lnaddr: add feature bit support to invoices

see https://github.com/lightningnetwork/lightning-rfc/pull/656

electrum/channel_db.py

@@ -38,7 +38,8 @@ from .sql_db import SqlDB, sql
 from . import constants
 from .util import bh2u, profiler, get_headers_dir, bfh, is_ip_address, list_enabled_bits
 from .logging import Logger
-from .lnutil import LN_FEATURES_IMPLEMENTED, LNPeerAddr, format_short_channel_id, ShortChannelID
+from .lnutil import (LNPeerAddr, format_short_channel_id, ShortChannelID,
+                     UnknownEvenFeatureBits, validate_features)
 from .lnverifier import LNChannelVerifier, verify_sig_for_channel_update
 from .lnmsg import decode_msg
 
@@ -47,15 +48,6 @@ if TYPE_CHECKING:
     from .lnchannel import Channel
 
 
-class UnknownEvenFeatureBits(Exception): pass
-
-def validate_features(features: int) -> None:
-    enabled_features = list_enabled_bits(features)
-    for fbit in enabled_features:
-        if (1 << fbit) & LN_FEATURES_IMPLEMENTED == 0 and fbit % 2 == 0:
-            raise UnknownEvenFeatureBits()
-
-
 FLAG_DISABLE   = 1 << 1
 FLAG_DIRECTION = 1 << 0
 

electrum/lnaddr.py

@@ -141,6 +141,14 @@ def tagged(char, l):
 def tagged_bytes(char, l):
     return tagged(char, bitstring.BitArray(l))
 
+def trim_to_min_length(bits):
+    # Get minimal length by trimming leading 5 bits at a time.
+    while bits.startswith('0b00000'):
+        if len(bits) == 5:
+            break  # v == 0
+        bits = bits[5:]
+    return bits
+
 # Discard trailing bits, convert to bytes.
 def trim_to_bytes(barr):
     # Adds a byte if necessary.
@@ -155,7 +163,7 @@ def pull_tagged(stream):
     length = stream.read(5).uint * 32 + stream.read(5).uint
     return (CHARSET[tag], stream.read(length * 5), stream)
 
-def lnencode(addr, privkey):
+def lnencode(addr: 'LnAddr', privkey):
     if addr.amount:
         amount = Decimal(str(addr.amount))
         # We can only send down to millisatoshi.
@@ -196,23 +204,24 @@ def lnencode(addr, privkey):
         elif k == 'd':
             data += tagged_bytes('d', v.encode())
         elif k == 'x':
-            # Get minimal length by trimming leading 5 bits at a time.
             expirybits = bitstring.pack('intbe:64', v)[4:64]
-            while expirybits.startswith('0b00000'):
-                if len(expirybits) == 5:
-                    break  # v == 0
-                expirybits = expirybits[5:]
+            expirybits = trim_to_min_length(expirybits)
             data += tagged('x', expirybits)
         elif k == 'h':
             data += tagged_bytes('h', sha256(v.encode('utf-8')).digest())
         elif k == 'n':
             data += tagged_bytes('n', v)
         elif k == 'c':
-            # Get minimal length by trimming leading 5 bits at a time.
             finalcltvbits = bitstring.pack('intbe:64', v)[4:64]
-            while finalcltvbits.startswith('0b00000'):
-                finalcltvbits = finalcltvbits[5:]
+            finalcltvbits = trim_to_min_length(finalcltvbits)
             data += tagged('c', finalcltvbits)
+        elif k == '9':
+            if v == 0:
+                continue
+            feature_bits = bitstring.BitArray(uint=v, length=v.bit_length())
+            while feature_bits.len % 5 != 0:
+                feature_bits.prepend('0b0')
+            data += tagged('9', feature_bits)
         else:
             # FIXME: Support unknown tags?
             raise ValueError("Unknown tag {}".format(k))
@@ -247,7 +256,7 @@ class LnAddr(object):
         self.signature = None
         self.pubkey = None
         self.currency = constants.net.SEGWIT_HRP if currency is None else currency
-        self.amount = amount
+        self.amount = amount  # in bitcoins
         self._min_final_cltv_expiry = 9
 
