wp_autosave( array $post_data )

function wp_autosave( $post_data ) {
	// Back-compat
	if ( ! defined( 'DOING_AUTOSAVE' ) )
		define( 'DOING_AUTOSAVE', true );

	$post_id = (int) $post_data['post_id'];
	$post_data['ID'] = $post_data['post_ID'] = $post_id;

	if ( false === wp_verify_nonce( $post_data['_wpnonce'], 'update-post_' . $post_id ) ) {
		return new WP_Error( 'invalid_nonce', __( 'Error while saving.' ) );
	}

	$post = get_post( $post_id );

	if ( ! current_user_can( 'edit_post', $post->ID ) ) {
		return new WP_Error( 'edit_posts', __( 'Sorry, you are not allowed to edit this item.' ) );
	}

	if ( 'auto-draft' == $post->post_status )
		$post_data['post_status'] = 'draft';

	if ( $post_data['post_type'] != 'page' && ! empty( $post_data['catslist'] ) )
		$post_data['post_category'] = explode( ',', $post_data['catslist'] );

	if ( ! wp_check_post_lock( $post->ID ) && get_current_user_id() == $post->post_author && ( 'auto-draft' == $post->post_status || 'draft' == $post->post_status ) ) {
		// Drafts and auto-drafts are just overwritten by autosave for the same user if the post is not locked
		return edit_post( wp_slash( $post_data ) );
	} else {
		// Non drafts or other users drafts are not overwritten. The autosave is stored in a special post revision for each user.
		return wp_create_post_autosave( wp_slash( $post_data ) );
	}
}