sessioncommunities.online/php/utils/room-invites.php

<?php
    /**
     * Return local path to room invite code.
	 * @param string $room_id Id of room to locate QR code for.
	 */
	function room_qr_code_path(string $room_id): string {
		global $QR_CODES;
		return "$QR_CODES/$room_id.png";
	}

    /**
     * Return server-relative path to room invite code.
	 * @param string $room_id Id of room to locate QR code for.
	 */
	function room_qr_code_path_relative(string $room_id): string {
		global $QR_CODES_RELATIVE;
		return "$QR_CODES_RELATIVE/$room_id.png";
	}

    
	/**
	 * Fetch QR invite of the given room and return its relative path.
	 * @param \CommunityRoom $room
     * @return string
	 */
	function room_qr_code($room): string {
		$room_id = $room->get_room_identifier();
		$png_cached = room_qr_code_path($room_id);
		if (file_exists($png_cached)) {
			return room_qr_code_path_relative($room_id);
		}
		log_debug("Fetching QR code for $room_id.");
		$png = file_get_contents($room->get_invite_url());
		if (empty($png)) {
			log_warning("$room_id returned empty QR code.");
		}
		file_put_contents($png_cached, $png);
		return room_qr_code_path_relative($room_id);
	}

	file_exists($QR_CODES) or mkdir($QR_CODES, 0755);
?>