README

/**
 * patError - simple and powerful error managemet system
 *
 * This is based on the PEAR error handling, if you like it
 * you should try some PEAR classes available at
 * http://pear.php.net
 * 
 * 2004-09-25
 *
 * @access      public
 * @package     patError
 *
 * @copyright   2003/2004 by the patTeam
 * @author      gERD Schaufelberger <gerd@php-tools.net>
 * @author      Sebastian Mordziol <argh@php-tools.net>
 * @author      Stephan Schmidt <schst@php-tools.net>
 * @license     LGPL
 * @link        http://www.php-tools.net
 */

Download at http://www.php-tools.net

This program and all associated files are released under the GNU Lesser
Public License, see http://www.gnu.org/licenses/lgpl.txt for details!

WHAT IS PATERROR?
=================
Inspired by the PEAR error handling, patError tries to solve the problem of
handling runtime-errors within your PHP-projects. Therefore patError
supplies the developer with a simple interface for "throwing" errors or
sending error-objects as return values. On the other side the errors are
"catched" automatically by the registered error-handler. 

patError also supports different error-levels. The three well-known error
levels: "notice", "warning" and "error" are built-in and can be used
without further configuration. patError also includes predefined
default-behaviour for each of these error levels. 

Beside these built-in error-levels, you can register your custom error
levels during runtime.  While switching from "developing" and "testing"
stage to "productive" you may also want to change the error-handling from
"verbose" to a more silent mode. For these purposes patError supports six
different modes of error-handling: 
 - ignore (does nothing)
 - trigger (triggers the corresponding php-error)
 - echo (prints error-level and -message)
 - verbose (like echo, but prints also the error-information-text)
 - callback (calls a user-function)
 - die (dies with error-message)

The "callback"-handler is the most powerful error-handler. While all the
other methods are built-in functions of patError (or, to be more exactly:
of patErrorManager), the callback-handler just calls a registered
user-function for error-treatment. So you can write your own error-handling
classes/functions suitable for your application. E.g. custom error-handlers
can be used to write log files or send emails. 

As mentioned above, a common need is to switch from one error-handling to
another. E.g. a suitable error-handler during the develoment process will
echo a lot of information direct to the output.  Later, in a productive
environment error-handling should be done more hidden - there is no need
bothering a visitor with strange warnings...  With patError you can switch
the error-handling very easy by registering another error-handler for each
error-level.

WHY USE PATERROR?
=================
1) patError is object oriented The manager returns error-objects that can
be handled very easy
   
2) Static API The patErrorManager supports a static interface for
configuration and raising errors. So you don't have to juggle object
references inside your application
   
3) Easy to use Just say: "patErrorManager::raiseError( 123, 'My personal
error', 'Some more information' );" The complete API consists of ten
functions:
	- Three of them are for configuration purpose: setErrorClass,
	  setErrorHandling, registerErrorLevel
	- Two utility functions: getErrorHandling, translateErrorLevel
	- Four methods for raising errors: raise, raiseError, raiseWarning,
	  raiseNotice
	- One for checking returned values: isError
	
4) Easy to install and integrate You just need two files copied into you
include directory, include one and patErrorManager will to the rest.
patError can also be installed via the PEAR installer.
   
5) patError is extensible patError allows to add custom error-handler.
Implementing your own handler is very easy: You just need a global function
or an object that supports the error-handling function.

6) patError is free and open! Like the other pat-classes patError is free
software and - of course - comes as source-code distribution. 
 
INSTALLATION
============
See install.txt for a basic set-up.

USAGE
=====
The package of patError consits of two main clases: patError and
patErrorManager (located in the corresponding PHP-files). While patError
implements the concrete error-class, the patErrorManager will be used as a
factory producing patError-objects.

1) Standard use-case
--------------------
Even if patError is designed for advanced programming, patError supports a
very simple API.  During programming the main task of patError will be
fetching thrown errors. Throwing an error is done by patErrorManager. 

