roundcubemail/program/actions/mail/attachment_display.php

<?php

/*
 +-----------------------------------------------------------------------+
 | This file is part of the Roundcube Webmail client                     |
 |                                                                       |
 | Copyright (C) The Roundcube Dev Team                                  |
 |                                                                       |
 | Licensed under the GNU General Public License version 3 or            |
 | any later version with exceptions for skins & plugins.                |
 | See the README file for a full license statement.                     |
 |                                                                       |
 | PURPOSE:                                                              |
 |   Display attachments in compose form                                 |
 +-----------------------------------------------------------------------+
 | Author: Thomas Bruederli <roundcube@gmail.com>                        |
 +-----------------------------------------------------------------------+
*/

class rcmail_action_mail_attachment_display extends rcmail_action_mail_attachment_upload
{
    protected static $mode = self::MODE_HTTP;

    /**
     * Request handler.
     *
     * @param array $args Arguments from the previous step(s)
     */
    public function run($args = [])
    {
        self::init();

        $rcmail = rcmail::get_instance();
        $file = $rcmail->get_uploaded_file(self::$file_id);

        self::display_uploaded_file($file);
        exit;
    }
}