code / nomsu

   1 #!/usr/bin/env nomsu -V7.0.0
   2 ###
   3     This file defines actions for encoding/decoding base 64, as specified in:
   4     https://tools.ietf.org/html/rfc4648
   5     
   6 $b64_str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
   7 $b64_chars = [: for $ in (1 to #$b64_str): add ($b64_str, character $)]
   8 $reverse_b64 = {: for ($i = $c) in $b64_chars: add $c = ($i - 1)}
   9 $reverse_b64."=" = 64
  10 set $reverse_b64's metatable to {.__index = ->0}
  11 test:
  12     $cases = ["", "Zg==", "Zm8=", "Zm9v", "Zm9vYg==", "Zm9vYmE=", "Zm9vYmFy"]
  13     for ($len = $encoded) in $cases:
  14         $plain = ("foobar", from 1 to ($len - 1))
  15         assume (base64 $plain) == $encoded
  16         assume (base64 decode $encoded) == $plain
  17 
  18 external:
  19     [base64 $str, base64 encode $str, $str base64] all mean:
  20         $chars = []
  21         for $i in (1 to #$str by 3):
  22             $bytes = [=lua "\$str:byte(\$i, \($i + 2))"]
  23             $chars, add $b64_chars.((($bytes.1 & 252) >> 2) + 1)
  24             if #$bytes is:
  25                 3:
  26                     $chars, add $b64_chars.((($bytes.1 & 3) << 4) + (($bytes.2 & 240) >> 4) + 1)
  27                     $chars, add $b64_chars.((($bytes.2 & 15) << 2) + (($bytes.3 & 192) >> 6) + 1)
  28                     $chars, add $b64_chars.(($bytes.3 & 63) + 1)
  29                 
  30                 2:
  31                     $chars, add $b64_chars.((($bytes.1 & 3) << 4) + (($bytes.2 & 240) >> 4) + 1)
  32                     $chars, add $b64_chars.((($bytes.2 & 15) << 2) + 1)
  33                     $chars, add "="
  34                 
  35                 1:
  36                     $chars, add $b64_chars.((($bytes.1 & 3) << 4) + 1)
  37                     $chars, add "="
  38                     $chars, add "="
  39         
  40         return ($chars, joined)
  41     (chr $) means (=lua "string.char(\$)")
  42     [decode base64 $str, $str base64 decoded, base64 decode $str] all mean:
  43         $chars = []
  44         for $i in (1 to #$str by 4):
  45             $indices = [: for $j in ($i to ($i + 3)): add $reverse_b64.($str, character $j)]
  46             $chars, add (chr (($indices.1 << 2) + (($indices.2 & 48) >> 4)))
  47             if (($str, character ($i + 2)) == "="): stop
  48             $chars, add (chr ((($indices.2 & 15) << 4) + (($indices.3 & 60) >> 2)))
  49             if (($str, character ($i + 3)) == "="): stop
  50             $chars, add (chr ((($indices.3 & 3) << 6) + $indices.4))
  51         return ($chars, joined)