19027031130

Committed 03 Nov 2025 07:27AM UTC coverage: 56.922% (-9.7%) from 66.639%

Build # 19027031130

Build Type

Pull #9334

github

Committed by

web-flow

Commit Message

Merge b9be11a16 into f938e40af

Pull Request Pull Request #9334: Use all valid routes during blinded path construction

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75.35

/lnrpc/invoicesrpc/addinvoice.go

package invoicesrpc

import (
        "bytes"
        "context"
        "crypto/rand"
        "errors"
        "fmt"
        "math"
        mathRand "math/rand"
        "sort"
        "time"

        "github.com/btcsuite/btcd/btcec/v2"
        "github.com/btcsuite/btcd/btcec/v2/ecdsa"
        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/chaincfg"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/wire"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/graph/db/models"
        "github.com/lightningnetwork/lnd/invoices"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/netann"
        "github.com/lightningnetwork/lnd/routing"
        "github.com/lightningnetwork/lnd/routing/blindedpath"
        "github.com/lightningnetwork/lnd/routing/route"
        "github.com/lightningnetwork/lnd/zpay32"
)

const (
        // DefaultInvoiceExpiry is the default invoice expiry for new MPP
        // invoices.
        DefaultInvoiceExpiry = 24 * time.Hour

        // DefaultAMPInvoiceExpiry is the default invoice expiry for new AMP
        // invoices.
        DefaultAMPInvoiceExpiry = 30 * 24 * time.Hour

        // hopHintFactor is factor by which we scale the total amount of
        // inbound capacity we want our hop hints to represent, allowing us to
        // have some leeway if peers go offline.
        hopHintFactor = 2

        // maxHopHints is the maximum number of hint paths that will be included
        // in an invoice.
        maxHopHints = 20
)

// AddInvoiceConfig contains dependencies for invoice creation.
type AddInvoiceConfig struct {
        // AddInvoice is called to add the invoice to the registry.
        AddInvoice func(ctx context.Context, invoice *invoices.Invoice,
                paymentHash lntypes.Hash) (uint64, error)

        // IsChannelActive is used to generate valid hop hints.
        IsChannelActive func(chanID lnwire.ChannelID) bool

        // ChainParams are required to properly decode invoice payment requests
        // that are marshalled over rpc.
        ChainParams *chaincfg.Params

        // NodeSigner is an implementation of the MessageSigner implementation
        // that's backed by the identity private key of the running lnd node.
        NodeSigner *netann.NodeSigner

        // DefaultCLTVExpiry is the default invoice expiry if no values is
        // specified.
        DefaultCLTVExpiry uint32

        // ChanDB is a global boltdb instance which is needed to access the
        // channel graph.
        ChanDB *channeldb.ChannelStateDB

        // Graph gives the invoice server access to various graph related
        // queries.
        Graph GraphSource

        // GenInvoiceFeatures returns a feature containing feature bits that
        // should be advertised on freshly generated invoices.
        GenInvoiceFeatures func() *lnwire.FeatureVector

        // GenAmpInvoiceFeatures returns a feature containing feature bits that
        // should be advertised on freshly generated AMP invoices.
        GenAmpInvoiceFeatures func() *lnwire.FeatureVector

        // GetAlias allows the peer's alias SCID to be retrieved for private
        // option_scid_alias channels.
        GetAlias func(lnwire.ChannelID) (lnwire.ShortChannelID, error)

        // BestHeight returns the current best block height that this node is
        // aware of.
        BestHeight func() (uint32, error)

        // QueryBlindedRoutes can be used to generate a few routes to this node
        // that can then be used in the construction of a blinded payment path.
        QueryBlindedRoutes func(lnwire.MilliSatoshi) ([]*route.Route, error)
}

// AddInvoiceData contains the required data to create a new invoice.
type AddInvoiceData struct {
        // An optional memo to attach along with the invoice. Used for record
        // keeping purposes for the invoice's creator, and will also be set in
        // the description field of the encoded payment request if the
        // description_hash field is not being used.
        Memo string

        // The preimage which will allow settling an incoming HTLC payable to
        // this preimage. If Preimage is set, Hash should be nil. If both
        // Preimage and Hash are nil, a random preimage is generated.
        Preimage *lntypes.Preimage

        // The hash of the preimage. If Hash is set, Preimage should be nil.
        // This condition indicates that we have a 'hold invoice' for which the
        // htlc will be accepted and held until the preimage becomes known.
        Hash *lntypes.Hash

