Set a default route via bridge if config doesn't specify any

plugin/net/cni.go

@@ -4,6 +4,8 @@ import (
 	"crypto/rand"
 	"encoding/json"
 	"fmt"
+	"net"
+	"os"
 
 	"github.com/appc/cni/pkg/ipam"
 	"github.com/appc/cni/pkg/skel"
@@ -15,6 +17,11 @@ import (
 	ipamplugin "github.com/weaveworks/weave/plugin/ipam"
 )
 
+var (
+	zeroNetwork = net.IPNet{IP: net.IPv4zero, Mask: net.IPv4Mask(0, 0, 0, 0)}
+	mask32      = net.IPv4Mask(0xff, 0xff, 0xff, 0xff)
+)
+
 type CNIPlugin struct {
 	weave *weaveapi.Client
 }
@@ -97,15 +104,17 @@ func (c *CNIPlugin) CmdAdd(args *skel.CmdArgs) error {
 		return cleanup(errorf("IPAM plugin failed to allocate IP address"))
 	}
 
-	err = common.WithNetNS(ns, func() error {
-		guest, err := netlink.LinkByName(local.PeerName)
+	// If config says nothing about routes or gateway, default one will be via the bridge
+	if result.IP4.Routes == nil && result.IP4.Gateway == nil {
+		bridgeIP, err := findBridgeIP(conf.BrName, result.IP4.IP)
 		if err != nil {
 			return cleanup(err)
 		}
-		if err = netlink.LinkSetName(guest, args.IfName); err != nil {
-			return err
-		}
-		return ipam.ConfigureIface(args.IfName, result)
+		result.IP4.Gateway = bridgeIP
+	}
+
+	err = common.WithNetNS(ns, func() error {
+		return setupGuestIP4(local.PeerName, args.IfName, result.IP4.IP, result.IP4.Gateway, result.IP4.Routes)
 	})
 	if err != nil {
 		return cleanup(errorf("error setting up interface: %s", err))
@@ -115,6 +124,76 @@ func (c *CNIPlugin) CmdAdd(args *skel.CmdArgs) error {
 	return result.Print()
 }
 
+func setupGuestIP4(origName, name string, ipnet net.IPNet, gw net.IP, routes []types.Route) error {
+	guest, err := netlink.LinkByName(origName)
+	if err != nil {
+		return err
+	}
+	if err = netlink.LinkSetName(guest, name); err != nil {
+		return err
+	}
+	if err = netlink.LinkSetUp(guest); err != nil {
+		return err
+	}
+	if routes == nil { // If config says nothing about routes, add a default one
+		if !ipnet.Contains(gw) {
+			// The bridge IP is not on the same subnet; add a specific route to it
+			gw32 := &net.IPNet{IP: gw, Mask: mask32}
+			if err = addRoute(guest, netlink.SCOPE_LINK, gw32, nil); err != nil {
+				return err
+			}
+		}
+		routes = []types.Route{{Dst: zeroNetwork}}
+	}
+	if err = netlink.AddrAdd(guest, &netlink.Addr{IPNet: &ipnet}); err != nil {
+		return fmt.Errorf("failed to add IP address to %q: %v", name, err)
+	}
+	for _, r := range routes {
+		if r.GW != nil {
+			err = addRoute(guest, netlink.SCOPE_UNIVERSE, &r.Dst, r.GW)
+		} else {
+			err = addRoute(guest, netlink.SCOPE_UNIVERSE, &r.Dst, gw)
+		}
+		if err != nil {
+			return fmt.Errorf("failed to add route '%v via %v dev %v': %v", r.Dst, gw, name, err)
+		}
+	}
+	return nil
+}
+
+func addRoute(link netlink.Link, scope netlink.Scope, dst *net.IPNet, gw net.IP) error {
+	err := netlink.RouteAdd(&netlink.Route{
+		LinkIndex: link.Attrs().Index,
+		Scope:     scope,
+		Dst:       dst,
+		Gw:        gw,
+	})
+	if os.IsExist(err) { // squash duplicate route errors
+		err = nil
+	}
+	return err
+}
+
+func findBridgeIP(bridgeName string, subnet net.IPNet) (net.IP, error) {
+	netdevs, err := common.GetBridgeNetDev(bridgeName)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to get netdev for %q bridge: %s", bridgeName, err)
+	}
+	if len(netdevs) == 0 {
+		return nil, fmt.Errorf("Could not find %q bridge", bridgeName)
+	}
+	if len(netdevs[0].CIDRs) == 0 {
+		return nil, fmt.Errorf("Bridge %q has no IP addresses", bridgeName)
+	}
+	for _, cidr := range netdevs[0].CIDRs {
+		if subnet.Contains(cidr.IP) {
+			return cidr.IP, nil
+		}
+	}
+	// None in the required subnet; just return the first one
+	return netdevs[0].CIDRs[0].IP, nil
+}
+
 func (c *CNIPlugin) CmdDel(args *skel.CmdArgs) error {
 	conf, err := loadNetConf(args.StdinData)
 	if err != nil {