     def __str__(self):
@@ -389,8 +398,16 @@ def lndecode(invoice: str, *, verbose=False, expected_hrp=None) -> LnAddr:
                 continue
             pubkeybytes = trim_to_bytes(tagdata)
             addr.pubkey = pubkeybytes
+
         elif tag == 'c':
             addr._min_final_cltv_expiry = tagdata.int
+
+        elif tag == '9':
+            features = tagdata.uint
+            addr.tags.append(('9', features))
+            from .lnutil import validate_features
+            validate_features(features)
+
         else:
             addr.unknown_tags.append((tag, tagdata))
 

electrum/lnonion.py

@@ -87,7 +87,7 @@ class LegacyHopDataPayload:
     @classmethod
     def from_tlv_dict(cls, d: dict) -> 'LegacyHopDataPayload':
         return LegacyHopDataPayload(
-            short_channel_id=d["short_channel_id"]["short_channel_id"],
+            short_channel_id=d["short_channel_id"]["short_channel_id"] if "short_channel_id" in d else b"\x00" * 8,
             amt_to_forward=d["amt_to_forward"]["amt_to_forward"],
             outgoing_cltv_value=d["outgoing_cltv_value"]["outgoing_cltv_value"],
         )

electrum/lnutil.py

@@ -165,6 +165,7 @@ class HandshakeFailed(LightningError): pass
 class ConnStringFormatError(LightningError): pass
 class UnknownPaymentHash(LightningError): pass
 class RemoteMisbehaving(LightningError): pass
+class UnknownEvenFeatureBits(Exception): pass
 
 class NotFoundChanAnnouncementForUpdate(Exception): pass
 
@@ -882,6 +883,16 @@ def ln_compare_features(our_features: 'LnFeatures', their_features: int) -> 'LnF
     return our_features
 
 
+def validate_features(features: int) -> None:
+    """Raises UnknownEvenFeatureBits if there is an unimplemented
+    mandatory feature.
+    """
+    enabled_features = list_enabled_bits(features)
+    for fbit in enabled_features:
+        if (1 << fbit) & LN_FEATURES_IMPLEMENTED == 0 and fbit % 2 == 0:
+            raise UnknownEvenFeatureBits(fbit)
+
+
 class LNPeerAddr:
 
     def __init__(self, host: str, port: int, pubkey: bytes):

electrum/tests/test_bolt11.py

@@ -6,6 +6,7 @@ import unittest
 
 from electrum.lnaddr import shorten_amount, unshorten_amount, LnAddr, lnencode, lndecode, u5_to_bitarray, bitarray_to_u5
 from electrum.segwit_addr import bech32_encode, bech32_decode
+from electrum.lnutil import UnknownEvenFeatureBits
 