Example:
<?PHP
	include_once 'include/patErrorManager.php';
	$err =& patErrorManager::raiseError( 'test:111', 'Test', 'Testing patErrorManager' );
?>

The example above shows the standard use-case of patErrorManager. The
static function raiseError accepts three arguments: 
 - unique error-number
 - a message
 - some additional information
 
The error-number and the messsage are obligatory, the additional
information are optional.  Using unique error-numbers allows you to
identify individual errors. See section ERROR CODES for more information
about this topic.  The message provided usually will printed by the
error-handler. This message should give you some information about the
error. Keep in mind, that a visitor or smart customer may read this message
(inside the HTML-code) - for reducing security risks you must not include
filenames or even username (or even worse passwords) in the error-message.
The third parameter contains additional information: the information part.
It is recommended that the information-part will never be shown to a
visitor. This part should be only shown to the developer or maintainer.
Therefore it should contain useful debugging information (e.g. SQL-query).

A more real-live example:
	$err =& patErrorManager::raiseWarning( 
                              'cache:999',
                              'Caching failed',
                              'Cannot write cache file: "/path/to/file.cache" - permission denied!', 
                           );

2) Return value: patError-object
--------------------------------
In both examples, the raiseXXX-functions return a patError-oject. Even if
this object has some public methods, you don't want to use them. Usually
the the registerd error-handler cares for the information stored in the
error-object. (By the way, the patError-object is just a container for the
parameters passed to the raiseXXX-function - why should you ask for them?). 

On the other hand, the patError-object is very suitable as return value of
a function call.  If something went wrong, just raiseSOMETHING and return
the patError-object. The caller can use the static function "isError" for
testing the return value:

Example: 
    // in the "main-routine" the answer must be checked:

    // include patErrorManager
    include_once 'patErrorManager.php';

    $result = checkAnswer( 41 );
    if( patErrorManager::isError( $result ) )
    {
        echo 'found error object!';
    }

   /**
    * imagine there is a glorious function,
    * this function returns TRUE if everything
    * went right or a patError-Object
    */
    function checkAnswer( $answer )
    {
        if( $answer != 42 )
        {
            return patErrorManager::raiseNotice( 'answer:42', 'Wrong Answer', "The Answer was '$answer', it should be 42"  );
        }
        return true;
    }

INGORE ERRORS
=============
Sometimes it is necessary to ignore errors or you call a some function
which result usually results in an error. patError also supports ignoring
errors in two different ways. 

Ignore Errors
-------------
The first and easiest way is to configure patError to ignore some errors
permanently. For modifing the configurations there are four class-methods: 
 - addIngore: add one or more codes to list
 - removeIgnore: remove one or more codes from list
 - getIgnore: recieve current configuration
 - clearIgnore: empty configuration
 
After adding error-codes to the ignore list, raising such an error will not
result in an error.

Example: 
    // add a single error-code to be ingored
    patErrorManager::addIngore( 'test:666' );
	
    // add list of error-codes
    patErrorManager::addIngore( array( 'foo:111', 'foo:222', 'foo:333, 'foo:444' ) );
	
    // try to raise an error
    $err =&	patErrorManager::raiseError( 'test:666', 'Beast Error', 'The number of the beast is a bad error.' );
    if( !patErrorManager::isError( $err ) )
    {
        echo 'This error was ignored!';
    }
	
Expecting Errors
----------------
The second way of ignoring errors was designed for local usage. In contrast
to ignoring errors permanently, the idea of expecting errors allows you to
ignore the next error if it belongs it was expected. This feature is
controled by the functions:
 - pushExpect: add one ore more codes to expection-stack
 - popExpect: remove last entry from stack
 - getExpect: recieve expection-stack
 - clearExpect: empty stack
 
Example: 
    // push a single error-code to exeption-stack
    patErrorManager::pushExcept( 'test:211' );
	
    // push list of error-codes to stack
    patErrorManager::pushExcept( array( 'test:311', 'test:322', 'test:333', 'test:344' ) );
	
    // try to raise an error
    $err =&	patErrorManager::raiseError( 'test:322', 'Yet another error', 'Some error are not really special' );
    if( !patErrorManager::isError( $err ) )
    {
        echo 'This error was expected and ignored!';
    }
	
ADVANCED USAGE
==============
Even if the programming interface of patError is quite simple, it comes
with a lot of advanced features. 

