Merge bitcoin/bitcoin#24864: contrib: Use asmap for ASN lookup in makeseeds

667e316bcb300eec131727a7ce54dd038031e267 contrib: Update makeseeds to asmap-nextgen (laanwj)
ae00b9e02c819a69293fdcdab91f57b33e9275d9 contrib: add seeds progress indicator and remove asmap one in makeseeds script (Jon Atack)
b54180303de0df9be7023577f35648225cf95443 contrib: Use asmap for ASN lookup in makeseeds (laanwj)

Pull request description:

  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 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: russeree <reese.russell@ymail.com>

ACKs for top commit:
  sipa:
    ACK 667e316bcb300eec131727a7ce54dd038031e267
  dunxen:
    re-ACK 667e316

Tree-SHA512: c4cedfbd1dee6be7547aa92dd9e262c46f0ff8099e647559b2a40eab0cc9874e9a813706630dd5c880390d23f432e789fb3e7e8a09f376f567071e68f5904c65

4 files changed, 850 insertions, 53 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..7a605d0b9e
--- /dev/null
+++ b/contrib/seeds/asmap.py
@@ -0,0 +1,815 @@
+# Copyright (c) 2022 Pieter Wuille
+# Distributed under the MIT software license, see the accompanying
+# file LICENSE or http://www.opensource.org/licenses/mit-license.php.
+
+"""
+This module provides the ASNEntry and ASMap classes.
+"""
+
+import copy
+import ipaddress
+import random
+import unittest
+from enum import Enum
+from functools import total_ordering
+from typing import Callable, Dict, Iterable, List, Optional, Tuple, Union, overload
+
+def net_to_prefix(net: Union[ipaddress.IPv4Network,ipaddress.IPv6Network]) -> List[bool]:
+    """
+    Convert an IPv4 or IPv6 network to a prefix represented as a list of bits.
+
+    IPv4 ranges are remapped to their IPv4-mapped IPv6 range (::ffff:0:0/96).
+    """
+    num_bits = net.prefixlen
+    netrange = int.from_bytes(net.network_address.packed, 'big')
+
+    # Map an IPv4 prefix into IPv6 space.
+    if isinstance(net, ipaddress.IPv4Network):
+        num_bits += 96
+        netrange += 0xffff00000000
+
+    # Strip unused bottom bits.
+    assert (netrange & ((1 << (128 - num_bits)) - 1)) == 0
+    return [((netrange >> (127 - i)) & 1) != 0 for i in range(num_bits)]
+
+def prefix_to_net(prefix: List[bool]) -> Union[ipaddress.IPv4Network,ipaddress.IPv6Network]:
+    """The reverse operation of net_to_prefix."""
+    # Convert to number
+    netrange = sum(b << (127 - i) for i, b in enumerate(prefix))
+    num_bits = len(prefix)
+    assert num_bits <= 128
+
+    # Return IPv4 range if in ::ffff:0:0/96
+    if num_bits >= 96 and (netrange >> 32) == 0xffff:
+        return ipaddress.IPv4Network((netrange & 0xffffffff, num_bits - 96), True)
+
+    # Return IPv6 range otherwise.
+    return ipaddress.IPv6Network((netrange, num_bits), True)
+
+# Shortcut for (prefix, ASN) entries.
+ASNEntry = Tuple[List[bool], int]
+
+# Shortcut for (prefix, old ASN, new ASN) entries.
+ASNDiff = Tuple[List[bool], int, int]
+
+class _VarLenCoder:
+    """
+    A class representing a custom variable-length binary encoder/decoder for
+    integers. Each object represents a different coder, with different parameters
+    minval and clsbits.
+
+    The encoding is easiest to describe using an example. Let's say minval=100 and
+    clsbits=[4,2,2,3]. In that case:
+    - x in [100..115]: encoded as [0] + [4-bit BE encoding of (x-100)].
+    - x in [116..119]: encoded as [1,0] + [2-bit BE encoding of (x-116)].
+    - x in [120..123]: encoded as [1,1,0] + [2-bit BE encoding of (x-120)].
+    - x in [124..131]: encoded as [1,1,1] + [3-bit BE encoding of (x-124)].
+
+    In general, every number is encoded as:
+    - First, k "1"-bits, where k is the class the number falls in (there is one class
+      per element of clsbits).
+    - Then, a "0"-bit, unless k is the highest class, in which case there is nothing.
+    - Lastly, clsbits[k] bits encoding in big endian the position in its class that
+      number falls into.
+    - Every class k consists of 2^clsbits[k] consecutive integers. k=0 starts at minval,
+      other classes start one past the last element of the class before it.
+    """
+
+    def __init__(self, minval: int, clsbits: List[int]):
+        """Construct a new _VarLenCoder."""
+        self._minval = minval
+        self._clsbits = clsbits
+        self._maxval = minval + sum(1 << b for b in clsbits) - 1
+
+    def can_encode(self, val: int) -> bool:
+        """Check whether value val is in the range this coder supports."""
