Bind client UDP sockets by peer family

src/udp.rs

@@ -1,6 +1,6 @@
 //! UDP error classification shared by Dosh clients, servers, and embedders.
 
-use std::net::SocketAddr;
+use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr};
 use std::time::{Duration, Instant};
 use tokio::net::UdpSocket;
 
@@ -17,6 +17,17 @@ pub fn is_transient_udp_send_error(err: &std::io::Error) -> bool {
     is_transient_udp_error(err)
 }
 
+pub fn unspecified_bind_addr_for_peer(peer: SocketAddr) -> SocketAddr {
+    match peer {
+        SocketAddr::V4(_) => SocketAddr::from((Ipv4Addr::UNSPECIFIED, 0)),
+        SocketAddr::V6(_) => SocketAddr::from((Ipv6Addr::UNSPECIFIED, 0)),
+    }
+}
+
+pub async fn bind_udp_for_peer(peer: SocketAddr) -> std::io::Result<UdpSocket> {
+    UdpSocket::bind(unspecified_bind_addr_for_peer(peer)).await
+}
+
 pub async fn send_udp_retrying_transient(
     socket: &UdpSocket,
     packet: &[u8],
@@ -106,8 +117,9 @@ fn is_transient_udp_os_error(_code: i32) -> bool {
 mod tests {
     use super::{
         is_transient_udp_error, is_transient_udp_send_error, recv_udp_retrying_transient,
-        send_udp_retrying_transient,
+        send_udp_retrying_transient, unspecified_bind_addr_for_peer,
     };
+    use std::net::{Ipv4Addr, Ipv6Addr, SocketAddr};
     use std::time::Duration;
     use tokio::net::UdpSocket;
 
@@ -127,6 +139,18 @@ mod tests {
         assert!(!is_transient_udp_send_error(&fatal));
     }
 
+    #[test]
+    fn peer_bind_addr_matches_peer_address_family() {
+        assert_eq!(
+            unspecified_bind_addr_for_peer(SocketAddr::from((Ipv4Addr::LOCALHOST, 50000))),
+            SocketAddr::from((Ipv4Addr::UNSPECIFIED, 0))
+        );
+        assert_eq!(
+            unspecified_bind_addr_for_peer(SocketAddr::from((Ipv6Addr::LOCALHOST, 50000))),
+            SocketAddr::from((Ipv6Addr::UNSPECIFIED, 0))
+        );
+    }
+
     #[tokio::test]
     async fn retrying_udp_send_and_receive_round_trip() {
         let receiver = UdpSocket::bind("127.0.0.1:0").await.unwrap();