+ if ( ! is_array( $wp_meta_keys ) ) {
+ $wp_meta_keys = array();
+ }
+
+ $defaults = array(
+ 'type' => 'string',
+ 'description' => '',
+ 'single' => false,
+ 'sanitize_callback' => null,
+ 'auth_callback' => null,
+ 'show_in_rest' => false,
+ );
+
+ // There used to be individual args for sanitize and auth callbacks
+ $has_old_sanitize_cb = false;
+ $has_old_auth_cb = false;
+
+ if ( is_callable( $args ) ) {
+ $args = array(
+ 'sanitize_callback' => $args,
+ );
+
+ $has_old_sanitize_cb = true;
+ } else {
+ $args = (array) $args;
+ }
+
+ if ( is_callable( $deprecated ) ) {
+ $args['auth_callback'] = $deprecated;
+ $has_old_auth_cb = true;
+ }
+
+ /**
+ * Filters the registration arguments when registering meta.
+ *
+ * @since 4.6.0
+ *
+ * @param array $args Array of meta registration arguments.
+ * @param array $defaults Array of default arguments.
+ * @param string $object_type Object type.
+ * @param string $meta_key Meta key.
+ */
+ $args = apply_filters( 'register_meta_args', $args, $defaults, $object_type, $meta_key );
+ $args = wp_parse_args( $args, $defaults );
+
+ // If `auth_callback` is not provided, fall back to `is_protected_meta()`.
+ if ( empty( $args['auth_callback'] ) ) {
+ if ( is_protected_meta( $meta_key, $object_type ) ) {
+ $args['auth_callback'] = '__return_false';
+ } else {
+ $args['auth_callback'] = '__return_true';
+ }
+ }
+
+ // Back-compat: old sanitize and auth callbacks are applied to all of an object type.
+ if ( is_callable( $args['sanitize_callback'] ) ) {
+ add_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'], 10, 3 );
+ }
+
+ if ( is_callable( $args['auth_callback'] ) ) {
+ add_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'], 10, 6 );
+ }
+
+ // Global registry only contains meta keys registered with the array of arguments added in 4.6.0.
+ if ( ! $has_old_auth_cb && ! $has_old_sanitize_cb ) {
+ $wp_meta_keys[ $object_type ][ $meta_key ] = $args;
+
+ return true;
+ }
+
+ return false;
+}
+
+/**
+ * Checks if a meta key is registered.
+ *
+ * @since 4.6.0
+ *
+ * @param string $object_type The type of object.
+ * @param string $meta_key The meta key.
+ *
+ * @return bool True if the meta key is registered to the object type. False if not.
+ */
+function registered_meta_key_exists( $object_type, $meta_key ) {
+ global $wp_meta_keys;
+
+ if ( ! is_array( $wp_meta_keys ) ) {
+ return false;
+ }
+
+ if ( ! isset( $wp_meta_keys[ $object_type ] ) ) {
+ return false;
+ }
+
+ if ( isset( $wp_meta_keys[ $object_type ][ $meta_key ] ) ) {
+ return true;
+ }
+
+ return false;
+}
+
+/**
+ * Unregisters a meta key from the list of registered keys.
+ *
+ * @since 4.6.0
+ *
+ * @param string $object_type The type of object.
+ * @param string $meta_key The meta key.
+ * @return bool True if successful. False if the meta key was not registered.
+ */
+function unregister_meta_key( $object_type, $meta_key ) {
+ global $wp_meta_keys;
+
+ if ( ! registered_meta_key_exists( $object_type, $meta_key ) ) {
+ return false;
+ }
+
+ $args = $wp_meta_keys[ $object_type ][ $meta_key ];
+
+ if ( isset( $args['sanitize_callback'] ) && is_callable( $args['sanitize_callback'] ) ) {
+ remove_filter( "sanitize_{$object_type}_meta_{$meta_key}", $args['sanitize_callback'] );
+ }
+
+ if ( isset( $args['auth_callback'] ) && is_callable( $args['auth_callback'] ) ) {
+ remove_filter( "auth_{$object_type}_meta_{$meta_key}", $args['auth_callback'] );
+ }
+
+ unset( $wp_meta_keys[ $object_type ][ $meta_key ] );
+
+ // Do some clean up
+ if ( empty( $wp_meta_keys[ $object_type ] ) ) {
+ unset( $wp_meta_keys[ $object_type ] );
+ }
+
+ return true;
+}
+
+/**
+ * Retrieves a list of registered meta keys for an object type.
+ *
+ * @since 4.6.0
+ *
+ * @param string $object_type The type of object. Post, comment, user, term.
+ * @return array List of registered meta keys.
+ */
+function get_registered_meta_keys( $object_type ) {
+ global $wp_meta_keys;
+
+ if ( ! is_array( $wp_meta_keys ) || ! isset( $wp_meta_keys[ $object_type ] ) ) {
+ return array();
+ }
+
+ return $wp_meta_keys[ $object_type ];
+}
+
+/**
+ * Retrieves registered metadata for a specified object.
+ *
+ * @since 4.6.0
+ *
+ * @param string $object_type Type of object to request metadata for. (e.g. comment, post, term, user)
+ * @param int $object_id ID of the object the metadata is for.
+ * @param string $meta_key Optional. Registered metadata key. If not specified, retrieve all registered
+ * metadata for the specified object.
+ * @return mixed A single value or array of values for a key if specified. An array of all registered keys
+ * and values for an object ID if not.
+ */
+function get_registered_metadata( $object_type, $object_id, $meta_key = '' ) {
+ if ( ! empty( $meta_key ) ) {
+ if ( ! registered_meta_key_exists( $object_type, $meta_key ) ) {
+ return false;
+ }
+ $meta_keys = get_registered_meta_keys( $object_type );
+ $meta_key_data = $meta_keys[ $meta_key ];
+
+ $data = get_metadata( $object_type, $object_id, $meta_key, $meta_key_data['single'] );
+
+ return $data;
+ }
+
+ $data = get_metadata( $object_type, $object_id );
+
+ $meta_keys = get_registered_meta_keys( $object_type );
+ $registered_data = array();
+
+ // Someday, array_filter()
+ foreach ( $meta_keys as $k => $v ) {
+ if ( isset( $data[ $k ] ) ) {
+ $registered_data[ $k ] = $data[ $k ];
+ }
+ }
+
+ return $registered_data;
+}
+
+/**
+ * Filter out `register_meta()` args based on a whitelist.
+ * `register_meta()` args may change over time, so requiring the whitelist
+ * to be explicitly turned off is a warranty seal of sorts.
+ *
+ * @access private
+ * @since 4.6.0
+ *
+ * @param array $args Arguments from `register_meta()`.
+ * @param array $default_args Default arguments for `register_meta()`.
+ *
+ * @return array Filtered arguments.
+ */
+function _wp_register_meta_args_whitelist( $args, $default_args ) {
+ $whitelist = array_keys( $default_args );
+
+ // In an anonymous function world, this would be better as an array_filter()
+ foreach ( $args as $key => $value ) {
+ if ( ! in_array( $key, $whitelist ) ) {
+ unset( $args[ $key ] );
+ }