Downloaded 18 times
![READ THE WEBSERVER ERROR LOG
Location depends on configuration
Typically/var/log/*/
PHPParseerror: [...]in/var/www/example.dev/public/index.phponline4"](https://image.slidesharecdn.com/effectivedebugging-140823102847-phpapp01/85/Effective-debugging-8-320.jpg)
![GREP FOR IT
$grep-rl"NotFound"*
...
src/Really/Not/Obvious/File.php
$grep-r"NotFound"*
...
src/Really/Not/Obvious/File.php 404=>'NotFound',
$catsrc/Really/Not/Obvious/File.php
...
functionerror(){
die($this->_statusCodes['404']);
}](https://image.slidesharecdn.com/effectivedebugging-140823102847-phpapp01/85/Effective-debugging-11-320.jpg)
![CAKEPHP AUTOMODELS
$model=ClassRegistry::init('MyModel');
$model->methodName();
SQLError:1064:YouhaveanerrorinyourSQLsyntax;[...]
check[...]fortherightsyntaxtousenear'methodName'
MyModeldoes nothave the function methodName
MyModelhas no behaviour bound implementing
methodName
$modelis an instance of AppModel](https://image.slidesharecdn.com/effectivedebugging-140823102847-phpapp01/85/Effective-debugging-36-320.jpg)
Uploaded byAndy Dawson
Effective debugging
The document outlines effective debugging techniques emphasizing that developers should focus on fixing problems rather than just identifying them. It provides practical examples and tools for debugging in PHP, including utilizing error logs, configuration settings, and the use of debugging functions. Additionally, it highlights common pitfalls in debugging and encourages asking for help when needed while ensuring one has collected adequate information.
More Related Content
Effective debugging
- 1. EFFECTIVE DEBUGGING SPEND TIMEFIXING PROBLEMS, NOT FINDING THEM /AndyDawson @AD7six
- 2. THE WEB ISJUST PLUMBING WITH BYTES Image:Wikipedia
- 3. OF COURSE IT'SNOT REALLY THAT SIMPLE Image:Flickr.com ↖ The hardestproblems to fix existhere. In the developer's head.
- 4. FIND IT WITHA HAMMER Image:Codinghorror.com //pickone thrownewException('Madeithere!'); print_r(debug_backtrace()); die(__FILE__.':'.__LINE__);
- 5. MOST APPS AREN'TTHAT SIMPLE Ahammer willwork, butitmighttake awhile. Image:energysystemsgroup.com
- 6. HELLO WORLD EXAMPLE "Where'smywebpage"
- 7. CHECK THE HTTPRESPONSE CODE Is itactually an error?
- 8. READ THE WEBSERVERERROR LOG Location depends on configuration Typically/var/log/*/ PHPParseerror: [...]in/var/www/example.dev/public/index.phponline4"
- 9.
- 10. NOT AN ERROREXAMPLE Notan error response code so no (direct) logmessages:"
- 11. GREP FOR IT $grep-rl"NotFound"* ... src/Really/Not/Obvious/File.php $grep-r"NotFound"* ... src/Really/Not/Obvious/File.php404=>'NotFound', $catsrc/Really/Not/Obvious/File.php ... functionerror(){ die($this->_statusCodes['404']); }
- 12. CAKEPHP HELLO WORLDEXAMPLE "Whythe Four Oh Four?"
- 13. CHECK THE ERRORLOG app/tmp/error.log
- 14.
- 15. DEBUG BASICS Configand functionseverydeveloper should know about
- 16. PHP CONFIG Inifile settingsare the defaults if notchanged (duh) display_errors(On/Off) log_errors(On) display_startup_errors(Off) error_reporting(On/Off) Runtime settings override the inifile -no effectif the file theyare in has aparse error (duh) ini_set('display_errors', 0/1)
- 17.
- 18.
- 19. A WAY TOREPRODUCE Have awayto consistentlyreproduce the error $curl-Ihttp://example.dev/ HTTP/1.1500InternalServerError Server:nginx Date:Sat,23Aug201410:33:46GMT Content-Type:text/html gitbisect-find regression errors quickly
- 20.
- 21. WEBGRIND Turn on xdebugprofiling,and look atwhatarequestis doing
- 22. CLI DEBUGGING Pause executionwith read: print_r($somethingInteresting); `readfoo`; Usefulwhen debuggingaloop.
