From: Thomas Karpiniec <tom.karpiniec@outlook.com>
Date: Sat, 8 Jun 2024 15:59:24 +0000 (+1000)
Subject: Groundwork for watching interface changes on Linux
X-Git-Tag: v0.1.0~17
X-Git-Url: https://code.octet-stream.net/netwatcher/commitdiff_plain/7cbddf0b21f7cf98b46c66a430eb8221f3622d55

Groundwork for watching interface changes on Linux
---

diff --git a/src/list_unix.rs b/src/list_unix.rs
index a6b2bd3..45ffc63 100644
--- a/src/list_unix.rs
+++ b/src/list_unix.rs
@@ -1,11 +1,9 @@
 use std::fmt::Write;
 use std::{collections::HashMap, net::IpAddr};
 
-use block2::Block;
-use nix::libc::c_long;
 use nix::{ifaddrs::getifaddrs, net::if_::if_nametoindex};
 
-use crate::{Error, IfIndex, Interface};
+use crate::{Error, Interface, List};
 
 struct CandidateInterface {
     name: String,
@@ -14,7 +12,7 @@ struct CandidateInterface {
     ips: Vec<IpAddr>,
 }
 
-pub(crate) fn list_interfaces() -> Result<HashMap<IfIndex, Interface>, Error> {
+pub(crate) fn list_interfaces() -> Result<List, Error> {
     let addrs = getifaddrs().map_err(|_| Error::Internal)?;
     let mut candidates = HashMap::new();
 
@@ -59,7 +57,7 @@ pub(crate) fn list_interfaces() -> Result<HashMap<IfIndex, Interface>, Error> {
             })
         })
         .collect();
-    Ok(ifs)
+    Ok(List(ifs))
 }
 
 fn format_mac(bytes: &[u8]) -> Result<String, Error> {
diff --git a/src/watch_linux.rs b/src/watch_linux.rs
index a987919..4e4049b 100644
--- a/src/watch_linux.rs
+++ b/src/watch_linux.rs
@@ -1,13 +1,57 @@
+use std::os::fd::AsRawFd;
+use std::os::fd::OwnedFd;
+
+use nix::libc::nlmsghdr;
+use nix::libc::RTMGRP_IPV4_IFADDR;
+use nix::libc::RTMGRP_IPV6_IFADDR;
+use nix::libc::RTMGRP_LINK;
+use nix::sys::socket::bind;
+use nix::sys::socket::recv;
+use nix::sys::socket::socket;
+use nix::sys::socket::AddressFamily;
+use nix::sys::socket::MsgFlags;
+use nix::sys::socket::NetlinkAddr;
+use nix::sys::socket::SockFlag;
+use nix::sys::socket::SockProtocol;
+use nix::sys::socket::SockType;
+
 use crate::Error;
 use crate::Update;
 
-pub(crate) struct WatchHandle;
+pub(crate) struct WatchHandle {
+    // PROBLEM: close() doesn't cancel recv() for a netlink socket
+    sockfd: OwnedFd,
+}
 
 pub(crate) fn watch_interfaces<F: FnMut(Update) + 'static>(
     callback: F,
 ) -> Result<WatchHandle, Error> {
-    // stop current worker thread
-    // post this into a thread that will use it
-    drop(callback);
-    Ok(WatchHandle)
+    let sockfd = start_watcher_thread(callback)?;
+    Ok(WatchHandle { sockfd })
+}
+
+fn start_watcher_thread<F: FnMut(Update) + 'static>(callback: F) -> Result<OwnedFd, Error> {
+    let sockfd = socket(AddressFamily::Netlink, SockType::Raw, SockFlag::empty(), Some(SockProtocol::NetlinkRoute))
+        .map_err(|_| Error::Internal)?; // TODO: proper errors
+    let sa_nl = NetlinkAddr::new(0, (RTMGRP_LINK | RTMGRP_IPV4_IFADDR | RTMGRP_IPV6_IFADDR) as u32);
+    bind(sockfd.as_raw_fd(), &sa_nl).map_err(|_| Error::Internal)?; // TODO: proper errors
+    let fd = sockfd.as_raw_fd();
+    println!("netlink socket on fd {}", fd);
+
+    std::thread::spawn(move || {
+        println!("watch thread running");
+        let mut buf = [0u8; 4096];
+        // recvmsg?
+        while let Ok(n) = recv(fd, &mut buf, MsgFlags::empty()) {
+            println!("something on the netlink socket: {} bytes", n);
+            let nlmsg_ptr = &buf as *const _ as *const nlmsghdr;
+            let nlmsg = unsafe { &*nlmsg_ptr };
+            // Right conventionally there's some trick here involving macros NLMSG_OK
+            // I can presumably do this using NetlinkGeneric too
+            // It's unclear whether this is worse or not - need to know what those macros do
+        }
+        println!("netlink recv thread terminating");
+    });
+    
+    Ok(sockfd)
 }