in invoker/core/src/main/java/com/google/cloud/functions/invoker/http/HttpResponseImpl.java [102:116]
public void flush() {
try {
// We can't use HttpServletResponse.flushBuffer() because we wrap the
// PrintWriter returned by HttpServletResponse in our own BufferedWriter
// to match our API. So we have to flush whichever of getWriter() or
// getOutputStream() works.
try {
getOutputStream().flush();
} catch (IllegalStateException e) {
getWriter().flush();
}
} catch (IOException e) {
// Too bad, can't flush.
}
}