pkg/snet: always use topology to resolve interfaces

This way we can resolve interfaces even if they are dynamically
changing.

pkg/snet/packet_conn.go

@@ -15,8 +15,8 @@
 package snet
 
 import (
+	"context"
 	"net"
-	"net/netip"
 	"syscall"
 	"time"
 
@@ -121,8 +121,9 @@ type SCIONPacketConn struct {
 	// SCMP message is received.
 	SCMPHandler SCMPHandler
 	// Metrics are the metrics exported by the conn.
-	Metrics      SCIONPacketConnMetrics
-	interfaceMap interfaceMap
+	Metrics SCIONPacketConnMetrics
+	// Topology provides interface information for the local AS.
+	Topology Topology
 }
 
 func (c *SCIONPacketConn) SetReadBuffer(bytes int) error {
@@ -286,7 +287,7 @@ func (c *SCIONPacketConn) lastHop(p *Packet) (*net.UDPAddr, error) {
 		if !path.Info.ConsDir {
 			ifID = path.SecondHop.ConsEgress
 		}
-		return c.interfaceMap.get(ifID)
+		return c.interfaceIDToAddr(ifID)
 	case epic.PathType:
 		var path epic.Path
 		if err := path.DecodeFromBytes(rpath.Raw); err != nil {
@@ -304,7 +305,7 @@ func (c *SCIONPacketConn) lastHop(p *Packet) (*net.UDPAddr, error) {
 		if !infoField.ConsDir {
 			ifID = hf.ConsEgress
 		}
-		return c.interfaceMap.get(ifID)
+		return c.interfaceIDToAddr(ifID)
 	case scion.PathType:
 		var path scion.Raw
 		if err := path.DecodeFromBytes(rpath.Raw); err != nil {
@@ -322,12 +323,26 @@ func (c *SCIONPacketConn) lastHop(p *Packet) (*net.UDPAddr, error) {
 		if !infoField.ConsDir {
 			ifID = hf.ConsEgress
 		}
-		return c.interfaceMap.get(ifID)
+		return c.interfaceIDToAddr(ifID)
 	default:
 		return nil, serrors.New("unknown path type", "type", rpath.PathType.String())
 	}
 }
 
+func (c *SCIONPacketConn) interfaceIDToAddr(ifID uint16) (*net.UDPAddr, error) {
+	ctx, cancel := context.WithTimeout(context.Background(), 500*time.Millisecond)
+	defer cancel()
+	intfs, err := c.Topology.Interfaces(ctx)
+	if err != nil {
+		return nil, serrors.Wrap("resolving interfaces address (fetching interfaces)", err, "interface", ifID)
+	}
+	addrPort, ok := intfs[ifID]
+	if !ok {
+		return nil, serrors.New("interface number not found", "interface", ifID)
+	}
+	return net.UDPAddrFromAddrPort(addrPort), nil
+}
+
 type SerializationOptions struct {
 	// If ComputeChecksums is true, the checksums in sent Packets are
 	// recomputed. Otherwise, the checksum value is left intact.
@@ -342,13 +357,3 @@ type SerializationOptions struct {
 	// unchanged.
 	InitializePaths bool
 }
-
-type interfaceMap map[uint16]netip.AddrPort
-
-func (m interfaceMap) get(id uint16) (*net.UDPAddr, error) {
-	addrPort, ok := m[id]
-	if !ok {
-		return nil, serrors.New("interface number not found", "interface", id)
-	}
-	return net.UDPAddrFromAddrPort(addrPort), nil
-}

pkg/snet/snet.go

@@ -95,10 +95,6 @@ func (n *SCIONNetwork) OpenRaw(ctx context.Context, addr *net.UDPAddr) (PacketCo
 	if err != nil {
 		return nil, err
 	}
-	ifAddrs, err := n.Topology.Interfaces(ctx)
-	if err != nil {
-		return nil, err
-	}
 	if addr.Port == 0 {
 		pconn, err = listenUDPRange(addr, start, end)
 	} else {
@@ -118,10 +114,10 @@ func (n *SCIONNetwork) OpenRaw(ctx context.Context, addr *net.UDPAddr) (PacketCo
 		return nil, err
 	}
 	return &SCIONPacketConn{
-		Conn:         pconn,
-		SCMPHandler:  n.SCMPHandler,
-		Metrics:      n.PacketConnMetrics,
-		interfaceMap: ifAddrs,
+		Conn:        pconn,
+		SCMPHandler: n.SCMPHandler,
+		Metrics:     n.PacketConnMetrics,
+		Topology:    n.Topology,
 	}, nil
 }