dummynet

#!/bin/bash
# Throttle bandwidth on OS X Yosemite. Based on
# https://mop.koeln/blog/2015/06/01/Limiting-bandwidth-on-Mac-OS-X-yosemite/

CMD_WITH_ARGS="$0 $*"
ANCHOR_NAME=custom_rules

while getopts :p:b: arg; do
  case $arg in
    p)
      PORT=$OPTARG
      ;;
    b)
      BW=$OPTARG
      ;;
  esac
  shift $((OPTIND-1))
done

: ${PORT:='80'}
: ${BW:='256kbit/s'}

restart_as_sudo() {
  local run_as="root"
  local cmd_with_args="$1"
  if [ "$USER" != "$run_as" ]; then
      prompt=$(cat <<EOF
sudo permissions are required to continue.
Enter your password:
EOF
)
  exec sudo -u $run_as -H -P -p "$prompt" $cmd_with_args
  exit ${?}  # sice we're 'execing' above, we won't reach this exit
             # unless something goes wrong.
  fi
}

start() {
  restart_as_sudo "$CMD_WITH_ARGS"

  echo "Throttling Port ${PORT} to Bandwidth '${BW}'"

  dnctl -fq flush

  # Create a custom anchor in pf. This will reload your standard pf
  # configuration plus a custom anchor named "custom_rules". We will
  # place our custom rules there.
  (cat /etc/pf.conf &&
   echo "dummynet-anchor \"${ANCHOR_NAME}\"" &&
   echo "anchor \"${ANCHOR_NAME}\"") | pfctl -f - 2>&1 | \
    grep -v ALTQ | \
    grep -v 'Use of -f option' | \
    grep -v 'present in the main' | \
    grep -v 'See /etc/pf.conf for further details' | \
    grep -v '^$'


  # Pipe the desired traffic to dummynet.
  cat <<EOF | pfctl -q -a ${ANCHOR_NAME} -f - 2>&1 | \
      grep -v ALTQ | \
      grep -v 'Use of -f option' | \
      grep -v 'present in the main' | \
      grep -v 'See /etc/pf.conf for further details' | \
      grep -v '^$'
  dummynet in quick proto tcp from any port $PORT to any pipe 1
EOF

  dnctl pipe 1 config bw $BW
  pfctl -E -q
}

stop() {
  restart_as_sudo "$CMD_WITH_ARGS"
  dnctl -f flush
  pfctl -f /etc/pf.conf 2>&1 | \
    grep -v ALTQ | \
    grep -v 'Use of -f option' | \
    grep -v 'present in the main' | \
    grep -v 'See /etc/pf.conf for further details' | \
    grep -v '^$'
}

case "$1" in
  start)
        start
        ;;
  stop)
        stop
        ;;
  restart)
       stop
       start
       ;;
  *)
        echo $"Usage: dummynet [-p PORT] [-b BANDWIDTH] {start|stop}"
        echo "The default port is '${PORT}', default bandwidth is '${BW}'"
        echo "'stop' resets firewall to defaults (-p, -b options are ignored)."
        exit 1
esac