net/url: add URL.Redacted() to return password-free string

Returning an URL.String() without the password is very useful for
situations where the URL is supposed to be logged and the password is
not useful to be shown.

This method re-uses URL.String() but with the password scrubbed and
substituted for a "xxxxx" in order to make it obvious that there was a
password. If the URL had no password then no "xxxxx" will be shown.

Fixes golang#34855

src/net/url/url.go

@@ -821,6 +821,16 @@ func (u *URL) String() string {
 	return buf.String()
 }
 
+// Redacted is like String but redacts any password with "xxxxx".
+// Only the password in u.URL is redacted.
+func (u *URL) Redacted() string {
+	rdkt := *u
+	if _, has := rdkt.User.Password(); has {
+		rdkt.User = UserPassword(rdkt.User.Username(), "xxxxx")
+	}
+	return rdkt.String()
+}
+
 // Values maps a string key to a list of values.
 // It is typically used for query parameters and form values.
 // Unlike in the http.Header map, the keys in a Values map

src/net/url/url_test.go

@@ -765,6 +765,74 @@ func TestURLString(t *testing.T) {
 	}
 }
 
+var maskedURLTestsPtr = []struct {
+	url        *URL
+	want       string
+	shouldMask bool
+}{
+	{
+		url: &URL{
+			Scheme: "http",
+			Host:   "host.tld",
+			Path:   "this:that",
+			User:   UserPassword("user", "password"),
+		},
+		want:       "http://user:xxxxx@host.tld/this:that",
+		shouldMask: true,
+	},
+	{
+		url: &URL{
+			Scheme: "http",
+			Host:   "host.tld",
+			Path:   "this:that",
+			User:   User("user"),
+		},
+		want:       "http://user@host.tld/this:that",
+		shouldMask: false,
+	},
+}
+
+var redactedURLTests = []struct {
+	url  *URL
+	want string
+}{
+	{
+		url: &URL{
+			Scheme: "http",
+			Host:   "host.tld",
+			Path:   "this:that",
+			User:   UserPassword("user", "password"),
+		},
+		want: "http://user:xxxxx@host.tld/this:that",
+	},
+	{
+		url: &URL{
+			Scheme: "http",
+			Host:   "host.tld",
+			Path:   "this:that",
+			User:   User("user"),
+		},
+		want: "http://user@host.tld/this:that",
+	},
+}
+
+func TestURLRedacted(t *testing.T) {
+	for _, tt := range redactedURLTests {
+		if got := tt.url.Redacted(); got != tt.want {
+			t.Errorf("%+v.Redacted() = %q; want %q", tt.url, got, tt.want)
+		}
+	}
+	for _, tt := range maskedURLTestsPtr {
+		if got := tt.url.Redacted(); got != tt.want {
+			t.Errorf("%+v.Redacted() = %q; want %q", tt.url, got, tt.want)
+		}
+
+		if tt.shouldMask && tt.url.Redacted() == tt.url.String() {
+			t.Errorf("%+v.Redacted() password should differ to %+v.String()", tt.url, tt.url)
+		}
+	}
+}
+
 type EscapeTest struct {
 	in  string
 	out string