        // The value of this invoice in millisatoshis.
        Value lnwire.MilliSatoshi

        // Hash (SHA-256) of a description of the payment. Used if the
        // description of payment (memo) is too long to naturally fit within the
        // description field of an encoded payment request.
        DescriptionHash []byte

        // Payment request expiry time in seconds. Default is 3600 (1 hour).
        Expiry int64

        // Fallback on-chain address.
        FallbackAddr string

        // Delta to use for the time-lock of the CLTV extended to the final hop.
        CltvExpiry uint64

        // Whether this invoice should include routing hints for private
        // channels.
        Private bool

        // HodlInvoice signals that this invoice shouldn't be settled
        // immediately upon receiving the payment.
        HodlInvoice bool

        // Amp signals whether or not to create an AMP invoice.
        //
        // NOTE: Preimage should always be set to nil when this value is true.
        Amp bool

        // BlindedPathCfg holds the config values to use when constructing
        // blinded paths to add to the invoice. A non-nil BlindedPathCfg signals
        // that this invoice should disguise the location of the recipient by
        // adding blinded payment paths to the invoice instead of revealing the
        // destination node's real pub key.
        BlindedPathCfg *BlindedPathConfig

        // RouteHints are optional route hints that can each be individually
        // used to assist in reaching the invoice's destination.
        RouteHints [][]zpay32.HopHint
}

// BlindedPathConfig holds the configuration values required for blinded path
// generation for invoices.
type BlindedPathConfig struct {
        // RoutePolicyIncrMultiplier is the amount by which policy values for
        // hops in a blinded route will be bumped to avoid easy probing. For
        // example, a multiplier of 1.1 will bump all appropriate the values
        // (base fee, fee rate, CLTV delta and min HLTC) by 10%.
        RoutePolicyIncrMultiplier float64

        // RoutePolicyDecrMultiplier is the amount by which appropriate policy
        // values for hops in a blinded route will be decreased to avoid easy
        // probing. For example, a multiplier of 0.9 will reduce appropriate
        // values (like maximum HTLC) by 10%.
        RoutePolicyDecrMultiplier float64

        // MinNumPathHops is the minimum number of hops that a blinded path
        // should be. Dummy hops will be used to pad any route with a length
        // less than this.
        MinNumPathHops uint8

        // DefaultDummyHopPolicy holds the default policy values to use for
        // dummy hops in a blinded path in the case where they cant be derived
        // through other means.
        DefaultDummyHopPolicy *blindedpath.BlindedHopPolicy

        // MaxNumPaths is the maximum number of blinded paths to select.
        MaxNumPaths uint8
}

// paymentHashAndPreimage returns the payment hash and preimage for this invoice
// depending on the configuration.
//
// For AMP invoices (when Amp flag is true), this method always returns a nil
// preimage. The hash value can be set externally by the user using the Hash
// field, or one will be generated randomly. The payment hash here only serves
// as a unique identifier for insertion into the invoice index, as there is
// no universal preimage for an AMP payment.
//
// For MPP invoices (when Amp flag is false), this method may return nil
// preimage when create a hodl invoice, but otherwise will always return a
// non-nil preimage and the corresponding payment hash. The valid combinations
// are parsed as follows:
//   - Preimage == nil && Hash == nil -> (random preimage, H(random preimage))
//   - Preimage != nil && Hash == nil -> (Preimage, H(Preimage))
//   - Preimage == nil && Hash != nil -> (nil, Hash)
func (d *AddInvoiceData) paymentHashAndPreimage() (
        *lntypes.Preimage, lntypes.Hash, error) {

        if d.Amp {
                return d.ampPaymentHashAndPreimage()
        }

        return d.mppPaymentHashAndPreimage()
}

// ampPaymentHashAndPreimage returns the payment hash to use for an AMP invoice.
// The preimage will always be nil.
func (d *AddInvoiceData) ampPaymentHashAndPreimage() (*lntypes.Preimage,
        lntypes.Hash, error) {

        switch {
        // Preimages cannot be set on AMP invoice.
        case d.Preimage != nil:
                return nil, lntypes.Hash{},
                        errors.New("preimage set on AMP invoice")

        // If a specific hash was requested, use that.
        case d.Hash != nil:
                return nil, *d.Hash, nil

