two mime encoding schemes

Lib/base64.py

@@ -0,0 +1,125 @@
+# Conversions to/from base64 transport encoding as per RFC-MIME (Dec 1991
+# version).
+
+# Parameters set by RFX-XXXX.
+MAXLINESIZE = 76 # Excluding the CRLF
+INVAR = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
+PAD = '='
+
+# Check that I typed that string correctly...
+if len(INVAR) <> 64: raise RuntimeError, 'wrong INVAR string!?!?'
+
+# Compute the inverse table, for decode().
+inverse = {}
+for i in range(64): inverse[INVAR[i]] = i
+del i
+inverse[PAD] = 0
+
+# Encode a file.
+def encode(input, output):
+	line = ''
+	BUFSIZE = 8192
+	leftover = ''
+	while 1:
+		s = input.read(BUFSIZE)
+		if not s: break
+		s = leftover + s
+		i = 0
+		while i+3 <= len(s):
+			quad = makequad(s[i:i+3])
+			i = i+3
+			if len(line) + 4 > MAXLINESIZE:
+				output.write(line + '\n')
+				line = ''
+			line = line + quad
+		leftover = s[i:]
+	if leftover:
+		quad = makeshortquad(leftover)
+		if len(line) + 4 > MAXLINESIZE:
+			output.write(line + '\n')
+			line = ''
+		line = line + quad
+	if line:
+		output.write(line + '\n')
+
+def makequad(s): # Return the quad for a 3 character string
+	x = ord(s[0])*0x10000 + ord(s[1])*0x100 + ord(s[2])
+	x, c4 = divmod(x, 64)
+	x, c3 = divmod(x, 64)
+	c1, c2 = divmod(x, 64)
+	return INVAR[c1] + INVAR[c2] +INVAR[c3] + INVAR[c4]
+
+def makeshortquad(s): # Return the quad value for a 1 or 2 character string
+	n = len(s)
+	while len(s) < 3:
+		s = s + '\0'
+	quad = makequad(s)
+	if n == 2:
+		quad = quad[:3] + PAD
+	elif n == 1:
+		quad = quad[:2] + 2*PAD
+	return quad
+
+# Decode a file.
+def decode(input, output):
+	BUFSIZE = 8192
+	bits, n, bytes, prev = 0, 0, '', ''
+	while 1:
+		line = input.readline()
+		if not line: break
+		for c in line:
+			if inverse.has_key(c):
+				bits = bits*64 + inverse[c]
+				n = n+6
+				if n == 24:
+					triplet = decodequad(bits)
+					if c == PAD:
+						if prev == PAD:
+							triplet = triplet[:1]
+						else:
+							triplet = triplet[:2]
+					bits, n = 0, 0
+					bytes = bytes + triplet
+					if len(bytes) > BUFSIZE:
+						output.write(bytes[:BUFSIZE])
+						bytes = bytes[BUFSIZE:]
+				prev = c
+	if bytes:
+		output.write(bytes)
+
+def decodequad(bits): # Turn 24 bits into 3 characters
+	bits, c3 = divmod(bits, 256)
+	c1, c2 = divmod(bits, 256)
+	return chr(c1) + chr(c2) + chr(c3)
+
+def encodestring(s):
+	import StringIO
+	f = StringIO.StringIO(s)
+	g = StringIO.StringIO()
+	encode(f, g)
+	return g.getvalue()
+
+def decodestring(s):
+	import StringIO
+	f = StringIO.StringIO(s)
+	g = StringIO.StringIO()
+	decode(f, g)
+	return g.getvalue()
+
+# Small test program, reads stdin, writes stdout.
+# no arg: encode, any arg: decode.
+def test():
+	import sys
+	if sys.argv[1:]:
+		decode(sys.stdin, sys.stdout)
+	else:
+		encode(sys.stdin, sys.stdout)
+
+def test1():
+	s0 = "Aladdin:open sesame"
+	s1 = encodestring(s0)
+	s2 = decodestring(s1)
+	print s0, `s1`, s2
+
+if __name__ == '__main__':
+	test()