126 lines
2.7 KiB
Python
126 lines
2.7 KiB
Python
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# Conversions to/from base64 transport encoding as per RFC-MIME (Dec 1991
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# version).
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# Parameters set by RFX-XXXX.
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MAXLINESIZE = 76 # Excluding the CRLF
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INVAR = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
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PAD = '='
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# Check that I typed that string correctly...
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if len(INVAR) <> 64: raise RuntimeError, 'wrong INVAR string!?!?'
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# Compute the inverse table, for decode().
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inverse = {}
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for i in range(64): inverse[INVAR[i]] = i
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del i
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inverse[PAD] = 0
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# Encode a file.
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def encode(input, output):
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line = ''
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BUFSIZE = 8192
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leftover = ''
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while 1:
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s = input.read(BUFSIZE)
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if not s: break
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s = leftover + s
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i = 0
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while i+3 <= len(s):
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quad = makequad(s[i:i+3])
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i = i+3
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if len(line) + 4 > MAXLINESIZE:
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output.write(line + '\n')
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line = ''
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line = line + quad
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leftover = s[i:]
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if leftover:
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quad = makeshortquad(leftover)
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if len(line) + 4 > MAXLINESIZE:
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output.write(line + '\n')
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line = ''
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line = line + quad
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if line:
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output.write(line + '\n')
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def makequad(s): # Return the quad for a 3 character string
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x = ord(s[0])*0x10000 + ord(s[1])*0x100 + ord(s[2])
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x, c4 = divmod(x, 64)
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x, c3 = divmod(x, 64)
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c1, c2 = divmod(x, 64)
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return INVAR[c1] + INVAR[c2] +INVAR[c3] + INVAR[c4]
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def makeshortquad(s): # Return the quad value for a 1 or 2 character string
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n = len(s)
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while len(s) < 3:
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s = s + '\0'
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quad = makequad(s)
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if n == 2:
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quad = quad[:3] + PAD
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elif n == 1:
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quad = quad[:2] + 2*PAD
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return quad
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# Decode a file.
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def decode(input, output):
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BUFSIZE = 8192
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bits, n, bytes, prev = 0, 0, '', ''
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while 1:
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line = input.readline()
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if not line: break
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for c in line:
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if inverse.has_key(c):
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bits = bits*64 + inverse[c]
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n = n+6
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if n == 24:
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triplet = decodequad(bits)
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if c == PAD:
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if prev == PAD:
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triplet = triplet[:1]
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else:
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triplet = triplet[:2]
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bits, n = 0, 0
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bytes = bytes + triplet
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if len(bytes) > BUFSIZE:
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output.write(bytes[:BUFSIZE])
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bytes = bytes[BUFSIZE:]
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prev = c
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if bytes:
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output.write(bytes)
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def decodequad(bits): # Turn 24 bits into 3 characters
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bits, c3 = divmod(bits, 256)
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c1, c2 = divmod(bits, 256)
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return chr(c1) + chr(c2) + chr(c3)
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def encodestring(s):
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import StringIO
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f = StringIO.StringIO(s)
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g = StringIO.StringIO()
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encode(f, g)
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return g.getvalue()
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def decodestring(s):
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import StringIO
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f = StringIO.StringIO(s)
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g = StringIO.StringIO()
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decode(f, g)
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return g.getvalue()
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# Small test program, reads stdin, writes stdout.
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# no arg: encode, any arg: decode.
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def test():
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import sys
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if sys.argv[1:]:
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decode(sys.stdin, sys.stdout)
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else:
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encode(sys.stdin, sys.stdout)
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def test1():
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s0 = "Aladdin:open sesame"
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s1 = encodestring(s0)
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s2 = decodestring(s1)
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print s0, `s1`, s2
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if __name__ == '__main__':
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test()
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