get_is_valid_id.php

<?php 
/** see attached meta.php for usage sample **/
function is_valid_id( $id ) {
	// added for a fallback if filter_var is disabled for php build
	if ( function_exists( 'filter_var' ) ) {
		$default_opts = array(
			'options' => array(
				'default'   => false, // value to return if the filter fails
				'min_range' => 1,
				'max_range' => PHP_INT_MAX
			)
		);

		apply_filters( ‘is_valid_id_options’, $default_opts ); // alternate filter name: 'filter_var_args' 

		// will cast as an int OR return false if value is not an (int)
		$checked = filter_var( $id, FILTER_VALIDATE_INT, $default_opts );
	} else {
		// if the id is a collection of only digits, not zero & not starting w/ zero
		if ( preg_match( '/^[^0][0-9]+$/', $id, $matches ) ) {

			// set checked val (could typecast as (int) if you want but be aware of BIGINT issues or (float) ).
			$checked = $matches[0];

		} else {

			// set checked as falsey (or throw exception )
			$checked = false;
		}
	}
	return $checked;
}

function get_is_valid_id($id){

	$checked = is_valid_id($id); 
	
	return apply_filters('is_valid_id', $checked, $id); 

}

meta.php

<?php
function get_meta_data($meta_type, $object_id, $meta_key = '', $single = false){
	// first make sure $object_id is set 
  	if ( ! $meta_type || ! $object_id ) {
		return false;
	}
	/** 
	 * REMOVED/REPLACED  if ( ! is_numeric($object_id) )
	 * Using the wrapper function that allows a developer to 
	 * filter the sanitization/validation of the ID value. 
	 **/
	$object_id = get_is_valid_id($object_id);
 	if( ! $object_id ){
		return false;
	}
  	$check = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, $single );
	if ( null !== $check ) {
		if ( $single && is_array( $check ) )
			return $check[0];
		else
			return $check;
	}
 	// this will now grab the record we added earlier on line 37 of 1_create_post_object.php
	// previously it would not passed the is_numeric() check
	$meta_cache = wp_cache_get($object_id, $meta_type . '_meta');
  	if ( !$meta_cache ) {
		$meta_cache = update_meta_cache( $meta_type, array( $object_id ) );
		$meta_cache = $meta_cache[$object_id];
	}
	if ( ! $meta_key ) {
		return $meta_cache;
	}
	if ( isset($meta_cache[$meta_key]) ) {
		if ( $single )
			return maybe_unserialize( $meta_cache[$meta_key][0] );
		else
			return array_map('maybe_unserialize', $meta_cache[$meta_key]);
	}
	if ($single)
		return '';
	else
		return array();
}

function update_metadata($meta_type, $object_id, $meta_key, $meta_value, $prev_value = '') {
	global $wpdb;

	if ( ! $meta_type || ! $meta_key ) {
		return false;
	}
  
  	/**
	 * No filter allowed here because we are adding content to the DB and that's risky
	 **/
	$object_id = is_valid_id( $object_id );
	if ( ! $object_id ) {
		return false;
	}

	$table = _get_meta_table( $meta_type );
	if ( ! $table ) {
		return false;
	}

	$column = sanitize_key($meta_type . '_id');
	$id_column = 'user' == $meta_type ? 'umeta_id' : 'meta_id';

	// expected_slashed ($meta_key)
	$raw_meta_key = $meta_key;
	$meta_key = wp_unslash($meta_key);
	$passed_value = $meta_value;
	$meta_value = wp_unslash($meta_value);
	$meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type );

