Link implementation in bridge driver

Signed-off-by: Madhu Venugopal <madhu@docker.com>

drivers/bridge/link.go

@@ -0,0 +1,80 @@
+package bridge
+
+import (
+	"fmt"
+	"net"
+
+	log "github.com/Sirupsen/logrus"
+	"github.com/docker/docker/pkg/iptables"
+	"github.com/docker/libnetwork/netutils"
+)
+
+type link struct {
+	parentIP string
+	childIP  string
+	ports    []netutils.PortBinding
+	bridge   string
+}
+
+func (l *link) String() string {
+	return fmt.Sprintf("%s <-> %s [%v] on %s", l.parentIP, l.childIP, l.ports, l.bridge)
+}
+
+func newLink(parentIP, childIP string, ports []netutils.PortBinding, bridge string) *link {
+	return &link{
+		childIP:  childIP,
+		parentIP: parentIP,
+		ports:    ports,
+		bridge:   bridge,
+	}
+
+}
+
+func (l *link) Enable() error {
+	// -A == iptables append flag
+	return linkContainers("-A", l.parentIP, l.childIP, l.ports, l.bridge, false)
+}
+
+func (l *link) Disable() {
+	// -D == iptables delete flag
+	err := linkContainers("-D", l.parentIP, l.childIP, l.ports, l.bridge, true)
+	if err != nil {
+		log.Errorf("Error removing IPTables rules for a link %s due to %s", l.String(), err.Error())
+	}
+	// Return proper error once we move to use a proper iptables package
+	// that returns typed errors
+}
+
+func linkContainers(action, parentIP, childIP string, ports []netutils.PortBinding, bridge string,
+	ignoreErrors bool) error {
+	var nfAction iptables.Action
+
+	switch action {
+	case "-A":
+		nfAction = iptables.Append
+	case "-I":
+		nfAction = iptables.Insert
+	case "-D":
+		nfAction = iptables.Delete
+	default:
+		return invalidIPTablesCfgError(action)
+	}
+
+	ip1 := net.ParseIP(parentIP)
+	if ip1 == nil {
+		return InvalidLinkIPAddrError(parentIP)
+	}
+	ip2 := net.ParseIP(childIP)
+	if ip2 == nil {
+		return InvalidLinkIPAddrError(childIP)
+	}
+
+	chain := iptables.Chain{Name: "DOCKER", Bridge: bridge}
+	for _, port := range ports {
+		err := chain.Link(nfAction, ip1, ip2, int(port.Port), port.Proto.String())
+		if !ignoreErrors && err != nil {
+			return err
+		}
+	}
+	return nil
+}