googleads-doubleclick

#!/bin/bash

help() {
   echo 'usage: sudo googleads-doubleclick allow|block'
   echo '       googleads-doubleclick --help'
   echo
   echo '   Will un/comment the `127.0.0.2 googleads.g.doubleclick.net`'
   echo '   entry in `/etc/hosts`.'
   echo
   echo '   This serves to black/whitelist that'
   echo '   host as needed in order to access google services which'
   echo '   redirect via that host if the respective cookie is not set'
   echo
   echo '   You probably want something like this:'
   echo
   echo '   user ALL=NOPASSWD: /path/to/googleads-doubleclick allow'
   echo '   user ALL=NOPASSWD: /path/to/googleads-doubleclick block'
   echo
   exit 1
}

[ "$1" == "--help" ] && help

set -e          # stop on error
set -u          # stop on undefined variable
set -o pipefail # stop part of pipeline failing

state_file=/tmp/googleads-doubleclick.state.lock

allow_googleads() {
  hosts allow googleads.g.doubleclick.net || exit 1
  # note that parent is accessing googleads
  echo $PPID >> $state_file
}

block_googleads() {
  # note that parent doesn't need googleads-doubleclick access any more
  sed --in-place "/^$PPID$/d" $state_file
  for i in `cat $state_file`; do
    if ps --pid $i > /dev/null; then
      # there is another process using googleads
      return
    fi
  done
  # else
  # no other process is using googleads
  > $state_file # empty the file

  hosts block googleads.g.doubleclick.net || exit 1
}

# use mutex
#
# see https://stackoverflow.com/a/50419392 on how this works
#
: >> $state_file # create a file if it doesn't exist
{
  flock $lock_fd # lock file by filedescriptor

  if [ "$1" == "allow" ]; then
    allow_googleads
  elif [ "$1" == "block" ]; then
    block_googleads
  else
    help
  fi
  
} {lock_fd}<$state_file