Guests can't join a room that's created on a different homeserver until a real user has joined that room from the same homeserver (SYN-655)

[matrixbot]

Submitted by @​dave:matrix.org

(Imported from https://matrix.org/jira/browse/SYN-655)

(Reported by @dbkr)

[matrixbot]

Jira watchers: @dbkr @richvdh

[matrixbot]

Links exported from Jira:

relates to #1559

[matrixbot]

Irrespective of peeking, apparently.

Just says, "Guest access not allowed"

-- @dbkr

[matrixbot]

Any idea why this might be? It sounds like a relatively easy fix?

-- @richvdh

[Half-Shot]

Got hit by this when working on https://github.com/Half-Shot/matrix-presents, because sharing a presentation between lots of folks is only really useful if some of them aren't required to log in.

Looks like

synapse/synapse/handlers/room_member.py

Lines 429 to 456 in 9dfcf47

	if effective_membership_state == Membership.JOIN:
	if requester.is_guest:
	guest_can_join = yield self._can_guest_join(current_state_ids)
	if not guest_can_join:
	# This should be an auth check, but guests are a local concept,
	# so don't really fit into the general auth process.
	raise AuthError(403, "Guest access not allowed")
	if not is_host_in_room:
	inviter = yield self._get_inviter(target.to_string(), room_id)
	if inviter and not self.hs.is_mine(inviter):
	remote_room_hosts.append(inviter.domain)
	content["membership"] = Membership.JOIN
	profile = self.profile_handler
	if not content_specified:
	content["displayname"] = yield profile.get_displayname(target)
	content["avatar_url"] = yield profile.get_avatar_url(target)
	if requester.is_guest:
	content["kind"] = "guest"
	remote_join_response = yield self._remote_join(
	requester, remote_room_hosts, room_id, target, content
	)
	return remote_join_response

checks the room's state for whether the guest can join a room, which obviously fails if we don't have the state for the room. I don't know whether the guest should try to join, and then leave if the permissions do not allow it (because effectively a guest is a real user over federation, and respecting the join rules for guests is more of a curtsey thing)

[richvdh]

gonna close this as a dup of #2065, because that one is clearer and has a link to a sytest