	/**
	 * Filters whether to update metadata of a specific type.
	 *
	 * The dynamic portion of the hook, `$meta_type`, refers to the meta
	 * object type (comment, post, or user). Returning a non-null value
	 * will effectively short-circuit the function.
	 *
	 * @since 3.1.0
	 *
	 * @param null|bool $check      Whether to allow updating metadata for the given type.
	 * @param int       $object_id  Object ID.
	 * @param string    $meta_key   Meta key.
	 * @param mixed     $meta_value Meta value. Must be serializable if non-scalar.
	 * @param mixed     $prev_value Optional. If specified, only update existing
	 *                              metadata entries with the specified value.
	 *                              Otherwise, update all entries.
	 */
	$check = apply_filters( "update_{$meta_type}_metadata", null, $object_id, $meta_key, $meta_value, $prev_value );
	if ( null !== $check )
		return (bool) $check;

	// Compare existing value to new value if no prev value given and the key exists only once.
	if ( empty($prev_value) ) {
		$old_value = get_metadata($meta_type, $object_id, $meta_key);
		if ( count($old_value) == 1 ) {
			if ( $old_value[0] === $meta_value )
				return false;
		}
	}

	$meta_ids = $wpdb->get_col( $wpdb->prepare( "SELECT $id_column FROM $table WHERE meta_key = %s AND $column = %d", $meta_key, $object_id ) );
	if ( empty( $meta_ids ) ) {
		return add_metadata( $meta_type, $object_id, $raw_meta_key, $passed_value );
	}

	$_meta_value = $meta_value;
	$meta_value = maybe_serialize( $meta_value );

	$data  = compact( 'meta_value' );
	$where = array( $column => $object_id, 'meta_key' => $meta_key );

	if ( !empty( $prev_value ) ) {
		$prev_value = maybe_serialize($prev_value);
		$where['meta_value'] = $prev_value;
	}

	foreach ( $meta_ids as $meta_id ) {
		/**
		 * Fires immediately before updating metadata of a specific type.
		 *
		 * The dynamic portion of the hook, `$meta_type`, refers to the meta
		 * object type (comment, post, or user).
		 *
		 * @since 2.9.0
		 *
		 * @param int    $meta_id    ID of the metadata entry to update.
		 * @param int    $object_id  Object ID.
		 * @param string $meta_key   Meta key.
		 * @param mixed  $meta_value Meta value.
		 */
		do_action( "update_{$meta_type}_meta", $meta_id, $object_id, $meta_key, $_meta_value );

		if ( 'post' == $meta_type ) {
			/**
			 * Fires immediately before updating a post's metadata.
			 *
			 * @since 2.9.0
			 *
			 * @param int    $meta_id    ID of metadata entry to update.
			 * @param int    $object_id  Object ID.
			 * @param string $meta_key   Meta key.
			 * @param mixed  $meta_value Meta value.
			 */
			do_action( 'update_postmeta', $meta_id, $object_id, $meta_key, $meta_value );
		}
	}

	$result = $wpdb->update( $table, $data, $where );
	if ( ! $result )
		return false;

	wp_cache_delete($object_id, $meta_type . '_meta');

	foreach ( $meta_ids as $meta_id ) {
		/**
		 * Fires immediately after updating metadata of a specific type.
		 *
		 * The dynamic portion of the hook, `$meta_type`, refers to the meta
		 * object type (comment, post, or user).
		 *
		 * @since 2.9.0
		 *
		 * @param int    $meta_id    ID of updated metadata entry.
		 * @param int    $object_id  Object ID.
		 * @param string $meta_key   Meta key.
		 * @param mixed  $meta_value Meta value.
		 */
		do_action( "updated_{$meta_type}_meta", $meta_id, $object_id, $meta_key, $_meta_value );

		if ( 'post' == $meta_type ) {
			/**
			 * Fires immediately after updating a post's metadata.
			 *
			 * @since 2.9.0
			 *
			 * @param int    $meta_id    ID of updated metadata entry.
			 * @param int    $object_id  Object ID.
			 * @param string $meta_key   Meta key.
			 * @param mixed  $meta_value Meta value.
			 */
			do_action( 'updated_postmeta', $meta_id, $object_id, $meta_key, $meta_value );
		}
	}

	return true;
}