From 9f3fc1958b92a7eb3f4d95a071780eac7d4666b5 Mon Sep 17 00:00:00 2001
From: Alexander Polakov <a.polakov@iconic.vc>
Date: Wed, 3 Jun 2020 15:14:34 +0300
Subject: [PATCH] example: netlink crate

---
 examples/Cargo.toml       |  7 ++++
 examples/netlink-route.rs | 83 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 examples/netlink-route.rs

diff --git a/examples/Cargo.toml b/examples/Cargo.toml
index 1ad5539a..9891a378 100644
--- a/examples/Cargo.toml
+++ b/examples/Cargo.toml
@@ -12,6 +12,9 @@ uds_windows = "0.1.4"
 inotify = { version = "0.8.2", default-features = false }
 nix = "0.17.0"
 timerfd = "1.1.1"
+netlink-sys = "0.2"
+netlink-packet-core = "0.1"
+netlink-packet-route = "0.2"
 
 [dev-dependencies]
 anyhow = "1.0.28"
@@ -38,6 +41,10 @@ tokio = { version = "0.2.18", default-features = false }
 tungstenite = "0.10.1"
 url = "2.1.1"
 
+[[example]]
+name = "netlink-route"
+path = "netlink-route.rs"
+
 [[example]]
 name = "async-h1-client"
 path = "async-h1-client.rs"
diff --git a/examples/netlink-route.rs b/examples/netlink-route.rs
new file mode 100644
index 00000000..2323ae77
--- /dev/null
+++ b/examples/netlink-route.rs
@@ -0,0 +1,83 @@
+use std::io;
+
+#[cfg(not(target_os = "linux"))]
+fn main() {
+    println!("This example works only on Linux!");
+}
+
+#[cfg(target_os = "linux")]
+fn main() -> io::Result<()> {
+    use netlink_packet_core::{NetlinkHeader, NetlinkMessage, NLM_F_DUMP, NLM_F_REQUEST};
+    use netlink_packet_route::{rtnl::link::nlas::Nla, LinkMessage, NetlinkPayload, RtnlMessage};
+    use netlink_sys::{Protocol, Socket, SocketAddr};
+    use smol::Async;
+    use std::process;
+
+    fn align(len: usize) -> usize {
+        const RTA_ALIGNTO: usize = 4;
+
+        ((len)+RTA_ALIGNTO-1) & !(RTA_ALIGNTO-1)
+    }
+
+    smol::run(async {
+        let mut socket = Socket::new(Protocol::Route)?;
+        socket.bind(&SocketAddr::new(process::id(), 1))?;
+        let mut socket = Async::new(socket)?;
+
+        let mut packet = NetlinkMessage {
+            header: NetlinkHeader {
+                sequence_number: 1,
+                flags: NLM_F_DUMP | NLM_F_REQUEST,
+                ..Default::default()
+            },
+            payload: RtnlMessage::GetLink(LinkMessage::default()).into(),
+        };
+        packet.finalize();
+
+        let mut buf = vec![0; packet.header.length as usize];
+        packet.serialize(&mut buf[..]);
+        socket.write_with_mut(|sock| sock.send(&buf, 0)).await?;
+
+        'out: loop {
+            let mut buf = [0; 4096];
+            let mut cursor = 0;
+
+            let (count, _) = socket
+                .read_with_mut(|sock| sock.recv_from(&mut buf, 0))
+                .await?;
+            loop {
+                if cursor >= count {
+                    break;
+                }
+                let msg_len = {
+                    let mut len_buf = [0; 4];
+                    len_buf.copy_from_slice(&buf[cursor..cursor + 4]);
+                    u32::from_ne_bytes(len_buf) as usize
+                };
+                let msg_len = align(msg_len);
+                let reply = NetlinkMessage::<RtnlMessage>::deserialize(&buf[cursor..cursor + msg_len])
+                    .expect("Failed to deserialize message");
+                match reply.payload {
+                    NetlinkPayload::InnerMessage(RtnlMessage::NewLink(link)) => {
+                        let name = link
+                            .nlas
+                            .iter()
+                            .filter_map(|nla| match nla {
+                                Nla::IfName(name) => Some(name.clone()),
+                                _ => None,
+                            })
+                            .next()
+                            .unwrap();
+                        println!("{}: {}", link.header.index, name);
+                    }
+                    _ => {
+                        break 'out;
+                    }
+                }
+                cursor += msg_len;
+            }
+        }
+
+        Ok(())
+    })
+}