lnchannel: rm HTLC value upper limit of ~42 mBTC

closes #7328
closes #7100
see lightning/bolts#877 (comment)

electrum/lnchannel.py

@@ -51,7 +51,7 @@
                      funding_output_script, SENT, RECEIVED, LOCAL, REMOTE, HTLCOwner, make_commitment_outputs,
                      ScriptHtlc, PaymentFailure, calc_fees_for_commitment_tx, RemoteMisbehaving, make_htlc_output_witness_script,
                      ShortChannelID, map_htlcs_to_ctx_output_idxs, LNPeerAddr,
-                     LN_MAX_HTLC_VALUE_MSAT, fee_for_htlc_output, offered_htlc_trim_threshold_sat,
+                     fee_for_htlc_output, offered_htlc_trim_threshold_sat,
                      received_htlc_trim_threshold_sat, make_commitment_output_to_remote_address)
 from .lnsweep import create_sweeptxs_for_our_ctx, create_sweeptxs_for_their_ctx
 from .lnsweep import create_sweeptx_for_their_revoked_htlc, SweepInfo
@@ -564,7 +564,6 @@ def __init__(self, state: 'StoredDict', *, sweep_address=None, name=None, lnwork
         self.revocation_store = RevocationStore(state["revocation_store"])
         self._can_send_ctx_updates = True  # type: bool
         self._receive_fail_reasons = {}  # type: Dict[int, (bytes, OnionRoutingFailure)]
-        self._ignore_max_htlc_value = False  # used in tests
         self.should_request_force_close = False
         self.unconfirmed_closing_txid = None # not a state, only for GUI
 
@@ -815,8 +814,6 @@ def _assert_can_add_htlc(self, *, htlc_proposer: HTLCOwner, amount_msat: int,
                 raise PaymentFailure("HTLC value must be positive")
             if amount_msat < chan_config.htlc_minimum_msat:
                 raise PaymentFailure(f'HTLC value too small: {amount_msat} msat')
-        if amount_msat > LN_MAX_HTLC_VALUE_MSAT and not self._ignore_max_htlc_value:
-            raise PaymentFailure(f"HTLC value over protocol maximum: {amount_msat} > {LN_MAX_HTLC_VALUE_MSAT} msat")
 
         # check proposer can afford htlc
         max_can_send_msat = self.available_to_spend(htlc_proposer, strict=strict)

electrum/lnutil.py

@@ -40,7 +40,6 @@
 HTLC_OUTPUT_WEIGHT = 172
 
 LN_MAX_FUNDING_SAT = pow(2, 24) - 1
-LN_MAX_HTLC_VALUE_MSAT = pow(2, 32) - 1
 
 # dummy address for fee estimation of funding tx
 def ln_dummy_address():

electrum/submarine_swaps.py

@@ -14,7 +14,7 @@
 from .transaction import PartialTxInput, PartialTxOutput, PartialTransaction
 from .transaction import script_GetOp, match_script_against_template, OPPushDataGeneric, OPPushDataPubkey
 from .util import log_exceptions
-from .lnutil import REDEEM_AFTER_DOUBLE_SPENT_DELAY, ln_dummy_address, LN_MAX_HTLC_VALUE_MSAT
+from .lnutil import REDEEM_AFTER_DOUBLE_SPENT_DELAY, ln_dummy_address
 from .bitcoin import dust_threshold
 from .logging import Logger
 from .lnutil import hex_to_bytes
@@ -450,7 +450,7 @@ async def get_pairs(self) -> None:
         self._max_amount = limits['maximal']
 
     def get_max_amount(self):
-        return min(self._max_amount, LN_MAX_HTLC_VALUE_MSAT // 1000)
+        return self._max_amount
 
     def check_invoice_amount(self, x):
         return x >= self.min_amount and x <= self._max_amount

electrum/tests/test_lnchannel.py

@@ -193,9 +193,6 @@ def create_test_channels(*, feerate=6000, local_msat=None, remote_msat=None,
     alice._fallback_sweep_address = bitcoin.pubkey_to_address('p2wpkh', alice.config[LOCAL].payment_basepoint.pubkey.hex())
     bob._fallback_sweep_address = bitcoin.pubkey_to_address('p2wpkh', bob.config[LOCAL].payment_basepoint.pubkey.hex())
 
-    alice._ignore_max_htlc_value = True
-    bob._ignore_max_htlc_value = True
-
     return alice, bob
 
 class TestFee(ElectrumTestCase):
@@ -683,29 +680,6 @@ def test_DesyncHTLCs(self):
         self.assertEqual(500000000000, bob_channel.available_to_spend(LOCAL))
         alice_channel.add_htlc(htlc_dict)
 
-    def test_max_htlc_value(self):
-        alice_channel, bob_channel = create_test_channels()
-        paymentPreimage = b"\x01" * 32
-        paymentHash = bitcoin.sha256(paymentPreimage)
-        htlc_dict = {
-            'payment_hash' : paymentHash,
-            'amount_msat' :  one_bitcoin_in_msat * 41 // 10,
-            'cltv_expiry' :  5,
-            'timestamp'   :  0,
-        }
-
-        alice_channel._ignore_max_htlc_value = False
-        bob_channel._ignore_max_htlc_value = False
-        with self.assertRaises(lnutil.PaymentFailure):
-            alice_channel.add_htlc(htlc_dict)
-        with self.assertRaises(lnutil.RemoteMisbehaving):
-            bob_channel.receive_htlc(htlc_dict)
-
-        alice_channel._ignore_max_htlc_value = True
-        bob_channel._ignore_max_htlc_value = True
-        alice_channel.add_htlc(htlc_dict)
-        bob_channel.receive_htlc(htlc_dict)
-
 
 class TestChanReserve(ElectrumTestCase):
     def setUp(self):