13153965138

Committed 05 Feb 2025 09:13AM UTC coverage: 49.301% (-9.5%) from 58.798%

Build # 13153965138

Build Type

Pull #9477

github

Committed by

ellemouton

Commit Message

docs: update release notes

Pull Request Pull Request #9477: discovery+graph: various preparations for moving funding tx validation to the gossiper

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69.7

/channeldb/invoices.go

package channeldb

import (
        "bytes"
        "context"
        "encoding/binary"
        "errors"
        "fmt"
        "io"
        "time"

        "github.com/lightningnetwork/lnd/graph/db/models"
        "github.com/lightningnetwork/lnd/htlcswitch/hop"
        invpkg "github.com/lightningnetwork/lnd/invoices"
        "github.com/lightningnetwork/lnd/kvdb"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/record"
        "github.com/lightningnetwork/lnd/tlv"
)

var (
        // invoiceBucket is the name of the bucket within the database that
        // stores all data related to invoices no matter their final state.
        // Within the invoice bucket, each invoice is keyed by its invoice ID
        // which is a monotonically increasing uint32.
        invoiceBucket = []byte("invoices")

        // paymentHashIndexBucket is the name of the sub-bucket within the
        // invoiceBucket which indexes all invoices by their payment hash. The
        // payment hash is the sha256 of the invoice's payment preimage. This
        // index is used to detect duplicates, and also to provide a fast path
        // for looking up incoming HTLCs to determine if we're able to settle
        // them fully.
        //
        // maps: payHash => invoiceKey
        invoiceIndexBucket = []byte("paymenthashes")

        // payAddrIndexBucket is the name of the top-level bucket that maps
        // payment addresses to their invoice number. This can be used
        // to efficiently query or update non-legacy invoices. Note that legacy
        // invoices will not be included in this index since they all have the
        // same, all-zero payment address, however all newly generated invoices
        // will end up in this index.
        //
        // maps: payAddr => invoiceKey
        payAddrIndexBucket = []byte("pay-addr-index")

        // setIDIndexBucket is the name of the top-level bucket that maps set
        // ids to their invoice number. This can be used to efficiently query or
        // update AMP invoice. Note that legacy or MPP invoices will not be
        // included in this index, since their HTLCs do not have a set id.
        //
        // maps: setID => invoiceKey
        setIDIndexBucket = []byte("set-id-index")

        // numInvoicesKey is the name of key which houses the auto-incrementing
        // invoice ID which is essentially used as a primary key. With each
        // invoice inserted, the primary key is incremented by one. This key is
        // stored within the invoiceIndexBucket. Within the invoiceBucket
        // invoices are uniquely identified by the invoice ID.
        numInvoicesKey = []byte("nik")

        // addIndexBucket is an index bucket that we'll use to create a
        // monotonically increasing set of add indexes. Each time we add a new
        // invoice, this sequence number will be incremented and then populated
        // within the new invoice.
        //
        // In addition to this sequence number, we map:
        //
        //   addIndexNo => invoiceKey
        addIndexBucket = []byte("invoice-add-index")

        // settleIndexBucket is an index bucket that we'll use to create a
        // monotonically increasing integer for tracking a "settle index". Each
        // time an invoice is settled, this sequence number will be incremented
        // as populate within the newly settled invoice.
        //
        // In addition to this sequence number, we map:
        //
        //   settleIndexNo => invoiceKey
        settleIndexBucket = []byte("invoice-settle-index")
)

const (
        // A set of tlv type definitions used to serialize invoice htlcs to the
        // database.
        //
        // NOTE: A migration should be added whenever this list changes. This
        // prevents against the database being rolled back to an older
        // format where the surrounding logic might assume a different set of
        // fields are known.
        chanIDType       tlv.Type = 1
        htlcIDType       tlv.Type = 3
        amtType          tlv.Type = 5
        acceptHeightType tlv.Type = 7
        acceptTimeType   tlv.Type = 9
        resolveTimeType  tlv.Type = 11
        expiryHeightType tlv.Type = 13
        htlcStateType    tlv.Type = 15
        mppTotalAmtType  tlv.Type = 17
        htlcAMPType      tlv.Type = 19
        htlcHashType     tlv.Type = 21
        htlcPreimageType tlv.Type = 23

        // A set of tlv type definitions used to serialize invoice bodiees.
        //
        // NOTE: A migration should be added whenever this list changes. This
        // prevents against the database being rolled back to an older
        // format where the surrounding logic might assume a different set of
        // fields are known.
        memoType            tlv.Type = 0
        payReqType          tlv.Type = 1
        createTimeType      tlv.Type = 2
        settleTimeType      tlv.Type = 3
        addIndexType        tlv.Type = 4
        settleIndexType     tlv.Type = 5
        preimageType        tlv.Type = 6
        valueType           tlv.Type = 7
        cltvDeltaType       tlv.Type = 8
        expiryType          tlv.Type = 9
        paymentAddrType     tlv.Type = 10
        featuresType        tlv.Type = 11
        invStateType        tlv.Type = 12
        amtPaidType         tlv.Type = 13
        hodlInvoiceType     tlv.Type = 14
        invoiceAmpStateType tlv.Type = 15

        // A set of tlv type definitions used to serialize the invoice AMP
        // state along-side the main invoice body.
        ampStateSetIDType       tlv.Type = 0
        ampStateHtlcStateType   tlv.Type = 1
        ampStateSettleIndexType tlv.Type = 2
        ampStateSettleDateType  tlv.Type = 3
        ampStateCircuitKeysType tlv.Type = 4
        ampStateAmtPaidType     tlv.Type = 5
)

// AddInvoice inserts the targeted invoice into the database. If the invoice has
// *any* payment hashes which already exists within the database, then the
// insertion will be aborted and rejected due to the strict policy banning any
// duplicate payment hashes. A side effect of this function is that it sets
// AddIndex on newInvoice.
func (d *DB) AddInvoice(_ context.Context, newInvoice *invpkg.Invoice,
        paymentHash lntypes.Hash) (uint64, error) {

        if err := invpkg.ValidateInvoice(newInvoice, paymentHash); err != nil {
                return 0, err
        }

        var invoiceAddIndex uint64
        err := kvdb.Update(d, func(tx kvdb.RwTx) error {
                invoices, err := tx.CreateTopLevelBucket(invoiceBucket)
                if err != nil {
                        return err
                }

                invoiceIndex, err := invoices.CreateBucketIfNotExists(
                        invoiceIndexBucket,
                )
                if err != nil {
                        return err
                }
                addIndex, err := invoices.CreateBucketIfNotExists(
                        addIndexBucket,
                )
                if err != nil {
                        return err
                }

                // Ensure that an invoice an identical payment hash doesn't
                // already exist within the index.
                if invoiceIndex.Get(paymentHash[:]) != nil {
                        return invpkg.ErrDuplicateInvoice
                }

                // Check that we aren't inserting an invoice with a duplicate
                // payment address. The all-zeros payment address is
                // special-cased to support legacy keysend invoices which don't
                // assign one. This is safe since later we also will avoid
                // indexing them and avoid collisions.
                payAddrIndex := tx.ReadWriteBucket(payAddrIndexBucket)
                if newInvoice.Terms.PaymentAddr != invpkg.BlankPayAddr {
                        paymentAddr := newInvoice.Terms.PaymentAddr[:]
                        if payAddrIndex.Get(paymentAddr) != nil {
                                return invpkg.ErrDuplicatePayAddr
                        }
                }

                // If the current running payment ID counter hasn't yet been
                // created, then create it now.
                var invoiceNum uint32
                invoiceCounter := invoiceIndex.Get(numInvoicesKey)
                if invoiceCounter == nil {
                        var scratch [4]byte
                        byteOrder.PutUint32(scratch[:], invoiceNum)
                        err := invoiceIndex.Put(numInvoicesKey, scratch[:])
                        if err != nil {
                                return err
                        }
                } else {
                        invoiceNum = byteOrder.Uint32(invoiceCounter)
                }

                newIndex, err := putInvoice(
                        invoices, invoiceIndex, payAddrIndex, addIndex,
                        newInvoice, invoiceNum, paymentHash,
                )
                if err != nil {
                        return err
                }

                invoiceAddIndex = newIndex
                return nil
        }, func() {
                invoiceAddIndex = 0
        })
        if err != nil {
                return 0, err
        }

        return invoiceAddIndex, err
}

// InvoicesAddedSince can be used by callers to seek into the event time series
// of all the invoices added in the database. The specified sinceAddIndex
// should be the highest add index that the caller knows of. This method will
// return all invoices with an add index greater than the specified
// sinceAddIndex.
//
// NOTE: The index starts from 1, as a result. We enforce that specifying a
// value below the starting index value is a noop.
func (d *DB) InvoicesAddedSince(_ context.Context, sinceAddIndex uint64) (
        []invpkg.Invoice, error) {

        var newInvoices []invpkg.Invoice

        // If an index of zero was specified, then in order to maintain
        // backwards compat, we won't send out any new invoices.
        if sinceAddIndex == 0 {
                return newInvoices, nil
        }

        var startIndex [8]byte
        byteOrder.PutUint64(startIndex[:], sinceAddIndex)

        err := kvdb.View(d, func(tx kvdb.RTx) error {
                invoices := tx.ReadBucket(invoiceBucket)
                if invoices == nil {
                        return nil
                }

                addIndex := invoices.NestedReadBucket(addIndexBucket)
                if addIndex == nil {
                        return nil
                }

