Debugging Drupal - How to Debug your Drupal Application

Debugging with
Drupal
The art of
Debugging
Anoop John, CTO
Vimal Joseph, Technical Architect

The Art of Debugging
Bugs everywhere...
SA-CORE-2014-005

Bug-free Software?

Debugging
It's hard enough to find an error in your code when
you're looking for it; it's even harder when you've
assumed your code is error-free.
Steve McConnel

Story Time
Tell us a story on your debugging experience

Set up Debugging Environment
PHP configuration (php.ini)
display_errors = On
log_errors = On
error_reporting = E_ALL | E_STRICT
Drupal modules
Devel
A good editor
Geany
Emacs is better – but learning curve is bit steep.
Learn to setup a development environment for a
given project quickly. Drush will help.

Debugging Tools - PHP
Basic PHP
print/echo
print_r()
exit()/die()
debug_backtrace()/debug_print_backtrace()

Debugging Tools - Drupal
drupal_set_message()
watchdog()
Views
views_trace()
Devel
dpm()
dargs()
dd()
ddebug_backtrace()
db_queryd()

Debugging Tools - HTML, JS,
CSS
Firebug
Web Developer Toolbar
Javascript debugger

Debugging Tools - CLI
Drush – a life saver.
archive-dump, archive-restore, vget, vset, php-
eval, sql-cli, sql-query, user-login etc..
Xdebug
cat, grep, awk, cut

General Approach for
Debugging
Understand the symptom
Understand the context
Define problem statement
Replicate bug
Read through code
Isolate location in code causing bug
Understand code
Understand data / context
Understand cause
Identify solution
Fix bug

Tips for Debugging Code
Trial and error may work – but do not rely on that
Binary search is the best method to isolate a bug
Learn to navigate through code
Learn to read logs
Webserver Access/Error logs
Database Error logs
Drupal error logs
Be familiar with the shell commands
cat, zcat, grep, less etc..

Errors, Notices, Warnings
Warning: htmlspecialchars() expects
parameter 1 to be string, array given in
check_plain() (line 1566 of
/var/www/d7/includes/bootstrap.inc).
Invalid argument supplied for foreach()
in /var/www/d7/includes/common.inc on
line 1919.
Illegal offset type in isset or empty in
/home/pgil1/public_html/modules/taxon
omy/taxonomy.module on line 1090.

Backtrace – your guide
views_trace
debug_backtrace
debug_print_backtrace
ddebug_backtrace

// function drupal_set_message() bootstrap.inc
if ($type == 'error') {
// here are some alternatives – views_trace()
// is part of views module
// $message .= '<pre>' . print_r(debug_backtrace(),
TRUE) . '</pre>';
// $message .= '<pre>' . views_trace() . '</pre>';
}
// Or in function watchdog() bootstrap.inc
if ($type == 'php') {
$message .= '<pre>'. print_r(debug_backtrace(),
1) .'</pre>';
//$message .= '<pre>'. views_trace() .'</pre>';
}
// Or in the function which error occurred
ddebug_backtrace(); or dpm() or print_r() //make sure
to add the necessary conditions so that the debug

// Debuging cron
// module_invoke() module.inc
if ($hook == 'cron') {
watchdog('debugging', "CRON: Calling
$module");
}
// Errors like “Cannot use object of type
stdClass as array”
// Insert right before the moment of disaster
if (!is_array($x)) {
dpm(ddebug_backtrace(TRUE));
}

Tips for Debugging HTML, CSS,
JS
Inspect using Firebug
Create test HTML
Set custom properties
Walk through JS code execution
Inspect variables

Zyxware Technologies and Drupal
Zyxware is a leading contributor to Drupal from India and is one of only
six Featured Service Providers from India listed on drupal.org
● Over 40,000 websites use our modules and themes
● More than 30 contributed modules and themes
● Maintainer of Search404, a top 100 Drupal module
● Over 1000 commits at drupal.org
● Contributes all patches back to Drupal
● Our profile on drupal.org - http://drupal.org/user/222163
● Knowledge partnerships with Acquia, New Relic and Volacci

● Freedom Walk, a 44 day walk by a team of
Free Software Evangelists across the length of
Kerala to promote Free Software
● Building RithuOS, an Operating System for Engineering
students with Free Software Engineering applications
● GNU/Linux Install Fests in Schools, Colleges and at Technopark.
● Local language (Malayalam) computing camps in colleges
● Building and Maintenance of Freedom Toaster, a Free Software
kiosk
● Conducting Free Software workshops and
lectures in colleges in Kerala
Free Software and Zyxware Technologies

• Check us out at http://www.zyxware.com
• Mail us at drupal@zyxware.com
• Like us at http://www.facebook.com/zyxware
• Follow us at http://www.twitter.com/zyxware
• Connect with us at
http://www.linkedin.com/companies/zyxware-technologies
• Talk to us at +91-9495969446 between 9AM - 9PM IST
• Skype me at aj_zyxware
Contact Us

Thank you …

Credits
http://randyfay.com/content/debugging-techniques
http://www.lullabot.com/articles/quick_and_dirty_de
bugging

Debugging Drupal - How to Debug your Drupal Application

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