net/url: ResolveReference doesn't handled path escaping #16947
Description
The URL.ResolveReference method uses the unescaped version of the path (rather than RawPath), and so loses the URL's desired escaping and makes incorrect decisions if the path contains escaped slashes (%2f).
As a simple example:
base := http://example.com/foo%2fbar/
ref := ../up
url := base.ResolveReference(ref) // == http://example.com/foo/up
The correct answer should be http://example.com/up
See https://play.golang.org/p/Xptwz1obCZ for an example comparing the behaviour of %2f and %20 (an interesting case is also with %2d – the final URL is correct, but you lose the desired escaping of the hyphen).
I think the fix is to make ResolveReference operate on the EscapedPath values, and unescape at the end.
/cc @bradfitz