        // Otherwise generate a random hash value, just needs to be unique to be
        // added to the invoice index.
        default:
                var paymentHash lntypes.Hash
                if _, err := rand.Read(paymentHash[:]); err != nil {
                        return nil, lntypes.Hash{}, err
                }

                return nil, paymentHash, nil
        }
}

// mppPaymentHashAndPreimage returns the payment hash and preimage to use for an
// MPP invoice.
func (d *AddInvoiceData) mppPaymentHashAndPreimage() (*lntypes.Preimage,
        lntypes.Hash, error) {

        var (
                paymentPreimage *lntypes.Preimage
                paymentHash     lntypes.Hash
        )

        switch {

        // Only either preimage or hash can be set.
        case d.Preimage != nil && d.Hash != nil:
                return nil, lntypes.Hash{},
                        errors.New("preimage and hash both set")

        // If no hash or preimage is given, generate a random preimage.
        case d.Preimage == nil && d.Hash == nil:
                paymentPreimage = &lntypes.Preimage{}
                if _, err := rand.Read(paymentPreimage[:]); err != nil {
                        return nil, lntypes.Hash{}, err
                }
                paymentHash = paymentPreimage.Hash()

        // If just a hash is given, we create a hold invoice by setting the
        // preimage to unknown.
        case d.Preimage == nil && d.Hash != nil:
                paymentHash = *d.Hash

        // A specific preimage was supplied. Use that for the invoice.
        case d.Preimage != nil && d.Hash == nil:
                preimage := *d.Preimage
                paymentPreimage = &preimage
                paymentHash = d.Preimage.Hash()
        }

        return paymentPreimage, paymentHash, nil
}

// AddInvoice attempts to add a new invoice to the invoice database. Any
// duplicated invoices are rejected, therefore all invoices *must* have a
// unique payment preimage.
func AddInvoice(ctx context.Context, cfg *AddInvoiceConfig,
        invoice *AddInvoiceData) (*lntypes.Hash, *invoices.Invoice, error) {

        blind := invoice.BlindedPathCfg != nil

        if invoice.Amp && blind {
                return nil, nil, fmt.Errorf("AMP invoices with blinded paths " +
                        "are not yet supported")
        }

        paymentPreimage, paymentHash, err := invoice.paymentHashAndPreimage()
        if err != nil {
                return nil, nil, err
        }

        // The size of the memo, receipt and description hash attached must not
        // exceed the maximum values for either of the fields.
        if len(invoice.Memo) > invoices.MaxMemoSize {
                return nil, nil, fmt.Errorf("memo too large: %v bytes "+
                        "(maxsize=%v)", len(invoice.Memo),
                        invoices.MaxMemoSize)
        }
        if len(invoice.DescriptionHash) > 0 &&
                len(invoice.DescriptionHash) != 32 {

                return nil, nil, fmt.Errorf("description hash is %v bytes, "+
                        "must be 32", len(invoice.DescriptionHash))
        }

        // We set the max invoice amount to 100k BTC, which itself is several
        // multiples off the current block reward.
        maxInvoiceAmt := btcutil.Amount(btcutil.SatoshiPerBitcoin * 100000)

        switch {
        // The value of the invoice must not be negative.
        case int64(invoice.Value) < 0:
                return nil, nil, fmt.Errorf("payments of negative value "+
                        "are not allowed, value is %v", int64(invoice.Value))

        // Also ensure that the invoice is actually realistic, while preventing
        // any issues due to underflow.
        case invoice.Value.ToSatoshis() > maxInvoiceAmt:
                return nil, nil, fmt.Errorf("invoice amount %v is "+
                        "too large, max is %v", invoice.Value.ToSatoshis(),
                        maxInvoiceAmt)
        }

        amtMSat := invoice.Value

        // We also create an encoded payment request which allows the
        // caller to compactly send the invoice to the payer. We'll create a
        // list of options to be added to the encoded payment request. For now
        // we only support the required fields description/description_hash,
        // expiry, fallback address, and the amount field.
        var options []func(*zpay32.Invoice)

        // We only include the amount in the invoice if it is greater than 0.
        // By not including the amount, we enable the creation of invoices that
        // allow the payer to specify the amount of satoshis they wish to send.
        if amtMSat > 0 {
                options = append(options, zpay32.Amount(amtMSat))
        }

        // If specified, add a fallback address to the payment request.
        if len(invoice.FallbackAddr) > 0 {
                addr, err := btcutil.DecodeAddress(
                        invoice.FallbackAddr, cfg.ChainParams,
                )
                if err != nil {
                        return nil, nil, fmt.Errorf("invalid fallback "+
                                "address: %v", err)
                }

                if !addr.IsForNet(cfg.ChainParams) {
                        return nil, nil, fmt.Errorf("fallback address is not "+
                                "for %s", cfg.ChainParams.Name)
                }

                options = append(options, zpay32.FallbackAddr(addr))
        }

        var expiry time.Duration
        switch {
        // An invoice expiry has been provided by the caller.
        case invoice.Expiry > 0:

