pyln.client: new functionality to access Gossmap.

It doesn't do much work, but it does parse the gossmap file and extract
nodes and channels.

[ Fixup by Michael Schmoock <michael@schmoock.net> ]
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

contrib/pyln-client/pyln/client/__init__.py

@@ -1,6 +1,6 @@
 from .lightning import LightningRpc, RpcError, Millisatoshi
 from .plugin import Plugin, monkey_patch, RpcException
-
+from .gossmap import Gossmap
 
 __version__ = "0.10.1"
 
@@ -12,5 +12,6 @@ __all__ = [
     "RpcException",
     "Millisatoshi",
     "__version__",
-    "monkey_patch"
+    "monkey_patch",
+    "Gossmap",
 ]

contrib/pyln-client/pyln/client/gossmap.py

@@ -0,0 +1,188 @@
+#! /usr/bin/python3
+
+from pyln.spec.bolt7 import (channel_announcement, channel_update,
+                             node_announcement)
+from typing import Dict, List, Optional
+
+import io
+import struct
+
+# These duplicate constants in lightning/common/gossip_store.h
+GOSSIP_STORE_VERSION = 9
+GOSSIP_STORE_LEN_DELETED_BIT = 0x80000000
+GOSSIP_STORE_LEN_PUSH_BIT = 0x40000000
+GOSSIP_STORE_LEN_MASK = (~(GOSSIP_STORE_LEN_PUSH_BIT
+                           | GOSSIP_STORE_LEN_DELETED_BIT))
+
+# These duplicate constants in lightning/gossipd/gossip_store_wiregen.h
+WIRE_GOSSIP_STORE_PRIVATE_CHANNEL = 4104
+WIRE_GOSSIP_STORE_PRIVATE_UPDATE = 4102
+WIRE_GOSSIP_STORE_DELETE_CHAN = 4103
+WIRE_GOSSIP_STORE_ENDED = 4105
+
+
+class GossipStoreHeader(object):
+    def __init__(self, buf: bytes):
+        length, self.crc, self.timestamp = struct.unpack('>III', buf)
+        self.deleted = (length & GOSSIP_STORE_LEN_DELETED_BIT) != 0
+        self.length = (length & GOSSIP_STORE_LEN_MASK)
+
+
+# FIXME!
+class short_channel_id(int):
+    pass
+
+
+class point(bytes):
+    pass
+
+
+class GossmapChannel(object):
+    def __init__(self,
+                 announce: bytes,
+                 announce_offset: int,
+                 scid,
+                 node1_id: point,
+                 node2_id: point,
+                 is_private: bool):
+        self.announce = announce
+        self.announce_offset = announce_offset
+        self.is_private = is_private
+        self.scid = scid
+        self.node1_id = node1_id
+        self.node2_id = node2_id
+        self.updates: List[Optional[bytes]] = [None, None]
+        self.updates_offset: List[Optional[int]] = [None, None]
+
+
+class GossmapNode(object):
+    def __init__(self, node_id: point):
+        self.announce = None
+        self.announce_offset = None
+        self.channels = []
+        self.node_id = node_id
+
+
+class Gossmap(object):
+    """Class to represent the gossip map of the network"""
+    def __init__(self, store_filename: str = "gossip_store"):
+        self.store_filename = store_filename
+        self.store_file = open(store_filename, "rb")
+        self.store_buf = bytes()
+        self.nodes: Dict[point, GossmapNode] = {}
+        self.channels: Dict[short_channel_id, GossmapChannel] = {}
+        version = self.store_file.read(1)
+        if version[0] != GOSSIP_STORE_VERSION:
+            raise ValueError("Invalid gossip store version {}".format(version))
+        self.bytes_read = 1
+        self.refresh()
+
+    def _new_channel(self,
+                     announce: bytes,
+                     announce_offset: int,
+                     scid: short_channel_id,
+                     node1_id: point,
+                     node2_id: point,
+                     is_private: bool):
+        c = GossmapChannel(announce, announce_offset,
+                           scid, node1_id, node2_id,
+                           is_private)
+        if node1_id not in self.nodes:
+            self.nodes[node1_id] = GossmapNode(node1_id)
+        if node2_id not in self.nodes:
+            self.nodes[node2_id] = GossmapNode(node2_id)
+
+        self.channels[scid] = c
+        self.nodes[node1_id].channels.append(c)
+        self.nodes[node2_id].channels.append(c)
+
+    def _del_channel(self, scid: short_channel_id):
+        c = self.channels[scid]
+        n1 = self.nodes[c.node1_id]
+        n2 = self.nodes[c.node2_id]
+        n1.channels.remove(c)
+        n2.channels.remove(c)
+        # Beware self-channels n1-n1!
+        if len(n1.channels) == 0 and n1 != n2:
+            del self.nodes[c.node1_id]
+        if len(n2.channels):
+            del self.nodes[c.node2_id]
+
+    def add_channel(self, rec: bytes, off: int, is_private: bool):
+        fields = channel_announcement.read(io.BytesIO(rec[2:]), {})
+        self._new_channel(rec, off, fields['short_channel_id'],
+                          fields['node_id_1'], fields['node_id_2'],
+                          is_private)
+
+    def update_channel(self, rec: bytes, off: int):
+        fields = channel_update.read(io.BytesIO(rec[2:]), {})
+        direction = fields['channel_flags'] & 1
+        c = self.channels[fields['short_channel_id']]
+        c.updates[direction] = rec
+        c.updates_offset = off
+
+    def add_node_announcement(self, rec: bytes, off: int):
+        fields = node_announcement.read(io.BytesIO(rec[2:]), {})
+        self.nodes[fields['node_id']].announce = rec
+        self.nodes[fields['node_id']].announce_offset = off
+
+    def reopen_store(self):
+        assert False
+
+    def remove_channel_by_deletemsg(self, rec: bytes):
+        scid, = struct.unpack(">Q", rec[2:])
+        # It might have already been deleted when we skipped it.
+        if scid in self.channels:
+            self._del_channel(scid)
+
+    def _pull_bytes(self, length: int) -> bool:
+        """Pull bytes from file into our internal buffer"""
+        if len(self.store_buf) < length:
+            self.store_buf += self.store_file.read(length
+                                                   - len(self.store_buf))
+        return len(self.store_buf) >= length
+
+    def _read_record(self) -> Optional[bytes]:
+        """If a whole record is not in the file, returns None.
+        If deleted, returns empty."""
+        if not self._pull_bytes(12):
+            return None
+        hdr = GossipStoreHeader(self.store_buf[:12])
+        if not self._pull_bytes(12 + hdr.length):
+            return None
+        self.bytes_read += len(self.store_buf)
+        ret = self.store_buf[12:]
+        self.store_buf = bytes()
+        if hdr.deleted:
+            ret = bytes()
+        return ret
+
+    def refresh(self):
+        """Catch up with any changes to the gossip store"""
+        while True:
+            off = self.bytes_read
+            rec = self._read_record()
+            # EOF?
+            if rec is None:
+                break
+            # Deleted?
+            if len(rec) == 0:
+                continue
+
+            rectype, = struct.unpack(">H", rec[:2])
+            if rectype == channel_announcement.number:
+                self.add_channel(rec, off, False)
+            elif rectype == WIRE_GOSSIP_STORE_PRIVATE_CHANNEL:
+                self.add_channel(rec[2 + 8 + 2:], off + 2 + 8 + 2, True)
+            elif rectype == channel_update.number:
+                self.update_channel(rec, off)
+            elif rectype == WIRE_GOSSIP_STORE_PRIVATE_UPDATE:
+                self.update_channel(rec[2 + 2:], off + 2 + 2)
+            elif rectype == WIRE_GOSSIP_STORE_DELETE_CHAN:
+                self.remove_channel_by_deletemsg(rec)
+            elif rectype == node_announcement.number:
+                self.add_node_announcement(rec, off)
+            elif rectype == WIRE_GOSSIP_STORE_ENDED:
+                self.reopen_store()
+            else:
+                continue

