PHP

One of the sites I work on uses JpGraph to generate graphs for their reports. A few months ago we moved the site from an old server with PHP 4 to a new server with PHP 5 and started getting the error “JpGraph Error: Can’t access PHP_SELF, PHP global variable”. This post looks at the error and a couple of possible solutions to it.

The error message

Instead of generating the requested graph, JpGraph instead displays an image as follows, containing the error message “JpGraph Error: Can’t access PHP_SELF, PHP global variable. You can’t run PHP from command line if you want to use the ‘auto’ naming of cache or image files.”

We were running this from a web browser and not from the command line so the error message seemed a little odd. However it was clear that the functions are trying to access the PHP_SELF variable in some way that isn’t defined.

Reason for the error

A quick dig through the source and I found that it’s an old version of JpGraph designed for PHP 4. In several places in the jpgraph.php file were references to PHP_SELF using the old HTTP_SERVER_VARS array like so:

 global $HTTP_SERVER_VARS;
 if( $aCacheName=='auto' )
     $aCacheName=basename($HTTP_SERVER_VARS['PHP_SELF']);

How to resolve the error

There are two versions of JpGraph currently maintained, one for PHP 4 and one for PHP 5. You can download either of these from the JpGraph download page.

I figured grabbing the PHP 5 version might end up taking a while to test and make sure everything was working correctly so instead made a minor change to the jpgraph.php file by adding the following to the top of the script:

$HTTP_SERVER_VARS = array(
  'PHP_SELF' => $_SERVER['PHP_SELF']
 );

Each function call does “global $HTTP_SERVER_VARS” so even though this array won’t have gobal scope in PHP 5 it will still be available to all the functions that use it.

The alternative hack to the file would be to replace all the instances of $HTTP_SERVER_VARS with $_SERVER. The following example shows the earlier example changed to be like this.

 if( $aCacheName=='auto' )
     $aCacheName=basename($_SERVER['PHP_SELF']);

Conclusion

The “JpGraph Error: Can’t access PHP_SELF, PHP global variable” error is caused by the use of $HTTP_SERVER_VARS when running the scripts under PHP 5, a global array which has been deprecated and is no longer available in PHP 5 unless you enable the long arrays in the PHP config. The solution is to get the PHP 5 version of the library or apply one of the “hacks” I have supplied in the above examples.

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