                // We'll now run through each entry in the add index starting
                // at our starting index. We'll continue until we reach the
                // very end of the current key space.
                invoiceCursor := addIndex.ReadCursor()

                // We'll seek to the starting index, then manually advance the
                // cursor in order to skip the entry with the since add index.
                invoiceCursor.Seek(startIndex[:])
                addSeqNo, invoiceKey := invoiceCursor.Next()

                for ; addSeqNo != nil && bytes.Compare(addSeqNo, startIndex[:]) > 0; addSeqNo, invoiceKey = invoiceCursor.Next() {

                        // For each key found, we'll look up the actual
                        // invoice, then accumulate it into our return value.
                        invoice, err := fetchInvoice(
                                invoiceKey, invoices, nil, false,
                        )
                        if err != nil {
                                return err
                        }

                        newInvoices = append(newInvoices, invoice)
                }

                return nil
        }, func() {
                newInvoices = nil
        })
        if err != nil {
                return nil, err
        }

        return newInvoices, nil
}

// LookupInvoice attempts to look up an invoice according to its 32 byte
// payment hash. If an invoice which can settle the HTLC identified by the
// passed payment hash isn't found, then an error is returned. Otherwise, the
// full invoice is returned. Before setting the incoming HTLC, the values
// SHOULD be checked to ensure the payer meets the agreed upon contractual
// terms of the payment.
func (d *DB) LookupInvoice(_ context.Context, ref invpkg.InvoiceRef) (
        invpkg.Invoice, error) {

        var invoice invpkg.Invoice
        err := kvdb.View(d, func(tx kvdb.RTx) error {
                invoices := tx.ReadBucket(invoiceBucket)
                if invoices == nil {
                        return invpkg.ErrNoInvoicesCreated
                }
                invoiceIndex := invoices.NestedReadBucket(invoiceIndexBucket)
                if invoiceIndex == nil {
                        return invpkg.ErrNoInvoicesCreated
                }
                payAddrIndex := tx.ReadBucket(payAddrIndexBucket)
                setIDIndex := tx.ReadBucket(setIDIndexBucket)

                // Retrieve the invoice number for this invoice using
                // the provided invoice reference.
                invoiceNum, err := fetchInvoiceNumByRef(
                        invoiceIndex, payAddrIndex, setIDIndex, ref,
                )
                if err != nil {
                        return err
                }

                var setID *invpkg.SetID
                switch {
                // If this is a payment address ref, and the blank modified was
                // specified, then we'll use the zero set ID to indicate that
                // we won't want any HTLCs returned.
                case ref.PayAddr() != nil &&
                        ref.Modifier() == invpkg.HtlcSetBlankModifier:

                        var zeroSetID invpkg.SetID
                        setID = &zeroSetID

                // If this is a set ID ref, and the htlc set only modified was
                // specified, then we'll pass through the specified setID so
                // only that will be returned.
                case ref.SetID() != nil &&
                        ref.Modifier() == invpkg.HtlcSetOnlyModifier:

                        setID = (*invpkg.SetID)(ref.SetID())
                }

                // An invoice was found, retrieve the remainder of the invoice
                // body.
                i, err := fetchInvoice(
                        invoiceNum, invoices, []*invpkg.SetID{setID}, true,
                )
                if err != nil {
                        return err
                }
                invoice = i

                return nil
        }, func() {})
        if err != nil {
                return invoice, err
        }

        return invoice, nil
}

// fetchInvoiceNumByRef retrieve the invoice number for the provided invoice
// reference. The payment address will be treated as the primary key, falling
// back to the payment hash if nothing is found for the payment address. An
// error is returned if the invoice is not found.
func fetchInvoiceNumByRef(invoiceIndex, payAddrIndex, setIDIndex kvdb.RBucket,
        ref invpkg.InvoiceRef) ([]byte, error) {

        // If the set id is present, we only consult the set id index for this
        // invoice. This type of query is only used to facilitate user-facing
        // requests to lookup, settle or cancel an AMP invoice.
        setID := ref.SetID()
        if setID != nil {
                invoiceNumBySetID := setIDIndex.Get(setID[:])
                if invoiceNumBySetID == nil {
                        return nil, invpkg.ErrInvoiceNotFound
                }

                return invoiceNumBySetID, nil
        }

        payHash := ref.PayHash()
        payAddr := ref.PayAddr()

        getInvoiceNumByHash := func() []byte {
                if payHash != nil {
                        return invoiceIndex.Get(payHash[:])
                }
                return nil
        }

        getInvoiceNumByAddr := func() []byte {
                if payAddr != nil {
                        // Only allow lookups for payment address if it is not a
                        // blank payment address, which is a special-cased value
                        // for legacy keysend invoices.
                        if *payAddr != invpkg.BlankPayAddr {
                                return payAddrIndex.Get(payAddr[:])
                        }
                }
                return nil
        }

        invoiceNumByHash := getInvoiceNumByHash()
        invoiceNumByAddr := getInvoiceNumByAddr()
        switch {
        // If payment address and payment hash both reference an existing
        // invoice, ensure they reference the _same_ invoice.
        case invoiceNumByAddr != nil && invoiceNumByHash != nil:
                if !bytes.Equal(invoiceNumByAddr, invoiceNumByHash) {
                        return nil, invpkg.ErrInvRefEquivocation
                }

                return invoiceNumByAddr, nil

        // Return invoices by payment addr only.
        //
        // NOTE: We constrain this lookup to only apply if the invoice ref does
        // not contain a payment hash. Legacy and MPP payments depend on the
        // payment hash index to enforce that the HTLCs payment hash matches the
        // payment hash for the invoice, without this check we would
        // inadvertently assume the invoice contains the correct preimage for
        // the HTLC, which we only enforce via the lookup by the invoice index.
        case invoiceNumByAddr != nil && payHash == nil:
                return invoiceNumByAddr, nil

        // If we were only able to reference the invoice by hash, return the
        // corresponding invoice number. This can happen when no payment address
        // was provided, or if it didn't match anything in our records.
        case invoiceNumByHash != nil:
                return invoiceNumByHash, nil

        // Otherwise we don't know of the target invoice.
        default:
                return nil, invpkg.ErrInvoiceNotFound
        }
}

// FetchPendingInvoices returns all invoices that have not yet been settled or
// canceled. The returned map is keyed by the payment hash of each respective
// invoice.
func (d *DB) FetchPendingInvoices(_ context.Context) (
        map[lntypes.Hash]invpkg.Invoice, error) {

        result := make(map[lntypes.Hash]invpkg.Invoice)

        err := kvdb.View(d, func(tx kvdb.RTx) error {
                invoices := tx.ReadBucket(invoiceBucket)
                if invoices == nil {
                        return nil
                }

                invoiceIndex := invoices.NestedReadBucket(invoiceIndexBucket)
                if invoiceIndex == nil {
                        // Mask the error if there's no invoice
                        // index as that simply means there are no
                        // invoices added yet to the DB. In this case
                        // we simply return an empty list.
                        return nil
                }

                return invoiceIndex.ForEach(func(k, v []byte) error {
                        // Skip the special numInvoicesKey as that does not
                        // point to a valid invoice.
                        if bytes.Equal(k, numInvoicesKey) {
                                return nil
                        }

                        // Skip sub-buckets.
                        if v == nil {
                                return nil
                        }

                        invoice, err := fetchInvoice(v, invoices, nil, false)
                        if err != nil {
                                return err
                        }

                        if invoice.IsPending() {
                                var paymentHash lntypes.Hash
                                copy(paymentHash[:], k)
                                result[paymentHash] = invoice
                        }

                        return nil
                })
        }, func() {
                result = make(map[lntypes.Hash]invpkg.Invoice)
        })

        if err != nil {
                return nil, err
        }

        return result, nil
}

// QueryInvoices allows a caller to query the invoice database for invoices
// within the specified add index range.
func (d *DB) QueryInvoices(_ context.Context, q invpkg.InvoiceQuery) (
        invpkg.InvoiceSlice, error) {

        var resp invpkg.InvoiceSlice

        err := kvdb.View(d, func(tx kvdb.RTx) error {
                // If the bucket wasn't found, then there aren't any invoices
                // within the database yet, so we can simply exit.
                invoices := tx.ReadBucket(invoiceBucket)
                if invoices == nil {
                        return invpkg.ErrNoInvoicesCreated
                }

