Creating a room with invitees from non-federated HS fails, but the room is created though.

[bmarty]

When a client creates a room with invite and federation is denied with the invitee HS, the client get a 403 with body

{"errcode":"M_FORBIDDEN","error":"Federation denied with matrix.org."}

which is nice, but the room is actually created (no invitation is sent), which is a bit weird.

Synapse should ensure that it will be able to send invitations before creating the room, or create the room in memory and destroy it if something went wrong when sending the invitations.

Related workaround: element-hq/element-android#1969

[richvdh]

I'd expect us to have an issue for this already somewere.

[MadLittleMods]

Related issue to add a test for this scenario: #6122

[DMRobertson]

To do this:

synapse/synapse/handlers/room.py

Lines 801 to 806 in 945a092

	for i in invite_list:
	try:
	uid = UserID.from_string(i)
	parse_and_validate_server_name(uid.domain)
	except Exception:
	raise SynapseError(400, "Invalid user_id: %s" % (i,))

should also check that we can federate with uid.domain. If not, raise an appropriate SynapseError.