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// Package liquidity is responsible for monitoring our node's liquidity. It
// allows setting of a liquidity rule which describes the desired liquidity
// balance on a per-channel basis.
// Swap suggestions are limited to channels that are not currently being used
// for a pending swap. If we are currently processing an unrestricted swap (ie,
// a loop out with no outgoing channel targets set or a loop in with no last
// hop set), we will not suggest any swaps because these swaps will shift the
// balances of our channels in ways we can't predict.
// Fee restrictions are placed on swap suggestions to ensure that we only
// suggest swaps that fit the configured fee preferences.
// - Sweep Fee Rate Limit: the maximum sat/vByte fee estimate for our sweep
// transaction to confirm within our configured number of confirmations
// that we will suggest swaps for.
// - Maximum Swap Fee PPM: the maximum server fee, expressed as parts per
// million of the full swap amount
// - Maximum Routing Fee PPM: the maximum off-chain routing fees for the swap
// invoice, expressed as parts per million of the swap amount.
// - Maximum Prepay Routing Fee PPM: the maximum off-chain routing fees for the
// swap prepayment, expressed as parts per million of the prepay amount.
// - Maximum Prepay: the maximum now-show fee, expressed in satoshis. This
// amount is only payable in the case where the swap server broadcasts a htlc
// and the client fails to sweep the preimage.
// - Maximum miner fee: the maximum miner fee we are willing to pay to sweep the
// on chain htlc. Note that the client will use current fee estimates to
// sweep, so this value acts more as a sanity check in the case of a large fee
// spike.
// The maximum fee per-swap is calculated as follows:
// (swap amount * serverPPM/1e6) + miner fee + (swap amount * routingPPM/1e6)
// + (prepay amount * prepayPPM/1e6).
package liquidity
import (
const (
// defaultFailureBackoff is the default amount of time we backoff if
// a channel is part of a temporarily failed swap.
defaultFailureBackoff = time.Hour * 24
// FeeBase is the base that we use to express fees.
FeeBase = 1e6
// defaultSwapFeePPM is the default limit we place on swap fees,
// expressed as parts per million of swap volume, 0.5%.
defaultSwapFeePPM = 5000
// defaultRoutingFeePPM is the default limit we place on routing fees
// for the swap invoice, expressed as parts per million of swap volume,
// 1%.
defaultRoutingFeePPM = 10000
// defaultRoutingFeePPM is the default limit we place on routing fees
// for the prepay invoice, expressed as parts per million of prepay
// volume, 0.5%.
defaultPrepayRoutingFeePPM = 5000
// defaultMaximumMinerFee is the default limit we place on miner fees
// per swap. We apply a multiplier to this default fee to guard against
// the case where we have broadcast the preimage, then fees spike and
// we need to sweep the preimage.
defaultMaximumMinerFee = 15000 * 100
// defaultMaximumPrepay is the default limit we place on prepay
// invoices.
defaultMaximumPrepay = 30000
// defaultSweepFeeRateLimit is the default limit we place on estimated
// sweep fees, (750 * 4 /1000 = 3 sat/vByte).
defaultSweepFeeRateLimit = chainfee.SatPerKWeight(750)
// defaultMaxInFlight is the default number of in-flight automatically
// dispatched swaps we allow. Note that this does not enable automated
// swaps itself (because we want non-zero values to be expressed in
// suggestions as a dry-run).
defaultMaxInFlight = 1
// DefaultAutoloopTicker is the default amount of time between automated
// swap checks.
DefaultAutoloopTicker = time.Minute * 10
// autoloopSwapInitiator is the value we send in the initiator field of
// a swap request when issuing an automatic swap.
autoloopSwapInitiator = "autoloop"
var (
// defaultBudget is the default autoloop budget we set. This budget will
// only be used for automatically dispatched swaps if autoloop is
// explicitly enabled, so we are happy to set a non-zero value here. The
// amount chosen simply uses the current defaults to provide budget for
// a single swap. We don't have a swap amount to calculate our maximum
// routing fee, so we use 0.16 BTC for now.
defaultBudget = defaultMaximumMinerFee +
ppmToSat(funding.MaxBtcFundingAmount, defaultSwapFeePPM) +
ppmToSat(defaultMaximumPrepay, defaultPrepayRoutingFeePPM) +
ppmToSat(funding.MaxBtcFundingAmount, defaultRoutingFeePPM)
// defaultParameters contains the default parameters that we start our
// liquidity manger with.
