#! /usr/bin/env python

"""RFC 3548: Base16, Base32, Base64 Data Encodings"""

# Modified 04-Oct-1995 by Jack Jansen to use binascii module

# Modified 30-Dec-2003 by Barry Warsaw to add full RFC 3548 support

import re

import struct

import binascii

__all__ = [

    # Legacy interface exports traditional RFC 1521 Base64 encodings

    'encode', 'decode', 'encodestring', 'decodestring',

    # Generalized interface for other encodings

    'b64encode', 'b64decode', 'b32encode', 'b32decode',

    'b16encode', 'b16decode',

    # Standard Base64 encoding

    'standard_b64encode', 'standard_b64decode',

    # Some common Base64 alternatives.  As referenced by RFC 3458, see thread

    # starting at:

    #

    # http://zgp.org/pipermail/p2p-hackers/2001-September/000316.html

    'urlsafe_b64encode', 'urlsafe_b64decode',

    ]

_translation = [chr(_x) for _x in range(256)]

EMPTYSTRING = ''

def _translate(s, altchars):

    translation = _translation[:]

    for k, v in altchars.items():

        translation[ord(k)] = v

    return s.translate(''.join(translation))

# Base64 encoding/decoding uses binascii

def b64encode(s, altchars=None):

    """Encode a string using Base64.

    s is the string to encode.  Optional altchars must be a string of at least

    length 2 (additional characters are ignored) which specifies an

    alternative alphabet for the '+' and '/' characters.  This allows an

    application to e.g. generate url or filesystem safe Base64 strings.

    The encoded string is returned.

    """

    # Strip off the trailing newline

    encoded = binascii.b2a_base64(s)[:-1]

    if altchars is not None:

        return _translate(encoded, {'+': altchars[0], '/': altchars[1]})

    return encoded

def b64decode(s, altchars=None):

    """Decode a Base64 encoded string.

    s is the string to decode.  Optional altchars must be a string of at least

    length 2 (additional characters are ignored) which specifies the

    alternative alphabet used instead of the '+' and '/' characters.

    The decoded string is returned.  A TypeError is raised if s were

    incorrectly padded or if there are non-alphabet characters present in the

    string.

    """

    if altchars is not None:

        s = _translate(s, {altchars[0]: '+', altchars[1]: '/'})

    try:

        return binascii.a2b_base64(s)

    except binascii.Error, msg:

        # Transform this exception for consistency

        raise TypeError(msg)

def standard_b64encode(s):

    """Encode a string using the standard Base64 alphabet.

    s is the string to encode.  The encoded string is returned.

    """

    return b64encode(s)

def standard_b64decode(s):

    """Decode a string encoded with the standard Base64 alphabet.

    s is the string to decode.  The decoded string is returned.  A TypeError

    is raised if the string is incorrectly padded or if there are non-alphabet

    characters present in the string.

    """

    return b64decode(s)

def urlsafe_b64encode(s):

    """Encode a string using a url-safe Base64 alphabet.

    s is the string to encode.  The encoded string is returned.  The alphabet

    uses '-' instead of '+' and '_' instead of '/'.

    """

    return b64encode(s, '-_')

def urlsafe_b64decode(s):

    """Decode a string encoded with the standard Base64 alphabet.

    s is the string to decode.  The decoded string is returned.  A TypeError

    is raised if the string is incorrectly padded or if there are non-alphabet

    characters present in the string.

    The alphabet uses '-' instead of '+' and '_' instead of '/'.

