macos/ip-redirect

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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=$3
if [ "$dest" = "" ]; then
    dest="127.0.0.1"
fi

# Delete existing rule
sudo /sbin/ipfw list | grep "fwd $dest,$sport tcp from any" | awk '{ printf "sudo ipfw delete %s\n", $1 }' | /bin/sh

# Redirect incoming traffic
sudo /sbin/ipfw add $sport fwd $dest,$sport tcp from any to $dest $tport