defaultParameters = Parameters{
AutoFeeBudget: defaultBudget,
MaxAutoInFlight: defaultMaxInFlight,
ChannelRules: make(map[lnwire.ShortChannelID]*ThresholdRule),
FailureBackOff: defaultFailureBackoff,
SweepFeeRateLimit: defaultSweepFeeRateLimit,
SweepConfTarget: loop.DefaultSweepConfTarget,
MaximumSwapFeePPM: defaultSwapFeePPM,
MaximumRoutingFeePPM: defaultRoutingFeePPM,
MaximumPrepayRoutingFeePPM: defaultPrepayRoutingFeePPM,
MaximumMinerFee: defaultMaximumMinerFee,
MaximumPrepay: defaultMaximumPrepay,
// ErrZeroChannelID is returned if we get a rule for a 0 channel ID.
ErrZeroChannelID = fmt.Errorf("zero channel ID not allowed")
// ErrInvalidSweepFeeRateLimit is returned if an invalid sweep fee limit
// is set.
ErrInvalidSweepFeeRateLimit = fmt.Errorf("sweep fee rate limit must "+
"be > %v sat/vByte",
// ErrZeroMinerFee is returned if a zero maximum miner fee is set.
ErrZeroMinerFee = errors.New("maximum miner fee must be non-zero")
// ErrZeroSwapFeePPM is returned if a zero server fee ppm is set.
ErrZeroSwapFeePPM = errors.New("swap fee PPM must be non-zero")
// ErrZeroRoutingPPM is returned if a zero routing fee ppm is set.
ErrZeroRoutingPPM = errors.New("routing fee PPM must be non-zero")
// ErrZeroPrepayPPM is returned if a zero prepay routing fee ppm is set.
ErrZeroPrepayPPM = errors.New("prepay routing fee PPM must be non-zero")
// ErrZeroPrepay is returned if a zero maximum prepay is set.
ErrZeroPrepay = errors.New("maximum prepay must be non-zero")
// ErrNegativeBudget is returned if a negative swap budget is set.
ErrNegativeBudget = errors.New("swap budget must be >= 0")
// ErrZeroInFlight is returned is a zero in flight swaps value is set.
ErrZeroInFlight = errors.New("max in flight swaps must be >=0")
// ErrMinimumExceedsMaximumAmt is returned when the minimum configured
// swap amount is more than the maximum.
ErrMinimumExceedsMaximumAmt = errors.New("minimum swap amount " +
"exceeds maximum")
// ErrMaxExceedsServer is returned if the maximum swap amount set is
// more than the server offers.
ErrMaxExceedsServer = errors.New("maximum swap amount is more than " +
"server maximum")
// ErrMinLessThanServer is returned if the minimum swap amount set is
// less than the server minimum.
ErrMinLessThanServer = errors.New("minimum swap amount is less than " +
"server minimum")
// Config contains the external functionality required to run the
// liquidity manager.
type Config struct {
// AutoloopTicker determines how often we should check whether we want
// to dispatch an automated swap. We use a force ticker so that we can
// trigger autoloop in itests.
AutoloopTicker *ticker.Force
// LoopOutRestrictions returns the restrictions that the server applies
// to loop out swaps.
LoopOutRestrictions func(ctx context.Context) (*Restrictions, error)
// Lnd provides us with access to lnd's rpc servers.
Lnd *lndclient.LndServices
// ListLoopOut returns all of the loop our swaps stored on disk.
ListLoopOut func() ([]*loopdb.LoopOut, error)
// ListLoopIn returns all of the loop in swaps stored on disk.
ListLoopIn func() ([]*loopdb.LoopIn, error)
// LoopOutQuote gets swap fee, estimated miner fee and prepay amount for
// a loop out swap.
LoopOutQuote func(ctx context.Context,
request *loop.LoopOutQuoteRequest) (*loop.LoopOutQuote, error)
// LoopOut dispatches a loop out.
LoopOut func(ctx context.Context, request *loop.OutRequest) (
*loop.LoopOutSwapInfo, error)
// Clock allows easy mocking of time in unit tests.
Clock clock.Clock
// MinimumConfirmations is the minimum number of confirmations we allow
// setting for sweep target.
