loop/loopd/swapclient_server.go

package loopd

import (
	"context"
	"encoding/hex"
	"errors"
	"fmt"
	"sort"
	"sync"
	"time"

	"github.com/btcsuite/btcd/btcec/v2"
	"github.com/btcsuite/btcd/btcutil"
	"github.com/btcsuite/btcd/chaincfg"
	"github.com/lightninglabs/lndclient"
	"github.com/lightninglabs/loop"
	"github.com/lightninglabs/loop/labels"
	"github.com/lightninglabs/loop/liquidity"
	"github.com/lightninglabs/loop/loopdb"
	clientrpc "github.com/lightninglabs/loop/looprpc"
	"github.com/lightninglabs/loop/swap"
	looprpc "github.com/lightninglabs/loop/swapserverrpc"
	"github.com/lightningnetwork/lnd/lnrpc/walletrpc"
	"github.com/lightningnetwork/lnd/lntypes"
	"github.com/lightningnetwork/lnd/queue"
	"github.com/lightningnetwork/lnd/routing/route"
	"github.com/lightningnetwork/lnd/zpay32"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

const (
	completedSwapsCount = 5

	// minConfTarget is the minimum confirmation target we'll allow clients
	// to specify. This is driven by the minimum confirmation target allowed
	// by the backing fee estimator.
	minConfTarget = 2
)

var (
	// errIncorrectChain is returned when the format of the
	// destination address provided does not match the active chain.
	errIncorrectChain = errors.New("invalid address format for the " +
		"active chain")

	// errConfTargetTooLow is returned when the chosen confirmation target
	// is below the allowed minimum.
	errConfTargetTooLow = errors.New("confirmation target too low")

	// errBalanceTooLow is returned when the loop out amount can't be
	// satisfied given total balance of the selection of channels to loop
	// out on.
	errBalanceTooLow = errors.New(
		"channel balance too low for loop out amount",
	)

	// errInvalidAddress is returned when the destination address is of
	// an unsupported format such as P2PK or P2TR addresses.
	errInvalidAddress = errors.New(
		"invalid or unsupported address",
	)
)

// swapClientServer implements the grpc service exposed by loopd.
type swapClientServer struct {
	// Required by the grpc-gateway/v2 library for forward compatibility.
	clientrpc.UnimplementedSwapClientServer
	clientrpc.UnimplementedDebugServer

	network          lndclient.Network
	impl             *loop.Client
	liquidityMgr     *liquidity.Manager
	lnd              *lndclient.LndServices
	swaps            map[lntypes.Hash]loop.SwapInfo
	subscribers      map[int]chan<- interface{}
	statusChan       chan loop.SwapInfo
	nextSubscriberID int
	swapsLock        sync.Mutex
	mainCtx          context.Context
}

// LoopOut initiates an loop out swap with the given parameters. The call
// returns after the swap has been set up with the swap server. From that point
// onwards, progress can be tracked via the LoopOutStatus stream that is
// returned from Monitor().
func (s *swapClientServer) LoopOut(ctx context.Context,
	in *clientrpc.LoopOutRequest) (
	*clientrpc.SwapResponse, error) {

	log.Infof("Loop out request received")

	var sweepAddr btcutil.Address
	if in.Dest == "" {
		// Generate sweep address if none specified.
		var err error
		sweepAddr, err = s.lnd.WalletKit.NextAddr(
			context.Background(), "",
			walletrpc.AddressType_WITNESS_PUBKEY_HASH, false,
		)
		if err != nil {
			return nil, fmt.Errorf("NextAddr error: %v", err)
		}
	} else {
		var err error
		sweepAddr, err = btcutil.DecodeAddress(
			in.Dest, s.lnd.ChainParams,
		)
		if err != nil {
			return nil, fmt.Errorf("decode address: %v", err)
		}
	}

	sweepConfTarget, err := validateLoopOutRequest(
		ctx, s.lnd.Client, s.lnd.ChainParams, in, sweepAddr,
		s.impl.LoopOutMaxParts,
	)
	if err != nil {
		return nil, err
	}

	req := &loop.OutRequest{
		Amount:              btcutil.Amount(in.Amt),
		DestAddr:            sweepAddr,
		MaxMinerFee:         btcutil.Amount(in.MaxMinerFee),
		MaxPrepayAmount:     btcutil.Amount(in.MaxPrepayAmt),
		MaxPrepayRoutingFee: btcutil.Amount(in.MaxPrepayRoutingFee),
		MaxSwapRoutingFee:   btcutil.Amount(in.MaxSwapRoutingFee),
		MaxSwapFee:          btcutil.Amount(in.MaxSwapFee),
		SweepConfTarget:     sweepConfTarget,
		HtlcConfirmations:   in.HtlcConfirmations,
		SwapPublicationDeadline: time.Unix(
			int64(in.SwapPublicationDeadline), 0,
		),
		Label:     in.Label,
		Initiator: in.Initiator,
	}