                // Get the add index bucket which we will use to iterate through
                // our indexed invoices.
                invoiceAddIndex := invoices.NestedReadBucket(addIndexBucket)
                if invoiceAddIndex == nil {
                        return invpkg.ErrNoInvoicesCreated
                }

                // Create a paginator which reads from our add index bucket with
                // the parameters provided by the invoice query.
                paginator := newPaginator(
                        invoiceAddIndex.ReadCursor(), q.Reversed, q.IndexOffset,
                        q.NumMaxInvoices,
                )

                // accumulateInvoices looks up an invoice based on the index we
                // are given, adds it to our set of invoices if it has the right
                // characteristics for our query and returns the number of items
                // we have added to our set of invoices.
                accumulateInvoices := func(_, indexValue []byte) (bool, error) {
                        invoice, err := fetchInvoice(
                                indexValue, invoices, nil, false,
                        )
                        if err != nil {
                                return false, err
                        }

                        // Skip any settled or canceled invoices if the caller
                        // is only interested in pending ones.
                        if q.PendingOnly && !invoice.IsPending() {
                                return false, nil
                        }

                        // Get the creation time in Unix seconds, this always
                        // rounds down the nanoseconds to full seconds.
                        createTime := invoice.CreationDate.Unix()

                        // Skip any invoices that were created before the
                        // specified time.
                        if createTime < q.CreationDateStart {
                                return false, nil
                        }

                        // Skip any invoices that were created after the
                        // specified time.
                        if q.CreationDateEnd != 0 &&
                                createTime > q.CreationDateEnd {

                                return false, nil
                        }

                        // At this point, we've exhausted the offset, so we'll
                        // begin collecting invoices found within the range.
                        resp.Invoices = append(resp.Invoices, invoice)

                        return true, nil
                }

                // Query our paginator using accumulateInvoices to build up a
                // set of invoices.
                if err := paginator.query(accumulateInvoices); err != nil {
                        return err
                }

                // If we iterated through the add index in reverse order, then
                // we'll need to reverse the slice of invoices to return them in
                // forward order.
                if q.Reversed {
                        numInvoices := len(resp.Invoices)
                        for i := 0; i < numInvoices/2; i++ {
                                reverse := numInvoices - i - 1
                                resp.Invoices[i], resp.Invoices[reverse] =
                                        resp.Invoices[reverse], resp.Invoices[i]
                        }
                }

                return nil
        }, func() {
                resp = invpkg.InvoiceSlice{
                        InvoiceQuery: q,
                }
        })
        if err != nil && !errors.Is(err, invpkg.ErrNoInvoicesCreated) {
                return resp, err
        }

        // Finally, record the indexes of the first and last invoices returned
        // so that the caller can resume from this point later on.
        if len(resp.Invoices) > 0 {
                resp.FirstIndexOffset = resp.Invoices[0].AddIndex
                lastIdx := len(resp.Invoices) - 1
                resp.LastIndexOffset = resp.Invoices[lastIdx].AddIndex
        }

        return resp, nil
}

// UpdateInvoice attempts to update an invoice corresponding to the passed
// payment hash. If an invoice matching the passed payment hash doesn't exist
// within the database, then the action will fail with a "not found" error.
//
// The update is performed inside the same database transaction that fetches the
// invoice and is therefore atomic. The fields to update are controlled by the
// supplied callback.  When updating an invoice, the update itself happens
// in-memory on a copy of the invoice. Once it is written successfully to the
// database, the in-memory copy is returned to the caller.
func (d *DB) UpdateInvoice(_ context.Context, ref invpkg.InvoiceRef,
        setIDHint *invpkg.SetID, callback invpkg.InvoiceUpdateCallback) (
        *invpkg.Invoice, error) {

        var updatedInvoice *invpkg.Invoice
        err := kvdb.Update(d, func(tx kvdb.RwTx) error {
                invoices, err := tx.CreateTopLevelBucket(invoiceBucket)
                if err != nil {
                        return err
                }
                invoiceIndex, err := invoices.CreateBucketIfNotExists(
                        invoiceIndexBucket,
                )
                if err != nil {
                        return err
                }
                settleIndex, err := invoices.CreateBucketIfNotExists(
                        settleIndexBucket,
                )
                if err != nil {
                        return err
                }
                payAddrIndex := tx.ReadBucket(payAddrIndexBucket)
                setIDIndex := tx.ReadWriteBucket(setIDIndexBucket)

                // Retrieve the invoice number for this invoice using the
                // provided invoice reference.
                invoiceNum, err := fetchInvoiceNumByRef(
                        invoiceIndex, payAddrIndex, setIDIndex, ref,
                )
                if err != nil {
                        return err
                }

                // setIDHint can also be nil here, which means all the HTLCs
                // for AMP invoices are fetched. If the blank setID is passed
                // in, then no HTLCs are fetched for the AMP invoice. If a
                // specific setID is passed in, then only the HTLCs for that
                // setID are fetched for a particular sub-AMP invoice.
                invoice, err := fetchInvoice(
                        invoiceNum, invoices, []*invpkg.SetID{setIDHint}, false,
                )
                if err != nil {
                        return err
                }

                now := d.clock.Now()
                updater := &kvInvoiceUpdater{
                        db:                d,
                        invoicesBucket:    invoices,
                        settleIndexBucket: settleIndex,
                        setIDIndexBucket:  setIDIndex,
                        updateTime:        now,
                        invoiceNum:        invoiceNum,
                        invoice:           &invoice,
                        updatedAmpHtlcs:   make(ampHTLCsMap),
                        settledSetIDs:     make(map[invpkg.SetID]struct{}),
                }

                payHash := ref.PayHash()
                updatedInvoice, err = invpkg.UpdateInvoice(
                        payHash, updater.invoice, now, callback, updater,
                )
                if err != nil {
                        return err
                }

                // If this is an AMP update, then limit the returned AMP state
                // to only the requested set ID.
                if setIDHint != nil {
                        filterInvoiceAMPState(updatedInvoice, setIDHint)
                }

                return nil
        }, func() {
                updatedInvoice = nil
        })

        return updatedInvoice, err
}

// filterInvoiceAMPState filters the AMP state of the invoice to only include
// state for the specified set IDs.
func filterInvoiceAMPState(invoice *invpkg.Invoice, setIDs ...*invpkg.SetID) {
        filteredAMPState := make(invpkg.AMPInvoiceState)

        for _, setID := range setIDs {
                if setID == nil {
                        return
                }

                ampState, ok := invoice.AMPState[*setID]
                if ok {
                        filteredAMPState[*setID] = ampState
                }
        }

        invoice.AMPState = filteredAMPState
}

// ampHTLCsMap is a map of AMP HTLCs affected by an invoice update.
type ampHTLCsMap map[invpkg.SetID]map[models.CircuitKey]*invpkg.InvoiceHTLC

// kvInvoiceUpdater is an implementation of the InvoiceUpdater interface that
// is used with the kv implementation of the invoice database. Note that this
// updater is not concurrency safe and synchronizaton is expected to be handled
// on the DB level.
type kvInvoiceUpdater struct {
        db                *DB
        invoicesBucket    kvdb.RwBucket
        settleIndexBucket kvdb.RwBucket
        setIDIndexBucket  kvdb.RwBucket

        // updateTime is the timestamp for the update.
        updateTime time.Time

        // invoiceNum is a legacy key similar to the add index that is used
        // only in the kv implementation.
        invoiceNum []byte

        // invoice is the invoice that we're updating. As a side effect of the
        // update this invoice will be mutated.
        invoice *invpkg.Invoice

        // updatedAmpHtlcs holds the set of AMP HTLCs that were added or
        // cancelled as part of this update.
        updatedAmpHtlcs ampHTLCsMap

        // settledSetIDs holds the set IDs that are settled with this update.
        settledSetIDs map[invpkg.SetID]struct{}
}

// NOTE: this method does nothing in the k/v implementation of InvoiceUpdater.
func (k *kvInvoiceUpdater) AddHtlc(_ models.CircuitKey,
        _ *invpkg.InvoiceHTLC) error {

        return nil
}

// NOTE: this method does nothing in the k/v implementation of InvoiceUpdater.
func (k *kvInvoiceUpdater) ResolveHtlc(_ models.CircuitKey, _ invpkg.HtlcState,
        _ time.Time) error {

        return nil
}

// NOTE: this method does nothing in the k/v implementation of InvoiceUpdater.
func (k *kvInvoiceUpdater) AddAmpHtlcPreimage(_ [32]byte, _ models.CircuitKey,
        _ lntypes.Preimage) error {

        return nil
}

// NOTE: this method does nothing in the k/v implementation of InvoiceUpdater.
func (k *kvInvoiceUpdater) UpdateInvoiceState(_ invpkg.ContractState,
        _ *lntypes.Preimage) error {

        return nil
}

// NOTE: this method does nothing in the k/v implementation of InvoiceUpdater.
func (k *kvInvoiceUpdater) UpdateInvoiceAmtPaid(_ lnwire.MilliSatoshi) error {
        return nil
}

