MoQ Chat

Chat Operation

MoQ Relay The protocol requires a MoQ relay to act as a chat server. The relay maintains the set of connected clients that have announced a chat track.

Chat ID Every chat has a unique ID. The ID is a string of arbitrary length and uniquely identifies the chat. The creation of chat IDs and discovery of the relay is out of the scope of this document.

Track Names Each chat participant has a chat track. The namespace of the track is ("moq-chat", <id>, <user-id>, <device-id>, <timestamp>) and the name track is "chat".

id - the ID of the chatroom
user-id - the user ID
device-id - a unique identifier for each device for the user. This allows the same user to join the chat from multiple devices
timestamp - the timestamp in seconds when the track started, encoded as a string. This allows a stateless client to start publishing without accidentally overwriting a previously sent group and object. Note: the protocol will still function so long as each chat client selects a monotonically increasing number for this field. Using the common format described here could support future functionality like pulling chat history.

Joining the Chat To join the chat a participant sends a SUBSCRIBE_NAMESPACE message to the relay with a namespace prefix ("moq-chat", <id>). MoQ Relays track the current state of all announced namespaces and namespace subscriptions, and forward any matching ANNOUNCE or UNANNOUNCE messages to interested endpoints. The participant also sends an ANNOUNCE message for their chat track namespace.

Subscribing to Chat Messages When receiving an ANNOUNCE that matches the chat prefix, the client extracts the client's user-id, device-id and timestamp from the third, fourth and fifth tuple elements, respectively. The client SHOULD subscribe to the latest timestamp track for each (user-id, device-id) pair. Upon receiving an UNANNOUNCE, a client SHOULD UNSUBSCRIBE from that matching track if it had previously subscribed.

Chat Messages Each chat message is sent in a new Group and new Object. The format of a chat chat message this draft is UTF-8 Encoded text. There is no limit to the length of a chat message beyond those imposed on QUIC streams. Chat clients MUST send an END_OF_GROUP message for each Group. The starting Group ID for each track starts at 0 and increments by 1. The Object ID for each chat message starts at 0 and increments by 1.

Leaving the Chat When a user leaves the chat, they SHOULD send an UNANNOUNCE message for their namespace. They also SHOULD publish an object with status END_OF_TRACK_AND_GROUP on their chat track, since they will start a new track if they rejoin. Finally, they SHOULD send an UNSUBSCRIBE message for any tracks they subscribed to before closing their Transport Session. If all publishers of a given namespace disconnect from the relay abruptly, the relay will send UNANNOUNCE messages matching SUBSCRIBE_NAMESPACE to interested endpoints.

Stream Mapping The RECOMMENDED forwarding preference for the chat track is Subgroup, with all subgroup IDs set to 0, though clients MAY use other forwarding preferences at their discretion.

Session Closure by the Server If a client detects a MOQT session has been closed by the relay, it assumes the relay has exited or crashed, and does not attempt to reconnect.