text: #!/usr/bin/env python3
  # Copyright (c) 2013-2017 The Bitcoin Core developers
  # Distributed under the MIT software license, see the accompanying
  # file COPYING or http://www.opensource.org/licenses/mit-license.php.
  #
  # Generate seeds.txt from Pieter's DNS seeder
  #
  
  NSEEDS=512
  
  MAX_SEEDS_PER_ASN=2
  
  MIN_BLOCKS = 337600
  
  # These are hosts that have been observed to be behaving strangely (e.g.
  # aggressively connecting to every node).
  SUSPICIOUS_HOSTS = {
      "130.211.129.106", "178.63.107.226",
      "83.81.130.26", "88.198.17.7", "148.251.238.178", "176.9.46.6",
      "54.173.72.127", "54.174.10.182", "54.183.64.54", "54.194.231.211",
      "54.66.214.167", "54.66.220.137", "54.67.33.14", "54.77.251.214",
      "54.94.195.96", "54.94.200.247"
  }
  
  import re
  import sys
  import dns.resolver
  import collections
  
  PATTERN_IPV4 = re.compile(r"^((\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})):(\d+)$")
  PATTERN_IPV6 = re.compile(r"^\[([0-9a-z:]+)\]:(\d+)$")
  PATTERN_ONION = re.compile(r"^([abcdefghijklmnopqrstuvwxyz234567]{16}\.onion):(\d+)$")
  PATTERN_AGENT = re.compile(r"^(/Satoshi:0.13.(0|1|2|99)/|/MTTcoinCore:0.13.(0|1|2|99)/|/MTTcoinCore:0.14.(0|1|2|99)/|/MTTcoinCore:0.15.(0|1|2|99)/)$")
  
  def parseline(line):
      sline = line.split()
      if len(sline) < 11:
         return None
      m = PATTERN_IPV4.match(sline[0])
      sortkey = None
      ip = None
      if m is None:
          m = PATTERN_IPV6.match(sline[0])
          if m is None:
              m = PATTERN_ONION.match(sline[0])
              if m is None:
                  return None
              else:
                  net = 'onion'
                  ipstr = sortkey = m.group(1)
                  port = int(m.group(2))
          else:
              net = 'ipv6'
              if m.group(1) in ['::']: # Not interested in localhost
                  return None
              ipstr = m.group(1)
              sortkey = ipstr # XXX parse IPv6 into number, could use name_to_ipv6 from generate-seeds
              port = int(m.group(2))
      else:
          # Do IPv4 sanity check
          ip = 0
          for i in range(0,4):
              if int(m.group(i+2)) < 0 or int(m.group(i+2)) > 255:
                  return None
              ip = ip + (int(m.group(i+2)) << (8*(3-i)))
          if ip == 0:
              return None
          net = 'ipv4'
          sortkey = ip
          ipstr = m.group(1)
          port = int(m.group(6))
      # Skip bad results.
      if sline[1] == 0:
          return None
      # Extract uptime %.
      uptime30 = float(sline[7][:-1])
      # Extract Unix timestamp of last success.
      lastsuccess = int(sline[2])
      # Extract protocol version.
      version = int(sline[10])
      # Extract user agent.
      agent = sline[11][1:-1]
      # Extract service flags.
      service = int(sline[9], 16)
      # Extract blocks.
      blocks = int(sline[8])
      # Construct result.
      return {
          'net': net,
          'ip': ipstr,
          'port': port,
          'ipnum': ip,
          'uptime': uptime30,
          'lastsuccess': lastsuccess,
          'version': version,
          'agent': agent,
          'service': service,
          'blocks': blocks,
          'sortkey': sortkey,
      }
  
  def filtermultiport(ips):
      '''Filter out hosts with more nodes per IP'''
      hist = collections.defaultdict(list)
      for ip in ips:
          hist[ip['sortkey']].append(ip)
      return [value[0] for (key,value) in list(hist.items()) if len(value)==1]
  
  # Based on Greg Maxwell's seed_filter.py
  def filterbyasn(ips, max_per_asn, max_total):
      # Sift out ips by type
      ips_ipv4 = [ip for ip in ips if ip['net'] == 'ipv4']
      ips_ipv6 = [ip for ip in ips if ip['net'] == 'ipv6']
      ips_onion = [ip for ip in ips if ip['net'] == 'onion']
  
      # Filter IPv4 by ASN
      result = []
      asn_count = {}
      for ip in ips_ipv4:
          if len(result) == max_total:
              break
          try:
              asn = int([x.to_text() for x in dns.resolver.query('.'.join(reversed(ip['ip'].split('.'))) + '.origin.asn.cymru.com', 'TXT').response.answer][0].split('\"')[1].split(' ')[0])
              if asn not in asn_count:
                  asn_count[asn] = 0
              if asn_count[asn] == max_per_asn:
                  continue
              asn_count[asn] += 1
              result.append(ip)
          except:
              sys.stderr.write('ERR: Could not resolve ASN for "' + ip['ip'] + '"\n')
  
      # TODO: filter IPv6 by ASN
  
      # Add back non-IPv4
      result.extend(ips_ipv6)
      result.extend(ips_onion)
      return result
  
  def main():
      lines = sys.stdin.readlines()
      ips = [parseline(line) for line in lines]
  
      # Skip entries with valid address.
      ips = [ip for ip in ips if ip is not None]
      # Skip entries from suspicious hosts.
      ips = [ip for ip in ips if ip['ip'] not in SUSPICIOUS_HOSTS]
      # Enforce minimal number of blocks.
      ips = [ip for ip in ips if ip['blocks'] >= MIN_BLOCKS]
      # Require service bit 1.
      ips = [ip for ip in ips if (ip['service'] & 1) == 1]
      # Require at least 50% 30-day uptime.
      ips = [ip for ip in ips if ip['uptime'] > 50]
      # Require a known and recent user agent.
      ips = [ip for ip in ips if PATTERN_AGENT.match(ip['agent'])]
      # Sort by availability (and use last success as tie breaker)
      ips.sort(key=lambda x: (x['uptime'], x['lastsuccess'], x['ip']), reverse=True)
      # Filter out hosts with multiple bitcoin ports, these are likely abusive
      ips = filtermultiport(ips)
      # Look up ASNs and limit results, both per ASN and globally.
      ips = filterbyasn(ips, MAX_SEEDS_PER_ASN, NSEEDS)
      # Sort the results by IP address (for deterministic output).
      ips.sort(key=lambda x: (x['net'], x['sortkey']))
  
      for ip in ips:
          if ip['net'] == 'ipv6':
              print('[%s]:%i' % (ip['ip'], ip['port']))
          else:
              print('%s:%i' % (ip['ip'], ip['port']))
  
  if __name__ == '__main__':
      main()
  