From 9394b18b4e87efb4a0de004d2ac8461a3d8ee416 Mon Sep 17 00:00:00 2001
From: f321x <f321x@tutamail.com>
Date: Tue, 18 Feb 2025 15:16:11 +0100
Subject: [PATCH] add method list_enabled_ln_feature_bits

---
 electrum/lnutil.py   | 21 +++++++++++++++++----
 tests/test_lnutil.py | 15 +++++++++++----
 2 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/electrum/lnutil.py b/electrum/lnutil.py
index 1ad1703ae..0cc951b41 100644
--- a/electrum/lnutil.py
+++ b/electrum/lnutil.py
@@ -1468,28 +1468,28 @@ class LnFeatures(IntFlag):
 
     def for_init_message(self) -> 'LnFeatures':
         features = LnFeatures(0)
-        for flag in list_enabled_bits(self):
+        for flag in list_enabled_ln_feature_bits(self):
             if LnFeatureContexts.INIT & _ln_feature_contexts[1 << flag]:
                 features |= (1 << flag)
         return features
 
     def for_node_announcement(self) -> 'LnFeatures':
         features = LnFeatures(0)
-        for flag in list_enabled_bits(self):
+        for flag in list_enabled_ln_feature_bits(self):
             if LnFeatureContexts.NODE_ANN & _ln_feature_contexts[1 << flag]:
                 features |= (1 << flag)
         return features
 
     def for_invoice(self) -> 'LnFeatures':
         features = LnFeatures(0)
-        for flag in list_enabled_bits(self):
+        for flag in list_enabled_ln_feature_bits(self):
             if LnFeatureContexts.INVOICE & _ln_feature_contexts[1 << flag]:
                 features |= (1 << flag)
         return features
 
     def for_channel_announcement(self) -> 'LnFeatures':
         features = LnFeatures(0)
-        for flag in list_enabled_bits(self):
+        for flag in list_enabled_ln_feature_bits(self):
             ctxs = _ln_feature_contexts[1 << flag]
             if LnFeatureContexts.CHAN_ANN_AS_IS & ctxs:
                 features |= (1 << flag)
@@ -1627,6 +1627,19 @@ def get_ln_flag_pair_of_bit(flag_bit: int) -> int:
         return flag_bit - 1
 
 
+def list_enabled_ln_feature_bits(features: int) -> tuple[int, ...]:
+    """Returns a list of enabled feature bits. If both opt and req are set, only
+    req will be included in the result."""
+    all_enabled_bits = list_enabled_bits(features)
+    single_feature_bits: set[int] = set()
+    for bit in all_enabled_bits:
+        if bit % 2 == 0:  # even bit, always added
+            single_feature_bits.add(bit)
+        elif bit - 1 not in single_feature_bits:
+            # add if we haven't already added the corresponding req (even) bit
+            single_feature_bits.add(bit)
+    return tuple(sorted(single_feature_bits))
+
 
 class IncompatibleOrInsaneFeatures(Exception): pass
 class UnknownEvenFeatureBits(IncompatibleOrInsaneFeatures): pass
diff --git a/tests/test_lnutil.py b/tests/test_lnutil.py
index 79097fff4..561609601 100644
--- a/tests/test_lnutil.py
+++ b/tests/test_lnutil.py
@@ -7,15 +7,18 @@ import electrum_ecc as ecc
 
 from electrum import bitcoin
 from electrum.json_db import StoredDict
-from electrum.lnutil import (RevocationStore, get_per_commitment_secret_from_seed, make_offered_htlc,
-                             make_received_htlc, make_commitment, make_htlc_tx_witness, make_htlc_tx_output,
-                             make_htlc_tx_inputs, secret_to_pubkey, derive_blinded_pubkey, derive_privkey,
+from electrum.lnutil import (RevocationStore, get_per_commitment_secret_from_seed,
+                             make_offered_htlc,
+                             make_received_htlc, make_commitment, make_htlc_tx_witness,
+                             make_htlc_tx_output,
+                             make_htlc_tx_inputs, secret_to_pubkey, derive_blinded_pubkey,
+                             derive_privkey,
                              derive_pubkey, make_htlc_tx, extract_ctn_from_tx, UnableToDeriveSecret,
                              get_compressed_pubkey_from_bech32,
                              ScriptHtlc, calc_fees_for_commitment_tx, UpdateAddHtlc, LnFeatures,
                              ln_compare_features, IncompatibleLightningFeatures, ChannelType,
                              offered_htlc_trim_threshold_sat, received_htlc_trim_threshold_sat,
-                             ImportedChannelBackupStorage)
+                             ImportedChannelBackupStorage, list_enabled_ln_feature_bits)
 from electrum.util import bfh, MyEncoder
 from electrum.transaction import Transaction, PartialTransaction, Sighash
 from electrum.lnworker import LNWallet
@@ -1008,6 +1011,10 @@ class TestLNUtil(ElectrumTestCase):
                          LnFeatures.VAR_ONION_OPT,
                          ln_compare_features(f2, f1))
 
+    def test_list_enabled_ln_feature_bits(self):
+        self.assertEqual((0, 2, 6), list_enabled_ln_feature_bits(77))
+        self.assertEqual((), list_enabled_ln_feature_bits(0))
+
     def test_ln_features_supports(self):
         f_null = LnFeatures(0)
         f_opt = LnFeatures.OPTION_DATA_LOSS_PROTECT_OPT