I'm developing my own PHP framework and my code althought is working like it should, it's getting bigger and bigger; that of course leads to multiple ways for my framework to break, so I have decided it is time to implement Exception handling like any other PHP framework does, that 'nice' error view that tells you what might went wrong.
I have done my research and kind of understand how the Extension PHP default class works, I know that I'm able to extend this class and customize the error messages.
I also know that to trigger an Exception you gotta throw it and catch it with a "try/catch" statement, somethin like this...
class MyCustomException extends \Exception()
{
// My stuff
}
public function dontBeZero($number)
{
if ($number == 0) {
throw new MyCustomException('You gave me zero!!');
}
}
try {
dontBeZero(0);
} catch (MyCustomException $e) {
echo '<pre>';
$e->getMessage();
echo '</pre>';
}
I understand that, but my real question is: How does this popular frameworks such as Laravel, Symfony, etc manage to throw you a pretty message showing you what the error was, where do they keep all the logic that verifies whether it should or should not throw an exception, and most importantly where did they catch them?.
Most frameworks show these errors via a custom error handler. A popular one used by laravel is whoops.
You just need to register it as a custom handler, and you'll see the pretty error pages:
$whoops = new \Whoops\Run;
$whoops->pushHandler(new \Whoops\Handler\PrettyPageHandler);
$whoops->register();
Keep in mind, you should disable these on production (so that your stack traces/code isn't exposed).
See the two functions set_error_handler and set_exception_handler. These functions allow you to register a callback function which is called when an error or exception occurs.
These callback functions are called by the Php runtime and provided with error details as arguments. The error details include error line number, stack trace, file name and more. The callback function can then format and display this information
I'm currently working in PHP. I'm working on a error system for my CMS I'm building (for the fun of it). For fatal errors in my system (not in the php compiler) I created a FatalException class that extends the built in Exception class. Since these types of errors kinda halt the system anyway, I threw in a exit into the __construct.
class FatalException extends Exception{
public function __construct($message) {
exit("<h1 style='color:red;' >FATAL ERROR: $message </h1>");
}
}
So in my code I'll check something like the connection to the database and if it can't then I'll just throw a FatalException("Can't connect to database: $database_error_message"). It won't be in a try/catch block.
When I run the code and can't connect to the database, for example, all I see on the screen is a sentence in big red letters. So it works just fine, but is this bad practice/coding?
EDIT:
Actually in truth it didn't start out this way. I was originally logging the error and then exiting in the catch area, but then I thought, if all fatal errors are going to exit anyway then just put in the in constructor. Then I noticed it wasn't actually getting to the catch area it was exiting. So putting the statement in a try/catch block was kind of a moot point. Which lead to the question.
If you're going to exit() unconditionally in a constructor, there's not really much point making it a constructor, let alone making the class an Exception. You could more simply (and honestly) have a static function called Fatal::Die($message).
The point of exceptions is that they describe what the error is (by having different classes for different exceptions) and can be caught - even if only to log them to a file and bail out of the program.
What if a particular page of your site could actually cope fine without a database connection (just missing the "latest news" or something)? Then it could catch( Database_Exception $e ) and continue, while the rest of your site just falls straight into the last-ditch "oh no something went wrong" message.
A message in big red letters is also not a great error-handling mechanism for anything that someone other than you will use - either they end up seeing technical details of the error when you're not looking, or you don't know what went wrong because you hid that error.
Even you wrap exit() into a member function of an exception, you are not using the exception here for error handling, but just the exit() - the exception is never thrown, PHP comes to halt before that happens.
So it works just fine, but is this bad practice/coding?
Yes, it is bad practice. It also works just fine if you would have created yourself a function:
function error_exit($message) {
exit("<h1 style='color:red;' >FATAL ERROR: $message </h1>");
}
Instead think about whether you want to use Excpetions or you want to exit().
This is a bad idea imho. An exception needs to be caught in order to function properly. You may however create a method like ->error( $index ); that attaches to every object you make.
From there you can route the error to a specific class with a try / catch block to properly handle the errors.
class TestClass
{
public function error( $index )
{
try
{
// Convert index to exception and throw it.
}
catch ( Exception $e )
{
// Handle the error
}
}
}
$a = new TestClass();
$a->error( 1000 );
Do note that this will not work for exceptions that php throws, you'll need to catch these seperately or work with execution hubs.
Building upon a question I already asked regarding exceptions, I fear that I might be writing php functions wrong then, or abusing the use of exceptions. The reason I say this, is because if custom exceptions are to be caught using try/catch blocks then the following function:
public function get_specific_page($page) {
if (!is_array( $this->_page )){
throw new AisisCore_Template_TemplateException( "<div class='error'>Trying to get a property from a non array.</div>" );
}
return $this->_page[$page];
}
Would then be called such as:
try{
get_specific_page($page);
}
catch(Exception $e){
echo $e->getMessage();
}
The problem with this approach is that I have many functions that are written like this, either checking to see if a file exists, throwing an error. Checking to see if a value is set in an array, throwing an error and my issue is that the file which deals with these function calls may become over loaded with try catch.....
So my question is, how would I better write functions like this so that I don't have php files over loaded with try catch statements, yet still be able to have y own custom functions.
Is it as obvious as writing the try catch inside the function it's self?
The reason I ask, if because I am use to working with fameworks and in companies where we write our functions as you see above. How ver I have worked with code bases that have tons of these functions and I dont see half the files that are useing them doing a bunch of try catches...
Update:
I was looking through zend source to better understand exceptions and came across this:
public function setMessage($messageString, $messageKey = null)
{
if ($messageKey === null) {
$keys = array_keys($this->_messageTemplates);
foreach($keys as $key) {
$this->setMessage($messageString, $key);
}
return $this;
}
if (!isset($this->_messageTemplates[$messageKey])) {
require_once 'Zend/Validate/Exception.php';
throw new Zend_Validate_Exception("No message template exists for key '$messageKey'");
}
$this->_messageTemplates[$messageKey] = $messageString;
return $this;
}
You can see how they throw a new exception message near the bottom, this function is not called by doing:
try{}catch(){}
yet when it throws an exception, there is no issue with "uncaught exception with message"
In my opinion, your approach is correct in general. However, a few notes:
You should refrain from using HTML formatting in exception messages. Generally, you don't know how the exception that you throw will be handled. For example, an exception handler could just write the message to a log file (you don't want HTML formatting then), present it to the user in a special error view (in which case the view itself should contain the HTML formatting), or simply ignore it (no need for formatting then, anyway).
Catch only exceptions that you can handle. If you know that your function throws an AisisCore_Template_TemplateException, you should just catch that exception and let all other exceptions bubble up to an exception handler that can handle them. You can use set_exception_handler to define such an exception handler that catches all uncaught exceptions by default (this is probably the case in your example from Zend Framework). Plainly put: Only catch exceptions in places where you know how to handle them.
Only use exceptions as what the name implies: to handle (unexpected) exceptions in your control flow. Using exceptions to control the regular flow of your program is possible, but generally considered bad design (just as a side note, your code samples look alright).
For the sake of completeness, some alternatives to using exceptions:
Use return codes instead of exceptions. This is old-school C-style. The advantage is that you don't need to wrap statements with try/catch-statements. However, you have to check the return values of each procedure, which is easy to forget. When using exceptions on the other hand, you reduce the risk of unexpected errors, since uncaught exceptions produce a fatal error per default.
Use PHP errors. See the trigger_error function for this. Custom errors are however nearly impossible to catch in PHP (except by using set_error_handler, which only works at global level).
I have been dealing with PHP since 2000, but not very actively, and my knowledge of PHP5 is quite horrible. Recently I got my interest for webdevelopment back after a 5 year long break, and I started working on a project. I wrote a class for that project that became fairly large, but so far without any specific error handling.
The purpose of the class is to parse HTML files with a specific layout and handle its data, and it was more or less a training exercise for me to get back into the game. I started to rewrite the class now, and I decided it was time to be a little more professional about error handling than simply using die(), which I have been using a lot so far. I think we can all agree that is a terrible direction to take. I want the class to be quite project independent, so that I can distribute it to whoever wants to use it.
The HTML files I want to parse contain tables with specific bordercolors, trs with specific bgcolors, but the number of elements are dynamic. To validate that the HTML files actually have this specific pattern, I have the following sample (pseudo)code
public function Validate() {
$tables = getall('table', $this->data);
foreach ($tables as $table) {
if ($table->bordercolor != 'navy' && $table->cellspacing != 0) {
// Error
}
foreach ($tables->tr as $tr) {
if ($tr->bgcolor != '#fff') {
// Error
}
}
}
return true;
}
Where it says // Error, the HTML layout doesn't check out and my class should not attempt to parse it. Traditionally I would do this:
if ($table->bgcolor != '#fff') {
$this->error = 'Invalid HTML layout';
return false;
}
And from where I call the method I would use
if ($class->Validate() === false) {
exit_with_error($class->GetError()); // Simple return of $this->error
}
I've always thought it's a decent approach because of it's simplicity. However that's also a disadvantage as it doesn't really provide any in-depth information of the error apart from the text itself. I can't see where the error was triggered, what methods were called, etc.
Since I resumed my PHP hobby I have discovered exceptions. My problem with them is simply that I don't understand how to properly use them. And if I should use them at all. I would like my class to be portable; can I use exceptions to handle errors at all? And if yes, how can I communicate the errors (i.e. translate my traditional error handling)? Or perhaps there is an even better approach to take, which I don't know about.
Any help appreciated :)
You are certainly thinking along the right path. Typically, I like to separatte class design from error handling logic. In other words I don't want to have a bunch of $this->error = 'something' logic in the class, as why would you want to add extra code to every class to store/handle/report errors.
Now you get into exceptions vs. errors and when to use each. This is likely a subject for debate, but my personal preference has largely been to throw Exceptions in cases where you get to a point in your code that you cannot recover from or do not have the logic to handle. A great example of this, that I typically use, is throwing Exceptions right at the beginning of any class method that requires parameters of a certain sort or value. Like this example:
public method set_attribute($value) {
if (empty($value)) {
throw new Exception('You must send me something');
} else if (!is_string($value)) {
throw new Exception("You sent me something but it wasn't the string I was expecting.");
}
// method logic here
}
Here if the caller didn't give us a non-empty string, we throw an Exception, as we were not expecting this and we can't guarantee successful completion of the method without a proper value. There is not reason to continue with the method at all. We send the caller the exception with a message about the problem. Hopefully they invoked this method in a try-catch block and can gracefully handle the exception and pass it along up the call stack. If not, your code just stopped execution with fatal error from an uncaught exception (something really easy to catch in testing).
Triggering errors, I honestly use a lot less, and typically use them more for debug, warning purposes. An example of this might be a deprecated method that you still want to work, but you want to give the user an error on
public function old_method() {
trigger_error('This method had been deprecated. You should consider not using it anymore.'. E_USER_WARNING);
// method logic
}
Of course you can trigger whatever level of E_USER class warning here yourself.
Like I said, I tend to work a lot more with Exceptions, as they are also easily extensible for easy use with logging and such. I almost always would have a custom Exception class extending from PHP's base Exception class that also provides logging, etc.
The other thing to consider is global error handling and Exceptoin handling. I strongly recommend using these and having these be some of the very first lines of code in any new project. Again, it will give you much better control over how you log errors/exceptions than what you can get by default.
I don't see a problem with how you are doing it, but If you want to dive into Exceptions, learn how to use try/catch statements. Usually it would be something like this:
try {
//some code that may cause an error here
} catch (Exception e) {
//if a error is found, or an exception is thrown in the try statement, whatever here will execute
//you can get the error message by using e->getMessage()
}
you can read more about it here: http://php.net/manual/en/language.exceptions.php
I've been reading on in particular 'error logging' And I have come up with the function 'error_log' which seem to be a good tool to use to handle the error logging. But how is the smoothest and best way to use it?
If I have a
try {
//try a database connection...
} catch (PDOException $e) {
error_log($e->getMessage(), 3, "/var/tmp/my-errors.log");
}
This would log the error in the my-errors.log file. But what If I sometime need to change the position of where the file is, a new folder, or something. If I have tons of files I need to change them all.
Now I started of thinking to use a variable to set the path to the error log. Sure that could work, but what If I want to use the error_log in a function or class method? Then I would need to set the variable as global, but that is considered bad practise! But what If I shouldn't use the function deep in a class, wouldn't that also be considered bad practise? What is a good solution here?
