redir local converts IPv4-mapped IPv6 addresses to IPv4

- Dual-stack IPv6 will always return destination addresses in IPv4-mapped
  IPv6 addresses

crates/shadowsocks-service/src/local/redir/mod.rs

@@ -1,5 +1,7 @@
 //! Shadowsocks Local Transparent Proxy
 
+use std::net::{Ipv4Addr, Ipv6Addr};
+
 pub use self::server::Redir;
 
 mod redir_ext;
@@ -7,3 +9,13 @@ mod server;
 mod sys;
 mod tcprelay;
 mod udprelay;
+
+/// Helper function for converting IPv4 mapped IPv6 address
+///
+/// This is the same as `Ipv6Addr::to_ipv4_mapped`, but it is still unstable in the current libstd
+fn to_ipv4_mapped(ipv6: &Ipv6Addr) -> Option<Ipv4Addr> {
+    match ipv6.octets() {
+        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, a, b, c, d] => Some(Ipv4Addr::new(a, b, c, d)),
+        _ => None,
+    }
+}

crates/shadowsocks-service/src/local/redir/tcprelay/mod.rs

@@ -1,6 +1,11 @@
 //! Shadowsocks TCP transparent proxy
 
-use std::{io, net::SocketAddr, sync::Arc, time::Duration};
+use std::{
+    io,
+    net::{IpAddr, SocketAddr},
+    sync::Arc,
+    time::Duration,
+};
 
 use log::{debug, error, info, trace};
 use shadowsocks::{lookup_then, net::TcpListener as ShadowTcpListener, relay::socks5::Address};
@@ -15,7 +20,10 @@ use crate::{
         context::ServiceContext,
         loadbalancing::PingBalancer,
         net::{AutoProxyClientStream, AutoProxyIo},
-        redir::redir_ext::{TcpListenerRedirExt, TcpStreamRedirExt},
+        redir::{
+            redir_ext::{TcpListenerRedirExt, TcpStreamRedirExt},
+            to_ipv4_mapped,
+        },
         utils::establish_tcp_tunnel,
     },
 };
@@ -74,7 +82,7 @@ async fn handle_redir_client(
     balancer: PingBalancer,
     s: TcpStream,
     peer_addr: SocketAddr,
-    daddr: SocketAddr,
+    mut daddr: SocketAddr,
     nodelay: bool,
 ) -> io::Result<()> {
     // let svr_cfg = server.server_config();
@@ -90,6 +98,13 @@ async fn handle_redir_client(
     }
 
     // Get forward address from socket
+    //
+    // Try to convert IPv4 mapped IPv6 address for dual-stack mode.
+    if let SocketAddr::V6(ref a) = daddr {
+        if let Some(v4) = to_ipv4_mapped(a.ip()) {
+            daddr = SocketAddr::new(IpAddr::from(v4), a.port());
+        }
+    }
     let target_addr = Address::from(daddr);
     establish_client_tcp_redir(context, balancer, s, peer_addr, &target_addr, nodelay).await
 }

crates/shadowsocks-service/src/local/redir/udprelay/mod.rs

@@ -2,7 +2,7 @@
 
 use std::{
     io::{self, ErrorKind},
-    net::SocketAddr,
+    net::{IpAddr, SocketAddr},
     sync::Arc,
     time::Duration,
 };
@@ -20,7 +20,10 @@ use crate::{
         context::ServiceContext,
         loadbalancing::PingBalancer,
         net::{UdpAssociationManager, UdpInboundWrite},
-        redir::redir_ext::{RedirSocketOpts, UdpSocketRedirExt},
+        redir::{
+            redir_ext::{RedirSocketOpts, UdpSocketRedirExt},
+            to_ipv4_mapped,
+        },
     },
 };
 
@@ -38,7 +41,16 @@ struct UdpRedirInboundWriter {
 impl UdpInboundWrite for UdpRedirInboundWriter {
     async fn send_to(&self, peer_addr: SocketAddr, remote_addr: &Address, data: &[u8]) -> io::Result<()> {
         let addr = match *remote_addr {
-            Address::SocketAddress(sa) => sa,
+            Address::SocketAddress(sa) => {
+                // Try to convert IPv4 mapped IPv6 address if server is running on dual-stack mode
+                match sa {
+                    SocketAddr::V4(..) => sa,
+                    SocketAddr::V6(ref v6) => match to_ipv4_mapped(v6.ip()) {
+                        Some(v4) => SocketAddr::new(IpAddr::from(v4), v6.port()),
+                        None => sa,
+                    },
+                }
+            }
             Address::DomainNameAddress(..) => {
                 let err = io::Error::new(
                     ErrorKind::InvalidInput,
@@ -132,7 +144,7 @@ impl UdpRedir {
 
         let mut pkt_buf = [0u8; MAXIMUM_UDP_PAYLOAD_SIZE];
         loop {
-            let (recv_len, src, dst) = match listener.recv_dest_from(&mut pkt_buf).await {
+            let (recv_len, src, mut dst) = match listener.recv_dest_from(&mut pkt_buf).await {
                 Ok(o) => o,
                 Err(err) => {
                     error!("recv_dest_from failed with err: {}", err);
@@ -162,6 +174,13 @@ impl UdpRedir {
                 continue;
             }
 
+            // Try to convert IPv4 mapped IPv6 address for dual-stack mode.
+            if let SocketAddr::V6(ref a) = dst {
+                if let Some(v4) = to_ipv4_mapped(a.ip()) {
+                    dst = SocketAddr::new(IpAddr::from(v4), a.port());
+                }
+            }
+
             if let Err(err) = manager.send_to(src, Address::from(dst), pkt).await {
                 error!(
                     "udp packet relay {} -> {} with {} bytes failed, error: {}",