Extend Iptables interface with SaveInto

pkg/util/iptables/iptables.go

@@ -56,6 +56,8 @@ type Interface interface {
 	IsIpv6() bool
 	// Save calls `iptables-save` for table.
 	Save(table Table) ([]byte, error)
+	// SaveInto calls `iptables-save` for table and stores result in a given buffer.
+	SaveInto(table Table, buffer *bytes.Buffer) error
 	// Restore runs `iptables-restore` passing data through []byte.
 	// table is the Table to restore
 	// data should be formatted like the output of Save()
@@ -315,6 +317,20 @@ func (runner *runner) Save(table Table) ([]byte, error) {
 	return runner.exec.Command(cmdIPTablesSave, args...).CombinedOutput()
 }
 
+// SaveInto is part of Interface.
+func (runner *runner) SaveInto(table Table, buffer *bytes.Buffer) error {
+	runner.mu.Lock()
+	defer runner.mu.Unlock()
+
+	// run and return
+	args := []string{"-t", string(table)}
+	glog.V(4).Infof("running iptables-save %v", args)
+	cmd := runner.exec.Command(cmdIPTablesSave, args...)
+	cmd.SetStdout(buffer)
+	cmd.SetStderr(buffer)
+	return cmd.Run()
+}
+
 // Restore is part of Interface.
 func (runner *runner) Restore(table Table, data []byte, flush FlushFlag, counters RestoreCountersFlag) error {
 	// setup args