<?php
function legit() {
try {
if (1 == 1) {
throw new Exception('There was an error here');
}
} catch (Exception $e) {
throw new Exception('throw the error to the try-catch outside the function...');
}
}
try {
legit();
} catch (Exception $e) {
echo 'error here' . $e->getMessage();
//log it
}
This is an example of what I was talking about above (Not having the logging deep in a class/function... Is it a good way?)
Furtheron:
I am not quite sure how I should use the Exceptions in general. Let's say I want to do a INSERT to a database with SQL inside a method, would I use a try/catch and then rethrow the exception if it fails? Is that considered good practise? Examples please.
Firstly, I'd like to commend you for looking at the standard error methods within PHP. Unfortunately error_log has some limitations as you found out.
This is a long answer, read on to find out about:
Errors
Logging the error directly vs trigger_error and set_error_handler
Where good errors go bad - Fatal Errors.
Exceptions
SPL
What to do with them?
Code
Setup
Usage
TL;DR Use trigger_error for raising errors and set_error_handler for logging them.
Errors
=========
When things don't go as expected in your program, you will often want to raise an error so that someone or something is notified. An error is for a situation where the program may continue, but something noteworthy, possibly harmful or erroneous has occurred. At this point many people want to log the error immediately with their logging package of choice. I believe this is exactly the wrong thing to do. I recommend using trigger_error to raise the error so that it can be handled with a callback set by set_error_handler. Lets compare these options:
Logging the error directly
So, you have chosen your logging package. Now you are ready to spread the calls to your logger wherever an error occurs in your code. Lets look at a single call that you might make (I'll use a similar logger to the one in Jack's answer):
Logger::getLogger('standard')->error('Ouch, this hurts');
What do you need in place to run this code?
Class: Logger
Method: getLogger
Return: Object with method 'error'
These are the dependencies that are required to use this code. Everyone who wants to re-use this code will have to provide these dependencies. This means that a standard PHP configuration will no longer be sufficient to re-use your code. With the best case, using Dependency Injection you still require a logger object to be passed into all of your code that can emit an error.
Also, in addition to whatever the code is responsible for, it also has responsibility for logging the error. This goes against the Single Responsibility Principle.
We can see that logging the error directly is bad.
trigger_error to the rescue
PHP has a function called trigger_error which can be used to raise an error just like the standard functions do. The error levels that you use with it are defined in the error level constants. As a user you must use one of the user errors: E_USER_ERROR, E_USER_WARNING or the default value E_USER_NOTICE (other error levels are reserved for the standard functions etc.). Using a standard PHP function to raise the error allows the code to be re-used with any standard PHP installation! Our code is no longer responsible for logging the error (only making sure that it is raised).
Using trigger_error we only perform half of the error logging process (raising the error) and save the responsibility of responding to the error for the error handler which will be covered next.
Error Handler
We set a custom error handler with the set_error_handler function (see the code setup). This custom error handler replaces the standard PHP error handler that normally logs messages in the web server error log depending on the PHP configuration settings. We can still use this standard error handler by returning false within our custom error handler.
The custom error handler has a single responsibility: to respond to the error (including any logging that you want to do). Within the custom error handler you have full access to the system and can run any sort of logging that you want. Virtually any logger that uses the Observer design pattern will be ok (I'm not going to go into that as I believe it is of secondary importance). This should allow you to hook in new log observers to send the output to where you need it.
You have complete control to do what you like with the errors in a single maintainable part of your code. The error logging can now be changed quickly and easily from project to project or within a single project from page to page. Interestingly even # suppressed errors make it to the custom error handler with an errno of 0 which if the error_reporting mask is respected should not be reported.
