config: support unnumbered bgp peering

from configuration file:

```toml
[[neighbors]]
[[neighbors.afi-safis]]
neighbor-interface = "eth0"
peer-as = 65000
```

Signed-off-by: ISHIDA Wataru <ishida.wataru@lab.ntt.co.jp>

2 files changed, 67 insertions, 0 deletions

diff --git a/config/bgp_configs.go b/config/bgp_configs.go
index 44afcb82..1636073c 100644
--- a/config/bgp_configs.go
+++ b/config/bgp_configs.go
@@ -2477,6 +2477,8 @@ type NeighborState struct {
 	EstablishedCount uint32 `mapstructure:"established-count"`
 	// original -> gobgp:flops
 	Flops uint32 `mapstructure:"flops"`
+	// original -> gobgp:neighbor-interface
+	NeighborInterface string `mapstructure:"neighbor-interface"`
 }
 
 func (lhs *NeighborState) Equal(rhs *NeighborState) bool {
@@ -2551,6 +2553,9 @@ func (lhs *NeighborState) Equal(rhs *NeighborState) bool {
 	if lhs.Flops != rhs.Flops {
 		return false
 	}
+	if lhs.NeighborInterface != rhs.NeighborInterface {
+		return false
+	}
 	return true
 }
 
@@ -2583,6 +2588,8 @@ type NeighborConfig struct {
 	// original -> gobgp:admin-down
 	//gobgp:admin-down's original type is boolean
 	AdminDown bool `mapstructure:"admin-down"`
+	// original -> gobgp:neighbor-interface
+	NeighborInterface string `mapstructure:"neighbor-interface"`
 }
 
 func (lhs *NeighborConfig) Equal(rhs *NeighborConfig) bool {
@@ -2622,6 +2629,9 @@ func (lhs *NeighborConfig) Equal(rhs *NeighborConfig) bool {
 	if lhs.AdminDown != rhs.AdminDown {
 		return false
 	}
+	if lhs.NeighborInterface != rhs.NeighborInterface {
+		return false
+	}
 	return true
 }
 
diff --git a/config/default.go b/config/default.go
index ef3da7f1..e4cfeb4c 100644
--- a/config/default.go
+++ b/config/default.go
@@ -6,6 +6,7 @@ import (
 	"github.com/osrg/gobgp/packet/bmp"
 	"github.com/osrg/gobgp/packet/rtr"
 	"github.com/spf13/viper"
+	"github.com/vishvananda/netlink"
 	"net"
 )
 
@@ -71,6 +72,54 @@ func getIPv6LinkLocalAddress(ifname string) (string, error) {
 	return "", fmt.Errorf("no ipv6 link local address for %s", ifname)
 }
 
+func isLocalLinkLocalAddress(ifindex int, addr net.IP) (bool, error) {
+	ifi, err := net.InterfaceByIndex(ifindex)
+	if err != nil {
+		return false, err
+	}
+	addrs, err := ifi.Addrs()
+	if err != nil {
+		return false, err
+	}
+	for _, a := range addrs {
+		if ip, _, _ := net.ParseCIDR(a.String()); addr.Equal(ip) {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+func GetIPv6LinkLocalNeighborAddress(ifname string) (string, error) {
+	ifi, err := net.InterfaceByName(ifname)
+	if err != nil {
+		return "", err
+	}
+	neighs, err := netlink.NeighList(ifi.Index, netlink.FAMILY_V6)
+	if err != nil {
+		return "", err
+	}
+	cnt := 0
+	var addr net.IP
+	for _, neigh := range neighs {
+		local, err := isLocalLinkLocalAddress(ifi.Index, neigh.IP)
+		if err != nil {
+			return "", err
+		}
+		if neigh.IP.IsLinkLocalUnicast() && !local {
+			addr = neigh.IP
+			cnt += 1
+		}
+	}
+
+	if cnt == 0 {
+		return "", fmt.Errorf("no ipv6 link-local neighbor found")
+	} else if cnt > 1 {
+		return "", fmt.Errorf("found %d link-local neighbors. only support p2p link", cnt)
+	}
+
+	return fmt.Sprintf("%s%%%s", addr, ifname), nil
+}
+
 func SetDefaultNeighborConfigValues(n *Neighbor, asn uint32) error {
 	return setDefaultNeighborConfigValuesWithViper(nil, n, asn)
 }
@@ -103,6 +152,14 @@ func setDefaultNeighborConfigValuesWithViper(v *viper.Viper, n *Neighbor, asn ui
 		n.Timers.Config.IdleHoldTimeAfterReset = float64(DEFAULT_IDLE_HOLDTIME_AFTER_RESET)
 	}
 
+	if n.Config.NeighborInterface != "" {
+		addr, err := GetIPv6LinkLocalNeighborAddress(n.Config.NeighborInterface)
+		if err != nil {
+			return err
+		}
+		n.Config.NeighborAddress = addr
+	}
+
 	if n.Transport.Config.LocalAddress == "" {
 		if n.Config.NeighborAddress == "" {
 			return fmt.Errorf("no neighbor address/interface specified")