While fiddling with the Gmail API, I noticed that if I don't use any filters, the Users.messages: list method also returns messages sent and received through Google Hangout or Gmail Chat. Which is very nice.
The json object for a Hangout message is structured like an email (with payload, headers etc), but the only header provided is the sender. There's no information about the time the message is sent. I've looked through all other Gmail API methods (threads, history...) but none of them provides datetime information for chat messages.
Any idea if/how I could lookup a timestamp for chat/hangout messages (from within a backend process)?