                // We'll ensure that the specified expiry is restricted to sane
                // number of seconds. As a result, we'll reject an invoice with
                // an expiry greater than 1 year.
                maxExpiry := time.Hour * 24 * 365
                expSeconds := invoice.Expiry

                if float64(expSeconds) > maxExpiry.Seconds() {
                        return nil, nil, fmt.Errorf("expiry of %v seconds "+
                                "greater than max expiry of %v seconds",
                                float64(expSeconds), maxExpiry.Seconds())
                }

                expiry = time.Duration(invoice.Expiry) * time.Second

        // If no custom expiry is provided, use the default MPP expiry.
        case !invoice.Amp:
                expiry = DefaultInvoiceExpiry

        // Otherwise, use the default AMP expiry.
        default:
                expiry = DefaultAMPInvoiceExpiry
        }

        options = append(options, zpay32.Expiry(expiry))

        // If the description hash is set, then we add it do the list of
        // options. If not, use the memo field as the payment request
        // description.
        if len(invoice.DescriptionHash) > 0 {
                var descHash [32]byte
                copy(descHash[:], invoice.DescriptionHash[:])
                options = append(options, zpay32.DescriptionHash(descHash))
        } else {
                // Use the memo field as the description. If this is not set
                // this will just be an empty string.
                options = append(options, zpay32.Description(invoice.Memo))
        }

        if invoice.CltvExpiry > routing.MaxCLTVDelta {
                return nil, nil, fmt.Errorf("CLTV delta of %v is too large, "+
                        "max accepted is: %v", invoice.CltvExpiry,
                        math.MaxUint16)
        }

        // We'll use our current default CLTV value unless one was specified as
        // an option on the command line when creating an invoice.
        cltvExpiryDelta := uint64(cfg.DefaultCLTVExpiry)
        if invoice.CltvExpiry != 0 {
                // Disallow user-chosen final CLTV deltas below the required
                // minimum.
                if invoice.CltvExpiry < routing.MinCLTVDelta {
                        return nil, nil, fmt.Errorf("CLTV delta of %v must be "+
                                "greater than minimum of %v",
                                invoice.CltvExpiry, routing.MinCLTVDelta)
                }

                cltvExpiryDelta = invoice.CltvExpiry
        }

        // Only include a final CLTV expiry delta if this is not a blinded
        // invoice. In a blinded invoice, this value will be added to the total
        // blinded route CLTV delta value
        if !blind {
                options = append(options, zpay32.CLTVExpiry(cltvExpiryDelta))
        }

        // We make sure that the given invoice routing hints number is within
        // the valid range
        if len(invoice.RouteHints) > maxHopHints {
                return nil, nil, fmt.Errorf("number of routing hints must "+
                        "not exceed maximum of %v", maxHopHints)
        }

        // Include route hints if needed.
        if len(invoice.RouteHints) > 0 || invoice.Private {
                if blind {
                        return nil, nil, fmt.Errorf("can't set both hop " +
                                "hints and add blinded payment paths")
                }

                // Validate provided hop hints.
                for _, hint := range invoice.RouteHints {
                        if len(hint) == 0 {
                                return nil, nil, fmt.Errorf("number of hop " +
                                        "hint within a route must be positive")
                        }
                }

                totalHopHints := len(invoice.RouteHints)
                if invoice.Private {
                        totalHopHints = maxHopHints
                }

                hopHintsCfg := newSelectHopHintsCfg(cfg, totalHopHints)
                hopHints, err := PopulateHopHints(
                        hopHintsCfg, amtMSat, invoice.RouteHints,
                )
                if err != nil {
                        return nil, nil, fmt.Errorf("unable to populate hop "+
                                "hints: %v", err)
                }

                // Convert our set of selected hop hints into route
                // hints and add to our invoice options.
                for _, hopHint := range hopHints {
                        routeHint := zpay32.RouteHint(hopHint)

                        options = append(
                                options, routeHint,
                        )
                }
        }

        // Set our desired invoice features and add them to our list of options.
        var invoiceFeatures *lnwire.FeatureVector
        if invoice.Amp {
                invoiceFeatures = cfg.GenAmpInvoiceFeatures()
        } else {
                invoiceFeatures = cfg.GenInvoiceFeatures()
        }
        options = append(options, zpay32.Features(invoiceFeatures))