// UpdateAmpState updates the state of the AMP invoice identified by the setID.
func (k *kvInvoiceUpdater) UpdateAmpState(setID [32]byte,
        state invpkg.InvoiceStateAMP, circuitKey models.CircuitKey) error {

        if _, ok := k.updatedAmpHtlcs[setID]; !ok {
                switch state.State {
                case invpkg.HtlcStateAccepted:
                        // If we're just now creating the HTLCs for this set
                        // then we'll also pull in the existing HTLCs that are
                        // part of this set, so we can write them all to disk
                        // together (same value)
                        k.updatedAmpHtlcs[setID] = k.invoice.HTLCSet(
                                &setID, invpkg.HtlcStateAccepted,
                        )

                case invpkg.HtlcStateCanceled:
                        // Only HTLCs in the accepted state, can be cancelled,
                        // but we also want to merge that with HTLCs that may be
                        // canceled as well since it can be cancelled one by
                        // one.
                        k.updatedAmpHtlcs[setID] = k.invoice.HTLCSet(
                                &setID, invpkg.HtlcStateAccepted,
                        )

                        cancelledHtlcs := k.invoice.HTLCSet(
                                &setID, invpkg.HtlcStateCanceled,
                        )
                        for htlcKey, htlc := range cancelledHtlcs {
                                k.updatedAmpHtlcs[setID][htlcKey] = htlc
                        }

                case invpkg.HtlcStateSettled:
                        k.updatedAmpHtlcs[setID] = make(
                                map[models.CircuitKey]*invpkg.InvoiceHTLC,
                        )
                }
        }

        if state.State == invpkg.HtlcStateSettled {
                // Add the set ID to the set that was settled in this invoice
                // update. We'll use this later to update the settle index.
                k.settledSetIDs[setID] = struct{}{}
        }

        k.updatedAmpHtlcs[setID][circuitKey] = k.invoice.Htlcs[circuitKey]

        return nil
}

// Finalize finalizes the update before it is written to the database.
func (k *kvInvoiceUpdater) Finalize(updateType invpkg.UpdateType) error {
        switch updateType {
        case invpkg.AddHTLCsUpdate:
                return k.storeAddHtlcsUpdate()

        case invpkg.CancelHTLCsUpdate:
                return k.storeCancelHtlcsUpdate()

        case invpkg.SettleHodlInvoiceUpdate:
                return k.storeSettleHodlInvoiceUpdate()

        case invpkg.CancelInvoiceUpdate:
                // Persist all changes which where made when cancelling the
                // invoice. All HTLCs which were accepted are now canceled, so
                // we persist this state.
                return k.storeCancelHtlcsUpdate()
        }

        return fmt.Errorf("unknown update type: %v", updateType)
}

// storeCancelHtlcsUpdate updates the invoice in the database after cancelling a
// set of HTLCs.
func (k *kvInvoiceUpdater) storeCancelHtlcsUpdate() error {
        err := k.serializeAndStoreInvoice()
        if err != nil {
                return err
        }

        // If this is an AMP invoice, then we'll actually store the rest
        // of the HTLCs in-line with the invoice, using the invoice ID
        // as a prefix, and the AMP key as a suffix: invoiceNum ||
        // setID.
        if k.invoice.IsAMP() {
                return k.updateAMPInvoices()
        }

        return nil
}

// storeAddHtlcsUpdate updates the invoice in the database after adding a set of
// HTLCs.
func (k *kvInvoiceUpdater) storeAddHtlcsUpdate() error {
        invoiceIsAMP := k.invoice.IsAMP()

        for htlcSetID := range k.updatedAmpHtlcs {
                // Check if this SetID already exist.
                setIDInvNum := k.setIDIndexBucket.Get(htlcSetID[:])

                if setIDInvNum == nil {
                        err := k.setIDIndexBucket.Put(
                                htlcSetID[:], k.invoiceNum,
                        )
                        if err != nil {
                                return err
                        }
                } else if !bytes.Equal(setIDInvNum, k.invoiceNum) {
                        return invpkg.ErrDuplicateSetID{
                                SetID: htlcSetID,
                        }
                }
        }

        // If this is a non-AMP invoice, then the state can eventually go to
        // ContractSettled, so we pass in nil value as part of
        // setSettleMetaFields.
        if !invoiceIsAMP && k.invoice.State == invpkg.ContractSettled {
                err := k.setSettleMetaFields(nil)
                if err != nil {
                        return err
                }
        }

        // As we don't update the settle index above for AMP invoices, we'll do
        // it here for each sub-AMP invoice that was settled.
        for settledSetID := range k.settledSetIDs {
                settledSetID := settledSetID
                err := k.setSettleMetaFields(&settledSetID)
                if err != nil {
                        return err
                }
        }

        err := k.serializeAndStoreInvoice()
        if err != nil {
                return err
        }

        // If this is an AMP invoice, then we'll actually store the rest of the
        // HTLCs in-line with the invoice, using the invoice ID as a prefix,
        // and the AMP key as a suffix: invoiceNum || setID.
        if invoiceIsAMP {
                return k.updateAMPInvoices()
        }

        return nil
}

// storeSettleHodlInvoiceUpdate updates the invoice in the database after
// settling a hodl invoice.
func (k *kvInvoiceUpdater) storeSettleHodlInvoiceUpdate() error {
        err := k.setSettleMetaFields(nil)
        if err != nil {
                return err
        }

        return k.serializeAndStoreInvoice()
}

// setSettleMetaFields updates the metadata associated with settlement of an
// invoice. If a non-nil setID is passed in, then the value will be append to
// the invoice number as well, in order to allow us to detect repeated payments
// to the same AMP invoices "across time".
func (k *kvInvoiceUpdater) setSettleMetaFields(setID *invpkg.SetID) error {
        // Now that we know the invoice hasn't already been settled, we'll
        // update the settle index so we can place this settle event in the
        // proper location within our time series.
        nextSettleSeqNo, err := k.settleIndexBucket.NextSequence()
        if err != nil {
                return err
        }

        // Make a new byte array on the stack that can potentially store the 4
        // byte invoice number along w/ the 32 byte set ID. We capture valueLen
        // here which is the number of bytes copied so we can only store the 4
        // bytes if this is a non-AMP invoice.
        var indexKey [invoiceSetIDKeyLen]byte
        valueLen := copy(indexKey[:], k.invoiceNum)

        if setID != nil {
                valueLen += copy(indexKey[valueLen:], setID[:])
        }

        var seqNoBytes [8]byte
        byteOrder.PutUint64(seqNoBytes[:], nextSettleSeqNo)
        err = k.settleIndexBucket.Put(seqNoBytes[:], indexKey[:valueLen])
        if err != nil {
                return err
        }

        // If the setID is nil, then this means that this is a non-AMP settle,
        // so we'll update the invoice settle index directly.
        if setID == nil {
                k.invoice.SettleDate = k.updateTime
                k.invoice.SettleIndex = nextSettleSeqNo
        } else {
                // If the set ID isn't blank, we'll update the AMP state map
                // which tracks when each of the setIDs associated with a given
                // AMP invoice are settled.
                ampState := k.invoice.AMPState[*setID]

                ampState.SettleDate = k.updateTime
                ampState.SettleIndex = nextSettleSeqNo

                k.invoice.AMPState[*setID] = ampState
        }

        return nil
}

// updateAMPInvoices updates the set of AMP invoices in-place. For AMP, rather
// then continually write the invoices to the end of the invoice value, we
// instead write the invoices into a new key preifx that follows the main
// invoice number. This ensures that we don't need to continually decode a
// potentially massive HTLC set, and also allows us to quickly find the HLTCs
// associated with a particular HTLC set.
func (k *kvInvoiceUpdater) updateAMPInvoices() error {
        for setID, htlcSet := range k.updatedAmpHtlcs {
                // First write out the set of HTLCs including all the relevant
                // TLV values.
                var b bytes.Buffer
                if err := serializeHtlcs(&b, htlcSet); err != nil {
                        return err
                }

