route: add support for multipath routes

Add support for configuring multipath (ECMP) routes. This includes a
new `RouteNextHopBuilder` for creating nexthop entries with various
attributes.

`RouteMessageBuilder` now has a `multipath()` method to attach multiple
nexthops using the `RTA_MULTIPATH` attribute.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

Author: rwestphal

src/lib.rs

@@ -48,7 +48,7 @@ pub use crate::neighbour::{
 pub use crate::ns::{NetworkNamespace, NETNS_PATH, NONE_FS, SELF_NS_PATH};
 pub use crate::route::{
     IpVersion, RouteAddRequest, RouteDelRequest, RouteGetRequest, RouteHandle,
-    RouteMessageBuilder,
+    RouteMessageBuilder, RouteNextHopBuilder,
 };
 pub use crate::rule::{
     RuleAddRequest, RuleDelRequest, RuleGetRequest, RuleHandle,

src/route/builder.rs

@@ -9,7 +9,8 @@ use netlink_packet_route::{
     route::{
         MplsLabel, RouteAddress, RouteAttribute, RouteFlags, RouteHeader,
         RouteLwEnCapType, RouteLwTunnelEncap, RouteMessage, RouteMplsIpTunnel,
-        RouteProtocol, RouteScope, RouteType,
+        RouteNextHop, RouteNextHopFlags, RouteProtocol, RouteScope, RouteType,
+        RouteVia,
     },
     AddressFamily,
 };
@@ -20,6 +21,12 @@ pub struct RouteMessageBuilder<T = IpAddr> {
     _phantom: PhantomData<T>,
 }
 
+#[derive(Debug, Clone)]
+pub struct RouteNextHopBuilder {
+    address_family: AddressFamily,
+    nexthop: RouteNextHop,
+}
+
 impl<T> RouteMessageBuilder<T> {
     /// Create default RouteMessage with header set to:
     ///  * route: [RouteHeader::RT_TABLE_MAIN]
@@ -76,6 +83,14 @@ impl<T> RouteMessageBuilder<T> {
         self
     }
 
+    /// Sets multiple nexthop entries for the route.
+    pub fn multipath(mut self, nexthops: Vec<RouteNextHop>) -> Self {
+        self.message
+            .attributes
+            .push(RouteAttribute::MultiPath(nexthops));
+        self
+    }
+
     /// Sets the route priority (metric)
     pub fn priority(mut self, priority: u32) -> Self {
         self.message
@@ -467,3 +482,70 @@ impl Default for RouteMessageBuilder<MplsLabel> {
         Self::new()
     }
 }
+
+impl RouteNextHopBuilder {
+    /// Create default RouteNexthop for a route with the given address family.
+    pub fn new(address_family: AddressFamily) -> Self {
+        Self {
+            address_family,
+            nexthop: Default::default(),
+        }
+    }
+
+    /// Sets the nexthop interface index.
+    pub fn interface(mut self, index: u32) -> Self {
+        self.nexthop.interface_index = index;
+        self
+    }
+
+    /// Sets the nexthop (via) address.
+    pub fn via(mut self, addr: IpAddr) -> Result<Self, InvalidRouteMessage> {
+        use AddressFamily::*;
+        let attr = match (self.address_family, addr) {
+            (Inet, addr @ IpAddr::V4(_)) | (Inet6, addr @ IpAddr::V6(_)) => {
+                RouteAttribute::Gateway(addr.into())
+            }
+            (Inet, IpAddr::V6(v6)) => RouteAttribute::Via(RouteVia::Inet6(v6)),
+            (Mpls, _) => RouteAttribute::Via(addr.into()),
+            (af, _) => return Err(InvalidRouteMessage::AddressFamily(af)),
+        };
+        self.nexthop.attributes.push(attr);
+        Ok(self)
+    }
+
+    /// Marks the nexthop as directly reachable (on-link).
+    ///
+    /// Indicates that the nexthop is reachable without passing through a
+    /// connected subnet.
+    pub fn onlink(mut self) -> Self {
+        self.nexthop.flags.insert(RouteNextHopFlags::Onlink);
+        self
+    }
+
+    /// Sets the nexthop MPLS encapsulation labels.
+    pub fn mpls(mut self, labels: Vec<MplsLabel>) -> Self {
+        if labels.is_empty() {
+            return self;
+        }
+        if self.address_family == AddressFamily::Mpls {
+            self.nexthop
+                .attributes
+                .push(RouteAttribute::NewDestination(labels));
+        } else {
+            self.nexthop
+                .attributes
+                .push(RouteAttribute::EncapType(RouteLwEnCapType::Mpls));
+            let encap = RouteLwTunnelEncap::Mpls(
+                RouteMplsIpTunnel::Destination(labels),
+            );
+            self.nexthop
+                .attributes
+                .push(RouteAttribute::Encap(vec![encap]));
+        }
+        self
+    }
+
+    pub fn build(self) -> RouteNextHop {
+        self.nexthop
+    }
+}

src/route/mod.rs

@@ -8,6 +8,7 @@ mod handle;
 
 pub use self::add::RouteAddRequest;
 pub use self::builder::RouteMessageBuilder;
+pub use self::builder::RouteNextHopBuilder;
 pub use self::del::RouteDelRequest;
 pub use self::get::{IpVersion, RouteGetRequest};
 pub use self::handle::RouteHandle;