Finding and fixing bugs is a major chunk of any developers time. This talk describes the basic rules for effective debugging in any language, but shows how the tools available in PHP can be used to find and fix even the most elusive error

1. DEBUGGING
R U L E S A N D TO O L S
ian barber - http://phpir.com - @ianbarber

3. I did X
I wanted Y
Instead I got Z

4. http://www.debuggingrules.com

5. RULE 1
UNDERSTAND
THE SYSTEM

6. Bug
Wiki Tracker Frame
work
RTFM PHP
Doc
php.net

7. $field = $document->getField($fieldName);
if ($field->storeTermVector) {
/**
* @todo term vector storing support
*/
require_once
'Zend/Search/Lucene/Exception.php';
throw new Zend_Search_Lucene_Exception
('Store term vector functionality is not
supported yet.');
}

8. Komodo
Eclipse Zend
Studio
TOOLS
PHP Net
Storm Text Beans
Mate

9. RULE 2
MAKE IT
FAIL

10. Recreate And
Automate
PHP Unit
SimpleTest
Selenium
PHP Slim
JMeter
Ab

11. Time
Load Timing
User
Server
CONTROL
Env
VARIABLES
Request
Client DB
State
Session

12. [root@localhost ~]# pear channel-discover pear.phpunit.de
[root@localhost ~]# pear install phpunit/PHPUnit
class Test_User extends
PHPUnit_Framework_TestCase {
public function testUpdate() {
$r = ("a", "b");
try {
$u = User::fetch($this->newName);
$result = $u->update($r);
} catch (Id_Exception $e) {
$this->fail($e->getMessage());
}
$this->assertEquals($r, $u->getRoles());
}
}

13. http://seleniumhq.org/

14. class Example extends
PHPUnit_Extensions_SeleniumTestCase {
protected function setUp() {
$this->setBrowser("*chrome");
$this->setBrowserUrl("http://general.dev/");
}
public function testMyTestCase() {
$this->open("/");
$this->select("locale", "label=de");
$this->waitForPageToLoad("30000");
$this->assertTrue($this->isTextPresent(
"Datenbank-Einrichtung"));
}
}

15. http://jakarta.apache.org/jmeter/

16. RULE 3
QUIT THINKING
AND LOOK

17. if($this->hasRoles) {
$this->deleteRoles();
}
try {
foreach($submittedRoles as $role) {
$this->addRole($role);
}
} catch(Identity_Exception $e) {
$this->log->warn('Role add failed.');
throw new Service_Exception_BadRequest(
'Cannot add user role');
}

18. Instrumentation:
Inspect or Report

19. Xdebug
http://www.xdebug.org
[root@localhost ~]# pecl install xdebug
zend_extension=/usr/lib64/php/modules/xdebug.so

20. xdebug.profiler_enable=1
xdebug.profiler_output_dir=/tmp

21. xdebug.auto_trace=1
xdebug.collect_params=4

22. Key
Web Server
PHP Script
Key
Debugging Client XDebug
Debugging Commands

23. xdebug.remote_enable=1
xdebug.remote_port=9000
xdebug.remote_host=192.168.192.1
#xdebug.remote_connect_back=1

26. [root@localhost ~]# lsof -p 4365
COMMAND USER FD TYPE DEVICE NAME
httpd apache mem REG 253,0 /lib64/libssl.so.0.9.8e
httpd apache mem REG 253,0 /usr/lib64/php/modules/xdebug.so
httpd apache mem REG 253,0 /usr/lib64/libsqlite3.so.0.8.6
[root@localhost ~]# strace -cp 4365
Process 6910 attached - interrupt to quit
Process 6910 detached
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- -------------
36.91 0.037307 466 80 getdents
30.07 0.030393 950 32 7 access
17.04 0.017224 154 112 10 open
5.08 0.005136 12 444 9 lstat
3.87 0.003910 18 213 1 read
3.04 0.003071 29 107 close
2.57 0.002598 1299 2 writev
0.78 0.000785 1 631 stat

27. [root@localhost ~]# strace -Tp 4365
Process 6910 attached - interrupt to quit
epoll_wait(16, {{EPOLLIN, {u32=31389672, u64=47128707528680}}},
2, 10000) = 1 <6.926140>
accept(4, {sa_family=AF_INET6, sin6_port=htons(64930), inet_pton
(AF_INET6, "::ffff:192.168.192.1", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, [47128676139036]) = 17
<0.000094>
fcntl(17, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000035>
read(17,
"POST / HTTP/1.1rnHost: general.d"...,
8000) = 522 <0.000044>
stat("/mnt/hgfs/habari/htdocs/", {st_mode=S_IFDIR|0755,
st_size=408, ...}) = 0 <0.000527>
open("/mnt/hgfs/habari/htdocs/.htaccess",
O_RDONLY) = 18 <0.000457>
fcntl(17, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000037>