+        return self._minval <= val <= self._maxval
+
+    def encode(self, val: int, ret: List[int]) -> None:
+        """Append encoding of val onto integer list ret."""
+
+        assert self._minval <= val <= self._maxval
+        val -= self._minval
+        bits = 0
+        for k, bits in enumerate(self._clsbits):
+            if val >> bits:
+                # If the value will not fit in class k, subtract its range from v,
+                # emit a "1" bit and continue with the next class.
+                val -= 1 << bits
+                ret.append(1)
+            else:
+                if k + 1 < len(self._clsbits):
+                    # Unless we're in the last class, emit a "0" bit.
+                    ret.append(0)
+                break
+        # And then encode v (now the position within the class) in big endian.
+        ret.extend((val >> (bits - 1 - b)) & 1 for b in range(bits))
+
+    def encode_size(self, val: int) -> int:
+        """Compute how many bits are needed to encode val."""
+        assert self._minval <= val <= self._maxval
+        val -= self._minval
+        ret = 0
+        bits = 0
+        for k, bits in enumerate(self._clsbits):
+            if val >> bits:
+                val -= 1 << bits
+                ret += 1
+            else:
+                ret += k + 1 < len(self._clsbits)
+                break
+        return ret + bits
+
+    def decode(self, stream, bitpos) -> Tuple[int,int]:
+        """Decode a number starting at bitpos in stream, returning value and new bitpos."""
+        val = self._minval
+        bits = 0
+        for k, bits in enumerate(self._clsbits):
+            bit = 0
+            if k + 1 < len(self._clsbits):
+                bit = stream[bitpos]
+                bitpos += 1
+            if not bit:
+                break
+            val += 1 << bits
+        for i in range(bits):
+            bit = stream[bitpos]
+            bitpos += 1
+            val += bit << (bits - 1 - i)
+        return val, bitpos
+
+# Variable-length encoders used in the binary asmap format.
+_CODER_INS = _VarLenCoder(0, [0, 0, 1])
+_CODER_ASN = _VarLenCoder(1, list(range(15, 25)))
+_CODER_MATCH = _VarLenCoder(2, list(range(1, 9)))
+_CODER_JUMP = _VarLenCoder(17, list(range(5, 31)))
+
+class _Instruction(Enum):
+    """One instruction in the binary asmap format."""
+    # A return instruction, encoded as [0], returns a constant ASN. It is followed by
+    # an integer using the ASN encoding.
+    RETURN = 0
+    # A jump instruction, encoded as [1,0] inspects the next unused bit in the input
+    # and either continues execution (if 0), or skips a specified number of bits (if 1).
+    # It is followed by an integer, and then two subprograms. The integer uses jump encoding
+    # and corresponds to the length of the first subprogram (so it can be skipped).
+    JUMP = 1
+    # A match instruction, encoded as [1,1,0] inspects 1 or more of the next unused bits
+    # in the input with its argument. If they all match, execution continues. If they do
+    # not, failure is returned. If a default instruction has been executed before, instead
+    # of failure the default instruction's argument is returned. It is followed by an
+    # integer in match encoding, and a subprogram. That value is at least 2 bits and at
+    # most 9 bits. An n-bit value signifies matching (n-1) bits in the input with the lower
+    # (n-1) bits in the match value.
+    MATCH = 2
+    # A default instruction, encoded as [1,1,1] sets the default variable to its argument,
+    # and continues execution. It is followed by an integer in ASN encoding, and a subprogram.
+    DEFAULT = 3
+    # Not an actual instruction, but a way to encode the empty program that fails. In the
+    # encoder, it is used more generally to represent the failure case inside MATCH instructions,
+    # which may (if used inside the context of a DEFAULT instruction) actually correspond to
+    # a succesful return. In this usage, they're always converted to an actual MATCH or RETURN
+    # before the top level is reached (see make_default below).
+    END = 4
+
+class _BinNode:
+    """A class representing a (node of) the parsed binary asmap format."""
+
+    @overload
+    def __init__(self, ins: _Instruction): ...
+    @overload
+    def __init__(self, ins: _Instruction, arg1: int): ...
+    @overload
+    def __init__(self, ins: _Instruction, arg1: "_BinNode", arg2: "_BinNode"): ...
+    @overload
+    def __init__(self, ins: _Instruction, arg1: int, arg2: "_BinNode"): ...
