19924300449

Committed 04 Dec 2025 09:35AM UTC coverage: 53.479% (-1.9%) from 55.404%

Build # 19924300449

Build Type

Pull #10419

github

Committed by

web-flow

Commit Message

Merge f811805c6 into 20473482d

Pull Request Pull Request #10419: [docs] Document use-native-sql=true for SQL migration step 2

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87.36

/payments/db/payment.go

package paymentsdb

import (
        "bytes"
        "errors"
        "fmt"
        "time"

        "github.com/btcsuite/btcd/btcec/v2"
        "github.com/davecgh/go-spew/spew"
        sphinx "github.com/lightningnetwork/lightning-onion"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/routing/route"
)

// FailureReason encodes the reason a payment ultimately failed.
type FailureReason byte

const (
        // FailureReasonTimeout indicates that the payment did timeout before a
        // successful payment attempt was made.
        FailureReasonTimeout FailureReason = 0

        // FailureReasonNoRoute indicates no successful route to the
        // destination was found during path finding.
        FailureReasonNoRoute FailureReason = 1

        // FailureReasonError indicates that an unexpected error happened during
        // payment.
        FailureReasonError FailureReason = 2

        // FailureReasonPaymentDetails indicates that either the hash is unknown
        // or the final cltv delta or amount is incorrect.
        FailureReasonPaymentDetails FailureReason = 3

        // FailureReasonInsufficientBalance indicates that we didn't have enough
        // balance to complete the payment.
        FailureReasonInsufficientBalance FailureReason = 4

        // FailureReasonCanceled indicates that the payment was canceled by the
        // user.
        FailureReasonCanceled FailureReason = 5

        // TODO(joostjager): Add failure reasons for:
        // LocalLiquidityInsufficient, RemoteCapacityInsufficient.
)

// Error returns a human-readable error string for the FailureReason.
func (r FailureReason) Error() string {
        return r.String()
}

// String returns a human-readable FailureReason.
func (r FailureReason) String() string {
        switch r {
        case FailureReasonTimeout:
                return "timeout"
        case FailureReasonNoRoute:
                return "no_route"
        case FailureReasonError:
                return "error"
        case FailureReasonPaymentDetails:
                return "incorrect_payment_details"
        case FailureReasonInsufficientBalance:
                return "insufficient_balance"
        case FailureReasonCanceled:
                return "canceled"
        }

        return "unknown"
}

// PaymentCreationInfo is the information necessary to have ready when
// initiating a payment, moving it into state InFlight.
type PaymentCreationInfo struct {
        // PaymentIdentifier is the hash this payment is paying to in case of
        // non-AMP payments, and the SetID for AMP payments.
        PaymentIdentifier lntypes.Hash

        // Value is the amount we are paying.
        Value lnwire.MilliSatoshi

        // CreationTime is the time when this payment was initiated.
        CreationTime time.Time

        // PaymentRequest is the full payment request, if any.
        PaymentRequest []byte

        // FirstHopCustomRecords are the TLV records that are to be sent to the
        // first hop of this payment. These records will be transmitted via the
        // wire message (UpdateAddHTLC) only and therefore do not affect the
        // onion payload size.
        FirstHopCustomRecords lnwire.CustomRecords
}

// String returns a human-readable description of the payment creation info.
func (p *PaymentCreationInfo) String() string {
        return fmt.Sprintf("payment_id=%v, amount=%v, created_at=%v",
                p.PaymentIdentifier, p.Value, p.CreationTime)
}

// HTLCAttemptInfo contains static information about a specific HTLC attempt
// for a payment. This information is used by the router to handle any errors
// coming back after an attempt is made, and to query the switch about the
// status of the attempt.
type HTLCAttemptInfo struct {
        // AttemptID is the unique ID used for this attempt.
        AttemptID uint64

        // sessionKey is the raw bytes ephemeral key used for this attempt.
        // These bytes are lazily read off disk to save ourselves the expensive
        // EC operations used by btcec.PrivKeyFromBytes.
        sessionKey [btcec.PrivKeyBytesLen]byte

