b64test.py

import string
import math

b64Chars = (string.ascii_uppercase + string.ascii_lowercase + string.digits + "+/").encode()

b64BackChars = \
(
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
    -1, 0 , 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
    -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
)

def b64_chunk(byteChunk):
    byteChunk = byteChunk[:3]

    if len(byteChunk) == 3:
        ret = (
                byteChunk[0] >> 2,
                ((byteChunk[0] & 0x3) << 4) + (byteChunk[1] >> 4),
                ((byteChunk[1] & 0xF) << 2) + (byteChunk[2] >> 6),
                byteChunk[2] & 0x3F
              )

    if len(byteChunk) == 2:
        ret = (
                byteChunk[0] >> 2,
                ((byteChunk[0] & 0x3) << 4) + (byteChunk[1] >> 4),
                ((byteChunk[1] & 0xF) << 2),
                -1
              )

    if len(byteChunk) == 1:
        ret = (
                byteChunk[0] >> 2,
                ((byteChunk[0] & 0x3) << 4),
                -1,
                -1
              )

    if len(byteChunk) == 0:
        ret = (-1, -1, -1, -1)

    return ret


def b64_strChunk(byteChunk):
    byteChunk = b64_chunk(byteChunk)
    ret = bytearray()

    for i in byteChunk[::-1]:
        if i == -1:
            ret += b'='
        else:
            ret += b64Chars[i:i+1]

    ret = ret[::-1]
    return ret


def b64_encode(byteStream):
    ret = b''
    for i in range(math.ceil(len(byteStream) / 3)):
        i *= 3
        ret += b64_strChunk(byteStream[i:i+3])

    return ret



def b64_unstring(b64Chunk):
    ret = []

    for i in b64Chunk:
        if i == b'='[0]:
            ret.append(-1)
        elif b64BackChars[i] == -1:
            raise ValueError("\'{}\' not a valid base64 character".format(ord(i)))
        else:
            ret.append(b64BackChars[i])

    return ret


def b64_unchunk(b64Chunk):
    numChunk   = b64_unstring(b64Chunk)
    padCount   = 0
    padInvalid = 0

    ret = [-1] * 3

    for i in numChunk[::-1]:
        if i == -1:
            if padInvalid: raise ValueError("invalid padding for \"{}\"".format(b64Chunk.decode()))

            padCount += 1
        else:
            padInvalid = 1

    if padCount == 0:
        ret[0] = (numChunk[0] << 2) + (numChunk[1] >> 4)
        ret[1] = ((numChunk[1] & 0xF) << 4) + (numChunk[2] >> 2)
        ret[2] = ((numChunk[2] & 0x3) << 6) + numChunk[3]

    if padCount == 1:
        ret[0] = (numChunk[0] << 2) + (numChunk[1] >> 4)
        ret[1] = ((numChunk[1] & 0xF) << 4) + (numChunk[2] >> 2)

    if padCount == 2:
        ret[0] = (numChunk[0] << 2) + (numChunk[1] >> 4)

    if padCount == 3:
        raise ValueError("invalid amount of padding")

    return ret


def b64_strUnchunk(b64Chunk):
    byteChunk = b64_unchunk(b64Chunk)
    ret = bytearray()

    for i in byteChunk:
        if i == -1:
            break
        else:
            ret += bytes([i])

    return ret


def b64_decode(b64Stream):
    ret = b''
    for i in range(math.ceil(len(b64Stream) / 4)):
        i *= 4
        ret += b64_strUnchunk(b64Stream[i:i+4])

    return ret