basic_mpp: receive multi-part payments

electrum/lnchannel.py

@@ -969,10 +969,6 @@ def revoke_current_commitment(self):
             raise Exception("refusing to revoke as remote sig does not fit")
         with self.db_lock:
             self.hm.send_rev()
-        if self.lnworker:
-            received = self.hm.received_in_ctn(new_ctn)
-            for htlc in received:
-                self.lnworker.payment_received(self, htlc.payment_hash)
         last_secret, last_point = self.get_secret_and_point(LOCAL, new_ctn - 1)
         next_secret, next_point = self.get_secret_and_point(LOCAL, new_ctn + 1)
         return RevokeAndAck(last_secret, next_point)
@@ -1054,7 +1050,7 @@ def extract_preimage_from_htlc_txin(self, txin: TxInput) -> None:
             if is_sent:
                 self.lnworker.payment_sent(self, payment_hash)
             else:
-                self.lnworker.payment_received(self, payment_hash)
+                self.lnworker.payment_received(payment_hash)
 
     def balance(self, whose: HTLCOwner, *, ctx_owner=HTLCOwner.LOCAL, ctn: int = None) -> int:
         assert type(whose) is HTLCOwner

electrum/lnonion.py

@@ -498,6 +498,7 @@ class OnionFailureCode(IntEnum):
     CHANNEL_DISABLED =                        UPDATE | 20
     EXPIRY_TOO_FAR =                          21
     INVALID_ONION_PAYLOAD =                   PERM | 22
+    MPP_TIMEOUT =                             23
 
 
 # don't use these elsewhere, the names are ambiguous without context

electrum/lnpeer.py

@@ -1389,10 +1389,6 @@ def maybe_fulfill_htlc(
                 reason = OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS, data=b'')
                 return None, reason
         expected_received_msat = info.amount_msat
-        if expected_received_msat is not None and \
-                not (expected_received_msat <= htlc.amount_msat <= 2 * expected_received_msat):
-            reason = OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS, data=b'')
-            return None, reason
         # Check that our blockchain tip is sufficiently recent so that we have an approx idea of the height.
         # We should not release the preimage for an HTLC that its sender could already time out as
         # then they might try to force-close and it becomes a race.
@@ -1415,20 +1411,34 @@ def maybe_fulfill_htlc(
                 data=htlc.cltv_expiry.to_bytes(4, byteorder="big"))
             return None, reason
         try:
-            amount_from_onion = processed_onion.hop_data.payload["amt_to_forward"]["amt_to_forward"]
+            amt_to_forward = processed_onion.hop_data.payload["amt_to_forward"]["amt_to_forward"]
         except:
             reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_PAYLOAD, data=b'\x00\x00\x00')
             return None, reason
         try:
-            amount_from_onion = processed_onion.hop_data.payload["payment_data"]["total_msat"]
+            total_msat = processed_onion.hop_data.payload["payment_data"]["total_msat"]
         except:
-            pass  # fall back to "amt_to_forward"
-        if amount_from_onion > htlc.amount_msat:
-            reason = OnionRoutingFailureMessage(code=OnionFailureCode.FINAL_INCORRECT_HTLC_AMOUNT,
-                                                data=htlc.amount_msat.to_bytes(8, byteorder="big"))
+            total_msat = amt_to_forward # fall back to "amt_to_forward"
+
+        if amt_to_forward != htlc.amount_msat:
+            reason = OnionRoutingFailureMessage(
+                code=OnionFailureCode.FINAL_INCORRECT_HTLC_AMOUNT,
+                data=total_msat.to_bytes(8, byteorder="big"))
             return None, reason
-        # all good
-        return preimage, None
+        if expected_received_msat is None:
+            return preimage, None
+        if not (expected_received_msat <= total_msat <= 2 * expected_received_msat):
+            reason = OnionRoutingFailureMessage(code=OnionFailureCode.INCORRECT_OR_UNKNOWN_PAYMENT_DETAILS, data=b'')
+            return None, reason
+        accepted, expired = self.lnworker.htlc_received(chan.short_channel_id, htlc, expected_received_msat)
+        if accepted:
+            return preimage, None
+        elif expired:
+            reason = OnionRoutingFailureMessage(code=OnionFailureCode.MPP_TIMEOUT)
+            return None, reason
+        else:
+            # waiting for more htlcs
+            return None, None
 
