feat: Add TTL connection param to multicast

io/zenoh-links/zenoh-link-udp/src/lib.rs

@@ -107,6 +107,7 @@ impl LocatorInspector for UdpLocatorInspector {
 pub mod config {
     pub const UDP_MULTICAST_IFACE: &str = "iface";
     pub const UDP_MULTICAST_JOIN: &str = "join";
+    pub const UDP_MULTICAST_TTL: &str = "ttl";
 }
 
 pub async fn get_udp_addrs(address: Address<'_>) -> ZResult<impl Iterator<Item = SocketAddr>> {

io/zenoh-links/zenoh-link-udp/src/multicast.rs

@@ -272,7 +272,7 @@
                 .map_err(|e| zerror!("{}: {}", mcast_addr, e))?;
         }
 
-        // Bind the socket: let's bing to the unspecified address so we can join and read
+        // Bind the socket: let's bind to the unspecified address so we can join and read
         // from multiple multicast groups.
         let bind_mcast_addr = match mcast_addr.ip() {
             IpAddr::V4(_) => IpAddr::V4(Ipv4Addr::UNSPECIFIED),
@@ -321,6 +321,28 @@
         // https://docs.rs/tokio/latest/tokio/net/struct.UdpSocket.html#notes
         mcast_sock.set_nonblocking(true)?;
 
+        // If TTL is specified, add set the socket's TTL
+        if let Some(ttl_str) = config.get(UDP_MULTICAST_TTL) {
+            match &local_addr {
+                IpAddr::V4(_) => {
+                    let ttl = match ttl_str.parse::<u32>() {
+                        Ok(ttl) => ttl,
+                        Err(e) => bail!("Can not parse TTL '{}' to a u32: {}", ttl_str, e),
+                    };
+
+                    ucast_sock.set_multicast_ttl_v4(ttl).map_err(|e| {
+                        zerror!("Can not set multicast TTL {} on {}: {}", ttl, mcast_addr, e)
+                    })?;
+                }
+                IpAddr::V6(_) => {
+                    tracing::warn!(
+                            "UDP multicast hop limit not supported for v6 socket: {}. See https://github.com/rust-lang/rust/pull/138744.",
+                            mcast_addr
+                        );
+                }
+            }
+        }
+
         // Build the tokio multicast UdpSocket
         let mcast_sock = UdpSocket::from_std(mcast_sock.into())?;