Add example code of dumping routes

Signed-off-by: Gris Ge <[email protected]>

Author: cathay4t

examples/dump_routes.rs

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: MIT
+
+use netlink_packet_core::{
+    NetlinkHeader, NetlinkMessage, NetlinkPayload, NLM_F_DUMP, NLM_F_REQUEST,
+};
+use netlink_packet_route::{route::RouteMessage, RouteNetlinkMessage};
+use netlink_sys::{protocols::NETLINK_ROUTE, Socket, SocketAddr};
+
+fn main() {
+    let mut socket = Socket::new(NETLINK_ROUTE).unwrap();
+    let _port_number = socket.bind_auto().unwrap().port_number();
+    socket.connect(&SocketAddr::new(0, 0)).unwrap();
+
+    let mut nl_hdr = NetlinkHeader::default();
+    nl_hdr.flags = NLM_F_REQUEST | NLM_F_DUMP;
+    let mut packet = NetlinkMessage::new(
+        nl_hdr,
+        NetlinkPayload::from(RouteNetlinkMessage::GetRoute(
+            RouteMessage::default(),
+        )),
+    );
+
+    packet.finalize();
+
+    let mut buf = vec![0; packet.header.length as usize];
+
+    // Before calling serialize, it is important to check that the buffer in
+    // which we're emitting is big enough for the packet, other
+    // `serialize()` panics.
+
+    assert!(buf.len() == packet.buffer_len());
+
+    packet.serialize(&mut buf[..]);
+
+    println!(">>> {packet:?}");
+    if let Err(e) = socket.send(&buf[..], 0) {
+        println!("SEND ERROR {e}");
+    }
+
+    let mut receive_buffer = vec![0; 4096];
+    let mut offset = 0;
+
+    // we set the NLM_F_DUMP flag so we expect a multipart rx_packet in
+    // response.
+    while let Ok(size) = socket.recv(&mut &mut receive_buffer[..], 0) {
+        loop {
+            let bytes = &receive_buffer[offset..];
+            let rx_packet =
+                <NetlinkMessage<RouteNetlinkMessage>>::deserialize(bytes)
+                    .unwrap();
+            println!("<<< {rx_packet:?}");
+
+            if matches!(rx_packet.payload, NetlinkPayload::Done(_)) {
+                println!("Done!");
+                return;
+            }
+
+            offset += rx_packet.header.length as usize;
+            if offset == size || rx_packet.header.length == 0 {
+                offset = 0;
+                break;
+            }
+        }
+    }
+}