cpython/base64.py at 2.7 · python/cpython

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	#! /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 string
	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 encoded.translate(string.maketrans(b'+/', altchars[:2]))
	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 is
	incorrectly padded. Characters that are neither in the normal base-64
	alphabet nor the alternative alphabet are discarded prior to the padding
	check.
	"""
	if altchars is not None:
	s = s.translate(string.maketrans(altchars[:2], '+/'))
	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.

	Argument s is the string to decode. The decoded string is returned. A
	TypeError is raised if the string is incorrectly padded. Characters that
	are not in the standard alphabet are discarded prior to the padding
	check.
	"""
	return b64decode(s)

	_urlsafe_encode_translation = string.maketrans(b'+/', b'-_')
	_urlsafe_decode_translation = string.maketrans(b'-_', b'+/')

	def urlsafe_b64encode(s):
	"""Encode a string using the URL- and filesystem-safe Base64 alphabet.

	Argument s is the string to encode. The encoded string is returned. The
	alphabet uses '-' instead of '+' and '_' instead of '/'.
	"""
	return b64encode(s).translate(_urlsafe_encode_translation)

	def urlsafe_b64decode(s):
	"""Decode a string using the URL- and filesystem-safe Base64 alphabet.

	Argument s is the string to decode. The decoded string is returned. A
	TypeError is raised if the string is incorrectly padded. Characters that
	are not in the URL-safe base-64 alphabet, and are not a plus '+' or slash
	'/', are discarded prior to the padding check.

	The alphabet uses '-' instead of '+' and '_' instead of '/'.
	"""
	return b64decode(s.translate(_urlsafe_decode_translation))



	# 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[i5:(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 = s.translate(string.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('(?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 is
	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 into multiple lines of base-64 data."""
	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] != '-':
	with open(args[0], 'rb') as f:
	func(f, 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()