1) Wrapper functions
--------------------
If you want to become an advanced user of patError, you need to understand
the internal mechanism for throwing errors. 

The above examples showd functions, that can be used for raising errors.
Beside their names the functions 
 - raiseError
 - raiseWarning
 - raiseNotice 
are nearly identical. In other words, they are just wrappers for the base
function: "raise" for the predefined error-levels: "error", "warning" and
"notice". Therefore the following call is identical to the first example:

	$err = patErrorManager::raise( E_ERROR, 'test:111', 'Test', 'Testing patErrorManager' );

As you might guess, the build-in error-levels "error", "warning" and
"notice" just reuse the PHP core constants E_ERROR, E_WARNING and E_NOTICE. 

2) Configure Error Handling
---------------------------
Setting up patError will also be done using the static interface of
patErrorManager. patError supports three types for configuration: 
  - Adding custom error-levels
  - Change the error-handling
  - Setting an custom error-class

2.1) Custom Error Levels
------------------------
Using custom error-levels is quite simple. All you need is a number which
defines your custom error-level. If you are lazy, you may use one of the
predefined constants: E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE.
Otherwise you have to make sure, that your selected error-level does not
conflict with the build-in error-levels. Speaking "binary", a CUSTEM_LEVEL
must be chosen that fulfils the following expression:

     ( ( E_ERROR | E_WARNING | E_NOTICE ) & CUSTOM_LEVEL ) == 0

We recommend the usage of: 
     E_USER_ERROR, E_USER_WARNING and/or E_USER_NOTICE !

After selection of, let's say E_USER_ERROR the error-level can be
registered by the usage of the function called: registerErrorLevel. Now the
"new" error-level can be used as the predefined. 

Example: 
    patErrorManager::registerErrorLevel( E_USER_ERROR, "User Error" );
	
    // raise build-in-error
    patErrorManager::raise( E_ERROR, 'test:123', 'Build-in-error', 'Some information' );
    // raise custom error
    patErrorManager::raise( E_USER_ERROR, 'test:123', 'Some custom error', 'Some custom information' );
	
ATTENTION:
As shown, the custom error-level can be used as the built-in error-levels.
In order to avoid confusion, you have to keep in mind, that the
error-handling of new error-levels is set to 'ignore' by default! For
changing this, see section: Change error-handling
	
2.2) Change error-handling
--------------------------
As mentioned in the introduction, patError supports six named methods of error-handling:
 - ignore (does nothing)
 - trigger (triggers the corresponding php-error)
 - echo (prints error-level and -message)
 - verbose (like echo, but prints also the error-information-text)
 - callback (calls a user-function)
 - die (dies with error-message)

The default method for the build-in error-levels are: 

 - E_NOTICE -> echo
 - E_WARNING -> echo
 - E_ERROR -> die
 
The default method for custom error-levels is 'ignore'. 

Changing the error-handling methos can be done during runtime - usually
during the set-up process of your application. Setting and configuring the
error-handler will be done by the static function setErrorHandling. This
function accepts two or three arguments. The first arguemnt is the
error-level, 

the second argument is the named method of error-handling and the third,
optional parameter can be used to add further options. 

