Multinut LND (#492)

* amount in melt request

* apply fee limit

* more error handling

* wip: signal flag in /info

* clean up multinut

* decode mypy error lndrest

* fix test

* fix tests

* signal feature and blindmessages_deprecated

* setting

* fix blindedsignature method

* fix tests

* mint info file

* test mpp with lnd regtest

* nuts optionsl mint
 info

* try to enable mpp with lnd

* test mpp with third payment

.github/workflows/regtest.yml

@@ -65,6 +65,7 @@ jobs:
           MINT_LND_REST_ENDPOINT: https://localhost:8081/
           MINT_LND_REST_CERT: ./regtest/data/lnd-3/tls.cert
           MINT_LND_REST_MACAROON: ./regtest/data/lnd-3/data/chain/bitcoin/regtest/admin.macaroon
+          MINT_LND_ENABLE_MPP: true
           #   LND_GRPC_ENDPOINT: localhost
           #   LND_GRPC_PORT: 10009
           #   LND_GRPC_CERT: ./regtest/data/lnd-3/tls.cert

cashu/core/base.py

@@ -161,13 +161,18 @@ class Proof(BaseModel):
         return HTLCWitness.from_witness(self.witness).preimage
 
 
+class Proofs(BaseModel):
+    # NOTE: not used in Pydantic validation
+    __root__: List[Proof]
+
+
 class BlindedMessage(BaseModel):
     """
     Blinded message or blinded secret or "output" which is to be signed by the mint
     """
 
     amount: int
-    id: str
+    id: str  # Keyset id
     B_: str  # Hex-encoded blinded message
     witness: Union[str, None] = None  # witnesses (used for P2PK with SIG_ALL)
 
@@ -177,6 +182,28 @@ class BlindedMessage(BaseModel):
         return P2PKWitness.from_witness(self.witness).signatures
 
 
+class BlindedMessage_Deprecated(BaseModel):
+    """
+    Deprecated: BlindedMessage for v0 protocol (deprecated api routes) have no id field.
+
+    Blinded message or blinded secret or "output" which is to be signed by the mint
+    """
+
+    amount: int
+    B_: str  # Hex-encoded blinded message
+    witness: Union[str, None] = None  # witnesses (used for P2PK with SIG_ALL)
+
+    @property
+    def p2pksigs(self) -> List[str]:
+        assert self.witness, "Witness missing in output"
+        return P2PKWitness.from_witness(self.witness).signatures
+
+
+class BlindedMessages(BaseModel):
+    # NOTE: not used in Pydantic validation
+    __root__: List[BlindedMessage] = []
+
+
 class BlindedSignature(BaseModel):
     """
     Blinded signature or "promise" which is the signature on a `BlindedMessage`
@@ -314,7 +341,13 @@ class GetInfoResponse(BaseModel):
     description_long: Optional[str] = None
     contact: Optional[List[List[str]]] = None
     motd: Optional[str] = None
-    nuts: Optional[Dict[int, Dict[str, Any]]] = None
+    nuts: Optional[Dict[int, Any]] = None
+
+
+class Nut15MppSupport(BaseModel):
+    method: str
+    unit: str
+    mpp: bool
 
 
 class GetInfoResponse_deprecated(BaseModel):
@@ -329,19 +362,6 @@ class GetInfoResponse_deprecated(BaseModel):
     parameter: Optional[dict] = None
 
 
-class BlindedMessage_Deprecated(BaseModel):
-    # Same as BlindedMessage, but without the id field
-    amount: int
-    B_: str  # Hex-encoded blinded message
-    id: Optional[str] = None
-    witness: Union[str, None] = None  # witnesses (used for P2PK with SIG_ALL)
-
-    @property
-    def p2pksigs(self) -> List[str]:
-        assert self.witness, "Witness missing in output"
-        return P2PKWitness.from_witness(self.witness).signatures
-
-
 # ------- API: KEYS -------
 
 
@@ -425,6 +445,7 @@ class PostMeltQuoteRequest(BaseModel):
     request: str = Field(
         ..., max_length=settings.mint_max_request_length
     )  # output payment request
+    amount: Optional[int] = Field(default=None, gt=0)  # input amount
 
 
 class PostMeltQuoteResponse(BaseModel):
@@ -551,6 +572,12 @@ class PostRestoreRequest(BaseModel):
     )
 
 
+class PostRestoreRequest_Deprecated(BaseModel):
+    outputs: List[BlindedMessage_Deprecated] = Field(
+        ..., max_items=settings.mint_max_request_length
+    )
+
+
 class PostRestoreResponse(BaseModel):
     outputs: List[BlindedMessage] = []
     signatures: List[BlindedSignature] = []
@@ -656,6 +683,7 @@ class WalletKeyset:
         valid_to=None,
         first_seen=None,
         active=True,
+        use_deprecated_id=False,  # BACKWARDS COMPATIBILITY < 0.15.0
     ):
         self.valid_from = valid_from
         self.valid_to = valid_to
@@ -670,10 +698,19 @@ class WalletKeyset:
         else:
             self.id = id
 
+        # BEGIN BACKWARDS COMPATIBILITY < 0.15.0
+        if use_deprecated_id:
+            logger.warning(
+                "Using deprecated keyset id derivation for backwards compatibility <"
+                " 0.15.0"
+            )
+            self.id = derive_keyset_id_deprecated(self.public_keys)
+        # END BACKWARDS COMPATIBILITY < 0.15.0
+
         self.unit = Unit[unit]
 
         logger.trace(f"Derived keyset id {self.id} from public keys.")
-        if id and id != self.id:
+        if id and id != self.id and use_deprecated_id:
             logger.warning(
                 f"WARNING: Keyset id {self.id} does not match the given id {id}."
                 " Overwriting."
@@ -728,6 +765,8 @@ class MintKeyset:
     first_seen: Optional[str] = None
     version: Optional[str] = None
 
+    duplicate_keyset_id: Optional[str] = None  # BACKWARDS COMPATIBILITY < 0.15.0
+
     def __init__(
         self,
         *,
@@ -808,12 +847,6 @@ class MintKeyset:
         assert self.seed, "seed not set"
         assert self.derivation_path, "derivation path not set"
 