- 23. NOT CAKEPHP CODE? Aghettodebugfunction: functiondebug($var,$showHtml=null){ if(!defined('DEBUG')||!DEBUG){return;} if($showHtml===null){ $showHtml=php_sapi_name()==='cli'?false:true; } $var=var_export($var,true); if(!$showHtml){ echo$var; return; } echo'<pre>'.htmlspecialchars($var).'</pre>'; } createatracefunction(Debugger::trace)tooifneeded
- 24. LOGIC AIDES Justvoicingaproblem canfind the solution/error Image:Wikipedia
- 25. ERROR MESSAGES DON'TLIE PHP Parse error: syntax error, unexpected '$bar'(T_VARIABLE) in parse.php on line 3 $catfoo.php <?php ... if($foo||bar){ There's an accidentalnone-breakingspace on thatline
- 26. NETWORKING PROBLEMS If theproblem is noton the webserver -where is it?
- 27. NAMESERVER PROBLEMS No responsefrom nameservers is the same as adomain not existsing $digcakefest.org ;<<>>DiG9.8.3-P1<<>>cakefest.org ;;globaloptions:+cmd ;;Gotanswer: ;;->>HEADER<<-opcode:QUERY,status:SERVFAIL,id:15266 ;;flags:qrrdra;QUERY:1,ANSWER:0,AUTHORITY:0,ADDITIONAL:0 ;;QUESTIONSECTION: ;cakefest.org. IN A ;;Querytime:4142msec ;;SERVER:8.8.8.8#53(8.8.8.8) ;;WHEN:TueAug1916:26:592014 ;;MSGSIZE rcvd:30 ... ;;ANSWERSECTION: cakefest.org. 1568 IN A 50.56.232.22 ...
- 28. DNS PROBLEMS "No routeto host"means the ip requested isn'taccessible $traceroutecakefest.org traceroutetocakefest.org(50.56.232.22),64hopsmax,52bytepackets 1 172.26.81.1(172.26.81.1) 1.032ms 0.912ms 0.912ms 2 192.168.0.1(192.168.0.1) 2.777ms 1.267ms 2.338ms ... 12 rackspace-ic-302090-dls-bb1.c.telia.net(62.115.33.78) 152.340ms 15 9.367ms 146.339ms 13 *** 14 *** 15 *** If there are stars -there be problems
- 29. BACKEND SERVER IS DOWN 502Bad Gateway E.g. php-fpm or hhvm is notrunning Willbe in the webserver error log There willnotbe anyapplication logentries
- 30. PITFALLS TO AVOID Whatnottodo when debuggingcode
- 31. FIX PROBLEMS, NOTSYMPTOMS Don'tignore errors/warnings/notices Fix them in order, some errors willbe the concequence of earlier problems.
- 32. COMMON MISTAKES Notlookingfor errorlogs Readingor focussingon the wrongerror message Notreadingthe error message Notreadingthe error message aloud Misinterprettingthe error message Stoppingdebuggingtoo early. If "the problem"is aclass/function with source code -debug the source code of thatfunction New user: Ifound the problem, it's app/webroot/index.php!
- 33. IMPLICIT ASSUMPTIONS Be waryofimplictassumptions You're debuggingthe same file the browser is loading You're debuggingthe same application the browser is loading You're debuggingthe same server the browser is loading You're debuggingthe same requestthe browser is loading Conclusions so far are accurate WTF?Backup, and re-verifyeverything.
- 34. COMMON PROBLEMS And howto debug/identifythem
- 35. NO MODREWRITE Don'tlook atphpfiles -the error is atthe webserver. Enable mod rewrite Restartthe webserver
- 36. CAKEPHP AUTOMODELS $model=ClassRegistry::init('MyModel'); $model->methodName(); SQLError:1064:YouhaveanerrorinyourSQLsyntax;[...] check[...]fortherightsyntaxtousenear'methodName' MyModeldoes nothavethe function methodName MyModelhas no behaviour bound implementing methodName $modelis an instance of AppModel
- 37. CAKEPHP AUTOMODELS -IDENTIFICATION $model=ClassRegistry::init('MyModel'); debug(get_class($model)); ##########DEBUG########## 'MyModel' ########################### $model=ClassRegistry::init('MyModel'); debug(get_included_files()); ##########DEBUG########## array( ... ...app/Model/MyModel.php ... ) ###########################
- 38. CAN'T FIX IT (╯°□°）╯︵┻━┻ Can'tfind the problem/solution?-gethelp. Butfirst: Collectthe information you've got Write astandalone, reproducible example if possible Reduce the question to it's simplest, form Don'tover simplifyor make acontrived example Ask colleagues/the internet Brace for impact Stack overflow, the google group and irc as greatplaces to get help
- 39. SUMMARY Identifythe rightpartof arequesttodebug Fix errors in order Check your assumptions/conclusions ateveryWTF Formulate aquestion, and Ask for help Profit!