When Good Errors go Bad - Fatal Errors
It is not possible to continue from certain errors. The following error levels can not be handled from a custom error handler: E_ERROR, E_PARSE, E_CORE_ERROR, E_CORE_WARNING, E_COMPILE_ERROR, E_COMPILE_WARNING. When these sorts of errors are triggered by a standard function call the custom error handler is skipped and the system shuts down. This can be generated by:
call_this_function_that_obviously_does_not_exist_or_was_misspelt();
This is a serious mistake! It is impossible to recover from, and the system is about to shut down. Our only choice is to have a register_shutdown_function deal with the shutdown. However this function is executed whenever a script completes (successful, as well as unsuccessful). Using this and error_get_last some basic information can be logged (the system is almost shutdown at this point) when the last error was a fatal error. It can also be useful to send the correct status code and show an Internal Server Error type page of your choosing.
Exceptions
=============
Exceptions can be dealt with in a very similar way to basic errors. Instead of trigger_error an exception will be thrown by your code (manually with throw new Exception or from a standard function call). Use set_exception_handler to define the callback you want to use to handle the exception with.
SPL
The Standard PHP Library (SPL) provides exceptions. They are my preferred way of raising exceptions because like trigger_error they are a standard part of PHP which does not introduce extra dependencies to your code.
What to do with them?
When an exception is thrown there are three choices that can be made:
Catch it and fix it (the code then continues as if nothing bad happened).
Catch it, append useful information and re-throw it.
Let it bubble up to a higher level.
At each level of the stack these choices are made. Eventually once it bubbles up to the highest level the callback you set with set_exception_handler will be executed. This is where your logging code belongs (for the same reasons as the error handling) rather than spread throughout catch statements in your code.
3. Code
Setup
Error Handler
function errorHandler($errno , $errstr, $errfile, $errline, $errcontext)
{
// Perform your error handling here, respecting error_reporting() and
// $errno. This is where you can log the errors. The choice of logger
// that you use is based on your preference. So long as it implements
// the observer pattern you will be able to easily add logging for any
// type of output you desire.
}
$previousErrorHandler = set_error_handler('errorHandler');
Exception Handler
function exceptionHandler($e)
{
// Perform your exception handling here.
}
$previousExceptionHandler = set_exception_handler('exceptionHandler');
Shutdown Function
function shutdownFunction()
{
$err = error_get_last();
if (!isset($err))
{
return;
}
$handledErrorTypes = array(
E_USER_ERROR => 'USER ERROR',
E_ERROR => 'ERROR',
E_PARSE => 'PARSE',
E_CORE_ERROR => 'CORE_ERROR',
E_CORE_WARNING => 'CORE_WARNING',
E_COMPILE_ERROR => 'COMPILE_ERROR',
E_COMPILE_WARNING => 'COMPILE_WARNING');
// If our last error wasn't fatal then this must be a normal shutdown.
if (!isset($handledErrorTypes[$err['type']]))
{
return;
}
if (!headers_sent())
{
header('HTTP/1.1 500 Internal Server Error');
}
// Perform simple logging here.
}
register_shutdown_function('shutdownFunction');
Usage
Errors
// Notices.
trigger_error('Disk space is below 20%.', E_USER_NOTICE);
trigger_error('Disk space is below 20%.'); // Defaults to E_USER_NOTICE
// Warnings.
fopen('BAD_ARGS'); // E_WARNING fopen() expects at least 2 parameters, 1 given
trigger_error('Warning, this mode could be dangerous', E_USER_WARNING);
// Fatal Errors.
// This function has not been defined and so a fatal error is generated that
// does not reach the custom error handler.
this_function_has_not_been_defined();
// Execution does not reach this point.
// The following will be received by the custom error handler but is fatal.
trigger_error('Error in the code, cannot continue.', E_USER_ERROR);
// Execution does not reach this point.
Exceptions
Each of the three choices from before are listed here in a generic way, fix it, append to it and let it bubble up.
1 Loggable. Let it bubble up:
// Don't catch it.
// Either it will be caught by error handler
// Or PHP will log it as a fatal error
2 Fixable:
try
{
$value = code_that_can_generate_exception();
}
catch (Exception $e)
{
// We decide to emit a notice here (a warning could also be used).
trigger_error('We had to use the default value instead of ' .
'code_that_can_generate_exception\'s', E_USER_NOTICE);
// Fix the exception.
$value = DEFAULT_VALUE;
}
// Code continues executing happily here.
