lightning channel reserves

electrum/lnbase.py

@@ -390,6 +390,7 @@ class Peer(PrintError):
             ctn=-1,
             next_htlc_id=0,
             amount_msat=initial_msat,
+            reserve_sat=546,
         )
         per_commitment_secret_seed = keypair_generator(LnKeyFamily.REVOCATION_ROOT).privkey
         return local_config, per_commitment_secret_seed
@@ -451,6 +452,7 @@ class Peer(PrintError):
             ctn = -1,
             amount_msat=push_msat,
             next_htlc_id = 0,
+            reserve_sat = int.from_bytes(payload["channel_reserve_satoshis"], 'big'),
 
             next_per_commitment_point=remote_per_commitment_point,
             current_per_commitment_point=None,
@@ -561,6 +563,7 @@ class Peer(PrintError):
                     ctn = -1,
                     amount_msat=remote_balance_sat,
                     next_htlc_id = 0,
+                    reserve_sat = int.from_bytes(payload['channel_reserve_satoshis'], 'big'),
 
                     next_per_commitment_point=payload['first_per_commitment_point'],
                     current_per_commitment_point=None,
@@ -941,7 +944,6 @@ class Peer(PrintError):
         assert final_cltv <= cltv, (final_cltv, cltv)
         secret_key = os.urandom(32)
         onion = new_onion_packet([x.node_id for x in route], secret_key, hops_data, associated_data=payment_hash)
-        chan.check_can_pay(amount_msat)
         # create htlc
         htlc = {'amount_msat':amount_msat, 'payment_hash':payment_hash, 'cltv_expiry':cltv}
         htlc_id = chan.add_htlc(htlc)

electrum/lnchan.py

@@ -18,7 +18,7 @@ from .lnutil import sign_and_get_sig_string, privkey_to_pubkey, make_htlc_tx_wit
 from .lnutil import make_htlc_tx_with_open_channel, make_commitment, make_received_htlc, make_offered_htlc
 from .lnutil import HTLC_TIMEOUT_WEIGHT, HTLC_SUCCESS_WEIGHT
 from .lnutil import funding_output_script, LOCAL, REMOTE, HTLCOwner, make_closing_tx, make_commitment_outputs
-from .lnutil import ScriptHtlc, SENT, RECEIVED, PaymentFailure, calc_onchain_fees
+from .lnutil import ScriptHtlc, SENT, RECEIVED, PaymentFailure, calc_onchain_fees, RemoteMisbehaving
 from .transaction import Transaction, TxOutput, construct_witness
 from .simple_config import SimpleConfig, FEERATE_FALLBACK_STATIC_FEE
 
@@ -131,6 +131,7 @@ class Channel(PrintError):
         template = lambda: {
             'adds': {}, # Dict[HTLC_ID, UpdateAddHtlc]
             'settles': [], # List[HTLC_ID]
+            'fails': [], # List[HTLC_ID]
         }
         self.log = {LOCAL: template(), REMOTE: template()}
         for strname, subject in [('remote_log', REMOTE), ('local_log', LOCAL)]:
@@ -159,23 +160,23 @@ class Channel(PrintError):
     def get_state(self):
         return self._state
 
-    def check_can_pay(self, amount_msat: int) -> None:
-        # FIXME channel reserve
+    def _check_can_pay(self, amount_msat: int) -> None:
         if self.get_state() != 'OPEN':
             raise PaymentFailure('Channel not open')
         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')
-        if htlcsum(self.htlcs(LOCAL, only_pending=True)) + amount_msat > self.config[REMOTE].max_htlc_value_in_flight_msat:
-            raise PaymentFailure('HTLC value sum would exceed max allowed: {} msat'.format(self.config[REMOTE].max_htlc_value_in_flight_msat))
+        current_htlc_sum = htlcsum(self.htlcs(LOCAL, only_pending=True))
+        if current_htlc_sum + amount_msat > self.config[REMOTE].max_htlc_value_in_flight_msat:
+            raise PaymentFailure(f'HTLC value sum (sum of pending htlcs: {current_htlc_sum/1000} sat plus new htlc: {amount_msat/1000} sat) would exceed max allowed: {self.config[REMOTE].max_htlc_value_in_flight_msat/1000} sat')
         if amount_msat <= 0:  # FIXME htlc_minimum_msat
             raise PaymentFailure(f'HTLC value too small: {amount_msat} msat')
 
     def can_pay(self, amount_msat):
         try:
-            self.check_can_pay(amount_msat)
-        except:
+            self._check_can_pay(amount_msat)
+        except PaymentFailure:
             return False
         return True
 