                // Next store each HTLC in-line, using a prefix based off the
                // invoice number.
                invoiceSetIDKey := makeInvoiceSetIDKey(k.invoiceNum, setID[:])

                err := k.invoicesBucket.Put(invoiceSetIDKey[:], b.Bytes())
                if err != nil {
                        return err
                }
        }

        return nil
}

// serializeAndStoreInvoice is a helper function used to store invoices.
func (k *kvInvoiceUpdater) serializeAndStoreInvoice() error {
        var buf bytes.Buffer
        if err := serializeInvoice(&buf, k.invoice); err != nil {
                return err
        }

        return k.invoicesBucket.Put(k.invoiceNum, buf.Bytes())
}

// InvoicesSettledSince can be used by callers to catch up any settled invoices
// they missed within the settled invoice time series. We'll return all known
// settled invoice that have a settle index higher than the passed
// sinceSettleIndex.
//
// NOTE: The index starts from 1, as a result. We enforce that specifying a
// value below the starting index value is a noop.
func (d *DB) InvoicesSettledSince(_ context.Context, sinceSettleIndex uint64) (
        []invpkg.Invoice, error) {

        var settledInvoices []invpkg.Invoice

        // If an index of zero was specified, then in order to maintain
        // backwards compat, we won't send out any new invoices.
        if sinceSettleIndex == 0 {
                return settledInvoices, nil
        }

        var startIndex [8]byte
        byteOrder.PutUint64(startIndex[:], sinceSettleIndex)

        err := kvdb.View(d, func(tx kvdb.RTx) error {
                invoices := tx.ReadBucket(invoiceBucket)
                if invoices == nil {
                        return nil
                }

                settleIndex := invoices.NestedReadBucket(settleIndexBucket)
                if settleIndex == nil {
                        return nil
                }

                // We'll now run through each entry in the add index starting
                // at our starting index. We'll continue until we reach the
                // very end of the current key space.
                invoiceCursor := settleIndex.ReadCursor()

                // We'll seek to the starting index, then manually advance the
                // cursor in order to skip the entry with the since add index.
                invoiceCursor.Seek(startIndex[:])
                seqNo, indexValue := invoiceCursor.Next()

                for ; seqNo != nil && bytes.Compare(seqNo, startIndex[:]) > 0; seqNo, indexValue = invoiceCursor.Next() {
                        // Depending on the length of the index value, this may
                        // or may not be an AMP invoice, so we'll extract the
                        // invoice value into two components: the invoice num,
                        // and the setID (may not be there).
                        var (
                                invoiceKey [4]byte
                                setID      *invpkg.SetID
                        )

                        valueLen := copy(invoiceKey[:], indexValue)
                        if len(indexValue) == invoiceSetIDKeyLen {
                                setID = new(invpkg.SetID)
                                copy(setID[:], indexValue[valueLen:])
                        }

                        // For each key found, we'll look up the actual
                        // invoice, then accumulate it into our return value.
                        invoice, err := fetchInvoice(
                                invoiceKey[:], invoices, []*invpkg.SetID{setID},
                                true,
                        )
                        if err != nil {
                                return err
                        }

                        settledInvoices = append(settledInvoices, invoice)
                }

                return nil
        }, func() {
                settledInvoices = nil
        })
        if err != nil {
                return nil, err
        }

        return settledInvoices, nil
}

func putInvoice(invoices, invoiceIndex, payAddrIndex, addIndex kvdb.RwBucket,
        i *invpkg.Invoice, invoiceNum uint32, paymentHash lntypes.Hash) (
        uint64, error) {

        // Create the invoice key which is just the big-endian representation
        // of the invoice number.
        var invoiceKey [4]byte
        byteOrder.PutUint32(invoiceKey[:], invoiceNum)

        // Increment the num invoice counter index so the next invoice bares
        // the proper ID.
        var scratch [4]byte
        invoiceCounter := invoiceNum + 1
        byteOrder.PutUint32(scratch[:], invoiceCounter)
        if err := invoiceIndex.Put(numInvoicesKey, scratch[:]); err != nil {
                return 0, err
        }

        // Add the payment hash to the invoice index. This will let us quickly
        // identify if we can settle an incoming payment, and also to possibly
        // allow a single invoice to have multiple payment installations.
        err := invoiceIndex.Put(paymentHash[:], invoiceKey[:])
        if err != nil {
                return 0, err
        }

        // Add the invoice to the payment address index, but only if the invoice
        // has a non-zero payment address. The all-zero payment address is still
        // in use by legacy keysend, so we special-case here to avoid
        // collisions.
        if i.Terms.PaymentAddr != invpkg.BlankPayAddr {
                err = payAddrIndex.Put(i.Terms.PaymentAddr[:], invoiceKey[:])
                if err != nil {
                        return 0, err
                }
        }

        // Next, we'll obtain the next add invoice index (sequence
        // number), so we can properly place this invoice within this
        // event stream.
        nextAddSeqNo, err := addIndex.NextSequence()
        if err != nil {
                return 0, err
        }

        // With the next sequence obtained, we'll updating the event series in
        // the add index bucket to map this current add counter to the index of
        // this new invoice.
        var seqNoBytes [8]byte
        byteOrder.PutUint64(seqNoBytes[:], nextAddSeqNo)
        if err := addIndex.Put(seqNoBytes[:], invoiceKey[:]); err != nil {
                return 0, err
        }

        i.AddIndex = nextAddSeqNo

        // Finally, serialize the invoice itself to be written to the disk.
        var buf bytes.Buffer
        if err := serializeInvoice(&buf, i); err != nil {
                return 0, err
        }

        if err := invoices.Put(invoiceKey[:], buf.Bytes()); err != nil {
                return 0, err
        }

        return nextAddSeqNo, nil
}

// recordSize returns the amount of bytes this TLV record will occupy when
// encoded.
func ampRecordSize(a *invpkg.AMPInvoiceState) func() uint64 {
        var (
                b   bytes.Buffer
                buf [8]byte
        )

        // We know that encoding works since the tests pass in the build this
        // file is checked into, so we'll simplify things and simply encode it
        // ourselves then report the total amount of bytes used.
        if err := ampStateEncoder(&b, a, &buf); err != nil {
                // This should never error out, but we log it just in case it
                // does.
                log.Errorf("encoding the amp invoice state failed: %v", err)
        }

        return func() uint64 {
                return uint64(len(b.Bytes()))
        }
}

// serializeInvoice serializes an invoice to a writer.
//
// Note: this function is in use for a migration. Before making changes that
// would modify the on disk format, make a copy of the original code and store
// it with the migration.
func serializeInvoice(w io.Writer, i *invpkg.Invoice) error {
        creationDateBytes, err := i.CreationDate.MarshalBinary()
        if err != nil {
                return err
        }

        settleDateBytes, err := i.SettleDate.MarshalBinary()
        if err != nil {
                return err
        }

        var fb bytes.Buffer
        err = i.Terms.Features.EncodeBase256(&fb)
        if err != nil {
                return err
        }
        featureBytes := fb.Bytes()

        preimage := [32]byte(invpkg.UnknownPreimage)
        if i.Terms.PaymentPreimage != nil {
                preimage = *i.Terms.PaymentPreimage
                if preimage == invpkg.UnknownPreimage {
                        return errors.New("cannot use all-zeroes preimage")
                }
        }
        value := uint64(i.Terms.Value)
        cltvDelta := uint32(i.Terms.FinalCltvDelta)
        expiry := uint64(i.Terms.Expiry)

        amtPaid := uint64(i.AmtPaid)
        state := uint8(i.State)

        var hodlInvoice uint8
        if i.HodlInvoice {
                hodlInvoice = 1
        }

        tlvStream, err := tlv.NewStream(
                // Memo and payreq.
                tlv.MakePrimitiveRecord(memoType, &i.Memo),
                tlv.MakePrimitiveRecord(payReqType, &i.PaymentRequest),

                // Add/settle metadata.
                tlv.MakePrimitiveRecord(createTimeType, &creationDateBytes),
                tlv.MakePrimitiveRecord(settleTimeType, &settleDateBytes),
                tlv.MakePrimitiveRecord(addIndexType, &i.AddIndex),
                tlv.MakePrimitiveRecord(settleIndexType, &i.SettleIndex),

                // Terms.
                tlv.MakePrimitiveRecord(preimageType, &preimage),
                tlv.MakePrimitiveRecord(valueType, &value),
                tlv.MakePrimitiveRecord(cltvDeltaType, &cltvDelta),
                tlv.MakePrimitiveRecord(expiryType, &expiry),
                tlv.MakePrimitiveRecord(paymentAddrType, &i.Terms.PaymentAddr),
                tlv.MakePrimitiveRecord(featuresType, &featureBytes),

                // Invoice state.
                tlv.MakePrimitiveRecord(invStateType, &state),
                tlv.MakePrimitiveRecord(amtPaidType, &amtPaid),

                tlv.MakePrimitiveRecord(hodlInvoiceType, &hodlInvoice),

                // Invoice AMP state.
                tlv.MakeDynamicRecord(
                        invoiceAmpStateType, &i.AMPState,
                        ampRecordSize(&i.AMPState),
                        ampStateEncoder, ampStateDecoder,
                ),
        )
        if err != nil {
                return err
        }

        var b bytes.Buffer
        if err = tlvStream.Encode(&b); err != nil {
                return err
        }

        err = binary.Write(w, byteOrder, uint64(b.Len()))
        if err != nil {
                return err
        }

        if _, err = w.Write(b.Bytes()); err != nil {
                return err
        }