 from . import ElectrumTestCase
 
@@ -66,11 +67,22 @@ class TestBolt11(ElectrumTestCase):
             LnAddr(RHASH, amount=Decimal('1'), tags=[('h', longdescription)]),
             LnAddr(RHASH, currency='tb', tags=[('f', 'mk2QpYatsKicvFVuTAQLBryyccRXMUaGHP'), ('h', longdescription)]),
             LnAddr(RHASH, amount=24, tags=[
-                ('r', [(unhexlify('029e03a901b85534ff1e92c43c74431f7ce72046060fcf7a95c37e148f78c77255'), unhexlify('0102030405060708'), 1, 20, 3), (unhexlify('039e03a901b85534ff1e92c43c74431f7ce72046060fcf7a95c37e148f78c77255'), unhexlify('030405060708090a'), 2, 30, 4)]), ('f', '1RustyRX2oai4EYYDpQGWvEL62BBGqN9T'), ('h', longdescription)]),
+                ('r', [(unhexlify('029e03a901b85534ff1e92c43c74431f7ce72046060fcf7a95c37e148f78c77255'), unhexlify('0102030405060708'), 1, 20, 3),
+                       (unhexlify('039e03a901b85534ff1e92c43c74431f7ce72046060fcf7a95c37e148f78c77255'), unhexlify('030405060708090a'), 2, 30, 4)]),
+                ('f', '1RustyRX2oai4EYYDpQGWvEL62BBGqN9T'),
+                ('h', longdescription)]),
             LnAddr(RHASH, amount=24, tags=[('f', '3EktnHQD7RiAE6uzMj2ZifT9YgRrkSgzQX'), ('h', longdescription)]),
             LnAddr(RHASH, amount=24, tags=[('f', 'bc1qw508d6qejxtdg4y5r3zarvary0c5xw7kv8f3t4'), ('h', longdescription)]),
             LnAddr(RHASH, amount=24, tags=[('f', 'bc1qrp33g0q5c5txsp9arysrx4k6zdkfs4nce4xj0gdcccefvpysxf3qccfmv3'), ('h', longdescription)]),
             LnAddr(RHASH, amount=24, tags=[('n', PUBKEY), ('h', longdescription)]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 514)]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 8))]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 9))]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 11))]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 12))]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 13))]),
+            #LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 14))]),
+            LnAddr(RHASH, amount=24, tags=[('h', longdescription), ('9', 10 + (1 << 15))]),
         ]
 
         # Roundtrip
@@ -98,9 +110,18 @@ class TestBolt11(ElectrumTestCase):
         assert lnaddr.pubkey.serialize() == PUBKEY
 
     def test_min_final_cltv_expiry_decoding(self):
-        self.assertEqual(144, lndecode("lnsb500u1pdsgyf3pp5nmrqejdsdgs4n9ukgxcp2kcq265yhrxd4k5dyue58rxtp5y83s3qdqqcqzystrggccm9yvkr5yqx83jxll0qjpmgfg9ywmcd8g33msfgmqgyfyvqhku80qmqm8q6v35zvck2y5ccxsz5avtrauz8hgjj3uahppyq20qp6dvwxe", expected_hrp="sb").get_min_final_cltv_expiry())
+        lnaddr = lndecode("lnsb500u1pdsgyf3pp5nmrqejdsdgs4n9ukgxcp2kcq265yhrxd4k5dyue58rxtp5y83s3qdqqcqzystrggccm9yvkr5yqx83jxll0qjpmgfg9ywmcd8g33msfgmqgyfyvqhku80qmqm8q6v35zvck2y5ccxsz5avtrauz8hgjj3uahppyq20qp6dvwxe",
+                          expected_hrp="sb")
+        self.assertEqual(144, lnaddr.get_min_final_cltv_expiry())
 
     def test_min_final_cltv_expiry_roundtrip(self):
         lnaddr = LnAddr(RHASH, amount=Decimal('0.001'), tags=[('d', '1 cup coffee'), ('x', 60), ('c', 150)])
         invoice = lnencode(lnaddr, PRIVKEY)
         self.assertEqual(150, lndecode(invoice).get_min_final_cltv_expiry())
+
+    def test_features(self):
+        lnaddr = lndecode("lnbc25m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdees9qzsze992adudgku8p05pstl6zh7av6rx2f297pv89gu5q93a0hf3g7lynl3xq56t23dpvah6u7y9qey9lccrdml3gaqwc6nxsl5ktzm464sq73t7cl")
+        self.assertEqual(514, lnaddr.get_tag('9'))
+
+        with self.assertRaises(UnknownEvenFeatureBits):
+            lndecode("lnbc25m1pvjluezpp5qqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqqqsyqcyq5rqwzqfqypqdq5vdhkven9v5sxyetpdees9q4pqqqqqqqqqqqqqqqqqqszk3ed62snp73037h4py4gry05eltlp0uezm2w9ajnerhmxzhzhsu40g9mgyx5v3ad4aqwkmvyftzk4k9zenz90mhjcy9hcevc7r3lx2sphzfxz7")