inet.sh

#/bin/sh
set -eu

ip2dec () {
  local ip="$1"

  if test -z "$ip"; then
    printf "Argument required" 1>&2
    return 1
  fi

  if test "$(printf '%s' "$ip" | tr -dc "." | wc -c)" -gt 3; then
    printf "Invalid IPv4 address syntax: %s" "$ip" 1>&2
    return 1
  fi

  local chunk i=3 dec=0
  for chunk in $(printf '%s' "$ip" | sed 's/\./ /g'); do
    if ! test "$chunk" -eq "$chunk" 2>/dev/null; then
      printf "Each chunks of IPv4 address must be integer: %s" "$ip" 1>&2
      return 1
    fi

    if test "$((chunk >> 8))" -ne 0; then
      printf "Each chunks of IPv4 address must be in range (0 .. 255): %s" "$ip" 1>&2
      return 1
    fi

    dec=$(( dec + (chunk << 8 * i) ))
    i=$((i - 1))
  done

  printf '%d\n' "$dec"
}

dec2ip () {
  local dec="$1"

  if ! test "$dec" -eq "$dec" 2>/dev/null; then
    printf "dec2ip requires decimal: %s" "$dec" 1>&2
    return 1
  fi

  if test "$((dec >> 32))" -ne 0; then
    printf "dec2ip requires 32 bit integer: %s" "$dec" 1>&2
    return 1
  fi

  local i ip sep
  for i in $(seq 4); do
    ip=$(printf "%s%s%s" "$((dec & 0xff))" "${sep:-}" "${ip:-}")
    dec=$((dec >> 8))
    sep=.
  done

  printf '%s\n' "$ip"
}

cidr_match () {
  local ip_dec cidr
  ip_dec=$(ip2dec "$1")
  cidr="$2"

  local cidraddr cidrmask
  IFS=/ read -r cidraddr cidrmask <<__CIDR
$cidr
__CIDR

  local cidraddr_dec cidrmask_dec
  cidraddr_dec=$(ip2dec "$cidraddr")
  cidrmask_dec=$(mask2dec "$cidrmask")

  if test "$(( cidraddr_dec & cidrmask_dec ))" -ne "$cidraddr_dec"; then
    printf "Invalid CIDR address: %s" "$cidr" 1>&2
    return 1
  fi

  local masked_ip_dec=$((ip_dec & cidrmask_dec))

  test "$masked_ip_dec" -eq "$cidraddr_dec"
}

mask2dec () {
  local mask="$1"

  if ! test "$mask" -eq "$mask" 2>/dev/null; then
    printf "Integer required for mask: %s" "$mask" 1>&2
    return 1
  fi

  if test "$mask" -lt 0 -o 32 -lt "$mask"; then
    printf "Mask must be in range (0 .. 32): %s" "$mask" 1>&2
    return 1
  fi

  local dec=$(( -1 << (32 - mask) ))
  printf '%d\n' "$dec"
}