	switch {
	case in.LoopOutChannel != 0 && len(in.OutgoingChanSet) > 0: // nolint:staticcheck
		return nil, errors.New("loop_out_channel and outgoing_" +
			"chan_ids are mutually exclusive")

	case in.LoopOutChannel != 0: // nolint:staticcheck
		req.OutgoingChanSet = loopdb.ChannelSet{in.LoopOutChannel} // nolint:staticcheck

	default:
		req.OutgoingChanSet = in.OutgoingChanSet
	}

	info, err := s.impl.LoopOut(ctx, req)
	if err != nil {
		log.Errorf("LoopOut: %v", err)
		return nil, err
	}

	htlcAddress := info.HtlcAddress.String()
	resp := &clientrpc.SwapResponse{
		Id:            info.SwapHash.String(),
		IdBytes:       info.SwapHash[:],
		HtlcAddress:   htlcAddress,
		ServerMessage: info.ServerMessage,
	}

	if loopdb.CurrentProtocolVersion() < loopdb.ProtocolVersionHtlcV3 {
		resp.HtlcAddressP2Wsh = htlcAddress
	} else {
		resp.HtlcAddressP2Tr = htlcAddress
	}

	return resp, nil
}

func (s *swapClientServer) marshallSwap(loopSwap *loop.SwapInfo) (
	*clientrpc.SwapStatus, error) {

	var (
		state         clientrpc.SwapState
		failureReason = clientrpc.FailureReason_FAILURE_REASON_NONE
	)

	// Set our state var for non-failure states. If we get a failure, we
	// will update our failure reason. To remain backwards compatible with
	// previous versions where we squashed all failure reasons to a single
	// failure state, we set a failure reason for all our different failure
	// states, and set our failed state for all of them.
	switch loopSwap.State {
	case loopdb.StateInitiated:
		state = clientrpc.SwapState_INITIATED

	case loopdb.StatePreimageRevealed:
		state = clientrpc.SwapState_PREIMAGE_REVEALED

	case loopdb.StateHtlcPublished:
		state = clientrpc.SwapState_HTLC_PUBLISHED

	case loopdb.StateInvoiceSettled:
		state = clientrpc.SwapState_INVOICE_SETTLED

	case loopdb.StateSuccess:
		state = clientrpc.SwapState_SUCCESS

	case loopdb.StateFailOffchainPayments:
		failureReason = clientrpc.FailureReason_FAILURE_REASON_OFFCHAIN

	case loopdb.StateFailTimeout:
		failureReason = clientrpc.FailureReason_FAILURE_REASON_TIMEOUT

	case loopdb.StateFailSweepTimeout:
		failureReason = clientrpc.FailureReason_FAILURE_REASON_SWEEP_TIMEOUT

	case loopdb.StateFailInsufficientValue:
		failureReason = clientrpc.FailureReason_FAILURE_REASON_INSUFFICIENT_VALUE

	case loopdb.StateFailTemporary:
		failureReason = clientrpc.FailureReason_FAILURE_REASON_TEMPORARY

	case loopdb.StateFailIncorrectHtlcAmt:
		failureReason = clientrpc.FailureReason_FAILURE_REASON_INCORRECT_AMOUNT

	default:
		return nil, fmt.Errorf("unknown swap state: %v", loopSwap.State)
	}

	// If we have a failure reason, we have a failure state, so should use
	// our catchall failed state.
	if failureReason != clientrpc.FailureReason_FAILURE_REASON_NONE {
		state = clientrpc.SwapState_FAILED
	}

	var swapType clientrpc.SwapType
	var (
		htlcAddress      string
		htlcAddressP2TR  string
		htlcAddressP2WSH string
	)
	var outGoingChanSet []uint64
	var lastHop []byte

	switch loopSwap.SwapType {
	case swap.TypeIn:
		swapType = clientrpc.SwapType_LOOP_IN

		if loopSwap.HtlcAddressP2TR != nil {
			htlcAddressP2TR = loopSwap.HtlcAddressP2TR.EncodeAddress()
			htlcAddress = htlcAddressP2TR
		} else {
			htlcAddressP2WSH =
				loopSwap.HtlcAddressP2WSH.EncodeAddress()
			htlcAddress = htlcAddressP2WSH
		}

		if loopSwap.LastHop != nil {
			lastHop = loopSwap.LastHop[:]
		}

	case swap.TypeOut:
		swapType = clientrpc.SwapType_LOOP_OUT
		if loopSwap.HtlcAddressP2WSH != nil {
			htlcAddressP2WSH = loopSwap.HtlcAddressP2WSH.EncodeAddress()
			htlcAddress = htlcAddressP2WSH
		} else {
			htlcAddressP2TR = loopSwap.HtlcAddressP2TR.EncodeAddress()
			htlcAddress = htlcAddressP2TR
		}

