pyln-client/gossmap: adds channel satoshi capacity

This reads the `gossip_store_channel_amount` that always follows the
`channel_announcement` messages. Therefore it uses an internal variable
_last_scid to know what channel has been added last time.

Author: m-schmoock

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

@@ -1,7 +1,9 @@
 #! /usr/bin/python3
 
-from pyln.spec.bolt7 import (channel_announcement, channel_update,
-                             node_announcement)
+from pyln.spec.bolt7 import (channel_announcement,
+                             channel_update,
+                             node_announcement,
+                             gossip_store_channel_amount)
 from pyln.proto import ShortChannelId, PublicKey
 from typing import Any, Dict, List, Optional
 
@@ -60,8 +62,7 @@ def __init__(self,
         self.node2_id = node2_id
         self.updates_fields: List[Optional[Dict[str, Any]]] = [None, None]
         self.updates_offset: List[Optional[int]] = [None, None]
-
-        self.capacity = None  # TODO: where do we get this?
+        self.satoshis = None
         self.half_channels: List[GossmapHalfchannel] = [None, None]
 
     def update_channel(self,
@@ -135,6 +136,7 @@ def __init__(self, store_filename: str = "gossip_store"):
         self.store_buf = bytes()
         self.nodes: Dict[bytes, GossmapNode] = {}
         self.channels: Dict[ShortChannelId, GossmapChannel] = {}
+        self._last_scid: str = None
         version = self.store_file.read(1)
         if version[0] != GOSSIP_STORE_VERSION:
             raise ValueError("Invalid gossip store version {}".format(version))
@@ -156,6 +158,7 @@ def _new_channel(self,
         if node2_id not in self.nodes:
             self.nodes[node2_id] = GossmapNode(node2_id)
 
+        self._last_scid = scid
         self.channels[scid] = c
         self.nodes[node1_id].channels.append(c)
         self.nodes[node2_id].channels.append(c)
@@ -179,6 +182,11 @@ def add_channel(self, rec: bytes, off: int, is_private: bool):
                           GossmapNodeId(fields['node_id_1']), GossmapNodeId(fields['node_id_2']),
                           is_private)
 
+    def _set_channel_amount(self, rec: bytes):
+        """ Sets channel capacity of last added channel """
+        fields = gossip_store_channel_amount.read(io.BytesIO(rec[2:]), {})
+        self.channels[self._last_scid].satoshis = fields['satoshis']
+
     def get_channel(self, short_channel_id: ShortChannelId):
         """ Resolves a channel by its short channel id """
         if type(short_channel_id) == str:
@@ -252,6 +260,8 @@ def refresh(self):
                 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 == gossip_store_channel_amount.number:
+                self._set_channel_amount(rec)
             elif rectype == channel_update.number:
                 self.update_channel(rec, off)
             elif rectype == WIRE_GOSSIP_STORE_PRIVATE_UPDATE:

contrib/pyln-spec/bolt7/pyln/spec/bolt7/csv.py

@@ -80,4 +80,6 @@
     "msgdata,gossip_timestamp_filter,chain_hash,chain_hash,",
     "msgdata,gossip_timestamp_filter,first_timestamp,u32,",
     "msgdata,gossip_timestamp_filter,timestamp_range,u32,",
+    "msgtype,gossip_store_channel_amount,4101",
+    "msgdata,gossip_store_channel_amount,satoshis,u64,",
 ]