A couple of years ago, before I knew about Stack Overflow, I was working in an office with a lot of competition between the programmers. There, I had to code a web page in PHP with Drupal, that needed to get data from another site by RSS. What happened was that there was no way to get the data beforehand: the data depended on the content of the page which itself was dynamic, so the page stopped loading for a couple of seconds while PHP went to get the RSS data. That was bad. The page depended on a couple of parameters out of a huge list. So fetching all possible combinations in davance was out of the questions. It was some sort of search page, that included the results of a sister site, I think.
The first thing I did to improve that was to set up a caching system. When the page was loaded, it launched a Javascript method that saved the RSS data back into the database for this specific page, using AJAX. That meant that if the same page was requested again, the old data would be sent immediately. and the AJAX script would get the cache updated with the new data, if needed. The Javascript pretty much opened a hidden page on the site with a GET instruction that matched the current page’s parameters. It’s only a couple of days later that I realised that I could have cached the data without the AJAx. (Trust me, it’s easier to spot in hindsight.) But that’s not the issue I’m asking about.
But I was told not to do any caching at all. I was told that my AJAX page “exposed the API”. That a malicious user could hit the hidden page again and again to do a Denial of Service attack. I thought my AJAX was a temporary solution anyway, but that caching was needed. But mostly: wasn’t the DoS argument true of ANY page on the site? Did the fact that my hidden page did not appear in the menus and returned no content make it worse?
As I said, there was a lot of competition between programmers, so the people around me, who were unanimous, might have been right, or they may have tried to stop me from doing something that was bad because they were not the ones doing it. (It happened a lot.) But I’m still curious. I was fully aware that my AJAX thing was a hack. I wanted to change that system as soon as I found something better, but I thought that no caching at all was even worse. Which was true? Doesn’t, by that logic, ALL AJAX expose the API? If we look past the fact that my AJAX was an ugly hack, was it really that dangerous?
I’ll admit again and again that it was an ugly, temporary fix, but my question is about having a “hidden” page that returns no content that makes the server do something. How horrible is that?
If I read your post correctly, it seems as if the AJAX requested version of the page would know to invalidate the cache each time?
If that’s the case, then I suppose your co-worker might have been saying that the hidden page would be susceptible to a DDOS attack in a way that the full pageload wasn’t. I.E. The full pageload would get a cached version on each pageload after the first, where as the AJAX version would get fresh content each time. If that’s the case, then s/he’s right.
By “expose the API”, your co-worker was saying that you were exposing the URL of a page that was doing work that should be done in the background. The outside world should not know about a URL whose sole purpose is to do some heavy lifting task. As you even said, you found a backend solution that didn’t require the user’s browser knowing about your worker process at all.
Yes, having no cache at all when the page relies on heavy content is worse than having an ajax version of the page do the caching, but I think the warning from your coworker was that no page, EVEN if it’s AJAX, should have the power to break the cache in a way you didn’t expect or intend.