packer: Add PrefixedUi

packer/ui.go

@@ -14,6 +14,13 @@ type Ui interface {
 	Error(format string, a ...interface{})
 }
 
+// PrefixedUi is a UI that wraps another UI implementation and adds a
+// prefix to all the messages going out.
+type PrefixedUi struct {
+	Prefix string
+	Ui     Ui
+}
+
 // The ReaderWriterUi is a UI that writes and reads from standard Go
 // io.Reader and io.Writer.
 type ReaderWriterUi struct {
@@ -21,6 +28,14 @@ type ReaderWriterUi struct {
 	Writer io.Writer
 }
 
+func (u *PrefixedUi) Say(format string, a ...interface{}) {
+	u.Ui.Say(fmt.Sprintf("%s: %s", u.Prefix, format), a...)
+}
+
+func (u *PrefixedUi) Error(format string, a ...interface{}) {
+	u.Ui.Error(fmt.Sprintf("%s: %s", u.Prefix, format), a...)
+}
+
 func (rw *ReaderWriterUi) Say(format string, a ...interface{}) {
 	output := fmt.Sprintf(format, a...)
 	log.Printf("ui: %s", output)

packer/ui_test.go

@@ -13,6 +13,35 @@ func testUi() *ReaderWriterUi {
 	}
 }
 
+func TestPrefixedUi(t *testing.T) {
+	assert := asserts.NewTestingAsserts(t, true)
+
+	bufferUi := testUi()
+	prefixUi := &PrefixedUi{"mitchell", bufferUi}
+
+	prefixUi.Say("foo")
+	assert.Equal(readWriter(bufferUi), "mitchell: foo\n", "should have prefix")
+
+	prefixUi.Error("bar")
+	assert.Equal(readWriter(bufferUi), "mitchell: bar\n", "should have prefix")
+}
+
+func TestPrefixedUi_ImplUi(t *testing.T) {
+	var raw interface{}
+	raw = &PrefixedUi{}
+	if _, ok := raw.(Ui); !ok {
+		t.Fatalf("PrefixedUi must implement Ui")
+	}
+}
+
+func TestReaderWriterUi_ImplUi(t *testing.T) {
+	var raw interface{}
+	raw = &ReaderWriterUi{}
+	if _, ok := raw.(Ui); !ok {
+		t.Fatalf("ReaderWriterUi must implement Ui")
+	}
+}
+
 func TestReaderWriterUi_Error(t *testing.T) {
 	assert := asserts.NewTestingAsserts(t, true)