-        # we compute the keyset id from the public keys only if it is not
-        # loaded from the database. This is to allow for backwards compatibility
-        # with old keysets with new id's and vice versa. This code can be removed
-        # if there are only new keysets in the mint (> 0.15.0)
-        id_in_db = self.id
-
         if self.version_tuple < (0, 12):
             # WARNING: Broken key derivation for backwards compatibility with < 0.12
             self.private_keys = derive_keys_backwards_compatible_insecure_pre_0_12(
@@ -824,8 +857,7 @@ class MintKeyset:
                 f"WARNING: Using weak key derivation for keyset {self.id} (backwards"
                 " compatibility < 0.12)"
             )
-            # load from db or derive
+            self.id = derive_keyset_id_deprecated(self.public_keys)  # type: ignore
-            self.id = id_in_db or derive_keyset_id_deprecated(self.public_keys)  # type: ignore
         elif self.version_tuple < (0, 15):
             self.private_keys = derive_keys_sha256(self.seed, self.derivation_path)
             logger.trace(
@@ -833,13 +865,11 @@ class MintKeyset:
                 " compatibility < 0.15)"
             )
             self.public_keys = derive_pubkeys(self.private_keys)  # type: ignore
-            # load from db or derive
+            self.id = derive_keyset_id_deprecated(self.public_keys)  # type: ignore
-            self.id = id_in_db or derive_keyset_id_deprecated(self.public_keys)  # type: ignore
         else:
             self.private_keys = derive_keys(self.seed, self.derivation_path)
             self.public_keys = derive_pubkeys(self.private_keys)  # type: ignore
-            # load from db or derive
+            self.id = derive_keyset_id(self.public_keys)  # type: ignore
-            self.id = id_in_db or derive_keyset_id(self.public_keys)  # type: ignore
 
 
 # ------- TOKEN -------

cashu/core/settings.py

@@ -89,6 +89,7 @@ class MintLimits(MintSettings):
     )
     mint_max_request_length: int = Field(
         default=1000,
+        gt=0,
         title="Maximum request length",
         description="Maximum length of REST API request arrays.",
     )
@@ -100,16 +101,21 @@ class MintLimits(MintSettings):
     )
     mint_max_peg_in: int = Field(
         default=None,
+        gt=0,
         title="Maximum peg-in",
         description="Maximum amount for a mint operation.",
     )
     mint_max_peg_out: int = Field(
         default=None,
+        gt=0,
         title="Maximum peg-out",
         description="Maximum amount for a melt operation.",
     )
     mint_max_balance: int = Field(
-        default=None, title="Maximum mint balance", description="Maximum mint balance."
+        default=None,
+        gt=0,
+        title="Maximum mint balance",
+        description="Maximum mint balance.",
     )
 
 
@@ -171,6 +177,7 @@ class LndRestFundingSource(MintSettings):
     mint_lnd_rest_macaroon: Optional[str] = Field(default=None)
     mint_lnd_rest_admin_macaroon: Optional[str] = Field(default=None)
     mint_lnd_rest_invoice_macaroon: Optional[str] = Field(default=None)
+    mint_lnd_enable_mpp: bool = Field(default=False)
 
 
 class CoreLightningRestFundingSource(MintSettings):

cashu/lightning/base.py

@@ -3,7 +3,12 @@ from typing import Coroutine, Optional, Union
 
 from pydantic import BaseModel
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import (
+    Amount,
+    MeltQuote,
+    PostMeltQuoteRequest,
+    Unit,
+)
 
 
 class StatusResponse(BaseModel):
@@ -62,6 +67,7 @@ class PaymentStatus(BaseModel):
 
 
 class LightningBackend(ABC):
+    supports_mpp: bool = False
     supported_units: set[Unit]
     unit: Unit
 
@@ -107,7 +113,7 @@ class LightningBackend(ABC):
     @abstractmethod
     async def get_payment_quote(
         self,
-        bolt11: str,
+        melt_quote: PostMeltQuoteRequest,
     ) -> PaymentQuoteResponse:
         pass
 

cashu/lightning/blink.py

@@ -11,7 +11,7 @@ from bolt11 import (
 )
 from loguru import logger
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from ..core.settings import settings
 from .base import (
     InvoiceResponse,
@@ -375,7 +375,10 @@ class BlinkWallet(LightningBackend):
             preimage=preimage,
         )
 
-    async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
+    async def get_payment_quote(
+        self, melt_quote: PostMeltQuoteRequest
+    ) -> PaymentQuoteResponse:
+        bolt11 = melt_quote.request
         variables = {
             "input": {
                 "paymentRequest": bolt11,

cashu/lightning/corelightningrest.py

@@ -10,7 +10,7 @@ from bolt11 import (
 )
 from loguru import logger
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from ..core.helpers import fee_reserve
 from ..core.settings import settings
 from .base import (
@@ -316,8 +316,10 @@ class CoreLightningRestWallet(LightningBackend):
                 )
                 await asyncio.sleep(0.02)
 
-    async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
+    async def get_payment_quote(
-        invoice_obj = decode(bolt11)
+        self, melt_quote: PostMeltQuoteRequest
+    ) -> PaymentQuoteResponse:
+        invoice_obj = decode(melt_quote.request)
         assert invoice_obj.amount_msat, "invoice has no amount."
         amount_msat = int(invoice_obj.amount_msat)
         fees_msat = fee_reserve(amount_msat)

cashu/lightning/fake.py

@@ -15,7 +15,7 @@ from bolt11 import (
     encode,
 )
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from ..core.helpers import fee_reserve
 from ..core.settings import settings
 from .base import (
@@ -152,8 +152,10 @@ class FakeWallet(LightningBackend):
     #     amount = invoice_obj.amount_msat
     #     return InvoiceQuoteResponse(checking_id="", amount=amount)
 
-    async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
+    async def get_payment_quote(
-        invoice_obj = decode(bolt11)
+        self, melt_quote: PostMeltQuoteRequest
+    ) -> PaymentQuoteResponse:
+        invoice_obj = decode(melt_quote.request)
         assert invoice_obj.amount_msat, "invoice has no amount."
 
