Synapse fails to make DNS query for its own hostname when attempting invite via 3PID

Hi!

~Synapse makes DNS ANY (ALL) requests through use of twisted, which sometimes fail.~ EDIT: My bad, this was apparently not what was happening, see thread for discussion.

For example when I’m trying to invite ‘ma1sd-federation-test@kamax.io’ as per instructions on https://github.com/ma1uta/ma1sd/blob/master/docs/getting-started.md the invitation fails. Upon investigation I see the following in the logs:

Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/synapse/http/server.py", line 252, in _async_render_wrapper
    callback_return = await self._async_render(request)
  File "/usr/local/lib/python3.8/site-packages/synapse/http/server.py", line 430, in _async_render
    callback_return = await raw_callback_return
  File "/usr/local/lib/python3.8/site-packages/synapse/rest/client/v1/room.py", line 734, in on_POST
    await self.room_member_handler.do_3pid_invite(
  File "/usr/local/lib/python3.8/site-packages/synapse/handlers/room_member.py", line 879, in do_3pid_invite
    stream_id = await self._make_and_store_3pid_invite(
  File "/usr/local/lib/python3.8/site-packages/synapse/handlers/room_member.py", line 941, in _make_and_store_3pid_invite
    ) = await self.identity_handler.ask_id_server_for_third_party_invite(
  File "/usr/local/lib/python3.8/site-packages/synapse/handlers/identity.py", line 856, in ask_id_server_for_third_party_invite
    data = await self.blacklisting_http_client.post_json_get_json(
  File "/usr/local/lib/python3.8/site-packages/synapse/http/client.py", line 530, in post_json_get_json
    response = await self.request(
  File "/usr/local/lib/python3.8/site-packages/synapse/http/client.py", line 422, in request
    response = await make_deferred_yieldable(request_deferred)
  File "/usr/local/lib/python3.8/site-packages/twisted/internet/defer.py", line 654, in _runCallbacks
    current.result = callback(current.result, *args, **kw)
  File "/usr/local/lib/python3.8/site-packages/twisted/internet/endpoints.py", line 981, in startConnectionAttempts
    raise error.DNSLookupError(
twisted.internet.error.DNSLookupError: DNS lookup failed: no results for hostname lookup: matrix.nilsson.link.

Note that it’s trying to make a DNS lookup to my own server, on my own network which my local dns server responds to. ~Unfortunately the dns request is of type 255 or ANY/ALL which has been deprecated for many years. My DNS server, correctly, returns an empty response.~

BTW, the following code also fails (for me) when doing a lookup on matrix.org, because google’s DNS server responds with a HINFO instead of a A or AAA record (or CNAME):

import sys

from twisted.python import log
from twisted.names import client

from twisted.internet import reactor

if __name__ == "__main__":
    log.startLogging(sys.stdout)
    client.theResolver = client.Resolver(servers=[("8.8.8.8", 53)])

    def cb(*args):
        log.msg(args)

    def do_lookup(domain):
        d = client.getHostByName(domain)
        d.addBoth(cb)

    from twisted.internet import reactor
    reactor.callLater(0, do_lookup, "matrix.org")
    reactor.run()