@Override
        public void flush() throws IOException {
            try {
                super.flush();
                final byte[] bytes = toByteArray();
                trans_.write(bytes);
                trans_.flush();
            } catch (TTransportException ex) {
                throw new IOException(ex);
            }
            // Clears the internal memory buffer, since we've already
            // written it out.
            reset();
        }
Just a byte array output stream that forwards all data to
a TTransport when it is flushed or closed.
thrift/thrift0.13/src/main/java/com/linecorp/armeria/common/thrift/text/TTextProtocol.java