		outGoingChanSet = loopSwap.OutgoingChanSet

	default:
		return nil, errors.New("unknown swap type")
	}

	return &clientrpc.SwapStatus{
		Amt:              int64(loopSwap.AmountRequested),
		Id:               loopSwap.SwapHash.String(),
		IdBytes:          loopSwap.SwapHash[:],
		State:            state,
		FailureReason:    failureReason,
		InitiationTime:   loopSwap.InitiationTime.UnixNano(),
		LastUpdateTime:   loopSwap.LastUpdate.UnixNano(),
		HtlcAddress:      htlcAddress,
		HtlcAddressP2Tr:  htlcAddressP2TR,
		HtlcAddressP2Wsh: htlcAddressP2WSH,
		Type:             swapType,
		CostServer:       int64(loopSwap.Cost.Server),
		CostOnchain:      int64(loopSwap.Cost.Onchain),
		CostOffchain:     int64(loopSwap.Cost.Offchain),
		Label:            loopSwap.Label,
		LastHop:          lastHop,
		OutgoingChanSet:  outGoingChanSet,
	}, nil
}

// Monitor will return a stream of swap updates for currently active swaps.
func (s *swapClientServer) Monitor(in *clientrpc.MonitorRequest,
	server clientrpc.SwapClient_MonitorServer) error {

	log.Infof("Monitor request received")

	send := func(info loop.SwapInfo) error {
		rpcSwap, err := s.marshallSwap(&info)
		if err != nil {
			return err
		}

		return server.Send(rpcSwap)
	}

	// Start a notification queue for this subscriber.
	queue := queue.NewConcurrentQueue(20)
	queue.Start()

	// Add this subscriber to the global subscriber list. Also create a
	// snapshot of all pending and completed swaps within the lock, to
	// prevent subscribers from receiving duplicate updates.
	s.swapsLock.Lock()

	id := s.nextSubscriberID
	s.nextSubscriberID++
	s.subscribers[id] = queue.ChanIn()

	var pendingSwaps, completedSwaps []loop.SwapInfo
	for _, swap := range s.swaps {
		if swap.State.Type() == loopdb.StateTypePending {
			pendingSwaps = append(pendingSwaps, swap)
		} else {
			completedSwaps = append(completedSwaps, swap)
		}
	}

	s.swapsLock.Unlock()

	defer func() {
		s.swapsLock.Lock()
		delete(s.subscribers, id)
		s.swapsLock.Unlock()
		queue.Stop()
	}()

	// Sort completed swaps new to old.
	sort.Slice(completedSwaps, func(i, j int) bool {
		return completedSwaps[i].LastUpdate.After(
			completedSwaps[j].LastUpdate,
		)
	})

	// Discard all but top x latest.
	if len(completedSwaps) > completedSwapsCount {
		completedSwaps = completedSwaps[:completedSwapsCount]
	}

	// Concatenate both sets.
	filteredSwaps := append(pendingSwaps, completedSwaps...) // nolint: gocritic

	// Sort again, but this time old to new.
	sort.Slice(filteredSwaps, func(i, j int) bool {
		return filteredSwaps[i].LastUpdate.Before(
			filteredSwaps[j].LastUpdate,
		)
	})

	// Return swaps to caller.
	for _, swap := range filteredSwaps {
		if err := send(swap); err != nil {
			return err
		}
	}

	// As long as the client is connected, keep passing through swap
	// updates.
	for {
		select {
		case queueItem, ok := <-queue.ChanOut():
			if !ok {
				return nil
			}

			swap := queueItem.(loop.SwapInfo)
			if err := send(swap); err != nil {
				return err
			}

		// The client cancels the subscription.
		case <-server.Context().Done():
			return nil

		// The server is shutting down.
		case <-s.mainCtx.Done():
			return fmt.Errorf("server is shutting down")
		}
	}
}

// ListSwaps returns a list of all currently known swaps and their current
// status.
func (s *swapClientServer) ListSwaps(_ context.Context,
	_ *clientrpc.ListSwapsRequest) (*clientrpc.ListSwapsResponse, error) {

	var (
		rpcSwaps = make([]*clientrpc.SwapStatus, len(s.swaps))
		idx      = 0
		err      error
	)

	s.swapsLock.Lock()
	defer s.swapsLock.Unlock()

	// We can just use the server's in-memory cache as that contains the
	// most up-to-date state including temporary failures which aren't
	// persisted to disk. The swaps field is a map, that's why we need an
	// additional index.
	for _, swp := range s.swaps {
		swp := swp
		rpcSwaps[idx], err = s.marshallSwap(&swp)
		if err != nil {
			return nil, err
		}
		idx++
	}
	return &clientrpc.ListSwapsResponse{Swaps: rpcSwaps}, nil
}

// SwapInfo returns all known details about a single swap.
func (s *swapClientServer) SwapInfo(_ context.Context,
	req *clientrpc.SwapInfoRequest) (*clientrpc.SwapStatus, error) {

	swapHash, err := lntypes.MakeHash(req.Id)
	if err != nil {
		return nil, fmt.Errorf("error parsing swap hash: %v", err)
	}

	// Just return the server's in-memory cache here too as we also want to
	// return temporary failures to the client.
	swp, ok := s.swaps[swapHash]
	if !ok {
		return nil, fmt.Errorf("swap with hash %s not found", req.Id)
	}
	return s.marshallSwap(&swp)
}

