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wp-content/plugins/wordpress-seo/inc/class-wpseo-custom-fields.php

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+<?php
+/**
+ * WPSEO plugin file.
+ *
+ * @package WPSEO
+ */
+
+/**
+ * WPSEO_Custom_Fields.
+ */
+class WPSEO_Custom_Fields {
+
+	/**
+	 * Custom fields cache.
+	 *
+	 * @var array
+	 */
+	protected static $custom_fields = null;
+
+	/**
+	 * Retrieves the custom field names as an array.
+	 *
+	 * @link WordPress core: wp-admin/includes/template.php. Reused query from it.
+	 *
+	 * @return array The custom fields.
+	 */
+	public static function get_custom_fields() {
+		global $wpdb;
+
+		// Use cached value if available.
+		if ( ! is_null( self::$custom_fields ) ) {
+			return self::$custom_fields;
+		}
+
+		self::$custom_fields = [];
+
+		/**
+		 * Filters the number of custom fields to retrieve for the drop-down
+		 * in the Custom Fields meta box.
+		 *
+		 * @param int $limit Number of custom fields to retrieve. Default 30.
+		 */
+		$limit  = apply_filters( 'postmeta_form_limit', 30 );
+		$sql    = "SELECT DISTINCT meta_key
+			FROM $wpdb->postmeta
+			WHERE meta_key NOT BETWEEN '_' AND '_z' AND SUBSTRING(meta_key, 1, 1) != '_'
+			LIMIT %d";
+		$fields = $wpdb->get_col( $wpdb->prepare( $sql, $limit ) );
+
+		/**
+		 * Filters the custom fields that are auto-completed and replaced as replacement variables
+		 * in the meta box and sidebar.
+		 *
+		 * @param string[] $fields The custom field names.
+		 */
+		$fields = apply_filters( 'wpseo_replacement_variables_custom_fields', $fields );
+
+		if ( is_array( $fields ) ) {
+			self::$custom_fields = array_map( [ 'WPSEO_Custom_Fields', 'add_custom_field_prefix' ], $fields );
+		}
+
+		return self::$custom_fields;
+	}
+
+	/**
+	 * Adds the cf_ prefix to a field.
+	 *
+	 * @param string $field The field to prefix.
+	 *
+	 * @return string The prefixed field.
+	 */
+	private static function add_custom_field_prefix( $field ) {
+		return 'cf_' . $field;
+	}
+}