Pick IPv4 or IPv6 wildcard source addresses according to the destination

Fixes #10

src/anonymized_dns.rs

@@ -2,7 +2,7 @@ use crate::*;
 
 use byteorder::{BigEndian, ByteOrder};
 use failure::ensure;
-use std::net::{IpAddr, Ipv6Addr, SocketAddr};
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
 use std::sync::Arc;
 use tokio::net::UdpSocket;
 
@@ -52,7 +52,7 @@ pub async fn handle_anonymized_dns(
     let upstream_address = SocketAddr::new(ip, port);
     ensure!(
         !globals.listen_addrs.contains(&upstream_address)
-            && globals.external_addr != upstream_address,
+            && globals.external_addr != Some(upstream_address),
         "Would be relaying to self"
     );
     let encrypted_packet = &encrypted_packet[ANONYMIZED_DNSCRYPT_OVERHEAD..];
@@ -72,7 +72,23 @@ pub async fn handle_anonymized_dns(
             != ANONYMIZED_DNSCRYPT_QUERY_MAGIC,
         "Loop detected"
     );
-    let mut ext_socket = UdpSocket::bind(&globals.external_addr).await?;
+    let mut ext_socket = match globals.external_addr {
+        Some(x) => UdpSocket::bind(x).await?,
+        None => match upstream_address {
+            SocketAddr::V4(_) => {
+                UdpSocket::bind(SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::UNSPECIFIED, 0))).await?
+            }
+            SocketAddr::V6(s) => {
+                UdpSocket::bind(SocketAddr::V6(SocketAddrV6::new(
+                    Ipv6Addr::UNSPECIFIED,
+                    0,
+                    s.flowinfo(),
+                    s.scope_id(),
+                )))
+                .await?
+            }
+        },
+    };
     ext_socket.connect(&upstream_address).await?;
     ext_socket.send(&encrypted_packet).await?;
     let mut response = vec![0u8; DNSCRYPT_UDP_RESPONSE_MAX_SIZE];

src/config.rs

@@ -53,7 +53,7 @@ pub struct FilteringConfig {
 #[derive(Serialize, Deserialize, Debug, Clone)]
 pub struct Config {
     pub listen_addrs: Vec<ListenAddrConfig>,
-    pub external_addr: IpAddr,
+    pub external_addr: Option<IpAddr>,
     pub upstream_addr: SocketAddr,
     pub state_file: PathBuf,
     pub udp_timeout: u32,

src/globals.rs

@@ -25,7 +25,7 @@ pub struct Globals {
     pub provider_name: String,
     pub provider_kp: SignKeyPair,
     pub listen_addrs: Vec<SocketAddr>,
-    pub external_addr: SocketAddr,
+    pub external_addr: Option<SocketAddr>,
     pub upstream_addr: SocketAddr,
     pub tls_upstream_addr: Option<SocketAddr>,
     pub udp_timeout: Duration,

src/main.rs

@@ -237,13 +237,12 @@ async fn tls_proxy(
         Some(tls_upstream_addr) => tls_upstream_addr,
     };
     let std_socket = match globals.external_addr {
-        SocketAddr::V4(_) => net2::TcpBuilder::new_v4()?
-            .bind(&globals.external_addr)?
-            .to_tcp_stream()?,
-        SocketAddr::V6(_) => net2::TcpBuilder::new_v6()?
-            .only_v6(true)?
-            .bind(&globals.external_addr)?
-            .to_tcp_stream()?,
+        Some(x @ SocketAddr::V4(_)) => net2::TcpBuilder::new_v4()?.bind(&x)?.to_tcp_stream()?,
+        Some(x @ SocketAddr::V6(_)) => net2::TcpBuilder::new_v6()?.bind(&x)?.to_tcp_stream()?,
+        None => match tls_upstream_addr {
+            SocketAddr::V4(_) => net2::TcpBuilder::new_v4()?.to_tcp_stream()?,
+            SocketAddr::V6(_) => net2::TcpBuilder::new_v6()?.to_tcp_stream()?,
+        },
     };
     let mut ext_socket =
         TcpStream::connect_std(std_socket, tls_upstream_addr, &Default::default()).await?;
@@ -501,7 +500,7 @@ fn main() -> Result<(), Error> {
         provider_name if provider_name.starts_with("2.dnscrypt-cert.") => provider_name.to_string(),
         provider_name => format!("2.dnscrypt-cert.{}", provider_name),
     };
-    let external_addr = SocketAddr::new(config.external_addr, 0);
+    let external_addr = config.external_addr.map(|addr| SocketAddr::new(addr, 0));
 
     let mut runtime_builder = tokio::runtime::Builder::new();
     runtime_builder.name_prefix("encrypted-dns-");

src/resolver.rs

@@ -7,7 +7,7 @@ use byteorder::{BigEndian, ByteOrder};
 use rand::prelude::*;
 use siphasher::sip128::Hasher128;
 use std::hash::Hasher;
-use std::net::SocketAddr;
+use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
 use tokio::net::{TcpStream, UdpSocket};
 use tokio::prelude::*;
 
@@ -19,10 +19,15 @@ pub async fn resolve_udp(
     has_cached_response: bool,
 ) -> Result<Vec<u8>, Error> {
     let std_socket = match globals.external_addr {
-        SocketAddr::V4(_) => net2::UdpBuilder::new_v4()?.bind(&globals.external_addr)?,
-        SocketAddr::V6(_) => net2::UdpBuilder::new_v6()?
-            .only_v6(true)?
-            .bind(&globals.external_addr)?,
+        Some(x @ SocketAddr::V4(_)) => net2::UdpBuilder::new_v4()?.bind(&x)?,
+        Some(x @ SocketAddr::V6(_)) => net2::UdpBuilder::new_v6()?.bind(&x)?,
+        None => match globals.upstream_addr {
+            SocketAddr::V4(_) => net2::UdpBuilder::new_v4()?
+                .bind(SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::UNSPECIFIED, 0)))?,
+            SocketAddr::V6(s) => net2::UdpBuilder::new_v6()?.bind(SocketAddr::V6(
+                SocketAddrV6::new(Ipv6Addr::UNSPECIFIED, 0, s.flowinfo(), s.scope_id()),
+            ))?,
+        },
     };
     let mut ext_socket = UdpSocket::from_std(std_socket, &Default::default())?;
     ext_socket.connect(&globals.upstream_addr).await?;
@@ -66,13 +71,12 @@ pub async fn resolve_tcp(
     tid: u16,
 ) -> Result<Vec<u8>, Error> {
     let std_socket = match globals.external_addr {
-        SocketAddr::V4(_) => net2::TcpBuilder::new_v4()?
-            .bind(&globals.external_addr)?
-            .to_tcp_stream()?,
-        SocketAddr::V6(_) => net2::TcpBuilder::new_v6()?
-            .only_v6(true)?
-            .bind(&globals.external_addr)?
-            .to_tcp_stream()?,
+        Some(x @ SocketAddr::V4(_)) => net2::TcpBuilder::new_v4()?.bind(&x)?.to_tcp_stream()?,
+        Some(x @ SocketAddr::V6(_)) => net2::TcpBuilder::new_v6()?.bind(&x)?.to_tcp_stream()?,
+        None => match globals.upstream_addr {
+            SocketAddr::V4(_) => net2::TcpBuilder::new_v4()?.to_tcp_stream()?,
+            SocketAddr::V6(_) => net2::TcpBuilder::new_v6()?.to_tcp_stream()?,
+        },
     };
     let mut ext_socket =
         TcpStream::connect_std(std_socket, &globals.upstream_addr, &Default::default()).await?;