        // cachedSessionKey is our fully deserialized sesionKey. This value
        // may be nil if the attempt has just been read from disk and its
        // session key has not been used yet.
        cachedSessionKey *btcec.PrivateKey

        // Route is the route attempted to send the HTLC.
        Route route.Route

        // AttemptTime is the time at which this HTLC was attempted.
        AttemptTime time.Time

        // Hash is the hash used for this single HTLC attempt. For AMP payments
        // this will differ across attempts, for non-AMP payments each attempt
        // will use the same hash. This can be nil for older payment attempts,
        // in which the payment's PaymentHash in the PaymentCreationInfo should
        // be used.
        Hash *lntypes.Hash

        // onionBlob is the cached value for onion blob created from the sphinx
        // construction.
        onionBlob [lnwire.OnionPacketSize]byte

        // circuit is the cached value for sphinx circuit.
        circuit *sphinx.Circuit
}

// NewHtlcAttempt creates a htlc attempt.
func NewHtlcAttempt(attemptID uint64, sessionKey *btcec.PrivateKey,
        route route.Route, attemptTime time.Time,
        hash *lntypes.Hash) (*HTLCAttempt, error) {

        var scratch [btcec.PrivKeyBytesLen]byte
        copy(scratch[:], sessionKey.Serialize())

        info := HTLCAttemptInfo{
                AttemptID:        attemptID,
                sessionKey:       scratch,
                cachedSessionKey: sessionKey,
                Route:            route,
                AttemptTime:      attemptTime,
                Hash:             hash,
        }

        if err := info.attachOnionBlobAndCircuit(); err != nil {
                return nil, err
        }

        return &HTLCAttempt{HTLCAttemptInfo: info}, nil
}

// SessionKey returns the ephemeral key used for a htlc attempt. This function
// performs expensive ec-ops to obtain the session key if it is not cached.
func (h *HTLCAttemptInfo) SessionKey() *btcec.PrivateKey {
        if h.cachedSessionKey == nil {
                h.cachedSessionKey, _ = btcec.PrivKeyFromBytes(
                        h.sessionKey[:],
                )
        }

        return h.cachedSessionKey
}

// setSessionKey sets the session key for the htlc attempt.
//
// NOTE: Only used for testing.
//
//nolint:unused
func (h *HTLCAttemptInfo) setSessionKey(sessionKey *btcec.PrivateKey) {
        h.cachedSessionKey = sessionKey

        // Also set the session key as a raw bytes.
        var scratch [btcec.PrivKeyBytesLen]byte
        copy(scratch[:], sessionKey.Serialize())
        h.sessionKey = scratch
}

// OnionBlob returns the onion blob created from the sphinx construction.
func (h *HTLCAttemptInfo) OnionBlob() ([lnwire.OnionPacketSize]byte, error) {
        var zeroBytes [lnwire.OnionPacketSize]byte
        if h.onionBlob == zeroBytes {
                if err := h.attachOnionBlobAndCircuit(); err != nil {
                        return zeroBytes, err
                }
        }

        return h.onionBlob, nil
}

// Circuit returns the sphinx circuit for this attempt.
func (h *HTLCAttemptInfo) Circuit() (*sphinx.Circuit, error) {
        if h.circuit == nil {
                if err := h.attachOnionBlobAndCircuit(); err != nil {
                        return nil, err
                }
        }

        return h.circuit, nil
}

// attachOnionBlobAndCircuit creates a sphinx packet and caches the onion blob
// and circuit for this attempt.
func (h *HTLCAttemptInfo) attachOnionBlobAndCircuit() error {
        onionBlob, circuit, err := generateSphinxPacket(
                &h.Route, h.Hash[:], h.SessionKey(),
        )
        if err != nil {
                return err
        }

        copy(h.onionBlob[:], onionBlob)
        h.circuit = circuit

        return nil
}

// HTLCAttempt contains information about a specific HTLC attempt for a given
// payment. It contains the HTLCAttemptInfo used to send the HTLC, as well
// as a timestamp and any known outcome of the attempt.
type HTLCAttempt struct {
        HTLCAttemptInfo

