Netty源碼分析-WebSocketProtocolHandler

WebSocketProtocolHandler源碼分析

package io.netty.handler.codec.http.websocketx;


import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToMessageDecoder;

import java.util.List;

//WebSocketFrame的子類會進入此類處理
abstract class WebSocketProtocolHandler extends MessageToMessageDecoder<WebSocketFrame> {

	//默認true
    private final boolean dropPongFrames;

    WebSocketProtocolHandler() {
        this(true);
    }

    WebSocketProtocolHandler(boolean dropPongFrames) {
        this.dropPongFrames = dropPongFrames;
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, WebSocketFrame frame, List<Object> out) throws Exception {
    	//如果是Ping幀
        if (frame instanceof PingWebSocketFrame) {
        	//ByteBuf引用計數器+1，因爲父類會對frame.content進行釋放。
            frame.content().retain();
            //寫入Pong幀，在寫入完成後框架對frame.content進行釋放。
            ctx.channel().writeAndFlush(new PongWebSocketFrame(frame.content()));
            return;
        }
        //如果是Pong幀則不作處理
        if (frame instanceof PongWebSocketFrame && dropPongFrames) {
            return;
        }

        //其餘數據幀則先把引用計數器+1，在放入out
        //放入out的幀會傳遞到我們自定義的handler處理
        out.add(frame.retain());
    }

    //出現異常繼續傳遞並關閉socket連接
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.fireExceptionCaught(cause);
        ctx.close();
    }
}