         if self.unit == Unit.sat:

cashu/lightning/lnbits.py

@@ -6,7 +6,7 @@ from bolt11 import (
     decode,
 )
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from ..core.helpers import fee_reserve
 from ..core.settings import settings
 from .base import (
@@ -167,8 +167,10 @@ class LNbitsWallet(LightningBackend):
             preimage=data["preimage"],
         )
 
-    async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
+    async def get_payment_quote(
-        invoice_obj = decode(bolt11)
+        self, melt_quote: PostMeltQuoteRequest
+    ) -> PaymentQuoteResponse:
+        invoice_obj = decode(melt_quote.request)
         assert invoice_obj.amount_msat, "invoice has no amount."
         amount_msat = int(invoice_obj.amount_msat)
         fees_msat = fee_reserve(amount_msat)

cashu/lightning/lndrest.py

@@ -4,13 +4,15 @@ import hashlib
 import json
 from typing import AsyncGenerator, Dict, Optional
 
+import bolt11
 import httpx
 from bolt11 import (
+    TagChar,
     decode,
 )
 from loguru import logger
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from ..core.helpers import fee_reserve
 from ..core.settings import settings
 from .base import (
@@ -27,6 +29,7 @@ from .macaroon import load_macaroon
 class LndRestWallet(LightningBackend):
     """https://api.lightning.community/rest/index.html#lnd-rest-api-reference"""
 
+    supports_mpp = settings.mint_lnd_enable_mpp
     supported_units = set([Unit.sat, Unit.msat])
     unit = Unit.sat
 
@@ -70,6 +73,8 @@ class LndRestWallet(LightningBackend):
         self.client = httpx.AsyncClient(
             base_url=self.endpoint, headers=self.auth, verify=self.cert
         )
+        if self.supports_mpp:
+            logger.info("LNDRestWallet enabling MPP feature")
 
     async def status(self) -> StatusResponse:
         try:
@@ -148,6 +153,16 @@ class LndRestWallet(LightningBackend):
     async def pay_invoice(
         self, quote: MeltQuote, fee_limit_msat: int
     ) -> PaymentResponse:
+        # if the amount of the melt quote is different from the request
+        # call pay_partial_invoice instead
+        invoice = bolt11.decode(quote.request)
+        if invoice.amount_msat:
+            amount_msat = int(invoice.amount_msat)
+            if amount_msat != quote.amount * 1000 and self.supports_mpp:
+                return await self.pay_partial_invoice(
+                    quote, Amount(Unit.sat, quote.amount), fee_limit_msat
+                )
+
         # set the fee limit for the payment
         lnrpcFeeLimit = dict()
         lnrpcFeeLimit["fixed_msat"] = f"{fee_limit_msat}"
@@ -180,6 +195,91 @@ class LndRestWallet(LightningBackend):
             error_message=None,
         )
 
+    async def pay_partial_invoice(
+        self, quote: MeltQuote, amount: Amount, fee_limit_msat: int
+    ) -> PaymentResponse:
+        # set the fee limit for the payment
+        lnrpcFeeLimit = dict()
+        lnrpcFeeLimit["fixed_msat"] = f"{fee_limit_msat}"
+        invoice = bolt11.decode(quote.request)
+
+        invoice_amount = invoice.amount_msat
+        assert invoice_amount, "invoice has no amount."
+        total_amount_msat = int(invoice_amount)
+
+        payee = invoice.tags.get(TagChar.payee)
+        assert payee
+        pubkey = str(payee.data)
+
+        payer_addr_tag = invoice.tags.get(bolt11.TagChar("s"))
+        assert payer_addr_tag
+        payer_addr = str(payer_addr_tag.data)
+
+        # get the route
+        r = await self.client.post(
+            url=f"/v1/graph/routes/{pubkey}/{amount.to(Unit.sat).amount}",
+            json={"fee_limit": lnrpcFeeLimit},
+            timeout=None,
+        )
+
+        data = r.json()
+        if r.is_error or data.get("message"):
+            error_message = data.get("message") or r.text
+            return PaymentResponse(
+                ok=False,
+                checking_id=None,
+                fee=None,
+                preimage=None,
+                error_message=error_message,
+            )
+
+        # We need to set the mpp_record for a partial payment
+        mpp_record = {
+            "mpp_record": {
+                "payment_addr": base64.b64encode(bytes.fromhex(payer_addr)).decode(),
+                "total_amt_msat": total_amount_msat,
+            }
+        }
+
+        # add the mpp_record to the last hop
+        rout_nr = 0
+        data["routes"][rout_nr]["hops"][-1].update(mpp_record)
+
+        # send to route
+        r = await self.client.post(
+            url="/v2/router/route/send",
+            json={
+                "payment_hash": base64.b64encode(
+                    bytes.fromhex(invoice.payment_hash)
+                ).decode(),
+                "route": data["routes"][rout_nr],
+            },
+            timeout=None,
+        )
+
+        data = r.json()
+        if r.is_error or data.get("message"):
+            error_message = data.get("message") or r.text
+            return PaymentResponse(
+                ok=False,
+                checking_id=None,
+                fee=None,
+                preimage=None,
+                error_message=error_message,
+            )
+
+        ok = data.get("status") == "SUCCEEDED"
+        checking_id = invoice.payment_hash
+        fee_msat = int(data["route"]["total_fees_msat"])
+        preimage = base64.b64decode(data["preimage"]).hex()
+        return PaymentResponse(
+            ok=ok,
+            checking_id=checking_id,
+            fee=Amount(unit=Unit.msat, amount=fee_msat) if fee_msat else None,
+            preimage=preimage,
+            error_message=None,
+        )
+
     async def get_invoice_status(self, checking_id: str) -> PaymentStatus:
         r = await self.client.get(url=f"/v1/invoice/{checking_id}")
 
@@ -270,13 +370,29 @@ class LndRestWallet(LightningBackend):
                 )
                 await asyncio.sleep(5)
 
