Reverse proxy support does not work for subpath about unpub HOT 3 OPEN

<base href="/" />
...
<script defer src="main.dart.js"></script>

* browser requests http://localhost/unpub/
* apache redirects to http://localhost:4000
* unpub responses with index.html
* browser parses html and requests http://localhost/main.dart.js instead of http://localhost/unpub/main.dart.js
* apache doesn't redirect request and responses with 404

Uri.parse('http://localhost/unpub/').resolve('/api/smth').toString()
returns 'http://localhost/api/smth'
instead of 'http://localhost/unpub/api/smth'

  Map<String, dynamic> _versionToJson(UnpubVersion item, shelf.Request req) {
...
      'archive_url': _resolveUrl(req, '/packages/$name/versions/$version.tar.gz'),