        // Settle is the preimage of a successful payment. This serves as a
        // proof of payment. It will only be non-nil for settled payments.
        //
        // NOTE: Can be nil if payment is not settled.
        Settle *HTLCSettleInfo

        // Fail is a failure reason code indicating the reason the payment
        // failed. It is only non-nil for failed payments.
        //
        // NOTE: Can be nil if payment is not failed.
        Failure *HTLCFailInfo
}

// HTLCSettleInfo encapsulates the information that augments an HTLCAttempt in
// the event that the HTLC is successful.
type HTLCSettleInfo struct {
        // Preimage is the preimage of a successful HTLC. This serves as a proof
        // of payment.
        Preimage lntypes.Preimage

        // SettleTime is the time at which this HTLC was settled.
        SettleTime time.Time
}

// HTLCFailReason is the reason an htlc failed.
type HTLCFailReason byte

const (
        // HTLCFailUnknown is recorded for htlcs that failed with an unknown
        // reason.
        HTLCFailUnknown HTLCFailReason = 0

        // HTLCFailUnreadable is recorded for htlcs that had a failure message
        // that couldn't be decrypted.
        HTLCFailUnreadable HTLCFailReason = 1

        // HTLCFailInternal is recorded for htlcs that failed because of an
        // internal error.
        HTLCFailInternal HTLCFailReason = 2

        // HTLCFailMessage is recorded for htlcs that failed with a network
        // failure message.
        HTLCFailMessage HTLCFailReason = 3
)

// HTLCFailInfo encapsulates the information that augments an HTLCAttempt in the
// event that the HTLC fails.
type HTLCFailInfo struct {
        // FailTime is the time at which this HTLC was failed.
        FailTime time.Time

        // Message is the wire message that failed this HTLC. This field will be
        // populated when the failure reason is HTLCFailMessage.
        Message lnwire.FailureMessage

        // Reason is the failure reason for this HTLC.
        Reason HTLCFailReason

        // The position in the path of the intermediate or final node that
        // generated the failure message. Position zero is the sender node. This
        // field will be populated when the failure reason is either
        // HTLCFailMessage or HTLCFailUnknown.
        FailureSourceIndex uint32
}

// MPPaymentState wraps a series of info needed for a given payment, which is
// used by both MPP and AMP. This is a memory representation of the payment's
// current state and is updated whenever the payment is read from disk.
type MPPaymentState struct {
        // NumAttemptsInFlight specifies the number of HTLCs the payment is
        // waiting results for.
        NumAttemptsInFlight int

        // RemainingAmt specifies how much more money to be sent.
        RemainingAmt lnwire.MilliSatoshi

        // FeesPaid specifies the total fees paid so far that can be used to
        // calculate remaining fee budget.
        FeesPaid lnwire.MilliSatoshi

        // HasSettledHTLC is true if at least one of the payment's HTLCs is
        // settled.
        HasSettledHTLC bool

        // PaymentFailed is true if the payment has been marked as failed with
        // a reason.
        PaymentFailed bool
}

// MPPayment is a wrapper around a payment's PaymentCreationInfo and
// HTLCAttempts. All payments will have the PaymentCreationInfo set, any
// HTLCs made in attempts to be completed will populated in the HTLCs slice.
// Each populated HTLCAttempt represents an attempted HTLC, each of which may
// have the associated Settle or Fail struct populated if the HTLC is no longer
// in-flight.
type MPPayment struct {
        // SequenceNum is a unique identifier used to sort the payments in
        // order of creation.
        SequenceNum uint64

        // Info holds all static information about this payment, and is
        // populated when the payment is initiated.
        Info *PaymentCreationInfo

        // HTLCs holds the information about individual HTLCs that we send in
        // order to make the payment.
        HTLCs []HTLCAttempt

