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# Redirect TCP/IP traffic to a particular IP address from one port to another
# port. This is useful to handle incoming traffic on a standard reserved port
# like 80 or 443 for example in an unprivileged user process bound to a non
# reserved port.
# Example: ip-redirect 80 8090 10.1.1.1

sport=$1
tport=$2
dest=$3

# Redirect external incoming traffic
sudo /sbin/iptables -t nat -S PREROUTING | grep "\-d $dest/" | grep "\-p tcp" | grep "\-\-dport $sport" | grep "\-j DNAT" | sed "s/^-A/-D/" | awk -F "\t" '{ printf "sudo /sbin/iptables -t nat %s\n", $1 }' | /bin/sh
sudo /sbin/iptables -t nat -A PREROUTING --destination $dest -p tcp --dport $sport -j DNAT --to $dest:$tport

# Redirect local traffic as well
sudo /sbin/iptables -t nat -S OUTPUT | grep "\-d $dest/" | grep "\-p tcp" | grep "\-\-dport $sport" | grep "\-j DNAT" | sed "s/^-A/-D/" | awk -F "\t" '{ printf "sudo /sbin/iptables -t nat %s\n", $1 }' | /bin/sh
sudo /sbin/iptables -t nat -A OUTPUT --destination $dest -p tcp --dport $sport -j DNAT --to $dest:$tport