Hi Alfredo,

In order to develop your custom generic client you should implement the Network Protocol for Generic Client. In the linked document you can find the full documentation of an HTTP-based network protocol necessary to connect to Lightstreamer by a generic application.
The Lightstreamer JavaScript library, indeed, uses a quite different protocol, reserved and undocumented. For this reason it will not be of great help to you sniff a JS client.

Furthermore, note also that the Generic Client API should be enabled server side, so please check if the Lighstreamer server you are targetting has this option turned up.