-    async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
+    async def get_payment_quote(
-        invoice_obj = decode(bolt11)
+        self, melt_quote: PostMeltQuoteRequest
+    ) -> PaymentQuoteResponse:
+        # get amount from melt_quote or from bolt11
+        amount = (
+            Amount(Unit[melt_quote.unit], melt_quote.amount)
+            if melt_quote.amount
+            else None
+        )
+
+        invoice_obj = decode(melt_quote.request)
         assert invoice_obj.amount_msat, "invoice has no amount."
+
+        if amount:
+            amount_msat = amount.to(Unit.msat).amount
+        else:
             amount_msat = int(invoice_obj.amount_msat)
+
         fees_msat = fee_reserve(amount_msat)
         fees = Amount(unit=Unit.msat, amount=fees_msat)
+
         amount = Amount(unit=Unit.msat, amount=amount_msat)
+
         return PaymentQuoteResponse(
             checking_id=invoice_obj.payment_hash,
             fee=fees.to(self.unit, round="up"),

cashu/lightning/strike.py

@@ -4,7 +4,7 @@ from typing import Dict, Optional
 
 import httpx
 
-from ..core.base import Amount, MeltQuote, Unit
+from ..core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from ..core.settings import settings
 from .base import (
     InvoiceResponse,
@@ -118,7 +118,10 @@ class StrikeUSDWallet(LightningBackend):
             error_message=None,
         )
 
-    async def get_payment_quote(self, bolt11: str) -> PaymentQuoteResponse:
+    async def get_payment_quote(
+        self, melt_quote: PostMeltQuoteRequest
+    ) -> PaymentQuoteResponse:
+        bolt11 = melt_quote.request
         try:
             r = await self.client.post(
                 url=f"{self.endpoint}/v1/payment-quotes/lightning",

cashu/mint/ledger.py

@@ -575,9 +575,10 @@ class Ledger(LedgerVerification, LedgerSpendingConditions):
             )
         else:
             # not internal, get payment quote by backend
-            payment_quote = await self.backends[method][unit].get_payment_quote(request)
+            payment_quote = await self.backends[method][unit].get_payment_quote(
-            if not payment_quote.checking_id:
+                melt_quote=melt_quote
-                raise TransactionError("quote has no checking id")
+            )
+            assert payment_quote.checking_id, "quote has no checking id"
             # make sure the backend returned the amount with a correct unit
             if not payment_quote.amount.unit == unit:
                 raise TransactionError("payment quote amount units do not match")

cashu/mint/router.py

@@ -62,7 +62,8 @@ async def info() -> GetInfoResponse:
 
     supported_dict = dict(supported=True)
 
-    mint_features: Dict[int, Dict[str, Any]] = {
+    supported_dict = dict(supported=True)
+    mint_features: Dict[int, Any] = {
         4: dict(
             methods=method_settings[4],
             disabled=settings.mint_peg_out_only,
@@ -79,6 +80,21 @@ async def info() -> GetInfoResponse:
         12: supported_dict,
     }
 
+    # signal which method-unit pairs support MPP
+    for method, unit_dict in ledger.backends.items():
+        for unit in unit_dict.keys():
+            logger.trace(
+                f"method={method.name} unit={unit} supports_mpp={unit_dict[unit].supports_mpp}"
+            )
+            if unit_dict[unit].supports_mpp:
+                mint_features.setdefault(15, []).append(
+                    {
+                        "method": method.name,
+                        "unit": unit.name,
+                        "mpp": True,
+                    }
+                )
+
     return GetInfoResponse(
         name=settings.mint_info_name,
         pubkey=ledger.pubkey.serialize().hex() if ledger.pubkey else None,

cashu/mint/router_deprecated.py

@@ -20,7 +20,7 @@ from ..core.base import (
     PostMintQuoteRequest,
     PostMintRequest_deprecated,
     PostMintResponse_deprecated,
-    PostRestoreRequest,
+    PostRestoreRequest_Deprecated,
     PostRestoreResponse,
     PostSplitRequest_Deprecated,
     PostSplitResponse_Deprecated,
@@ -179,7 +179,7 @@ async def mint_deprecated(
     # BEGIN BACKWARDS COMPATIBILITY < 0.15
     # Mint expects "id" in outputs to know which keyset to use to sign them.
     outputs: list[BlindedMessage] = [
-        BlindedMessage(id=o.id or ledger.keyset.id, **o.dict(exclude={"id"}))
+        BlindedMessage(id=ledger.keyset.id, **o.dict(exclude={"id"}))
         for o in payload.outputs
     ]
     # END BACKWARDS COMPATIBILITY < 0.15
@@ -223,7 +223,7 @@ async def melt_deprecated(
     # BEGIN BACKWARDS COMPATIBILITY < 0.14: add "id" to outputs
     if payload.outputs:
         outputs: list[BlindedMessage] = [
-            BlindedMessage(id=o.id or ledger.keyset.id, **o.dict(exclude={"id"}))
+            BlindedMessage(id=ledger.keyset.id, **o.dict(exclude={"id"}))
             for o in payload.outputs
         ]
     else:
@@ -295,7 +295,7 @@ async def split_deprecated(
     assert payload.outputs, Exception("no outputs provided.")
     # BEGIN BACKWARDS COMPATIBILITY < 0.14: add "id" to outputs
     outputs: list[BlindedMessage] = [
-        BlindedMessage(id=o.id or ledger.keyset.id, **o.dict(exclude={"id"}))
+        BlindedMessage(id=ledger.keyset.id, **o.dict(exclude={"id"}))
         for o in payload.outputs
     ]
     # END BACKWARDS COMPATIBILITY < 0.14
@@ -372,7 +372,15 @@ async def check_spendable_deprecated(
     ),
     deprecated=True,
 )
-async def restore(payload: PostRestoreRequest) -> PostRestoreResponse:
+async def restore(payload: PostRestoreRequest_Deprecated) -> PostRestoreResponse:
     assert payload.outputs, Exception("no outputs provided.")
-    outputs, promises = await ledger.restore(payload.outputs)
+    if payload.outputs:
+        outputs: list[BlindedMessage] = [
+            BlindedMessage(id=ledger.keyset.id, **o.dict(exclude={"id"}))
+            for o in payload.outputs
+        ]
+    else:
+        outputs = []
+
+    outputs, promises = await ledger.restore(outputs)
     return PostRestoreResponse(outputs=outputs, signatures=promises)

cashu/wallet/api/router.py

@@ -189,7 +189,7 @@ async def swap(
 
     # pay invoice from outgoing mint
     await outgoing_wallet.load_proofs(reload=True)
-    quote = await outgoing_wallet.get_pay_amount_with_fees(invoice.bolt11)
+    quote = await outgoing_wallet.request_melt(invoice.bolt11)
     total_amount = quote.amount + quote.fee_reserve
     if outgoing_wallet.available_balance < total_amount:
         raise Exception("balance too low")
@@ -197,7 +197,7 @@ async def swap(
     _, send_proofs = await outgoing_wallet.split_to_send(
         outgoing_wallet.proofs, total_amount, set_reserved=True
     )
-    await outgoing_wallet.pay_lightning(
+    await outgoing_wallet.melt(
         send_proofs, invoice.bolt11, quote.fee_reserve, quote.quote
     )
 

cashu/wallet/cli/cli.py

@@ -177,16 +177,23 @@ async def cli(ctx: Context, host: str, walletname: str, unit: str, tests: bool):
 
