base64.py revision 3b8e1604e8dd4c871e5e8a22d6c738c7f2d39f3a 
1# Conversions to/from base64 transport encoding as per RFC-MIME (Dec 1991
2# version).
3
4# Parameters set by RFX-XXXX.
5MAXLINESIZE = 76 # Excluding the CRLF
6INVAR = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
7PAD = '='
8
9# Check that I typed that string correctly...
10if len(INVAR) <> 64: raise RuntimeError, 'wrong INVAR string!?!?'
11
12# Compute the inverse table, for decode().
13inverse = {}
14for i in range(64): inverse[INVAR[i]] = i
15del i
16inverse[PAD] = 0
17
18# Encode a file.
19def encode(input, output):
20	line = ''
21	BUFSIZE = 8192
22	leftover = ''
23	while 1:
24		s = input.read(BUFSIZE)
25		if not s: break
26		s = leftover + s
27		i = 0
28		while i+3 <= len(s):
29			quad = makequad(s[i:i+3])
30			i = i+3
31			if len(line) + 4 > MAXLINESIZE:
32				output.write(line + '\n')
33				line = ''
34			line = line + quad
35		leftover = s[i:]
36	if leftover:
37		quad = makeshortquad(leftover)
38		if len(line) + 4 > MAXLINESIZE:
39			output.write(line + '\n')
40			line = ''
41		line = line + quad
42	if line:
43		output.write(line + '\n')
44
45def makequad(s): # Return the quad for a 3 character string
46	x = ord(s[0])*0x10000 + ord(s[1])*0x100 + ord(s[2])
47	x, c4 = divmod(x, 64)
48	x, c3 = divmod(x, 64)
49	c1, c2 = divmod(x, 64)
50	return INVAR[c1] + INVAR[c2] +INVAR[c3] + INVAR[c4]
51
52def makeshortquad(s): # Return the quad value for a 1 or 2 character string
53	n = len(s)
54	while len(s) < 3:
55		s = s + '\0'
56	quad = makequad(s)
57	if n == 2:
58		quad = quad[:3] + PAD
59	elif n == 1:
60		quad = quad[:2] + 2*PAD
61	return quad
62
63# Decode a file.
64def decode(input, output):
65	BUFSIZE = 8192
66	bits, n, bytes, prev = 0, 0, '', ''
67	while 1:
68		line = input.readline()
69		if not line: break
70		for c in line:
71			if inverse.has_key(c):
72				bits = bits*64 + inverse[c]
73				n = n+6
74				if n == 24:
75					triplet = decodequad(bits)
76					if c == PAD:
77						if prev == PAD:
78							triplet = triplet[:1]
79						else:
80							triplet = triplet[:2]
81					bits, n = 0, 0
82					bytes = bytes + triplet
83					if len(bytes) > BUFSIZE:
84						output.write(bytes[:BUFSIZE])
85						bytes = bytes[BUFSIZE:]
86				prev = c
87	if bytes:
88		output.write(bytes)
89
90def decodequad(bits): # Turn 24 bits into 3 characters
91	bits, c3 = divmod(bits, 256)
92	c1, c2 = divmod(bits, 256)
93	return chr(c1) + chr(c2) + chr(c3)
94
95def encodestring(s):
96	import StringIO
97	f = StringIO.StringIO(s)
98	g = StringIO.StringIO()
99	encode(f, g)
100	return g.getvalue()
101
102def decodestring(s):
103	import StringIO
104	f = StringIO.StringIO(s)
105	g = StringIO.StringIO()
106	decode(f, g)
107	return g.getvalue()
108
109# Small test program, reads stdin, writes stdout.
110# no arg: encode, any arg: decode.
111def test():
112	import sys, getopt
113	try:
114		opts, args = getopt.getopt(sys.argv[1:], 'deut')
115	except getopt.error, msg:
116		print msg
117		print """usage: basd64 [-d] [-e] [-u] [-t] [file|-]
118		-d, -u: decode
119		-e: encode (default)
120		-t: decode string 'Aladdin:open sesame'"""
121	func = encode
122	for o, a in opts:
123		if o == '-e': func = encode
124		if o == '-d': func = decode
125		if o == '-u': func = decode
126		if o == '-t': test1(); return
127	if args and args[0] != '-':
128		func(open(args[0]), sys.stdout)
129	else:
130		func(sys.stdin, sys.stdout)
131
132def test1():
133	s0 = "Aladdin:open sesame"
134	s1 = encodestring(s0)
135	s2 = decodestring(s1)
136	print s0, `s1`, s2
137
138if __name__ == '__main__':
139	test()
140