Muc D-Bus tube: no way to guarantee that a member is identified before receiving messages from him
Submitted by Guillaume Desmottes @gdesmott
Assigned to Telepathy bugs list
Description
So, I'm working on implementing high level API in TpDBusTubeChannel to accept and offer the tube.
In the muc case, we have the DBusNames property allowing clients to identify members of the tube. I'd like to ensure that a member is identified (it's muc D-Bus name <-> TpContact mapping is known) before we receive any message from this contact on the tube; saving applications to have to deal with messages from unknown contacts.
http://telepathy.freedesktop.org/spec/Channel_Type_DBus_Tube.html#Property:DBusNames
But I'm afraid that's currently not possible. :\
When a contact joins the tube, the DBusNamesChanged signal is fired (so this signal is transmitted using the socket of the session bus). Then let's say we receive some traffic on the tube from this contact; this message is relayed by the CM through the socket of the tube D-Bus connection.
So we have information travelling on 2 different sockets making any ordering guarantee impossible!
Furthermore if the client wants to prepare the TpConctact before announcing it we really need a way to block the tube while it's preparing.
I see different options to approach this problem:
a) Block any traffic on the tube when DBusNamesChanged is fired with at least one contact added until the handle 'acks' this information and unblock the tube. Kinda nasty and breaks legacy D-Bus tube apps (but do we care tbh?).
b) Send the DBusNamesChanged information on the tube D-Bus connection as well, using a well known D-Bus API implemented by TpDBusTubeChannel on the tube. The CM could call a method ContactAdded(u: handle, s: id, s: dbus-name) or something and the client returns from this method when he's done preparing the contact; the tube staying blocked while this method is running. This looks like a better approach to me and doesn't break legay app: this method will just fail with NotImplemented.
Thoughts?