ZOOKEEPER-4907 Shouldn't throw "Len error" when server closing

[jiafu1115]

Refer to ZOOKEEPER-4907

We got the error:

2024-11-07 19:03:01,414 [myid:14] - WARN [nioEventLoopGroup-7-25:NettyServerCnxn@537] - Closing connection to /135.224.186.250:47051
java.io.IOException: Len error 794913900
at org.apache.zookeeper.server.NettyServerCnxn.receiveMessage(NettyServerCnxn.java:521)
at org.apache.zookeeper.server.NettyServerCnxn.processMessage(NettyServerCnxn.java:374)
at org.apache.zookeeper.server.NettyServerCnxnFactory$CnxnChannelHandler.channelRead(NettyServerCnxnFactory.java:357)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)
at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead

It cause us very confused about it whether we write some big data into zookeeper. Thus. After trouble shooting, we found that it is just the log/issue when closing the server caused by reelecting the leader sometimes. In actually. We don't send any big data.

So I think we can do one tiny code change to avoid throw the error which causing confusion to reduce trouble shooting effort.

[jiafu1115]

The root cause for the error throw is caused by follow logic:
when closing the server. the follow code don't have chance to get executed:
bb = ByteBuffer.allocate(len); //line 552
so the remain message (body) will be taken as the head msg again and parsed again as the header.
then body length is not right now. sometimes it over the max size.
So I move the server status check before the length check.