Archive for June, 2009

Error Handling and the PHP @ Operator

June 7th, 2009 by Sjan Evardsson

I have been trying to debug a plugin for WordPress (Shorten2Ping – I will keep plugging this because I think it is so nifty!) and I was running into a problem where the plugin would silently fail with nothing in the logs, no error printing to screen, just dead silence.

I turned on display_errors in php.ini for a while to see if anything would show up. Still nothing. So I started to look through the file again. I knew it was getting as far as creating the short url in bit.ly before it died, but nothing was getting entered into the database. So I started through the make_bitly_url() function and what jumped out and slapped me in the face? $json = @json_decode($response,true); That little, innocuous-looking @ was gulping the error message from a fatal error! (Namely, “Call to undefined function json_decode()“). It turns out that I had PHP compiled with –disable-json, which is default for Gentoo unless you have json in your USE flags.

According to the PHP docs for the Error Control Operator @:

Currently the “@” error-control operator prefix will even disable error reporting for critical errors that will terminate script execution. Among other things, this means that if you use “@” to suppress errors from a certain function and either it isn’t available or has been mistyped, the script will die right there with no indication as to why.

So, if you really must supress error messages, do so, but do so with care. In the case where a suppressed error may be fatal (as in this case) be sure to add documentation to that effect. As in “If this dies a silent death it may very well be that you do not have function xyz() enabled.”

And, note to self, when debugging PHP, the first thing to do is look for and remove the error control operator.

Interesting log activity

June 6th, 2009 by Sjan Evardsson

While trying to debug the Shorten2Ping plugin (a really nifty thing, if I could get it working) I went digging through my Apache error logs looking for any PHP errors. (Well, okay, I didn’t actually dig, I just did a last on the file.) What I saw was interesting, even though it did not help the debugging at all. In fact it kind of derailed the whole process. What I saw was an obvious attempt to find Horde on my server (which I did run temporarily a few years ago). My first guess was that there was a new exploit out for Horde. I did some digging around and found that, yes, indeedy, there is. I found the details of the exploit at securityvulns.com (which is a mirror of or mirrored by www.security.nnov.ru which is where the first relevant Google link took me.) Oddly enough I have not seen this show up on any other security sites yet, even though I see that the report on securityvulns.com is from March.

Anyhow, in case you are curious, here are the relevant lines from the log. (IPs have not been changed to protect the guilty.)

[Sat Jun 06 01:46:53 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/README
[Sat Jun 06 01:46:53 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde
[Sat Jun 06 01:46:54 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde2
[Sat Jun 06 01:46:55 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde3
[Sat Jun 06 01:46:56 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde-3.0.5
[Sat Jun 06 01:46:57 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde-3.0.6
[Sat Jun 06 01:46:58 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde-3.0.7
[Sat Jun 06 01:46:58 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde-3.0.8
[Sat Jun 06 01:46:59 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/horde-3.0.9
[Sat Jun 06 01:47:00 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/mail
[Sat Jun 06 01:47:01 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/email
[Sat Jun 06 01:47:02 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/webmail
[Sat Jun 06 01:47:03 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/newmail
[Sat Jun 06 01:47:03 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/mails
[Sat Jun 06 01:47:04 2009] [error] [client 81.210.76.194] File does not exist: /var/www/localhost/htdocs/evardsson.com/mailz