state: backup state

state/backup.go

@@ -0,0 +1,63 @@
+package state
+
+import (
+	"github.com/hashicorp/terraform/terraform"
+)
+
+// BackupState wraps a State that backs up the state on the first time that
+// a WriteState or PersistState is called.
+//
+// If Path exists, it will be overwritten.
+type BackupState struct {
+	Real State
+	Path string
+
+	done bool
+}
+
+func (s *BackupState) State() *terraform.State {
+	return s.Real.State()
+}
+
+func (s *BackupState) RefreshState() error {
+	return s.Real.RefreshState()
+}
+
+func (s *BackupState) WriteState(state *terraform.State) error {
+	if !s.done {
+		if err := s.backup(); err != nil {
+			return err
+		}
+	}
+
+	return s.Real.WriteState(state)
+}
+
+func (s *BackupState) PersistState() error {
+	if !s.done {
+		if err := s.backup(); err != nil {
+			return err
+		}
+	}
+
+	return s.Real.PersistState()
+}
+
+func (s *BackupState) backup() error {
+	state := s.Real.State()
+	if state == nil {
+		if err := s.Real.RefreshState(); err != nil {
+			return err
+		}
+
+		state = s.Real.State()
+	}
+
+	ls := &LocalState{Path: s.Path}
+	if err := ls.WriteState(state); err != nil {
+		return err
+	}
+
+	s.done = true
+	return nil
+}

state/backup_test.go

@@ -0,0 +1,29 @@
+package state
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestBackupState(t *testing.T) {
+	f, err := ioutil.TempFile("", "tf")
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	f.Close()
+	defer os.Remove(f.Name())
+
+	ls := testLocalState(t)
+	defer os.Remove(ls.Path)
+	TestState(t, &BackupState{
+		Real: ls,
+		Path: f.Name(),
+	})
+
+	if fi, err := os.Stat(f.Name()); err != nil {
+		t.Fatalf("err: %s", err)
+	} else if fi.Size() == 0 {
+		t.Fatalf("bad: %d", fi.Size())
+	}
+}