        // FailureReason is the failure reason code indicating the reason the
        // payment failed.
        //
        // NOTE: Will only be set once the daemon has given up on the payment
        // altogether.
        FailureReason *FailureReason

        // Status is the current PaymentStatus of this payment.
        Status PaymentStatus

        // State is the current state of the payment that holds a number of key
        // insights and is used to determine what to do on each payment loop
        // iteration.
        State *MPPaymentState
}

// Terminated returns a bool to specify whether the payment is in a terminal
// state.
func (m *MPPayment) Terminated() bool {
        // If the payment is in terminal state, it cannot be updated.
        return m.Status.updatable() != nil
}

// TerminalInfo returns any HTLC settle info recorded. If no settle info is
// recorded, any payment level failure will be returned. If neither a settle
// nor a failure is recorded, both return values will be nil.
func (m *MPPayment) TerminalInfo() (*HTLCAttempt, *FailureReason) {
        for _, h := range m.HTLCs {
                if h.Settle != nil {
                        return &h, nil
                }
        }

        return nil, m.FailureReason
}

// SentAmt returns the sum of sent amount and fees for HTLCs that are either
// settled or still in flight.
func (m *MPPayment) SentAmt() (lnwire.MilliSatoshi, lnwire.MilliSatoshi) {
        var sent, fees lnwire.MilliSatoshi
        for _, h := range m.HTLCs {
                if h.Failure != nil {
                        continue
                }

                // The attempt was not failed, meaning the amount was
                // potentially sent to the receiver.
                sent += h.Route.ReceiverAmt()
                fees += h.Route.TotalFees()
        }

        return sent, fees
}

// InFlightHTLCs returns the HTLCs that are still in-flight, meaning they have
// not been settled or failed.
func (m *MPPayment) InFlightHTLCs() []HTLCAttempt {
        var inflights []HTLCAttempt
        for _, h := range m.HTLCs {
                if h.Settle != nil || h.Failure != nil {
                        continue
                }

                inflights = append(inflights, h)
        }

        return inflights
}

// GetAttempt returns the specified htlc attempt on the payment.
func (m *MPPayment) GetAttempt(id uint64) (*HTLCAttempt, error) {
        // TODO(yy): iteration can be slow, make it into a tree or use BS.
        for _, htlc := range m.HTLCs {
                htlc := htlc
                if htlc.AttemptID == id {
                        return &htlc, nil
                }
        }

        return nil, errors.New("htlc attempt not found on payment")
}

// Registrable returns an error to specify whether adding more HTLCs to the
// payment with its current status is allowed. A payment can accept new HTLC
// registrations when it's newly created, or none of its HTLCs is in a terminal
// state.
func (m *MPPayment) Registrable() error {
        // If updating the payment is not allowed, we can't register new HTLCs.
        // Otherwise, the status must be either `StatusInitiated` or
        // `StatusInFlight`.
        if err := m.Status.updatable(); err != nil {
                return err
        }

        // Exit early if this is not inflight.
        if m.Status != StatusInFlight {
                return nil
        }

        // There are still inflight HTLCs and we need to check whether there
        // are settled HTLCs or the payment is failed. If we already have
        // settled HTLCs, we won't allow adding more HTLCs.
        if m.State.HasSettledHTLC {
                return ErrPaymentPendingSettled
        }

        // If the payment is already failed, we won't allow adding more HTLCs.
        if m.State.PaymentFailed {
                return ErrPaymentPendingFailed
        }

        // Otherwise we can add more HTLCs.
        return nil
}

// setState creates and attaches a new MPPaymentState to the payment. It also
// updates the payment's status based on its current state.
func (m *MPPayment) setState() error {
        // Fetch the total amount and fees that has already been sent in
        // settled and still in-flight shards.
        sentAmt, fees := m.SentAmt()

        // Sanity check we haven't sent a value larger than the payment amount.
        totalAmt := m.Info.Value
        if sentAmt > totalAmt {
                return fmt.Errorf("%w: sent=%v, total=%v",
                        ErrSentExceedsTotal, sentAmt, totalAmt)
        }

