shortenv6.py

# Copyright (c) 2009 Jannis Andrija Schnitzer
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

from base64 import b64encode as base64_encode, b64decode as base64_decode

def n_at_once(string, n):
    """Return an iterator over substrings of the given string
    with length n"""
    while string:
        prefix, string = string[:n], string[n:]
        yield prefix

def shorten(address):    
    address = address.lower() # ensure we yield the same string on case differences
    splices = address.split(':')
    result = []
    for splice in splices:
        if not splice:
            result.append('_')
        else:
            splice = splice.rjust(4, '0')
            for hex_number in n_at_once(splice, 2):
                hex_number = int(hex_number, 16)
                result.append(chr(hex_number))
    return base64_encode(''.join(result))

def expand(address):
    address = base64_decode(address)
    pieces = []
    for character in address:
        if character == '_':
            pieces.extend(['', ''])
        else:
            pieces.append(hex(ord(character))[2:].rjust(2, '0'))
    print pieces
    return ':'.join(''.join(splices).lstrip('0') for splices in n_at_once(pieces, 2))