So, I'm sending PATCH requests to a server side, built with Lithium PHP Framework, and in side the controller actions I see that the $request->data is empty ... and I can't use the sent data.
What could be the problem? ...
(If I change the client side to send POST requests - then all is fine ... but the Lithium PHP Framework rely on the request type ... and so it breaks if the request type is PATCH ? ...)
What version of Lithium is used? Lithium didn't support PATCH method until this commit. See how support for PATCH was added in that commit so it should populate $request->data now.
Try to update to the most recent version of Lithium or just apply that patch to check if it solves the problem.
What web server are you using ? I had the same problem with li3_server library (https://github.com/daschl/li3_server). I changed to nginx and it worked fine.