How to determine the message status (read/unread) in chat?

Question

How to determine the message status (read/unread). Chat is realized with the XMPP protocol.

Answer 1

XEP-0184: Message Delivery Receipts supports notifying senders when their message has been delivered. You might be able to use that as a building block, as long as you don't expect existing clients to send these receipts -- the XEP is not widely-implemented today.