contrib: Use asmap for ASN lookup in makeseeds

Add an argument `-a` to provide a asmap file to do the IP to ASN
lookups.

This speeds up the script greatly, and makes the output deterministic.
Also removes the dependency on `dns.lookup`.

I've annotated the output with ASxxxx comments to provide a way to
verify the functionality.

For now I've added instructions in README.md to download and use the
`demo.map` from the asmap repository. When we have some other mechanism
for distributing asmap files we could switch to that.

This continues #24824. I've removed all the fallbacks and extra
complexity, as everyone will be using the same instructions anyway.

Co-authored-by: Pieter Wuille <pieter.wuille@gmail.com>
Co-authored-by: James O'Beirne <james.obeirne@pm.me>
Co-authored-by: russeree <reese.russell@ymail.com>

4 files changed, 120 insertions, 48 deletions

diff --git a/contrib/seeds/.gitignore b/contrib/seeds/.gitignore
index e4a39d6093..d9a2451f70 100644
--- a/contrib/seeds/.gitignore
+++ b/contrib/seeds/.gitignore
@@ -1 +1,2 @@
 seeds_main.txt
+asmap-filled.dat
diff --git a/contrib/seeds/README.md b/contrib/seeds/README.md
index c53446bfb0..b2ea7522ac 100644
--- a/contrib/seeds/README.md
+++ b/contrib/seeds/README.md
@@ -8,21 +8,11 @@ and remove old versions as necessary (at a minimum when GetDesirableServiceFlags
 changes its default return value, as those are the services which seeds are added
 to addrman with).
 
-The seeds compiled into the release are created from sipa's DNS seed data, like this:
+The seeds compiled into the release are created from sipa's DNS seed and AS map
+data. Run the following commands from the `/contrib/seeds` directory:
 
     curl https://bitcoin.sipa.be/seeds.txt.gz | gzip -dc > seeds_main.txt
-    python3 makeseeds.py < seeds_main.txt > nodes_main.txt
+    curl https://bitcoin.sipa.be/asmap-filled.dat > asmap-filled.dat
+    python3 makeseeds.py -a asmap-filled.dat < seeds_main.txt > nodes_main.txt
     cat nodes_main_manual.txt >> nodes_main.txt
     python3 generate-seeds.py . > ../../src/chainparamsseeds.h
-
-## Dependencies
-
-Ubuntu, Debian:
-
-    sudo apt-get install python3-dnspython
-
-and/or for other operating systems:
-
-    pip install dnspython
-
-See https://dnspython.readthedocs.io/en/latest/installation.html for more information.
diff --git a/contrib/seeds/asmap.py b/contrib/seeds/asmap.py
new file mode 100644
index 0000000000..e7e05a1d10
--- /dev/null
+++ b/contrib/seeds/asmap.py
@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+# Copyright (c) 2013-2020 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+import ipaddress
+
+# Convert a byte array to a bit array
+def DecodeBytes(byts):
+    return [(byt >> i) & 1 for byt in byts for i in range(8)]
+
+def DecodeBits(stream, bitpos, minval, bit_sizes):
+    val = minval
+    for pos in range(len(bit_sizes)):
+        bit_size = bit_sizes[pos]
+        if pos + 1 < len(bit_sizes):
+            bit = stream[bitpos]
+            bitpos += 1
+        else:
+            bit = 0
+        if bit:
+            val += (1 << bit_size)
+        else:
+            for b in range(bit_size):
+                bit = stream[bitpos]
+                bitpos += 1
+                val += bit << (bit_size - 1 - b)
+            return (val, bitpos)
+    assert(False)
+
+def DecodeType(stream, bitpos):
+    return DecodeBits(stream, bitpos, 0, [0, 0, 1])
+
+def DecodeASN(stream, bitpos):
+    return DecodeBits(stream, bitpos, 1, [15, 16, 17, 18, 19, 20, 21, 22, 23, 24])
+
+def DecodeMatch(stream, bitpos):
+    return DecodeBits(stream, bitpos, 2, [1, 2, 3, 4, 5, 6, 7, 8])
+
+def DecodeJump(stream, bitpos):
+    return DecodeBits(stream, bitpos, 17, [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30])
+
+def Interpret(asmap, num, bits):
+    pos = 0
+    default = None
+    while True:
+        assert(len(asmap) >= pos + 1)
+        (opcode, pos) = DecodeType(asmap, pos)
+        if opcode == 0:
+            (asn, pos) = DecodeASN(asmap, pos)
+            return asn
+        elif opcode == 1:
+            (jump, pos) = DecodeJump(asmap, pos)
+            if (num >> (bits - 1)) & 1:
+                pos += jump
+            bits -= 1
+        elif opcode == 2:
+            (match, pos) = DecodeMatch(asmap, pos)
+            matchlen = match.bit_length() - 1
+            for bit in range(matchlen):
+                if ((num >> (bits - 1)) & 1) != ((match >> (matchlen - 1 - bit)) & 1):
+                    return default
+                bits -= 1
+        elif opcode == 3:
+            (default, pos) = DecodeASN(asmap, pos)
+        else:
+            assert(False)
+
+
+
+def decode_ip(ip: str) -> int:
+    addr = ipaddress.ip_address(ip)
+    if isinstance(addr, ipaddress.IPv4Address):
+        return int.from_bytes(addr.packed, 'big') + 0xffff00000000
+    elif isinstance(addr, ipaddress.IPv6Address):
+        return int.from_bytes(addr.packed, 'big')
+
+class ASMap:
+    def __init__(self, filename):
+        '''
+        Instantiate an ASMap from a file.
+        '''
+        with open(filename, "rb") as f:
+            self.asmap = DecodeBytes(f.read())
+
+    def lookup_asn(self, ip):
+        '''
+        Look up the ASN for an IP, returns an ASN id as integer or None if not
+        known.
+        '''
+        return Interpret(self.asmap, decode_ip(ip), 128)
diff --git a/contrib/seeds/makeseeds.py b/contrib/seeds/makeseeds.py
index 78eb04a836..23b40cf028 100755
--- a/contrib/seeds/makeseeds.py
+++ b/contrib/seeds/makeseeds.py
@@ -6,12 +6,14 @@
 # Generate seeds.txt from Pieter's DNS seeder
 #
 
