pallectrum/electrum/trampoline.py

import io
import os
import random
import dataclasses
from typing import Mapping, Tuple, Optional, List, Iterable, Sequence, Set, Any
from types import MappingProxyType

from .lnutil import LnFeatures, PaymentFeeBudget, FeeBudgetExceeded
from .lnonion import (
    calc_hops_data_for_payment, new_onion_packet, OnionPacket, TRAMPOLINE_HOPS_DATA_SIZE, PER_HOP_HMAC_SIZE
)
from .lnrouter import TrampolineEdge, is_route_within_budget, LNPaymentTRoute
from .lnutil import NoPathFound
from .lntransport import LNPeerAddr
from . import constants
from .logging import get_logger
from .util import random_shuffled_copy


_logger = get_logger(__name__)

# hardcoded list
# TODO for some pubkeys, there are multiple network addresses we could try
TRAMPOLINE_NODES_MAINNET = {
    'ACINQ':                  LNPeerAddr(host='node.acinq.co',           port=9735, pubkey=bytes.fromhex('03864ef025fde8fb587d989186ce6a4a186895ee44a926bfc370e2c366597a3f8f')),
    'Electrum trampoline':    LNPeerAddr(host='lightning.electrum.org',  port=9740, pubkey=bytes.fromhex('03ecef675be448b615e6176424070673ef8284e0fd19d8be062a6cb5b130a0a0d1')),
    'trampoline hodlisterco': LNPeerAddr(host='trampoline.hodlister.co', port=9740, pubkey=bytes.fromhex('02ce014625788a61411398f83c945375663972716029ef9d8916719141dc109a1c')),
}

TRAMPOLINE_NODES_TESTNET = {
    'endurance': LNPeerAddr(host='34.250.234.192', port=9735, pubkey=bytes.fromhex('03933884aaf1d6b108397e5efe5c86bcf2d8ca8d2f700eda99db9214fc2712b134')),
    'Electrum trampoline': LNPeerAddr(host='lightning.electrum.org', port=9739, pubkey=bytes.fromhex('02bf82e22f99dcd7ac1de4aad5152ce48f0694c46ec582567f379e0adbf81e2d0f')),
}

_TRAMPOLINE_NODES_UNITTESTS = {}  # used in unit tests


def hardcoded_trampoline_nodes() -> Mapping[str, LNPeerAddr]:
    if _TRAMPOLINE_NODES_UNITTESTS:
        return _TRAMPOLINE_NODES_UNITTESTS
    elif constants.net.NET_NAME == "mainnet":
        return TRAMPOLINE_NODES_MAINNET
    elif constants.net.NET_NAME == "testnet":
        return TRAMPOLINE_NODES_TESTNET
    else:
        return {}


def trampolines_by_id():
    return dict([(x.pubkey, x) for x in hardcoded_trampoline_nodes().values()])


def is_hardcoded_trampoline(node_id: bytes) -> bool:
    return node_id in trampolines_by_id()


def encode_routing_info(r_tags: Sequence[Sequence[Sequence[Any]]]) -> List[bytes]:
    routes = []
    for route in r_tags:
        result = bytes([len(route)])
        for step in route:
            pubkey, scid, feebase, feerate, cltv = step
            result += pubkey
            result += scid
            result += int.to_bytes(feebase, length=4, byteorder="big", signed=False)
            result += int.to_bytes(feerate, length=4, byteorder="big", signed=False)
            result += int.to_bytes(cltv, length=2, byteorder="big", signed=False)
        routes.append(result)
    return routes


def decode_routing_info(rinfo: bytes) -> Sequence[Sequence[Sequence[Any]]]:
    if not rinfo:
        return []
    r_tags = []
    with io.BytesIO(bytes(rinfo)) as s:
        while True:
            route = []
            route_len = s.read(1)
            if not route_len:
                break
            for step in range(route_len[0]):
                pubkey = s.read(33)
                scid = s.read(8)
                feebase = int.from_bytes(s.read(4), byteorder="big")
                feerate = int.from_bytes(s.read(4), byteorder="big")
                cltv = int.from_bytes(s.read(2), byteorder="big")
                route.append((pubkey, scid, feebase, feerate, cltv))
            r_tags.append(route)
    return r_tags