+
+    def __init__(self, ins: _Instruction, arg1=None, arg2=None):
+        """
+        Construct a new asmap node. Possibilities are:
+        - _BinNode(_Instruction.RETURN, asn)
+        - _BinNode(_Instruction.JUMP, node_0, node_1)
+        - _BinNode(_Instruction.MATCH, val, node)
+        - _BinNode(_Instruction.DEFAULT, asn, node)
+        - _BinNode(_Instruction.END)
+        """
+        self.ins = ins
+        self.arg1 = arg1
+        self.arg2 = arg2
+        if ins == _Instruction.RETURN:
+            assert isinstance(arg1, int)
+            assert arg2 is None
+            self.size = _CODER_INS.encode_size(ins.value) + _CODER_ASN.encode_size(arg1)
+        elif ins == _Instruction.JUMP:
+            assert isinstance(arg1, _BinNode)
+            assert isinstance(arg2, _BinNode)
+            self.size = (_CODER_INS.encode_size(ins.value) + _CODER_JUMP.encode_size(arg1.size) +
+                         arg1.size + arg2.size)
+        elif ins == _Instruction.DEFAULT:
+            assert isinstance(arg1, int)
+            assert isinstance(arg2, _BinNode)
+            self.size = _CODER_INS.encode_size(ins.value) + _CODER_ASN.encode_size(arg1) + arg2.size
+        elif ins == _Instruction.MATCH:
+            assert isinstance(arg1, int)
+            assert isinstance(arg2, _BinNode)
+            self.size = (_CODER_INS.encode_size(ins.value) + _CODER_MATCH.encode_size(arg1)
+                         + arg2.size)
+        elif ins == _Instruction.END:
+            assert arg1 is None
+            assert arg2 is None
+            self.size = 0
+        else:
+            assert False
+
+    @staticmethod
+    def make_end() -> "_BinNode":
+        """Constructor for a _BinNode with just an END instruction."""
+        return _BinNode(_Instruction.END)
+
+    @staticmethod
+    def make_leaf(val: int) -> "_BinNode":
+        """Constructor for a _BinNode of just a RETURN instruction."""
+        assert val is not None and val > 0
+        return _BinNode(_Instruction.RETURN, val)
+
+    @staticmethod
+    def make_branch(node0: "_BinNode", node1: "_BinNode") -> "_BinNode":
+        """
+        Construct a _BinNode corresponding to running either the node0 or node1 subprogram,
+        based on the next input bit. It exploits shortcuts that are possible in the encoding,
+        and uses either a JUMP, MATCH, or END instruction.
+        """
+        if node0.ins == _Instruction.END and node1.ins == _Instruction.END:
+            return node0
+        if node0.ins == _Instruction.END:
+            if node1.ins == _Instruction.MATCH and node1.arg1 <= 0xFF:
+                return _BinNode(node1.ins, node1.arg1 + (1 << node1.arg1.bit_length()), node1.arg2)
+            return _BinNode(_Instruction.MATCH, 3, node1)
+        if node1.ins == _Instruction.END:
+            if node0.ins == _Instruction.MATCH and node0.arg1 <= 0xFF:
+                return _BinNode(node0.ins, node0.arg1 + (1 << (node0.arg1.bit_length() - 1)),
+                                node0.arg2)
+            return _BinNode(_Instruction.MATCH, 2, node0)
+        return _BinNode(_Instruction.JUMP, node0, node1)
+
+    @staticmethod
+    def make_default(val: int, sub: "_BinNode") -> "_BinNode":
+        """
+        Construct a _BinNode that corresponds to the specified subprogram, with the specified
+        default value. It exploits shortcuts that are possible in the encoding, and will use
+        either a DEFAULT or a RETURN instruction."""
+        assert val is not None and val > 0
+        if sub.ins == _Instruction.END:
+            return _BinNode(_Instruction.RETURN, val)
+        if sub.ins in (_Instruction.RETURN, _Instruction.DEFAULT):
+            return sub
+        return _BinNode(_Instruction.DEFAULT, val, sub)
+
+@total_ordering
+class ASMap:
+    """
+    A class whose objects represent a mapping from subnets to ASNs.
+
+    Internally the mapping is stored as a binary trie, but can be converted
+    from/to a list of ASNEntry objects, and from/to the binary asmap file format.
+
+    In the trie representation, nodes are represented as bare lists for efficiency
+    and ease of manipulation:
+    - [0] means an unassigned subnet (no ASN mapping for it is present)
+    - [int] means a subnet mapped entirely to the specified ASN.
+    - [node,node] means a subnet whose lower half and upper half have different
+    -             mappings, represented by new trie nodes.
+    """
+
+    def update(self, prefix: List[bool], asn: int) -> None:
+        """Update this ASMap object to map prefix to the specified asn."""
+        assert asn == 0 or _CODER_ASN.can_encode(asn)
+
+        def recurse(node: List, offset: int) -> None:
+            if offset == len(prefix):
+                # Reached the end of prefix; overwrite this node.
+                node.clear()
+                node.append(asn)
+                return
+            if len(node) == 1:
+                # Need to descend into a leaf node; split it up.
+                oldasn = node[0]
+                node.clear()
+                node.append([oldasn])
+                node.append([oldasn])
+            # Descend into the node.