MinimumConfirmations int32
// Parameters is a set of parameters provided by the user which guide
// how we assess liquidity.
type Parameters struct {
// Autoloop enables automatic dispatch of swaps.
Autoloop bool
// AutoFeeBudget is the total amount we allow to be spent on
// automatically dispatched swaps. Once this budget has been used, we
// will stop dispatching swaps until the budget is increased or the
// start date is moved.
AutoFeeBudget btcutil.Amount
// AutoFeeStartDate is the date from which we will include automatically
// dispatched swaps in our current budget, inclusive.
AutoFeeStartDate time.Time
// MaxAutoInFlight is the maximum number of in-flight automatically
// dispatched swaps we allow.
MaxAutoInFlight int
// FailureBackOff is the amount of time that we require passes after a
// channel has been part of a failed loop out swap before we suggest
// using it again.
// TODO(carla): add exponential backoff
FailureBackOff time.Duration
// SweepFeeRateLimit is the limit that we place on our estimated sweep
// fee. A swap will not be suggested if estimated fee rate is above this
// value.
SweepFeeRateLimit chainfee.SatPerKWeight
// SweepConfTarget is the number of blocks we aim to confirm our sweep
// transaction in. This value affects the on chain fees we will pay.
SweepConfTarget int32
// MaximumPrepay is the maximum prepay amount we are willing to pay per
// swap.
MaximumPrepay btcutil.Amount
// MaximumSwapFeePPM is the maximum server fee we are willing to pay per
// swap expressed as parts per million of the swap volume.
MaximumSwapFeePPM int
// MaximumRoutingFeePPM is the maximum off-chain routing fee we
// are willing to pay for off chain invoice routing fees per swap,
// expressed as parts per million of the swap amount.
MaximumRoutingFeePPM int
// MaximumPrepayRoutingFeePPM is the maximum off-chain routing fee we
// are willing to pay for off chain prepay routing fees per swap,
// expressed as parts per million of the prepay amount.
MaximumPrepayRoutingFeePPM int
// MaximumMinerFee is the maximum on chain fee that we cap our miner
// fee at in case where we need to claim on chain because we have
// revealed the preimage, but fees have spiked. We will not initiate a
// swap if we estimate that the sweep cost will be above our sweep
// fee limit, and we use fee estimates at time of sweep to set our fees,
// so this is just a sane cap covering the special case where we need to
// sweep during a fee spike.
MaximumMinerFee btcutil.Amount
// ClientRestrictions are the restrictions placed on swap size by the
// client.
ClientRestrictions Restrictions
// ChannelRules maps a short channel ID to a rule that describes how we
// would like liquidity to be managed.
ChannelRules map[lnwire.ShortChannelID]*ThresholdRule
// String returns the string representation of our parameters.
func (p Parameters) String() string {
channelRules := make([]string, 0, len(p.ChannelRules))
for channel, rule := range p.ChannelRules {
channelRules = append(
channelRules, fmt.Sprintf("%v: %v", channel, rule),
return fmt.Sprintf("channel rules: %v, failure backoff: %v, sweep "+
"fee rate limit: %v, sweep conf target: %v, maximum prepay: "+
"%v, maximum miner fee: %v, maximum swap fee ppm: %v, maximum "+
"routing fee ppm: %v, maximum prepay routing fee ppm: %v, "+
"auto budget: %v, budget start: %v, max auto in flight: %v, "+
"minimum swap size=%v, maximum swap size=%v",
strings.Join(channelRules, ","), p.FailureBackOff,
p.SweepFeeRateLimit, p.SweepConfTarget, p.MaximumPrepay,
p.MaximumMinerFee, p.MaximumSwapFeePPM,
p.MaximumRoutingFeePPM, p.MaximumPrepayRoutingFeePPM,
p.AutoFeeBudget, p.AutoFeeStartDate, p.MaxAutoInFlight,
p.ClientRestrictions.Minimum, p.ClientRestrictions.Maximum)
// validate checks whether a set of parameters is valid. It takes the minimum
// confirmations we allow for sweep confirmation target as a parameter.
func (p Parameters) validate(minConfs int32, server *Restrictions) error {
for channel, rule := range p.ChannelRules {
if channel.ToUint64() == 0 {
return ErrZeroChannelID
if err := rule.validate(); err != nil {
return fmt.Errorf("channel: %v has invalid rule: %v",
channel.ToUint64(), err)
// Check that our sweep limit is above our minimum fee rate. We use
// absolute fee floor rather than kw floor because we will allow users
// to specify fee rate is sat/vByte and want to allow 1 sat/vByte.