        // Only if this is a _non_ AMP invoice do we serialize the HTLCs
        // in-line with the rest of the invoice.
        if i.IsAMP() {
                return nil
        }

        return serializeHtlcs(w, i.Htlcs)
}

// serializeHtlcs serializes a map containing circuit keys and invoice htlcs to
// a writer.
func serializeHtlcs(w io.Writer,
        htlcs map[models.CircuitKey]*invpkg.InvoiceHTLC) error {

        for key, htlc := range htlcs {
                // Encode the htlc in a tlv stream.
                chanID := key.ChanID.ToUint64()
                amt := uint64(htlc.Amt)
                mppTotalAmt := uint64(htlc.MppTotalAmt)
                acceptTime := putNanoTime(htlc.AcceptTime)
                resolveTime := putNanoTime(htlc.ResolveTime)
                state := uint8(htlc.State)

                var records []tlv.Record
                records = append(records,
                        tlv.MakePrimitiveRecord(chanIDType, &chanID),
                        tlv.MakePrimitiveRecord(htlcIDType, &key.HtlcID),
                        tlv.MakePrimitiveRecord(amtType, &amt),
                        tlv.MakePrimitiveRecord(
                                acceptHeightType, &htlc.AcceptHeight,
                        ),
                        tlv.MakePrimitiveRecord(acceptTimeType, &acceptTime),
                        tlv.MakePrimitiveRecord(resolveTimeType, &resolveTime),
                        tlv.MakePrimitiveRecord(expiryHeightType, &htlc.Expiry),
                        tlv.MakePrimitiveRecord(htlcStateType, &state),
                        tlv.MakePrimitiveRecord(mppTotalAmtType, &mppTotalAmt),
                )

                if htlc.AMP != nil {
                        setIDRecord := tlv.MakeDynamicRecord(
                                htlcAMPType, &htlc.AMP.Record,
                                htlc.AMP.Record.PayloadSize,
                                record.AMPEncoder, record.AMPDecoder,
                        )
                        records = append(records, setIDRecord)

                        hash32 := [32]byte(htlc.AMP.Hash)
                        hashRecord := tlv.MakePrimitiveRecord(
                                htlcHashType, &hash32,
                        )
                        records = append(records, hashRecord)

                        if htlc.AMP.Preimage != nil {
                                preimage32 := [32]byte(*htlc.AMP.Preimage)
                                preimageRecord := tlv.MakePrimitiveRecord(
                                        htlcPreimageType, &preimage32,
                                )
                                records = append(records, preimageRecord)
                        }
                }

                // Convert the custom records to tlv.Record types that are ready
                // for serialization.
                customRecords := tlv.MapToRecords(htlc.CustomRecords)

                // Append the custom records. Their ids are in the experimental
                // range and sorted, so there is no need to sort again.
                records = append(records, customRecords...)

                tlvStream, err := tlv.NewStream(records...)
                if err != nil {
                        return err
                }

                var b bytes.Buffer
                if err := tlvStream.Encode(&b); err != nil {
                        return err
                }

                // Write the length of the tlv stream followed by the stream
                // bytes.
                err = binary.Write(w, byteOrder, uint64(b.Len()))
                if err != nil {
                        return err
                }

                if _, err := w.Write(b.Bytes()); err != nil {
                        return err
                }
        }

        return nil
}

// putNanoTime returns the unix nano time for the passed timestamp. A zero-value
// timestamp will be mapped to 0, since calling UnixNano in that case is
// undefined.
func putNanoTime(t time.Time) uint64 {
        if t.IsZero() {
                return 0
        }
        return uint64(t.UnixNano())
}

// getNanoTime returns a timestamp for the given number of nano seconds. If zero
// is provided, an zero-value time stamp is returned.
func getNanoTime(ns uint64) time.Time {
        if ns == 0 {
                return time.Time{}
        }
        return time.Unix(0, int64(ns))
}

// fetchFilteredAmpInvoices retrieves only a select set of AMP invoices
// identified by the setID value.
func fetchFilteredAmpInvoices(invoiceBucket kvdb.RBucket, invoiceNum []byte,
        setIDs ...*invpkg.SetID) (map[models.CircuitKey]*invpkg.InvoiceHTLC,
        error) {

        htlcs := make(map[models.CircuitKey]*invpkg.InvoiceHTLC)
        for _, setID := range setIDs {
                invoiceSetIDKey := makeInvoiceSetIDKey(invoiceNum, setID[:])

                htlcSetBytes := invoiceBucket.Get(invoiceSetIDKey[:])
                if htlcSetBytes == nil {
                        // A set ID was passed in, but we don't have this
                        // stored yet, meaning that the setID is being added
                        // for the first time.
                        return htlcs, invpkg.ErrInvoiceNotFound
                }

                htlcSetReader := bytes.NewReader(htlcSetBytes)
                htlcsBySetID, err := deserializeHtlcs(htlcSetReader)
                if err != nil {
                        return nil, err
                }

                for key, htlc := range htlcsBySetID {
                        htlcs[key] = htlc
                }
        }

        return htlcs, nil
}

// forEachAMPInvoice is a helper function that attempts to iterate over each of
// the HTLC sets (based on their set ID) for the given AMP invoice identified
// by its invoiceNum. The callback closure is called for each key within the
// prefix range.
func forEachAMPInvoice(invoiceBucket kvdb.RBucket, invoiceNum []byte,
        callback func(key, htlcSet []byte) error) error {

        invoiceCursor := invoiceBucket.ReadCursor()

        // Seek to the first key that includes the invoice data itself.
        invoiceCursor.Seek(invoiceNum)

        // Advance to the very first key _after_ the invoice data, as this is
        // where we'll encounter our first HTLC (if any are present).
        cursorKey, htlcSet := invoiceCursor.Next()

        // If at this point, the cursor key doesn't match the invoice num
        // prefix, then we know that this HTLC doesn't have any set ID HTLCs
        // associated with it.
        if !bytes.HasPrefix(cursorKey, invoiceNum) {
                return nil
        }

        // Otherwise continue to iterate until we no longer match the prefix,
        // executing the call back at each step.
        for ; cursorKey != nil && bytes.HasPrefix(cursorKey, invoiceNum); cursorKey, htlcSet = invoiceCursor.Next() {
                err := callback(cursorKey, htlcSet)
                if err != nil {
                        return err
                }
        }

        return nil
}

// fetchAmpSubInvoices attempts to use the invoiceNum as a prefix  within the
// AMP bucket to find all the individual HTLCs (by setID) associated with a
// given invoice. If a list of set IDs are specified, then only HTLCs
// associated with that setID will be retrieved.
func fetchAmpSubInvoices(invoiceBucket kvdb.RBucket, invoiceNum []byte,
        setIDs ...*invpkg.SetID) (map[models.CircuitKey]*invpkg.InvoiceHTLC,
        error) {

        // If a set of setIDs was specified, then we can skip the cursor and
        // just read out exactly what we need.
        if len(setIDs) != 0 && setIDs[0] != nil {
                return fetchFilteredAmpInvoices(
                        invoiceBucket, invoiceNum, setIDs...,
                )
        }

        // Otherwise, iterate over all the htlc sets that are prefixed beside
        // this invoice in the main invoice bucket.
        htlcs := make(map[models.CircuitKey]*invpkg.InvoiceHTLC)
        err := forEachAMPInvoice(invoiceBucket, invoiceNum,
                func(key, htlcSet []byte) error {
                        htlcSetReader := bytes.NewReader(htlcSet)
                        htlcsBySetID, err := deserializeHtlcs(htlcSetReader)
                        if err != nil {
                                return err
                        }

                        for key, htlc := range htlcsBySetID {
                                htlcs[key] = htlc
                        }

                        return nil
                },
        )

        if err != nil {
                return nil, err
        }

        return htlcs, nil
}

// fetchInvoice attempts to read out the relevant state for the invoice as
// specified by the invoice number. If the setID fields are set, then only the
// HTLC information pertaining to those set IDs is returned.
func fetchInvoice(invoiceNum []byte, invoices kvdb.RBucket,
        setIDs []*invpkg.SetID, filterAMPState bool) (invpkg.Invoice, error) {

        invoiceBytes := invoices.Get(invoiceNum)
        if invoiceBytes == nil {
                return invpkg.Invoice{}, invpkg.ErrInvoiceNotFound
        }

        invoiceReader := bytes.NewReader(invoiceBytes)

        invoice, err := deserializeInvoice(invoiceReader)
        if err != nil {
                return invpkg.Invoice{}, err
        }