    """

    return b64decode(s, '-_')

# Base32 encoding/decoding must be done in Python

_b32alphabet = {

    0: 'A',  9: 'J', 18: 'S', 27: '3',

    1: 'B', 10: 'K', 19: 'T', 28: '4',

    2: 'C', 11: 'L', 20: 'U', 29: '5',

    3: 'D', 12: 'M', 21: 'V', 30: '6',

    4: 'E', 13: 'N', 22: 'W', 31: '7',

    5: 'F', 14: 'O', 23: 'X',

    6: 'G', 15: 'P', 24: 'Y',

    7: 'H', 16: 'Q', 25: 'Z',

    8: 'I', 17: 'R', 26: '2',

    }

_b32tab = _b32alphabet.items()

_b32tab.sort()

_b32tab = [v for k, v in _b32tab]

_b32rev = dict([(v, long(k)) for k, v in _b32alphabet.items()])

def b32encode(s):

    """Encode a string using Base32.

    s is the string to encode.  The encoded string is returned.

    """

    parts = []

    quanta, leftover = divmod(len(s), 5)

    # Pad the last quantum with zero bits if necessary

    if leftover:

        s += ('\0' * (5 - leftover))

        quanta += 1

    for i in range(quanta):

        # c1 and c2 are 16 bits wide, c3 is 8 bits wide.  The intent of this

        # code is to process the 40 bits in units of 5 bits.  So we take the 1

        # leftover bit of c1 and tack it onto c2.  Then we take the 2 leftover

        # bits of c2 and tack them onto c3.  The shifts and masks are intended

        # to give us values of exactly 5 bits in width.

        c1, c2, c3 = struct.unpack('!HHB', s[i*5:(i+1)*5])

        c2 += (c1 & 1) << 16 # 17 bits wide

        c3 += (c2 & 3) << 8  # 10 bits wide

        parts.extend([_b32tab[c1 >> 11],         # bits 1 - 5

                      _b32tab[(c1 >> 6) & 0x1f], # bits 6 - 10

                      _b32tab[(c1 >> 1) & 0x1f], # bits 11 - 15

                      _b32tab[c2 >> 12],         # bits 16 - 20 (1 - 5)

                      _b32tab[(c2 >> 7) & 0x1f], # bits 21 - 25 (6 - 10)

                      _b32tab[(c2 >> 2) & 0x1f], # bits 26 - 30 (11 - 15)

                      _b32tab[c3 >> 5],          # bits 31 - 35 (1 - 5)

                      _b32tab[c3 & 0x1f],        # bits 36 - 40 (1 - 5)

                      ])

    encoded = EMPTYSTRING.join(parts)

    # Adjust for any leftover partial quanta

    if leftover == 1:

        return encoded[:-6] + '======'

    elif leftover == 2:

        return encoded[:-4] + '===='

    elif leftover == 3:

        return encoded[:-3] + '==='

    elif leftover == 4:

        return encoded[:-1] + '='

    return encoded

def b32decode(s, casefold=False, map01=None):

    """Decode a Base32 encoded string.

    s is the string to decode.  Optional casefold is a flag specifying whether

    a lowercase alphabet is acceptable as input.  For security purposes, the

    default is False.

    RFC 3548 allows for optional mapping of the digit 0 (zero) to the letter O

    (oh), and for optional mapping of the digit 1 (one) to either the letter I

    (eye) or letter L (el).  The optional argument map01 when not None,

    specifies which letter the digit 1 should be mapped to (when map01 is not

    None, the digit 0 is always mapped to the letter O).  For security

    purposes the default is None, so that 0 and 1 are not allowed in the

    input.

    The decoded string is returned.  A TypeError is raised if s were

    incorrectly padded or if there are non-alphabet characters present in the

    string.

    """

    quanta, leftover = divmod(len(s), 8)

    if leftover:

        raise TypeError('Incorrect padding')

    # Handle section 2.4 zero and one mapping.  The flag map01 will be either

    # False, or the character to map the digit 1 (one) to.  It should be

    # either L (el) or I (eye).

    if map01:

        s = _translate(s, {'0': 'O', '1': map01})

    if casefold:

        s = s.upper()

    # Strip off pad characters from the right.  We need to count the pad

    # characters because this will tell us how many null bytes to remove from

    # the end of the decoded string.

    padchars = 0

    mo = re.search('(?P<pad>[=]*)$', s)

    if mo:

        padchars = len(mo.group('pad'))

        if padchars > 0:

            s = s[:-padchars]

