[Modify] Add it

websocket-sharp/WebSocket.cs

@@ -810,6 +810,51 @@ namespace WebSocketSharp
       return true;
     }
 
+    private bool checkIfAvailable (
+      bool client,
+      bool server,
+      bool connecting,
+      bool open,
+      bool closing,
+      bool closed,
+      out string message
+    )
+    {
+      message = null;
+
+      if (!client && _client) {
+        message = "This operation isn't available in: client";
+        return false;
+      }
+
+      if (!server && !_client) {
+        message = "This operation isn't available in: server";
+        return false;
+      }
+
+      if (!connecting && _readyState == WebSocketState.Connecting) {
+        message = "This operation isn't available in: connecting";
+        return false;
+      }
+
+      if (!open && _readyState == WebSocketState.Open) {
+        message = "This operation isn't available in: open";
+        return false;
+      }
+
+      if (!closing && _readyState == WebSocketState.Closing) {
+        message = "This operation isn't available in: closing";
+        return false;
+      }
+
+      if (!closed && _readyState == WebSocketState.Closed) {
+        message = "This operation isn't available in: closed";
+        return false;
+      }
+
+      return true;
+    }
+
     private bool checkReceivedFrame (WebSocketFrame frame, out string message)
     {
       message = null;