mkblocks.sh

#!/bin/sh
##############################################################################
#
# Copyright 2015 spf-tools team (see AUTHORS)
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
#     Unless required by applicable law or agreed to in writing, software
#     distributed under the License is distributed on an "AS IS" BASIS,
#     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#     See the License for the specific language governing permissions and
#     limitations under the License.
#
##############################################################################
#
# Usage: ./mkblocks.sh <domain> <prefix> <policy>
#  E.g.: ./mkblocks.sh microsoft.com _spf

test -n "$DEBUG" && set -x

for cmd in awk grep sed cut
do
  type $cmd >/dev/null || exit 1
done

a="/$0"; a=${a%/*}; a=${a:-.}; a=${a#/}/; BINDIR=$(cd $a; pwd)
. $BINDIR/include/global.inc.sh

# Read settings from config file
test -z "$DOMAIN" && { test -r $SPFTRC && . $SPFTRC; }

# Default values
domain=${DOMAIN:-"spf-tools.eu.org"}
prefix="spf"
suffix=""
policy="~all"
delim="^"
header="v=spf1"
length=257
strlength=255
start=1

usage() {
    cat <<-EOF
	Usage: mkblocks.sh [OPTION]... [DOMAIN]
	Make blocks out of decomposed SPF records.

	Available options:
	  -h HEADER                  set SPF header
	  -l LENGTH                  set desired packet length
	  -L STRLENGTH               set desired DNS STRING length
	                             WARNINIG: hosted DNS may have own limits
	  -p PREFIX                  set SPF prefix
	  -x SUFFIX                  set SPF suffix
	  -o POLICY                  set default SPF policy
	  -d DELIM                   set delimiter of output
	  -s START                   set the numbering start

	Default values:
	  HEADER = $header
	  LENGTH = $length
	  STRLENGTH = $strlength
	  PREFIX = $prefix
	  SUFFIX = $suffix
	  POLICY = $policy
	  DELIM  = $delim
	  START  = $start
	EOF
    exit 1
}

while getopts "h:l:L:p:x:o:d:s:-" opt; do
  case $opt in
    h) test -n "$OPTARG" && header=$OPTARG;;
    l) test -n "$OPTARG" && length=$OPTARG;;
    L) test -n "$OPTARG" && strlength=$OPTARG;;
    p) test -n "$OPTARG" && prefix=$OPTARG;;
    x) test -n "$OPTARG" && suffix=$OPTARG;;
    o) test -n "$OPTARG" && policy=$OPTARG;;
    d) test -n "$OPTARG" && delim=$OPTARG;;
    s) test -n "$OPTARG" && start=$OPTARG;;
    *) usage;;
  esac
done
shift $((OPTIND-1))

# For backward compatibility the options are also positional
domain=${1:-"$domain"}
prefix=${2:-"$prefix"}
policy=${3:-"$policy"}

# One-char placeholder substitued for number later
MYX=#

incldomain="${prefix}${MYX}${suffix}.$domain"
footer="include:$incldomain $policy"
counter=$((start))

mysed() {
  sed "s/$MYX/$1/"
}

myout() {
  local mycounter=${3:-'1'}
  rrlabel=$1
  if [ $mycounter -eq 1 ]; then
      #first resource label of chain is bare domain
      rrlabel="$domain"
  fi
  mystart=$(echo $rrlabel | mysed $((mycounter-1)))
  myrest=$(echo $2 | mysed $((mycounter)))
  output=$(printf "$header $myrest" | awk "{gsub(/.{$strlength}/,\"&\\\" \\\"\")}1")
  echo ${mystart}${delim}\"$output\"
}


while
  read block
do
  blocksprev=$blocks
  test -n "$blocks" && blocks="${blocks} ${block}" || blocks=$block
  compare="$header $blocks $footer"
  test $(echo $compare | wc -c) -ge $length && {
    myout $incldomain "${blocksprev} ${footer}" $counter
    blocks=$block
    counter=$((counter+1))
    test $counter -gt 10 && { echo "Too many DNS look-ups!" 1>&2; exit 1; }
  }
done

# Corner case for last entry not containing any include
test -n "$blocks" && myout $incldomain "$blocks $policy" $counter