def is_legacy_relay(invoice_features, r_tags) -> Tuple[bool, Set[bytes]]:
    """Returns if we deal with a legacy payment and the list of trampoline pubkeys in the invoice.
    """
    invoice_features = LnFeatures(invoice_features)
    # trampoline-supporting wallets:
    if invoice_features.supports(LnFeatures.OPTION_TRAMPOLINE_ROUTING_OPT_ECLAIR)\
       or invoice_features.supports(LnFeatures.OPTION_TRAMPOLINE_ROUTING_OPT_ELECTRUM):
        # If there are no r_tags (routing hints) included, the wallet doesn't have
        # private channels and is probably directly connected to a trampoline node.
        # Any trampoline node should be able to figure out a path to the receiver and
        # we can use an e2e payment.
        if not r_tags:
            return False, set()
        else:
            # - We choose one routing hint at random, and
            #   use end-to-end trampoline if that node is a trampoline-forwarder (TF).
            # - In case of e2e, the route will have either one or two TFs (one neighbour of sender,
            #   and one neighbour of recipient; and these might coincide). Note that there are some
            #   channel layouts where two TFs are needed for a payment to succeed, e.g. both
            #   endpoints connected to T1 and T2, and sender only has send-capacity with T1, while
            #   recipient only has recv-capacity with T2.
            singlehop_r_tags = [x for x in r_tags if len(x) == 1]
            invoice_trampolines = [x[0][0] for x in singlehop_r_tags]
            invoice_trampolines = set(invoice_trampolines)
            if invoice_trampolines:
                return False, invoice_trampolines
    # if trampoline receiving is not supported or the forwarder is not known as a trampoline,
    # we send a legacy payment
    return True, set()


PLACEHOLDER_FEE = None


def _extend_trampoline_route(
        route: List[TrampolineEdge],
        *,
        start_node: bytes = None,
        end_node: bytes,
        pay_fees: bool = True,
):
    """Extends the route and modifies it in place."""
    if start_node is None:
        assert route
        start_node = route[-1].end_node
    trampoline_features = LnFeatures.VAR_ONION_OPT
    # get policy for *start_node*
    # note: trampoline nodes are supposed to advertise their fee and cltv in node_update message.
    #       However, in the temporary spec, they do not.
    #       They also don't send their fee policy in the error message if we lowball the fee...
    route.append(
        TrampolineEdge(
            start_node=start_node,
            end_node=end_node,
            fee_base_msat=PLACEHOLDER_FEE if pay_fees else 0,
            fee_proportional_millionths=PLACEHOLDER_FEE if pay_fees else 0,
            cltv_delta=576 if pay_fees else 0,
            node_features=trampoline_features))


def _allocate_fee_along_route(
    route: List[TrampolineEdge],
    *,
    budget: PaymentFeeBudget,
    trampoline_fee_level: int,
) -> None:
    # calculate budget_to_use, based on given max available "budget"
    if trampoline_fee_level == 0:
        budget_to_use = 0
    else:
        assert trampoline_fee_level > 0
        MAX_LEVEL = 6
        if trampoline_fee_level > MAX_LEVEL:
            raise FeeBudgetExceeded("highest trampoline fee level reached")
        budget_to_use = budget.fee_msat // (2 ** (MAX_LEVEL - trampoline_fee_level))
    _logger.debug(f"_allocate_fee_along_route(). {trampoline_fee_level=}, {budget.fee_msat=}, {budget_to_use=}")
    # replace placeholder fees
    for edge in route:
        assert edge.fee_base_msat in (0, PLACEHOLDER_FEE), edge.fee_base_msat
        assert edge.fee_proportional_millionths in (0, PLACEHOLDER_FEE), edge.fee_proportional_millionths
    edges_to_update = [
        edge for edge in route
        if edge.fee_base_msat == PLACEHOLDER_FEE]
    for edge in edges_to_update:
        edge.fee_base_msat = budget_to_use // len(edges_to_update)
        edge.fee_proportional_millionths = 0


def _choose_second_trampoline(
    my_trampoline: bytes,
    trampolines: Iterable[bytes],
    failed_routes: Iterable[Sequence[str]],
) -> bytes:
    trampolines = set(trampolines)
    if my_trampoline in trampolines:
        trampolines.discard(my_trampoline)
    for r in failed_routes:
        if len(r) > 2:
            t2 = bytes.fromhex(r[1])
            if t2 in trampolines:
                trampolines.discard(t2)
    if not trampolines:
        raise NoPathFound('all routes have failed')
    return random.choice(list(trampolines))


def create_trampoline_route(
        *,
        amount_msat: int,
        min_final_cltv_delta: int,
        invoice_pubkey: bytes,
        invoice_features: int,
        my_pubkey: bytes,
        my_trampoline: bytes,  # the first trampoline in the path; which we are directly connected to
        r_tags,
        trampoline_fee_level: int,
        use_two_trampolines: bool,
        failed_routes: Iterable[Sequence[str]],
        budget: PaymentFeeBudget,
) -> LNPaymentTRoute:
    # we decide whether to convert to a legacy payment
    is_legacy, invoice_trampolines = is_legacy_relay(invoice_features, r_tags)

    # we build a route of trampoline hops and extend the route list in place
    route = []

    # our first trampoline hop is decided by the channel we use
    _extend_trampoline_route(
        route, start_node=my_pubkey, end_node=my_trampoline,
        pay_fees=False,
    )

    if is_legacy:
        # we add another different trampoline hop for privacy
        if use_two_trampolines:
            trampolines = trampolines_by_id()
            second_trampoline = _choose_second_trampoline(my_trampoline, list(trampolines.keys()), failed_routes)
            _extend_trampoline_route(route, end_node=second_trampoline)
        # the last trampoline onion must contain routing hints for the last trampoline
        # node to find the recipient
        # Due to space constraints it is not guaranteed for all route hints to get included in the onion
        invoice_routing_info: List[bytes] = encode_routing_info(r_tags)
        assert invoice_routing_info == encode_routing_info(decode_routing_info(b''.join(invoice_routing_info)))
        # lnwire invoice_features for trampoline is u64
        invoice_features = invoice_features & 0xffffffffffffffff
        route[-1].invoice_routing_info = invoice_routing_info
        route[-1].invoice_features = invoice_features
        route[-1].outgoing_node_id = invoice_pubkey
    else:
        if invoice_trampolines:
            if my_trampoline in invoice_trampolines:
                short_route = [my_trampoline.hex(), invoice_pubkey.hex()]
                if short_route in failed_routes:
                    add_trampoline = True
                else:
                    add_trampoline = False
            else:
                add_trampoline = True
            if add_trampoline:
                second_trampoline = _choose_second_trampoline(my_trampoline, invoice_trampolines, failed_routes)
                _extend_trampoline_route(route, end_node=second_trampoline)

    # Add final edge. note: eclair requires an encrypted t-onion blob even in legacy case.
    # Also needed for fees for last TF!
    if route[-1].end_node != invoice_pubkey:
        _extend_trampoline_route(route, end_node=invoice_pubkey)

    # replace placeholder fees in route
    _allocate_fee_along_route(route, budget=budget, trampoline_fee_level=trampoline_fee_level)

    # check that we can pay amount and fees
    if not is_route_within_budget(
        route=route,
        budget=budget,
        amount_msat_for_dest=amount_msat,
        cltv_delta_for_dest=min_final_cltv_delta,
    ):
        raise FeeBudgetExceeded(f"route exceeds budget: budget: {budget}")
    return route


def create_trampoline_onion(
    *,
    route: LNPaymentTRoute,
    amount_msat: int,
    final_cltv_abs: int,
    total_msat: int,
    payment_hash: bytes,
    payment_secret: bytes,
) -> Tuple[OnionPacket, int, int]:
    # all edges are trampoline
    hops_data, amount_msat, cltv_abs = calc_hops_data_for_payment(
        route,
        amount_msat,
        final_cltv_abs=final_cltv_abs,
        total_msat=total_msat,
        payment_secret=payment_secret)
    # detect trampoline hops.
    payment_path_pubkeys = [x.node_id for x in route]
    num_hops = len(payment_path_pubkeys)
    routing_info_payload_index: Optional[int] = None
    for i in range(num_hops):
        route_edge = route[i]
        assert route_edge.is_trampoline()
        payload = dict(hops_data[i].payload)
        if i < num_hops - 1:
            payload.pop('short_channel_id')
            next_edge = route[i+1]
            assert next_edge.is_trampoline()
            payload["outgoing_node_id"] = {"outgoing_node_id": next_edge.node_id}
        # only for final
        if i == num_hops - 1:
            payload["payment_data"] = {
                "payment_secret": payment_secret,
                "total_msat": total_msat
            }
        # legacy
        if i == num_hops - 2 and route_edge.invoice_features:
            payload["invoice_features"] = {"invoice_features": route_edge.invoice_features}
            routing_info_payload_index = i
            payload["payment_data"] = {
                "payment_secret": payment_secret,
                "total_msat": total_msat
            }
        hops_data[i] = dataclasses.replace(hops_data[i], payload=payload)

    if (index := routing_info_payload_index) is not None:
        # fill the remaining payload space with available routing hints (r_tags)
        payload = dict(hops_data[index].payload)
        # try different r_tag order on each attempt
        invoice_routing_info = random_shuffled_copy(route[index].invoice_routing_info)
        remaining_payload_space = TRAMPOLINE_HOPS_DATA_SIZE \
                                  - sum(len(hop.to_bytes()) + PER_HOP_HMAC_SIZE for hop in hops_data)
        routing_info_to_use = []
        for encoded_r_tag in invoice_routing_info:
            if remaining_payload_space < 50:
                break  # no r_tag will fit here anymore
            r_tag_size = len(encoded_r_tag)
            if r_tag_size > remaining_payload_space:
                continue
            routing_info_to_use.append(encoded_r_tag)
            remaining_payload_space -= r_tag_size
        # add the chosen r_tags to the payload
        payload["invoice_routing_info"] = {"invoice_routing_info": b''.join(routing_info_to_use)}
        hops_data[index] = dataclasses.replace(hops_data[index], payload=payload)
        _logger.debug(f"Using {len(routing_info_to_use)} of {len(invoice_routing_info)} r_tags")

    trampoline_session_key = os.urandom(32)
    trampoline_onion = new_onion_packet(payment_path_pubkeys, trampoline_session_key, hops_data, associated_data=payment_hash, trampoline=True)
    trampoline_onion = dataclasses.replace(
        trampoline_onion,
        _debug_hops_data=hops_data,
        _debug_route=route,
    )
    return trampoline_onion, amount_msat, cltv_abs


def create_trampoline_route_and_onion(
        *,
        amount_msat: int,  # that final receiver gets
        total_msat: int,
        min_final_cltv_delta: int,
        invoice_pubkey: bytes,
        invoice_features,
        my_pubkey: bytes,
        node_id: bytes,
        r_tags,
        payment_hash: bytes,
        payment_secret: bytes,
        local_height: int,
        trampoline_fee_level: int,
        use_two_trampolines: bool,
        failed_routes: Iterable[Sequence[str]],
        budget: PaymentFeeBudget,
) -> Tuple[LNPaymentTRoute, OnionPacket, int, int]:
    # create route for the trampoline_onion
    trampoline_route = create_trampoline_route(
        amount_msat=amount_msat,
        min_final_cltv_delta=min_final_cltv_delta,
        my_pubkey=my_pubkey,
        invoice_pubkey=invoice_pubkey,
        invoice_features=invoice_features,
        my_trampoline=node_id,
        r_tags=r_tags,
        trampoline_fee_level=trampoline_fee_level,
        use_two_trampolines=use_two_trampolines,
        failed_routes=failed_routes,
        budget=budget,
    )
    # compute onion and fees
    final_cltv_abs = local_height + min_final_cltv_delta
    trampoline_onion, amount_with_fees, bucket_cltv_abs = create_trampoline_onion(
        route=trampoline_route,
        amount_msat=amount_msat,
        final_cltv_abs=final_cltv_abs,
        total_msat=total_msat,
        payment_hash=payment_hash,
        payment_secret=payment_secret)
    bucket_cltv_delta = bucket_cltv_abs - local_height
    return trampoline_route, trampoline_onion, amount_with_fees, bucket_cltv_delta