7.9.4 The mysqlnd plugin API

Copyright 1997-2022 the PHP Documentation Group.

The following is a list of functions provided in themysqlndplugin API:

  • mysqlnd_plugin_register()

  • mysqlnd_plugin_count()

  • mysqlnd_plugin_get_plugin_connection_data()

  • mysqlnd_plugin_get_plugin_result_data()

  • mysqlnd_plugin_get_plugin_stmt_data()

  • mysqlnd_plugin_get_plugin_net_data()

  • mysqlnd_plugin_get_plugin_protocol_data()

  • mysqlnd_conn_get_methods()

  • mysqlnd_result_get_methods()

  • mysqlnd_result_meta_get_methods()

  • mysqlnd_stmt_get_methods()

  • mysqlnd_net_get_methods()

  • mysqlnd_protocol_get_methods()

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)

Themysqlndplugin concept employs these features, and additionally enjoys an open architecture.

No Restrictions

A plugin has full access to the inner workings ofmysqlnd. 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 cooperate withmysqlnditself.

Table 7.13 Issues: an example of chaining and cooperation

Extension mysqlnd.query() pointer call stack if calling parent
ext/mysqlnd mysqlnd.query() mysqlnd.query
ext/mysqlnd_cache mysqlnd_cache.query()
  1. mysqlnd_cache.query()

  2. mysqlnd.query

ext/mysqlnd_monitor mysqlnd_monitor.query()
  1. mysqlnd_monitor.query()

  2. mysqlnd_cache.query()

  3. mysqlnd.query


In this scenario, a cache (ext/mysqlnd_cache) and a monitor (ext/mysqlnd_monitor) plugin are loaded. Both subclassConnection::query(). Plugin registration happens atMINITusing the logic shown previously. PHP calls extensions in alphabetical order by default. Plugins are not aware of each other and do not set extension dependencies.

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 themysqlndC plugin API to PHP:

  • 任何PHP应用t MySQLries to establish a connection to 192.168.2.29

  • The PHP application will either useext/mysql,ext/mysqliorPDO_MYSQL. All three PHP MySQL extensions usemysqlndto establish the connection to 192.168.2.29.

  • Mysqlndcalls its connect method, which has been subclassed byext/mysqlnd_plugin.

  • ext/mysqlnd_plugincalls the userspace hookproxy::connect()registered by the user.

  • The userspace hook changes the connection host IP from 192.168.2.29 to 127.0.0.1 and returns the connection established byparent::connect().

  • ext/mysqlnd_pluginperforms the equivalent ofparent::connect(127.0.0.1)by calling the originalmysqlndmethod for establishing a connection.

  • ext/mysqlndestablishes a connection and returns toext/mysqlnd_plugin.ext/mysqlnd_pluginreturns 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.