In v20, WebSocketServer is a new 4D class that enables creation of a WebSocket server for WebSocket connections. WebSocket servers are run via the 4D Web Server. Consequently, the web server must be started before a WebSocket server can be created. When initiating a WebSocket server, it is recommended to programmatically check if the web server has started beforehand. To do this, use the WEB server command like below:

$web_server:=WEB Server(Web server host database) If (Not($web_server.isRunning))    $web_server.start() End if

The above code instantiates the host database’s web server object, and then uses its “isRunning” property to verify if the web server is running. Then, it uses the start( ) method to programmatically start the web server if it’s not already running.