packer: {{timestamp}} is the same for an entire build [GH-744]

CHANGELOG.md

@@ -61,6 +61,8 @@ BUG FIXES:
 * core: User variables can now be used for non-string fields. [GH-598]
 * core: Fix bad download paths if the download URL contained a "."
   before a "/" [GH-716]
+* core: "{{timestamp}}" values will always be the same for the entire
+  duration of a build. [GH-744]
 * builder/virtualbox: don't download guest additions if disabled. [GH-731]
 * post-processor/vsphere: Uploads VM properly. [GH-694]
 * post-processor/vsphere: Process user variables.

packer/config_template.go

@@ -9,6 +9,15 @@ import (
 	"time"
 )
 
+// InitTime is the UTC time when this package was initialized. It is
+// used as the timestamp for all configuration templates so that they
+// match for a single build.
+var InitTime time.Time
+
+func init() {
+	InitTime = time.Now().UTC()
+}
+
 // ConfigTemplate processes string data as a text/template with some common
 // elements and functions available. Plugin creators should process as
 // many fields as possible through this.
@@ -89,7 +98,7 @@ func templateISOTime() string {
 }
 
 func templateTimestamp() string {
-	return strconv.FormatInt(time.Now().UTC().Unix(), 10)
+	return strconv.FormatInt(InitTime.Unix(), 10)
 }
 
 func templateUuid() string {

packer/config_template_test.go

@@ -49,6 +49,17 @@ func TestConfigTemplateProcess_timestamp(t *testing.T) {
 	if math.Abs(float64(currentTime-val)) > 10 {
 		t.Fatalf("val: %d (current: %d)", val, currentTime)
 	}
+
+	time.Sleep(2 * time.Second)
+
+	result2, err := tpl.Process(`{{timestamp}}`, nil)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if result != result2 {
+		t.Fatalf("bad: %#v %#v", result, result2)
+	}
 }
 
 func TestConfigTemplateProcess_user(t *testing.T) {