// LoopOutTerms returns the terms that the server enforces for loop out swaps.
func (s *swapClientServer) LoopOutTerms(ctx context.Context,
	req *clientrpc.TermsRequest) (*clientrpc.OutTermsResponse, error) {

	log.Infof("Loop out terms request received")

	terms, err := s.impl.LoopOutTerms(ctx)
	if err != nil {
		log.Errorf("Terms request: %v", err)
		return nil, err
	}

	return &clientrpc.OutTermsResponse{
		MinSwapAmount: int64(terms.MinSwapAmount),
		MaxSwapAmount: int64(terms.MaxSwapAmount),
		MinCltvDelta:  terms.MinCltvDelta,
		MaxCltvDelta:  terms.MaxCltvDelta,
	}, nil
}

// LoopOutQuote returns a quote for a loop out swap with the provided
// parameters.
func (s *swapClientServer) LoopOutQuote(ctx context.Context,
	req *clientrpc.QuoteRequest) (*clientrpc.OutQuoteResponse, error) {

	confTarget, err := validateConfTarget(
		req.ConfTarget, loop.DefaultSweepConfTarget,
	)
	if err != nil {
		return nil, err
	}
	quote, err := s.impl.LoopOutQuote(ctx, &loop.LoopOutQuoteRequest{
		Amount:          btcutil.Amount(req.Amt),
		SweepConfTarget: confTarget,
		SwapPublicationDeadline: time.Unix(
			int64(req.SwapPublicationDeadline), 0,
		),
	})
	if err != nil {
		return nil, err
	}

	return &clientrpc.OutQuoteResponse{
		HtlcSweepFeeSat: int64(quote.MinerFee),
		PrepayAmtSat:    int64(quote.PrepayAmount),
		SwapFeeSat:      int64(quote.SwapFee),
		SwapPaymentDest: quote.SwapPaymentDest[:],
		ConfTarget:      confTarget,
	}, nil
}

// GetTerms returns the terms that the server enforces for swaps.
func (s *swapClientServer) GetLoopInTerms(ctx context.Context,
	req *clientrpc.TermsRequest) (*clientrpc.InTermsResponse, error) {

	log.Infof("Loop in terms request received")

	terms, err := s.impl.LoopInTerms(ctx)
	if err != nil {
		log.Errorf("Terms request: %v", err)
		return nil, err
	}

	return &clientrpc.InTermsResponse{
		MinSwapAmount: int64(terms.MinSwapAmount),
		MaxSwapAmount: int64(terms.MaxSwapAmount),
	}, nil
}

// GetQuote returns a quote for a swap with the provided parameters.
func (s *swapClientServer) GetLoopInQuote(ctx context.Context,
	req *clientrpc.QuoteRequest) (*clientrpc.InQuoteResponse, error) {

	log.Infof("Loop in quote request received")

	htlcConfTarget, err := validateLoopInRequest(
		req.ConfTarget, req.ExternalHtlc,
	)
	if err != nil {
		return nil, err
	}

	var (
		routeHints [][]zpay32.HopHint
		lastHop    *route.Vertex
	)

	if req.LoopInLastHop != nil {
		lastHopVertex, err := route.NewVertexFromBytes(
			req.LoopInLastHop,
		)
		if err != nil {
			return nil, err
		}
		lastHop = &lastHopVertex
	}

	if len(req.LoopInRouteHints) != 0 {
		routeHints, err = unmarshallRouteHints(req.LoopInRouteHints)
		if err != nil {
			return nil, err
		}
	}

	quote, err := s.impl.LoopInQuote(ctx, &loop.LoopInQuoteRequest{
		Amount:         btcutil.Amount(req.Amt),
		HtlcConfTarget: htlcConfTarget,
		ExternalHtlc:   req.ExternalHtlc,
		LastHop:        lastHop,
		RouteHints:     routeHints,
		Private:        req.Private,
	})
	if err != nil {
		return nil, err
	}

	return &clientrpc.InQuoteResponse{
		HtlcPublishFeeSat: int64(quote.MinerFee),
		SwapFeeSat:        int64(quote.SwapFee),
		ConfTarget:        htlcConfTarget,
	}, nil
}

// unmarshallRouteHints unmarshalls a list of route hints.
func unmarshallRouteHints(rpcRouteHints []*looprpc.RouteHint) (
	[][]zpay32.HopHint, error) {

	routeHints := make([][]zpay32.HopHint, 0, len(rpcRouteHints))
	for _, rpcRouteHint := range rpcRouteHints {
		routeHint := make(
			[]zpay32.HopHint, 0, len(rpcRouteHint.HopHints),
		)
		for _, rpcHint := range rpcRouteHint.HopHints {
			hint, err := unmarshallHopHint(rpcHint)
			if err != nil {
				return nil, err
			}

			routeHint = append(routeHint, hint)
		}
		routeHints = append(routeHints, routeHint)
	}

	return routeHints, nil
}

// unmarshallHopHint unmarshalls a single hop hint.
func unmarshallHopHint(rpcHint *looprpc.HopHint) (zpay32.HopHint, error) {
	pubBytes, err := hex.DecodeString(rpcHint.NodeId)
	if err != nil {
		return zpay32.HopHint{}, err
	}

	pubkey, err := btcec.ParsePubKey(pubBytes)
	if err != nil {
		return zpay32.HopHint{}, err
	}

	return zpay32.HopHint{
		NodeID:                    pubkey,
		ChannelID:                 rpcHint.ChanId,
		FeeBaseMSat:               rpcHint.FeeBaseMsat,
		FeeProportionalMillionths: rpcHint.FeeProportionalMillionths,
		CLTVExpiryDelta:           uint16(rpcHint.CltvExpiryDelta),
	}, nil
}