if p.SweepFeeRateLimit < chainfee.AbsoluteFeePerKwFloor {
return ErrInvalidSweepFeeRateLimit
// Check that our confirmation target is above our required minimum.
if p.SweepConfTarget < minConfs {
return fmt.Errorf("confirmation target must be at least: %v",
// Check that we have non-zero fee limits.
if p.MaximumSwapFeePPM == 0 {
return ErrZeroSwapFeePPM
if p.MaximumRoutingFeePPM == 0 {
return ErrZeroRoutingPPM
if p.MaximumPrepayRoutingFeePPM == 0 {
return ErrZeroPrepayPPM
if p.MaximumPrepay == 0 {
return ErrZeroPrepay
if p.MaximumMinerFee == 0 {
return ErrZeroMinerFee
if p.AutoFeeBudget < 0 {
return ErrNegativeBudget
if p.MaxAutoInFlight <= 0 {
return ErrZeroInFlight
err := validateRestrictions(server, &p.ClientRestrictions)
if err != nil {
return err
return nil
// validateRestrictions checks that client restrictions fall within the server's
// restrictions.
func validateRestrictions(server, client *Restrictions) error {
zeroMin := client.Minimum == 0
zeroMax := client.Maximum == 0
if zeroMin && zeroMax {
return nil
// If we have a non-zero maximum, we need to ensure it is greater than
// our minimum (which is fine if min is zero), and does not exceed the
// server's maximum.
if !zeroMax {
if client.Minimum > client.Maximum {
return ErrMinimumExceedsMaximumAmt
if client.Maximum > server.Maximum {
return ErrMaxExceedsServer
if zeroMin {
return nil
// If the client set a minimum, ensure it is at least equal to the
// server's limit.
if client.Minimum < server.Minimum {
return ErrMinLessThanServer
return nil
// Manager contains a set of desired liquidity rules for our channel
// balances.
type Manager struct {
// cfg contains the external functionality we require to determine our
// current liquidity balance.
cfg *Config
// params is the set of parameters we are currently using. These may be
// updated at runtime.
params Parameters
// paramsLock is a lock for our current set of parameters.
paramsLock sync.Mutex
// Run periodically checks whether we should automatically dispatch a loop out.
// We run this loop even if automated swaps are not currently enabled rather
// than managing starting and stopping the ticker as our parameters are updated.
func (m *Manager) Run(ctx context.Context) error {
defer m.cfg.AutoloopTicker.Stop()
for {
select {
case <-m.cfg.AutoloopTicker.Ticks():
if err := m.autoloop(ctx); err != nil {
log.Errorf("autoloop failed: %v", err)
case <-ctx.Done():
return ctx.Err()
// NewManager creates a liquidity manager which has no rules set.
func NewManager(cfg *Config) *Manager {
return &Manager{
cfg: cfg,
params: defaultParameters,
// GetParameters returns a copy of our current parameters.
func (m *Manager) GetParameters() Parameters {
defer m.paramsLock.Unlock()
return cloneParameters(m.params)
// SetParameters updates our current set of parameters if the new parameters
// provided are valid.
func (m *Manager) SetParameters(ctx context.Context, params Parameters) error {
restrictions, err := m.cfg.LoopOutRestrictions(ctx)
if err != nil {
return err
err = params.validate(m.cfg.MinimumConfirmations, restrictions)
if err != nil {
return err
defer m.paramsLock.Unlock()
m.params = cloneParameters(params)
return nil
// cloneParameters creates a deep clone of a parameters struct so that callers
// cannot mutate our parameters. Although our parameters struct itself is not
// a reference, we still need to clone the contents of maps.
func cloneParameters(params Parameters) Parameters {
paramCopy := params
paramCopy.ChannelRules = make(
for channel, rule := range params.ChannelRules {
ruleCopy := *rule
paramCopy.ChannelRules[channel] = &ruleCopy
return paramCopy
// autoloop gets a set of suggested swaps and dispatches them automatically if
// we have automated looping enabled.
func (m *Manager) autoloop(ctx context.Context) error {
swaps, err := m.SuggestSwaps(ctx, true)
if err != nil {
return err
for _, swap := range swaps {
// Create a copy of our range var so that we can reference it.
