private void initByteBuffToReadInto(int length) {
    this.data = rpcServer.bbAllocator.allocate(length);
    this.callCleanup = data::release;
  }
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