From 77374c3a9c7daf972ffc73f6440f72d8ab6a90b2 Mon Sep 17 00:00:00 2001
From: sta <sta.blockhead@gmail.com>
Date: Mon, 16 Dec 2019 21:47:36 +0900
Subject: [PATCH] [Modify] Throw an exception

---
 websocket-sharp/Net/HttpListenerResponse.cs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/websocket-sharp/Net/HttpListenerResponse.cs b/websocket-sharp/Net/HttpListenerResponse.cs
index 4e0a6059..0db7b7e6 100644
--- a/websocket-sharp/Net/HttpListenerResponse.cs
+++ b/websocket-sharp/Net/HttpListenerResponse.cs
@@ -249,6 +249,11 @@ namespace WebSocketSharp.Net
         if (_disposed)
           throw new ObjectDisposedException (GetType ().ToString ());
 
+        if (_headersSent) {
+          var msg = "The response is already being sent.";
+          throw new InvalidOperationException (msg);
+        }
+
         _contentEncoding = value;
       }
     }