protected long channelWrite(GatheringByteChannel channel, BufferChain bufferChain)
    throws IOException {
    long count = bufferChain.write(channel);
    if (count > 0) {
      this.metrics.sentBytes(count);
    }
    return count;
  }
Return the socket (ip+port) on which the RPC server is listening to. May return null if the
listener channel is closed.
@return the socket (ip+port) on which the RPC server is listening to, or null if this
        information cannot be determined
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/SimpleRpcServer.java