【ZooKeeper Notes 29】 修复“ZooKeeper客户端打印当前连接的服务器地址为null”的Bug问题描述

问题描述

公司之前进行了几次机房容灾演习中，经常是模拟一个机房挂掉的场景，把一个机房的网络切掉，使得这个机房内部网络通信正常，与外部的网络不通。在容灾演习过程中，我们发现ZK的客户端应用中出现大量类似这样的日志：

An exception was thrown while closing send thread for ession 0x for server null, unexpected error, closing socket connection and attempting  

从这个日志中，红色部分出现的是null。当时看到这个情况，觉得，正常情况正在，这个地方应用出现的是那个被隔离的机房中部署的ZooKeeper的机器IP的，但是这里出现的是null，非常困惑。

具体描述也可以在这里查看：https://issues.apache.org/jira/browse/ZOOKEEPER-1480

问题定位

看了下3.4.3及其以前版本的ZooKeeper代码，发现问题出在这里，日志打印的逻辑在这里：

} catch (Throwable e) {      if (closing) {          if (LOG.isDebugEnabled()) {              // closing so this is expected              LOG.debug("An exception was thrown while closing send thread for session 0x"                      + Long.toHexString(getSessionId())                      + " : " + e.getMessage());          }          break;      } else {          // this is ugly, you have a better way speak up          if (e instanceof SessionExpiredException) {              LOG.info(e.getMessage() + ", closing socket connection");          } else if (e instanceof SessionTimeoutException) {              LOG.info(e.getMessage() + RETRY_CONN_MSG);          } else if (e instanceof EndOfStreamException) {              LOG.info(e.getMessage() + RETRY_CONN_MSG);          } else if (e instanceof RWServerFoundException) {              LOG.info(e.getMessage());          } else {              LOG.warn(                      "Session 0x"                              + Long.toHexString(getSessionId())                              + " for server "                              + clientCnxnSocket.getRemoteSocketAddress()                              + ", unexpected error"                              + RETRY_CONN_MSG, e);          }  

可以看到，在打印日志过程，是通过clientCnxnSocket.getRemoteSocketAddress() 来获取当前连接的服务器地址的，那再来看下这个方法：

/**      * Returns the address to which the socket is connected.      * @return ip address of the remote side of the connection or null if not connected      */     @Override     SocketAddress getRemoteSocketAddress() {         // a lot could go wrong here, so rather than put in a bunch of code         // to check for nulls all down the chain let's do it the simple         // yet bulletproof way         try {             return ((SocketChannel) sockKey.channel()).socket()                     .getRemoteSocketAddress();         } catch (NullPointerException e) {             return null;         } }     /**      * Returns the address of the endpoint this socket is connected to, or      * <code>null</code> if it is unconnected.      * @return a <code>SocketAddress</code> reprensenting the remote endpoint of this      *         socket, or <code>null</code> if it is not connected yet.      * @see #getInetAddress()      * @see #getPort()      * @see #connect(SocketAddress, int)      * @see #connect(SocketAddress)      * @since 1.4      */     public SocketAddress getRemoteSocketAddress() {       if (!isConnected())         return null;       return new InetSocketAddress(getInetAddress(), getPort()); } 

所以，现在基本就可以定位问题了，如果服务器端非正常关闭socket连接（例如容灾演习的时候把机房网络切断），那么getRemoteSocketAddress这个方法就会返回null了，也就是日志中为什么出现null的原因了。 

问题解决

这个日志输出对于开发人员来说非常重要，在排查问题过程中可以清楚的定位当时是哪台服务器出现问题，但是这里一旦输出null，那么将无从下手。这里我做了一些改进，确保出现问题的时候，客户端能够输出当前出现问题的服务器IP。在这里下载补丁：https://github.com/downloads/nileader/taokeeper/getCurrentZooKeeperAddr_for_3.4.3.patch

首先是给org.apache.zookeeper.client.HostProvider类添加两个接口，分别用于获取“当前地址列中正在使用的地址序号”和获取“所有地址列表”。关于ZooKeeper客户端地址列表获取和随机原理，具体可以查看这个文章《ZooKeeper客户端地址列表的随机原理》。

public interface HostProvider {     …… ……     /**       * Get current index that is connecting or connected.       * @see ZOOKEEPER-1480:https://issues.apache.org/jira/browse/ZOOKEEPER-1480      * */     public int getCurrentIndex();     /**      * Get all server address that config when use zookeeper client.      * @return List       * @see ZOOKEEPER-1480:https://issues.apache.org/jira/browse/ZOOKEEPER-1480      */     public List<InetSocketAddress> getAllServerAddress();      } 

其次是修改org.apache.zookeeper.ClientCnxn类中日志输出逻辑：

/**          * Get current zookeeper addr that client is connected or connecting.<br>          * Note:The method will return null if can't not get host ip.          * */         private InetSocketAddress getCurrentZooKeeperAddr(){             try {                 InetSocketAddress addr = null;                 if( null == hostProvider || null == hostProvider.getAllServerAddress() )                     return addr;                 int index = hostProvider.getCurrentIndex();                 if ( index >= 0  ) {                     addr = hostProvider.getAllServerAddress().get( index );                 }                 return addr;             } catch ( Exception e ) {                 return null;             }         } …… ……         //get current ZK host to log         InetSocketAddress addr = getCurrentZooKeeperAddr();                  LOG.warn(             "Session 0x"                     + Long.toHexString(getSessionId())                     + " for server ip: " + addr + ", detail conn: "                     + clientCnxnSocket.getRemoteSocketAddress()                     + ", unexpected error"                     + RETRY_CONN_MSG, e);