lnaddr: encode min_final_cltv into invoice

electrum/lnaddr.py

@@ -205,6 +205,12 @@ def lnencode(addr, privkey):
             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:]
+            data += tagged('c', finalcltvbits)
         else:
             # FIXME: Support unknown tags?
             raise ValueError("Unknown tag {}".format(k))
@@ -240,7 +246,7 @@ class LnAddr(object):
         self.pubkey = None
         self.currency = constants.net.SEGWIT_HRP if currency is None else currency
         self.amount = amount
-        self.min_final_cltv_expiry = 9
+        self._min_final_cltv_expiry = 9
 
     def __str__(self):
         return "LnAddr[{}, amount={}{} tags=[{}]]".format(
@@ -249,6 +255,10 @@ class LnAddr(object):
             ", ".join([k + '=' + str(v) for k, v in self.tags])
         )
 
+    def get_min_final_cltv_expiry(self) -> int:
+        return self._min_final_cltv_expiry
+
+
 def lndecode(a, verbose=False, expected_hrp=None):
     if expected_hrp is None:
         expected_hrp = constants.net.SEGWIT_HRP
@@ -354,7 +364,7 @@ def lndecode(a, verbose=False, expected_hrp=None):
             pubkeybytes = trim_to_bytes(tagdata)
             addr.pubkey = pubkeybytes
         elif tag == 'c':
-            addr.min_final_cltv_expiry = tagdata.int
+            addr._min_final_cltv_expiry = tagdata.int
         else:
             addr.unknown_tags.append((tag, tagdata))
 

electrum/lnworker.py

@@ -263,7 +263,7 @@ class LNWorker(PrintError):
                 break
         else:
             raise Exception("ChannelDB returned path with short_channel_id {} that is not in channel list".format(bh2u(short_channel_id)))
-        coro = peer.pay(route, chan, amount_msat, payment_hash, addr.min_final_cltv_expiry)
+        coro = peer.pay(route, chan, amount_msat, payment_hash, addr.get_min_final_cltv_expiry())
         return addr, peer, asyncio.run_coroutine_threadsafe(coro, self.network.asyncio_loop)
 
     def _create_route_from_invoice(self, decoded_invoice, amount_msat) -> List[RouteEdge]:

electrum/tests/test_bolt11.py

@@ -57,8 +57,7 @@ class TestBolt11(unittest.TestCase):
 
         tests = [
             LnAddr(RHASH, tags=[('d', '')]),
-            LnAddr(RHASH, amount=Decimal('0.001'),
-                   tags=[('d', '1 cup coffee'), ('x', 60)]),
+            LnAddr(RHASH, amount=Decimal('0.001'), tags=[('d', '1 cup coffee'), ('x', 60)]),
             LnAddr(RHASH, amount=Decimal('1'), tags=[('h', longdescription)]),
             LnAddr(RHASH, currency='tb', tags=[('f', 'mk2QpYatsKicvFVuTAQLBryyccRXMUaGHP'), ('h', longdescription)]),
             LnAddr(RHASH, amount=24, tags=[
@@ -93,5 +92,10 @@ class TestBolt11(unittest.TestCase):
         lnaddr = lndecode(bech32_encode(hrp, bitarray_to_u5(databits)), True)
         assert lnaddr.pubkey.serialize() == PUBKEY
 
-    def test_min_final_cltv_expiry(self):
-        self.assertEquals(lndecode("lnsb500u1pdsgyf3pp5nmrqejdsdgs4n9ukgxcp2kcq265yhrxd4k5dyue58rxtp5y83s3qdqqcqzystrggccm9yvkr5yqx83jxll0qjpmgfg9ywmcd8g33msfgmqgyfyvqhku80qmqm8q6v35zvck2y5ccxsz5avtrauz8hgjj3uahppyq20qp6dvwxe", expected_hrp="sb").min_final_cltv_expiry, 144)
+    def test_min_final_cltv_expiry_decoding(self):
+        self.assertEquals(144, lndecode("lnsb500u1pdsgyf3pp5nmrqejdsdgs4n9ukgxcp2kcq265yhrxd4k5dyue58rxtp5y83s3qdqqcqzystrggccm9yvkr5yqx83jxll0qjpmgfg9ywmcd8g33msfgmqgyfyvqhku80qmqm8q6v35zvck2y5ccxsz5avtrauz8hgjj3uahppyq20qp6dvwxe", expected_hrp="sb").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.assertEquals(150, lndecode(invoice).get_min_final_cltv_expiry())