@@ -196,6 +197,7 @@ class Channel(PrintError):
         should be called when preparing to send an outgoing HTLC.
         """
         assert type(htlc) is dict
+        self._check_can_pay(htlc['amount_msat'])
         htlc = UpdateAddHtlc(**htlc, htlc_id=self.config[LOCAL].next_htlc_id)
         self.log[LOCAL]['adds'][htlc.htlc_id] = htlc
         self.print_error("add_htlc")
@@ -210,7 +212,10 @@ class Channel(PrintError):
         """
         assert type(htlc) is dict
         htlc = UpdateAddHtlc(**htlc, htlc_id = self.config[REMOTE].next_htlc_id)
-        self.log[REMOTE]['adds'][htlc.htlc_id] = htlc
+        if self.available_to_spend(REMOTE) < htlc.amount_msat:
+            raise RemoteMisbehaving('Remote dipped below channel reserve')
+        adds = self.log[REMOTE]['adds']
+        adds[htlc.htlc_id] = htlc
         self.print_error("receive_htlc")
         self.config[REMOTE]=self.config[REMOTE]._replace(next_htlc_id=htlc.htlc_id + 1)
         return htlc.htlc_id
@@ -228,10 +233,8 @@ class Channel(PrintError):
         any). The HTLC signatures are sorted according to the BIP 69 order of the
         HTLC's on the commitment transaction.
         """
-        for htlc in self.log[LOCAL]['adds'].values():
-            if htlc.locked_in[LOCAL] is None:
-                htlc.locked_in[LOCAL] = self.config[LOCAL].ctn
         self.print_error("sign_next_commitment")
+        self.lock_in_htlc_changes(LOCAL)
 
         pending_remote_commitment = self.pending_remote_commitment
         sig_64 = sign_and_get_sig_string(pending_remote_commitment, self.config[LOCAL], self.config[REMOTE])
@@ -265,6 +268,17 @@ class Channel(PrintError):
 
         return sig_64, htlcsigs
 
+    def lock_in_htlc_changes(self, subject):
+        for sub in (LOCAL, REMOTE):
+            for htlc_id in self.log[-sub]['fails']:
+                adds = self.log[sub]['adds']
+                htlc = adds.pop(htlc_id)
+            self.log[-sub]['fails'].clear()
+
+        for htlc in self.log[subject]['adds'].values():
+            if htlc.locked_in[subject] is None:
+                htlc.locked_in[subject] = self.config[subject].ctn
+
     def receive_new_commitment(self, sig, htlc_sigs):
         """
         ReceiveNewCommitment process a signature for a new commitment state sent by
@@ -276,11 +290,8 @@ class Channel(PrintError):
         state, then this newly added commitment becomes our current accepted channel
         state.
         """
-
         self.print_error("receive_new_commitment")
-        for htlc in self.log[REMOTE]['adds'].values():
-            if htlc.locked_in[REMOTE] is None:
-                htlc.locked_in[REMOTE] = self.config[REMOTE].ctn
+        self.lock_in_htlc_changes(REMOTE)
         assert len(htlc_sigs) == 0 or type(htlc_sigs[0]) is bytes
 
         pending_local_commitment = self.pending_local_commitment
@@ -479,9 +490,16 @@ class Channel(PrintError):
         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))
+        return self.balance(subject)\
+                - htlcsum(self.log[subject]['adds'].values())\
+                - self.config[subject].reserve_sat * 1000\
+                - calc_onchain_fees(
+                      # TODO should we include a potential new htlc, when we are called from receive_htlc?
+                      len(list(self.included_htlcs(subject, LOCAL)) + list(self.included_htlcs(subject, REMOTE))),
+                      self.pending_feerate(subject),
+                      subject == LOCAL,
+                      self.constraints.is_initiator,
+                  )[subject]
 
