Which event is always triggered when the client sends data to a virtual server using TCP.

`HTTP_DATA` is specifically triggered by HTTP application data, not all client data sent over TCP.

The `CLIENT_DATA` event is a generic TCP event that fires every time the client sends data to the virtual server on an established TCP connection. It is protocol-agnostic at the application layer, meaning it triggers for HTTP, FTP, raw TCP, or any other data sent by the client.

`HTTP_REQUEST` is triggered by the initial HTTP request headers, not all data sent by the client over TCP.

`VS_CONNECTED` is triggered when a connection is *established* between the client and the virtual server, not when data is *sent* on that connection.