// Probe requests the server to probe the client's node to test inbound
// liquidity.
func (s *swapClientServer) Probe(ctx context.Context,
	req *clientrpc.ProbeRequest) (*clientrpc.ProbeResponse, error) {

	log.Infof("Probe request received")

	var lastHop *route.Vertex
	if req.LastHop != nil {
		lastHopVertex, err := route.NewVertexFromBytes(req.LastHop)
		if err != nil {
			return nil, err
		}

		lastHop = &lastHopVertex
	}

	routeHints, err := unmarshallRouteHints(req.RouteHints)
	if err != nil {
		return nil, err
	}

	err = s.impl.Probe(ctx, &loop.ProbeRequest{
		Amount:     btcutil.Amount(req.Amt),
		LastHop:    lastHop,
		RouteHints: routeHints,
	})
	if err != nil {
		return nil, err
	}

	return &clientrpc.ProbeResponse{}, nil
}

func (s *swapClientServer) LoopIn(ctx context.Context,
	in *clientrpc.LoopInRequest) (*clientrpc.SwapResponse, error) {

	log.Infof("Loop in request received")

	htlcConfTarget, err := validateLoopInRequest(
		in.HtlcConfTarget, in.ExternalHtlc,
	)
	if err != nil {
		return nil, err
	}

	// Check that the label is valid.
	if err := labels.Validate(in.Label); err != nil {
		return nil, err
	}

	routeHints, err := unmarshallRouteHints(in.RouteHints)
	if err != nil {
		return nil, err
	}

	req := &loop.LoopInRequest{
		Amount:         btcutil.Amount(in.Amt),
		MaxMinerFee:    btcutil.Amount(in.MaxMinerFee),
		MaxSwapFee:     btcutil.Amount(in.MaxSwapFee),
		HtlcConfTarget: htlcConfTarget,
		ExternalHtlc:   in.ExternalHtlc,
		Label:          in.Label,
		Initiator:      in.Initiator,
		Private:        in.Private,
		RouteHints:     routeHints,
	}
	if in.LastHop != nil {
		lastHop, err := route.NewVertexFromBytes(in.LastHop)
		if err != nil {
			return nil, err
		}
		req.LastHop = &lastHop
	}
	swapInfo, err := s.impl.LoopIn(ctx, req)
	if err != nil {
		log.Errorf("Loop in: %v", err)
		return nil, err
	}

	response := &clientrpc.SwapResponse{
		Id:            swapInfo.SwapHash.String(),
		IdBytes:       swapInfo.SwapHash[:],
		ServerMessage: swapInfo.ServerMessage,
	}

	if loopdb.CurrentProtocolVersion() < loopdb.ProtocolVersionHtlcV3 {
		p2wshAddr := swapInfo.HtlcAddressP2WSH.String()
		response.HtlcAddress = p2wshAddr
		response.HtlcAddressP2Wsh = p2wshAddr
	} else {
		p2trAddr := swapInfo.HtlcAddressP2TR.String()
		response.HtlcAddress = p2trAddr
		response.HtlcAddressP2Tr = p2trAddr
	}

	return response, nil
}

// GetLsatTokens returns all tokens that are contained in the LSAT token store.
func (s *swapClientServer) GetLsatTokens(ctx context.Context,
	_ *clientrpc.TokensRequest) (*clientrpc.TokensResponse, error) {

	log.Infof("Get LSAT tokens request received")

	tokens, err := s.impl.LsatStore.AllTokens()
	if err != nil {
		return nil, err
	}

	rpcTokens := make([]*clientrpc.LsatToken, len(tokens))
	idx := 0
	for key, token := range tokens {
		macBytes, err := token.BaseMacaroon().MarshalBinary()
		if err != nil {
			return nil, err
		}
		rpcTokens[idx] = &clientrpc.LsatToken{
			BaseMacaroon:       macBytes,
			PaymentHash:        token.PaymentHash[:],
			PaymentPreimage:    token.Preimage[:],
			AmountPaidMsat:     int64(token.AmountPaid),
			RoutingFeePaidMsat: int64(token.RoutingFeePaid),
			TimeCreated:        token.TimeCreated.Unix(),
			Expired:            !token.IsValid(),
			StorageName:        key,
		}
		idx++
	}