+            recurse(node[prefix[offset]], offset + 1)
+            # If the result is two identical leaf children, merge them.
+            if len(node[0]) == 1 and len(node[1]) == 1 and node[0] == node[1]:
+                oldasn = node[0][0]
+                node.clear()
+                node.append(oldasn)
+        recurse(self._trie, 0)
+
+    def update_multi(self, entries: List[Tuple[List[bool], int]]) -> None:
+        """Apply multiple update operations, where longer prefixes take precedence."""
+        entries.sort(key=lambda entry: len(entry[0]))
+        for prefix, asn in entries:
+            self.update(prefix, asn)
+
+    def _set_trie(self, trie) -> None:
+        """Set trie directly. Internal use only."""
+        def recurse(node: List) -> None:
+            if len(node) < 2:
+                return
+            recurse(node[0])
+            recurse(node[1])
+            if len(node[0]) == 2:
+                return
+            if node[0] == node[1]:
+                if len(node[0]) == 0:
+                    node.clear()
+                else:
+                    asn = node[0][0]
+                    node.clear()
+                    node.append(asn)
+        recurse(trie)
+        self._trie = trie
+
+    def __init__(self, entries: Optional[Iterable[ASNEntry]] = None) -> None:
+        """Construct an ASMap object from an optional list of entries."""
+        self._trie = [0]
+        if entries is not None:
+            def entry_key(entry):
+                """Sort function that places shorter prefixes first."""
+                prefix, asn = entry
+                return len(prefix), prefix, asn
+            for prefix, asn in sorted(entries, key=entry_key):
+                self.update(prefix, asn)
+
+    def lookup(self, prefix: List[bool]) -> Optional[int]:
+        """Look up a prefix. Returns ASN, or 0 if unassigned, or None if indeterminate."""
+        node = self._trie
+        for bit in prefix:
+            if len(node) == 1:
+                break
+            node = node[bit]
+        if len(node) == 1:
+            return node[0]
+        return None
+
+    def _to_entries_flat(self, fill: bool = False) -> List[ASNEntry]:
+        """Convert an ASMap object to a list of non-overlapping (prefix, asn) objects."""
+        prefix : List[bool] = []
+
+        def recurse(node: List) -> List[ASNEntry]:
+            ret = []
+            if len(node) == 1:
+                if node[0] > 0:
+                    ret = [(list(prefix), node[0])]
+            elif len(node) == 2:
+                prefix.append(False)
+                ret = recurse(node[0])
+                prefix[-1] = True
+                ret += recurse(node[1])
+                prefix.pop()
+                if fill and len(ret) > 1:
+                    asns = set(x[1] for x in ret)
+                    if len(asns) == 1:
+                        ret = [(list(prefix), list(asns)[0])]
+            return ret
+        return recurse(self._trie)
+
+    def _to_entries_minimal(self, fill: bool = False) -> List[ASNEntry]:
+        """Convert a trie to a minimal list of ASNEntry objects, exploiting overlap."""
+        prefix : List[bool] = []
+
+        def recurse(node: List) -> (Tuple[Dict[Optional[int], List[ASNEntry]], bool]):
+            if len(node) == 1 and node[0] == 0:
+                return {None if fill else 0: []}, True
+            if len(node) == 1:
+                return {node[0]: [], None: [(list(prefix), node[0])]}, False
+            ret: Dict[Optional[int], List[ASNEntry]] = {}
+            prefix.append(False)
+            left, lhole = recurse(node[0])
+            prefix[-1] = True
+            right, rhole = recurse(node[1])
+            prefix.pop()
+            hole = not fill and (lhole or rhole)
+            def candidate(ctx: Optional[int], res0: Optional[List[ASNEntry]],
+                    res1: Optional[List[ASNEntry]]):
+                if res0 is not None and res1 is not None:
+                    if ctx not in ret or len(res0) + len(res1) < len(ret[ctx]):
+                        ret[ctx] = res0 + res1
+            for ctx in set(left) | set(right):
+                candidate(ctx, left.get(ctx), right.get(ctx))
+                candidate(ctx, left.get(None), right.get(ctx))
+                candidate(ctx, left.get(ctx), right.get(None))
+            if not hole:
+                for ctx in list(ret):
+                    if ctx is not None:
+                        candidate(None, [(list(prefix), ctx)], ret[ctx])
+            if None in ret:
+                ret = {ctx:entries for ctx, entries in ret.items()
+                       if ctx is None or len(entries) < len(ret[None])}
+            if hole:
+                ret = {ctx:entries for ctx, entries in ret.items() if ctx is None or ctx == 0}
+            return ret, hole
+        res, _ = recurse(self._trie)
+        return res[0] if 0 in res else res[None]
+
+    def __str__(self) -> str:
+        """Convert this ASMap object to a string containing Python code constructing it."""