        // Generate and set a random payment address for this payment. If the
        // sender understands payment addresses, this can be used to avoid
        // intermediaries probing the receiver. If the invoice does not have
        // blinded paths, then this will be encoded in the invoice itself.
        // Otherwise, it will instead be embedded in the encrypted recipient
        // data of blinded paths. In the blinded path case, this will be used
        // for the PathID.
        var paymentAddr [32]byte
        if _, err := rand.Read(paymentAddr[:]); err != nil {
                return nil, nil, err
        }

        if blind {
                blindCfg := invoice.BlindedPathCfg

                // Use the 10-min-per-block assumption to get a rough estimate
                // of the number of blocks until the invoice expires. We want
                // to make sure that the blinded path definitely does not expire
                // before the invoice does, and so we add a healthy buffer.
                invoiceExpiry := uint32(expiry.Minutes() / 10)
                blindedPathExpiry := invoiceExpiry * 2

                // Add BlockPadding to the finalCltvDelta so that the receiving
                // node does not reject the HTLC if some blocks are mined while
                // the payment is in-flight. Note that unlike vanilla invoices,
                // with blinded paths, the recipient is responsible for adding
                // this block padding instead of the sender.
                finalCLTVDelta := uint32(cltvExpiryDelta)
                finalCLTVDelta += uint32(routing.BlockPadding)

                //nolint:ll
                paths, err := blindedpath.BuildBlindedPaymentPaths(
                        &blindedpath.BuildBlindedPathCfg{
                                FindRoutes:              cfg.QueryBlindedRoutes,
                                FetchChannelEdgesByID:   cfg.Graph.FetchChannelEdgesByID,
                                FetchOurOpenChannels:    cfg.ChanDB.FetchAllOpenChannels,
                                PathID:                  paymentAddr[:],
                                ValueMsat:               invoice.Value,
                                BestHeight:              cfg.BestHeight,
                                MinFinalCLTVExpiryDelta: finalCLTVDelta,
                                BlocksUntilExpiry:       blindedPathExpiry,
                                AddPolicyBuffer: func(
                                        p *blindedpath.BlindedHopPolicy) (
                                        *blindedpath.BlindedHopPolicy, error) {

                                        //nolint:ll
                                        return blindedpath.AddPolicyBuffer(
                                                p, blindCfg.RoutePolicyIncrMultiplier,
                                                blindCfg.RoutePolicyDecrMultiplier,
                                        )
                                },
                                MinNumHops:            blindCfg.MinNumPathHops,
                                DefaultDummyHopPolicy: blindCfg.DefaultDummyHopPolicy,
                                MaxNumPaths:           blindCfg.MaxNumPaths,
                        },
                )
                if err != nil {
                        return nil, nil, err
                }

                for _, path := range paths {
                        options = append(options, zpay32.WithBlindedPaymentPath(
                                path,
                        ))
                }
        } else {
                options = append(options, zpay32.PaymentAddr(paymentAddr))
        }

        // Create and encode the payment request as a bech32 (zpay32) string.
        creationDate := time.Now()
        payReq, err := zpay32.NewInvoice(
                cfg.ChainParams, paymentHash, creationDate, options...,
        )
        if err != nil {
                return nil, nil, err
        }

        payReqString, err := payReq.Encode(zpay32.MessageSigner{
                SignCompact: func(msg []byte) ([]byte, error) {
                        // For an invoice without a blinded path, the main node
                        // key is used to sign the invoice so that the sender
                        // can derive the true pub key of the recipient.
                        if !blind {
                                return cfg.NodeSigner.SignMessageCompact(
                                        msg, false,
                                )
                        }

                        // For an invoice with a blinded path, we use an
                        // ephemeral key to sign the invoice since we don't want
                        // the sender to be able to know the real pub key of
                        // the recipient.
                        ephemKey, err := btcec.NewPrivateKey()
                        if err != nil {
                                return nil, err
                        }

                        return ecdsa.SignCompact(
                                ephemKey, chainhash.HashB(msg), true,
                        ), nil
                },
        })
        if err != nil {
                return nil, nil, err
        }

        newInvoice := &invoices.Invoice{
                CreationDate:   creationDate,
                Memo:           []byte(invoice.Memo),
                PaymentRequest: []byte(payReqString),
                Terms: invoices.ContractTerm{
                        FinalCltvDelta:  int32(payReq.MinFinalCLTVExpiry()),
                        Expiry:          payReq.Expiry(),
                        Value:           amtMSat,
                        PaymentPreimage: paymentPreimage,
                        PaymentAddr:     paymentAddr,
                        Features:        invoiceFeatures,
                },
                HodlInvoice: invoice.HodlInvoice,
        }

        log.Tracef("[addinvoice] adding new invoice %v",
                lnutils.SpewLogClosure(newInvoice))