     def fulfill_htlc(self, chan: Channel, htlc_id: int, preimage: bytes):
         self.logger.info(f"_fulfill_htlc. chan {chan.short_channel_id}. htlc_id {htlc_id}")
@@ -1669,7 +1679,7 @@ async def htlc_switch(self):
                 for htlc_id, (local_ctn, remote_ctn, onion_packet_hex, forwarding_info) in unfulfilled.items():
                     if not chan.hm.is_add_htlc_irrevocably_committed_yet(htlc_proposer=REMOTE, htlc_id=htlc_id):
                         continue
-                    chan.logger.info(f'found unfulfilled htlc: {htlc_id}')
+                    #chan.logger.info(f'found unfulfilled htlc: {htlc_id}')
                     htlc = chan.hm.get_htlc_by_id(REMOTE, htlc_id)
                     payment_hash = htlc.payment_hash
                     error_reason = None  # type: Optional[OnionRoutingFailureMessage]
@@ -1694,7 +1704,6 @@ async def htlc_switch(self):
                             error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.INVALID_ONION_VERSION, data=sha256(onion_packet_bytes))
                         if self.network.config.get('test_fail_htlcs_with_temp_node_failure'):
                             error_reason = OnionRoutingFailureMessage(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
-
                     if not error_reason:
                         if processed_onion.are_we_final:
                             preimage, error_reason = self.maybe_fulfill_htlc(

electrum/lnworker.py

@@ -86,6 +86,7 @@
 
 
 NUM_PEERS_TARGET = 4
+MPP_EXPIRY = 120
 
 
 FALLBACK_NODE_LIST_TESTNET = (
@@ -164,7 +165,8 @@ class ErrorAddingPeer(Exception): pass
 LNWALLET_FEATURES = BASE_FEATURES\
     | LnFeatures.OPTION_DATA_LOSS_PROTECT_REQ\
     | LnFeatures.OPTION_STATIC_REMOTEKEY_REQ\
-    | LnFeatures.GOSSIP_QUERIES_REQ
+    | LnFeatures.GOSSIP_QUERIES_REQ\
+    | LnFeatures.BASIC_MPP_OPT
 
 LNGOSSIP_FEATURES = BASE_FEATURES\
     | LnFeatures.GOSSIP_QUERIES_OPT\
@@ -581,6 +583,7 @@ def __init__(self, wallet: 'Abstract_Wallet', xprv):
             self._channels[bfh(channel_id)] = Channel(c, sweep_address=self.sweep_address, lnworker=self)
 
         self.pending_payments = defaultdict(asyncio.Future)  # type: Dict[bytes, asyncio.Future[BarePaymentAttemptLog]]
+        self.pending_htlcs = defaultdict(set) # type: Dict[bytes, set]
 
         self.swap_manager = SwapManager(wallet=self.wallet, lnworker=self)
         # detect inflight payments
@@ -1284,6 +1287,24 @@ def save_payment_info(self, info: PaymentInfo) -> None:
             self.payments[key] = info.amount_msat, info.direction, info.status
         self.wallet.save_db()
 
+    def htlc_received(self, short_channel_id, htlc, expected_msat):
+        status = self.get_payment_status(htlc.payment_hash)
+        if status == PR_PAID:
+            return True, None
+        s = self.pending_htlcs[htlc.payment_hash]
+        if (short_channel_id, htlc) not in s:
+            s.add((short_channel_id, htlc))
+        total = sum([htlc.amount_msat for scid, htlc in s])
+        first_timestamp = min([htlc.timestamp for scid, htlc in s])
+        expired = time.time() - first_timestamp > MPP_EXPIRY
+        if total >= expected_msat and not expired:
+            # status must be persisted
+            self.payment_received(htlc.payment_hash)
+            return True, None
+        if expired:
+            return None, True
+        return None, None
+
     def get_payment_status(self, payment_hash):
         info = self.get_payment_info(payment_hash)
         return info.status if info else PR_UNPAID
@@ -1359,10 +1380,10 @@ def payment_sent(self, chan, payment_hash: bytes):
             util.trigger_callback('payment_succeeded', self.wallet, key)
         util.trigger_callback('ln_payment_completed', payment_hash, chan.channel_id)
 
-    def payment_received(self, chan, payment_hash: bytes):
+    def payment_received(self, payment_hash: bytes):
         self.set_payment_status(payment_hash, PR_PAID)
         util.trigger_callback('request_status', self.wallet, payment_hash.hex(), PR_PAID)
-        util.trigger_callback('ln_payment_completed', payment_hash, chan.channel_id)
+        #util.trigger_callback('ln_payment_completed', payment_hash, chan.channel_id)
 
     async def _calc_routing_hints_for_invoice(self, amount_msat: Optional[int]):
         """calculate routing hints (BOLT-11 'r' field)"""

electrum/tests/test_lnpeer.py

@@ -132,6 +132,7 @@ def __init__(self, *, local_keypair: Keypair, chans: Iterable['Channel'], tx_que
         # used in tests
         self.enable_htlc_settle = asyncio.Event()
         self.enable_htlc_settle.set()
+        self.pending_htlcs = defaultdict(set)
 
     def get_invoice_status(self, key):
         pass
@@ -167,6 +168,7 @@ def save_channel(self, chan):
     set_invoice_status = LNWallet.set_invoice_status
     set_payment_status = LNWallet.set_payment_status
     get_payment_status = LNWallet.get_payment_status
+    htlc_received = LNWallet.htlc_received
     await_payment = LNWallet.await_payment
     payment_received = LNWallet.payment_received
     payment_sent = LNWallet.payment_sent