This document discusses errors, exceptions, and logging in PHP. It describes the different types of PHP errors and how exceptions can be used to handle errors and failures more object-oriented way. Exceptions allow for more descriptive error handling than basic errors. The document also recommends logging errors and exceptions for easier debugging. Various logging options for PHP are presented, including Monolog and other libraries that support the PSR-3 logging standard. Capturing errors, exceptions, and logging messages is discussed.

1. Errors, Exceptions & Logging
by James Titcumb
at PHPNW13 Uncon

2. Errors

3. ● Something broke… :)
● e.g.
○ Can’t connect to MySQL (mysqli_connect)
○ No such file or directory (fopen)
● Usually from PHP core
● Sometimes fatal (stop execution)
What are errors?

4. Types of PHP Errors
● E_ERROR
● E_WARNING
● E_NOTICE
● E_PARSE
● Others (E_STRICT, E_DEPRECATED) etc.
● User errors (E_USER_ERROR etc.)

5. E_ERROR
<?php
foo();
// Fatal error: Call to undefined
function foo() in /in//in/N2gbL on
line 3

6. E_WARNING
<?php
fopen('foo', 'r');
// Warning: fopen(foo): failed to
open stream: No such file or
directory in /in//in/tZHGY on line
3

7. E_NOTICE
<?php
$a = $b;
// Notice: Undefined variable: b in
/in//in/9dPC5 on line 3

8. E_PARSE
<?php
x c
// Parse error: syntax error,
unexpected 'c' (T_STRING) in
/in//in/fkEaj on line 3

9. Problems?
source: http://www.dpaddbags.com/blog/episode-119-technology-sucks/

10. Problems.
● Depends on “error_reporting” php.ini setting
● Displaying errors is UGLY
● Existence of “@” operator
● Only logs to file or syslog
● Easily ignored
● Not very “OO”

11. Ways Around
// Will raise E_NOTICE
fopen($somefile, 'r');
// No error! :)
if (file_exists($somefile)) {
fopen($somefile, 'r');
} else {
// nice handling...
}

12. Exceptions

13. ● Something still broke
● Wider scope:
○ Logic errors
○ Flow control (for errors)
● “Catchable”
● Turn into fatal errors if not caught
● They are classes (can make your own)
● Common in other OO languages
What are exceptions?

14. Jargon Buster
● throw
Triggering an exception
● try
Try to run a piece of code which *may* throw an
exception
● catch
Handle an exception
● finally
Always run some code after a try/catch block

15. ● Built in to PHP
● More descriptive than just “Exception”, e.g.:
○ InvalidArgumentException
○ LogicException
○ OutOfBoundsException
○ RuntimeException
○ see PHP manual for more
SPL Exceptions

16. Example (throw)
class Division
{
public function divide($a, $b)
{
if ($b == 0) {
throw new Exception(‘div by zero’);
}
return ($a / $b);
}
}

17. Example (catch)
$division = new Division();
try
{
$result = $division->divide(5, 0);
}
catch (Exception $exception)
{
$logger->warning($exception-
>getMessage());
}

18. Logging

20. Why use logging?
● Easier to find problems
● More detail
● “paper trail” for code
● Log where you want

21. What about Apache’s error_log?
source: http://up-ship.com/blog/?p=20903

22. Why?
● error_log is too basic (message, file, line)
● difficult to read / parse
● depends on “error_reporting” setting

23. ● monolog
● phpconsole
● log4php
● RavenPHP + Sentry
● FirePHP (dev environment)
● Roll your own
Logging Options

24. Requirements (for everyone)
● Fire & forget
● Minimum or zero latency
● Highly available
● Should be PSR-3 compatible
● Log everything:
○ Exceptions
○ Errors
○ Fatal Errors

25. How they work...
source: http://mirror-sg-wv1.gallery.hd.org/_c/natural-science/cogs-with-meshed-teeth-AJHD.jpg.html

26. Capture Method
Data Storage
Logger (PSR-3)
Handler / Adapter
Typical PSR-3 Compatible Design

27. MonologErrorHandler
->handleException()
MongoDB
MonologLogger
->log()
MonologHandler
->handle()
Monolog

28. EdLogHandlerErrorHandler
->handleException()
RabbitMQ
EdLogLogger
->log()
EdLogPublisherAmqpPublisher
->publish()
Logging Server
Low Latency (using AMQP)
JSON payload

29. Capturing Logging
Use these and send output to $logger
● set_exception_handler()
○ Handles all uncaught exceptions
● set_error_handler()
○ Handles most errors
● register_shutdown_function()
○ Handles fatal errors

30. Sending Log Messages
● PSR-3 makes it easy
● However you want…
● Monolog has loads:
○ syslog-compatible / error_log
○ Email, HipChat
○ AMQP, Sentry, Zend Monitor, Graylog2
○ Redis, MongoDB, CouchDB

31. Summary
● PHP generates errors usually
● Exceptions are great in OOP context
● More control with exceptions
● Logging is important
● Logging is easy
● Short term investment, long term benefit
● NO EXCUSES!

32. Questions?

33. Thanks!
@asgrim
github.com/asgrim