     def amounts(self):
         remote_settled= htlcsum(self.htlcs(REMOTE, False))
@@ -536,8 +554,11 @@ class Channel(PrintError):
         res = []
         for htlc in update_log['adds'].values():
             locked_in = htlc.locked_in[subject]
-
-            if locked_in is None or only_pending == (htlc.htlc_id in other_log['settles']):
+            settled = htlc.htlc_id in other_log['settles']
+            failed =  htlc.htlc_id in other_log['fails']
+            if locked_in is None:
+                continue
+            if only_pending == (settled or failed):
                 continue
             res.append(htlc)
         return res
@@ -561,11 +582,11 @@ class Channel(PrintError):
 
     def fail_htlc(self, htlc_id):
         self.print_error("fail_htlc")
-        self.log[REMOTE]['adds'].pop(htlc_id)
+        self.log[LOCAL]['fails'].append(htlc_id)
 
     def receive_fail_htlc(self, htlc_id):
         self.print_error("receive_fail_htlc")
-        self.log[LOCAL]['adds'].pop(htlc_id)
+        self.log[REMOTE]['fails'].append(htlc_id)
 
     @property
     def current_height(self):
@@ -665,8 +686,8 @@ class Channel(PrintError):
 
     def make_commitment(self, subject, this_point) -> Transaction:
         remote_msat, local_msat = self.amounts()
-        assert local_msat >= 0
-        assert remote_msat >= 0
+        assert local_msat >= 0, local_msat
+        assert remote_msat >= 0, remote_msat
         this_config = self.config[subject]
         other_config = self.config[-subject]
         other_htlc_pubkey = derive_pubkey(other_config.htlc_basepoint.pubkey, this_point)

electrum/lnutil.py

@@ -37,6 +37,7 @@ common = [
     ('max_htlc_value_in_flight_msat' , int),
     ('max_accepted_htlcs' , int),
     ('initial_msat' , int),
+    ('reserve_sat', int),
 ]
 
 ChannelConfig = NamedTuple('ChannelConfig', common)
@@ -65,6 +66,7 @@ class HandshakeFailed(LightningError): pass
 class PaymentFailure(LightningError): pass
 class ConnStringFormatError(LightningError): pass
 class UnknownPaymentHash(LightningError): pass
+class RemoteMisbehaving(LightningError): pass
 
 
 # TODO make configurable?

electrum/tests/test_lnchan.py

@@ -11,6 +11,8 @@ import binascii
 
 from electrum.lnutil import SENT, LOCAL, REMOTE, RECEIVED
 
+one_bitcoin_in_msat = bitcoin.COIN * 1000
+
 def create_channel_state(funding_txid, funding_index, funding_sat, local_feerate, is_initiator, local_amount, remote_amount, privkeys, other_pubkeys, seed, cur, nex, other_node_id, l_dust, r_dust, l_csv, r_csv):
     assert local_amount > 0
     assert remote_amount > 0
@@ -29,12 +31,13 @@ def create_channel_state(funding_txid, funding_index, funding_sat, local_feerate
                 revocation_basepoint=other_pubkeys[4],
                 to_self_delay=r_csv,
                 dust_limit_sat=r_dust,
-                max_htlc_value_in_flight_msat=500000 * 1000,
+                max_htlc_value_in_flight_msat=one_bitcoin_in_msat * 5,
                 max_accepted_htlcs=5,
                 initial_msat=remote_amount,
                 ctn = 0,
                 next_htlc_id = 0,
                 amount_msat=remote_amount,
+                reserve_sat=0,
 
                 next_per_commitment_point=nex,
                 current_per_commitment_point=cur,
@@ -48,12 +51,13 @@ def create_channel_state(funding_txid, funding_index, funding_sat, local_feerate
                 revocation_basepoint=privkeys[4],
                 to_self_delay=l_csv,
                 dust_limit_sat=l_dust,
-                max_htlc_value_in_flight_msat=500000 * 1000,
+                max_htlc_value_in_flight_msat=one_bitcoin_in_msat * 5,
                 max_accepted_htlcs=5,
                 initial_msat=local_amount,
                 ctn = 0,
                 next_htlc_id = 0,
                 amount_msat=local_amount,
+                reserve_sat=0,
 
                 per_commitment_secret_seed=seed,
                 funding_locked_received=True,
@@ -101,13 +105,15 @@ def create_test_channels(feerate=6000, local=None, remote=None):
     bob_cur = lnutil.secret_to_pubkey(int.from_bytes(lnutil.get_per_commitment_secret_from_seed(bob_seed, lnutil.RevocationStore.START_INDEX), "big"))
     bob_next = lnutil.secret_to_pubkey(int.from_bytes(lnutil.get_per_commitment_secret_from_seed(bob_seed, lnutil.RevocationStore.START_INDEX - 1), "big"))
 