3 Append:
Observe below how the code_that_can_generate_exception() does not know about $context. The catch block at this level has more information which it can append to the exception if it is useful by rethrowing it.
try
{
$context = 'foo';
$value = code_that_can_generate_exception();
}
catch (Exception $e)
{
// Raise another exception, with extra information and the existing
// exception set as the previous exception.
throw new Exception('Context: ' . $context, 0, $e);
}
It has been requested to make this answer more applicable to a larger audience, so here goes.
Preamble
Error handling is usually not the first thing you will want to think about when writing an application; as an indirect result it gets bolted on as the need arises. However, it doesn't have to cost much to leverage existing mechanisms in PHP either.
It's a fairly lengthy article, so I've broken it down into logical sets of text.
Triggering errors
Within PHP there are two distinct ways for errors to get triggered:
Errors from PHP itself (e.g. using undefined variables) or internal functions (e.g. imagecreatefromjpeg could not open a file),
Errors triggered by user code using trigger_error,
These are usually printed on your page (unless display_errors is switched off or error_reporting is zero), which should be standard for production machines unless you write perfect code like me ... moving on); those errors can also be captured, giving you a glimpse into any hitch in the code, by using set_error_handler explained later.
Throwing exceptions
Exceptions are different from errors in three main ways:
The code that handles them may be far removed from the place where they are thrown from. The variable state at the origin must be explicitly passed to the Exception constructor, otherwise you only have the stack trace.
The code between the exception and the catch is skipped entirely, whereas after an error occurs (and it was not fatal) the code still continues.
They can be extended from the main Exception class; this allows you to catch and handle specific exceptions but let others bubble down the stack until they're caught by other code. See also: http://www.php.net/manual/en/language.exceptions.php
An example of throwing exceptions is given later on.
Handling errors
Capturing and handling errors is pretty straightforward by registering an error handler, e.g.:
function my_error_handler($errno, $errstr, $errfile = 'unknown', $errline = 0, array $errcontext = array())
{
// $errcontext is very powerful, it gives you the variable state at the point of error; this can be a pretty big variable in certain cases, but it may be extremely valuable for debugging
// if error_reporting() returns 0, it means the error control operator was used (#)
printf("%s [%d] occurred in %s:%d\n%s\n", $errstr, $errno, $errfile, $errline, print_r($errcontext, true));
// if necessary, you can retrieve the stack trace that led up to the error by calling debug_backtrace()
// if you return false here, the standard PHP error reporting is performed
}
set_error_handler('my_error_handler');
For kicks, you can turn all the errors into an ErrorException as well by registering the following error handler (PHP >= 5.1):
function exception_error_handler($errno, $errstr, $errfile, $errline)
{
throw new ErrorException($errstr, $errno, 0, $errfile, $errline);
}
set_error_handler("exception_error_handler");
Handling exceptions
In most cases you handle exceptions as close as possible to the code that caused it to allow for backup plans. For instance, you attempt to insert a database record and a primary key constraint exception is thrown; you can recover by updating the record instead (contrived as most databases can handle this by themselves). Some exceptions just can't be handled locally, so you want those to cascade down. Example:
function insertRecord($user, $name)
{
try {
if (true) {
throw new Exception('This exception should not be handled here');
}
// this code is not executed
$this->db->insert('users', array('uid' => $user, 'name' => $name));
} catch (PDOException $e) {
// attempt to fix; an exception thrown here will cascade down
throw $e; // rethrow exception
// since PHP 5.3.0 you can also nest exceptions
throw new Exception("Could not insert '$name'", -1, $e);
} catch (WhatEverException $e) {
// guess what, we can handle whatever too
}
}
The slippery exception
So what happens when you don't catch an exception anywhere? You can catch that too by using set_exception_handler.
function my_exception_handler(Exception $exception)
{
// do your stuff here, just don't throw another exception here
}
set_exception_handler('my_exception_handler');
This is not encouraged unless you have no meaningful way to handle the exception anywhere in your code.
Logging the error / exception
Now that you're handling the error you have to log it somewhere. For my example, I use a project that Apache ported from Java to PHP, called LOG4PHP. There are others, but it illustrates the importance of a flexible logging facility.
It uses the following concepts:
Loggers - named entities that perform logging upon your behalf; they can be specific to a class in your project or shared as a common logger,
Appenders - each log request can be sent to one or more destinations (email, database, text file) based on predefined conditions (such as log level),
Levels - logs are classified from debug messages to fatal errors.