contrib/pyln-client/requirements.txt

@@ -1 +1,2 @@
 recommonmark>=0.7.*
+pyln-bolt7

contrib/pyln-client/tests/test_gossmap.py

@@ -0,0 +1,38 @@
+from pyln.client import Gossmap
+
+import os.path
+import lzma
+
+
+def unxz_data_tmp(src, tmp_path, dst, wmode):
+    fulldst = os.path.join(tmp_path, dst)
+    with open(fulldst, wmode) as out:
+        with lzma.open(os.path.join(os.path.dirname(__file__), "data", src), "rb")as f:
+            out.write(f.read())
+    return fulldst
+
+
+def test_gossmap(tmp_path):
+    sfile = unxz_data_tmp("gossip_store-part1.xz", tmp_path, "gossip_store", "xb")
+    g = Gossmap(sfile)
+
+    chans = len(g.channels)
+    nodes = len(g.nodes)
+
+    g.refresh()
+    assert chans == len(g.channels)
+    assert nodes == len(g.nodes)
+
+    # Now append.
+    unxz_data_tmp("gossip_store-part2.xz", tmp_path, "gossip_store", "ab")
+
+    g.refresh()
+
+    # It will notice the new ones.
+    assert chans < len(g.channels)
+    assert nodes < len(g.nodes)
+
+    # Whole load at the same time gives the same results.
+    g2 = Gossmap(sfile)
+    assert set(g.channels.keys()) == set(g2.channels.keys())
+    assert set(g.nodes.keys()) == set(g2.nodes.keys())