protected int channelDataRead(ReadableByteChannel channel, ByteBuff buf) throws IOException {
    int count = buf.read(channel);
    if (count > 0) {
      this.rpcServer.metrics.receivedBytes(count);
    }
    return count;
  }
Read off the wire. If there is not enough data to read, update the connection state with what
we have and returns.
@return Returns -1 if failure (and caller will close connection), else zero or more.
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/SimpleServerRpcConnection.java