swap := swap
loopOut, err := m.cfg.LoopOut(ctx, &swap)
if err != nil {
return err
log.Infof("loop out automatically dispatched: hash: %v, "+
"address: %v", loopOut.SwapHash,
return nil
// ForceAutoLoop force-ticks our auto-out ticker.
func (m *Manager) ForceAutoLoop(ctx context.Context) error {
select {
case m.cfg.AutoloopTicker.Force <- m.cfg.Clock.Now():
return nil
case <-ctx.Done():
return ctx.Err()
// SuggestSwaps returns a set of swap suggestions based on our current liquidity
// balance for the set of rules configured for the manager, failing if there are
// no rules set. It takes an autoloop boolean that indicates whether the
// suggestions are being used for our internal autolooper. This boolean is used
// to determine the information we add to our swap suggestion and whether we
// return any suggestions.
func (m *Manager) SuggestSwaps(ctx context.Context, autoloop bool) (
[]loop.OutRequest, error) {
defer m.paramsLock.Unlock()
// If we have no rules set, exit early to avoid unnecessary calls to
// lnd and the server.
if len(m.params.ChannelRules) == 0 {
return nil, nil
// If our start date is in the future, we interpret this as meaning that
// we should start using our budget at this date. This means that we
// have no budget for the present, so we just return.
if m.params.AutoFeeStartDate.After(m.cfg.Clock.Now()) {
log.Debugf("autoloop fee budget start time: %v is in "+
"the future", m.params.AutoFeeStartDate)
return nil, nil
// Before we get any swap suggestions, we check what the current fee
// estimate is to sweep within our target number of confirmations. If
// This fee exceeds the fee limit we have set, we will not suggest any
// swaps at present.
estimate, err := m.cfg.Lnd.WalletKit.EstimateFee(
ctx, m.params.SweepConfTarget,
if err != nil {
return nil, err
if estimate > m.params.SweepFeeRateLimit {
log.Debugf("Current fee estimate to sweep within: %v blocks "+
"%v sat/vByte exceeds limit of: %v sat/vByte",
return nil, nil
// Get the current server side restrictions, combined with the client
// set restrictions, if any.
outRestrictions, err := m.getLoopOutRestrictions(ctx)
if err != nil {
return nil, err
// List our current set of swaps so that we can determine which channels
// are already being utilized by swaps. Note that these calls may race
// with manual initiation of swaps.
loopOut, err := m.cfg.ListLoopOut()
if err != nil {
return nil, err
loopIn, err := m.cfg.ListLoopIn()
if err != nil {
return nil, err
// Get a summary of our existing swaps so that we can check our autoloop
// budget.
summary, err := m.checkExistingAutoLoops(ctx, loopOut)
if err != nil {
return nil, err
if summary.totalFees() >= m.params.AutoFeeBudget {
log.Debugf("autoloop fee budget: %v exhausted, %v spent on "+
"completed swaps, %v reserved for ongoing swaps "+
"(upper limit)",
m.params.AutoFeeBudget, summary.spentFees,
return nil, nil
// If we have already reached our total allowed number of in flight
// swaps, we do not suggest any more at the moment.
allowedSwaps := m.params.MaxAutoInFlight - summary.inFlightCount
if allowedSwaps <= 0 {
log.Debugf("%v autoloops allowed, %v in flight",
m.params.MaxAutoInFlight, summary.inFlightCount)
return nil, nil
eligible, err := m.getEligibleChannels(ctx, loopOut, loopIn)
if err != nil {
return nil, err
var suggestions []loop.OutRequest
for _, channel := range eligible {
channelID := lnwire.NewShortChanIDFromInt(channel.ChannelID)
rule, ok := m.params.ChannelRules[channelID]
if !ok {
balance := newBalances(channel)
suggestion := rule.suggestSwap(balance, outRestrictions)
// We can have nil suggestions in the case where no action is
// required, so we skip over them.
if suggestion == nil {
// Get a quote for a swap of this amount.
quote, err := m.cfg.LoopOutQuote(
ctx, &loop.LoopOutQuoteRequest{
Amount: suggestion.Amount,
SweepConfTarget: m.params.SweepConfTarget,
SwapPublicationDeadline: m.cfg.Clock.Now(),
if err != nil {
return nil, err
log.Debugf("quote for suggestion: %v, swap fee: %v, "+
"miner fee: %v, prepay: %v", suggestion, quote.SwapFee,
quote.MinerFee, quote.PrepayAmount)
// Check that the estimated fees for the suggested swap are
// below the fee limits configured by the manager.
