Working with bytes.

[Anton Vredegoor]

anton at vredegoor.doge.nl (Anton Vredegoor) wrote:

> http://www.faqs.org/rfcs/rfc1924.html 

Replying to my own post. I was using lowercase letters before
uppercase and did some other non compliant things. Because I was using
random data I didn't notice. The code below should reproduce the
rfc1924 example. 

Anton

from binascii import hexlify
from string import digits, ascii_lowercase, ascii_uppercase

_rfc1924_letters =  ascii_uppercase + ascii_lowercase
_rfc1924_chars = digits+_rfc1924_letters+'!#$%&()*+-;<=>?@^_`{|}~'
_rfc1924_table = dict([(c,i) for i,c in enumerate(_rfc1924_chars)])
_rfc1924_bases = [85L**i for i in range(19,-1,-1)]

def bytes_to_rfc1924(sixteen):
    res = []
    i = 0L
    for byte in sixteen:
        i <<= 8
        i |= ord(byte)
    for j in range(20):
        i,k = divmod(i,85)
        res.append(_rfc1924_chars[k])
    res.reverse()
    return "".join(res)

def rfc1924_to_bytes(twenty):
    res = []
    i = 0L
    for b,byte in zip(_rfc1924_bases,twenty):
        i +=  b * _rfc1924_table[byte]
    for j in range(16):
        i,k = divmod(i,256)
        res.append(chr(k))
    res.reverse()
    return "".join(res)

def bytes_as_ipv6(bytes):
    addr = [bytes[i:i+2] for i in range(0,16,2)]
    return ":".join(map(hexlify,addr))
    
def test():
    s = "4)+k&C#VzJ4br>0wv%Yp"
    bytes = rfc1924_to_bytes(s)
    check = bytes_to_rfc1924(bytes)
    assert s == check
    addr = bytes_as_ipv6(bytes)
    print addr
    
if __name__=='__main__':
    test()

output:

1080:0000:0000:0000:0008:0800:200c:417a