        // With all sanity checks passed, write the invoice to the database.
        _, err = cfg.AddInvoice(ctx, newInvoice, paymentHash)
        if err != nil {
                return nil, nil, err
        }

        return &paymentHash, newInvoice, nil
}

// chanCanBeHopHint returns true if the target channel is eligible to be a hop
// hint.
func chanCanBeHopHint(channel *HopHintInfo, cfg *SelectHopHintsCfg) (
        *models.ChannelEdgePolicy, bool) {

        // Since we're only interested in our private channels, we'll skip
        // public ones.
        if channel.IsPublic {
                return nil, false
        }

        // Make sure the channel is active.
        if !channel.IsActive {
                log.Debugf("Skipping channel %v due to not "+
                        "being eligible to forward payments",
                        channel.ShortChannelID)
                return nil, false
        }

        // To ensure we don't leak unadvertised nodes, we'll make sure our
        // counterparty is publicly advertised within the network.  Otherwise,
        // we'll end up leaking information about nodes that intend to stay
        // unadvertised, like in the case of a node only having private
        // channels.
        var remotePub [33]byte
        copy(remotePub[:], channel.RemotePubkey.SerializeCompressed())
        isRemoteNodePublic, err := cfg.IsPublicNode(remotePub)
        if err != nil {
                log.Errorf("Unable to determine if node %x "+
                        "is advertised: %v", remotePub, err)
                return nil, false
        }

        if !isRemoteNodePublic {
                log.Debugf("Skipping channel %v due to "+
                        "counterparty %x being unadvertised",
                        channel.ShortChannelID, remotePub)
                return nil, false
        }

        // Fetch the policies for each end of the channel.
        info, p1, p2, err := cfg.FetchChannelEdgesByID(channel.ShortChannelID)
        if err != nil {
                // In the case of zero-conf channels, it may be the case that
                // the alias SCID was deleted from the graph, and replaced by
                // the confirmed SCID. Check the Graph for the confirmed SCID.
                confirmedScid := channel.ConfirmedScidZC
                info, p1, p2, err = cfg.FetchChannelEdgesByID(confirmedScid)
                if err != nil {
                        log.Errorf("Unable to fetch the routing policies for "+
                                "the edges of the channel %v: %v",
                                channel.ShortChannelID, err)
                        return nil, false
                }
        }

        // Now, we'll need to determine which is the correct policy for HTLCs
        // being sent from the remote node.
        var remotePolicy *models.ChannelEdgePolicy
        if bytes.Equal(remotePub[:], info.NodeKey1Bytes[:]) {
                remotePolicy = p1
        } else {
                remotePolicy = p2
        }

        return remotePolicy, true
}

// HopHintInfo contains the channel information required to create a hop hint.
type HopHintInfo struct {
        // IsPublic indicates whether a channel is advertised to the network.
        IsPublic bool

        // IsActive indicates whether the channel is online and available for
        // use.
        IsActive bool

        // FundingOutpoint is the funding txid:index for the channel.
        FundingOutpoint wire.OutPoint

        // RemotePubkey is the public key of the remote party that this channel
        // is in.
        RemotePubkey *btcec.PublicKey

        // RemoteBalance is the remote party's balance (our current incoming
        // capacity).
        RemoteBalance lnwire.MilliSatoshi

        // ShortChannelID is the short channel ID of the channel.
        ShortChannelID uint64

        // ConfirmedScidZC is the confirmed SCID of a zero-conf channel. This
        // may be used for looking up a channel in the graph.
        ConfirmedScidZC uint64

        // ScidAliasFeature denotes whether the channel has negotiated the
        // option-scid-alias feature bit.
        ScidAliasFeature bool
}

func newHopHintInfo(c *channeldb.OpenChannel, isActive bool) *HopHintInfo {
        isPublic := c.ChannelFlags&lnwire.FFAnnounceChannel != 0

        return &HopHintInfo{
                IsPublic:         isPublic,
                IsActive:         isActive,
                FundingOutpoint:  c.FundingOutpoint,
                RemotePubkey:     c.IdentityPub,
                RemoteBalance:    c.LocalCommitment.RemoteBalance,
                ShortChannelID:   c.ShortChannelID.ToUint64(),
                ConfirmedScidZC:  c.ZeroConfRealScid().ToUint64(),
                ScidAliasFeature: c.ChanType.HasScidAliasFeature(),
        }
}

