The following is a list of functions provided in the
mysqlnd plugin API:
There is no formal definition of what a plugin is and how a plugin mechanism works.
Components often found in plugins mechanisms are:
A plugin manager
A plugin API
Application services (or modules)
Application service APIs (or module APIs)
mysqlnd plugin concept employs these
features, and additionally enjoys an open architecture.
A plugin has full access to the inner workings of
mysqlnd. There are no security limits or
restrictions. Everything can be overwritten to implement
friendly or hostile algorithms. It is recommended you only
deploy plugins from a trusted source.
As discussed previously, plugins can use pointers freely. These pointers are not restricted in any way, and can point into another plugin's data. Simple offset arithmetic can be used to read another plugin's data.
It is recommended that you write cooperative plugins, and that
you always call the parent method. The plugins should always
Table 4.15. Issues: an example of chaining and cooperation
|Extension||mysqlnd.query() pointer||call stack if calling parent|
In this scenario, a cache (
and a monitor (
are loaded. Both subclass
Connection::query(). Plugin registration
MINIT using the logic shown
previously. PHP calls extensions in alphabetical order by
default. Plugins are not aware of each other and do not set
By default the plugins call the parent implementation of the query method in their derived version of the method.
PHP Extension Recap
This is a recap of what happens when using an example plugin,
ext/mysqlnd_plugin, which exposes the
mysqlnd C plugin API to PHP:
Any PHP MySQL application tries to establish a connection to 192.168.2.29
The PHP application will either use
PDO_MYSQL. All three PHP MySQL
mysqlnd to establish the
connection to 192.168.2.29.
Mysqlnd calls its connect method, which
has been subclassed by
ext/mysqlnd_plugin calls the userspace
proxy::connect() registered by the
The userspace hook changes the connection host IP from
192.168.2.29 to 127.0.0.1 and returns the connection
ext/mysqlnd_plugin performs the
by calling the original
for establishing a connection.
ext/mysqlnd establishes a connection and
ext/mysqlnd_plugin returns as well.
Whatever PHP MySQL extension had been used by the application, it receives a connection to 127.0.0.1. The PHP MySQL extension itself returns to the PHP application. The circle is closed.