err = m.checkFeeLimits(quote, suggestion.Amount)
if err != nil {
log.Infof("suggestion: %v expected fees too high: %v",
suggestion, err)
outRequest, err := m.makeLoopOutRequest(
ctx, suggestion, quote, autoloop,
if err != nil {
return nil, err
suggestions = append(suggestions, outRequest)
// If we have no suggestions after we have applied all of our limits,
// just return.
if len(suggestions) == 0 {
return nil, nil
// Sort suggestions by amount in descending order.
sort.SliceStable(suggestions, func(i, j int) bool {
return suggestions[i].Amount > suggestions[j].Amount
// Run through our suggested swaps in descending order of amount and
// return all of the swaps which will fit within our remaining budget.
var (
available = m.params.AutoFeeBudget - summary.totalFees()
inBudget []loop.OutRequest
for _, swap := range suggestions {
fees := worstCaseOutFees(
swap.MaxPrepayRoutingFee, swap.MaxSwapRoutingFee,
swap.MaxSwapFee, swap.MaxMinerFee, swap.MaxPrepayAmount,
// If the maximum fee we expect our swap to use is less than the
// amount we have available, we add it to our set of swaps that
// fall within the budget and decrement our available amount.
if fees <= available {
available -= fees
inBudget = append(inBudget, swap)
// If we're out of budget, or we have hit the max number of
// swaps that we want to dispatch at one time, exit early.
if available == 0 || allowedSwaps == len(inBudget) {
// If we are getting suggestions for automatically dispatched swaps,
// and they are not enabled in our parameters, we just log the swap
// suggestions and return an empty set of suggestions.
if autoloop && !m.params.Autoloop {
for _, swap := range inBudget {
log.Debugf("recommended autoloop: %v sats over "+
"%v", swap.Amount, swap.OutgoingChanSet)
return nil, nil
return inBudget, nil
// getLoopOutRestrictions queries the server for its latest swap size
// restrictions, validates client restrictions (if present) against these
// values and merges the client's custom requirements with the server's limits
// to produce a single set of limitations for our swap.
func (m *Manager) getLoopOutRestrictions(ctx context.Context) (*Restrictions,
error) {
restrictions, err := m.cfg.LoopOutRestrictions(ctx)
if err != nil {
return nil, err
// It is possible that the server has updated its restrictions since
// we validated our client restrictions, so we validate again to ensure
// that our restrictions are within the server's bounds.
err = validateRestrictions(restrictions, &m.params.ClientRestrictions)
if err != nil {
return nil, err
// If our minimum is more than the server's minimum, we set it.
if m.params.ClientRestrictions.Minimum > restrictions.Minimum {
restrictions.Minimum = m.params.ClientRestrictions.Minimum
// If our maximum set and is less than the server's maximum, we set it.
if m.params.ClientRestrictions.Maximum != 0 &&
m.params.ClientRestrictions.Maximum < restrictions.Maximum {
restrictions.Maximum = m.params.ClientRestrictions.Maximum
return restrictions, nil
// makeLoopOutRequest creates a loop out request from a suggestion. Since we
// do not get any information about our off-chain routing fees when we request
// a quote, we just set our prepay and route maximum fees directly from the
// amounts we expect to route. The estimation we use elsewhere is the repo is
// route-independent, which is a very poor estimation so we don't bother with
// checking against this inaccurate constant. We use the exact prepay amount
// and swap fee given to us by the server, but use our maximum miner fee anyway
// to give us some leeway when performing the swap. We take an auto-out which
// determines whether we set a label identifying this swap as automatically
// dispatched, and decides whether we set a sweep address (we don't bother for
// non-auto requests, because the client api will set it anyway).