        // Get any terminal info for this payment.
        settle, failure := m.TerminalInfo()

        // Now determine the payment's status.
        status, err := decidePaymentStatus(m.HTLCs, m.FailureReason)
        if err != nil {
                return err
        }

        // Update the payment state and status.
        m.State = &MPPaymentState{
                NumAttemptsInFlight: len(m.InFlightHTLCs()),
                RemainingAmt:        totalAmt - sentAmt,
                FeesPaid:            fees,
                HasSettledHTLC:      settle != nil,
                PaymentFailed:       failure != nil,
        }
        m.Status = status

        return nil
}

// SetState calls the internal method setState. This is a temporary method
// to be used by the tests in routing. Once the tests are updated to use mocks,
// this method can be removed.
//
// TODO(yy): delete.
func (m *MPPayment) SetState() error {
        return m.setState()
}

// NeedWaitAttempts decides whether we need to hold creating more HTLC attempts
// and wait for the results of the payment's inflight HTLCs. Return an error if
// the payment is in an unexpected state.
func (m *MPPayment) NeedWaitAttempts() (bool, error) {
        // Check when the remainingAmt is not zero, which means we have more
        // money to be sent.
        if m.State.RemainingAmt != 0 {
                switch m.Status {
                // If the payment is newly created, no need to wait for HTLC
                // results.
                case StatusInitiated:
                        return false, nil

                // If we have inflight HTLCs, we'll check if we have terminal
                // states to decide if we need to wait.
                case StatusInFlight:
                        // We still have money to send, and one of the HTLCs is
                        // settled. We'd stop sending money and wait for all
                        // inflight HTLC attempts to finish.
                        if m.State.HasSettledHTLC {
                                log.Warnf("payment=%v has remaining amount "+
                                        "%v, yet at least one of its HTLCs is "+
                                        "settled", m.Info.PaymentIdentifier,
                                        m.State.RemainingAmt)

                                return true, nil
                        }

                        // The payment has a failure reason though we still
                        // have money to send, we'd stop sending money and wait
                        // for all inflight HTLC attempts to finish.
                        if m.State.PaymentFailed {
                                return true, nil
                        }

                        // Otherwise we don't need to wait for inflight HTLCs
                        // since we still have money to be sent.
                        return false, nil

                // We need to send more money, yet the payment is already
                // succeeded. Return an error in this case as the receiver is
                // violating the protocol.
                case StatusSucceeded:
                        return false, fmt.Errorf("%w: parts of the payment "+
                                "already succeeded but still have remaining "+
                                "amount %v", ErrPaymentInternal,
                                m.State.RemainingAmt)

                // The payment is failed and we have no inflight HTLCs, no need
                // to wait.
                case StatusFailed:
                        return false, nil

                // Unknown payment status.
                default:
                        return false, fmt.Errorf("%w: %s",
                                ErrUnknownPaymentStatus, m.Status)
                }
        }

        // Now we determine whether we need to wait when the remainingAmt is
        // already zero.
        switch m.Status {
        // When the payment is newly created, yet the payment has no remaining
        // amount, return an error.
        case StatusInitiated:
                return false, fmt.Errorf("%w: %v",
                        ErrPaymentInternal, m.Status)

        // If the payment is inflight, we must wait.
        //
        // NOTE: an edge case is when all HTLCs are failed while the payment is
        // not failed we'd still be in this inflight state. However, since the
        // remainingAmt is zero here, it means we cannot be in that state as
        // otherwise the remainingAmt would not be zero.
        case StatusInFlight:
                return true, nil

        // If the payment is already succeeded, no need to wait.
        case StatusSucceeded:
                return false, nil

        // If the payment is already failed, yet the remaining amount is zero,
        // return an error as this indicates an error state. We will only each
        // this status when there are no inflight HTLCs and the payment is
        // marked as failed with a reason, which means the remainingAmt must
        // not be zero because our sentAmt is zero.
        case StatusFailed:
                return false, fmt.Errorf("%w: %v",
                        ErrPaymentInternal, m.Status)