28. [root@localhost ~]# strace -Tp 4365
Process 6910 attached - interrupt to quit
epoll_wait(16, {{EPOLLIN, {u32=31389672, u64=47128707528680}}},
2, 10000) = 1 <6.926140>
accept(4, {sa_family=AF_INET6, sin6_port=htons(64930), inet_pton
(AF_INET6, "::ffff:192.168.192.1", &sin6_addr),
sin6_flowinfo=0, sin6_scope_id=0}, [47128676139036]) = 17
<0.000094>
fcntl(17, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000035>
read(17,
"POST / HTTP/1.1rnHost: general.d"...,
8000) = 522 <0.000044>
stat("/mnt/hgfs/habari/htdocs/", {st_mode=S_IFDIR|0755,
st_size=408, ...}) = 0 <0.000527>
open("/mnt/hgfs/habari/htdocs/.htaccess",
O_RDONLY) = 18 <0.000457>

29. Zend Drupal
Log syslog
sfLogger
Kohana
Log
error_log("Message for the PHP log")
error_log("Log to email", 1, "me@foo.com");
error_log("Log to a file",3, "/tmp/m.log");
error_log("Message for the SAPI log", 4);

30. MQ Syslog File
LOGGING
SYSTEM
Gearman Database Pipe

31. FirePHP

32. [root@localhost ~]# pear channel-discover pear.firephp.org
[root@localhost ~]# pear install firephp/FirePHPCore
require_once('FirePHPCore/FirePHP.class.php');
ob_start();
$firephp = FirePHP::getInstance(true);
doStuff($firephp);
$firephp->warn('Done Stuff');
$firephp->error('An error!');
$firephp->log($_GET);
ob_end_flush();
function doStuff($firephp) {
$firephp->trace('Stuff Backtrace');
echo "This page intentionally blank";
}

33. RULE 4
DIVIDE AND
CONQUER

34. <?xml version="1.0" encoding="UTF-8"?>
<phpunit bootstrap="./TestHelper.php"
colors="true">
<testsuite name="Commonlib Tests">
<directory>./library/Cl/</directory>
<directory>./library/Sso/</directory>
</testsuite>
<filter>
<whitelist>
<directory suffix=".php">../Sso/</directory>
<directory suffix=".php">../Cl/</directory>
</whitelist>
</filter>
</phpunit>

35. Folder Root
CL SSO
Auth Client Model User
Adapter Plugin Exception Abstract
SSO SFDC Gearman

36. <?php
$worker = new GearmanWorker();
$worker->addServer();
$worker->addFunction(
"allow_access", "allowAccess");
$worker->addFunction(
"deny_access", "denyAccess");
while ($worker->work());

37. Git Bisect
git bisect start
git bisect bad
git bisect good <known good rev>
git bisect ?
git bisect reset

38. good bad
1
Request View
2
Front 3
Controller Plugin
Input Model
Filter
Controller

39. Firewall
Cache
Web Server
Database

40. Tamper
Data
Curl
Firewall
Wireshark
Cache Netcat
Web Server
MySQL
Proxy Xdebug
Database

41. Tamper Data
https://addons.mozilla.org/firefox/addon/966

42. Wireshark
http://www.wireshark.org/

44. [root@localhost ~]# { echo -ne "HTTP/1.0 200 OKrn
rn"; cat test.html; } | nc -l 8080
GET / HTTP/1.1
User-Agent: curl/7.19.7 (i386-apple-darwin10.0.0)
libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
Host: general.dev:8080
Accept: */*
[root@localhost ~]# curl http://general.dev:8080 -v
* About to connect() to general.dev port 8080 (#0)
* Trying 192.168.192.129... connected
* Connected to general.dev (192.168.192.129) port
8080 (#0)
> GET / HTTP/1.1
> User-Agent: curl/7.19.7 (i386-apple-darwin10.0.0)
libcurl/7.19.7 OpenSSL/0.9.8l zlib/1.2.3
> Host: general.dev:8080

45. local log_file = 'mysql.log'
local fh = io.open(log_file, "a+")
function read_query( packet )
if string.byte(packet) == proxy.COM_QUERY
then
local query = string.sub(packet, 2)
fh:write( string.format("%sn",query))
fh:flush()
end
end
MySQL Proxy