Basic usage to illustrate different message levels:
Logger::getLogger('main')->info('We have lift off');
Logger::getLogger('main')->warn('Rocket is a bit hot');
Logger::getLogger('main')->error('Houston, we have a problem');
Using these concepts you can model a pretty powerful logging facility; for example, without changing above code, you can implement the following setup:
Collect all debug messages in a database for developers to look at; you might disable this on the production server,
Collect warnings into a daily file that you might email at the end of the day,
Have immediate emails sent on fatal errors.
Define it, then use it :)
define('ERRORLOG_PATH', '/var/tmp/my-errors.log');
error_log($e->getMessage(), 3, ERRORLOG_PATH);
Alternatively just make the third parameter of error_log optional, defaulting it to the path you want.
As an addition, for error logging (and in fact all logging) I would use event dispatcher, in a way that symfony framework does.
Take a look at this sf component (its very lightweight dependency, entire framework is not required, there are maybe 3 relevant php classes and 2 interfaces)
https://github.com/symfony/EventDispatcher
this way you can create dispatcher somewhere in your application bootstrap:
use Symfony\Component\EventDispatcher\EventDispatcher;
use Symfony\Component\EventDispatcher\Event;
$dispatcher = new EventDispatcher();
//register listeners
$dispatcher->addListener('application.log', function (Event $event) {
//do anything you want
});
Then you can raise an event in any place of your code by something like
$dispatcher->dispatch(new GenericEvent('application.log', array('message' => 'some log', 'priority' => 'high'));
Of course you can subclass event class with your own events:
class LogEvent extends GenericEvent {
public function __construct($message, $priority = 'INFO') {
parent::__construct('application.log', array('message'=>$message,'priority'=>$priority));
}
public function getMessage() { return $this->getArgument('message'); }
public function getPriority() { return $this->getArgument('priority'); }
}
// now raising LogEvent is much cleaner:
$dispatcher->dispatch(new LogEvent('some log'));
This will also allow you to create more customized events like ExceptionEvent
class ExceptionEvent extends GenericEvent {
public function __construct(Exception $cause) {
parent::__construct('exception.event', array('cause' => $cause));
}
}
And handle them accordingly.
Advantages
you separate logging logic from your application
you can easily add and remove loggers in runtime
you can easily register as many loggers you want (i.e. DebugLogger which logs everything into text file, ErrorLogger which logs only errors to error_log, CriticalLogger which logs only critical errors on production environment and sends them by email to administrator, etc.)
you can use event dispatcher for more things than just logging (in fact for every job for which observer pattern is appropriate)
actual logger becomes nothing more than 'implementation detail' - it's so easy to replace that it doesn't matter where your logs go - you will be able to replace log destination at any time without having to refactor names of your methods, or changing anything in code.
it will be easy to implement complex log routing logic or globally change log format (by configuring loggers)
everything becomes even more flexible if you use dependency injection for both listeners (loggers) and dispatcher (into classes that notifies log event)
Actual Logging
As someone already stated, I would advice to go with out-of-the-box library, like mentioned Monolog, Zend_Log or log4php, there is probably no reason to code these things by hand (and the last thing you want is broken error logger!)
PS: Treat code snippets as pseudo-code, I didn't test them. Details can be found in docs of mentioned libraries.
If you still need a custom way of handling logs (i.e. you don't want to use standard trigger_error()), I'd recommend looking at Zend_Log (http://framework.zend.com/manual/en/zend.log.overview.html) for these reasons:
this can be used as a standalone component, ZF is not a full-stack framework. You may copy only Zend_Loader and Zend_Log namespaces , instantiate Zend_Loader and use it. See below:
require_once('Zend/Loader/Autoloader.php');
$loader = Zend_Loader_Autoloader::getInstance();
$logger = new Zend_Log();
$writer = new Zend_Log_Writer_Stream('php://output');
$logger->addWriter($writer);
$logger->log('Informational message', Zend_Log::INFO);
You were offered many logging libraries, but I believe that Zend team (founders of PHP lang) know what they do
You may use any writers (database, STDOUT - see above, file, whatever, you may customize it to write your own to post log messages to a web service even)
log levels
may change log format (but the one that is out-of-box is great to my mind). The above example with standard formatter will produce something like this:
2012-05-07T23:57:23+03:00 INFO (6): Informational message
just read the reference, it may be configured to catch php errors
If the PHP way of handling errors is not flexible enough for you (e.g. sometimes you want to log to database, sometimes to file, sometimes whatever else), you need to use / create a custom PHP logging framework.
