urbit/pkg/arvo/lib/base64.hoon
2020-02-27 12:43:46 -08:00

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:: |base64: flexible base64 encoding for little-endian atoms
::
:: pad: include padding when encoding, require when decoding
:: url: use url-safe characters '-' for '+' and '_' for '/'
::
=+ [pad=& url=|]
|%
::
+$ byte @D
+$ word24 @
::
++ div-ceil
:: divide, rounding up.
|= [x=@ y=@] ^- @
?: =(0 (mod x y))
(div x y)
+((div x y))
::
++ explode-bytes
:: Explode a bytestring into list of bytes. Result is in LSB order.
|= =octs ^- (list byte)
=/ atom-byte-width (met 3 q.octs)
=/ leading-zeros (sub p.octs atom-byte-width)
(weld (reap leading-zeros 0) (rip 3 q.octs))
::
++ explode-words
:: Explode a bytestring to words of bit-width `wid`. Result is in LSW order.
|= [wid=@ =octs]
^- (list @)
=/ atom-bit-width (met 0 q.octs)
=/ octs-bit-width (mul 8 p.octs)
=/ atom-word-width (div-ceil atom-bit-width wid)
=/ rslt-word-width (div-ceil octs-bit-width wid)
=/ pad (sub rslt-word-width atom-word-width)
=/ x (ripn wid q.octs)
%+ weld x
(reap pad 0)
::
:: +en:base64: encode +octs to base64 cord
::
:: Encode an `octs` into a base64 string.
::
:: First, we break up the input into a list of 24-bit words. The input
:: might not be a multiple of 24-bits, so we add 0-2 padding bytes at
:: the end (to the least-significant side, with a left-shift).
::
:: Then, we encode each block into four base64 characters.
::
:: Finally we remove the padding that we added at the beginning: for
:: each byte that was added, we replace one character with an = (unless
:: `pad` is false, in which case we just remove the extra characters).
::
++ en
^- $-(octs cord)
::
=/ cha
?: url
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_'
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
::
|^ |= bs=octs ^- cord
=/ [padding=@ blocks=(list word24)]
(octs-to-blocks bs)
(crip (flop (unpad padding (encode-blocks blocks))))
::
++ octs-to-blocks
|= bs=octs ^- [padding=@ud (list word24)]
=/ padding=@ud (~(dif fo 3) 0 p.bs)
=/ padded=octs [(add padding p.bs) (lsh 3 padding (rev 3 bs))]
[padding (explode-words 24 padded)]
::
++ unpad
|= [extra=@ t=tape] ^- tape
=/ without (slag extra t)
?. pad without
(weld (reap extra '=') without)
::
++ encode-blocks
|= ws=(list word24) ^- tape
(zing (turn ws encode-block))
::
++ encode-block
|= w=word24 ^- tape
=/ a (cut 3 [(cut 0 [0 6] w) 1] cha)
=/ b (cut 3 [(cut 0 [6 6] w) 1] cha)
=/ c (cut 3 [(cut 0 [12 6] w) 1] cha)
=/ d (cut 3 [(cut 0 [18 6] w) 1] cha)
~[a b c d]
--
::
:: +de:base64: decode base64 cord to (unit @)
::
++ de
|= a=cord
^- (unit octs)
(rush a parse)
:: +parse:base64: parse base64 cord to +octs
::
++ parse
=< ^- $-(nail (like octs))
%+ sear reduce
;~ plug
%- plus ;~ pose
(cook |=(a=@ (sub a 'A')) (shim 'A' 'Z'))
(cook |=(a=@ (sub a 'G')) (shim 'a' 'z'))
(cook |=(a=@ (add a 4)) (shim '0' '9'))
(cold 62 (just ?:(url '-' '+')))
(cold 63 (just ?:(url '_' '/')))
==
(stun 0^2 (cold %0 tis))
==
|%
:: +reduce:parse:base64: reduce, measure, and swap base64 digits
::
++ reduce
|= [dat=(list @) dap=(list @)]
^- (unit octs)
=/ lat (lent dat)
=/ lap (lent dap)
=/ dif (~(dif fo 4) 0 lat)
?: &(pad !=(dif lap))
:: padding required and incorrect
~&(%base-64-padding-err-one ~)
?: &(!pad !=(0 lap))
:: padding not required but present
~&(%base-64-padding-err-two ~)
=/ len (sub (mul 3 (div (add lat dif) 4)) dif)
:+ ~ len
%+ swp 3
(repn 6 (flop (weld dat (reap dif 0))))
--
--