While this is not documented in the spec (but should be), Riot (and other clients) revoke 3PID invites by sending a m.room.third_party_invite event with an empty ({}) content to the room's state.
When the invited 3PID gets associated with a MXID, the identity server (which doesn't know about revocations) sends down to the MXID's homeserver all of the undelivered invites it has for this 3PID. The homeserver then tries to talk to the inviting homeserver in order to exchange these invite for m.room.member events.
When one of the invite is revoked, the inviting homeserver responds with a 500 error because it tries to extract a 'display_name' property from the content, which is empty. This might cause the invited server to consider that the server is down and not try to exchange other, valid invites (or at least delay it).
This fix handles the case of revoked invites by avoiding trying to fetch a 'display_name' from the original invite's content, and letting the m.room.member event fail the auth rules (because, since the original invite's content is empty, it doesn't have public keys), which results in sending a 403 with the correct error message to the invited server.
Another small fixup noticed during work on a larger PR. The `origin` field of `add_display_name_to_third_party_invite` is not used and likely was just carried over from the `on_PUT` method of `FederationThirdPartyInviteExchangeServlet` which, like all other servlets, provides an `origin` argument.
Since it's not used anywhere in the handler function though, we should remove it from the function arguments.
Python will return a tuple whether there are parentheses around the returned values or not.
I'm just sick of my editor complaining about this all over the place :)
I had to add quite a lot of logging to diagnose a problem with 3pid
invites - we only logged the one failure which isn't all that
informative.
NB. I'm not convinced the logic of this loop is right: I think it
should just accept a single valid signature from a trusted source
rather than fail if *any* signature is invalid. Also it should
probably not skip the rest of middle loop if a check fails? However,
I'm deliberately not changing the logic here.
Fixes that when a user exchanges a 3PID invite for a proper invite over
federation it does not include the `invite_room_state` key.
This was due to synapse incorrectly sending out two invite requests.
When processing an incoming event over federation, we may try and
resolve any unexpected differences in auth events. This is a
non-essential process and so should not stop the processing of the event
if it fails (e.g. due to the remote disappearing or not implementing the
necessary endpoints).
Fixes#3330
I was staring at this function trying to figure out wtf it was actually
doing. This is (hopefully) a non-functional refactor which makes it a bit
clearer.
Currently if a call to `/get_missing_events` fails we log an exception
and stop processing the top level event we received over federation.
Instead let's try and handle it sensibly given it is a somewhat expected
failure mode.
When filtering events to send to server we check more than just history
visibility. However when deciding whether to backfill or not we only
care about the history visibility.
