installer: Template: Make it gob-decodable

installer/template.go

@@ -3,6 +3,7 @@ package installer
 import (
 	"bufio"
 	"bytes"
+	"encoding/gob"
 	"io"
 	"strings"
 
@@ -58,6 +59,33 @@ func (t Template) ReplaceStringToString(s string) (string, error) {
 	)
 }
 
+func (t Template) GobEncode() ([]byte, error) {
+	buf := &bytes.Buffer{}
+	enc := gob.NewEncoder(buf)
+	err := enc.Encode(t.serviceName)
+	if err != nil {
+		return nil, err
+	}
+	err = enc.Encode(t.variables)
+	if err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func (t *Template) GobDecode(data []byte) error {
+	dec := gob.NewDecoder(bytes.NewReader(data))
+	err := dec.Decode(&t.serviceName)
+	if err != nil {
+		return err
+	}
+	err = dec.Decode(&t.variables)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func (t Template) replaceTag(w io.Writer, varName string) (int, error) {
 	if val, err := t.variables.Get(t.serviceName, varName); err == nil {
 		// Matched a variable local to the service.

installer/template_test.go

@@ -3,6 +3,7 @@ package installer_test
 import (
 	"bytes"
 	"errors"
+	"reflect"
 	"strings"
 	"testing"
 
@@ -96,6 +97,23 @@ func TestReplaceReader(t *testing.T) {
 	}
 }
 
+func TestGobCodec(t *testing.T) {
+	expected := installer.NewTemplate(serviceName, createVariables("var1", "value1"))
+
+	data, err := expected.GobEncode()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var result installer.Template
+	err = result.GobDecode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !reflect.DeepEqual(result, expected) {
+		t.Fatalf("expected decoded template %#v. Got %#v", expected, result)
+	}
+}
+
 const serviceName = "service1"
 
 func createVariables(keyVal ...string) repo.Variables {

repo/variables.go

@@ -145,6 +145,12 @@ func (vars *Variables) GobDecode(data []byte) error {
 	if err != nil {
 		return err
 	}
+	if len(vars.Common) == 0 {
+		// gob allocates an empty map even if we encoded a nil map.
+		// We want to replicate the behavior of NewVariables, so if
+		// gob allocated an empty map, we reset it to nil.
+		vars.Common = nil
+	}
 	err = dec.Decode(&vars.resolved)
 	if err != nil {
 		return err