kivy: add "clear all gossip" button in ln gossip dialog

One usecase is perhaps to save space if using trampoline anyway...
more importantly, if using gossip, LNGossip is heavily filtering what messages we request and get,
and e.g. can missing new NodeAnnouncements, etc,
and this is a quick-and-dirty workaround to force a fresh start.

electrum/channel_db.py

@@ -51,6 +51,7 @@ if TYPE_CHECKING:
     from .network import Network
     from .lnchannel import Channel
     from .lnrouter import RouteEdge
+    from .simple_config import SimpleConfig
 
 
 FLAG_DISABLE   = 1 << 1
@@ -304,7 +305,7 @@ class ChannelDB(SqlDB):
     NUM_MAX_RECENT_PEERS = 20
 
     def __init__(self, network: 'Network'):
-        path = os.path.join(get_headers_dir(network.config), 'gossip_db')
+        path = self.get_file_path(network.config)
         super().__init__(network.asyncio_loop, path, commit_interval=100)
         self.lock = threading.RLock()
         self.num_nodes = 0
@@ -328,6 +329,10 @@ class ChannelDB(SqlDB):
         self.data_loaded = asyncio.Event()
         self.network = network # only for callback
 
+    @classmethod
+    def get_file_path(cls, config: 'SimpleConfig') -> str:
+        return os.path.join(get_headers_dir(config), 'gossip_db')
+
     def update_counts(self):
         self.num_nodes = len(self._nodes)
         self.num_channels = len(self._channels)

electrum/gui/kivy/main_window.py

@@ -783,6 +783,33 @@ class ElectrumWindow(App, Logger):
             self._channels_dialog = LightningChannelsDialog(self)
         self._channels_dialog.open()
 
+    def delete_ln_gossip_dialog(self):
+        def delete_gossip(b: bool):
+            if not b:
+                return
+            if self.network:
+                self.network.run_from_another_thread(
+                    self.network.stop_gossip(full_shutdown=True))
+
+            os.unlink(gossip_db_file)
+            self.show_error(_("Local gossip database deleted."))
+            self.network.start_gossip()
+
+        if self.network is None or self.network.channel_db is None:
+            return  # TODO show msg to user, or the button should be disabled instead
+        gossip_db_file = self.network.channel_db.get_file_path(self.electrum_config)
+        try:
+            size_mb = os.path.getsize(gossip_db_file) / (1024**2)
+        except OSError:
+            self.logger.exception("Cannot get file size.")
+            return
+        d = Question(
+            _('Do you want to delete the local gossip database?') + '\n' +
+            '(' + _('file size') + f': {size_mb:.2f} MiB)\n' +
+            _('It will be automatically re-downloaded after, unless you disable the gossip.'),
+            delete_gossip)
+        d.open()
+
     def on_channel(self, evt, wallet, chan):
         if self._channels_dialog:
             Clock.schedule_once(lambda dt: self._channels_dialog.update())

electrum/gui/kivy/uix/ui_screens/lightning.kv

@@ -26,3 +26,14 @@ Popup:
                 SettingsItem:
                     title: _("Pending") + ': ' + str(app.lightning_gossip_num_queries)
                     description: _("Channel updates to query.")
+        BoxLayout:
+            size_hint: 1, None
+            height: '48dp'
+            Button:
+                size_hint: 0.5, None
+                height: '48dp'
+                text: _('Clear all gossip')
+                on_release: app.delete_ln_gossip_dialog()
+            Widget:
+                size_hint: 0.5, None
+                height: '48dp'