ad-blocker.sh

#!/bin/sh

###########################
# (C) 2017 Steven Black
###########################
#
# 2017-04-17 - 1.0.0 Initial release
# 2017-04-18 - 1.1.0 Improved modularization; added functionality for white & black lists
# 2017-04-25 - 1.1.1 Relocated conf dir to /usr/local/etc
# 2017-04-25 - 1.1.2 Relocate script dir; update checks to create conf templates 
# 2017-05-17 - 1.1.3 Remove local declarations for improved compatibility
# 2017-05-17 - 1.1.4 Cleanup syntax as per shellcheck.net suggestions
#
###########################

# routine for ensuring all necessary dependencies are found
check_deps () {
  Deps="date grep mv rm sed wget whoami su"
  MissingDeps=0

  for NeededDep in $Deps; do
    if ! hash "$NeededDep" > /dev/null 2>&1; then
      printf "Command not found in PATH: %s\n" "$NeededDep" >&2
      MissingDeps=$((MissingDeps+1))
    fi
  done

  if [ $MissingDeps -gt 0 ]; then
    printf "%d commands not found in PATH; aborting\n" "$MissingDeps" >&2
    exit 1
  fi
}

# check for whitelist/blacklist configuration files & create templates if not present
check_conf () {
  WhiteList="${ConfDir}/ad-blocker-wl.conf"
  BlackList="${ConfDir}/ad-blocker-bl.conf"

  # if no white list found, then create a template & instructions
  if [ ! -f "$WhiteList" ]; then
    echo "No white list found; creating template" >&2
	
	{ echo "# White list of domains to remain unblocked for ad-blocker.sh"; 
      echo "# Add one fully-qualified domain name per line"; 
      echo "# Comments are indicated by a '#' as the first character"; 
      echo "# example:"; 
      echo "# ad.example.com"; } > "$WhiteList"
  fi

  # if no black list found, then create a template & instructions
  if [ ! -f "$BlackList" ]; then
    echo "No black list found; creating template" >&2

    { echo "# Black list of additional domains for ad-blocker.sh"; 
      echo "# Add one fully-qualified domain name per line"; 
      echo "# Comments are indicted by a '#' as the first character"; 
      echo "# example:"; 
      echo "# ad.example.com"; } > "$BlackList"
  fi
}

# verify running as proper user
# if not, attempt to switch and abort if cannot
check_user () {
  User=$(whoami)
  if [ "$User" != "DNSServer" ]; then
    echo "Running as $User; switching to DNSServer" >&2
    su -m DNSServer "$0" "$@" || exit 1
	exit 0
  fi
}

# fetch the blocklist from yoyo.org and update the path element
# for each entry to comply with the Synology setup
fetch_blocklist () {
  BlocklistURL="http://pgl.yoyo.org/as/serverlist.php?hostformat=bindconfig&showintro=0&mimetype=plaintext"

  # the "-O-" tells wget to send the file to standard out instead of a real file
  # this makes it suitable for piping and eliminates need for another temp file
  wget -O- "$BlocklistURL" | \
    sed -e 's/null.zone.file/\/etc\/zone\/master\/null.zone.file/g' > "/tmp/ad-blocker.new"
}

# user-specified list of domains to be blocked in addition to those from yoyo.org
apply_blacklist () {
  BlackList="${ConfDir}/ad-blocker-bl.conf"
  BlockList="/tmp/ad-blocker.new"

  # skip if the config doesn't exist
  if [ ! -f "$BlackList" ]; then
    return 0;
  fi

  # process the blacklist skipping over any comment lines
  while read -r Line
  do
    # strip the line if it starts with a '#'
    # if the line was stripped, then continue on to the next line
    Domain=$(echo "$Line" | grep -v "^[[:space:]*\#]")
    if [ -z "$Domain" ]; then
      continue;
    fi
	
    # if domain already listed then skip it and continue on to the next line
    # make sure you don't get a false positive with a partial match
    # by using the "-w" option on grep
    Found=$(grep -w "$Domain" "$BlockList")
    if [ ! -z "$Found" ]; then
      continue;
    fi

    # domain not found, so append it to the list
    echo "zone \"$Domain\" { type master; notify no; file \"/etc/zone/master/null.zone.file\"; };" >> "$BlockList"

  done < "$BlackList"
}

# user-specified list of domains to remain unblocked
apply_whitelist () {
  WhiteList="${ConfDir}/ad-blocker-wl.conf"
  BlockList="/tmp/ad-blocker.new"
  BlockListTmp="/tmp/ad-blocker.tmp"

  # skip if the config doesn't exist
  if [ ! -f "$WhiteList" ]; then
    return 0
  fi

  # process the whitelist skipping over any comment lines
  while read -r Line
  do
    # strip the line if it starts with a '#'
    # if the line was stripped, then continue on to the next line
    Domain=$(echo "$Line" | grep -v "^[[:space:]*\#]")
    if [ -z "$Domain" ]; then
      continue;
    fi

    # copy every line in the blocklist *except* those matching the whitelisted domain
    # into a temp file and then copy the temp file back over the original source
    grep -w -v "$Domain" "$BlockList" > "$BlockListTmp"
    mv "$BlockListTmp" "$BlockList"
  done < "$WhiteList"
}

# make sure the include statement is added to the ZoneDataFile
update_zone_data () {
  ZoneDataFile="${ZoneDataDir}/null.zone.file"
  ZoneDataDB="${ZoneDataDir}/ad-blocker.db"
  BlockList="/tmp/ad-blocker.new"

  # move the final version of the block list to the final location
  mv "$BlockList" "$ZoneDataDB"

  # safety check: make sure both files exist before proceeding
  # check for the include statement in the ZoneDataFile
  # if it is present do nothing, else append the include statement to the ZoneDataFile
  if [ -f "$ZoneDataDB" ] && [ -f "$ZoneDataFile" ]; then
    Matches=$(grep 'include "/etc/zone/data/ad-blocker.db";' "$ZoneDataFile")
    if [ -z "$Matches" ]; then
      echo '' >> "$ZoneDataFile"
      echo 'include "/etc/zone/data/ad-blocker.db";' >> "$ZoneDataFile"
    fi
  fi
}

# update the ZoneMasterFile with an new serial number
update_zone_master () {
  Now=$(date +"%Y%m%d")
  ZoneMasterFile="${ZoneMasterDir}/null.zone.file" 

  if [ -f "$ZoneMasterFile" ]; then
    rm -f "$ZoneMasterFile"
  fi

  # rebuild the zone master file with the updated serial number
  { echo '$TTL 86400     ; one day';
    echo '@ IN SOA ns.null.zone.file. mail.null.zone.file. (';
    echo '  '${Now}'00   ; serial number YYYYMMDDNN';
    echo '  86400        ; refresh 1 day';
    echo '  7200         ; retry 2 hours';
    echo '  864000       ; expire 10 days';
    echo '  86400 )      ; min ttl 1 day';
    echo '  IN NS  ns.null.zone.file.';
    echo '  IN A   127.0.0.1';
    echo '* IN A   127.0.0.1'; } > "$ZoneMasterFile"

  # reload the server config to pick up the changes
  "${RootDir}"/script/reload.sh
}

# Global vars for common paths
ConfDir="/usr/local/etc"
RootDir="/var/packages/DNSServer/target"
ZoneDir="${RootDir}/named/etc/zone"
ZoneDataDir="${ZoneDir}/data"
ZoneMasterDir="${ZoneDir}/master"

# Main Routine
check_deps
check_conf
check_user "$@"
fetch_blocklist
apply_blacklist
apply_whitelist
update_zone_data
update_zone_master

exit 0