internal: use http.TimeFormat to marshal Time values

internal/elements.go

@@ -321,7 +321,7 @@ func (t *Time) UnmarshalText(b []byte) error {
 }
 
 func (t *Time) MarshalText() ([]byte, error) {
-	s := time.Time(*t).Format(time.RFC1123Z)
+	s := time.Time(*t).UTC().Format(http.TimeFormat)
 	return []byte(s), nil
 }
 

internal/elements_test.go

@@ -1,9 +1,11 @@
 package internal
 
 import (
+	"bytes"
 	"encoding/xml"
 	"strings"
 	"testing"
+	"time"
 )
 
 // https://tools.ietf.org/html/rfc4918#section-9.6.2
@@ -32,3 +34,26 @@ func TestMultistatus_Get_error(t *testing.T) {
 		t.Errorf("HTTPError.Code = %v, expected 423", httpErr.Code)
 	}
 }
+
+func TestTimeRoundTrip(t *testing.T) {
+	now := Time(time.Now().UTC())
+	want, err := now.MarshalText()
+	if err != nil {
+		t.Fatalf("could not marshal time: %+v", err)
+	}
+
+	var got Time
+	err = got.UnmarshalText(want)
+	if err != nil {
+		t.Fatalf("could not unmarshal time: %+v", err)
+	}
+
+	raw, err := got.MarshalText()
+	if err != nil {
+		t.Fatalf("could not marshal back: %+v", err)
+	}
+
+	if got, want := raw, want; !bytes.Equal(got, want) {
+		t.Fatalf("invalid round-trip:\ngot= %s\nwant=%s", got, want)
+	}
+}