        // If this is an AMP invoice we'll also attempt to read out the set of
        // HTLCs that were paid to prior set IDs, if needed.
        if !invoice.IsAMP() {
                return invoice, nil
        }

        if shouldFetchAMPHTLCs(invoice, setIDs) {
                invoice.Htlcs, err = fetchAmpSubInvoices(
                        invoices, invoiceNum, setIDs...,
                )
                // TODO(positiveblue): we should fail when we are not able to
                // fetch all the HTLCs for an AMP invoice. Multiple tests in
                // the invoice and channeldb package break if we return this
                // error. We need to update them when we migrate this logic to
                // the sql implementation.
                if err != nil {
                        log.Errorf("unable to fetch amp htlcs for inv "+
                                "%v and setIDs %v: %w", invoiceNum, setIDs, err)
                }

                if filterAMPState {
                        filterInvoiceAMPState(&invoice, setIDs...)
                }
        }

        return invoice, nil
}

// shouldFetchAMPHTLCs returns true if we need to fetch the set of HTLCs that
// were paid to the relevant set IDs.
func shouldFetchAMPHTLCs(invoice invpkg.Invoice, setIDs []*invpkg.SetID) bool {
        // For AMP invoice that already have HTLCs populated (created before
        // recurring invoices), then we don't need to read from the prefix
        // keyed section of the bucket.
        if len(invoice.Htlcs) != 0 {
                return false
        }

        // If the "zero" setID was specified, then this means that no HTLC data
        // should be returned alongside of it.
        if len(setIDs) != 0 && setIDs[0] != nil &&
                *setIDs[0] == invpkg.BlankPayAddr {

                return false
        }

        return true
}

// fetchInvoiceStateAMP retrieves the state of all the relevant sub-invoice for
// an AMP invoice. This methods only decode the relevant state vs the entire
// invoice.
func fetchInvoiceStateAMP(invoiceNum []byte,
        invoices kvdb.RBucket) (invpkg.AMPInvoiceState, error) {

        // Fetch the raw invoice bytes.
        invoiceBytes := invoices.Get(invoiceNum)
        if invoiceBytes == nil {
                return nil, invpkg.ErrInvoiceNotFound
        }

        r := bytes.NewReader(invoiceBytes)

        var bodyLen int64
        err := binary.Read(r, byteOrder, &bodyLen)
        if err != nil {
                return nil, err
        }

        // Next, we'll make a new TLV stream that only attempts to decode the
        // bytes we actually need.
        ampState := make(invpkg.AMPInvoiceState)
        tlvStream, err := tlv.NewStream(
                // Invoice AMP state.
                tlv.MakeDynamicRecord(
                        invoiceAmpStateType, &ampState, nil,
                        ampStateEncoder, ampStateDecoder,
                ),
        )
        if err != nil {
                return nil, err
        }

        invoiceReader := io.LimitReader(r, bodyLen)
        if err = tlvStream.Decode(invoiceReader); err != nil {
                return nil, err
        }

        return ampState, nil
}

func deserializeInvoice(r io.Reader) (invpkg.Invoice, error) {
        var (
                preimageBytes [32]byte
                value         uint64
                cltvDelta     uint32
                expiry        uint64
                amtPaid       uint64
                state         uint8
                hodlInvoice   uint8

                creationDateBytes []byte
                settleDateBytes   []byte
                featureBytes      []byte
        )

        var i invpkg.Invoice
        i.AMPState = make(invpkg.AMPInvoiceState)
        tlvStream, err := tlv.NewStream(
                // Memo and payreq.
                tlv.MakePrimitiveRecord(memoType, &i.Memo),
                tlv.MakePrimitiveRecord(payReqType, &i.PaymentRequest),

                // Add/settle metadata.
                tlv.MakePrimitiveRecord(createTimeType, &creationDateBytes),
                tlv.MakePrimitiveRecord(settleTimeType, &settleDateBytes),
                tlv.MakePrimitiveRecord(addIndexType, &i.AddIndex),
                tlv.MakePrimitiveRecord(settleIndexType, &i.SettleIndex),

                // Terms.
                tlv.MakePrimitiveRecord(preimageType, &preimageBytes),
                tlv.MakePrimitiveRecord(valueType, &value),
                tlv.MakePrimitiveRecord(cltvDeltaType, &cltvDelta),
                tlv.MakePrimitiveRecord(expiryType, &expiry),
                tlv.MakePrimitiveRecord(paymentAddrType, &i.Terms.PaymentAddr),
                tlv.MakePrimitiveRecord(featuresType, &featureBytes),

                // Invoice state.
                tlv.MakePrimitiveRecord(invStateType, &state),
                tlv.MakePrimitiveRecord(amtPaidType, &amtPaid),

                tlv.MakePrimitiveRecord(hodlInvoiceType, &hodlInvoice),

                // Invoice AMP state.
                tlv.MakeDynamicRecord(
                        invoiceAmpStateType, &i.AMPState, nil,
                        ampStateEncoder, ampStateDecoder,
                ),
        )
        if err != nil {
                return i, err
        }

        var bodyLen int64
        err = binary.Read(r, byteOrder, &bodyLen)
        if err != nil {
                return i, err
        }

        lr := io.LimitReader(r, bodyLen)
        if err = tlvStream.Decode(lr); err != nil {
                return i, err
        }

        preimage := lntypes.Preimage(preimageBytes)
        if preimage != invpkg.UnknownPreimage {
                i.Terms.PaymentPreimage = &preimage
        }

        i.Terms.Value = lnwire.MilliSatoshi(value)
        i.Terms.FinalCltvDelta = int32(cltvDelta)
        i.Terms.Expiry = time.Duration(expiry)
        i.AmtPaid = lnwire.MilliSatoshi(amtPaid)
        i.State = invpkg.ContractState(state)

        if hodlInvoice != 0 {
                i.HodlInvoice = true
        }

        err = i.CreationDate.UnmarshalBinary(creationDateBytes)
        if err != nil {
                return i, err
        }

        err = i.SettleDate.UnmarshalBinary(settleDateBytes)
        if err != nil {
                return i, err
        }

        rawFeatures := lnwire.NewRawFeatureVector()
        err = rawFeatures.DecodeBase256(
                bytes.NewReader(featureBytes), len(featureBytes),
        )
        if err != nil {
                return i, err
        }

        i.Terms.Features = lnwire.NewFeatureVector(
                rawFeatures, lnwire.Features,
        )

        i.Htlcs, err = deserializeHtlcs(r)
        return i, err
}

func encodeCircuitKeys(w io.Writer, val interface{}, buf *[8]byte) error {
        if v, ok := val.(*map[models.CircuitKey]struct{}); ok {
                // We encode the set of circuit keys as a varint length prefix.
                // followed by a series of fixed sized uint8 integers.
                numKeys := uint64(len(*v))

                if err := tlv.WriteVarInt(w, numKeys, buf); err != nil {
                        return err
                }

                for key := range *v {
                        scidInt := key.ChanID.ToUint64()

                        if err := tlv.EUint64(w, &scidInt, buf); err != nil {
                                return err
                        }
                        if err := tlv.EUint64(w, &key.HtlcID, buf); err != nil {
                                return err
                        }
                }

                return nil
        }

        return tlv.NewTypeForEncodingErr(val, "*map[CircuitKey]struct{}")
}

func decodeCircuitKeys(r io.Reader, val interface{}, buf *[8]byte,
        l uint64) error {

        if v, ok := val.(*map[models.CircuitKey]struct{}); ok {
                // First, we'll read out the varint that encodes the number of
                // circuit keys encoded.
                numKeys, err := tlv.ReadVarInt(r, buf)
                if err != nil {
                        return err
                }

                // Now that we know how many keys to expect, iterate reading
                // each one until we're done.
                for i := uint64(0); i < numKeys; i++ {
                        var (
                                key  models.CircuitKey
                                scid uint64
                        )

                        if err := tlv.DUint64(r, &scid, buf, 8); err != nil {
                                return err
                        }

                        key.ChanID = lnwire.NewShortChanIDFromInt(scid)

                        err := tlv.DUint64(r, &key.HtlcID, buf, 8)
                        if err != nil {
                                return err
                        }

                        (*v)[key] = struct{}{}
                }

                return nil
        }

        return tlv.NewTypeForDecodingErr(val, "*map[CircuitKey]struct{}", l, l)
}

// ampStateEncoder is a custom TLV encoder for the AMPInvoiceState record.
func ampStateEncoder(w io.Writer, val interface{}, buf *[8]byte) error {
        if v, ok := val.(*invpkg.AMPInvoiceState); ok {
                // We'll encode the AMP state as a series of KV pairs on the
                // wire with a length prefix.
                numRecords := uint64(len(*v))

                // First, we'll write out the number of records as a var int.
                if err := tlv.WriteVarInt(w, numRecords, buf); err != nil {
                        return err
                }

                // With that written out, we'll now encode the entries
                // themselves as a sub-TLV record, which includes its _own_
                // inner length prefix.
                for setID, ampState := range *v {
                        setID := [32]byte(setID)
                        ampState := ampState

                        htlcState := uint8(ampState.State)
                        settleDate := ampState.SettleDate
                        settleDateBytes, err := settleDate.MarshalBinary()
                        if err != nil {
                                return err
                        }