	return &clientrpc.TokensResponse{Tokens: rpcTokens}, nil
}

// GetLiquidityParams gets our current liquidity manager's parameters.
func (s *swapClientServer) GetLiquidityParams(_ context.Context,
	_ *clientrpc.GetLiquidityParamsRequest) (*clientrpc.LiquidityParameters,
	error) {

	cfg := s.liquidityMgr.GetParameters()

	totalRules := len(cfg.ChannelRules) + len(cfg.PeerRules)

	rpcCfg := &clientrpc.LiquidityParameters{
		SweepConfTarget:   cfg.SweepConfTarget,
		FailureBackoffSec: uint64(cfg.FailureBackOff.Seconds()),
		Autoloop:          cfg.Autoloop,
		AutoloopBudgetSat: uint64(cfg.AutoFeeBudget),
		AutoMaxInFlight:   uint64(cfg.MaxAutoInFlight),
		Rules: make(
			[]*clientrpc.LiquidityRule, 0, totalRules,
		),
		MinSwapAmount:  uint64(cfg.ClientRestrictions.Minimum),
		MaxSwapAmount:  uint64(cfg.ClientRestrictions.Maximum),
		HtlcConfTarget: cfg.HtlcConfTarget,
	}

	switch f := cfg.FeeLimit.(type) {
	case *liquidity.FeeCategoryLimit:
		satPerByte := f.SweepFeeRateLimit.FeePerKVByte() / 1000

		rpcCfg.SweepFeeRateSatPerVbyte = uint64(satPerByte)

		rpcCfg.MaxMinerFeeSat = uint64(f.MaximumMinerFee)
		rpcCfg.MaxSwapFeePpm = f.MaximumSwapFeePPM
		rpcCfg.MaxRoutingFeePpm = f.MaximumRoutingFeePPM
		rpcCfg.MaxPrepayRoutingFeePpm = f.MaximumPrepayRoutingFeePPM
		rpcCfg.MaxPrepaySat = uint64(f.MaximumPrepay)

	case *liquidity.FeePortion:
		rpcCfg.FeePpm = f.PartsPerMillion

	default:
		return nil, fmt.Errorf("unknown fee limit: %T", cfg.FeeLimit)
	}

	// Zero golang time is different to a zero unix time, so we only set
	// our start date if it is non-zero.
	if !cfg.AutoFeeStartDate.IsZero() {
		rpcCfg.AutoloopBudgetStartSec = uint64(
			cfg.AutoFeeStartDate.Unix(),
		)
	}

	for channel, rule := range cfg.ChannelRules {
		rpcRule := newRPCRule(channel.ToUint64(), nil, rule)
		rpcCfg.Rules = append(rpcCfg.Rules, rpcRule)
	}

	for peer, rule := range cfg.PeerRules {
		peer := peer
		rpcRule := newRPCRule(0, peer[:], rule)
		rpcCfg.Rules = append(rpcCfg.Rules, rpcRule)
	}

	return rpcCfg, nil
}

func newRPCRule(channelID uint64, peer []byte,
	rule *liquidity.SwapRule) *clientrpc.LiquidityRule {

	rpcRule := &clientrpc.LiquidityRule{
		ChannelId:         channelID,
		Pubkey:            peer,
		Type:              clientrpc.LiquidityRuleType_THRESHOLD,
		IncomingThreshold: uint32(rule.MinimumIncoming),
		OutgoingThreshold: uint32(rule.MinimumOutgoing),
		SwapType:          clientrpc.SwapType_LOOP_OUT,
	}

	if rule.Type == swap.TypeIn {
		rpcRule.SwapType = clientrpc.SwapType_LOOP_IN
	}

	return rpcRule
}

// SetLiquidityParams attempts to set our current liquidity manager's
// parameters.
func (s *swapClientServer) SetLiquidityParams(ctx context.Context,
	in *clientrpc.SetLiquidityParamsRequest) (*clientrpc.SetLiquidityParamsResponse,
	error) {

	err := s.liquidityMgr.SetParameters(ctx, in.Parameters)
	if err != nil {
		return nil, err
	}

	return &clientrpc.SetLiquidityParamsResponse{}, nil
}

// SuggestSwaps provides a list of suggested swaps based on lnd's current
// channel balances and rules set by the liquidity manager.
func (s *swapClientServer) SuggestSwaps(ctx context.Context,
	_ *clientrpc.SuggestSwapsRequest) (*clientrpc.SuggestSwapsResponse, error) {

	suggestions, err := s.liquidityMgr.SuggestSwaps(ctx, false)
	switch err {
	case liquidity.ErrNoRules:
		return nil, status.Error(codes.FailedPrecondition, err.Error())

	case nil:

	default:
		return nil, err
	}

	resp := &clientrpc.SuggestSwapsResponse{
		LoopOut: make(
			[]*clientrpc.LoopOutRequest, len(suggestions.OutSwaps),
		),
		LoopIn: make(
			[]*clientrpc.LoopInRequest, len(suggestions.InSwaps),
		),
	}

