The Right Way to Build Configurable PHP Applications_PHP Tutorial

This article illustrates several ways to create configurable PHP applications. The article also explores the ideal configuration points in an application and seeks a balance between an application being too configurable and being too closed.

If you plan to make your PHP application available to other people or companies, you need to make sure that the application is configurable. At a minimum, allow users to set up database logins and passwords in a secure manner so that the material within them is not made public.

This article demonstrates several techniques for storing configuration settings and editing these settings. In addition, the article also provides guidance on which elements need to be made configurable and how to avoid falling into the dilemma of over- or under-configuration.

​Configuration using INI file

PHP has built-in support for configuration files. This is accomplished through an initialization file (INI) mechanism such as a php.ini file, where constants such as database connection timeouts or how sessions are stored are defined. If you wish, you can customize the configuration for your application in this php.ini file. To illustrate, I added the following lines of code to the php.ini file.

​myapptempdir=foo

Then, I wrote a small PHP script to read this configuration item, as shown in Listing 1.

List 1. ini1.php

function get_template_directory()
{
​$v = get_cfg_var( "myapptempdir" );
return ( $v == null ) ? "tempdir" : $v;
}

echo( get_template_directory()."n" );
?>

​When running this code in the command line, the following results are obtained:

% php ini1.php
foo
%

marvelous. But why can't we use the standard INI function to get the value of the myapptempdir configuration item? I did some research and found that in most cases, custom configuration items cannot be obtained using these methods. However, it is accessible using the get_cfg_var function.

To make this method simpler, encapsulate access to the variable in a second function that takes the configuration key name and a default value as parameters, as shown below.

Listing 2. ini2.php

function get_ini_value( $n, $dv )
{
​$c = get_cfg_var( $n );
return ( $c == null ) ? $dv : $c;
}

function get_template_directory()
{
return get_ini_value( "myapptempdir", "tempdir" );
}

This is a good overview of how to access an INI file, so if you want to use a different mechanism or store the INI file somewhere else, you don't have to go through the trouble of changing a bunch of functions.

I don't recommend using INI files for application configuration, for two reasons. First, while this makes it easier to read the INI file, it makes it almost impossible to write the INI file safely. So this is only suitable for read-only configuration items. Second, the php.ini file is shared across all applications on the server, so I don't think application-specific configuration items should be written in that file.

What do you need to know about INI files? The most important thing is how to reset the include path to add configuration items as shown below.

Listing 3. ini3.php

echo( ini_get("include_path")."n" );
ini_set("include_path",
ini_get("include_path").":./mylib" );
echo( ini_get("include_path")."n" );
?>

In this example, I added my local mylib directory to the include path, so I can require PHP files from that directory without adding the path to the require statement.

Configuration in PHP

A common alternative to storing configuration entries in an INI file is to use a simple PHP script to persist the data. Below is an example.

Listing 4. config.php

# Specify the location of the temporary directory
#
$TEMPLATE_DIRECTORY = "tempdir";
?>

The code using this constant is as follows.

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