+import argparse
 import re
 import sys
-import dns.resolver
 import collections
 from typing import List, Dict, Union
 
+from asmap import ASMap
+
 NSEEDS=512
 
 MAX_SEEDS_PER_ASN = {
@@ -123,34 +125,8 @@ def filtermultiport(ips: List[Dict]) -> List[Dict]:
         hist[ip['sortkey']].append(ip)
     return [value[0] for (key,value) in list(hist.items()) if len(value)==1]
 
-def lookup_asn(net: str, ip: str) -> Union[int, None]:
-    """ Look up the asn for an `ip` address by querying cymru.com
-    on network `net` (e.g. ipv4 or ipv6).
-
-    Returns in integer ASN or None if it could not be found.
-    """
-    try:
-        if net == 'ipv4':
-            ipaddr = ip
-            prefix = '.origin'
-        else:                  # http://www.team-cymru.com/IP-ASN-mapping.html
-            res = str()                         # 2001:4860:b002:23::68
-            for nb in ip.split(':')[:4]:  # pick the first 4 nibbles
-                for c in nb.zfill(4):           # right padded with '0'
-                    res += c + '.'              # 2001 4860 b002 0023
-            ipaddr = res.rstrip('.')            # 2.0.0.1.4.8.6.0.b.0.0.2.0.0.2.3
-            prefix = '.origin6'
-
-        asn = int([x.to_text() for x in dns.resolver.resolve('.'.join(
-                   reversed(ipaddr.split('.'))) + prefix + '.asn.cymru.com',
-                   'TXT').response.answer][0].split('\"')[1].split(' ')[0])
-        return asn
-    except Exception as e:
-        sys.stderr.write(f'ERR: Could not resolve ASN for "{ip}": {e}\n')
-        return None
-
 # Based on Greg Maxwell's seed_filter.py
-def filterbyasn(ips: List[Dict], max_per_asn: Dict, max_per_net: int) -> List[Dict]:
+def filterbyasn(asmap: ASMap, ips: List[Dict], max_per_asn: Dict, max_per_net: int) -> List[Dict]:
     """ Prunes `ips` by
     (a) trimming ips to have at most `max_per_net` ips from each net (e.g. ipv4, ipv6); and
     (b) trimming ips to have at most `max_per_asn` ips from each asn in each net.
@@ -173,13 +149,14 @@ def filterbyasn(ips: List[Dict], max_per_asn: Dict, max_per_net: int) -> List[Di
             # do not add this ip as we already too many
             # ips from this network
             continue
-        asn = lookup_asn(ip['net'], ip['ip'])
-        if asn is None or asn_count[asn] == max_per_asn[ip['net']]:
+        asn = asmap.lookup_asn(ip['ip'])
+        if asn is None or asn_count[ip['net'], asn] == max_per_asn[ip['net']]:
             # do not add this ip as we already have too many
             # ips from this ASN on this network
             continue
-        asn_count[asn] += 1
+        asn_count[ip['net'], asn] += 1
         net_count[ip['net']] += 1
+        ip['asn'] = asn
         result.append(ip)
 
     # Add back Onions (up to max_per_net)
@@ -195,7 +172,18 @@ def ip_stats(ips: List[Dict]) -> str:
 
     return f"{hist['ipv4']:6d} {hist['ipv6']:6d} {hist['onion']:6d}"
 
+def parse_args():
+    argparser = argparse.ArgumentParser(description='Generate a list of bitcoin node seed ip addresses.')
+    argparser.add_argument("-a","--asmap", help='the location of the asmap asn database file (required)', required=True)
+    return argparser.parse_args()
+
 def main():
+    args = parse_args()
+
+    print(f'Loading asmap database "{args.asmap}"…', end='', file=sys.stderr, flush=True)
+    asmap = ASMap(args.asmap)
+    print('Done.', file=sys.stderr)
+
     lines = sys.stdin.readlines()
     ips = [parseline(line) for line in lines]
 
@@ -230,15 +218,18 @@ def main():
     ips = filtermultiport(ips)
     print(f'{ip_stats(ips):s} Filter out hosts with multiple bitcoin ports', file=sys.stderr)
     # Look up ASNs and limit results, both per ASN and globally.
-    ips = filterbyasn(ips, MAX_SEEDS_PER_ASN, NSEEDS)
+    ips = filterbyasn(asmap, ips, MAX_SEEDS_PER_ASN, NSEEDS)
     print(f'{ip_stats(ips):s} Look up ASNs and limit results per ASN and per net', file=sys.stderr)
     # 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']))
+            print(f"[{ip['ip']}]:{ip['port']}", end="")
         else:
-            print('%s:%i' % (ip['ip'], ip['port']))
+            print(f"{ip['ip']}:{ip['port']}", end="")
+        if 'asn' in ip:
+            print(f" # AS{ip['asn']}", end="")
+        print()
 
 if __name__ == '__main__':
     main()