lnchannel: ctx output-ordering: identical htlcs are ordered by CLTV

electrum/lnchannel.py

@@ -340,6 +340,7 @@ class Channel(Logger):
         htlc_sigs = htlc_sigs[:] # copy cause we will delete now
         for htlcs, we_receive in [(self.included_htlcs(LOCAL, SENT, ctn=next_local_ctn), False),
                                   (self.included_htlcs(LOCAL, RECEIVED, ctn=next_local_ctn), True)]:
+            # FIXME this is quadratic. BOLT-02: "corresponding to the ordering of the commitment transaction"
             for htlc in htlcs:
                 idx = self.verify_htlc(htlc, htlc_sigs, we_receive, pending_local_commitment)
                 del htlc_sigs[idx]

electrum/lnutil.py

@@ -93,7 +93,11 @@ class FeeUpdate(NamedTuple):
 
 ChannelConstraints = namedtuple("ChannelConstraints", ["capacity", "is_initiator", "funding_txn_minimum_depth"])
 
-ScriptHtlc = namedtuple('ScriptHtlc', ['redeem_script', 'htlc'])
+
+class ScriptHtlc(NamedTuple):
+    redeem_script: bytes
+    htlc: 'UpdateAddHtlc'
+
 
 class Outpoint(NamedTuple("Outpoint", [('txid', str), ('output_index', int)])):
     def to_str(self):
@@ -475,6 +479,13 @@ def make_commitment(ctn, local_funding_pubkey, remote_funding_pubkey,
     remote_address = make_commitment_output_to_remote_address(remote_payment_pubkey)
     # TODO trim htlc outputs here while also considering 2nd stage htlc transactions
 
+    # BOLT-03: "Transaction Input and Output Ordering
+    #           Lexicographic ordering: see BIP69. In the case of identical HTLC outputs,
+    #           the outputs are ordered in increasing cltv_expiry order."
+    # so we sort by cltv_expiry now; and the later BIP69-sort is assumed to be *stable*
+    htlcs = list(htlcs)
+    htlcs.sort(key=lambda x: x.htlc.cltv_expiry)
+
     htlc_outputs, c_outputs_filtered = make_commitment_outputs(fees_per_participant, local_amount, remote_amount,
         (bitcoin.TYPE_ADDRESS, local_address), (bitcoin.TYPE_ADDRESS, remote_address), htlcs, dust_limit_sat)
 

electrum/tests/test_lnutil.py

@@ -495,7 +495,7 @@ class TestLNUtil(unittest.TestCase):
             (1, 2000 * 1000),
             (3, 3000 * 1000),
             (4, 4000 * 1000)]:
-            htlc_obj[num] = UpdateAddHtlc(amount_msat=msat, payment_hash=bitcoin.sha256(htlc_payment_preimage[num]), cltv_expiry=None, htlc_id=None, timestamp=0)
+            htlc_obj[num] = UpdateAddHtlc(amount_msat=msat, payment_hash=bitcoin.sha256(htlc_payment_preimage[num]), cltv_expiry=0, htlc_id=None, timestamp=0)
         htlcs = [ScriptHtlc(htlc[x], htlc_obj[x]) for x in range(5)]
 
         our_commit_tx = make_commitment(

electrum/transaction.py

@@ -958,6 +958,7 @@ class Transaction:
             txin['sequence'] = nSequence
 
     def BIP69_sort(self, inputs=True, outputs=True):
+        # NOTE: other parts of the code rely on these sorts being *stable* sorts
         if inputs:
             self._inputs.sort(key = lambda i: (i['prevout_hash'], i['prevout_n']))
         if outputs: