I have been using Android SDK, I tried this with 4.1.0-6.0.0 versions of SDK, it is broken on them all.
I send RETRIEVE_PARTICIPANTS_INFO intent and get the response in PARTICIPANTS_INFO_RETRIEVED, but it is formatted in something which is nearly json, but not quite. It is missing quotes. So gson fails. I tried debugging ParticipantsService class, which is a wrapper around those intents, also uses gson for parsing, it fails on the same parsing issue as I do when I do it.
Only way I can work around the issue is to have an insane protocol, where when a participant joins the room, everyone who gets PARTICIPANT_JOINED broadcast, pings the participant with its participant ID via endpoint message, which gets acked. It is like the “'morning/'morning” fish scene from Monty Python’s Meaning of Life.