fix get_local_ipaddr for IPv6-only

src/interface/shared.rs

@@ -1,24 +1,8 @@
+use std::net::Ipv6Addr;
 #[cfg(feature = "gateway")]
 use std::net::{IpAddr, Ipv4Addr, SocketAddr, UdpSocket};
 
-/// Retrieve the IP address of the default network interface.
-///
-/// This function attempts to bind a UDP socket to an unspecified IP address (0.0.0.0)
-/// and port (0), which allows the system to select an appropriate IP address and port.
-/// After binding, it attempts to connect the socket to a designated non-routable IP address
-/// (`10.254.254.254` on port 1). This is a trick commonly used to prompt the OS to
-/// populate the socket's local address with the IP address of the interface that would
-/// route to the specified address.
-///
-/// The function returns the local IP address if these operations succeed.
-/// If any operation fails (binding, connecting, or retrieving the address),
-/// the function returns `None`, indicating the inability to determine the local IP.
-///
-/// Returns:
-/// - `Some(IpAddr)`: IP address of the default network interface if successful.
-/// - `None`: If any error occurs during the operations.
-#[cfg(feature = "gateway")]
-pub fn get_local_ipaddr() -> Option<IpAddr> {
+fn try_ipv4() -> Option<IpAddr> {
     // Attempt to bind a UDP socket to an unspecified address and port.
     let socket = match UdpSocket::bind(SocketAddr::new(IpAddr::V4(Ipv4Addr::UNSPECIFIED), 0)) {
         Ok(s) => s,
@@ -39,3 +23,51 @@ pub fn get_local_ipaddr() -> Option<IpAddr> {
         Err(_) => return None,
     };
 }
+
+fn try_ipv6() -> Option<IpAddr> {
+    // same thing but for IPv6
+    let socket = match UdpSocket::bind(SocketAddr::new(IpAddr::V6(Ipv6Addr::UNSPECIFIED), 0)) {
+        Ok(s) => s,
+        Err(_) => return None,
+    };
+    match socket.connect(SocketAddr::new(
+        IpAddr::V6(Ipv6Addr::new(
+            0xfdff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff,
+        )),
+        1,
+    )) {
+        Ok(()) => (),
+        Err(_) => return None,
+    };
+    match socket.local_addr() {
+        Ok(addr) => return Some(addr.ip()),
+        Err(_) => return None,
+    };
+}
+
+/// Retrieve the IP address of the default network interface.
+///
+/// This function attempts to bind a UDP socket to an unspecified IP address (0.0.0.0 or ::)
+/// and port (0), which allows the system to select an appropriate IP address and port.
+/// After binding, it attempts to connect the socket to a designated non-routable IP address
+/// (`10.254.254.254` or `fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff` on port 1). This is a
+/// trick commonly used to prompt the OS to populate the socket's local address with the IP
+/// address of the interface that would route to the specified address.
+///
+/// The function returns the local IP address if these operations succeed.
+/// If any operation fails (binding, connecting, or retrieving the address),
+/// the function returns `None`, indicating the inability to determine the local IP.
+///
+/// Returns:
+/// - `Some(IpAddr)`: IP address of the default network interface if successful.
+/// - `None`: If any error occurs during the operations.
+#[cfg(feature = "gateway")]
+pub fn get_local_ipaddr() -> Option<IpAddr> {
+    // binding the IPv4 socket can actually succeed but a later step will fail in IPv6-only,
+    // we call `try_ipv6` in any case where `try_ipv4` fails
+    if let Some(addr) = try_ipv4() {
+        Some(addr)
+    } else {
+        try_ipv6()
+    }
+}