private void onDataFlush(ByteBuf buffer) {
        if (!buffer.isReadable()) {
            // response stream will be open only if there is something to write to it
            return;
        }
        if (responseWriter == null) {
            // create response stream, write headers adn mark response 'committed'
            responseWriter = HttpResponse.streaming();
            final ResponseHeaders responseHeaders = responseHeaders();
            responseWriter.write(responseHeaders);
            committed = true; // response is irreversible from this point on
        }
        responseWriter.write(HttpData.wrap(buffer));
    }
Implements {@link org.jboss.resteasy.spi.HttpResponse}.
resteasy/src/main/java/com/linecorp/armeria/server/resteasy/ResteasyHttpResponseImpl.java