irr-prune

#!/usr/bin/env python3

# Quick and dirty script to minimize an IRR database to use only by
# bgpq3/bgpq4. The core idea is we have to only keep what is needed
# for "!i" (expand an AS-SET), "!gas" and "!6as" (get routes from
# specified AS) to work.

import sys
import re


START = 1
SKIPOBJECT = 2         # skip current object
KEEPATTRIBUTE = 3      # also, keep current object
SKIPATTRIBUTE = 4      # also, keep current object

names = re.compile(rb"^(?:as-set|aut-num|route|route6|route-set):")
attributes = re.compile(rb"^(?:origin|mnt-by|mbrs-by-ref|member-of|members|"
                        rb"mp-members|roa-status|source):")
comments = set(b"#%")
continuation = set(b" \t+")
state = START
for line in sys.stdin.buffer:
    if line == b"" or line == b"\n" or line == b"\r\n":
        # Empty line, end of the current object
        if state not in {SKIPOBJECT, START}:
            sys.stdout.buffer.write(line)
        state = START
        continue
    if line[0] in comments:
        # Skip comments
        continue
    if state == START:
        # Outside of an object
        if names.match(line):
            sys.stdout.buffer.write(line)
            state = KEEPATTRIBUTE
            continue
        state = SKIPOBJECT
        continue
    if state == SKIPOBJECT:
        # Skip current object until the end
        continue
    if state in {SKIPATTRIBUTE, KEEPATTRIBUTE}:
        if line[0] in continuation:
            # Continuation
            if state == KEEPATTRIBUTE:
                sys.stdout.buffer.write(line)
            continue
        if attributes.match(line):
            sys.stdout.buffer.write(line)
            state = KEEPATTRIBUTE
            continue
        state = SKIPATTRIBUTE
        continue
    raise RuntimeError("Illegal state")