+        return f"ASMap({self._trie})"
+
+    def to_entries(self, overlapping: bool = True, fill: bool = False) -> List[ASNEntry]:
+        """
+        Convert the mappings in this ASMap object to a list of ASNEntry objects.
+
+        Arguments:
+            overlapping: Permit the subnets in the resulting ASNEntry to overlap.
+                         Setting this can result in a shorter list.
+            fill:        Permit the resulting ASNEntry objects to cover subnets that
+                         are unassigned in this ASMap object. Setting this can
+                         result in a shorter list.
+        """
+        if overlapping:
+            return self._to_entries_minimal(fill)
+        return self._to_entries_flat(fill)
+
+    @staticmethod
+    def from_random(num_leaves: int = 10, max_asn: int = 6,
+                    unassigned_prob: float = 0.5) -> "ASMap":
+        """
+        Construct a random ASMap object, with specified:
+         - Number of leaves in its trie (at least 1)
+         - Maximum ASN value (at least 1)
+         - Probability for leaf nodes to be unassigned
+
+        The number of leaves in the resulting object may be less than what is
+        requested. This method is mostly intended for testing.
+        """
+        assert num_leaves >= 1
+        assert max_asn >= 1 or unassigned_prob == 1
+        assert _CODER_ASN.can_encode(max_asn)
+        assert 0.0 <= unassigned_prob <= 1.0
+        trie: List = []
+        leaves = [trie]
+        ret = ASMap()
+        for i in range(1, num_leaves):
+            idx = random.randrange(i)
+            leaf = leaves[idx]
+            lastleaf = leaves.pop()
+            if idx + 1 < i:
+                leaves[idx] = lastleaf
+            leaf.append([])
+            leaf.append([])
+            leaves.append(leaf[0])
+            leaves.append(leaf[1])
+        for leaf in leaves:
+            if random.random() >= unassigned_prob:
+                leaf.append(random.randrange(1, max_asn + 1))
+            else:
+                leaf.append(0)
+        #pylint: disable=protected-access
+        ret._set_trie(trie)
+        return ret
+
+    def _to_binnode(self, fill: bool = False) -> _BinNode:
+        """Convert a trie to a _BinNode object."""
+        def recurse(node: List) -> Tuple[Dict[Optional[int], _BinNode], bool]:
+            if len(node) == 1 and node[0] == 0:
+                return {(None if fill else 0): _BinNode.make_end()}, True
+            if len(node) == 1:
+                return {None: _BinNode.make_leaf(node[0]), node[0]: _BinNode.make_end()}, False
+            ret: Dict[Optional[int], _BinNode] = {}
+            left, lhole = recurse(node[0])
+            right, rhole = recurse(node[1])
+            hole = (lhole or rhole) and not fill
+
+            def candidate(ctx: Optional[int], arg1, arg2, func: Callable):
+                if arg1 is not None and arg2 is not None:
+                    cand = func(arg1, arg2)
+                    if ctx not in ret or cand.size < ret[ctx].size:
+                        ret[ctx] = cand
+
+            for ctx in set(left) | set(right):
+                candidate(ctx, left.get(ctx), right.get(ctx), _BinNode.make_branch)
+                candidate(ctx, left.get(None), right.get(ctx), _BinNode.make_branch)
+                candidate(ctx, left.get(ctx), right.get(None), _BinNode.make_branch)
+            if not hole:
+                for ctx in set(ret) - set([None]):
+                    candidate(None, ctx, ret[ctx], _BinNode.make_default)
+            if None in ret:
+                ret = {ctx:enc for ctx, enc in ret.items()
+                       if ctx is None or enc.size < ret[None].size}
+            if hole:
+                ret = {ctx:enc for ctx, enc in ret.items() if ctx is None or ctx == 0}
+            return ret, hole
+        res, _ = recurse(self._trie)
+        return res[0] if 0 in res else res[None]
+
+    @staticmethod
+    def _from_binnode(binnode: _BinNode) -> "ASMap":
+        """Construct an ASMap object from a _BinNode. Internal use only."""
+        def recurse(node: _BinNode, default: int) -> List:
+            if node.ins == _Instruction.RETURN:
+                return [node.arg1]
+            if node.ins == _Instruction.JUMP:
+                return [recurse(node.arg1, default), recurse(node.arg2, default)]
+            if node.ins == _Instruction.MATCH:
+                val = node.arg1
+                sub = recurse(node.arg2, default)
+                while val >= 2:
+                    bit = val & 1
+                    val >>= 1
+                    if bit:
+                        sub = [[default], sub]
+                    else:
+                        sub = [sub, [default]]
+                return sub
+            assert node.ins == _Instruction.DEFAULT
+            return recurse(node.arg2, node.arg1)
+        ret = ASMap()
+        if binnode.ins != _Instruction.END:
+            #pylint: disable=protected-access
+            ret._set_trie(recurse(binnode, 0))
+        return ret
+
+    def to_binary(self, fill: bool = False) -> bytes:
+        """
+        Convert this ASMap object to binary.