    # Now decode the full quanta

    parts = []

    acc = 0

    shift = 35

    for c in s:

        val = _b32rev.get(c)

        if val is None:

            raise TypeError('Non-base32 digit found')

        acc += _b32rev[c] << shift

        shift -= 5

        if shift < 0:

            parts.append(binascii.unhexlify('%010x' % acc))

            acc = 0

            shift = 35

    # Process the last, partial quanta

    last = binascii.unhexlify('%010x' % acc)

    if padchars == 0:

        last = ''                       # No characters

    elif padchars == 1:

        last = last[:-1]

    elif padchars == 3:

        last = last[:-2]

    elif padchars == 4:

        last = last[:-3]

    elif padchars == 6:

        last = last[:-4]

    else:

        raise TypeError('Incorrect padding')

    parts.append(last)

    return EMPTYSTRING.join(parts)

# RFC 3548, Base 16 Alphabet specifies uppercase, but hexlify() returns

# lowercase.  The RFC also recommends against accepting input case

# insensitively.

def b16encode(s):

    """Encode a string using Base16.

    s is the string to encode.  The encoded string is returned.

    """

    return binascii.hexlify(s).upper()

def b16decode(s, casefold=False):

    """Decode a Base16 encoded string.

    s is the string to decode.  Optional casefold is a flag specifying whether

    a lowercase alphabet is acceptable as input.  For security purposes, the

    default is False.

    The decoded string is returned.  A TypeError is raised if s were

    incorrectly padded or if there are non-alphabet characters present in the

    string.

    """

    if casefold:

        s = s.upper()

    if re.search('[^0-9A-F]', s):

        raise TypeError('Non-base16 digit found')

    return binascii.unhexlify(s)

# Legacy interface.  This code could be cleaned up since I don't believe

# binascii has any line length limitations.  It just doesn't seem worth it

# though.

MAXLINESIZE = 76 # Excluding the CRLF

MAXBINSIZE = (MAXLINESIZE//4)*3

def encode(input, output):

    """Encode a file."""

    while True:

        s = input.read(MAXBINSIZE)

        if not s:

            break

        while len(s) < MAXBINSIZE:

            ns = input.read(MAXBINSIZE-len(s))

            if not ns:

                break

            s += ns

        line = binascii.b2a_base64(s)

        output.write(line)

def decode(input, output):

    """Decode a file."""

    while True:

        line = input.readline()

        if not line:

            break

        s = binascii.a2b_base64(line)

        output.write(s)

def encodestring(s):

    """Encode a string."""

    pieces = []

    for i in range(0, len(s), MAXBINSIZE):

        chunk = s[i : i + MAXBINSIZE]

        pieces.append(binascii.b2a_base64(chunk))

    return "".join(pieces)

def decodestring(s):

    """Decode a string."""

    return binascii.a2b_base64(s)

# Useable as a script...

def test():

    """Small test program"""

    import sys, getopt

    try:

        opts, args = getopt.getopt(sys.argv[1:], 'deut')

    except getopt.error, msg:

        sys.stdout = sys.stderr

        print msg

        print """usage: %s [-d|-e|-u|-t] [file|-]

        -d, -u: decode

        -e: encode (default)

        -t: encode and decode string 'Aladdin:open sesame'"""%sys.argv[0]

        sys.exit(2)

    func = encode

    for o, a in opts:

        if o == '-e': func = encode

        if o == '-d': func = decode

        if o == '-u': func = decode

        if o == '-t': test1(); return

    if args and args[0] != '-':

        func(open(args[0], 'rb'), sys.stdout)

    else:

        func(sys.stdin, sys.stdout)

def test1():

    s0 = "Aladdin:open sesame"

    s1 = encodestring(s0)

    s2 = decodestring(s1)

    print s0, repr(s1), s2

if __name__ == '__main__':

    test()