 @cli.command("pay", help="Pay Lightning invoice.")
 @click.argument("invoice", type=str)
+@click.argument(
+    "amount",
+    type=int,
+    required=False,
+)
 @click.option(
     "--yes", "-y", default=False, is_flag=True, help="Skip confirmation.", type=bool
 )
 @click.pass_context
 @coro
-async def pay(ctx: Context, invoice: str, yes: bool):
+async def pay(
+    ctx: Context, invoice: str, amount: Optional[int] = None, yes: bool = False
+):
     wallet: Wallet = ctx.obj["WALLET"]
     await wallet.load_mint()
     await print_balance(ctx)
-    quote = await wallet.get_pay_amount_with_fees(invoice)
+    quote = await wallet.request_melt(invoice, amount)
     logger.debug(f"Quote: {quote}")
     total_amount = quote.amount + quote.fee_reserve
     if not yes:
@@ -209,7 +216,7 @@ async def pay(ctx: Context, invoice: str, yes: bool):
         return
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     try:
-        melt_response = await wallet.pay_lightning(
+        melt_response = await wallet.melt(
             send_proofs, invoice, quote.fee_reserve, quote.quote
         )
     except Exception as e:
@@ -334,14 +341,14 @@ async def swap(ctx: Context):
     invoice = await incoming_wallet.request_mint(amount)
 
     # pay invoice from outgoing mint
-    quote = await outgoing_wallet.get_pay_amount_with_fees(invoice.bolt11)
+    quote = await outgoing_wallet.request_melt(invoice.bolt11)
     total_amount = quote.amount + quote.fee_reserve
     if outgoing_wallet.available_balance < total_amount:
         raise Exception("balance too low")
     _, send_proofs = await outgoing_wallet.split_to_send(
         outgoing_wallet.proofs, total_amount, set_reserved=True
     )
-    await outgoing_wallet.pay_lightning(
+    await outgoing_wallet.melt(
         send_proofs, invoice.bolt11, quote.fee_reserve, quote.quote
     )
 

cashu/wallet/lightning/lightning.py

@@ -55,7 +55,7 @@ class LightningWallet(Wallet):
         Returns:
             bool: True if successful
         """
-        quote = await self.get_pay_amount_with_fees(pr)
+        quote = await self.request_melt(pr)
         total_amount = quote.amount + quote.fee_reserve
         assert total_amount > 0, "amount is not positive"
         if self.available_balance < total_amount:
@@ -63,9 +63,7 @@ class LightningWallet(Wallet):
             return PaymentResponse(ok=False)
         _, send_proofs = await self.split_to_send(self.proofs, total_amount)
         try:
-            resp = await self.pay_lightning(
+            resp = await self.melt(send_proofs, pr, quote.fee_reserve, quote.quote)
-                send_proofs, pr, quote.fee_reserve, quote.quote
-            )
             if resp.change:
                 fees_paid_sat = quote.fee_reserve - sum_promises(resp.change)
             else:

cashu/wallet/mint_info.py

@@ -0,0 +1,38 @@
+from typing import Any, Dict, List, Optional
+
+from pydantic import BaseModel
+
+from ..core.base import Nut15MppSupport, Unit
+
+
+class MintInfo(BaseModel):
+    name: Optional[str]
+    pubkey: Optional[str]
+    version: Optional[str]
+    description: Optional[str]
+    description_long: Optional[str]
+    contact: Optional[List[List[str]]]
+    motd: Optional[str]
+    nuts: Optional[Dict[int, Any]]
+
+    def __str__(self):
+        return f"{self.name} ({self.description})"
+
+    def supports_nut(self, nut: int) -> bool:
+        if self.nuts is None:
+            return False
+        return nut in self.nuts
+
+    def supports_mpp(self, method: str, unit: Unit) -> bool:
+        if not self.nuts:
+            return False
+        nut_15 = self.nuts.get(15)
+        if not nut_15 or not self.supports_nut(15):
+            return False
+
+        for entry in nut_15:
+            entry_obj = Nut15MppSupport.parse_obj(entry)
+            if entry_obj.method == method and entry_obj.unit == unit.name:
+                return True
+
+        return False

cashu/wallet/wallet.py

@@ -71,6 +71,7 @@ from ..wallet.crud import (
 )
 from . import migrations
 from .htlc import WalletHTLC
+from .mint_info import MintInfo
 from .p2pk import WalletP2PK
 from .secrets import WalletSecrets
 from .wallet_deprecated import LedgerAPIDeprecated
@@ -130,7 +131,7 @@ class LedgerAPI(LedgerAPIDeprecated, object):
     keysets: Dict[str, WalletKeyset]  # holds keysets
     mint_keyset_ids: List[str]  # holds active keyset ids of the mint
     unit: Unit
-    mint_info: GetInfoResponse  # holds info about mint
+    mint_info: MintInfo  # holds info about mint
     tor: TorProxy
     db: Database
     httpx: httpx.AsyncClient
@@ -269,9 +270,10 @@ class LedgerAPI(LedgerAPIDeprecated, object):
         logger.debug(f"Mint keysets: {self.mint_keyset_ids}")
         return self.mint_keyset_ids
 