+
+        Argument:
+            fill: permit the resulting binary encoder to contain mappers for
+                  unassigned subnets in this ASMap object. Doing so may
+                  reduce the size of the encoding.
+        Returns:
+            A bytes object with the encoding of this ASMap object.
+        """
+        bits: List[int] = []
+
+        def recurse(node: _BinNode) -> None:
+            _CODER_INS.encode(node.ins.value, bits)
+            if node.ins == _Instruction.RETURN:
+                _CODER_ASN.encode(node.arg1, bits)
+            elif node.ins == _Instruction.JUMP:
+                _CODER_JUMP.encode(node.arg1.size, bits)
+                recurse(node.arg1)
+                recurse(node.arg2)
+            elif node.ins == _Instruction.DEFAULT:
+                _CODER_ASN.encode(node.arg1, bits)
+                recurse(node.arg2)
+            else:
+                assert node.ins == _Instruction.MATCH
+                _CODER_MATCH.encode(node.arg1, bits)
+                recurse(node.arg2)
+
+        binnode = self._to_binnode(fill)
+        if binnode.ins != _Instruction.END:
+            recurse(binnode)
+
+        val = 0
+        nbits = 0
+        ret = []
+        for bit in bits:
+            val += (bit << nbits)
+            nbits += 1
+            if nbits == 8:
+                ret.append(val)
+                val = 0
+                nbits = 0
+        if nbits:
+            ret.append(val)
+        return bytes(ret)
+
+    @staticmethod
+    def from_binary(bindata: bytes) -> Optional["ASMap"]:
+        """Decode an ASMap object from the provided binary encoding."""
+
+        bits: List[int] = []
+        for byte in bindata:
+            bits.extend((byte >> i) & 1 for i in range(8))
+
+        def recurse(bitpos: int) -> Tuple[_BinNode, int]:
+            insval, bitpos = _CODER_INS.decode(bits, bitpos)
+            ins = _Instruction(insval)
+            if ins == _Instruction.RETURN:
+                asn, bitpos = _CODER_ASN.decode(bits, bitpos)
+                return _BinNode(ins, asn), bitpos
+            if ins == _Instruction.JUMP:
+                jump, bitpos = _CODER_JUMP.decode(bits, bitpos)
+                left, bitpos1 = recurse(bitpos)
+                if bitpos1 != bitpos + jump:
+                    raise ValueError("Inconsistent jump")
+                right, bitpos = recurse(bitpos1)
+                return _BinNode(ins, left, right), bitpos
+            if ins == _Instruction.MATCH:
+                match, bitpos = _CODER_MATCH.decode(bits, bitpos)
+                sub, bitpos = recurse(bitpos)
+                return _BinNode(ins, match, sub), bitpos
+            assert ins == _Instruction.DEFAULT
+            asn, bitpos = _CODER_ASN.decode(bits, bitpos)
+            sub, bitpos = recurse(bitpos)
+            return _BinNode(ins, asn, sub), bitpos
+
+        if len(bits) == 0:
+            binnode = _BinNode(_Instruction.END)
+        else:
+            try:
+                binnode, bitpos = recurse(0)
+            except (ValueError, IndexError):
+                return None
+            if bitpos < len(bits) - 7:
+                return None
+            if not all(bit == 0 for bit in bits[bitpos:]):
+                return None
+
+        return ASMap._from_binnode(binnode)
+
+    def __lt__(self, other: "ASMap") -> bool:
+        return self._trie < other._trie
+
+    def __eq__(self, other: object) -> bool:
+        if isinstance(other, ASMap):
+            return self._trie == other._trie
+        return False
+
+    def extends(self, req: "ASMap") -> bool:
+        """Determine whether this matches req for all subranges where req is assigned."""
+        def recurse(actual: List, require: List) -> bool:
+            if len(require) == 1 and require[0] == 0:
+                return True
+            if len(require) == 1:
+                if len(actual) == 1:
+                    return bool(require[0] == actual[0])
+                return recurse(actual[0], require) and recurse(actual[1], require)
+            if len(actual) == 2:
+                return recurse(actual[0], require[0]) and recurse(actual[1], require[1])
+            return recurse(actual, require[0]) and recurse(actual, require[1])
+        assert isinstance(req, ASMap)
+        #pylint: disable=protected-access
+        return recurse(self._trie, req._trie)
+
+    def diff(self, other: "ASMap") -> List[ASNDiff]:
+        """Compute the diff from self to other."""
