Debugging Ideas


Seagull uses the class /trunk/lib/SGL/ErrorHandler.php to override PHP's default error handling. Errors basically fall into two categories, those that are thrown by the system and those thrown by the developer. Beyond this distinction, an error can be a PHP error, ie, originating from the PHP engine or thrown by the developer with PHP's trigger_error() function, or a PEAR error.


Which Types of Errors Handled

Seagull's error handing allows you to customise the output of any error type by defining thresholds in the application configuration. In the event of an error the following happens:

  • error output is hidden from the screen unless a parse error occurs in which case the script is not executed, therefore the error handler cannot come into play
  • if logging is enabled in Configuration, errors up to the threshold you define are logged to the target of your choice, ie, file, db, etc.
  • errors that reach the SGL_EMAIL_ADMIN_THRESHOLD are emailed to the administrator. It is a good idea to set this to PEAR_LOG_WARNING for a live site, although PEAR_LOG_EMERG is fine for development. The email to admin grabs a bunch of useful extra info: last query, client details, etc

Which Code Does the Work

In terms of the code, PHP errors are handled by /trunk/lib/SGL/ErrorHandler.php which basically uses set_error_handler() and PEAR errors are handled by the pearErrorHandler() fn, in the SGL_Task_SetupPearErrorCallback() task, which is the callback referenced by

PEAR::setErrorHandling(PEAR_ERROR_CALLBACK, 'pearErrorHandler');

The error severity is dynamically passed to the logs, with the severity level mapped to PEAR::Log's level with a simple PHP/PEAR mapping, see the ErrorHandler? constructor for details.

If you're on a linux system, you can uncomment the highlight_file fn in the ErrorHandler class, unfortunately this coredumps on windows.

Making the Most of File Logging

Any linux user will automatically tail a log file interactively to catch errors/feedback as they happen, however, this is not automatic for windows users. All is not lost, there are many unix emulation tools windows users can take advantage of, some more complex than others, to get the same effect. MSYS is an ideal lightweight package, a couple MB download, painless install, and gives you identical unix tail functionality.

tail -f [path-to-seagull]/var/log/php_log.txt

Other windows programs simulating tail: mTAIL

To enable logging go the the Configuration screen, choose the 'Logs' section and select enable. The debug priority gives the most feedback.

How to Handle Notices

By default, reporting of E_NOTICE level errors is enabled. Seagull is coded to E_ALL and it's a good idea to get your classes to work to this level. If you want to suppress the notice errors simply comment the 'notice' element of the errorType array in /trunk/lib/SGL/ErrorHandler.php.

Additionally, if you know you have a block of code that throws notices, you can wrap it as follows to keep a notice-free output:

//  code that throws notices

Developer Triggered Errors

To throw errors, developers are encouraged to use Seagull's static method:

SGL::raiseError('message text', [SGL_ERROR_CONST], [PEAR_ERROR_DIE])

The first parameter is the message you wish to raise, the optional second parameter is any of the Seagull error constants defined in constants.php, and the optional 3rd parameter, PEAR_ERROR_DIE, will halt program execution. If the 3rd argument is used, the 1st arg message is sent to the screen regardless of whether debug is enabled or not.

Many developers familiar with DB_DataObject will notice similarities here, the method signature is the same, functionality almost identical, but the implementation is simpler.

SGL Error Constants

        //  error codes to use with SGL::raiseError()
        //  start at -100 in order not to conflict with PEAR::DB error codes
        define('SGL_ERROR_INVALIDARGS',         -101);  // wrong args to function
        define('SGL_ERROR_INVALIDCONFIG',       -102);  // something wrong with the config
        define('SGL_ERROR_NODATA',              -103);  // no data available
        define('SGL_ERROR_NOCLASS',             -104);  // no class exists
        define('SGL_ERROR_NOMETHOD',            -105);  // no method exists
        define('SGL_ERROR_NOAFFECTEDROWS',      -106);  // no rows where affected by update/insert/delete
        define('SGL_ERROR_NOTSUPPORTED'  ,      -107);  // limit queries on unsuppored databases
        define('SGL_ERROR_INVALIDCALL',         -108);  // overload getter/setter failure
        define('SGL_ERROR_INVALIDAUTH',         -109);
        define('SGL_ERROR_EMAILFAILURE',        -110);
        define('SGL_ERROR_DBFAILURE',           -111);
        define('SGL_ERROR_BANNEDUSER',          -113);
        define('SGL_ERROR_NOFILE',              -114);
        define('SGL_ERROR_INVALIDFILEPERMS',    -115);
        define('SGL_ERROR_INVALIDSESSION',      -116);
        define('SGL_ERROR_INVALIDPOST',         -117);
        define('SGL_ERROR_INVALIDTRANSLATION',  -118);
        define('SGL_ERROR_FILEUNWRITABLE',      -119);
        define('SGL_ERROR_INVALIDMETHODPERMS',  -120);
        define('SGL_ERROR_INVALIDREQUEST',      -121);
        define('SGL_ERROR_INVALIDTYPE',         -122);
        define('SGL_ERROR_RECURSION',           -123);


Using the Zend Debugger

One of the best ways to track down problems is by using a debugger like what's supplied with the Zend IDE. One catch is that you often need to access pages requiring authentication, so you have to start a session, login, then navigate back to the page where the problem is. An easy way to get around this is set the Configuration option 'Enable authentication' to no. This allows you to access any resource in the framework as if you were an admin user, without having to login.

