text: #! /usr/bin/env python3
  
  """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
  # Modified 22-May-2007 by Guido van Rossum to use bytes everywhere
  
  import re
  import struct
  import binascii
  
  
  __all__ = [
      # Legacy interface exports traditional RFC 1521 Base64 encodings
      'encode', 'decode', 'encodebytes', 'decodebytes',
      # 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',
      ]
  
  
  bytes_types = (bytes, bytearray)  # Types acceptable as binary data
  
  def _bytes_from_decode_data(s):
      if isinstance(s, str):
          try:
              return s.encode('ascii')
          except UnicodeEncodeError:
              raise ValueError('string argument should contain only ASCII characters')
      elif isinstance(s, bytes_types):
          return s
      else:
          raise TypeError("argument should be bytes or ASCII string, not %s" % s.__class__.__name__)
  
  
  
  # Base64 encoding/decoding uses binascii
  
  def b64encode(s, altchars=None):
      """Encode a byte string using Base64.
  
      s is the byte string to encode.  Optional altchars must be a byte
      string of length 2 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 byte string is returned.
      """
      if not isinstance(s, bytes_types):
          raise TypeError("expected bytes, not %s" % s.__class__.__name__)
      # Strip off the trailing newline
      encoded = binascii.b2a_base64(s)[:-1]
      if altchars is not None:
          if not isinstance(altchars, bytes_types):
              raise TypeError("expected bytes, not %s"
                              % altchars.__class__.__name__)
          assert len(altchars) == 2, repr(altchars)
          return encoded.translate(bytes.maketrans(b'+/', altchars))
      return encoded
  
  
  def b64decode(s, altchars=None, validate=False):
      """Decode a Base64 encoded byte string.
  
      s is the byte string to decode.  Optional altchars must be a
      string of length 2 which specifies the alternative alphabet used
      instead of the '+' and '/' characters.
  
      The decoded string is returned.  A binascii.Error is raised if s is
      incorrectly padded.
  
      If validate is False (the default), non-base64-alphabet characters are
      discarded prior to the padding check.  If validate is True,
      non-base64-alphabet characters in the input result in a binascii.Error.
      """
      s = _bytes_from_decode_data(s)
      if altchars is not None:
          altchars = _bytes_from_decode_data(altchars)
          assert len(altchars) == 2, repr(altchars)
          s = s.translate(bytes.maketrans(altchars, b'+/'))
      if validate and not re.match(b'^[A-Za-z0-9+/]*={0,2}$', s):
          raise binascii.Error('Non-base64 digit found')
      return binascii.a2b_base64(s)
  
  
  def standard_b64encode(s):
      """Encode a byte string using the standard Base64 alphabet.
  
      s is the byte string to encode.  The encoded byte string is returned.
      """
      return b64encode(s)
  
  def standard_b64decode(s):
      """Decode a byte string encoded with the standard Base64 alphabet.
  
      s is the byte string to decode.  The decoded byte string is
      returned.  binascii.Error is raised if the input is incorrectly
      padded or if there are non-alphabet characters present in the
      input.
      """
      return b64decode(s)
  
  
  _urlsafe_encode_translation = bytes.maketrans(b'+/', b'-_')
  _urlsafe_decode_translation = bytes.maketrans(b'-_', b'+/')
  
  def urlsafe_b64encode(s):
      """Encode a byte string using a url-safe Base64 alphabet.
  
      s is the byte string to encode.  The encoded byte string is
      returned.  The alphabet uses '-' instead of '+' and '_' instead of
      '/'.
      """
      return b64encode(s).translate(_urlsafe_encode_translation)
  
  def urlsafe_b64decode(s):
      """Decode a byte string encoded with the standard Base64 alphabet.
  
      s is the byte string to decode.  The decoded byte string is
      returned.  binascii.Error is raised if the input is incorrectly
      padded or if there are non-alphabet characters present in the
      input.
  
      The alphabet uses '-' instead of '+' and '_' instead of '/'.
      """
      s = _bytes_from_decode_data(s)
      s = s.translate(_urlsafe_decode_translation)
      return b64decode(s)
  
  
  
  # Base32 encoding/decoding must be done in Python
  _b32alphabet = {
      0: b'A',  9: b'J', 18: b'S', 27: b'3',
      1: b'B', 10: b'K', 19: b'T', 28: b'4',
      2: b'C', 11: b'L', 20: b'U', 29: b'5',
      3: b'D', 12: b'M', 21: b'V', 30: b'6',
      4: b'E', 13: b'N', 22: b'W', 31: b'7',
      5: b'F', 14: b'O', 23: b'X',
      6: b'G', 15: b'P', 24: b'Y',
      7: b'H', 16: b'Q', 25: b'Z',
      8: b'I', 17: b'R', 26: b'2',
      }
  
