Compare ASMaps with respect to specific addresses

Introduce diff_addrs subcommand as means for a Bitcoin-centric
comparison of two ASMaps.

In addition to two ASMaps, the subcommand reads addresses from
a (getnodeaddresses-compatible) file, and provides information on
addresses that have mismatching ASN according to the two ASMaps.

contrib/asmap/asmap-tool.py

@@ -6,7 +6,9 @@
 import argparse
 import sys
 import ipaddress
+import json
 import math
+from collections import defaultdict
 
 import asmap
 
@@ -113,6 +115,18 @@ def main():
     parser_diff.add_argument('infile2', type=argparse.FileType('rb'),
                              help="second file to compare (text or binary)")
 
+    parser_diff_addrs = subparsers.add_parser("diff_addrs",
+                                              help="compute difference between two asmap files for a set of addresses")
+    parser_diff_addrs.add_argument('-s', '--show-addresses', dest="show_addresses", default=False, action="store_true",
+                                   help="include reassigned addresses in the output")
+    parser_diff_addrs.add_argument("infile1", type=argparse.FileType("rb"),
+                                   help="first file to compare (text or binary)")
+    parser_diff_addrs.add_argument("infile2", type=argparse.FileType("rb"),
+                                   help="second file to compare (text or binary)")
+    parser_diff_addrs.add_argument("addrs_file", type=argparse.FileType("r"),
+                                   help="address file containing getnodeaddresses output to use in the comparison "
+                                   "(make sure to set the count parameter to zero to get all node addresses, "
+                                   "e.g. 'bitcoin-cli getnodeaddresses 0 > addrs.json')")
     args = parser.parse_args()
     if args.subcommand is None:
         parser.print_help()
@@ -148,6 +162,33 @@ def main():
             f"# {ipv4_changed}{ipv4_change_str} IPv4 addresses changed; "
             f"{ipv6_changed}{ipv6_change_str} IPv6 addresses changed"
         )
+    elif args.subcommand == "diff_addrs":
+        state1 = load_file(args.infile1)
+        state2 = load_file(args.infile2)
+        address_info = json.load(args.addrs_file)
+        addrs = {a["address"] for a in address_info if a["network"] in ["ipv4", "ipv6"]}
+        reassignments = defaultdict(list)
+        for addr in addrs:
+            net = ipaddress.ip_network(addr)
+            prefix = asmap.net_to_prefix(net)
+            old_asn = state1.lookup(prefix)
+            new_asn = state2.lookup(prefix)
+            if new_asn != old_asn:
+                reassignments[(old_asn, new_asn)].append(addr)
+        reassignments = sorted(reassignments.items(), key=lambda item: len(item[1]), reverse=True)
+        num_reassignment_type = defaultdict(int)
+        for (old_asn, new_asn), reassigned_addrs in reassignments:
+            num_reassigned = len(reassigned_addrs)
+            num_reassignment_type[(bool(old_asn), bool(new_asn))] += num_reassigned
+            old_asn_str = f"AS{old_asn}" if old_asn else "unassigned"
+            new_asn_str = f"AS{new_asn}" if new_asn else "unassigned"
+            opt = ": " + ", ".join(reassigned_addrs) if args.show_addresses else ""
+            print(f"{num_reassigned} address(es) reassigned from {old_asn_str} to {new_asn_str}{opt}")
+        num_reassignments = sum(len(addrs) for _, addrs in reassignments)
+        share = num_reassignments / len(addrs) if len(addrs) > 0 else 0
+        print(f"Summary: {num_reassignments:,} ({share:.2%}) of {len(addrs):,} addresses were reassigned "
+              f"(migrations={num_reassignment_type[True, True]}, assignments={num_reassignment_type[False, True]}, "
+              f"unassignments={num_reassignment_type[True, False]})")
     else:
         parser.print_help()
         sys.exit("No command provided.")