feat(core): Updates to nut18 and nut26 payment request

cashu/core/base.py

@@ -1678,12 +1678,19 @@ class NUT10Option(BaseModel):
     t: Optional[List[List[str]]] = None  # tags
 
 
+class SupportedMethod(BaseModel):
+    mn: str  # method name
+    mf: Optional[int] = None  # per-method fee, absent = 0
+
+
 class PaymentRequest(BaseModel):
     i: Optional[str] = None  # payment id
     a: Optional[int] = None  # amount
     u: Optional[str] = None  # unit
     s: Optional[bool] = None  # single use
     m: Optional[List[str]] = None  # mints
+    mp: Optional[bool] = None  # mint list preferred
+    sm: Optional[List[SupportedMethod]] = None  # supported methods
     d: Optional[str] = None  # description
     t: Optional[List[Transport]] = None  # transports
     nut10: Optional[NUT10Option] = None

cashu/core/mint_info.py

@@ -3,9 +3,14 @@
 
 from pydantic import BaseModel
 
-from .base import Method, Unit
-from .models import MintInfoContact, MintInfoProtectedEndpoint, Nut15MppSupport
-from .nuts.nuts import BLIND_AUTH_NUT, CLEAR_AUTH_NUT, MPP_NUT, WEBSOCKETS_NUT
+from .base import Method, SupportedMethod, Unit
+from .models import (
+    MeltMethodSetting,
+    MintInfoContact,
+    MintInfoProtectedEndpoint,
+    Nut15MppSupport,
+)
+from .nuts.nuts import BLIND_AUTH_NUT, CLEAR_AUTH_NUT, MELT_NUT, MPP_NUT, WEBSOCKETS_NUT
 
 
 def _match_protected_endpoint(endpoint_path: str, request_path: str) -> bool:
@@ -67,6 +72,36 @@ def supports_mpp(self, method: str, unit: Unit) -> bool:
 
         return False
 
+    def payment_request_method_fee(
+        self, sm: Optional[List[SupportedMethod]], unit: Unit
+    ) -> Optional[int]:
+        """
+        Given the `sm` (supported methods) list from a NUT-18/26 payment request,
+        return the lowest per-method fee this mint owes for melting via one of the
+        listed methods in `unit`, or `None` if it melts none of them.
+        """
+        if not sm:
+            return 0
+        if not self.nuts:
+            return None
+        nut_05 = self.nuts.get(MELT_NUT)
+        if not nut_05 or not nut_05.get("methods"):
+            return None
+
+        melt_methods = [MeltMethodSetting.model_validate(e) for e in nut_05["methods"]]
+
+        lowest_fee: Optional[int] = None
+        for entry in sm:
+            supported = any(
+                m.method == entry.mn and m.unit == unit.name for m in melt_methods
+            )
+            if supported:
+                fee = entry.mf or 0
+                if lowest_fee is None or fee < lowest_fee:
+                    lowest_fee = fee
+
+        return lowest_fee
+
     def supports_websocket_mint_quote(self, method: Method, unit: Unit) -> bool:
         if not self.nuts or not self.supports_nut(WEBSOCKETS_NUT):
             return False

cashu/core/nuts/nut26.py

@@ -12,7 +12,7 @@
     bech32_encode as _bech32_encode,
 )
 
-from ..base import NUT10Option, PaymentRequest, Transport
+from ..base import NUT10Option, PaymentRequest, SupportedMethod, Transport
 
 BECH32M_CONST = 0x2BC830A3
 HRP = "creqb"
@@ -248,6 +248,32 @@ def _decode_nut10(data: bytes) -> NUT10Option:
         t=tags if tags else None,
     )
 
+# ─── Supported method encode/decode ─────────────────────────────────
+
+def _encode_supported_method(sm: SupportedMethod) -> bytes:
+    inner = _tlv_entry(0x01, sm.mn.encode())
+    if sm.mf is not None:
+        inner += _tlv_entry(0x02, struct.pack(">Q", sm.mf))
+    return inner
+
+def _decode_supported_method(data: bytes) -> SupportedMethod:
+    entries = _tlv_parse(data)
+    mn: Optional[str] = None
+    mf: Optional[int] = None
+
+    for tag, val in entries:
+        if tag == 0x01:
+            mn = val.decode()
+        elif tag == 0x02:
+            if len(val) != 8:
+                raise ValueError("Invalid method fee length")
+            mf = struct.unpack(">Q", val)[0]
+
+    if mn is None:
+        raise ValueError("Missing method name in supported method")
+
+    return SupportedMethod(mn=mn, mf=mf)
+
 # ─── PaymentRequest <-> TLV bytes ───────────────────────────────────
 
