[#547] process websocket CloseFrame

- If an endpoint receives a Close frame and did not previously send a
Close frame, the endpoint MUST send a Close frame in response.

src/main/java/com/corundumstudio/socketio/transport/WebSocketTransport.java

@@ -80,8 +80,7 @@ public class WebSocketTransport extends ChannelInboundHandlerAdapter {
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         if (msg instanceof CloseWebSocketFrame) {
-            ctx.channel().close();
-            ReferenceCountUtil.release(msg);
+          ctx.channel().writeAndFlush(msg).addListener(ChannelFutureListener.CLOSE);
         } else if (msg instanceof BinaryWebSocketFrame
                     || msg instanceof TextWebSocketFrame) {
             ByteBufHolder frame = (ByteBufHolder) msg;

src/test/java/com/corundumstudio/socketio/transport/WebSocketTransportTest.java

@@ -0,0 +1,53 @@
+/*
+ * @(#)WebSocketTransportTest.java 2018. 5. 23.
+ *
+ * Copyright 2018 NAVER Corp. All rights Reserved. NAVER PROPRIETARY/CONFIDENTIAL. Use is subject to
+ * license terms.
+ */
+package com.corundumstudio.socketio.transport;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.embedded.EmbeddedChannel;
+import io.netty.handler.codec.http.websocketx.CloseWebSocketFrame;
+
+/**
+ * @author hangsu.cho@navercorp.com
+ *
+ */
+public class WebSocketTransportTest {
+
+  /**
+   * Test method for {@link com.corundumstudio.socketio.transport.WebSocketTransport#channelRead()}.
+   */
+  @Test
+  public void testCloseFrame() {
+    EmbeddedChannel channel = createChannel();
+
+    channel.writeInbound(new CloseWebSocketFrame());
+    Object msg = channel.readOutbound();
+
+    // https://tools.ietf.org/html/rfc6455#section-5.5.1
+    // If an endpoint receives a Close frame and did not previously send a Close frame, the endpoint
+    // MUST send a Close frame in response.
+    assertTrue(msg instanceof CloseWebSocketFrame);
+  }
+
+  private EmbeddedChannel createChannel() {
+    return new EmbeddedChannel(new WebSocketTransport(false, null, null, null, null) {
+      /*
+       * (non-Javadoc)
+       * 
+       * @see
+       * com.corundumstudio.socketio.transport.WebSocketTransport#channelInactive(io.netty.channel.
+       * ChannelHandlerContext)
+       */
+      @Override
+      public void channelInactive(ChannelHandlerContext ctx) throws Exception {}
+    });
+  }
+
+}