+        prefix: List[bool] = []
+        ret: List[ASNDiff] = []
+
+        def recurse(old_node: List, new_node: List):
+            if len(old_node) == 1 and len(new_node) == 1:
+                if old_node[0] != new_node[0]:
+                    ret.append((list(prefix), old_node[0], new_node[0]))
+            else:
+                old_left: List = old_node if len(old_node) == 1 else old_node[0]
+                old_right: List = old_node if len(old_node) == 1 else old_node[1]
+                new_left: List = new_node if len(new_node) == 1 else new_node[0]
+                new_right: List = new_node if len(new_node) == 1 else new_node[1]
+                prefix.append(False)
+                recurse(old_left, new_left)
+                prefix[-1] = True
+                recurse(old_right, new_right)
+                prefix.pop()
+        assert isinstance(other, ASMap)
+        #pylint: disable=protected-access
+        recurse(self._trie, other._trie)
+        return ret
+
+    def __copy__(self) -> "ASMap":
+        """Construct a copy of this ASMap object. Its state will not be shared."""
+        ret = ASMap()
+        #pylint: disable=protected-access
+        ret._set_trie(copy.deepcopy(self._trie))
+        return ret
+
+    def __deepcopy__(self, _) -> "ASMap":
+        # ASMap objects do not allow sharing of the _trie member, so we don't need the memoization.
+        return self.__copy__()
+
+
+class TestASMap(unittest.TestCase):
+    """Unit tests for this module."""
+
+    def test_ipv6_prefix_roundtrips(self) -> None:
+        """Test that random IPv6 network ranges roundtrip through prefix encoding."""
+        for _ in range(20):
+            net_bits = random.getrandbits(128)
+            for prefix_len in range(0, 129):
+                masked_bits = (net_bits >> (128 - prefix_len)) << (128 - prefix_len)
+                net = ipaddress.IPv6Network((masked_bits.to_bytes(16, 'big'), prefix_len))
+                prefix = net_to_prefix(net)
+                self.assertTrue(len(prefix) <= 128)
+                net2 = prefix_to_net(prefix)
+                self.assertEqual(net, net2)
+
+    def test_ipv4_prefix_roundtrips(self) -> None:
+        """Test that random IPv4 network ranges roundtrip through prefix encoding."""
+        for _ in range(100):
+            net_bits = random.getrandbits(32)
+            for prefix_len in range(0, 33):
+                masked_bits = (net_bits >> (32 - prefix_len)) << (32 - prefix_len)
+                net = ipaddress.IPv4Network((masked_bits.to_bytes(4, 'big'), prefix_len))
+                prefix = net_to_prefix(net)
+                self.assertTrue(32 <= len(prefix) <= 128)
+                net2 = prefix_to_net(prefix)
+                self.assertEqual(net, net2)
+
+    def test_asmap_roundtrips(self) -> None:
+        """Test case that verifies random ASMap objects roundtrip to/from entries/binary."""
+        # Iterate over the number of leaves the random test ASMap objects have.
+        for leaves in range(1, 20):
+            # Iterate over the number of bits in the AS numbers used.
+            for asnbits in range(0, 24):
+                # Iterate over the probability that leaves are unassigned.
+                for pct in range(101):
+                    # Construct a random ASMap object according to the above parameters.
+                    asmap = ASMap.from_random(num_leaves=leaves, max_asn=1 + (1 << asnbits),
+                                              unassigned_prob=0.01 * pct)
+                    # Run tests for to_entries and construction from those entries, both
+                    # for overlapping and non-overlapping ones.
+                    for overlapping in [False, True]:
+                        entries = asmap.to_entries(overlapping=overlapping, fill=False)
+                        random.shuffle(entries)
+                        asmap2 = ASMap(entries)
+                        assert asmap2 is not None
+                        self.assertEqual(asmap2, asmap)
+                        entries = asmap.to_entries(overlapping=overlapping, fill=True)
+                        random.shuffle(entries)
+                        asmap2 = ASMap(entries)
+                        assert asmap2 is not None
+                        self.assertTrue(asmap2.extends(asmap))
+
+                    # Run tests for to_binary and construction from binary.
+                    enc = asmap.to_binary(fill=False)
+                    asmap3 = ASMap.from_binary(enc)
+                    assert asmap3 is not None
+                    self.assertEqual(asmap3, asmap)
+                    enc = asmap.to_binary(fill=True)
+                    asmap3 = ASMap.from_binary(enc)
+                    assert asmap3 is not None
+                    self.assertTrue(asmap3.extends(asmap))
+
+    def test_patching(self) -> None:
+        """Test behavior of update, lookup, extends, and diff."""
+        #pylint: disable=too-many-locals,too-many-nested-blocks
+        # Iterate over the number of leaves the random test ASMap objects have.
+        for leaves in range(1, 20):
+            # Iterate over the number of bits in the AS numbers used.
+            for asnbits in range(0, 10):
+                # Iterate over the probability that leaves are unassigned.
+                for pct in range(0, 101):
+                    # Construct a random ASMap object according to the above parameters.
+                    asmap = ASMap.from_random(num_leaves=leaves, max_asn=1 + (1 << asnbits),
+                                              unassigned_prob=0.01 * pct)
+                    # Make a copy of that asmap object to which patches will be applied.
