Uncaught InvalidCodepoint exception in POST /register

[DMRobertson]

https://sentry.matrix.org/sentry/sydent/issues/235984/events/eb7b2ee8efc645fd816bb38641c7e3a6/

StopIteration: _RoutingResult(host_header=b'https://chat.dev.glamster.io:443', tls_server_name=b'https://chat.dev.glamster.io', target_host=b'https://chat.dev.glamster.io', target_port=443)
  File "twisted/internet/defer.py", line 1661, in _inlineCallbacks
    result = current_context.run(gen.send, result)

InvalidCodepoint: Codepoint U+003A at position 6 of 'https://chat' not allowed
  File "sydent/http/servlets/__init__.py", line 184, in render
    result = await f(self, request)
  File "sydent/http/servlets/registerservlet.py", line 78, in render_POST
    1024 * 5,
  File "sydent/http/httpclient.py", line 60, in get_json
    uri.encode("utf8"),
  File "twisted/internet/defer.py", line 1661, in _inlineCallbacks
    result = current_context.run(gen.send, result)
  File "sydent/http/matrixfederationagent.py", line 164, in request
    routing.tls_server_name.decode("ascii")
  File "sydent/http/federation_tls_options.py", line 112, in get_options
    return ClientTLSOptions(host, self._options._makeContext())
  File "sydent/http/federation_tls_options.py", line 78, in __init__
    self._hostnameBytes = _idnaBytes(hostname)
  File "sydent/http/federation_tls_options.py", line 60, in _idnaBytes
    return idna.encode(text)
  File "idna/core.py", line 371, in encode
    s = alabel(label)
  File "idna/core.py", line 272, in alabel
    ulabel(label_bytes)
  File "idna/core.py", line 312, in ulabel
    check_label(label_bytes)
  File "idna/core.py", line 263, in check_label
    raise InvalidCodepoint('Codepoint {} at position {} of {} not allowed'.format(_unot(cp_value), pos+1, repr(label)))

idna.encode(text) might raise.

Encountered when someone tried to register with their host set to 'https://chat.dev.HOSTNAME.TLD. There shouldn't be a protocol; idna complained when it saw the colon.

Suggest catching idna.IDNAError in the call to get_options in matrixfederationagent.py, and doing something so that we return 400 BAD REQUEST.