        // Unknown payment status.
        default:
                return false, fmt.Errorf("%w: %s",
                        ErrUnknownPaymentStatus, m.Status)
        }
}

// GetState returns the internal state of the payment.
func (m *MPPayment) GetState() *MPPaymentState {
        return m.State
}

// GetStatus returns the current status of the payment.
func (m *MPPayment) GetStatus() PaymentStatus {
        return m.Status
}

// GetHTLCs returns all the HTLCs for this payment.
func (m *MPPayment) GetHTLCs() []HTLCAttempt {
        return m.HTLCs
}

// AllowMoreAttempts is used to decide whether we can safely attempt more HTLCs
// for a given payment state. Return an error if the payment is in an
// unexpected state.
func (m *MPPayment) AllowMoreAttempts() (bool, error) {
        // Now check whether the remainingAmt is zero or not. If we don't have
        // any remainingAmt, no more HTLCs should be made.
        if m.State.RemainingAmt == 0 {
                // If the payment is newly created, yet we don't have any
                // remainingAmt, return an error.
                if m.Status == StatusInitiated {
                        return false, fmt.Errorf("%w: initiated payment has "+
                                "zero remainingAmt",
                                ErrPaymentInternal)
                }

                // Otherwise, exit early since all other statuses with zero
                // remainingAmt indicate no more HTLCs can be made.
                return false, nil
        }

        // Otherwise, the remaining amount is not zero, we now decide whether
        // to make more attempts based on the payment's current status.
        //
        // If at least one of the payment's attempts is settled, yet we haven't
        // sent all the amount, it indicates something is wrong with the peer
        // as the preimage is received. In this case, return an error state.
        if m.Status == StatusSucceeded {
                return false, fmt.Errorf("%w: payment already succeeded but "+
                        "still have remaining amount %v",
                        ErrPaymentInternal, m.State.RemainingAmt)
        }

        // Now check if we can register a new HTLC.
        err := m.Registrable()
        if err != nil {
                log.Warnf("Payment(%v): cannot register HTLC attempt: %v, "+
                        "current status: %s", m.Info.PaymentIdentifier,
                        err, m.Status)

                return false, nil
        }

        // Now we know we can register new HTLCs.
        return true, nil
}

// generateSphinxPacket generates then encodes a sphinx packet which encodes
// the onion route specified by the passed layer 3 route. The blob returned
// from this function can immediately be included within an HTLC add packet to
// be sent to the first hop within the route.
func generateSphinxPacket(rt *route.Route, paymentHash []byte,
        sessionKey *btcec.PrivateKey) ([]byte, *sphinx.Circuit, error) {

        // Now that we know we have an actual route, we'll map the route into a
        // sphinx payment path which includes per-hop payloads for each hop
        // that give each node within the route the necessary information
        // (fees, CLTV value, etc.) to properly forward the payment.
        sphinxPath, err := rt.ToSphinxPath()
        if err != nil {
                return nil, nil, err
        }

        log.Tracef("Constructed per-hop payloads for payment_hash=%x: %v",
                paymentHash, lnutils.NewLogClosure(func() string {
                        path := make(
                                []sphinx.OnionHop, sphinxPath.TrueRouteLength(),
                        )
                        for i := range path {
                                hopCopy := sphinxPath[i]
                                path[i] = hopCopy
                        }

                        return spew.Sdump(path)
                }),
        )

        // Next generate the onion routing packet which allows us to perform
        // privacy preserving source routing across the network.
        sphinxPacket, err := sphinx.NewOnionPacket(
                sphinxPath, sessionKey, paymentHash,
                sphinx.DeterministicPacketFiller,
        )
        if err != nil {
                return nil, nil, err
        }

        // Finally, encode Sphinx packet using its wire representation to be
        // included within the HTLC add packet.
        var onionBlob bytes.Buffer
        if err := sphinxPacket.Encode(&onionBlob); err != nil {
                return nil, nil, err
        }

        log.Tracef("Generated sphinx packet: %v",
                lnutils.NewLogClosure(func() string {
                        // We make a copy of the ephemeral key and unset the
                        // internal curve here in order to keep the logs from
                        // getting noisy.
                        key := *sphinxPacket.EphemeralKey
                        packetCopy := *sphinxPacket
                        packetCopy.EphemeralKey = &key

