Debugging techniques for PHP Jochen Daum Automatem Ltd PHPUG Auckland meetup 20 Oct 2009

Jochen Daum

Automatem Ltd

PHPUG Auckland meetup 20 Oct 2009

Overview My background PHP functions Error and logging set-up Debugging techniques The human side of debugging – you! Non-code debugging tools

My background

PHP functions

Error and logging set-up

Debugging techniques

The human side of debugging – you!

Non-code debugging tools

My background ASP 3.0 experience since 1997 Required “website on a CD” in 2001 Luckily can't do that with ASP ;) Backend programmer for website company Styrofirm in 2002 Build and maintained PHPDbEditTk (Sourceforge) for fast scaffolding 4 major systems still in operation and maintenance now Started Automatem in 2004

ASP 3.0 experience since 1997

Required “website on a CD” in 2001

Luckily can't do that with ASP ;)

Backend programmer for website company Styrofirm in 2002

Build and maintained PHPDbEditTk (Sourceforge) for fast scaffolding

4 major systems still in operation and maintenance now

Started Automatem in 2004

My (debugging) background Only had the luxury to build everything from scratch when I was employed with Cabletalk Other times had to work with other people's code

Only had the luxury to build everything from scratch when I was employed with Cabletalk

Other times had to work with other people's code

Goals Debug faster Debug for solving problems Understanding code is not the goal

Debug faster

Debug for solving problems

Understanding code is not the goal

PHP facilities overview echo() / var_dump() / print_r() / die () debug_backtrace ()/debug_print_backtrace() get_defined_vars () / get_declared_classes() / method_exists() Error display and logging isset()

echo() / var_dump() / print_r() / die ()

debug_backtrace ()/debug_print_backtrace()

get_defined_vars () / get_declared_classes() / method_exists()

Error display and logging

isset()

echo() Echo($var) prints out $var Prints “Array” for arrays (Catchable) fatal error for objects Don't use for debugging, waste of time.

Echo($var) prints out $var

Prints “Array” for arrays

(Catchable) fatal error for objects

Don't use for debugging, waste of time.

var_dump() / print_r() Prints variable and its type Works with all types including arrays, objects, resources Unlimited depth Shows references var_dump <---> print_r output differences

Prints variable and its type

Works with all types including arrays, objects, resources

Unlimited depth

Shows references

var_dump <---> print_r output differences

var_dump()/print_r() by mail() Useful when debugging a live site var_dump() needs use of output buffering print_r can return value: print_r($var,true);

Useful when debugging a live site

var_dump() needs use of output buffering

print_r can return value: print_r($var,true);

debug_backtrace() Prints stack trace of function calls with variables passed Shows file, line number, class, object, passed variables Can easily get messy (see example) Returns array. print_debug_backtrace() prints right away, but also messy

Prints stack trace of function calls with variables passed

Shows file, line number, class, object, passed variables

Can easily get messy (see example)

Returns array. print_debug_backtrace() prints right away, but also messy

my_debug_backtrace() Prefer to see only line numbers my_debug_backtrace() (for code see http://nz.php.net/manual/en/function.debug-backtrace.php#85915 )

Prefer to see only line numbers

my_debug_backtrace() (for code see http://nz.php.net/manual/en/function.debug-backtrace.php#85915 )

Error types http://nz.php.net/manual/en/errorfunc.constants.php E_ERROR Fatal run-time errors. Script stops. Run out of memory using array as object etc E_PARSE Compile-time parse errors. Syntax errors E_WARNING Run-time warnings Database connection failed, division by 0 4 E_NOTICE (integer) Notices

http://nz.php.net/manual/en/errorfunc.constants.php

E_ERROR Fatal run-time errors. Script stops.

Run out of memory

using array as object etc

E_PARSE Compile-time parse errors.

Syntax errors

E_WARNING Run-time warnings

Database connection failed, division by 0

4 E_NOTICE (integer) Notices

Error Types (2) http://nz.php.net/manual/en/errorfunc.constants.php E_WARNING Run-time warnings Database connection failed Division by 0 4 E_NOTICE (integer) Notices Variable not declared Typo Array index missing

http://nz.php.net/manual/en/errorfunc.constants.php

E_WARNING Run-time warnings

Database connection failed

Division by 0

4 E_NOTICE (integer) Notices

Variable not declared

Typo

Array index missing

Error Logging Can be configured in php.ini or through ini_set() (nearly all of them) display_errors: 0,1,'stderr' (fcgi only) Should be disabled on live site Enabled on development site, otherwise no error shown at all! Doesn't affect Fatal Errors

Can be configured in php.ini or through ini_set() (nearly all of them)

display_errors: 0,1,'stderr' (fcgi only)

Should be disabled on live site

Enabled on development site, otherwise no error shown at all!