// newHopHint returns a new hop hint using the relevant data from a hopHintInfo
// and a ChannelEdgePolicy.
func newHopHint(hopHintInfo *HopHintInfo,
        chanPolicy *models.ChannelEdgePolicy) zpay32.HopHint {

        return zpay32.HopHint{
                NodeID:      hopHintInfo.RemotePubkey,
                ChannelID:   hopHintInfo.ShortChannelID,
                FeeBaseMSat: uint32(chanPolicy.FeeBaseMSat),
                FeeProportionalMillionths: uint32(
                        chanPolicy.FeeProportionalMillionths,
                ),
                CLTVExpiryDelta: chanPolicy.TimeLockDelta,
        }
}

// SelectHopHintsCfg contains the dependencies required to obtain hop hints
// for an invoice.
type SelectHopHintsCfg struct {
        // IsPublicNode is returns a bool indicating whether the node with the
        // given public key is seen as a public node in the graph from the
        // graph's source node's point of view.
        IsPublicNode func(pubKey [33]byte) (bool, error)

        // FetchChannelEdgesByID attempts to lookup the two directed edges for
        // the channel identified by the channel ID.
        FetchChannelEdgesByID func(chanID uint64) (*models.ChannelEdgeInfo,
                *models.ChannelEdgePolicy, *models.ChannelEdgePolicy,
                error)

        // GetAlias allows the peer's alias SCID to be retrieved for private
        // option_scid_alias channels.
        GetAlias func(lnwire.ChannelID) (lnwire.ShortChannelID, error)

        // FetchAllChannels retrieves all open channels currently stored
        // within the database.
        FetchAllChannels func() ([]*channeldb.OpenChannel, error)

        // IsChannelActive checks whether the channel identified by the provided
        // ChannelID is considered active.
        IsChannelActive func(chanID lnwire.ChannelID) bool

        // MaxHopHints is the maximum number of hop hints we are interested in.
        MaxHopHints int
}

func newSelectHopHintsCfg(invoicesCfg *AddInvoiceConfig,
        maxHopHints int) *SelectHopHintsCfg {

        return &SelectHopHintsCfg{
                FetchAllChannels:      invoicesCfg.ChanDB.FetchAllChannels,
                IsChannelActive:       invoicesCfg.IsChannelActive,
                IsPublicNode:          invoicesCfg.Graph.IsPublicNode,
                FetchChannelEdgesByID: invoicesCfg.Graph.FetchChannelEdgesByID,
                GetAlias:              invoicesCfg.GetAlias,
                MaxHopHints:           maxHopHints,
        }
}

// sufficientHints checks whether we have sufficient hop hints, based on the
// any of the following criteria:
//   - Hop hint count: the number of hints have reach our max target.
//   - Total incoming capacity (for non-zero invoice amounts): the sum of the
//     remote balance amount in the hints is bigger of equal than our target
//     (currently twice the invoice amount)
//
// We limit our number of hop hints like this to keep our invoice size down,
// and to avoid leaking all our private channels when we don't need to.
func sufficientHints(nHintsLeft int, currentAmount,
        targetAmount lnwire.MilliSatoshi) bool {

        if nHintsLeft <= 0 {
                log.Debugf("Reached targeted number of hop hints")
                return true
        }

        if targetAmount != 0 && currentAmount >= targetAmount {
                log.Debugf("Total hint amount: %v has reached target hint "+
                        "bandwidth: %v", currentAmount, targetAmount)
                return true
        }

        return false
}

// getPotentialHints returns a slice of open channels that should be considered
// for the hopHint list in an invoice. The slice is sorted in descending order
// based on the remote balance.
func getPotentialHints(cfg *SelectHopHintsCfg) ([]*channeldb.OpenChannel,
        error) {

        // TODO(positiveblue): get the channels slice already filtered by
        // private == true and sorted by RemoteBalance?
        openChannels, err := cfg.FetchAllChannels()
        if err != nil {
                return nil, err
        }

        privateChannels := make([]*channeldb.OpenChannel, 0, len(openChannels))
        for _, oc := range openChannels {
                isPublic := oc.ChannelFlags&lnwire.FFAnnounceChannel != 0
                if !isPublic {
                        privateChannels = append(privateChannels, oc)
                }
        }

