do it similar on the client

turns out you can join multiple multicast groups on the same socket.
And then I think the OS or the network somehow decides how to route
packets to you. Without touching anything else, if I'm plugged into
Ethernet, it picks that address (when running client on the desktop)
and when I unplug it, it picks the laptop's WiFi.

src/client.rs

@@ -9,23 +9,29 @@ pub async fn client <I : Iterator <Item=String>> (mut args: I) -> Result <(), Ap
 	use rand::RngCore;
 	
 	let common_params = app_common::Params::default ();
-	let mut bind_addr = "0.0.0.0".to_string ();
+	let mut bind_addrs = vec! [];
 	
 	while let Some (arg) = args.next () {
 		match arg.as_str () {
 			"--bind-addr" => {
-				bind_addr = match args.next () {
+				bind_addrs.push (match args.next () {
 					None => return Err (CliArgError::MissingArgumentValue (arg).into ()),
-					Some (x) => x
-				};
+					Some (x) => Ipv4Addr::from_str (&x)?
+				});
 			},
 			_ => return Err (CliArgError::UnrecognizedArgument (arg).into ()),
 		}
 	}
 	
-	let socket = UdpSocket::bind (&format! ("{}:0", bind_addr)).await?;
+	if bind_addrs.is_empty () {
+		bind_addrs = get_ips ()?;
+	}
 	
-	socket.join_multicast_v4 (common_params.multicast_addr, Ipv4Addr::from_str (&bind_addr)?)?;
+	let socket = UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, 0)).await?;
+	
+	for bind_addr in bind_addrs {
+		socket.join_multicast_v4 (common_params.multicast_addr, bind_addr)?;
+	}
 	
 	let mut idem_id = [0u8; 8];
 	rand::thread_rng ().fill_bytes (&mut idem_id);

src/server.rs

@@ -12,28 +12,13 @@ pub async fn server <I: Iterator <Item=String>> (args: I) -> Result <(), AppErro
 {
 	let params = configure (args)?;
 	
-	// This was too hard to do in a functional style
-	let mut tasks = vec! [];
+	let socket = UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, params.common.server_port)).await?;
 	
 	for bind_addr in &params.bind_addrs {
-		let socket = match UdpSocket::bind (SocketAddrV4::new (Ipv4Addr::UNSPECIFIED, params.common.server_port)).await {
-			Err (e) => {
-				println! ("Error binding socket: {:?}", e);
-				continue;
-			},
-			Ok (x) => x,
-		};
-		
 		socket.join_multicast_v4 (params.common.multicast_addr, *bind_addr)?;
-		
-		dbg! (bind_addr);
-		
-		tasks.push (tokio::spawn (serve_interface (params.clone (), socket)));
 	}
 	
-	for task in tasks {
-		task.await??;
-	}
+	serve_interface (params, socket).await?;
 	
 	Ok (())
 }
@@ -68,7 +53,7 @@ fn configure <I: Iterator <Item=String>> (mut args: I) -> Result <Params, AppErr
 	}
 	
 	if bind_addrs.is_empty () {
-		println! ("No bind addresses found, auto-detecting all local IPs");
+		println! ("No bind addresses given, auto-detecting all local IPs");
 		bind_addrs = get_ips ()?;
 	}
 	
@@ -80,7 +65,10 @@ fn configure <I: Iterator <Item=String>> (mut args: I) -> Result <Params, AppErr
 	})
 }
 
-async fn serve_interface (params: Params, socket: UdpSocket) 
+async fn serve_interface (
+	params: Params, 
+	socket: UdpSocket,
+) 
 -> Result <(), AppError>
 {
 	let mut recent_idem_ids = Vec::with_capacity (32);