An overview of xdebug, the PHP debugging tool

1. xdebug
Shedding light on your code.

2. Who Is This Guy?
Bryce Embry
Application Developer at
Vanderbilt University Medical Center
Devoted user of Opera web browser
Ambivalent user of Windows Desktop
Handyman, cook, hobbyist musician, husband, & father

3. In this session…
▪ What is xdebug?
▪ Getting Started
▪ Tracing
▪ Profiling
▪ Debugging
▪ Debug Demo

4. What is xdebug

5. Tracing
List all the
functions being
called, and who is
calling them.

6. Profiling
See how long
each of those
function calls
takes

7. Debugging
Pause code execution
See variable values
Walk through code one
step at a time

8. Code Coverage
Identify which lines of a
script have been
executed during a
request.
This feature is used by
other programs to create
test coverage reports

9. Enhanced PHP Error Messages
Without
xdebug
With
xdebug

10. Getting Started

11. Two Part Install
▪ Server:
– Install xdebug extension to PHP
– Configure php.ini
– Restart web server
▪ Client
– Install browser extension

12. Server: Install Xdebug
http://xdebug.org/wizard.php

13. Server: Configure php
php.ini
phpinfo()

14. Client: URL Triggers
To trigger xdebug, need to use a cookie or add parameters to
the URL.
Doing this by hand violates the programming principle, “Work hard
to be lazy”.

15. Client: Bookmarklets
PHPStorm has a site to create
“bookmarklets” to add trigger
parameters to your URL.
https://www.jetbrains.com/phpstorm/marklets/

16. Client: Browser Extension
Firefox has an
extension
available.

17. Client: Browser Extension
Chrome has a better extension,
especially if you look at the
contributors.

18. Tracing

19. Running a trace
1. In
browser,
activate
trace
2. Load
web page
3. On server,
find trace file
4. Review
trace file

20. Trace Sample
foreach loop vs array_map

21. Sample Configurations
phpinfo
()
php.i
ni
https://xdebug.org/docs/execution_trace

22. Configuration Options
trace_enable_trigger Turn “on” to allow traces
trace_enable_trigger_valu
e
Sets a passcode that must be passed by browser to start a trace
trace_format Sets the output format for a trace as human-readable, machine readable, or HTML
trace_options Turn “on” to have trace data appended to a file instead of creating new file.
trace_output_dir Sets directory where trace file will be saved.
Make sure this directory is readable by the PHP process (ie Apache)
If using HTML output, set this as a web-accessible directory
trace_output_name Sets name for trace file. The extension “.xt” will be appended by default.
Can include variables such as:
%t = timestamp %R = $_SERVER[‘REQUEST_URI’]

23. Nifty Tool: xdebug-trace-tree
https://github.com/splitbrain/xdebug-trace-tree

24. Profiling

25. Running a profile
1. In browser,
activate
profile
2. Load web
page
3. Look for new
cachegrind file on
server.
4. Open in IDE
or KcacheGrind

26. Sample Profiles
kCacheGrin
d
PHPStorm

27. Sample Configurations
phpinfo
()
php.ini

28. Configuration Options
profiler_append Turn “on” to have data appended to existing file instead of creating a new file.
profiler_enable Turn “on” if you want constant profiling. (Hint: You don’t.)
profiler_enable_trigger Turn “on” to allow profiling to be activated by a browser trigger
profiler_enable_trigger_valu
e
Sets a passcode that must be passed by browser to start a profile
profiler_output_dir Sets directory where profile file will be saved.
Make sure this directory is readable by the PHP process (ie Apache)
profiler_output_name Sets name for profile file.
Can include variables such as:
%t = timestamp %s = script name

29. Nifty Tool: kcachegrind
https://kcachegrind.github.io/html/Home.html

30. Debugging

31. How debugging works
Web server IDE & Browser
http request / 80
dbgp / 9000
http response / 80

32. Debugging with xdebug
1. Set pause
point in code
2. Turn
on
listening
in IDE
3. Enable
debug in
browser
5. Walk through
code in the IDE
as it is executed
4. Load page
in browser

33. Sample Configurations
phpinfo
()
php.ini

34. Configuration Options
remote_enable Turn “on” to enable debugging
Remote_host Set the host name or IP address of the debugging client computer.
Can only have one value, so good way to lock down xdebug to only one user.
Remote_connect_back Turn “on” to ignore the remote_host setting and connect back to any xdebug
client. Useful if multiple developers are running from same debug server.
Remote_port Set the port xdebug uses for communication. Default is 9000.
Remote_mode Set to “req” to connect to debug client when code begins.
Set to “jit” to connect to debut client only on failure.

35. Tip: Map your code
If you have two
copies of code (local
and server), make
sure they are mapped
in the IDE and in-
sync. Otherwise,
xdebug will lie to you.

36. Tip: Debugging is one-way
Once you’ve passed
a point in code,
you can’t go back.

37. Tip: Navigating Code
Step
over
Step
into
Composer/Autoload/Classloader
Symfony/Component/Routing
Step
Out

38. Debug Demo

39. To show in demo
▪ Start / stop debug process
▪ Stepping through code
▪ Conditional break points
▪ Modifying values in running code

40. Questions?

41. End Notes
Resources:
xdebug.org
www.thornview.com
Presentation by:
Bryce.Embry@vanderbilt.edu
Fonts:
Sketchy - http://dl.dafont.com/dl/?f=sketchy
DJB Chalk It Up - http://dl.dafont.com/dl/?f=djb_chalk_it_up
Source Sans Pro - http://www.fontsquirrel.com/fonts/source-sans-pro