Example: 
    patErrorManager::setErrorHandling( E_WARNING, 'verbose' );
    patErrorManager::setErrorHandling( E_NOTICE, 'ignore' );

In the above example, the error-level for E_WARNING and E_NOTICE will be
changed to 'verbose' and 'ignore'. The next example shows how to set
multiple error-levels within a single function call: 

    patErrorManager::setErrorHandling( ( E_WARNING | E_ERROR ), 'die' );

If you are not familiar with this syntax read the php-documetation about
the function: error_reporting.

Of course, the most powerful error-handling method is the 'callback'
method. Setting your custom error-handler works like the examples above.
All you have to add is a third parameter, containing a 'call-able' value
(see php-documentation about the function is_callable). 

The example below shows how to set an error-handler-object as error-handler
for E_ERROR.  For further information about custom error-handler see
section. Custom error handler

    include_once 'include/patErrorHandlerDebug.php';
    $errorHandler	=&	new	patErrorHandlerDebug;

    // setup handler for each error-level
    patErrorManager::setErrorHandling( E_ERROR, 'callback', array( $errorHandler, 'niceDie' ) );


2.3) Custom error class
-----------------------
Raising an error always return an instance of the error-class patError. Even if patError should 
satisfy common needs, the patError-package also allows to replace the error-class by any custom-class. 
Writing an error-class should be quite simple:
 - write a class that extends patError
 - overwrite some functions if necessary
 - name the file like the error-class itself and append ".php"
 - put the file in the directory where you store patErrorManager.php and patError.php

Following these rules allows patErrorManager to autoload the class on demand. Furthermore extending
the base-class patError is mandatory, otherwise patErrorManager::isError() won't work. 
 
3) Custom error handler
-----------------------
Error handler are used to performe a specified action for each error.
PatError allows to configure different handlers for different error-levels.
See section 2.2 Change error-handling.  As mentioned above, the
callback-method allows you to use your own code for handling error-objects.
All you have to do is to write a class that implements the error-handling
routine(s).

   /**
	* my first error handler
    * 
    * @package      patErrorManager
    * @subpackage   Examples
    * @author       gERD Schaufelberger <gerd@php-tools.net>
    * @version      0.1
    * @license      LGPL
    * @link         http://www.php-tools.net
    */
    class firstErrorHandler
    {
       /**
        * routine that handles warnings
        * @param object error object
        * @return object error object
        */
        function &handleWarning( &$error )
        {
            echo $error->getMessage() . "<br>\n";
            return $error;
        }
        
       /**
        * routine that handles real critical errors
        * @param object error object
        * @return object error object
        */
        function &handleError( &$error )
        {
            // log messages and info to a file
            
            // send email to somebody
            
            return $error;
        }
    }

In order to activate your custom handler, follow the instructions in
section 2.2 Change error-handling.

ERROR CODES
===========
Please notice: the list of error codes in errorcodes.txt is deprecated!

Currently the error codes are not used inside patError. So patError won't
mind if the error codes are not unique. Furthermore inside pat there was
some kind of chaos about error-codes :-(. We had some trouble about unique
numbers used in different classes and in avoiding collisions. 

Finally we decided to define the error-codes as id-string. In other words,
each code should be a unique string instead of a unique integer-value. Of
course, strings are more complex to handle inside patError, they are more
human readable and it should be easy to avoid collisions. 

Even if you may chooce a very custom string, we'll recommend to use to
define the error-codes as mentioned in the examples above. Handy
error-codes are:

	'test:123', 'patErrorManager:1', 'myApplication:7'

These examples use a string ("test", "patErrorManager", "myApplication") as
a prefix and a numeric value as suffix. The prefix tells you the source of
the error and the suffix what has happend.  Using error-codes like this,
allows you to define constants within your application without worring
about other error-codes from other applications.

For further seperation you may use error-codes with multiple colons inside:

  'application:nodule:123', 'patSession:Storage:Native:2'

With this syntax it should be very easy to sort errors by applications,
libraries and modules...


regards, gERD
Viel Spaß am Gerät, gERD
wernerwa / pat-error

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