Werkzeug: TypeError em BaseRequest.trusted_hosts quando um nome de host começa com um '.'

Adicionar um nome de host começando com . a wrappers.BaseRequest.trusted_hosts resulta em TypeError: must be str, not bytes (Python 3.6) ou TypeError: Can't convert 'bytes' object to str implicitly (Python 3.4), como em werkzeug.wsgi.host_is_trusted , _normalize primeiro chama _encode_idna , que codifica ref para bytes e então se começar com '.', é concatenado com o '.' , misturando assim str e bytes .

Aplicativo de amostra

from flask import Flask, request

class TrustedHosts:
    """Flask extension setting `werkzeug.wrappers.BaseRequest.trusted_hosts`."""
    def __init__(self, app=None, trusted_hosts=None):
        self.app = app
        self.trusted_hosts = trusted_hosts
        if app is not None:
            self.init_app(app)

    def init_app(self, app):
        app.before_request(self.set_trusted_hosts)

    def set_trusted_hosts(self):
        # As host is a <strong i="20">@cached_property</strong> this should before its first access.
        request.trusted_hosts = self.trusted_hosts
        print(request.host)

app = Flask(__name__)
TrustedHosts(app, trusted_hosts=['.example.com'])

@app.route('/')
def index():
    return 'OK'

Rastreamento de pilha completo

Traceback (most recent call last):
  File "c:\program files\python36\lib\site-packages\flask\app.py", line 1982, in wsgi_app
    response = self.full_dispatch_request()
  File "c:\program files\python36\lib\site-packages\flask\app.py", line 1614, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "c:\program files\python36\lib\site-packages\flask\app.py", line 1517, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "c:\program files\python36\lib\site-packages\flask\_compat.py", line 33, in reraise
    raise value
  File "c:\program files\python36\lib\site-packages\flask\app.py", line 1610, in full_dispatch_request
    rv = self.preprocess_request()
  File "c:\program files\python36\lib\site-packages\flask\app.py", line 1831, in preprocess_request
    rv = func()
  File "D:\Dropbox\p\kb\python\web\flask\trusted_hosts.py", line 17, in set_trusted_hosts
    print(request.host)
  File "c:\program files\python36\lib\site-packages\werkzeug\local.py", line 347, in __getattr__
    return getattr(self._get_current_object(), name)
  File "c:\program files\python36\lib\site-packages\werkzeug\utils.py", line 73, in __get__
    value = self.func(obj)
  File "c:\program files\python36\lib\site-packages\werkzeug\wrappers.py", line 635, in host
    return get_host(self.environ, trusted_hosts=self.trusted_hosts)
  File "c:\program files\python36\lib\site-packages\werkzeug\wsgi.py", line 160, in get_host
    if not host_is_trusted(rv, trusted_hosts):
  File "c:\program files\python36\lib\site-packages\werkzeug\wsgi.py", line 132, in host_is_trusted
    if suffix_match and hostname.endswith('.' + ref):
TypeError: must be str, not bytes
127.0.0.1 - - [11/Dec/2017 17:11:18] "GET / HTTP/1.1" 500 -