Send RTMP messages to client handler

Add optional callback `handle_rtmp_message/2` to ClientHandlerBehaviour

lib/membrane_rtmp_plugin/rtmp_server/client_handler.ex

@@ -48,12 +48,19 @@ defmodule Membrane.RTMPServer.ClientHandler do
   """
   @callback handle_connection_closed(state :: state()) :: state()
 
+  @doc """
+  The optional callback invoked when the client handler receives a RTMP message.
+  """
+  @callback handle_rtmp_message(msg :: term(), state()) :: state()
+
   @doc """
   The callback invoked when the client handler receives a message
   that is not recognized as an internal message of the client handler.
   """
   @callback handle_info(msg :: term(), state()) :: state()
 
+  @optional_callbacks handle_rtmp_message: 2
+
   @doc """
   Makes the client handler ask client for the desired number of buffers
   """
@@ -185,6 +192,25 @@ defmodule Membrane.RTMPServer.ClientHandler do
 
     state = Enum.reduce(events, state, &handle_event/2)
 
+    state =
+      if state.handler
+         && state.handler_state
+         && Kernel.function_exported?(state.handler, :handle_rtmp_message, 2) do
+
+      new_handler_state =
+        Enum.reduce(messages, state.handler_state, fn
+          ({%Membrane.RTMP.Header{}, message}, handler_state) when is_map(message) ->
+            state.handler.handle_rtmp_message(message, handler_state)
+          (message, handler_state) when is_map(message) ->
+            state.handler.handle_rtmp_message(message, handler_state)
+          (_, handler_state) -> handler_state
+        end)
+
+      %{state | handler_state: new_handler_state}
+    else
+      state
+    end
+
     request_data(state)
 
     {:noreply,