net/url: make URL implement encoding.BinaryMarshaler, BinaryUnmarshaler

This makes it possible to use URLs with gob.

Ideally we'd also implement TextMarshaler and TextUnmarshaler,
but that would change the JSON encoding of a URL from something like:

	{"Scheme":"https","Opaque":"","User":null,"Host":"www.google.com","Path":"/x","RawPath":"","ForceQuery":false,"RawQuery":"y=z","Fragment":""}

to something like:

	"https://www.google.com/x?y=z"

That'd be nice, but it would break code expecting the old form.

Fixes #10964.

Change-Id: I83f06bc2bedd2ba8a5d8eef03ea0056d045c258f
Reviewed-on: https://go-review.googlesource.com/31467Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/net/url/url.go

@@ -1025,3 +1025,19 @@ func portOnly(hostport string) string {
 	}
 	return hostport[colon+len(":"):]
 }
+
+// Marshaling interface implementations.
+// Would like to implement MarshalText/UnmarshalText but that will change the JSON representation of URLs.
+
+func (u *URL) MarshalBinary() (text []byte, err error) {
+	return []byte(u.String()), nil
+}
+
+func (u *URL) UnmarshalBinary(text []byte) error {
+	u1, err := Parse(string(text))
+	if err != nil {
+		return err
+	}
+	*u = *u1
+	return nil
+}

src/net/url/url_test.go

@@ -5,6 +5,10 @@
 package url
 
 import (
+	"bytes"
+	encodingPkg "encoding"
+	"encoding/gob"
+	"encoding/json"
 	"fmt"
 	"io"
 	"net"
@@ -1624,3 +1628,54 @@ func TestURLPort(t *testing.T) {
 		}
 	}
 }
+
+var _ encodingPkg.BinaryMarshaler = (*URL)(nil)
+var _ encodingPkg.BinaryUnmarshaler = (*URL)(nil)
+
+func TestJSON(t *testing.T) {
+	u, err := Parse("https://www.google.com/x?y=z")
+	if err != nil {
+		t.Fatal(err)
+	}
+	js, err := json.Marshal(u)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// If only we could implement TextMarshaler/TextUnmarshaler,
+	// this would work:
+	//
+	// if string(js) != strconv.Quote(u.String()) {
+	// 	t.Errorf("json encoding: %s\nwant: %s\n", js, strconv.Quote(u.String()))
+	// }
+
+	u1 := new(URL)
+	err = json.Unmarshal(js, u1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if u1.String() != u.String() {
+		t.Errorf("json decoded to: %s\nwant: %s\n", u1, u)
+	}
+}
+
+func TestGob(t *testing.T) {
+	u, err := Parse("https://www.google.com/x?y=z")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var w bytes.Buffer
+	err = gob.NewEncoder(&w).Encode(u)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	u1 := new(URL)
+	err = gob.NewDecoder(&w).Decode(u1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if u1.String() != u.String() {
+		t.Errorf("json decoded to: %s\nwant: %s\n", u1, u)
+	}
+}