+                    # It starts off being equal to asmap.
+                    patched = copy.copy(asmap)
+                    # Keep a list of patches performed.
+                    patches: List[ASNEntry] = []
+                    # Initially there cannot be any difference.
+                    self.assertEqual(asmap.diff(patched), [])
+                    # Make 5 patches, each building on top of the previous ones.
+                    for _ in range(0, 5):
+                        # Construct a random path and new ASN to assign it to, apply it to patched,
+                        # and remember it in patches.
+                        pathlen = random.randrange(5)
+                        path = [random.getrandbits(1) != 0 for _ in range(pathlen)]
+                        newasn = random.randrange(1 + (1 << asnbits))
+                        patched.update(path, newasn)
+                        patches = [(path, newasn)] + patches
+
+                        # Compute the diff, and whether asmap extends patched, and the other way
+                        # around.
+                        diff = asmap.diff(patched)
+                        self.assertEqual(asmap == patched, len(diff) == 0)
+                        extends = asmap.extends(patched)
+                        back_extends = patched.extends(asmap)
+                        # Determine whether those extends results are consistent with the diff
+                        # result.
+                        self.assertEqual(extends, all(d[2] == 0 for d in diff))
+                        self.assertEqual(back_extends, all(d[1] == 0 for d in diff))
+                        # For every diff found:
+                        for path, old_asn, new_asn in diff:
+                            # Verify asmap and patched actually differ there.
+                            self.assertTrue(old_asn != new_asn)
+                            self.assertEqual(asmap.lookup(path), old_asn)
+                            self.assertEqual(patched.lookup(path), new_asn)
+                            for _ in range(2):
+                                # Extend the path far enough that it's smaller than any mapped
+                                # range, and check the lookup holds there too.
+                                spec_path = list(path)
+                                while len(spec_path) < 32:
+                                    spec_path.append(random.getrandbits(1) != 0)
+                                self.assertEqual(asmap.lookup(spec_path), old_asn)
+                                self.assertEqual(patched.lookup(spec_path), new_asn)
+                                # Search through the list of performed patches to find the last one
+                                # applying to the extended path (note that patches is in reverse
+                                # order, so the first match should work).
+                                found = False
+                                for patch_path, patch_asn in patches:
+                                    if spec_path[:len(patch_path)] == patch_path:
+                                        # When found, it must match whatever the result was patched
+                                        # to.
+                                        self.assertEqual(new_asn, patch_asn)
+                                        found = True
+                                        break
+                                # And such a patch must exist.
+                                self.assertTrue(found)
+
+if __name__ == '__main__':
+    unittest.main()
diff --git a/contrib/seeds/makeseeds.py b/contrib/seeds/makeseeds.py
index 78eb04a836..37c6f5fd7c 100755
--- a/contrib/seeds/makeseeds.py
+++ b/contrib/seeds/makeseeds.py
@@ -6,12 +6,15 @@
 # Generate seeds.txt from Pieter's DNS seeder
 #
 
+import argparse
+import ipaddress
 import re
 import sys
-import dns.resolver
 import collections
 from typing import List, Dict, Union
 
+from asmap import ASMap, net_to_prefix
+
 NSEEDS=512
 
 MAX_SEEDS_PER_ASN = {
@@ -45,7 +48,7 @@ def parseline(line: str) -> Union[dict, None]:
     sline = line.split()
     if len(sline) < 11:
         # line too short to be valid, skip it.
-       return None
+        return None
     m = PATTERN_IPV4.match(sline[0])
     sortkey = None
     ip = None
@@ -123,34 +126,8 @@ 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.
@@ -165,21 +142,18 @@ def filterbyasn(ips: List[Dict], max_per_asn: Dict, max_per_net: int) -> List[Di
     asn_count: Dict[int, int] = collections.defaultdict(int)
 
     for i, ip in enumerate(ips_ipv46):
-        if i % 10 == 0:
-            # give progress update
-            print(f"{i:6d}/{len(ips_ipv46)} [{100*i/len(ips_ipv46):04.1f}%]\r", file=sys.stderr, end='', flush=True)
-
         if net_count[ip['net']] == max_per_net:
             # 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(net_to_prefix(ipaddress.ip_network(ip['ip'])))
+        if not asn 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)
@@ -195,9 +169,23 @@ 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)
+    with open(args.asmap, 'rb') as f:
+        asmap = ASMap.from_binary(f.read())
+    print('Done.', file=sys.stderr)
+
+    print('Loading and parsing DNS seeds…', end='', file=sys.stderr, flush=True)
     lines = sys.stdin.readlines()
     ips = [parseline(line) for line in lines]
+    print('Done.', file=sys.stderr)
 
     print('\x1b[7m  IPv4   IPv6  Onion Pass                                               \x1b[0m', file=sys.stderr)
     print(f'{ip_stats(ips):s} Initial', file=sys.stderr)
@@ -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()