记录一次netty websocket 错误

异常1

An exceptionCaught() event was fired, and it reached at the tail of the pipeline. It usually means the last handler in the pipeline did not handle the exception.

异常意思是为在handler进行异常处理。初步异常处理代码如下

 @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx,cause);
        log.error("exception ", cause);
        Channel channel = ctx.channel();
        if (channel.isActive()) {
            channel.close();
        }
    }

解决方法：
去掉： super.exceptionCaught(ctx,cause);
异常处理重写就不需要走默认方法了

异常2

io.netty.util.IllegalReferenceCountException refCnt: 0, decrement: 1

代码如下：

@Override
    protected void channelRead0(ChannelHandlerContext ctx, Object o) throws Exception {
        if (o instanceof TextWebSocketFrame) {
            TextWebSocketFrame msg = (TextWebSocketFrame) o;
            //报错
            ctx.writeAndFlush(msg);

            //正常
            ctx.writeAndFlush(msg.retain());

            String text = msg.text();
            //正常
            ctx.writeAndFlush(new TextWebSocketFrame(text));
        } else {
            log.info("do some thing");
        }
    }

初步理解是netty的frame有内存自动释放，对象的生命周期由引用计数器控制，ByteBuf就是如此，每个对象的初始化引用计数为1，调用一次release方法，引用计数器会减1，当尝试访问计数器为0的，对象时，会抛出IllegalReferenceCountException，正如ensureAccessible的实现