Question: What causes the following error in Apache’s error logs?
[IP_address] Undeclared entity warning at line 226, column 1
Answer: A fairly popular, yet, poorly written WordPress plugin.
The first time this error hit the Weblogs.us error_log, one had no clue what was causing it. Unfortunately, the error does not indicate what file triggers the error. However, it will include the referring URI, if applicable. That’s how one found the specific virtual host on the Weblogs.us server that was triggering the error. Next, was finding the infringing code. To do this, one added define('WP_DEBUG', true); to the wp-config.php file for the virtual host. Now, there will be an avalanche of errors and warnings for most sites, all that needs to be done is sift through them and look for ones like “undeclared variable” and “undeclared index”.
Now, what was the actual culprit? The Twitter-for-Wordpress plugin. Specifically, lines 100, and 158. Line 100 tries to increment a non-initialized variable. To fix the issue on line 100, add a new line between line 66 and 67 and place in it $i = 0;. The error on line 158 is it tries to use the undeclared variable $username. What probably happened was author copied the line directly from line 53, while not properly modified for its location. Line 158 should read:
$messages = fetch_rss('http://twitter.com/statuses/user_timeline/'.$item['username'].'.rss');
After these two changes everything should be good to go. Yes, the plugin author was notified of these problems. We’ll see when they officially get fixed in the plugin.
-John Havlik
[end of transmission, stay tuned]