func (m *Manager) makeLoopOutRequest(ctx context.Context,
suggestion *LoopOutRecommendation, quote *loop.LoopOutQuote,
autoloop bool) (loop.OutRequest, error) {
prepayMaxFee := ppmToSat(
quote.PrepayAmount, m.params.MaximumPrepayRoutingFeePPM,
routeMaxFee := ppmToSat(
suggestion.Amount, m.params.MaximumRoutingFeePPM,
request := loop.OutRequest{
Amount: suggestion.Amount,
OutgoingChanSet: loopdb.ChannelSet{
MaxPrepayRoutingFee: prepayMaxFee,
MaxSwapRoutingFee: routeMaxFee,
MaxMinerFee: m.params.MaximumMinerFee,
MaxSwapFee: quote.SwapFee,
MaxPrepayAmount: quote.PrepayAmount,
SweepConfTarget: m.params.SweepConfTarget,
Initiator: autoloopSwapInitiator,
if autoloop {
request.Label = labels.AutoloopLabel(swap.TypeOut)
addr, err := m.cfg.Lnd.WalletKit.NextAddr(ctx)
if err != nil {
return loop.OutRequest{}, err
request.DestAddr = addr
return request, nil
// worstCaseOutFees calculates the largest possible fees for a loop out swap,
// comparing the fees for a successful swap to the cost when the client pays
// the prepay because they failed to sweep the on chain htlc. This is unlikely,
// because we expect clients to be online to sweep, but we want to account for
// every outcome so we include it.
func worstCaseOutFees(prepayRouting, swapRouting, swapFee, minerFee,
prepayAmount btcutil.Amount) btcutil.Amount {
var (
successFees = prepayRouting + minerFee + swapFee + swapRouting
noShowFees = prepayRouting + prepayAmount
if noShowFees > successFees {
return noShowFees
return successFees
// existingAutoLoopSummary provides a summary of the existing autoloops which
// were dispatched during our current budget period.
type existingAutoLoopSummary struct {
// spentFees is the amount we have spent on completed swaps.
spentFees btcutil.Amount
// pendingFees is the worst-case amount of fees we could spend on in
// flight autoloops.
pendingFees btcutil.Amount
// inFlightCount is the total number of automated swaps that are
// currently in flight. Note that this may race with swap completion,
// but not with initiation of new automated swaps, this is ok, because
// it can only lead to dispatching fewer swaps than we could have (not
// too many).
inFlightCount int
// totalFees returns the total amount of fees that automatically dispatched
// swaps may consume.
func (e *existingAutoLoopSummary) totalFees() btcutil.Amount {
return e.spentFees + e.pendingFees
// checkExistingAutoLoops calculates the total amount that has been spent by
// automatically dispatched swaps that have completed, and the worst-case fee
// total for our set of ongoing, automatically dispatched swaps as well as a
// current in-flight count.
func (m *Manager) checkExistingAutoLoops(ctx context.Context,
loopOuts []*loopdb.LoopOut) (*existingAutoLoopSummary, error) {
var summary existingAutoLoopSummary
for _, out := range loopOuts {
if out.Contract.Label != labels.AutoloopLabel(swap.TypeOut) {
// If we have a pending swap, we are uncertain of the fees that
// it will end up paying. We use the worst-case estimate based
// on the maximum values we set for each fee category. This will
// likely over-estimate our fees (because we probably won't
// spend our maximum miner amount). If a swap is not pending,
// it has succeeded or failed so we just record our actual fees
// for the swap provided that the swap completed after our
// budget start date.
if out.State().State.Type() == loopdb.StateTypePending {
prepay, err := m.cfg.Lnd.Client.DecodePaymentRequest(
ctx, out.Contract.PrepayInvoice,
if err != nil {
return nil, err
summary.pendingFees += worstCaseOutFees(
} else if !out.LastUpdateTime().Before(m.params.AutoFeeStartDate) {
summary.spentFees += out.State().Cost.Total()
return &summary, nil
// getEligibleChannels takes lists of our existing loop out and in swaps, and
// gets a list of channels that are not currently being utilized for a swap.
// If an unrestricted swap is ongoing, we return an empty set of channels
// because we don't know which channels balances it will affect.
func (m *Manager) getEligibleChannels(ctx context.Context,
loopOut []*loopdb.LoopOut, loopIn []*loopdb.LoopIn) (
[]lndclient.ChannelInfo, error) {
var (
existingOut = make(map[lnwire.ShortChannelID]bool)
existingIn = make(map[route.Vertex]bool)
failedOut = make(map[lnwire.ShortChannelID]time.Time)
// Failure cutoff is the most recent failure timestamp we will still
// consider a channel eligible. Any channels involved in swaps that have
// failed since this point will not be considered.
failureCutoff := m.cfg.Clock.Now().Add(m.params.FailureBackOff * -1)
for _, out := range loopOut {
var (
state = out.State().State
chanSet = out.Contract.OutgoingChanSet
// If a loop out swap failed due to off chain payment after our
// failure cutoff, we add all of its channels to a set of
// recently failed channels. It is possible that not all of
// these channels were used for the swap, but we play it safe
// and back off for all of them.
