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WebSockets.md

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WebSocket Interface

To enable the WebSocket interface for a specific device you need to set the Device or Node Application to websocket. You may also set the Group name as explained below.

To connect to the WebSocket, open URL ws://server:8080/ws/<Type>/<Name>/<Format>. The URL is used to select both the target device(s) as well as the desired format.

Type / Name Behaviour
/devices/123/... Connects to a device with a DevEUI=123.
/nodes/456/... Connects to an active node with a DevAddr=456.
/groups/ABC/... Connects to all websocket devices whose Group name is set to ABC.

Multiple parallel connections may be established to one URL. When the device sends a frame, all connected clients will receive the application data. Any of the clients may then send a response back. If multiple clients send data to the device the frames will be enqueued and sent one by one. The enqueued Downlinks can be viewed via the Node Administration page.

Format Behaviour
.../raw Transmits the raw application data only, no port numbers nor flags.
.../json Transmits JSON structures described in the JSON Payload documentation.

For example, ws://127.0.0.1:8080/ws/nodes/11223344/json connects to the DevAddr 11223344 using the JSON format.

The Backend Handlers are applicable also to WebSockets. If a JSON handler is defined for the Device / Node Group the Parse Uplink and Build Downlink functions are invoked to handle the "fields" attribute.

Keep-alive

By default, the WebSocket connection will be closed if the client (e.g. your web browser) sends for 1 hour no data back to the server. This is to avoid stale connections.

To keep the connection open for a longer time:

  • You can adjust the {websocket_timeout, 360000} configuration parameter to a higher value (in milliseconds).
  • You can even set {websocket_timeout, infinity} to disable the session expiration.
  • Or the client (browser) needs to keep sending ping frames.

The ping frames may not be enabled by default. To enable ping frames in Firefox, go to about:config and set network.websocket.timeout.ping.request to (for example) 120 (seconds).

Demo page

Demo client is available at http://127.0.0.1:8080/admin/ws.html. Select the target device or a group (DevEUI, DevAddr or Group) and the desired format (Raw or JSON) and establish a WebSocket connection. The page will display data received from the device and allow you to send data back.

In the Raw mode all information must be entered as a string of hexadecimal digits, without any spaces. Each byte is represented by exactly 2 digits. For example, "4849" represents ASCII string "01".

In the JSON mode the JSON structure described above is used for both uplinks and downlinks.