Wordpress 自定义字段上传图片

Question

我想在wordpress上传自定义图片，图片文件没有正确上传到上传文件夹，上传的图片显示0个bits文件。 以下是我的代码

function save_extra_user_profile_fields( $user_id ) {
    if ( empty( $_POST['_wpnonce'] ) || ! wp_verify_nonce( $_POST['_wpnonce'], 'update-user_' . $user_id ) ) {
        return;
    }
    
    if ( !current_user_can( 'edit_user', $user_id ) ) { 
        return false; 
    }  
   
        $image_url = $_POST['extra_pic'];
        $upload_dir = wp_upload_dir();
        $image_data = file_get_contents( $image_url );

        $filename = basename( $image_url );       
        if ( wp_mkdir_p( $upload_dir['path'] ) ) {
            $file = $upload_dir['path'] . '/' . $filename;
        }
        else {
          $file = $upload_dir['basedir'] . '/' . $filename;
        }        
        file_put_contents( $file, $image_data );        
        $wp_filetype = wp_check_filetype( $filename, null );        
        $attachment = array(
          'post_mime_type' => $wp_filetype['type'],
          'post_title' => sanitize_file_name( $filename ),
          'post_content' => 'additional pic',
          'post_status' => 'inherit'
        );        
        $attach_id = wp_insert_attachment( $attachment, $file );
        require_once( ABSPATH . 'wp-admin/includes/image.php' );
        $attach_data = wp_generate_attachment_metadata( $attach_id, $file );
        wp_update_attachment_metadata( $attach_id, $attach_data ); 
    
update_user_meta( $user_id, 'extra_pic', $_POST['extra_pic'] );
    
}