Data channels

A device can open two data channels. The SFU copies what the device sends to every viewer that opens them. Only the viewer that controls the device can send back.

flowchart LR
  Device["Device<br/>_lossy and _reliable"] -- "copied to every viewer" --> SFU(("Realtime SFU"))
  SFU --> A["Viewer A<br/>controls the device"]
  SFU --> B["Viewer B<br/>waits in line"]
  A -. "only the controller reaches the device" .-> SFU
  SFU -.-> Device

Create each channel with negotiated: true and the id from the worker. The messages are protocol.Packet from packet.proto, with the text in raw.

On the device複製段落連結

1. Before the offer, create a negotiated channel server-events with id 0.
2. Send the offer with data_channels: true.
3. Create _lossy and _reliable with the ids in channels.
4. control tells you who controls the device.

On a viewer複製段落連結

The token request needs data_channels: true.

1. Send subscribe with data: [device_id].
2. Send take_control. If someone else has control, you wait in line.
3. When subscribed shows can_reply: true, send control_ready within 5 seconds.
4. Send release_control to give up control, or your place in line.

Control belongs to the device, not to a room. A viewer in another room of the same device can take over. When a viewer goes away for more than 30 seconds, the next viewer in line gets control.