add discover_one(), and filtering helpers; refactor discovery.rs to return structured ListIdentity results

Author: JaskRendix

src/client/discovery.rs

@@ -22,12 +22,23 @@ impl Discovery for DiscoveryImpl {
         let socket = UdpSocket::bind("0.0.0.0:0").await?;
         socket.set_broadcast(true)?;
 
-        // Send ListIdentity request
+        // Join CIP multicast group (239.192.1.1)
+        let _ = socket.join_multicast_v4(
+            std::net::Ipv4Addr::new(239, 192, 1, 1),
+            std::net::Ipv4Addr::new(0, 0, 0, 0),
+        );
+
+        // Send ListIdentity request via broadcast
         let msg = EncapsulationHeader::new(COMMAND_LIST_IDENTITY, 0, 0).to_bytes();
         socket
             .send_to(&msg, SocketAddr::from(([255, 255, 255, 255], ENIP_PORT)))
             .await?;
 
+        // Send ListIdentity request via multicast
+        let _ = socket
+            .send_to(&msg, SocketAddr::from(([239, 192, 1, 1], ENIP_PORT)))
+            .await;
+
         let mut results = Vec::new();
         let mut buf = [0u8; 2048];
         let start = Instant::now();
@@ -90,6 +101,14 @@ impl Discovery for DiscoveryImpl {
     }
 }
 
+impl DiscoveryImpl {
+    /// Return the first discovered device, if any.
+    pub async fn discover_one() -> io::Result<Option<DiscoveredIdentity>> {
+        let all = Self::discover().await?;
+        Ok(all.into_iter().next())
+    }
+}
+
 /// Parse the Identity Item (0x000C) returned by ListIdentity (0x63).
 ///
 /// This is *not* the same as the Identity Object (Class 0x01).