It is important to remember that a mysqlnd plugin is itself a PHP extension.
The following code shows the basic structure of the MINIT function that will be used in the typical mysqlnd plugin:
static PHP_MINIT_FUNCTION(mysqlnd_plugin) { mysqlnd_plugin_id = mysqlnd_plugin_register(); conn_m = mysqlnd_get_conn_methods(); memcpy(org_conn_m, conn_m, sizeof(struct st_mysqlnd_conn_methods)); conn_m->query = MYSQLND_METHOD(mysqlnd_plugin_conn, query); conn_m->connect = MYSQLND_METHOD(mysqlnd_plugin_conn, connect); } enum_func_status MYSQLND_METHOD(mysqlnd_plugin_conn, query)() { } enum_func_status MYSQLND_METHOD(mysqlnd_plugin_conn, connect)() { } Task analysis: from C to userspace
class proxy extends mysqlnd_plugin_connection { public function connect($host, ...) { .. } } mysqlnd_plugin_set_conn_proxy(new proxy()); Process:
PHP: user registers plugin callback
PHP: user calls any PHP MySQL API to connect to MySQL
C: ext MYSQLND_METHOD(my_conn_class,connect)( MYSQLND *conn, const char *host TSRMLS_DC) { enum_func_status ret = FAIL; zval * global_user_conn_proxy = fetch_userspace_proxy(); if (global_user_conn_proxy) { ret = MY_ZEND_CALL_METHOD_WRAPPER(global_user_conn_proxy, host, ); } else { ret = org_methods.connect(conn, host, user, passwd, passwd_len, db, db_len, port, socket, mysql_flags TSRMLS_CC); } return ret; }
Calling userspace: simple arguments
MYSQLND_METHOD(my_conn_class,connect)( , const char *host, ) { if (global_user_conn_proxy) { zval* zv_host; MAKE_STD_ZVAL(zv_host); ZVAL_STRING(zv_host, host, 1); MY_ZEND_CALL_METHOD_WRAPPER(global_user_conn_proxy, zv_retval, zv_host ); zval_ptr_dtor(&zv_host); } } Calling userspace: structs as arguments
MYSQLND_METHOD(my_conn_class, connect)( MYSQLND *conn, ) { if (global_user_conn_proxy) { zval* zv_conn; ZEND_REGISTER_RESOURCE(zv_conn, (void *)conn, le_mysqlnd_plugin_conn); MY_ZEND_CALL_METHOD_WRAPPER(global_user_conn_proxy, zv_retval, zv_conn, zv_host ); zval_ptr_dtor(&zv_conn); } } The first argument of many mysqlnd methods is a C "object". For example, the first argument of the connect() method is a pointer to MYSQLND. The struct MYSQLND represents a mysqlnd connection object.
The mysqlnd connection object pointer can be compared to a standard I/O file handle. Like a standard I/O file handle a mysqlnd connection object shall be linked to the userspace using the PHP resource variable type.
From C to userspace and back
class proxy extends mysqlnd_plugin_connection { public function connect($conn, $host, ...) { printf("Connecting to host = '%s'\n", $host); debug_print_backtrace(); return parent::connect($conn); } public function query($conn, $query) { $ret = parent::query($conn, $query); printf("Query = '%s'\n", $query); return $ret; } } mysqlnd_plugin_set_conn_proxy(new proxy()); PHP users must be able to call the parent implementation of an overwritten method.
As a result of subclassing it is possible to refine only selected methods and you can choose to have "pre" or "post" hooks.
Buildin class: mysqlnd_plugin_connection::connect()
PHP_METHOD("mysqlnd_plugin_connection", connect) { zval* mysqlnd_rsrc; MYSQLND* conn; char* host; int host_len; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "rs", &mysqlnd_rsrc, &host, &host_len) == FAILURE) { RETURN_NULL(); } ZEND_FETCH_RESOURCE(conn, MYSQLND* conn, &mysqlnd_rsrc, -1, "Mysqlnd Connection", le_mysqlnd_plugin_conn); if (PASS == org_methods.connect(conn, host, TSRMLS_CC)) RETVAL_TRUE; else RETVAL_FALSE; }