ok(Ok(socket)),
                 Ok(Err(e)) => Ok(Err((addr, e))),
@@ -381,7 +380,7 @@ pub async fn connect(
         match res? {
             Ok(Ok(socket)) => {
                 // We've got a successful connection, so we can abort all other
-                // on-going attempts.
+                // ongoing attempts.
                 join_set.abort_all();
 
                 debug!(