  _b32tab = [v[0] for k, v in sorted(_b32alphabet.items())]
  _b32rev = dict([(v[0], k) for k, v in _b32alphabet.items()])
  
  
  def b32encode(s):
      """Encode a byte string using Base32.
  
      s is the byte string to encode.  The encoded byte string is returned.
      """
      if not isinstance(s, bytes_types):
          raise TypeError("expected bytes, not %s" % s.__class__.__name__)
      quanta, leftover = divmod(len(s), 5)
      # Pad the last quantum with zero bits if necessary
      if leftover:
          s = s + bytes(5 - leftover)  # Don't use += !
          quanta += 1
      encoded = bytes()
      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
          encoded += bytes([_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)
                            ])
      # Adjust for any leftover partial quanta
      if leftover == 1:
          return encoded[:-6] + b'======'
      elif leftover == 2:
          return encoded[:-4] + b'===='
      elif leftover == 3:
          return encoded[:-3] + b'==='
      elif leftover == 4:
          return encoded[:-1] + b'='
      return encoded
  
  
  def b32decode(s, casefold=False, map01=None):
      """Decode a Base32 encoded byte string.
  
      s is the byte 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 byte string is returned.  binascii.Error is raised if
      the input is incorrectly padded or if there are non-alphabet
      characters present in the input.
      """
      s = _bytes_from_decode_data(s)
      quanta, leftover = divmod(len(s), 8)
      if leftover:
          raise binascii.Error('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 is not None:
          map01 = _bytes_from_decode_data(map01)
          assert len(map01) == 1, repr(map01)
          s = s.translate(bytes.maketrans(b'01', b'O' + 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(b'(?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(bytes('%010x' % acc, "ascii")))
              acc = 0
              shift = 35
      # Process the last, partial quanta
      last = binascii.unhexlify(bytes('%010x' % acc, "ascii"))
      if padchars == 0:
          last = b''                      # 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 binascii.Error('Incorrect padding')
      parts.append(last)
      return b''.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 byte string using Base16.
  
      s is the byte string to encode.  The encoded byte string is returned.
      """
      if not isinstance(s, bytes_types):
          raise TypeError("expected bytes, not %s" % s.__class__.__name__)
      return binascii.hexlify(s).upper()
  
  
  def b16decode(s, casefold=False):
      """Decode a Base16 encoded byte string.
  
      s is the byte 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 byte string is returned.  binascii.Error is raised if
      s were incorrectly padded or if there are non-alphabet characters
      present in the string.
      """
      s = _bytes_from_decode_data(s)
      if casefold:
          s = s.upper()
      if re.search(b'[^0-9A-F]', s):
          raise binascii.Error('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.  The files should be opened in binary mode.
  
  MAXLINESIZE = 76 # Excluding the CRLF
  MAXBINSIZE = (MAXLINESIZE//4)*3
  
  def encode(input, output):
      """Encode a file; input and output are binary files."""
      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; input and output are binary files."""
      while True:
          line = input.readline()
          if not line:
              break
          s = binascii.a2b_base64(line)
          output.write(s)
  
  
  def encodebytes(s):
      """Encode a bytestring into a bytestring containing multiple lines
      of base-64 data."""
      if not isinstance(s, bytes_types):
          raise TypeError("expected bytes, not %s" % s.__class__.__name__)
      pieces = []
      for i in range(0, len(s), MAXBINSIZE):
          chunk = s[i : i + MAXBINSIZE]
          pieces.append(binascii.b2a_base64(chunk))
      return b"".join(pieces)
  
  def encodestring(s):
      """Legacy alias of encodebytes()."""
      import warnings
      warnings.warn("encodestring() is a deprecated alias, use encodebytes()",
                    DeprecationWarning, 2)
      return encodebytes(s)
  
  
  def decodebytes(s):
      """Decode a bytestring of base-64 data into a bytestring."""
      if not isinstance(s, bytes_types):
          raise TypeError("expected bytes, not %s" % s.__class__.__name__)
      return binascii.a2b_base64(s)
  
  def decodestring(s):
      """Legacy alias of decodebytes()."""
      import warnings
      warnings.warn("decodestring() is a deprecated alias, use decodebytes()",
                    DeprecationWarning, 2)
      return decodebytes(s)
  
  
  # Usable as a script...
  def main():
      """Small main program"""
      import sys, getopt
      try:
          opts, args = getopt.getopt(sys.argv[1:], 'deut')
      except getopt.error as 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': test(); return
      if args and args[0] != '-':
          with open(args[0], 'rb') as f:
              func(f, sys.stdout.buffer)
      else:
          func(sys.stdin.buffer, sys.stdout.buffer)
  
  
  def test():
      s0 = b"Aladdin:open sesame"
      print(repr(s0))
      s1 = encodebytes(s0)
      print(repr(s1))
      s2 = decodebytes(s1)
      print(repr(s2))
      assert s0 == s2
  
  
  if __name__ == '__main__':
      main()
  