lnchannel: implement "freezing" channels (for sending)

and expose it in Qt GUI

electrum/gui/qt/channels_list.py

@@ -1,12 +1,13 @@
 # -*- coding: utf-8 -*-
 import traceback
 from enum import IntEnum
+from typing import Sequence, Optional
 
 from PyQt5 import QtCore, QtGui
 from PyQt5.QtCore import Qt
 from PyQt5.QtWidgets import (QMenu, QHBoxLayout, QLabel, QVBoxLayout, QGridLayout, QLineEdit,
                              QPushButton, QAbstractItemView)
-from PyQt5.QtGui import QFont
+from PyQt5.QtGui import QFont, QStandardItem, QBrush
 
 from electrum.util import bh2u, NotEnoughFunds, NoDynamicFeeEstimates
 from electrum.i18n import _
@@ -15,7 +16,7 @@ from electrum.wallet import Abstract_Wallet
 from electrum.lnutil import LOCAL, REMOTE, format_short_channel_id, LN_MAX_FUNDING_SAT
 
 from .util import (MyTreeView, WindowModalDialog, Buttons, OkButton, CancelButton,
-                   EnterButton, WaitingDialog, MONOSPACE_FONT)
+                   EnterButton, WaitingDialog, MONOSPACE_FONT, ColorScheme)
 from .amountedit import BTCAmountEdit, FreezableLineEdit
 
 
@@ -43,6 +44,8 @@ class ChannelsList(MyTreeView):
         Columns.CHANNEL_STATUS: _('Status'),
     }
 
+    _default_item_bg_brush = None  # type: Optional[QBrush]
+
     def __init__(self, parent):
         super().__init__(parent, self.create_menu, stretch_column=self.Columns.NODE_ID,
                          editable_columns=[])
@@ -141,6 +144,12 @@ class ChannelsList(MyTreeView):
         cc = self.add_copy_menu(menu, idx)
         cc.addAction(_("Long Channel ID"), lambda: self.place_text_on_clipboard(channel_id.hex(),
                                                                                 title=_("Long Channel ID")))
+
+        if not chan.is_frozen():
+            menu.addAction(_("Freeze"), lambda: chan.set_frozen(True))
+        else:
+            menu.addAction(_("Unfreeze"), lambda: chan.set_frozen(False))
+
         funding_tx = self.parent.wallet.db.get_transaction(chan.funding_outpoint.txid)
         if funding_tx:
             menu.addAction(_("View funding transaction"), lambda: self.parent.show_transaction(funding_tx))
@@ -169,9 +178,12 @@ class ChannelsList(MyTreeView):
             return
         for row in range(self.model().rowCount()):
             item = self.model().item(row, self.Columns.NODE_ID)
-            if item.data(ROLE_CHANNEL_ID) == chan.channel_id:
-                for column, v in enumerate(self.format_fields(chan)):
-                    self.model().item(row, column).setData(v, QtCore.Qt.DisplayRole)
+            if item.data(ROLE_CHANNEL_ID) != chan.channel_id:
+                continue
+            for column, v in enumerate(self.format_fields(chan)):
+                self.model().item(row, column).setData(v, QtCore.Qt.DisplayRole)
+            items = [self.model().item(row, column) for column in self.Columns]
+            self._update_chan_frozen_bg(chan=chan, items=items)
         self.update_can_send(lnworker)
 
     @QtCore.pyqtSlot(Abstract_Wallet)
@@ -187,13 +199,31 @@ class ChannelsList(MyTreeView):
         for chan in lnworker.channels.values():
             items = [QtGui.QStandardItem(x) for x in self.format_fields(chan)]
             self.set_editability(items)
+            if self._default_item_bg_brush is None:
+                self._default_item_bg_brush = items[self.Columns.NODE_ID].background()
             items[self.Columns.NODE_ID].setData(chan.channel_id, ROLE_CHANNEL_ID)
             items[self.Columns.NODE_ID].setFont(QFont(MONOSPACE_FONT))
             items[self.Columns.LOCAL_BALANCE].setFont(QFont(MONOSPACE_FONT))
             items[self.Columns.REMOTE_BALANCE].setFont(QFont(MONOSPACE_FONT))
+            self._update_chan_frozen_bg(chan=chan, items=items)
             self.model().insertRow(0, items)
         self.sortByColumn(self.Columns.SHORT_CHANID, Qt.DescendingOrder)
 
