lnchan: add available_to_spend()

electrum/gui/qt/channels_list.py

@@ -23,10 +23,19 @@ class ChannelsList(MyTreeWidget):
         self.status = QLabel('')
 
     def format_fields(self, chan):
+        labels = {}
+        for subject in (REMOTE, LOCAL):
+            available = chan.available_to_spend(subject)//1000
+            label = self.parent.format_amount(available)
+            bal_other = chan.balance(-subject)//1000
+            available_other = chan.available_to_spend(-subject)//1000
+            if bal_other != available_other:
+                label += ' (+' + self.parent.format_amount(bal_other - available_other) + ')'
+            labels[subject] = label
         return [
             bh2u(chan.node_id),
-            self.parent.format_amount(chan.balance(LOCAL)//1000),
-            self.parent.format_amount(chan.balance(REMOTE)//1000),
+            labels[LOCAL],
+            labels[REMOTE],
             chan.get_state()
         ]
 

electrum/lnchan.py

@@ -155,11 +155,9 @@ class Channel(PrintError):
         return self._state
 
     def check_can_pay(self, amount_msat):
-        # FIXME what about channel_reserve_satoshis? will the remote fail the channel if we go below? test.
-        # FIXME what about tx fees
         if self.get_state() != 'OPEN':
             raise PaymentFailure('Channel not open')
-        if self.balance(LOCAL) < amount_msat:
+        if self.available_to_spend(LOCAL) < amount_msat:
             raise PaymentFailure('Not enough local balance')
         if len(self.htlcs(LOCAL, only_pending=True)) + 1 > self.config[REMOTE].max_accepted_htlcs:
             raise PaymentFailure('Too many HTLCs already in channel')
@@ -461,6 +459,11 @@ class Channel(PrintError):
         assert initial == self.config[subject].amount_msat
         return initial
 
+    def available_to_spend(self, subject):
+        # FIXME what about channel_reserve_satoshis? will the remote fail the channel if we go below? test.
+        # FIXME what about tx fees
+        return self.balance(subject) - htlcsum(self.htlcs(subject, only_pending=True))
+
     def amounts(self):
         remote_settled= htlcsum(self.htlcs(REMOTE, False))
         local_settled= htlcsum(self.htlcs(LOCAL, False))

electrum/tests/test_lnchan.py

@@ -339,6 +339,7 @@ class TestDust(unittest.TestCase):
         aliceHtlcIndex = alice_channel.add_htlc(htlc)
         bobHtlcIndex = bob_channel.receive_htlc(htlc)
         force_state_transition(alice_channel, bob_channel)
+        self.assertEqual(alice_channel.available_to_spend(LOCAL), alice_channel.balance(LOCAL) - htlc['amount_msat'])
         self.assertEqual(len(alice_channel.local_commitment.outputs()), 3)
         self.assertEqual(len(bob_channel.local_commitment.outputs()), 2)
         default_fee = calc_static_fee(0)