Refactor network creation and initialization into strategies

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/network/strategy.go

@@ -0,0 +1,32 @@
+package network
+
+import (
+	"errors"
+	"github.com/dotcloud/docker/pkg/libcontainer"
+)
+
+var (
+	ErrNotValidStrategyType = errors.New("not a valid network strategy type")
+)
+
+var strategies = map[string]NetworkStrategy{
+	"veth": &Veth{},
+}
+
+// NetworkStrategy represends a specific network configuration for
+// a containers networking stack
+type NetworkStrategy interface {
+	Create(*libcontainer.Network, int) (libcontainer.Context, error)
+	Initialize(*libcontainer.Network, libcontainer.Context) error
+}
+
+// GetStrategy returns the specific network strategy for the
+// provided type.  If no strategy is registered for the type an
+// ErrNotValidStrategyType is returned.
+func GetStrategy(tpe string) (NetworkStrategy, error) {
+	s, exists := strategies[tpe]
+	if !exists {
+		return nil, ErrNotValidStrategyType
+	}
+	return s, nil
+}