[#2768] Correctly duplicate buffer for CloseWebSocketFrames

Motivation:

The _0XFF_0X00 buffer is not duplicated and empty after the first usage preventing the connection close to happen on subsequent close frames.

Modifications:

Correctly duplicate the buffer.

Result:

Multiple CloseWebSocketFrames are handled correctly.

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocket00FrameEncoder.java

@@ -48,8 +48,9 @@ public class WebSocket00FrameEncoder extends MessageToMessageEncoder<WebSocketFr
             out.add(data.retain());
             out.add(_0XFF.duplicate());
         } else if (msg instanceof CloseWebSocketFrame) {
-            // Close frame
-            out.add(_0XFF_0X00);
+            // Close frame, needs to call duplicate to allow multiple writes.
+            // See https://github.com/netty/netty/issues/2768
+            out.add(_0XFF_0X00.duplicate());
         } else {
             // Binary frame
             ByteBuf data = msg.content();

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocket00FrameEncoderTest.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2014 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+package io.netty.handler.codec.http.websocketx;
+
+import io.netty.buffer.ByteBuf;
+import io.netty.channel.embedded.EmbeddedChannel;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class WebSocket00FrameEncoderTest {
+
+    // Test for https://github.com/netty/netty/issues/2768
+    @Test
+    public void testMultipleWebSocketCloseFrames() {
+        EmbeddedChannel channel = new EmbeddedChannel(new WebSocket00FrameEncoder());
+        Assert.assertTrue(channel.writeOutbound(new CloseWebSocketFrame()));
+        Assert.assertTrue(channel.writeOutbound(new CloseWebSocketFrame()));
+        Assert.assertTrue(channel.finish());
+        assertCloseWebSocketFrame(channel);
+        assertCloseWebSocketFrame(channel);
+        Assert.assertNull(channel.readOutbound());
+    }
+
+    private static void assertCloseWebSocketFrame(EmbeddedChannel channel) {
+        ByteBuf buf = channel.readOutbound();
+        Assert.assertEquals(2, buf.readableBytes());
+        Assert.assertEquals((byte) 0xFF, buf.readByte());
+        Assert.assertEquals((byte) 0x00, buf.readByte());
+        buf.release();
+    }
+}