#!/bin/bash

# dnsquery: build a packet that would be worthy of sending to a DNS server...

##############################################################################
# Utility functions: this is not a complete set. See shdns for the full set...
##############################################################################

# The state of a given bit in the byte
dumpbit(){
  local temp
  temp=$1

  if [ $1 -gt $(( $2 - 1 )) ]
  then
    echo -n "1"
    temp=$(( $1 - $2 ))
  else
    echo -n "0"
  fi

  return $temp
}

# Is a given bit on?
testbit(){
  return `dumpbit $1 $2`
}

# Turn on a given bit in the byte
twiddlebit(){
  local temp
  temp=$1

  testbit $1 $2
  if [ $? = 1 ]
  then
    if [ $3 = 0 ]
    then
      temp=$(( $temp - $2 ))
    fi
  else 
    if [ $3 = 1 ]
    then
      temp=$(( $temp + $2 ))
    fi
  fi

  return $temp
}

###############################################################################

######################
# DNS header
######################

# Identification: 2 bytes, uniqueish
temp=`echo $$ | wc -c | tr -d " "`
b1=$(( $temp - 2 ))
b2=$(( $temp - 1 ))
echo -n `echo $$ | cut -b "$b1,$b2"`

# Flags: 2 bytes
twiddlebit 0 1 1; temp=$?   # Turn on recursion
echo -en "\\$temp"
echo -en "\\000"

# Number of questions
echo -en "\\000\\001"

# Number of answer RRs
echo -en "\\000\\000"

# Number of authority RRs
echo -en "\\000\\000"

# Number of additional RRs
echo -en "\\000\\000"

######################
# Question
######################

# Query name
for name in `echo $1 | tr "." " "`
do
  len=`echo $name | wc -c | tr -d " "`
  len=`printf "%03d" $(( $len - 1 ))`
  echo -en "\\$len$name"
done

# Query type
case $2 in
A )
  echo -en "\\000\\001";;

NS )
  echo -en "\\000\\002";;

CNAME )
  echo -en "\\000\\005";;

PTR )
  echo -en "\\000\\014";;

HINFO )
  echo -en "\\000\\015";;

MX )
  echo -en "\\000\\017";;

* )
  echo "Unknown query";;
esac

# Query class
echo -en "\\001"

exit