nim-stew/stew/base64.nim

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Nim

## Copyright (c) 2018 Status Research & Development GmbH
## Licensed under either of
## * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
## * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.
## This module implements BASE64 encoding and decoding procedures.
type
Base64Status* {.pure.} = enum
Error,
Success,
Incorrect,
Overrun
Base64Alphabet* = object
decode*: array[128, int8]
encode*: array[64, uint8]
Base64* = object
## Type to use RFC4648 alphabet without padding
Base64Pad* = object
## Type to use RFC4648 alphabet with padding
Base64Url* = object
## Type to use RFC4648 URL alphabet without padding
Base64UrlPad* = object
## Type to use RFC4648 URL alphabet with padding
Base64PadTypes* = Base64Pad | Base64UrlPad
## All types with padding support
Base64NoPadTypes* = Base64 | Base64Url
## All types without padding support
Base64Types* = Base64 | Base64Pad | Base64Url | Base64UrlPad
## All types
Base64Error* = object of CatchableError
## Base64 specific exception type
proc newAlphabet64*(s: string): Base64Alphabet =
doAssert(len(s) == 64)
for i in 0..<len(s):
result.encode[i] = cast[uint8](s[i])
for i in 0..<len(result.decode):
result.decode[i] = -1
for i in 0..<len(result.encode):
result.decode[int(result.encode[i])] = int8(i)
const
B64Alphabet* = newAlphabet64("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdef" &
"ghijklmnopqrstuvwxyz0123456789+/")
B64UrlAlphabet* = newAlphabet64("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdef" &
"ghijklmnopqrstuvwxyz0123456789-_")
proc encodedLength*(btype: typedesc[Base64Types],
length: int): int {.inline.} =
## Return estimated length of BASE64 encoded value for plain length
## ``length``.
result = (((length + 2) div 3) * 4) + 1
proc decodedLength*(btype: typedesc[Base64Types],
length: int): int {.inline.} =
## Return estimated length of decoded value of BASE64 encoded value of length
## ``length``.
when (btype is Base64Pad) or (btype is Base64UrlPad):
result = ((length + 3 - 1) div 3) * 4
elif (btype is Base64) or (btype is Base64Url):
result = (length * 4 + 3 - 1) div 3
proc encode*(btype: typedesc[Base64Types], inbytes: openarray[byte],
outstr: var openarray[char], outlen: var int): Base64Status =
## Encode array of bytes ``inbytes`` using BASE64 encoding and store
## result to ``outstr``.
##
## On success ``Base64Status.Success`` will be returned and ``outlen`` will
## be set to number of characters stored inside of ``outstr``.
##
## If length of ``outstr`` is not enough then ``Base64Status.Overrun`` will
## be returned and ``outlen`` will be set to number of characters required.
when (btype is Base64) or (btype is Base64Pad):
const alphabet = B64Alphabet
elif (btype is Base64Url) or (btype is Base64UrlPad):
const alphabet = B64UrlAlphabet
let length = len(inbytes)
if len(outstr) < btype.encodedLength(length):
outlen = btype.encodedLength(length)
result = Base64Status.Overrun
else:
var offset = 0
var i = 0
while i < (length - 2):
outstr[offset] = chr(alphabet.encode[(inbytes[i] shr 2) and 0x3F'u8])
inc(offset)
outstr[offset] = chr(alphabet.encode[((inbytes[i] and 0x03) shl 4) or
((inbytes[i + 1] and 0xF0) shr 4)])
inc(offset)
outstr[offset] = chr(alphabet.encode[((inbytes[i + 1] and 0x0F) shl 2) or
((inbytes[i + 2] and 0xC0) shr 6)])
inc(offset)
outstr[offset] = chr(alphabet.encode[inbytes[i + 2] and 0x3F])
inc(offset)
i += 3
if i < length:
outstr[offset] = chr(alphabet.encode[(inbytes[i] shr 2) and 0x3F])
inc(offset)
if i == length - 1:
outstr[offset] = chr(alphabet.encode[(inbytes[i] and 0x03) shl 4])
inc(offset)
when (btype is Base64Pad) or (btype is Base64UrlPad):
outstr[offset] = '='
inc(offset)
else:
outstr[offset] = chr(alphabet.encode[((inbytes[i] and 0x03) shl 4) or
((inbytes[i + 1] and 0xF0) shr 4)])
inc(offset)
outstr[offset] = chr(alphabet.encode[(inbytes[i + 1] and 0x0F) shl 2])
inc(offset)
when (btype is Base64Pad) or (btype is Base64UrlPad):
outstr[offset] = '='
inc(offset)