// We only backoff for off temporary failures. In the case of
// chain payment failures, our swap failed to route and we do
// not want to repeatedly try to route through bad channels
// which remain unbalanced because they cannot route a swap, so
// we backoff.
if state == loopdb.StateFailOffchainPayments {
failedAt := out.LastUpdate().Time
if failedAt.After(failureCutoff) {
for _, id := range chanSet {
chanID := lnwire.NewShortChanIDFromInt(
failedOut[chanID] = failedAt
// Skip completed swaps, they can't affect our channel balances.
// Swaps that fail temporarily are considered to be in a pending
// state, so we will also check that channels being used by
// these swaps. This is important, because a temporarily failed
// swap could be re-dispatched on restart, affecting our
// balances.
if state.Type() != loopdb.StateTypePending {
if len(chanSet) == 0 {
log.Debugf("Ongoing unrestricted loop out: "+
"%v, no suggestions at present", out.Hash)
return nil, nil
for _, id := range chanSet {
chanID := lnwire.NewShortChanIDFromInt(id)
existingOut[chanID] = true
for _, in := range loopIn {
// Skip completed swaps, they can't affect our channel balances.
if in.State().State.Type() != loopdb.StateTypePending {
if in.Contract.LastHop == nil {
log.Debugf("Ongoing unrestricted loop in: "+
"%v, no suggestions at present", in.Hash)
return nil, nil
existingIn[*in.Contract.LastHop] = true
channels, err := m.cfg.Lnd.Client.ListChannels(ctx)
if err != nil {
return nil, err
// Run through our set of channels and skip over any channels that
// are currently being utilized by a restricted swap (where restricted
// means that a loop out limited channels, or a loop in limited last
// hop).
var eligible []lndclient.ChannelInfo
for _, channel := range channels {
shortID := lnwire.NewShortChanIDFromInt(channel.ChannelID)
lastFail, recentFail := failedOut[shortID]
if recentFail {
log.Debugf("Channel: %v not eligible for "+
"suggestions, was part of a failed swap at: %v",
channel.ChannelID, lastFail)
if existingOut[shortID] {
log.Debugf("Channel: %v not eligible for "+
"suggestions, ongoing loop out utilizing "+
"channel", channel.ChannelID)
if existingIn[channel.PubKeyBytes] {
log.Debugf("Channel: %v not eligible for "+
"suggestions, ongoing loop in utilizing "+
"peer", channel.ChannelID)
eligible = append(eligible, channel)
return eligible, nil
// checkFeeLimits takes a set of fees for a swap and checks whether they exceed
// our swap limits.
func (m *Manager) checkFeeLimits(quote *loop.LoopOutQuote,
swapAmt btcutil.Amount) error {
maxFee := ppmToSat(swapAmt, m.params.MaximumSwapFeePPM)
if quote.SwapFee > maxFee {
return fmt.Errorf("quoted swap fee: %v > maximum swap fee: %v",
quote.SwapFee, maxFee)
if quote.MinerFee > m.params.MaximumMinerFee {
return fmt.Errorf("quoted miner fee: %v > maximum miner "+
"fee: %v", quote.MinerFee, m.params.MaximumMinerFee)
if quote.PrepayAmount > m.params.MaximumPrepay {
return fmt.Errorf("quoted prepay: %v > maximum prepay: %v",
quote.PrepayAmount, m.params.MaximumPrepay)
return nil
// satPerKwToSatPerVByte converts sat per kWeight to sat per vByte.
func satPerKwToSatPerVByte(satPerKw chainfee.SatPerKWeight) int64 {
return int64(satPerKw.FeePerKVByte() / 1000)
// ppmToSat takes an amount and a measure of parts per million for the amount
// and returns the amount that the ppm represents.
func ppmToSat(amount btcutil.Amount, ppm int) btcutil.Amount {
return btcutil.Amount(uint64(amount) * uint64(ppm) / FeeBase)
func mSatToSatoshis(amount lnwire.MilliSatoshi) btcutil.Amount {
return btcutil.Amount(amount / 1000)