-    return \
+    alice, bob = \
         lnchan.Channel(
             create_channel_state(funding_txid, funding_index, funding_sat, feerate, True, local_amount, remote_amount, alice_privkeys, bob_pubkeys, alice_seed, bob_cur, bob_next, b"\x02"*33, l_dust=200, r_dust=1300, l_csv=5, r_csv=4), "alice"), \
         lnchan.Channel(
             create_channel_state(funding_txid, funding_index, funding_sat, feerate, False, remote_amount, local_amount, bob_privkeys, alice_pubkeys, bob_seed, alice_cur, alice_next, b"\x01"*33, l_dust=1300, r_dust=200, l_csv=4, r_csv=5), "bob")
 
-one_bitcoin_in_msat = bitcoin.COIN * 1000
+    alice.set_state('OPEN')
+    bob.set_state('OPEN')
+    return alice, bob
 
 class TestFee(unittest.TestCase):
     """
@@ -134,7 +140,7 @@ class TestChannel(unittest.TestCase):
 
         self.paymentPreimage = b"\x01" * 32
         paymentHash = bitcoin.sha256(self.paymentPreimage)
-        self.htlc = {
+        self.htlc_dict = {
             'payment_hash' : paymentHash,
             'amount_msat' :  one_bitcoin_in_msat,
             'cltv_expiry' :  5,
@@ -143,9 +149,9 @@ class TestChannel(unittest.TestCase):
         # First Alice adds the outgoing HTLC to her local channel's state
         # update log. Then Alice sends this wire message over to Bob who adds
         # this htlc to his remote state update log.
-        self.aliceHtlcIndex = self.alice_channel.add_htlc(self.htlc)
+        self.aliceHtlcIndex = self.alice_channel.add_htlc(self.htlc_dict)
 
-        self.bobHtlcIndex = self.bob_channel.receive_htlc(self.htlc)
+        self.bobHtlcIndex = self.bob_channel.receive_htlc(self.htlc_dict)
         self.htlc = self.bob_channel.log[lnutil.REMOTE]['adds'][0]
 
     def test_SimpleAddSettleWorkflow(self):
@@ -318,7 +324,120 @@ class TestChannel(unittest.TestCase):
         bob_channel.receive_revocation(alice_revocation)
         self.assertEqual(fee, bob_channel.constraints.feerate)
 
+    def test_AddHTLCNegativeBalance(self):
+        self.htlc_dict['payment_hash'] = bitcoin.sha256(32 * b'\x02')
+        self.alice_channel.add_htlc(self.htlc_dict)
+        self.htlc_dict['payment_hash'] = bitcoin.sha256(32 * b'\x03')
+        self.alice_channel.add_htlc(self.htlc_dict)
+        # now there are three htlcs (one was in setUp)
+
+        # Alice now has an available balance of 2 BTC. We'll add a new HTLC of
+        # value 2 BTC, which should make Alice's balance negative (since she
+        # has to pay a commitment fee).
+        new = dict(self.htlc_dict)
+        new['amount_msat'] *= 2
+        new['payment_hash'] = bitcoin.sha256(32 * b'\x04')
+        with self.assertRaises(lnutil.PaymentFailure) as cm:
+            self.alice_channel.add_htlc(new)
+        self.assertEqual(('Not enough local balance',), cm.exception.args)
+
+class TestAvailableToSpend(unittest.TestCase):
+    def test_DesyncHTLCs(self):
+        alice_channel, bob_channel = create_test_channels()
+
+        paymentPreimage = b"\x01" * 32
+        paymentHash = bitcoin.sha256(paymentPreimage)
+        htlc_dict = {
+            'payment_hash' : paymentHash,
+            'amount_msat' :  int(4.1 * one_bitcoin_in_msat),
+            'cltv_expiry' :  5,
+        }
+
+        alice_idx = alice_channel.add_htlc(htlc_dict)
+        bob_idx = bob_channel.receive_htlc(htlc_dict)
+        force_state_transition(alice_channel, bob_channel)
+        bob_channel.fail_htlc(bob_idx)
+        alice_channel.receive_fail_htlc(alice_idx)
+        # Alice now has gotten all her original balance (5 BTC) back, however,
+        # adding a new HTLC at this point SHOULD fail, since if she adds the
+        # HTLC and signs the next state, Bob cannot assume she received the
+        # FailHTLC, and must assume she doesn't have the necessary balance
+        # available.
+        # We try adding an HTLC of value 1 BTC, which should fail because the
+        # balance is unavailable.
+        htlc_dict = {
+            'payment_hash' : paymentHash,
+            'amount_msat' :  one_bitcoin_in_msat,
+            'cltv_expiry' :  5,
+        }
+        with self.assertRaises(lnutil.PaymentFailure):
+            alice_channel.add_htlc(htlc_dict)
+        # Now do a state transition, which will ACK the FailHTLC, making Alice
+        # able to add the new HTLC.
+        force_state_transition(alice_channel, bob_channel)
+        alice_channel.add_htlc(htlc_dict)
 