-    async def _load_mint_info(self) -> GetInfoResponse:
+    async def _load_mint_info(self) -> MintInfo:
         """Loads the mint info from the mint."""
-        self.mint_info = await self._get_info()
+        mint_info_resp = await self._get_info()
+        self.mint_info = MintInfo(**mint_info_resp.dict())
         logger.debug(f"Mint info: {self.mint_info}")
         return self.mint_info
 
@@ -518,11 +520,15 @@ class LedgerAPI(LedgerAPIDeprecated, object):
 
     @async_set_httpx_client
     @async_ensure_mint_loaded
-    async def melt_quote(self, payment_request: str) -> PostMeltQuoteResponse:
+    async def melt_quote(
+        self, payment_request: str, amount: Optional[int] = None
+    ) -> PostMeltQuoteResponse:
         """Checks whether the Lightning payment is internal."""
         invoice_obj = bolt11.decode(payment_request)
         assert invoice_obj.amount_msat, "invoice must have amount"
-        payload = PostMeltQuoteRequest(unit=self.unit.name, request=payment_request)
+        payload = PostMeltQuoteRequest(
+            unit=self.unit.name, request=payment_request, amount=amount
+        )
         resp = await self.httpx.post(
             join(self.url, "/v1/melt/quote/bolt11"),
             json=payload.dict(),
@@ -536,7 +542,7 @@ class LedgerAPI(LedgerAPIDeprecated, object):
             quote_id = "deprecated_" + str(uuid.uuid4())
             return PostMeltQuoteResponse(
                 quote=quote_id,
-                amount=invoice_obj.amount_msat // 1000,
+                amount=amount or invoice_obj.amount_msat // 1000,
                 fee_reserve=ret.fee or 0,
                 paid=False,
                 expiry=invoice_obj.expiry,
@@ -582,7 +588,7 @@ class LedgerAPI(LedgerAPIDeprecated, object):
         if resp.status_code == 404:
             invoice = await get_lightning_invoice(id=quote, db=self.db)
             assert invoice, f"no invoice found for id {quote}"
-            ret: PostMeltResponse_deprecated = await self.pay_lightning_deprecated(
+            ret: PostMeltResponse_deprecated = await self.melt_deprecated(
                 proofs=proofs, outputs=outputs, invoice=invoice.bolt11
             )
             return PostMeltResponse(
@@ -987,7 +993,21 @@ class Wallet(LedgerAPI, WalletP2PK, WalletHTLC, WalletSecrets):
         send_proofs = new_proofs[len(frst_outputs) :]
         return keep_proofs, send_proofs
 
-    async def pay_lightning(
+    async def request_melt(
+        self, invoice: str, amount: Optional[int] = None
+    ) -> PostMeltQuoteResponse:
+        """
+        Fetches a melt quote from the mint and either uses the amount in the invoice or the amount provided.
+        """
+        if amount and not self.mint_info.supports_mpp("bolt11", self.unit):
+            raise Exception("Mint does not support MPP, cannot specify amount.")
+        melt_quote = await self.melt_quote(invoice, amount)
+        logger.debug(
+            f"Mint wants {self.unit.str(melt_quote.fee_reserve)} as fee reserve."
+        )
+        return melt_quote
+
+    async def melt(
         self, proofs: List[Proof], invoice: str, fee_reserve_sat: int, quote_id: str
     ) -> PostMeltResponse:
         """Pays a lightning invoice and returns the status of the payment.
@@ -1520,17 +1540,6 @@ class Wallet(LedgerAPI, WalletP2PK, WalletHTLC, WalletSecrets):
 
     # ---------- TRANSACTION HELPERS ----------
 
-    async def get_pay_amount_with_fees(self, invoice: str):
-        """
-        Decodes the amount from a Lightning invoice and returns the
-        total amount (amount+fees) to be paid.
-        """
-        melt_quote = await self.melt_quote(invoice)
-        logger.debug(
-            f"Mint wants {self.unit.str(melt_quote.fee_reserve)} as fee reserve."
-        )
-        return melt_quote
-
     async def split_to_send(
         self,
         proofs: List[Proof],

cashu/wallet/wallet_deprecated.py

@@ -298,7 +298,7 @@ class LedgerAPIDeprecated(SupportsHttpxClient, SupportsMintURL):
 
     @async_set_httpx_client
     @async_ensure_mint_loaded_deprecated
-    async def pay_lightning_deprecated(
+    async def melt_deprecated(
         self, proofs: List[Proof], invoice: str, outputs: Optional[List[BlindedMessage]]
     ):
         """

tests/conftest.py

@@ -44,6 +44,7 @@ settings.mint_derivation_path_list = []
 settings.mint_private_key = "TEST_PRIVATE_KEY"
 settings.mint_seed_decryption_key = ""
 settings.mint_max_balance = 0
+settings.mint_lnd_enable_mpp = True
 
 assert "test" in settings.cashu_dir
 shutil.rmtree(settings.cashu_dir, ignore_errors=True)

tests/test_mint_init.py

@@ -249,11 +249,11 @@ async def test_startup_regtest_pending_quote_pending(wallet: Wallet, ledger: Led
     invoice_payment_request = str(invoice_dict["payment_request"])
 
     # wallet pays the invoice
-    quote = await wallet.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet.melt_quote(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     asyncio.create_task(
-        wallet.pay_lightning(
+        wallet.melt(
             proofs=send_proofs,
             invoice=invoice_payment_request,
             fee_reserve_sat=quote.fee_reserve,
@@ -294,11 +294,11 @@ async def test_startup_regtest_pending_quote_success(wallet: Wallet, ledger: Led
     invoice_payment_request = str(invoice_dict["payment_request"])
 
     # wallet pays the invoice
-    quote = await wallet.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet.melt_quote(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     asyncio.create_task(
-        wallet.pay_lightning(
+        wallet.melt(
             proofs=send_proofs,
             invoice=invoice_payment_request,
             fee_reserve_sat=quote.fee_reserve,
@@ -344,11 +344,11 @@ async def test_startup_regtest_pending_quote_failure(wallet: Wallet, ledger: Led
     preimage_hash = invoice_obj.payment_hash
 