outlen = offset
result = Base64Status.Success
proc encode*(btype: typedesc[Base64Types],
inbytes: openarray[byte]): string {.inline.} =
## Encode array of bytes ``inbytes`` using BASE64 encoding and return
## encoded string.
var size = btype.encodedLength(len(inbytes))
result = newString(size)
if btype.encode(inbytes, result.toOpenArray(0, size - 1),
size) == Base64Status.Success:
result.setLen(size)
else:
result = ""
proc decode*[T: byte|char](btype: typedesc[Base64Types], instr: openarray[T],
outbytes: var openarray[byte], outlen: var int): Base64Status =
## Decode BASE64 string and store array of bytes to ``outbytes``. On success
## ``Base64Status.Success`` will be returned and ``outlen`` will be set
## to number of bytes stored.
##
## Length of ``outbytes`` must be equal or more then ``len(instr) + 4``.
##
## If ``instr`` has characters which are not part of BASE64 alphabet, then
## ``Base64Status.Incorrect`` will be returned and ``outlen`` will be set to
## ``0``.
##
## If length of ``outbytes`` is not enough to store decoded bytes, then
## ``Base64Status.Overrun`` will be returned and ``outlen`` will be set to
## number of bytes required.
when (btype is Base64) or (btype is Base64Pad):
const alphabet = B64Alphabet
elif (btype is Base64Url) or (btype is Base64UrlPad):
const alphabet = B64UrlAlphabet
if len(instr) == 0:
outlen = 0
return Base64Status.Success
let length = btype.decodedLength(len(instr))
if length > len(outbytes):
outlen = length
return Base64Status.Overrun
var inlen = len(instr)
when (btype is Base64PadTypes):
for i in countdown(inlen - 1, 0):
if instr[i] != '=':
break
dec(inlen)
let reminder = inlen mod 4
let limit = inlen - reminder
var buffer: array[4, byte]
var i, k: int
while i < limit:
for j in 0..<4:
if (cast[byte](instr[i + j]) and 0x80'u8) != 0:
outlen = 0
zeroMem(addr outbytes[0], i + 3)
return Base64Status.Incorrect
let ch = alphabet.decode[cast[int8](instr[i + j])]
if ch == -1:
outlen = 0
zeroMem(addr outbytes[0], i + 3)
return Base64Status.Incorrect
buffer[j] = cast[byte](ch)
outbytes[k] = cast[byte]((buffer[0] shl 2) or (buffer[1] shr 4))
inc(k)
outbytes[k] = cast[byte]((buffer[1] shl 4) or (buffer[2] shr 2))
inc(k)
outbytes[k] = cast[byte]((buffer[2] shl 6) or buffer[3])
inc(k)
i += 4
if reminder > 0:
if reminder == 1:
outlen = 0
return Base64Status.Incorrect
for j in 0..<reminder:
if (cast[byte](instr[i + j]) and 0x80'u8) != 0:
outlen = 0
return Base64Status.Incorrect
let ch = alphabet.decode[cast[int8](instr[i + j])]
if ch == -1:
outlen = 0
return Base64Status.Incorrect
buffer[j] = cast[byte](ch)
if reminder > 1:
outbytes[k] = cast[byte]((buffer[0] shl 2) or (buffer[1] shr 4))
inc(k)
if reminder > 2:
outbytes[k] = cast[byte]((buffer[1] shl 4) or (buffer[2] shr 2))
inc(k)
outlen = k
result = Base64Status.Success
proc decode*[T: byte|char](btype: typedesc[Base64Types],
instr: openarray[T]): seq[byte] =
## Decode BASE64 string ``instr`` and return sequence of bytes as result.
if len(instr) == 0:
result = newSeq[byte]()
else:
var length = 0
result = newSeq[byte](btype.decodedLength(len(instr)))
if btype.decode(instr, result, length) == Base64Status.Success:
result.setLen(length)
else:
raise newException(Base64Error, "Incorrect base64 string")