+    def _update_chan_frozen_bg(self, *, chan: Channel, items: Sequence[QStandardItem]):
+        assert self._default_item_bg_brush is not None
+        for col in [
+            self.Columns.LOCAL_BALANCE,
+            self.Columns.REMOTE_BALANCE,
+            self.Columns.CHANNEL_STATUS,
+        ]:
+            item = items[col]
+            if chan.is_frozen():
+                item.setBackground(ColorScheme.BLUE.as_color(True))
+                item.setToolTip(_("This channel is frozen. Frozen channels will not be used for outgoing payments."))
+            else:
+                item.setBackground(self._default_item_bg_brush)
+                item.setToolTip("")
+
     def update_can_send(self, lnworker):
         msg = _('Can send') + ' ' + self.parent.format_amount(lnworker.can_send())\
               + ' ' + self.parent.base_unit() + '; '\

electrum/lnchannel.py

@@ -390,7 +390,22 @@ class Channel(Logger):
     def is_redeemed(self):
         return self.get_state() == channel_states.REDEEMED
 
-    def _check_can_pay(self, amount_msat: int) -> None:
+    def is_frozen(self) -> bool:
+        """Whether the user has marked this channel as frozen.
+        Frozen channels are not supposed to be used for new outgoing payments.
+        (note that payment-forwarding ignores this option)
+        """
+        return self.storage.get('frozen_for_sending', False)
+
+    def set_frozen(self, b: bool) -> None:
+        self.storage['frozen_for_sending'] = bool(b)
+        if self.lnworker:
+            self.lnworker.network.trigger_callback('channel', self)
+
+    def _assert_we_can_add_htlc(self, amount_msat: int) -> None:
+        """Raises PaymentFailure if the local party cannot add this new HTLC.
+        (this is relevant both for payments initiated by us and when forwarding)
+        """
         # TODO check if this method uses correct ctns (should use "latest" + 1)
         if self.is_closed():
             raise PaymentFailure('Channel closed')
@@ -398,6 +413,8 @@ class Channel(Logger):
             raise PaymentFailure('Channel not open', self.get_state())
         if not self.can_send_ctx_updates():
             raise PaymentFailure('Channel cannot send ctx updates')
+        if not self.can_send_update_add_htlc():
+            raise PaymentFailure('Channel cannot add htlc')
         if self.available_to_spend(LOCAL) < amount_msat:
             raise PaymentFailure(f'Not enough local balance. Have: {self.available_to_spend(LOCAL)}, Need: {amount_msat}')
         if len(self.hm.htlcs(LOCAL)) + 1 > self.config[REMOTE].max_accepted_htlcs:
@@ -409,9 +426,14 @@ class Channel(Logger):
         if amount_msat < self.config[REMOTE].htlc_minimum_msat:
             raise PaymentFailure(f'HTLC value too small: {amount_msat} msat')
 
-    def can_pay(self, amount_msat):
+    def can_pay(self, amount_msat: int) -> bool:
+        """Returns whether we can initiate a new payment of given value.
+        (we are the payer, not just a forwarding node)
+        """
+        if self.is_frozen():
+            return False
         try:
-            self._check_can_pay(amount_msat)
+            self._assert_we_can_add_htlc(amount_msat)
         except PaymentFailure:
             return False
         return True
@@ -430,11 +452,10 @@ class Channel(Logger):
 
         This docstring is from LND.
         """
-        assert self.can_send_ctx_updates(), f"cannot update channel. {self.get_state()!r} {self.peer_state!r}"
         if isinstance(htlc, dict):  # legacy conversion  # FIXME remove
             htlc = UpdateAddHtlc(**htlc)
         assert isinstance(htlc, UpdateAddHtlc)
-        self._check_can_pay(htlc.amount_msat)
+        self._assert_we_can_add_htlc(htlc.amount_msat)
         if htlc.htlc_id is None:
             htlc = attr.evolve(htlc, htlc_id=self.hm.get_next_htlc_id(LOCAL))
         with self.db_lock: