I couldn’t resist another dorky software engineering post. Non dorks may stop reading here.
At work the other day, while debugging my code, I noticed that one of my servlets was getting called twice for each page load. What was even more mysterious was that the second call would happen as the page was partially loaded. I scoured my code for iframes, accidental use of the servlet, rouge AJAX calls and so on, but couldn’t find a thing. I resorted to just commenting out huge chunks of the page at a time to see which parts were causing the second page load. After a while, I narrowed it down to this:
<img src="$imgUrl" />
Where $imgUrl
is a variable who’s value is filled in at runtime. So, you might
be wondering how the heck an img
tag can cause the entire page to reload?
Well, it turns out (at least in Firefox 3) that if you have an img
tag with a
blank src
attribute, the browser tries to load an image at your base
URL—that is, the URL of the page you’re on. Therefore, every time
$imgUrl
turned out to be blank, my browser would re-request the page I was
on. This, of course, caused a bad performance hit, was screwing up statistics
and so on.
Moral of the story: make sure that your img
tags never have an empty src
attribute.
Bryan Covell
If you enjoyed this post, you may also like my books, Hello, Startup and Terraform: Up & Running. If you need help with DevOps or infrastructure, reach out to me at Gruntwork.