The Zend debugger extension binaries for your webserver can be downloaded from here:

Installing is pretty straight-forward (from the readme.txt in one of the archives above):

Zend Debugger installation instructions
1. Locate or ZendDebugger.dll file that is compiled for the
   correct version of PHP (4.3.x, 4.4.x, 5.0.x, 5.1.x, 5.2.x) in the 
   appropriate directory.
2. Add the following line to the php.ini file:
   Linux and Mac OS X: zend_extension=/full/path/to/
   Windows:            zend_extension_ts=/full/path/to/ZendDebugger.dll
3. Add the following lines to the php.ini file:
4. Place dummy.php file in the document root directory.
5. Restart web server.

Debug sesssions

  • debug sessions are available in >= Seagull 0.6.3

Developers can also invoke a privileged debug session - this option is available on production sites. The concept is simple, as long as the developer knows the secret key and passes it into the session, debug info will be available to him/her. This can be quite handy when certain errors only occur when dealing with live data.

To setup a debug session take the following steps:

  1. in the Config -> Debug screen, set 'enable debug session' to true
  2. in Config -> General set a secret key that will be used to invoke the session, under 'admin key'
  3. log out
  4. start the privileged session by calling a URL like
  5. any variables or data your expose in the following conditional will be displayed
    if (SGL_Config::get('debug.sessionDebugAllowed')) {
        echo 'this is debug';

Debugging Db_DataObject

As most developers familiar with the Db_DataObject package will know, there is a built-in mechanism for displaying debug info for the class. In the Db_DataObject config array, which is set towards the bottom of init.php, there is a key passed named 'debug' which, by default, is set to zero. Db_DataObject recognises 5 levels of debug info, 5 being the most verbose - change this setting to send debug info to the screen.

Debugging CLI Apps

Mr. Beaver has some invaluable advice here, read about it :


export  QUERY_STRING="start_debug=1&debug_port=10000&debug_fastfile=1&debug_host=

Debugging XML-RPC Apps

Similar idea, see the commented out line in this file:

Debugging Ajax Apps

There are basically two options:

Using Zend

From the Zend toolbar available in Firefox, choose Debug Menu -> Next page. The fire an Ajax request by clicking in the browser appropriately - the debug session will start.

Using Unit Tests

  • requires >= Seagull 0.6.3

Within the unit test you can create a sub-request that is of type Ajax, ie so SGL_Request_Ajax is called and the Ajax-specific filter chain, if it has been defined, it called. Use the following convention:

$req = SGL_Request::singleton(true, SGL_REQUEST_AJAX);
$req->set('moduleName', 'foo');
$req->set('action', 'getPersonById');
$req->set('usrId', 1);
SGL_Config::set('debug.authorisationEnabled', false);

Examining global NameSpace

Often it quite helpful to examine the Seagull NameSpace to see what your variables are doing. Some of framework-related variables can be found in $GLOBALS_SGL?, the best way to see what you've got is:


optionally contained with PRE tags, to improve formatting. Also useful is the ability to examine the request object, then verify against the input object to see if you've successfully mapped the desired, filtered data as expected. To do this you can echo out the request object at the beginning of any validate() method:


or echo the input object end the end of any validate method, to see what's getting passed back to the controller.


Using the Debug Block

As of 0.6.1, in Config you can enable [debug][enableDebugBlock], and the next time you run the Seagull rebuild action in the maintenance section, a debug block will appear in the left hand column. This block allows you to run rebuilds easily without having to navigate to the relevant admin section. Currently it is only enabled for admins.

Verifying Input

print '<pre>'; print_r($input); print '</pre>';

add to the end of your validate() method, This will allow it so you can see which vars are successfully being assigned to the input object from the request.

Unit Tests

Seagull comes with a test runner app that's built on top of SimpleTest


For more info on unit testing see Standards/UnitTesting

Testing tools

There are different tools for testing an PHP application, e.g.:

  • SimpleTest
  • PEAR::PHPUnit and this PEAR::PHPUnit homepage
  • phpt

Tutorials / Articles about (Unit)Testing:

UAT Testing


There is also an Eclipse plugin called Solex ( with the same functionality but the ability to apply extraction and replacement rules.