this seems okay

storage/packable/packable.go

@@ -1,5 +1,11 @@
 package packable
 
+import (
+	"bytes"
+	"encoding/gob"
+	"net/url"
+)
+
 type Packable interface {
 	Encode() ([]byte, error)
 	Decode([]byte) error
@@ -20,7 +26,50 @@ func (s *String) Decode(b []byte) error {
 	return nil
 }
 
-func NewString(s string) *String {
-	w := String(s)
+func NewString(s ...string) *String {
+	if len(s) == 0 {
+		s = append(s, "")
+	}
+	w := String(s[0])
 	return &w
 }
+
+type URL struct {
+	Scheme string
+	Host   string
+	Path   string
+}
+
+func (u *URL) URL() *url.URL {
+	return &url.URL{
+		Scheme: u.Scheme,
+		Host:   u.Host,
+		Path:   u.Path,
+	}
+}
+
+func (u *URL) Encode() ([]byte, error) {
+	buf := bytes.NewBuffer(nil)
+	g := gob.NewEncoder(buf)
+	if err := g.Encode(*u); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+func (u *URL) Decode(b []byte) error {
+	buf := bytes.NewBuffer(b)
+	g := gob.NewDecoder(buf)
+	return g.Decode(&u)
+}
+
+func NewURL(u ...*url.URL) *URL {
+	if len(u) == 0 {
+		u = append(u, &url.URL{})
+	}
+	return &URL{
+		Scheme: u[0].Scheme,
+		Host:   u[0].Host,
+		Path:   u[0].Path,
+	}
+}

storage/packable/packable_test.go

@@ -1,6 +1,9 @@
 package packable
 
-import "testing"
+import (
+	"net/url"
+	"testing"
+)
 
 func TestPackableString(t *testing.T) {
 	raw := "hello"
@@ -21,3 +24,24 @@ func TestPackableString(t *testing.T) {
 		t.Errorf("wrong decoded string: %v vs %v", x, raw)
 	}
 }
+
+func TestPackableURL(t *testing.T) {
+	raw := &url.URL{
+		Scheme: "a",
+		Host:   "b",
+		Path:   "c",
+	}
+	s := NewURL(raw)
+
+	packed, err := s.Encode()
+	if err != nil {
+		t.Errorf("cannot encode URL: %v", err)
+	}
+
+	x := NewURL()
+	if err := x.Decode(packed); err != nil {
+		t.Errorf("cannot decode URL: %v", err)
+	} else if *x != *s {
+		t.Errorf("wrong decoded URL: %v (%T) vs %v (%T)", x, x, s, s)
+	}
+}