46. RULE 5
CHANGE ONE
THING AT
A TIME

47. [root@localhost ~]#: svn st
M index.php
[root@localhost ~]#: git stash save
Saved working directory and index state WIP
on master: 0e22fdd Initial checkin
HEAD is now at 0e22fdd Initial checkin
[root@localhost ~]#: git status
# On branch master
nothing to commit (working directory clean)
Source Control

48. [root@localhost ~]#: svn log .
-------------------------------------------
r4341 | rickc | 2010-09-24 03:01 | 3 lines
Don't test if Post::tags is empty before
getting tags. There may be a performance
hit for this. It can be dealt with if it is
noticable. Fixes ticket #1235. Props to ilo
for the patch.
Note that Post still needs to be updated to
use real Tags, not an array of slug/label
pairs as the tags member.
--------------------------------------------
Source Control

49. Known Good
[root@localhost ~]# diff -yw web.conf web2.conf
<VirtualHost *:80> <VirtualHost *:80>
ServerAdmin root@e.com ServerAdmin root@e.com
DocumentRoot /www/htdocs | DocumentRoot /www/hdocs
ServerName general.dev ServerName general.dev
ErrorLog logs/error_log ErrorLog logs/error_log
</VirtualHost> </VirtualHost>

50. RULE 6
KEEP AN
AUDIT TRAIL

51. Hot Key Log
http://www.blacktree.com/
http://do.davebsd.com/
https://launchpad.net/mb
http://simplenoteapp.com/

52. Backpack Journal
http://backpackit.com/

53. [root@localhost htdocs]# history 20
365 ls /mnt/hgfs/habari/
366 ls
367 vi /etc/httpd/conf.d/web.conf
368 setenforce 0
369 /etc/init.d/httpd restart
370 vi /var/log/httpd/error_log
371 cd /mnt/hgfs/habari/
372 ls
373 cd htdocs/
374 ls
375 cd scripts/
376 ls
377 cd ..
378 ls
379 vi /etc/php.ini

54. RULE 7
CHECK THE
PLUG

55. Sources of Plugs
[root@localhost ~]# apachectl -M
Loaded Modules:
core_module (static)
mpm_prefork_module (static)
http_module (static)
so_module (static)
[root@localhost ~]# whoami
auth_basic_module (shared)
root
auth_digest_module (shared)
[root@localhost ~]# ifconfig
authn_file_module (shared)
eth0 Link encap:Ethernet HWad
authn_alias_module (shared)
authn_anon_module inet addr:192.168.192.129
(shared)
inet6 addr: fe80::20c:29ff:
authn_dbm_module (shared)

56. RULE 8
GET A FRESH
VIEW

57. if(!is_string($i)) {
throw new Xapian_Exception('Incorrect
query type, expecting string or array of
strings');
}
$q = $this->getParser()->parse_query($i);

58. if(!is_string($i)) {
throw new Xapian_Exception('Incorrect
query type, expecting string or array of
strings');
}
$q = $this->getParser()->parse_query($i,
FLAG_SPELLING_CORRECTION);

59. “Grovelling is not
a substitute for
doing your
homework”
- ESR
http://www.catb.org/esr/faqs/smart-questions.html

62. RULE 9
IF YOU DIDN’T
FIX IT -
IT AIN’T FIXED

63. Five Whys
The page is blank: Why?
There is a fatal error: Why?
No mb_check_encoding(): Why?
mbstring is not installed: Why?
It isn’t part of the build: Why?
It was setup for another project.

64. The Rules
1. Understand The System
2. Make It Fail
3. Quit Thinking And Look
4. Divide And Conquer
5. Change One Thing At A Time
6. Keep An Audit Trail
7. Check The Plug
8. Get A Fresh View
9. If You Didn’t Fix It, It Ain’t Fixed

65. Questions
?

66. Image Credits
When men were men and wore white coats - by Jitze
http://www.flickr.com/photos/jitze1942/4292084185/
Vacuum Tube Etch-A-Sketch - by Jurvetson
http://www.flickr.com/photos/jurvetson/197768962/
Classic - by Oskay
http://www.flickr.com/photos/oskay/1364147095
Firmware Bug - by Oskay
http://www.flickr.com/photos/oskay/1364148351
Ready to hop - by Oskay
http://www.flickr.com/photos/oskay/1364153441/
Albino - by Oskay
http://www.flickr.com/photos/oskay/1364143833
Coming Through! - by Oskay
http://www.flickr.com/photos/oskay/1364147807
Tux the Pinguin - by Patrick van der Velden
From the photographer’s private collection

67. THANKANDTOOLS
DEBUGGING: RULES
YOU
http://joind.in/2173