#!/bin/bash
do {
	#////////////////////////////////////
	# DietPi
	#
	#////////////////////////////////////
	# Created by Daniel Knight / daniel.knight@dietpi.com / dietpi.com
	#////////////////////////////////////
	#
	# Info:
	# - Obtains the optimal MTU size.
	#
	# Usage:
	# - dietpi-optimal_mtu 					| Tests using google.com
	# - dietpi-optimal_mtu URL/IP address	| Tests using the provided URL/IP
	#////////////////////////////////////

	#Grab Input
	setglobal URL = ''www.google.com''
	if test $1 != "" {
		setglobal URL = $1
	}

	#Import DietPi-Globals ---------------------------------------------------------------
	source /DietPi/dietpi/func/dietpi-globals
	export G_PROGRAM_NAME='DietPi-Optimal_mtu'
	#Import DietPi-Globals ---------------------------------------------------------------

	setglobal MTU_SIZE = '1500'
	setglobal TEST_MTU_SIZE = '0'
	setglobal SUCCESS = '0'

	#-----------------------------------------------------------------------------------
	echo -e "DietPi - MTU optimal size tool\n - Finding optimal MTU size, please wait..."
	while (($SUCCESS == 0))
	{
		#remove ipv4 icmp headers from total size
		setglobal TEST_MTU_SIZE = $shExpr(' $MTU_SIZE - 28 ')

		echo -e "Testing MTU: $MTU_SIZE"
		if sh-expr ' $(ping -c 1 -s $TEST_MTU_SIZE -M do $URL | grep -ci -m1 '+1 error') == 0 '{
			setglobal SUCCESS = '1'
			echo -e "\nCompleted:\n - MTU optimal size = $MTU_SIZE\n"
		} elif sh-expr ' $MTU_SIZE <= 0 ' {
			echo -e "\nERROR:\n - Failed to find MTU size\n"
		} else {
			sh-expr 'MTU_SIZE--'
		}
	}

	#-----------------------------------------------------------------------------------
	exit
	#-----------------------------------------------------------------------------------
}