net/url: allow spaces in IPv6 zone identifier for Windows

Windows: putting spaces where they don't belong since Windows NT 3.1.

Fixes #14002.

Change-Id: I48ba8a7bfe3f27f83c8aa8355a8d355933d6c5df
Reviewed-on: https://go-review.googlesource.com/18855Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/url/url.go

@@ -193,8 +193,9 @@ func unescape(s string, mode encoding) (string, error) {
 				// that are valid host name bytes in their unescaped form.
 				// That is, you can use escaping in the zone identifier but not
 				// to introduce bytes you couldn't just write directly.
+				// But Windows puts spaces here! Yay.
 				v := unhex(s[i+1])<<4 | unhex(s[i+2])
-				if s[i:i+3] != "%25" && shouldEscape(v, encodeHost) {
+				if s[i:i+3] != "%25" && v != ' ' && shouldEscape(v, encodeHost) {
 					return "", EscapeError(s[i : i+3])
 				}
 			}

src/net/url/url_test.go

@@ -531,6 +531,17 @@ var urltests = []URLTest{
 		},
 		"",
 	},
+	// spaces in hosts are disallowed but escaped spaces in IPv6 scope IDs are grudgingly OK.
+	// This happens on Windows.
+	// golang.org/issue/14002
+	{
+		"tcp://[2020::2020:20:2020:2020%25Windows%20Loves%20Spaces]:2020",
+		&URL{
+			Scheme: "tcp",
+			Host:   "[2020::2020:20:2020:2020%Windows Loves Spaces]:2020",
+		},
+		"",
+	},
 }
 
 // more useful string for debugging than fmt's struct printer