PHP Debugging

We use the PHP extension Xdebug for debugging purposes. In the following we describe the Xdebug Debug and Profile feature. For more features and details please refer to the Xdebug documentation.

Xdebug Debug

The Xdebug Debug Feature allows you to walk through your code to debug control flow and examine data structures. You can use any IDE that supports Xdebug (DBGp protocol). This also includes PhpStorm and Visual Studio Code (with the PHP Debug Extension).

To start you need to load XDebug and enable the Debug feature in ~/cnf/php.ini and reload php with php-reload.

zend_extension = xdebug.so
xdebug.mode = debug
xdebug.start_with_request = yes

Afterwards, Xdebug sends debugging information to a predefined address and port. To allow debug sessions with multiple websites at the same time, a random port is assigned to each website at xdebug.client_port. If you debugg a website on our server you ned to reverse forward this port to your local machine/IDE.

ssh -R 127.0.0.1:15750:127.0.0.1:9003 <username>@<hostname>
     ▲             ▲              ▲         ▲
     │             │              │         │
     │       xdebug.client_port   │    Website name and Server
Reverse forward                Your IDE

Your IDE now has access to the debugging information at 127.0.0.1:9003 (Xdebug default port).

Tip

Use php -r 'echo ini_get("xdebug.client_port");' to get the debugging port.

Custom Port/Host

Set the xdebug.client_port and xdebug.client_host string within the Custom JSON Server Level Configuration:

{
  "xdebug::client_port": "9003",
  "xdebug::client_host": "127.0.0.1"
}

Warning

If set, those values will apply for all websites on this server. You’ll loose the ability to debug multiple websites concurrently.

Xdebug Profile

The Profile feature allows you to find bottlenecks in your script and visualize those with an external tool such as KCacheGrind or WinCacheGrind.

To start you need to load XDebug and enable the Profile feature in ~/cnf/php.ini and reload php with php-reload.

zend_extension = xdebug.so
xdebug.mode = profile
xdebug.start_with_request = yes

By default, profiler output will be written into the ~/tmp/ directory.

Warning

Enable profiling can generate a lot of data. Make sure your diskspace is sufficient to store this files and disable profiling as soon as possible

Trigger

Both features, Debug and Profile, support a trigger. The trigger ensures that the feature is not activated for every, but only for selected requests. For this you ned to set xdebug.start_with_request in ~/cnf/php.ini to trigger and reload php with php-reload.

xdebug.mode = debug,profile
xdebug.start_with_request = trigger

Cou can trigger Xdebug Debug and Profile by using the XDEBUG_TRIGGER GET/POST parameter, or set a cookie with the name XDEBUG_TRIGGER. There are also browser extensions that do this for you.