Fix memory leak (#51)

* Fix memory leak

The `Tasker::Task` that pings each websocket was not being cleaned up
and garbage-collected, which meant that the WebSocket itself was also
not being GCed since it (and the WebSocketPinger itself) was referenced
inside the task block, leading to a leak for every single WebSocket.

I had a feeling this was the case because CPU and RAM consumption were
not static after a lot of WebSockets had been connected, even if they
were *no longer* connected. Turns out every single WebSocket was still
being pinged or raising an exception if it were closed. That exception
was not causing the `Tasker::Task` to stop.

* Update src/cable/websocket_pinger.cr

Co-authored-by: Jeremy Woertink <[email protected]>

src/cable/handler.cr

@@ -25,7 +25,7 @@ module Cable
         # Send welcome message to the client
         socket.send({type: Cable.message(:welcome)}.to_json)
 
-        Cable::WebsocketPinger.build(socket)
+        ws_pinger = Cable::WebsocketPinger.build(socket)
 
         socket.on_ping do
           socket.pong context.request.path
@@ -44,6 +44,7 @@ module Cable
         end
 
         socket.on_close do
+          ws_pinger.stop
           Cable.server.remove_connection(connection_id)
           Cable::Logger.info { "Finished \"#{path}\" [WebSocket] for #{remote_address} at #{Time.utc.to_s}" }
         end

src/cable/websocket_pinger.cr

@@ -5,6 +5,7 @@ module Cable
     class PingStoppedException < Exception; end
 
     @@seconds : Int32 | Float64 = 3
+    @task : Tasker::Task
 
     def self.run_every(value : Int32 | Float64, &block)
       @@seconds = value
@@ -23,10 +24,14 @@ module Cable
     end
 
     def initialize(@socket : HTTP::WebSocket)
-      Tasker.every(Cable::WebsocketPinger.seconds.seconds) do
+      @task = Tasker.every(Cable::WebsocketPinger.seconds.seconds) do
         raise PingStoppedException.new("Stopped") if @socket.closed?
         @socket.send({type: Cable.message(:ping), message: Time.utc.to_unix}.to_json)
       end
     end
+
+    def stop
+      @task.cancel
+    end
   end
 end