terraform: read/write diff to binary format

terraform/diff.go

@@ -2,7 +2,9 @@ package terraform
 
 import (
 	"bytes"
+	"encoding/gob"
 	"fmt"
+	"io"
 	"sort"
 	"strings"
 	"sync"
@@ -14,6 +16,24 @@ type Diff struct {
 	once      sync.Once
 }
 
+// ReadDiff reads a diff structure out of a reader in the format that
+// was written by WriteDiff.
+func ReadDiff(src io.Reader) (*Diff, error) {
+	var result *Diff
+
+	dec := gob.NewDecoder(src)
+	if err := dec.Decode(&result); err != nil {
+		return nil, err
+	}
+
+	return result, nil
+}
+
+// WriteDiff writes a diff somewhere in a binary format.
+func WriteDiff(d *Diff, dst io.Writer) error {
+	return gob.NewEncoder(dst).Encode(d)
+}
+
 func (d *Diff) init() {
 	d.once.Do(func() {
 		if d.Resources == nil {

terraform/diff_test.go

@@ -1,6 +1,8 @@
 package terraform
 
 import (
+	"bytes"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -61,6 +63,44 @@ func TestResourceDiff_RequiresNew_nil(t *testing.T) {
 	}
 }
 
+func TestReadWriteDiff(t *testing.T) {
+	diff := &Diff{
+		Resources: map[string]*ResourceDiff{
+			"nodeA": &ResourceDiff{
+				Attributes: map[string]*ResourceAttrDiff{
+					"foo": &ResourceAttrDiff{
+						Old: "foo",
+						New: "bar",
+					},
+					"bar": &ResourceAttrDiff{
+						Old:         "foo",
+						NewComputed: true,
+					},
+					"longfoo": &ResourceAttrDiff{
+						Old:         "foo",
+						New:         "bar",
+						RequiresNew: true,
+					},
+				},
+			},
+		},
+	}
+
+	buf := new(bytes.Buffer)
+	if err := WriteDiff(diff, buf); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual, err := ReadDiff(buf)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if !reflect.DeepEqual(actual, diff) {
+		t.Fatalf("bad: %#v", actual)
+	}
+}
+
 const diffStrBasic = `
 CREATE: nodeA
   bar:     "foo" => "<computed>"