1.
Errors, Exceptions & Logging
by James Titcumb
at PHP Hampshire Oct ‘13

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

19.
Why use logging?
● Easier to find problems
● More detail
● “paper trail” for code
● Log where you want

20.
What about Apache’s error_log?
source: http://up-ship.com/blog/?p=20903

21.
Why?
● error_log is too basic (message, file, line)
● difficult to read / parse
● depends on “error_reporting” setting

22.
● monolog
● phpconsole
● log4php
● RavenPHP + Sentry
● FirePHP (dev environment)
● Roll your own
Logging Options

23.
Requirements (for everyone)
● Fire & forget
● Minimum or zero latency
● Highly available
● Should be PSR-3 compatible
● Log everything:
○ Exceptions
○ Errors
○ Fatal Errors

24.
How they work...
source: http://mirror-sg-wv1.gallery.hd.org/_c/natural-science/cogs-with-meshed-teeth-AJHD.jpg.html

25.
Capture Method
Data Storage
Logger (PSR-3)
Handler / Adapter
Typical PSR-3 Compatible Design

26.
MonologErrorHandler
->handleException()
MongoDB
MonologLogger
->log()
MonologHandler
->handle()
Monolog

27.
EdLogHandlerErrorHandler
->handleException()
RabbitMQ
EdLogLogger
->log()
EdLogPublisherAmqpPublisher
->publish()
Logging Server
Low Latency (using AMQP)
JSON payload

28.
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

29.
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

30.
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!

31.
Questions?

32.
Feedback please...
https://joind.in/9452

33.
Thanks!
@asgrim
github.com/asgrim