	for i, swap := range suggestions.OutSwaps {
		resp.LoopOut[i] = &clientrpc.LoopOutRequest{
			Amt:                 int64(swap.Amount),
			OutgoingChanSet:     swap.OutgoingChanSet,
			MaxSwapFee:          int64(swap.MaxSwapFee),
			MaxMinerFee:         int64(swap.MaxMinerFee),
			MaxPrepayAmt:        int64(swap.MaxPrepayAmount),
			MaxSwapRoutingFee:   int64(swap.MaxSwapRoutingFee),
			MaxPrepayRoutingFee: int64(swap.MaxPrepayRoutingFee),
			SweepConfTarget:     swap.SweepConfTarget,
		}
	}

	for i, swap := range suggestions.InSwaps {
		loopIn := &clientrpc.LoopInRequest{
			Amt:            int64(swap.Amount),
			MaxSwapFee:     int64(swap.MaxSwapFee),
			MaxMinerFee:    int64(swap.MaxMinerFee),
			HtlcConfTarget: swap.HtlcConfTarget,
		}

		if swap.LastHop != nil {
			loopIn.LastHop = swap.LastHop[:]
		}

		resp.LoopIn[i] = loopIn
	}

	for id, reason := range suggestions.DisqualifiedChans {
		autoloopReason, err := rpcAutoloopReason(reason)
		if err != nil {
			return nil, err
		}

		exclChan := &clientrpc.Disqualified{
			Reason:    autoloopReason,
			ChannelId: id.ToUint64(),
		}

		resp.Disqualified = append(resp.Disqualified, exclChan)
	}

	for pubkey, reason := range suggestions.DisqualifiedPeers {
		autoloopReason, err := rpcAutoloopReason(reason)
		if err != nil {
			return nil, err
		}

		clonedPubkey := route.Vertex{}
		copy(clonedPubkey[:], pubkey[:])

		exclChan := &clientrpc.Disqualified{
			Reason: autoloopReason,
			Pubkey: clonedPubkey[:],
		}

		resp.Disqualified = append(resp.Disqualified, exclChan)
	}

	return resp, nil
}

func rpcAutoloopReason(reason liquidity.Reason) (clientrpc.AutoReason, error) {
	switch reason {
	case liquidity.ReasonNone:
		return clientrpc.AutoReason_AUTO_REASON_UNKNOWN, nil

	case liquidity.ReasonBudgetNotStarted:
		return clientrpc.AutoReason_AUTO_REASON_BUDGET_NOT_STARTED, nil

	case liquidity.ReasonSweepFees:
		return clientrpc.AutoReason_AUTO_REASON_SWEEP_FEES, nil

	case liquidity.ReasonBudgetElapsed:
		return clientrpc.AutoReason_AUTO_REASON_BUDGET_ELAPSED, nil

	case liquidity.ReasonInFlight:
		return clientrpc.AutoReason_AUTO_REASON_IN_FLIGHT, nil

	case liquidity.ReasonSwapFee:
		return clientrpc.AutoReason_AUTO_REASON_SWAP_FEE, nil

	case liquidity.ReasonMinerFee:
		return clientrpc.AutoReason_AUTO_REASON_MINER_FEE, nil

	case liquidity.ReasonPrepay:
		return clientrpc.AutoReason_AUTO_REASON_PREPAY, nil

	case liquidity.ReasonFailureBackoff:
		return clientrpc.AutoReason_AUTO_REASON_FAILURE_BACKOFF, nil

	case liquidity.ReasonLoopOut:
		return clientrpc.AutoReason_AUTO_REASON_LOOP_OUT, nil

	case liquidity.ReasonLoopIn:
		return clientrpc.AutoReason_AUTO_REASON_LOOP_IN, nil

	case liquidity.ReasonLiquidityOk:
		return clientrpc.AutoReason_AUTO_REASON_LIQUIDITY_OK, nil

	case liquidity.ReasonBudgetInsufficient:
		return clientrpc.AutoReason_AUTO_REASON_BUDGET_INSUFFICIENT, nil

	case liquidity.ReasonFeePPMInsufficient:
		return clientrpc.AutoReason_AUTO_REASON_SWAP_FEE, nil

	default:
		return 0, fmt.Errorf("unknown autoloop reason: %v", reason)
	}
}

// processStatusUpdates reads updates on the status channel and processes them.
//
// NOTE: This must run inside a goroutine as it blocks until the main context
// shuts down.
func (s *swapClientServer) processStatusUpdates(mainCtx context.Context) {
	for {
		select {
		// On updates, refresh the server's in-memory state and inform
		// subscribers about the changes.
		case swp := <-s.statusChan:
			s.swapsLock.Lock()
			s.swaps[swp.SwapHash] = swp

			for _, subscriber := range s.subscribers {
				select {
				case subscriber <- swp:
				case <-mainCtx.Done():
					s.swapsLock.Unlock()
					return
				}
			}

			s.swapsLock.Unlock()

		// Server is shutting down.
		case <-mainCtx.Done():
			return
		}
	}
}

// validateConfTarget ensures the given confirmation target is valid. If one
// isn't specified (0 value), then the default target is used.
func validateConfTarget(target, defaultTarget int32) (int32, error) {
	switch {
	case target == 0:
		return defaultTarget, nil