                        return spew.Sdump(packetCopy)
                }),
        )

        return onionBlob.Bytes(), &sphinx.Circuit{
                SessionKey:  sessionKey,
                PaymentPath: sphinxPath.NodeKeys(),
        }, nil
}

// verifyAttempt validates that a new HTLC attempt is compatible with the
// existing payment and its in-flight HTLCs. This function checks:
//  1. MPP (Multi-Path Payment) compatibility between attempts
//  2. Blinded payment consistency
//  3. Amount validation
//  4. Total payment amount limits
func verifyAttempt(payment *MPPayment, attempt *HTLCAttemptInfo) error {
        // If the final hop has encrypted data, then we know this is a
        // blinded payment. In blinded payments, MPP records are not set
        // for split payments and the recipient is responsible for using
        // a consistent PathID across the various encrypted data
        // payloads that we received from them for this payment. All we
        // need to check is that the total amount field for each HTLC
        // in the split payment is correct.
        isBlinded := len(attempt.Route.FinalHop().EncryptedData) != 0

        // Make sure any existing shards match the new one with regards
        // to MPP options.
        mpp := attempt.Route.FinalHop().MPP

        // MPP records should not be set for attempts to blinded paths.
        if isBlinded && mpp != nil {
                return ErrMPPRecordInBlindedPayment
        }

        for _, h := range payment.InFlightHTLCs() {
                hMpp := h.Route.FinalHop().MPP
                hBlinded := len(h.Route.FinalHop().EncryptedData) != 0

                // If this is a blinded payment, then no existing HTLCs
                // should have MPP records.
                if isBlinded && hMpp != nil {
                        return ErrMPPRecordInBlindedPayment
                }

                // If the payment is blinded (previous attempts used blinded
                // paths) and the attempt is not, or vice versa, return an
                // error.
                if isBlinded != hBlinded {
                        return ErrMixedBlindedAndNonBlindedPayments
                }

                // If this is a blinded payment, then we just need to
                // check that the TotalAmtMsat field for this shard
                // is equal to that of any other shard in the same
                // payment.
                if isBlinded {
                        if attempt.Route.FinalHop().TotalAmtMsat !=
                                h.Route.FinalHop().TotalAmtMsat {

                                return ErrBlindedPaymentTotalAmountMismatch
                        }

                        continue
                }

                switch {
                // We tried to register a non-MPP attempt for a MPP
                // payment.
                case mpp == nil && hMpp != nil:
                        return ErrMPPayment

                // We tried to register a MPP shard for a non-MPP
                // payment.
                case mpp != nil && hMpp == nil:
                        return ErrNonMPPayment

                // Non-MPP payment, nothing more to validate.
                case mpp == nil:
                        continue
                }

                // Check that MPP options match.
                if mpp.PaymentAddr() != hMpp.PaymentAddr() {
                        return ErrMPPPaymentAddrMismatch
                }

                if mpp.TotalMsat() != hMpp.TotalMsat() {
                        return ErrMPPTotalAmountMismatch
                }
        }

        // If this is a non-MPP attempt, it must match the total amount
        // exactly. Note that a blinded payment is considered an MPP
        // attempt.
        amt := attempt.Route.ReceiverAmt()
        if !isBlinded && mpp == nil && amt != payment.Info.Value {
                return ErrValueMismatch
        }

        // Ensure we aren't sending more than the total payment amount.
        sentAmt, _ := payment.SentAmt()
        if sentAmt+amt > payment.Info.Value {
                return fmt.Errorf("%w: attempted=%v, payment amount=%v",
                        ErrValueExceedsAmt, sentAmt+amt, payment.Info.Value)
        }

        return nil
}

lightningnetwork / lnd / 19924300449

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