Nginx user_id encoder/decoder from http://stackoverflow.com/a/19037624/739667

nginx_uid.py

# http://stackoverflow.com/a/19037624/739667
import base64
import socket
import struct


def decode_cookie(cookie):
    """decode a u cookie into an uid

    :param cookie: a cookie value that will be decoded into a uid
    :return: string representing the uid

    This algorithm is for version 2 of http://wiki.nginx.org/HttpUseridModule.

    This nginx module follows the apache mod_uid module algorithm, which is
    documented here: http://www.lexa.ru/programs/mod-uid-eng.html.

    """
    # get the raw binary value
    binary_cookie = base64.b64decode(cookie)

    # unpack into 4 parts, each a network byte orderd 32 bit unsigned int
    unsigned_ints = struct.unpack('!4I', binary_cookie)

    # convert from network (big-endian) to host byte (probably little-endian) order
    host_byte_order_ints = [socket.ntohl(i) for i in unsigned_ints]

    # convert to upper case hex value
    uid = 'u=' + ''.join(['{0:08X}'.format(h) for h in host_byte_order_ints])

    return uid


def encode_uid(uid):
    """encode an uid into a u cookie

    :param uid: an uid that will be encoded into a cookie.
    :return: string representing the u cookie

    The algorithm is for version 2 of http://wiki.nginx.org/HttpUseridModule.

    This nginx module follows the apache mod_uid module algorithm, which is
    documented here: http://www.lexa.ru/programs/mod-uid-eng.html.

    """
    # get the hex value of the uid
    hex_value = uid.split('=')[1]

    # convert 128 bit string into 4 32 bit integers
    host_byte_order_ints = [int(hex_value[i:i+8], 16) for i in range(0, 32, 8)]

    # convert from host byte (probably little-endian) to network byte (big-endian) order
    unsigned_ints = [socket.htonl(i) for i in host_byte_order_ints]

    # convert to raw binary value
    binary_cookie = struct.pack('!4I', *unsigned_ints)

    # get the base64 version of the cookie
    cookie = base64.b64encode(binary_cookie)

    return cookie