     # wallet pays the invoice
-    quote = await wallet.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet.melt_quote(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     asyncio.create_task(
-        wallet.pay_lightning(
+        wallet.melt(
             proofs=send_proofs,
             invoice=invoice_payment_request,
             fee_reserve_sat=quote.fee_reserve,

tests/test_mint_lightning_blink.py

@@ -2,7 +2,7 @@ import pytest
 import respx
 from httpx import Response
 
-from cashu.core.base import Amount, MeltQuote, Unit
+from cashu.core.base import Amount, MeltQuote, PostMeltQuoteRequest, Unit
 from cashu.core.settings import settings
 from cashu.lightning.blink import MINIMUM_FEE_MSAT, BlinkWallet  # type: ignore
 
@@ -192,7 +192,10 @@ async def test_blink_get_payment_quote():
     # response says 1 sat fees but invoice (1000 sat) * 0.5% is 5 sat so we expect 5 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 1}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
-    quote = await blink.get_payment_quote(payment_request)
+    melt_quote_request = PostMeltQuoteRequest(
+        unit=Unit.sat.name, request=payment_request
+    )
+    quote = await blink.get_payment_quote(melt_quote_request)
     assert quote.checking_id == payment_request
     assert quote.amount == Amount(Unit.sat, 1000)  # sat
     assert quote.fee == Amount(Unit.sat, 5)  # sat
@@ -200,7 +203,10 @@ async def test_blink_get_payment_quote():
     # response says 10 sat fees but invoice (1000 sat) * 0.5% is 5 sat so we expect 10 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 10}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
-    quote = await blink.get_payment_quote(payment_request)
+    melt_quote_request = PostMeltQuoteRequest(
+        unit=Unit.sat.name, request=payment_request
+    )
+    quote = await blink.get_payment_quote(melt_quote_request)
     assert quote.checking_id == payment_request
     assert quote.amount == Amount(Unit.sat, 1000)  # sat
     assert quote.fee == Amount(Unit.sat, 10)  # sat
@@ -208,7 +214,10 @@ async def test_blink_get_payment_quote():
     # response says 10 sat fees but invoice (4973 sat) * 0.5% is 24.865 sat so we expect 25 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 10}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
-    quote = await blink.get_payment_quote(payment_request_4973)
+    melt_quote_request_4973 = PostMeltQuoteRequest(
+        unit=Unit.sat.name, request=payment_request_4973
+    )
+    quote = await blink.get_payment_quote(melt_quote_request_4973)
     assert quote.checking_id == payment_request_4973
     assert quote.amount == Amount(Unit.sat, 4973)  # sat
     assert quote.fee == Amount(Unit.sat, 25)  # sat
@@ -216,7 +225,10 @@ async def test_blink_get_payment_quote():
     # response says 0 sat fees but invoice (1 sat) * 0.5% is 0.005 sat so we expect MINIMUM_FEE_MSAT/1000 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"amount": 0}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
-    quote = await blink.get_payment_quote(payment_request_1)
+    melt_quote_request_1 = PostMeltQuoteRequest(
+        unit=Unit.sat.name, request=payment_request_1
+    )
+    quote = await blink.get_payment_quote(melt_quote_request_1)
     assert quote.checking_id == payment_request_1
     assert quote.amount == Amount(Unit.sat, 1)  # sat
     assert quote.fee == Amount(Unit.sat, MINIMUM_FEE_MSAT // 1000)  # msat
@@ -228,7 +240,10 @@ async def test_blink_get_payment_quote_backend_error():
     # response says error but invoice (1000 sat) * 0.5% is 5 sat so we expect 10 sat
     mock_response = {"data": {"lnInvoiceFeeProbe": {"errors": [{"message": "error"}]}}}
     respx.post(blink.endpoint).mock(return_value=Response(200, json=mock_response))
-    quote = await blink.get_payment_quote(payment_request)
+    melt_quote_request = PostMeltQuoteRequest(
+        unit=Unit.sat.name, request=payment_request
+    )
+    quote = await blink.get_payment_quote(melt_quote_request)
     assert quote.checking_id == payment_request
     assert quote.amount == Amount(Unit.sat, 1000)  # sat
     assert quote.fee == Amount(Unit.sat, 5)  # sat

tests/test_mint_operations.py

@@ -73,7 +73,7 @@ async def test_melt_external(wallet1: Wallet, ledger: Ledger):
     invoice_dict = get_real_invoice(64)
     invoice_payment_request = invoice_dict["payment_request"]
 
-    mint_quote = await wallet1.get_pay_amount_with_fees(invoice_payment_request)
+    mint_quote = await wallet1.melt_quote(invoice_payment_request)
     total_amount = mint_quote.amount + mint_quote.fee_reserve
     keep_proofs, send_proofs = await wallet1.split_to_send(wallet1.proofs, total_amount)
     melt_quote = await ledger.melt_quote(

tests/test_mint_regtest.py

@@ -41,12 +41,12 @@ async def test_regtest_pending_quote(wallet: Wallet, ledger: Ledger):
     invoice_payment_request = str(invoice_dict["payment_request"])
 
     # wallet pays the invoice
-    quote = await wallet.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet.melt_quote(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     asyncio.create_task(ledger.melt(proofs=send_proofs, quote=quote.quote))
     # asyncio.create_task(
-    #     wallet.pay_lightning(
+    #     wallet.melt(
     #         proofs=send_proofs,
     #         invoice=invoice_payment_request,
     #         fee_reserve_sat=quote.fee_reserve,

tests/test_wallet.py

@@ -271,7 +271,7 @@ async def test_melt(wallet1: Wallet):
         invoice_payment_hash = str(invoice.payment_hash)
         invoice_payment_request = invoice.bolt11
 
-    quote = await wallet1.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet1.request_melt(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
 
     if is_regtest:
@@ -285,7 +285,7 @@ async def test_melt(wallet1: Wallet):
 
     _, send_proofs = await wallet1.split_to_send(wallet1.proofs, total_amount)
 
-    melt_response = await wallet1.pay_lightning(
+    melt_response = await wallet1.melt(
         proofs=send_proofs,
         invoice=invoice_payment_request,
         fee_reserve_sat=quote.fee_reserve,

tests/test_wallet_regtest.py

@@ -43,11 +43,11 @@ async def test_regtest_pending_quote(wallet: Wallet, ledger: Ledger):
     invoice_payment_request = str(invoice_dict["payment_request"])
 
