From 333ad153d07c1f082590a00a4b24efd7a19621b9 Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Wed, 18 Jun 2014 20:46:13 -0700
Subject: [PATCH] terraform: add a format byte to the diff file so we can
 iterate maybe

---
 terraform/diff.go | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/terraform/diff.go b/terraform/diff.go
index 5d1b656e1..f184b3093 100644
--- a/terraform/diff.go
+++ b/terraform/diff.go
@@ -3,6 +3,7 @@ package terraform
 import (
 	"bytes"
 	"encoding/gob"
+	"errors"
 	"fmt"
 	"io"
 	"sort"
@@ -10,6 +11,8 @@ import (
 	"sync"
 )
 
+const diffFormatByte byte = 1
+
 // Diff tracks the differences between resources to apply.
 type Diff struct {
 	Resources map[string]*ResourceDiff
@@ -21,6 +24,19 @@ type Diff struct {
 func ReadDiff(src io.Reader) (*Diff, error) {
 	var result *Diff
 
+	var formatByte [1]byte
+	n, err := src.Read(formatByte[:])
+	if err != nil {
+		return nil, err
+	}
+	if n != len(formatByte) {
+		return nil, errors.New("failed to read diff version byte")
+	}
+
+	if formatByte[0] != diffFormatByte {
+		return nil, fmt.Errorf("unknown diff file version: %d", formatByte[0])
+	}
+
 	dec := gob.NewDecoder(src)
 	if err := dec.Decode(&result); err != nil {
 		return nil, err
@@ -31,6 +47,14 @@ func ReadDiff(src io.Reader) (*Diff, error) {
 
 // WriteDiff writes a diff somewhere in a binary format.
 func WriteDiff(d *Diff, dst io.Writer) error {
+	n, err := dst.Write([]byte{diffFormatByte})
+	if err != nil {
+		return err
+	}
+	if n != 1 {
+		return errors.New("failed to write diff version byte")
+	}
+
 	return gob.NewEncoder(dst).Encode(d)
 }