on_verify_batman

#!/bin/bash
# https://forum.freifunk.net/t/bessere-verteilung-von-knoten-clients-auf-sn-unter-fastd/12445

# peer limit may be used as a failsafe and not be changed.
# use this script as fastd on_verify to roughly balance peers. 
# If you feel that management should be even stricter and cause 
# fastd-peers to re-connect to other gateways, then also use the 
# cron-script that is adjusting the peer limit. This may be useful after 
# an outage.
#
# Managing client count per gateway would be a lot nicer, but the
# client count for the whole network can only be obtained by querying 
# other infrastructure (map/api).
set -ix
# things to adjust to your server
fastdsockets=( "/var/run/fastd/fastd.sock", "/var/run/fastd/fastd2.sock" )
fastdconf="/etc/fastd/sn4/main.conf"
BATCTL="/usr/local/sbin/batctl"
MINPEERS=50
BUFFERPERCENTAGE=10

# check if batctl is avail
# otherwise we could try to read from proc sys directly
# this script should not do harm if it is broken => successful exit, 
# fastd will accept the peer.
[ -x $BATCTL ] || exit 0

# estimate network size and amount of gateways
net_peer_amount=$($BATCTL o |wc -l)
gwamount=$(($($BATCTL gwl -H |wc -l)-1))

## dirty count fastdconnections, 
## timeout means that connection on verify need 0.2 seconds, some consider this long!
# 0.2 seconds per verify means there can 50 connections be verified per second. 
connected_peer_amount=0
for socket in ${fastdsockets[@]}
do
  connectd_peer_thisinstance=$(timeout .2 ncat -U  $fastdsocket |grep -c -o established)
  ((connected_peer_amount+=connectd_peer_thisinstance))
done

# set connection limit and doing so, consider a buffersize
connection_average_estimate=$(( net_peer_amount / gwamount )) 
connection_limit_estimate=$((connection_average_estimate + (connection_limit_estimate * BUFFERPERCENTAGE)/100))

[[ $connection_limit_estimate -lt $MINPEERS ]] && connection_limit_estimate=$MINPEERS

# get actual peer limit
peerlimit=$(grep -oP '(?<=^peer\slimit\s)[0-9]+(?=\s*;$)' $fastdconf)

[[ $peerlimit -gt $connection_limit_estimate ]] &&
[[ $connection_limit_estimate -gt $connected_peer_amount ]] && exit 0

exit 1