+class TestChanReserve(unittest.TestCase):
+    def setUp(self):
+        alice_channel, bob_channel = create_test_channels()
+        alice_min_reserve = int(.5 * one_bitcoin_in_msat // 1000)
+        alice_channel.config[LOCAL] =\
+            alice_channel.config[LOCAL]._replace(reserve_sat=alice_min_reserve)
+        bob_channel.config[REMOTE] =\
+            bob_channel.config[REMOTE]._replace(reserve_sat=alice_min_reserve)
+        # We set Bob's channel reserve to a value that is larger than
+        # his current balance in the channel. This will ensure that
+        # after a channel is first opened, Bob can still receive HTLCs
+        # even though his balance is less than his channel reserve.
+        bob_min_reserve = 6 * one_bitcoin_in_msat // 1000
+        bob_channel.config[LOCAL] =\
+            bob_channel.config[LOCAL]._replace(reserve_sat=bob_min_reserve)
+        alice_channel.config[REMOTE] =\
+            alice_channel.config[REMOTE]._replace(reserve_sat=bob_min_reserve)
+
+        self.bob_min = bob_min_reserve
+        self.alice_min = bob_min_reserve
+        self.alice_channel = alice_channel
+        self.bob_channel = bob_channel
+
+    def test_part1(self):
+        # Add an HTLC that will increase Bob's balance. This should succeed,
+        # since Alice stays above her channel reserve, and Bob increases his
+        # balance (while still being below his channel reserve).
+        #
+        # Resulting balances:
+        #	Alice:	4.5
+        #	Bob:	5.0
+        paymentPreimage = b"\x01" * 32
+        paymentHash = bitcoin.sha256(paymentPreimage)
+        htlc_dict = {
+            'payment_hash' : paymentHash,
+            'amount_msat' :  int(.5 * one_bitcoin_in_msat),
+            'cltv_expiry' :  5,
+        }
+        self.alice_channel.add_htlc(htlc_dict)
+        self.bob_channel.receive_htlc(htlc_dict)
+        # Force a state transition, making sure this HTLC is considered valid
+        # even though the channel reserves are not met.
+        force_state_transition(self.alice_channel, self.bob_channel)
+
+        aliceSelfBalance = self.alice_channel.balance(LOCAL)\
+                - lnchan.htlcsum(self.alice_channel.htlcs(LOCAL, True))
+        bobBalance = self.bob_channel.balance(REMOTE)\
+                - lnchan.htlcsum(self.alice_channel.htlcs(REMOTE, True))
+        self.assertEqual(aliceSelfBalance, one_bitcoin_in_msat*4.5)
+        self.assertEqual(bobBalance, one_bitcoin_in_msat*5)
+        # Now let Bob try to add an HTLC. This should fail, since it will
+        # decrease his balance, which is already below the channel reserve.
+        #
+        # Resulting balances:
+        #	Alice:	4.5
+        #	Bob:	5.0
+        with self.assertRaises(lnutil.PaymentFailure):
+            htlc_dict['payment_hash'] = bitcoin.sha256(32 * b'\x02')
+            self.bob_channel.add_htlc(htlc_dict)
+        with self.assertRaises(lnutil.RemoteMisbehaving):
+            self.alice_channel.receive_htlc(htlc_dict)
 
 class TestDust(unittest.TestCase):
     def test_DustLimit(self):
@@ -339,7 +458,6 @@ 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)