	// Ensure the target respects our minimum threshold.
	case target < minConfTarget:
		return 0, fmt.Errorf("%w: A confirmation target of at "+
			"least %v must be provided", errConfTargetTooLow,
			minConfTarget)

	default:
		return target, nil
	}
}

// validateLoopInRequest fails if the mutually exclusive conf target and
// external parameters are both set.
func validateLoopInRequest(htlcConfTarget int32, external bool) (int32, error) {
	// If the htlc is going to be externally set, the htlcConfTarget should
	// not be set, because it has no relevance when the htlc is external.
	if external && htlcConfTarget != 0 {
		return 0, errors.New("external and htlc conf target cannot " +
			"both be set")
	}

	// If the htlc is being externally published, we do not need to set a
	// confirmation target.
	if external {
		return 0, nil
	}

	return validateConfTarget(htlcConfTarget, loop.DefaultHtlcConfTarget)
}

// validateLoopOutRequest validates the confirmation target, destination
// address and label of the loop out request. It also checks that the requested
// loop amount is valid given the available balance.
func validateLoopOutRequest(ctx context.Context, lnd lndclient.LightningClient,
	chainParams *chaincfg.Params, req *clientrpc.LoopOutRequest,
	sweepAddr btcutil.Address, maxParts uint32) (int32, error) {

	// Check that the provided destination address has the correct format
	// for the active network.
	if !sweepAddr.IsForNet(chainParams) {
		return 0, fmt.Errorf("%w: Current active network is %s",
			errIncorrectChain, chainParams.Name)
	}

	// Check that the provided destination address is a supported
	// address format.
	switch sweepAddr.(type) {
	case *btcutil.AddressWitnessScriptHash,
		*btcutil.AddressWitnessPubKeyHash,
		*btcutil.AddressScriptHash,
		*btcutil.AddressPubKeyHash:

	default:
		return 0, errInvalidAddress
	}

	// Check that the label is valid.
	if err := labels.Validate(req.Label); err != nil {
		return 0, err
	}

	channels, err := lnd.ListChannels(ctx, false, false)
	if err != nil {
		return 0, err
	}

	unlimitedChannels := len(req.OutgoingChanSet) == 0
	outgoingChanSetMap := make(map[uint64]bool)
	for _, chanID := range req.OutgoingChanSet {
		outgoingChanSetMap[chanID] = true
	}

	var activeChannelSet []lndclient.ChannelInfo
	for _, c := range channels {
		// Don't bother looking at inactive channels.
		if !c.Active {
			continue
		}

		// If no outgoing channel set was specified then all active
		// channels are considered. However, if a channel set was
		// specified then only the specified channels are considered.
		if unlimitedChannels || outgoingChanSetMap[c.ChannelID] {
			activeChannelSet = append(activeChannelSet, c)
		}
	}

	// Determine if the loop out request is theoretically possible given
	// the amount requested, the maximum possible routing fees,
	// the available channel set and the fact that equal splitting is
	// used for MPP.
	requiredBalance := btcutil.Amount(req.Amt + req.MaxSwapRoutingFee)
	isRoutable, _ := hasBandwidth(activeChannelSet, requiredBalance,
		int(maxParts))
	if !isRoutable {
		return 0, fmt.Errorf("%w: Requested swap amount of %d "+
			"sats along with the maximum routing fee of %d sats "+
			"is more than what can be routed given current state "+
			"of the channel set", errBalanceTooLow, req.Amt,
			req.MaxSwapRoutingFee)
	}

	return validateConfTarget(
		req.SweepConfTarget, loop.DefaultSweepConfTarget,
	)
}

// hasBandwidth simulates the MPP splitting logic that will be used by LND when
// attempting to route the payment. This function is used to evaluate if a
// payment will be routable given the splitting logic used by LND.
// It returns true if the amount is routable given the channel set and the
// maximum number of shards allowed. If the amount is routable then the number
// of shards used is also returned. This function makes an assumption that the
// minimum loop amount divided by max parts will not be less than the minimum
// shard amount. If the MPP logic changes, then this function should be updated.
func hasBandwidth(channels []lndclient.ChannelInfo, amt btcutil.Amount,
	maxParts int) (bool, int) {

	scratch := make([]btcutil.Amount, len(channels))
	var totalBandwidth btcutil.Amount
	for i, channel := range channels {
		scratch[i] = channel.LocalBalance
		totalBandwidth += channel.LocalBalance
	}

	if totalBandwidth < amt {
		return false, 0
	}

	split := amt
	for shard := 0; shard <= maxParts; {
		paid := false
		for i := 0; i < len(scratch); i++ {
			if scratch[i] >= split {
				scratch[i] -= split
				amt -= split
				paid = true
				shard++
				break
			}
		}

		if amt == 0 {
			return true, shard
		}

		if !paid {
			split /= 2
		} else {
			split = amt
		}
	}

	return false, 0
}