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//! Netlink-based namespace event subscriber.
//!
//! Receives RTM_NEWNSID and RTM_DELNSID events from the kernel.
//!
//! # Kernel Version Requirements
//!
//! - Linux 3.8+: Basic RTM_*NSID support
//! - Linux 4.9+: Reliable multicast delivery (recommended)
//!
//! # Limitations
//!
//! NSID events are triggered when namespace IDs are assigned or removed,
//! which doesn't always correspond to named namespace creation via `ip netns add`.
//! For tracking named namespaces, use `NamespaceWatcher` (filesystem-based) instead.
//!
//! # Example
//!
//! ```ignore
//! use nlink::netlink::namespace_events::{NamespaceEventSubscriber, NamespaceNetlinkEvent};
//!
//! let mut subscriber = NamespaceEventSubscriber::new().await?;
//!
//! while let Some(event) = subscriber.recv().await? {
//! match event {
//! NamespaceNetlinkEvent::NewNsId { nsid, pid, .. } => {
//! println!("New namespace ID {} from pid {:?}", nsid, pid);
//! }
//! NamespaceNetlinkEvent::DelNsId { nsid } => {
//! println!("Namespace ID {} removed", nsid);
//! }
//! }
//! }
//! ```
use super::{
error::Result,
messages::NsIdMessage,
socket::{NetlinkSocket, Protocol},
types::nsid::{RTM_DELNSID, RTM_NEWNSID, RTNLGRP_NSID},
};
/// Namespace-related netlink events.
#[derive(Debug, Clone, PartialEq, Eq)]
#[non_exhaustive]
pub enum NamespaceNetlinkEvent {
/// A new namespace ID was assigned.
NewNsId {
/// The namespace ID (local to this netns)
nsid: u32,
/// Process ID that triggered this (if available)
pid: Option<u32>,
/// File descriptor reference (if available)
fd: Option<i32>,
},
/// A namespace ID was removed.
DelNsId {
/// The namespace ID that was removed
nsid: u32,
},
}
/// Subscribe to namespace netlink events.
///
/// Listens for RTM_NEWNSID and RTM_DELNSID multicast messages.
pub struct NamespaceEventSubscriber {
socket: NetlinkSocket,
}
impl NamespaceEventSubscriber {
/// Create a new subscriber for namespace events.
///
/// Subscribes to the RTNLGRP_NSID multicast group.
///
/// # Errors
///
/// Returns an error if:
/// - Socket creation fails
/// - Multicast group subscription fails (may require CAP_NET_ADMIN)
pub async fn new() -> Result<Self> {
let mut socket = NetlinkSocket::new(Protocol::Route)?;
// Subscribe to namespace ID multicast group
socket.add_membership(RTNLGRP_NSID)?;
Ok(Self { socket })
}
/// Receive the next namespace event.
///
/// Blocks until a namespace event is received or an error occurs.
/// Returns `Ok(None)` if the socket is closed.
pub async fn recv(&mut self) -> Result<Option<NamespaceNetlinkEvent>> {
loop {
let data = self.socket.recv_msg().await?;
if data.is_empty() {
return Ok(None);
}
if let Some(event) = self.parse_message(&data) {
return Ok(Some(event));
}
// Not a namespace event, continue waiting
}
}
/// Parse a netlink message into a namespace event.
fn parse_message(&self, data: &[u8]) -> Option<NamespaceNetlinkEvent> {
// Netlink header is 16 bytes
if data.len() < 16 {
return None;
}
let msg_len = u32::from_ne_bytes(data[0..4].try_into().ok()?) as usize;
let msg_type = u16::from_ne_bytes(data[4..6].try_into().ok()?);
if msg_len > data.len() || msg_len < 16 {
return None;
}
let payload = &data[16..msg_len];
match msg_type {
RTM_NEWNSID => {
let msg = NsIdMessage::parse(payload)?;
let nsid = msg.nsid?; // NSID is required
Some(NamespaceNetlinkEvent::NewNsId {
nsid,
pid: msg.pid,
fd: msg.fd,
})
}
RTM_DELNSID => {
let msg = NsIdMessage::parse(payload)?;
let nsid = msg.nsid?;
Some(NamespaceNetlinkEvent::DelNsId { nsid })
}
_ => None,
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[tokio::test]
async fn test_subscriber_creation() {
// May require CAP_NET_ADMIN
let result = NamespaceEventSubscriber::new().await;
// Don't assert - depends on permissions
if result.is_err() {
eprintln!(
"Subscriber creation failed (may need CAP_NET_ADMIN): {:?}",
result.err()
);
}
}
#[test]
fn test_event_equality() {
let event1 = NamespaceNetlinkEvent::NewNsId {
nsid: 1,
pid: Some(1234),
fd: None,
};
let event2 = NamespaceNetlinkEvent::NewNsId {
nsid: 1,
pid: Some(1234),
fd: None,
};
assert_eq!(event1, event2);
let event3 = NamespaceNetlinkEvent::DelNsId { nsid: 5 };
let event4 = NamespaceNetlinkEvent::DelNsId { nsid: 5 };
assert_eq!(event3, event4);
}
}