CNRoutesGen.py

#!/usr/bin/env python3
import urllib.request
import re
from collections import namedtuple
from math import log

def ip2num(ip_address: str) -> int:
    a, b, c, d = map(int, ip_address.split("."))
    return (a << 24) + (b << 16) + (c << 8) + d

def num2ip(num: int) -> str:
    ip = [0 for _ in range(4)]
    
    for i in range(3, -1, -1):
        num, r = divmod(num, 256)
        ip[i] = str(r)
    return ".".join(ip)

lg = lambda x: log(x, 2)

# Returns the position of the rightest 1 of a num as binary. 
def rightest_one(num: int) -> int:
    r = 0
    i = 0
    while num > 0:
        num, r = divmod(num, 2)
        if r == 1:
            return i
        i += 1
    return i

print("Download data from APNIC...")

with urllib.request.urlopen("https://ftp.apnic.net/apnic/stats/apnic/delegated-apnic-latest") as c:
    rir_data = c.read().decode("ASCII")

rir_stats = ((ip2num(e.group(1)), int(e.group(3))) for e in re.finditer(r"apnic\|CN\|ipv4\|((\d{0,3}\.){3}\d{0,3})\|(\d+)\|\d{8}\|[assigned|allocated]", rir_data, re.A))

print("Data downloaded.")

rir_stats = sorted(rir_stats, key=lambda e: e[0])

# Assume: the above data is sorted and has no overlap.

# shrink
shrinked_entries = []

last_entry = rir_stats[0]
for entry in rir_stats[1:]:
    #print(entry)
    if entry[0] - last_entry[0] == last_entry[1]: # consecutive ip range pair
        #print("merge {} with {}".format(last_entry, entry))
        last_entry = last_entry[0], last_entry[1] + entry[1] # merge
    else:
        shrinked_entries.append(last_entry)
        #print(last_entry)
        #__import__("time").sleep(2)
        last_entry = entry

# blow up
entries = []

for (addr, c) in shrinked_entries:
    while c != 0:
        # Assume: all CIDR are well-formed (couterexample: 1.0.1.0/16).
        b = min(c, 2 ** int(lg(c)), 2 ** rightest_one(addr)) 
        
        entries.append("{0}/{1}".format(num2ip(addr), 32 - int(lg(b))))
        
        c -= b
        addr += b
        #assert b == 2 ** (32 - entries[-1][1])

with open("./test.txt", "w", encoding="ASCII") as f:
    f.write("\n".join(entries))
print("Generated successfully with {} routes.".format(len(entries)))