You can browse through the discussion in https://stackoverflow.com/questions/341154/php-logging-framework or just go and give the top choice, KLogger, a try. I am not sure, though, if it supports custom destinations for logging. But at the very least, it's a small and easy-to-read class and you should be able to extend it further for your own needs.
I'd go with Tom vand der Woerdt's logging solution, simplest and most effective for your requirements.
As for the other question:
You do not need to catch / rethrow the exception inside the function unless there is a specific kind of exception you have a solution for.
Somewhat simplistic example:
define('ERRORLOG_PATH', '/var/tmp/my-errors.log');
function do_something($in)
{
if (is_good($in))
{
try {
return get_data($in);
} catch (NoDataException $e) {
// Since it's not too big a deal that nothing
// was found, we just return false.
return false;
}
} else {
throw new InvalidArguementException('$in is not good');
}
}
function get_data($data)
{
if (!is_int($data))
{
InvalidArguementException('No');
}
$get = //do some getting.
if (!$get)
{
throw new NoDataException('No data was found.');
} else {
return $get;
}
}
try {
do_something('value');
} catch (Exception $e) {
error_log($e->getMessage(), 3, ERRORLOG_PATH);
die ('Something went wrong :(');
}
Here you'd only catch the NoDataException because you have some other logic to sort that out, all other errors fall though to the first catch and are handled by the top catch because all thrown exceptions must at some point in their hierarchy inherit from Exception.
Obviously if you throw an Exception again (outside the initial try {} or in the top catch {}) your script will exit with an Uncaught Exception error and error logging is lost.
If you wanted to go all the way, you could also implement a custom error handling function using set_error_handler() and put your logging in there too.
There are two challenges to meet. The first is to be flexible in logging to different channels. In this case you should take a look at for example Monolog.
The second challenge is to weave in that logging into your application. Imho the best case is no to use logging explicitly. Here for example aspect orientation comes in handy. A good sample is flow3.
But this is more a bird's eye view on the problem...
I use my own function which allows me to write multiple types of log files by setting or changing the second parameter.
I get past the conceptual questions you are asking about "what is the right way" to do it, by including the log function in a library of functions that I consider "native" to my development projects.
That way I can consider those functions to be just part of "MY" php core, like date() or time()
In this basic version of dlog, I also handle arrays. while I originally used this to log errors, I ended up using it for other 'quick and dirty' short term tracking such as logging the times that the code entered a certain section, and user logins, etc.
function dlog($message,$type="php-dlog")
{
if(!is_array($message) )
$message=trim($message);
error_log(date("m/d/Y h:i:s").":".print_r($message,true)."\n",3, "/data/web/logs/$_SERVER[HTTP_HOST]-$type.log");
}
Most error loggers and exception loggers are useless to most people because they haven't got access to the log files.
I prefer to use a custom error handler and a custom exception handler and have those, during production, log errors directly to the database if the system is running on a database.
During development, when display_errors are set, they log nothing as all errors gets raised in the browser.
And as a side note to that: Don't make your custom error handler throw exceptions! It's a really bad idea. It can cause bugs in the buffer handler and in some of the extensions. Also some core PHP functions like fopen() causes a warning or notice on failure, these should be dealt with accordingly and should not halt the application has an exception would do.
The mention of having the error handler throwing exceptions in the PHP documentation is a note bug.
As KNL states, which is quite right, but unfortunately as of yet undocumented, having errors throwing exceptions is not something recommended by the PHP developers and someone made a mistake in the documentation. It can indeed cause bugs with many extensions so don't do it.
This has already been debated on #PHP on irc.
The "However, errors can be simply translated to exceptions with ErrorException." on http://php.net/manual/en/language.exceptions.php is going to be removed.