Doesn't affect Fatal Errors

Error Logging (1) log_errors: 0,1 to log errors to a file error_log: 'syslog', file_path File to send logs to log_errors_max_len, ignore_repeated_errors, ignore_repeated_source Configuration options of how errors get logged

log_errors: 0,1 to log errors to a file

error_log: 'syslog', file_path

File to send logs to

log_errors_max_len, ignore_repeated_errors, ignore_repeated_source

Configuration options of how errors get logged

Debugging techniques Backtracing Divide and conquer

Backtracing

Divide and conquer

Back tracing Start where output is created: Actual html, json or Xml output Error message/ fatal error Go back step by step until the source is found, for example of: A variable value A problem Example: backtrace through Joomla site

Start where output is created:

Actual html, json or Xml output

Error message/ fatal error

Go back step by step until the source is found, for example of:

A variable value

A problem

Example: backtrace through Joomla site

Divide and conquer Assume that code is a black box, you don't need to understand it Look at debug_backtrace Start debugging in the middle of the list of functions. Work your way either way of the code.

Assume that code is a black box, you don't need to understand it

Look at debug_backtrace

Start debugging in the middle of the list of functions.

Work your way either way of the code.

My code guidelines ...as they relate to debugging Have a coding style and be consistent Indenting Where the brackets go directory/file structure E_NOTICE on! Takes a bit of work, but worth it

...as they relate to debugging

Have a coding style and be consistent

Indenting

Where the brackets go

directory/file structure

E_NOTICE on!

Takes a bit of work, but worth it

My code guidelines (2) No if without else “the code will never go here” - are you sure? No switch without default No foreach without if

No if without else

“the code will never go here” - are you sure?

No switch without default

No foreach without if

My code guidelines (3) Reduce lines of code Use libraries Centralise everything Don't change if not broken

Reduce lines of code

Use libraries

Centralise everything

Don't change if not broken

Development IDE Breakpoint Conditional breakpoint Debugging: Text Editor vs. IDE Text Editor var_dump() or var_dump();die(); If ($cond){ var_dump();//die(); }

Development IDE

Breakpoint

Conditional breakpoint

Text Editor

var_dump() or var_dump();die();

If ($cond){ var_dump();//die(); }

Debugging: Text Editor vx. IDE Development IDE Stack trace Inspect array/object value Text Editor print_r(debug_backtrace());//die(); Complicated/ lots of var_dump();

Development IDE

Stack trace

Inspect array/object value

Text Editor

print_r(debug_backtrace());//die();

Complicated/ lots of var_dump();

Debugging: Text Editor vs. IDE Development IDE Watch Variable/ Expression Text Editor Lots of (!) var_dump()

Development IDE

Watch Variable/ Expression

Text Editor

Lots of (!) var_dump()

Human aspects of debugging Tiredness Confidence Focus

Tiredness

Confidence

Focus

Human aspects of debugging Tiredness Get some sleep Be wiling to put problem aside

Tiredness

Get some sleep

Be wiling to put problem aside

Human aspects of debugging Confidence Generally start with smaller projects Plan more time if you solve a certain kind of problem first time Helps to be familiar with some frameworks and CMS systems: you will notice how they all use similar approaches

Confidence

Generally start with smaller projects

Plan more time if you solve a certain kind of problem first time

Helps to be familiar with some frameworks and CMS systems: you will notice how they all use similar approaches

Human aspects of programming Focus Debugging requires concentration If you won't have time at your hand, don't start going into something

Focus

Debugging requires concentration

If you won't have time at your hand, don't start going into something

Other debugging tools CVS/ Subversion/ Git/ Diff Firebug net console/ Fiddler/ Wireshark FirePHP Issue tracker

CVS/ Subversion/ Git/ Diff

Firebug net console/ Fiddler/ Wireshark

FirePHP

Issue tracker