     # wallet pays the invoice
-    quote = await wallet.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet.melt_quote(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     asyncio.create_task(
-        wallet.pay_lightning(
+        wallet.melt(
             proofs=send_proofs,
             invoice=invoice_payment_request,
             fee_reserve_sat=quote.fee_reserve,
@@ -83,11 +83,11 @@ async def test_regtest_failed_quote(wallet: Wallet, ledger: Ledger):
     preimage_hash = invoice_obj.payment_hash
 
     # wallet pays the invoice
-    quote = await wallet.get_pay_amount_with_fees(invoice_payment_request)
+    quote = await wallet.melt_quote(invoice_payment_request)
     total_amount = quote.amount + quote.fee_reserve
     _, send_proofs = await wallet.split_to_send(wallet.proofs, total_amount)
     asyncio.create_task(
-        wallet.pay_lightning(
+        wallet.melt(
             proofs=send_proofs,
             invoice=invoice_payment_request,
             fee_reserve_sat=quote.fee_reserve,

tests/test_wallet_regtest_mpp.py

@@ -0,0 +1,127 @@
+import asyncio
+from typing import List
+
+import pytest
+import pytest_asyncio
+
+from cashu.core.base import Method, Proof
+from cashu.mint.ledger import Ledger
+from cashu.wallet.wallet import Wallet
+from tests.conftest import SERVER_ENDPOINT
+from tests.helpers import (
+    get_real_invoice,
+    is_fake,
+    pay_if_regtest,
+)
+
+
+@pytest_asyncio.fixture(scope="function")
+async def wallet():
+    wallet = await Wallet.with_db(
+        url=SERVER_ENDPOINT,
+        db="test_data/wallet",
+        name="wallet",
+    )
+    await wallet.load_mint()
+    yield wallet
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(is_fake, reason="only regtest")
+async def test_regtest_pay_mpp(wallet: Wallet, ledger: Ledger):
+    # make sure that mpp is supported by the bolt11-sat backend
+    if not ledger.backends[Method["bolt11"]][wallet.unit].supports_mpp:
+        pytest.skip("backend does not support mpp")
+
+    # make sure wallet knows the backend supports mpp
+    assert wallet.mint_info.supports_mpp("bolt11", wallet.unit)
+
+    # top up wallet twice so we have enough for two payments
+    topup_invoice = await wallet.request_mint(128)
+    pay_if_regtest(topup_invoice.bolt11)
+    proofs1 = await wallet.mint(128, id=topup_invoice.id)
+    assert wallet.balance == 128
+
+    topup_invoice = await wallet.request_mint(128)
+    pay_if_regtest(topup_invoice.bolt11)
+    proofs2 = await wallet.mint(128, id=topup_invoice.id)
+    assert wallet.balance == 256
+
+    # this is the invoice we want to pay in two parts
+    invoice_dict = get_real_invoice(64)
+    invoice_payment_request = invoice_dict["payment_request"]
+
+    async def pay_mpp(amount: int, proofs: List[Proof], delay: float = 0.0):
+        await asyncio.sleep(delay)
+        # wallet pays 32 sat of the invoice
+        quote = await wallet.melt_quote(invoice_payment_request, amount=32)
+        assert quote.amount == amount
+        await wallet.melt(
+            proofs,
+            invoice_payment_request,
+            fee_reserve_sat=quote.fee_reserve,
+            quote_id=quote.quote,
+        )
+
+    # call pay_mpp twice in parallel to pay the full invoice
+    # we delay the second payment so that the wallet doesn't derive the same blindedmessages twice due to a race condition
+    await asyncio.gather(pay_mpp(32, proofs1), pay_mpp(32, proofs2, delay=0.5))
+
+    assert wallet.balance <= 256 - 64
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(is_fake, reason="only regtest")
+async def test_regtest_pay_mpp_incomplete_payment(wallet: Wallet, ledger: Ledger):
+    # make sure that mpp is supported by the bolt11-sat backend
+    if not ledger.backends[Method["bolt11"]][wallet.unit].supports_mpp:
+        pytest.skip("backend does not support mpp")
+
+    # make sure wallet knows the backend supports mpp
+    assert wallet.mint_info.supports_mpp("bolt11", wallet.unit)
+
+    # top up wallet twice so we have enough for three payments
+    topup_invoice = await wallet.request_mint(128)
+    pay_if_regtest(topup_invoice.bolt11)
+    proofs1 = await wallet.mint(128, id=topup_invoice.id)
+    assert wallet.balance == 128
+
+    topup_invoice = await wallet.request_mint(128)
+    pay_if_regtest(topup_invoice.bolt11)
+    proofs2 = await wallet.mint(128, id=topup_invoice.id)
+    assert wallet.balance == 256
+
+    topup_invoice = await wallet.request_mint(128)
+    pay_if_regtest(topup_invoice.bolt11)
+    proofs3 = await wallet.mint(128, id=topup_invoice.id)
+    assert wallet.balance == 384
+
+    # this is the invoice we want to pay in two parts
+    invoice_dict = get_real_invoice(64)
+    invoice_payment_request = invoice_dict["payment_request"]
+
+    async def pay_mpp(amount: int, proofs: List[Proof], delay: float = 0.0):
+        await asyncio.sleep(delay)
+        # wallet pays 32 sat of the invoice
+        quote = await wallet.melt_quote(invoice_payment_request, amount=amount)
+        assert quote.amount == amount
+        await wallet.melt(
+            proofs,
+            invoice_payment_request,
+            fee_reserve_sat=quote.fee_reserve,
+            quote_id=quote.quote,
+        )
+
+    # instead: call pay_mpp twice in the background, sleep for a bit, then check if the payment was successful (it should not be)
+    asyncio.create_task(pay_mpp(32, proofs1))
+    asyncio.create_task(pay_mpp(16, proofs2, delay=0.5))
+    await asyncio.sleep(2)
+
+    # payment is still pending because the full amount has not been paid
+    assert wallet.balance == 384
+
+    # send the remaining 16 sat to complete the payment
+    asyncio.create_task(pay_mpp(16, proofs3, delay=0.5))
+    await asyncio.sleep(2)
+
+    assert wallet.balance <= 384 - 64