 def _pr_to_tlv(pr: PaymentRequest) -> bytes:
@@ -273,17 +299,23 @@ def _pr_to_tlv(pr: PaymentRequest) -> bytes:
             out += _tlv_entry(0x07, _encode_transport(tr))
     if pr.nut10 is not None:
         out += _tlv_entry(0x08, _encode_nut10(pr.nut10))
+    if pr.mp is not None:
+        out += _tlv_entry(0x09, bytes([1 if pr.mp else 0]))
+    if pr.sm:
+        for method in pr.sm:
+            out += _tlv_entry(0x0A, _encode_supported_method(method))
     return out
 
 def _tlv_to_pr(data: bytes) -> PaymentRequest:
     entries = _tlv_parse(data)
     kwargs: dict = {}
     mints: List[str] = []
     transports: List[Transport] = []
+    supported_methods: List[SupportedMethod] = []
 
     for tag, val in entries:
         if len(val) == 0 and tag in (0x01,):
-            raise ValueError("Empty value for transport tag")
+            raise ValueError("Empty value for id tag")
         if tag == 0x01:
             kwargs["i"] = val.decode()
         elif tag == 0x02:
@@ -307,11 +339,17 @@ def _tlv_to_pr(data: bytes) -> PaymentRequest:
             transports.append(_decode_transport(val))
         elif tag == 0x08:
             kwargs["nut10"] = _decode_nut10(val)
+        elif tag == 0x09:
+            kwargs["mp"] = val[0] == 1
+        elif tag == 0x0A:
+            supported_methods.append(_decode_supported_method(val))
 
     if mints:
         kwargs["m"] = mints
     if transports:
         kwargs["t"] = transports
+    if supported_methods:
+        kwargs["sm"] = supported_methods
 
     return PaymentRequest(**kwargs)
 

cashu/wallet/cli/cli.py

@@ -25,6 +25,8 @@
     Method,
     MintQuote,
     MintQuoteState,
+    PaymentRequest,
+    SupportedMethod,
     TokenV4,
     Unit,
 )
@@ -33,6 +35,8 @@
 from ...core.logging import configure_logger
 from ...core.models import PostMintQuoteResponse
 from ...core.nuts.nut18 import deserialize as deserialize_payment_request
+from ...core.nuts.nut18 import serialize as serialize_payment_request
+from ...core.nuts.nut26 import serialize as serialize_payment_request_bech32
 from ...core.settings import settings
 from ...tor.tor import TorProxy
 from ...wallet.crud import (
@@ -296,18 +300,36 @@ async def pay(
         if pr.a:
             print(f"Amount: {wallet.unit.str(pr.a)} ({pr.a} {pr.u})")
 
-        if pr.m and wallet.url not in pr.m:
+        # The mint list is strict unless `mp` is explicitly true (preferred)
+        mint_outside_list = pr.m is not None and wallet.url not in pr.m
+        if mint_outside_list and not pr.mp:
             print(
                 f"Error: Current mint {wallet.url} is not accepted by the receiver.")
             print(f"Accepted mints: {pr.m}")
             return
 
+        # The sending mint must support (melt via) one of the requested methods
+        method_fee = wallet.mint_info.payment_request_method_fee(pr.sm, wallet.unit)
+        if method_fee is None:
+            print(f"Error: Current mint does not support a requested method: {pr.sm}")
+            return
+
         amount_to_pay = pr.a
         if not amount_to_pay:
             # TODO: Handle amounts not specified in request (ask user)
             print("Error: Amount not specified in payment request.")
             return
 
+        # The method fee applies only when paying from a mint outside the mint
+        # list, or when no mint list is set at all
+        fee_applies = pr.m is None or mint_outside_list
+        if fee_applies and method_fee:
+            amount_to_pay += method_fee
+            print(
+                f"Adding method fee of {wallet.unit.str(method_fee)} "
+                "(paying from a mint outside the preferred list)."
+            )
+
         if not yes and not ctx.obj.get("YES"):
             message = f"Pay {wallet.unit.str(amount_to_pay)}?"
             click.confirm(
@@ -478,6 +500,94 @@ async def pay(
     await print_balance(ctx)
 
 
+def _parse_supported_method(spec: str) -> Optional[SupportedMethod]:
+    """Parse a `--method` value of the form `name` or `name:fee` into a
+    SupportedMethod, or return None if `fee` isn't a non-negative int."""
+    mn, sep, fee_str = spec.partition(":")
+    if not sep:
+        return SupportedMethod(mn=mn)
+    try:
+        fee = int(fee_str)
+    except ValueError:
+        return None
+    if fee < 0:
+        return None
+    return SupportedMethod(mn=mn, mf=fee)
+
+
+@cli.command("request", help="Create a NUT-18 payment request.")
+@click.argument("amount", type=int)
+@click.option("--description", "-d", default=None, help="Human-readable description.")
+@click.option(
+    "--mint",
+    "-m",
+    "mints",
+    multiple=True,
+    help="Accepted mint URL (repeatable, defaults to the current mint).",
+)
+@click.option(
+    "--preferred",
+    default=False,
+    is_flag=True,
+    help="Treat the mint list as preferred rather than strict.",
+)
+@click.option(
+    "--method",
+    "methods",
+    multiple=True,
+    help=(
+        "Required supported method as name or name:fee, e.g. bolt11 or"
+        " onchain:50 (repeatable). The fee applies only when the payer's"
+        " mint is outside a preferred mint list."
+    ),
+)
+@click.option(
+    "--single-use", "-s", default=False, is_flag=True, help="Mark the request single use."
+)
+@click.option(
+    "--bech32", default=False, is_flag=True, help="Encode as a NUT-26 bech32m request."
+)
+@click.pass_context
+@coro
+@init_auth_wallet
+async def request(
+    ctx: Context,
+    amount: int,
+    description: Optional[str],
+    mints: tuple,
+    preferred: bool,
+    methods: tuple,
+    single_use: bool,
+    bech32: bool,
+):
+    wallet: Wallet = ctx.obj["WALLET"]
+    await wallet.load_mint()
+
+    supported_methods = []
+    for spec in methods:
+        parsed = _parse_supported_method(spec)
+        if parsed is None:
+            print(f"Error: Invalid --method '{spec}', fee must be a non-negative int.")
+            return
+        supported_methods.append(parsed)
+
+    pr = PaymentRequest(
+        a=amount,
+        u=wallet.unit.name,
+        m=list(mints) or [wallet.url],
+        mp=True if preferred else None,
+        sm=supported_methods or None,
+        s=True if single_use else None,
+        d=description,
+    )
+    encoded = (
+        serialize_payment_request_bech32(pr)
+        if bech32
+        else serialize_payment_request(pr)
+    )
+    print(encoded)
+
+
 @cli.command("invoice", help="Create Lighting invoice.")
 @click.argument("amount", type=float)
 @click.option("memo", "-m", default="", help="Memo for the invoice.", type=str)

tests/mint/test_mint_fees.py

@@ -119,6 +119,34 @@ async def test_wallet_selection_with_fee(wallet1: Wallet, ledger: Ledger):
     assert sum_proofs(send_proofs_with_fees) == 11
 
 
+@pytest.mark.asyncio
+@pytest.mark.skipif(is_regtest, reason="only works with FakeWallet")
+async def test_payment_request_dust_proofs_net_of_input_fees(
+    wallet1: Wallet, ledger: Ledger
+):
+    """the requested amount `a` (plus any method fee) is net of
+    input fees. A payer selecting from many small (dust) proofs on a
+    fee-charging keyset must top up the selection so the receiver's net
+    value still meets the requested amount, rather than underpay.
+    """
+    set_ledger_keyset_fees(250, ledger, wallet1)
+
+    mint_quote = await wallet1.request_mint(20)
+    await pay_if_regtest(mint_quote.request)
+    await wallet1.mint(20, split=[1] * 20, quote_id=mint_quote.quote)
+
+    amount_to_pay = 10
+    send_proofs, fees = await wallet1.select_to_send(
+        wallet1.proofs, amount_to_pay, include_fees=True
+    )
+    # every selected proof is 1-sat dust
+    assert all(p.amount == 1 for p in send_proofs)
+    # the invariant this payment-request flow relies on:
+    # sum(proofs) - input_fee(proofs) >= amount_to_pay
+    assert sum_proofs(send_proofs) - fees >= amount_to_pay
+    assert sum_proofs(send_proofs) == amount_to_pay + fees
+
+
 @pytest.mark.asyncio
 @pytest.mark.skipif(is_regtest, reason="only works with FakeWallet")
 async def test_wallet_swap_to_send_with_fee(wallet1: Wallet, ledger: Ledger):