        // Sort the channels in descending remote balance.
        compareRemoteBalance := func(i, j int) bool {
                iBalance := privateChannels[i].LocalCommitment.RemoteBalance
                jBalance := privateChannels[j].LocalCommitment.RemoteBalance
                return iBalance > jBalance
        }
        sort.Slice(privateChannels, compareRemoteBalance)

        return privateChannels, nil
}

// shouldIncludeChannel returns true if the channel passes all the checks to
// be a hopHint in a given invoice.
func shouldIncludeChannel(cfg *SelectHopHintsCfg,
        channel *channeldb.OpenChannel,
        alreadyIncluded map[uint64]bool) (zpay32.HopHint, lnwire.MilliSatoshi,
        bool) {

        if _, ok := alreadyIncluded[channel.ShortChannelID.ToUint64()]; ok {
                return zpay32.HopHint{}, 0, false
        }

        chanID := lnwire.NewChanIDFromOutPoint(
                channel.FundingOutpoint,
        )

        hopHintInfo := newHopHintInfo(channel, cfg.IsChannelActive(chanID))

        // If this channel can't be a hop hint, then skip it.
        edgePolicy, canBeHopHint := chanCanBeHopHint(hopHintInfo, cfg)
        if edgePolicy == nil || !canBeHopHint {
                return zpay32.HopHint{}, 0, false
        }

        if hopHintInfo.ScidAliasFeature {
                alias, err := cfg.GetAlias(chanID)
                if err != nil {
                        return zpay32.HopHint{}, 0, false
                }

                if alias.IsDefault() || alreadyIncluded[alias.ToUint64()] {
                        return zpay32.HopHint{}, 0, false
                }

                hopHintInfo.ShortChannelID = alias.ToUint64()
        }

        // Now that we know this channel use usable, add it as a hop hint and
        // the indexes we'll use later.
        hopHint := newHopHint(hopHintInfo, edgePolicy)
        return hopHint, hopHintInfo.RemoteBalance, true
}

// selectHopHints iterates a list of potential hints selecting the valid hop
// hints until we have enough hints or run out of channels.
//
// NOTE: selectHopHints expects potentialHints to be already sorted in
// descending priority.
func selectHopHints(cfg *SelectHopHintsCfg, nHintsLeft int,
        targetBandwidth lnwire.MilliSatoshi,
        potentialHints []*channeldb.OpenChannel,
        alreadyIncluded map[uint64]bool) [][]zpay32.HopHint {

        currentBandwidth := lnwire.MilliSatoshi(0)
        hopHints := make([][]zpay32.HopHint, 0, nHintsLeft)
        for _, channel := range potentialHints {
                enoughHopHints := sufficientHints(
                        nHintsLeft, currentBandwidth, targetBandwidth,
                )
                if enoughHopHints {
                        return hopHints
                }

                hopHint, remoteBalance, include := shouldIncludeChannel(
                        cfg, channel, alreadyIncluded,
                )

                if include {
                        // Now that we now this channel use usable, add it as a hop
                        // hint and the indexes we'll use later.
                        hopHints = append(hopHints, []zpay32.HopHint{hopHint})
                        currentBandwidth += remoteBalance
                        nHintsLeft--
                }
        }

        // We do not want to leak information about how our remote balance is
        // distributed in our private channels. We shuffle the selected ones
        // here so they do not appear in order in the invoice.
        mathRand.Shuffle(
                len(hopHints), func(i, j int) {
                        hopHints[i], hopHints[j] = hopHints[j], hopHints[i]
                },
        )
        return hopHints
}

// PopulateHopHints will select up to cfg.MaxHophints from the current open
// channels. The set of hop hints will be returned as a slice of functional
// options that'll append the route hint to the set of all route hints.
//
// TODO(roasbeef): do proper sub-set sum max hints usually << numChans.
func PopulateHopHints(cfg *SelectHopHintsCfg, amtMSat lnwire.MilliSatoshi,
        forcedHints [][]zpay32.HopHint) ([][]zpay32.HopHint, error) {

        hopHints := forcedHints

        // If we already have enough hints we don't need to add any more.
        nHintsLeft := cfg.MaxHopHints - len(hopHints)
        if nHintsLeft <= 0 {
                return hopHints, nil
        }

        alreadyIncluded := make(map[uint64]bool)
        for _, hopHint := range hopHints {
                alreadyIncluded[hopHint[0].ChannelID] = true
        }

        potentialHints, err := getPotentialHints(cfg)
        if err != nil {
                return nil, err
        }

        targetBandwidth := amtMSat * hopHintFactor
        selectedHints := selectHopHints(
                cfg, nHintsLeft, targetBandwidth, potentialHints,
                alreadyIncluded,
        )

        hopHints = append(hopHints, selectedHints...)
        return hopHints, nil
}

lightningnetwork / lnd / 19027031130

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