                        amtPaid := uint64(ampState.AmtPaid)

                        var ampStateTlvBytes bytes.Buffer
                        tlvStream, err := tlv.NewStream(
                                tlv.MakePrimitiveRecord(
                                        ampStateSetIDType, &setID,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateHtlcStateType, &htlcState,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateSettleIndexType,
                                        &ampState.SettleIndex,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateSettleDateType,
                                        &settleDateBytes,
                                ),
                                tlv.MakeDynamicRecord(
                                        ampStateCircuitKeysType,
                                        &ampState.InvoiceKeys,
                                        func() uint64 {
                                                // The record takes 8 bytes to
                                                // encode the set of circuits,
                                                // 8 bytes for the scid for the
                                                // key, and 8 bytes for the HTLC
                                                // index.
                                                keys := ampState.InvoiceKeys
                                                numKeys := uint64(len(keys))
                                                size := tlv.VarIntSize(numKeys)
                                                dataSize := (numKeys * 16)

                                                return size + dataSize
                                        },
                                        encodeCircuitKeys, decodeCircuitKeys,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateAmtPaidType, &amtPaid,
                                ),
                        )
                        if err != nil {
                                return err
                        }

                        err = tlvStream.Encode(&ampStateTlvBytes)
                        if err != nil {
                                return err
                        }

                        // We encode the record with a varint length followed by
                        // the _raw_ TLV bytes.
                        tlvLen := uint64(len(ampStateTlvBytes.Bytes()))
                        if err := tlv.WriteVarInt(w, tlvLen, buf); err != nil {
                                return err
                        }

                        _, err = w.Write(ampStateTlvBytes.Bytes())
                        if err != nil {
                                return err
                        }
                }

                return nil
        }

        return tlv.NewTypeForEncodingErr(val, "channeldb.AMPInvoiceState")
}

// ampStateDecoder is a custom TLV decoder for the AMPInvoiceState record.
func ampStateDecoder(r io.Reader, val interface{}, buf *[8]byte,
        l uint64) error {

        if v, ok := val.(*invpkg.AMPInvoiceState); ok {
                // First, we'll decode the varint that encodes how many set IDs
                // are encoded within the greater map.
                numRecords, err := tlv.ReadVarInt(r, buf)
                if err != nil {
                        return err
                }

                // Now that we know how many records we'll need to read, we can
                // iterate and read them all out in series.
                for i := uint64(0); i < numRecords; i++ {
                        // Read out the varint that encodes the size of this
                        // inner TLV record.
                        stateRecordSize, err := tlv.ReadVarInt(r, buf)
                        if err != nil {
                                return err
                        }

                        // Using this information, we'll create a new limited
                        // reader that'll return an EOF once the end has been
                        // reached so the stream stops consuming bytes.
                        innerTlvReader := io.LimitedReader{
                                R: r,
                                N: int64(stateRecordSize),
                        }

                        var (
                                setID           [32]byte
                                htlcState       uint8
                                settleIndex     uint64
                                settleDateBytes []byte
                                invoiceKeys     = make(
                                        map[models.CircuitKey]struct{},
                                )
                                amtPaid uint64
                        )
                        tlvStream, err := tlv.NewStream(
                                tlv.MakePrimitiveRecord(
                                        ampStateSetIDType, &setID,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateHtlcStateType, &htlcState,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateSettleIndexType, &settleIndex,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateSettleDateType,
                                        &settleDateBytes,
                                ),
                                tlv.MakeDynamicRecord(
                                        ampStateCircuitKeysType,
                                        &invoiceKeys, nil,
                                        encodeCircuitKeys, decodeCircuitKeys,
                                ),
                                tlv.MakePrimitiveRecord(
                                        ampStateAmtPaidType, &amtPaid,
                                ),
                        )
                        if err != nil {
                                return err
                        }

                        err = tlvStream.Decode(&innerTlvReader)
                        if err != nil {
                                return err
                        }

                        var settleDate time.Time
                        err = settleDate.UnmarshalBinary(settleDateBytes)
                        if err != nil {
                                return err
                        }

                        (*v)[setID] = invpkg.InvoiceStateAMP{
                                State:       invpkg.HtlcState(htlcState),
                                SettleIndex: settleIndex,
                                SettleDate:  settleDate,
                                InvoiceKeys: invoiceKeys,
                                AmtPaid:     lnwire.MilliSatoshi(amtPaid),
                        }
                }

                return nil
        }

        return tlv.NewTypeForDecodingErr(
                val, "channeldb.AMPInvoiceState", l, l,
        )
}

// deserializeHtlcs reads a list of invoice htlcs from a reader and returns it
// as a map.
func deserializeHtlcs(r io.Reader) (map[models.CircuitKey]*invpkg.InvoiceHTLC,
        error) {

        htlcs := make(map[models.CircuitKey]*invpkg.InvoiceHTLC)
        for {
                // Read the length of the tlv stream for this htlc.
                var streamLen int64
                if err := binary.Read(r, byteOrder, &streamLen); err != nil {
                        if err == io.EOF {
                                break
                        }

                        return nil, err
                }

                // Limit the reader so that it stops at the end of this htlc's
                // stream.
                htlcReader := io.LimitReader(r, streamLen)

                // Decode the contents into the htlc fields.
                var (
                        htlc                    invpkg.InvoiceHTLC
                        key                     models.CircuitKey
                        chanID                  uint64
                        state                   uint8
                        acceptTime, resolveTime uint64
                        amt, mppTotalAmt        uint64
                        amp                     = &record.AMP{}
                        hash32                  = &[32]byte{}
                        preimage32              = &[32]byte{}
                )
                tlvStream, err := tlv.NewStream(
                        tlv.MakePrimitiveRecord(chanIDType, &chanID),
                        tlv.MakePrimitiveRecord(htlcIDType, &key.HtlcID),
                        tlv.MakePrimitiveRecord(amtType, &amt),
                        tlv.MakePrimitiveRecord(
                                acceptHeightType, &htlc.AcceptHeight,
                        ),
                        tlv.MakePrimitiveRecord(acceptTimeType, &acceptTime),
                        tlv.MakePrimitiveRecord(resolveTimeType, &resolveTime),
                        tlv.MakePrimitiveRecord(expiryHeightType, &htlc.Expiry),
                        tlv.MakePrimitiveRecord(htlcStateType, &state),
                        tlv.MakePrimitiveRecord(mppTotalAmtType, &mppTotalAmt),
                        tlv.MakeDynamicRecord(
                                htlcAMPType, amp, amp.PayloadSize,
                                record.AMPEncoder, record.AMPDecoder,
                        ),
                        tlv.MakePrimitiveRecord(htlcHashType, hash32),
                        tlv.MakePrimitiveRecord(htlcPreimageType, preimage32),
                )
                if err != nil {
                        return nil, err
                }

                parsedTypes, err := tlvStream.DecodeWithParsedTypes(htlcReader)
                if err != nil {
                        return nil, err
                }

                if _, ok := parsedTypes[htlcAMPType]; !ok {
                        amp = nil
                }

                var preimage *lntypes.Preimage
                if _, ok := parsedTypes[htlcPreimageType]; ok {
                        pimg := lntypes.Preimage(*preimage32)
                        preimage = &pimg
                }

                var hash *lntypes.Hash
                if _, ok := parsedTypes[htlcHashType]; ok {
                        h := lntypes.Hash(*hash32)
                        hash = &h
                }

                key.ChanID = lnwire.NewShortChanIDFromInt(chanID)
                htlc.AcceptTime = getNanoTime(acceptTime)
                htlc.ResolveTime = getNanoTime(resolveTime)
                htlc.State = invpkg.HtlcState(state)
                htlc.Amt = lnwire.MilliSatoshi(amt)
                htlc.MppTotalAmt = lnwire.MilliSatoshi(mppTotalAmt)
                if amp != nil && hash != nil {
                        htlc.AMP = &invpkg.InvoiceHtlcAMPData{
                                Record:   *amp,
                                Hash:     *hash,
                                Preimage: preimage,
                        }
                }

                // Reconstruct the custom records fields from the parsed types
                // map return from the tlv parser.
                htlc.CustomRecords = hop.NewCustomRecords(parsedTypes)

                htlcs[key] = &htlc
        }

        return htlcs, nil
}

// invoiceSetIDKeyLen is the length of the key that's used to store the
// individual HTLCs prefixed by their ID along side the main invoice within the
// invoiceBytes. We use 4 bytes for the invoice number, and 32 bytes for the
// set ID.
const invoiceSetIDKeyLen = 4 + 32

// makeInvoiceSetIDKey returns the prefix key, based on the set ID and invoice
// number where the HTLCs for this setID will be stored udner.
func makeInvoiceSetIDKey(invoiceNum, setID []byte) [invoiceSetIDKeyLen]byte {
        // Construct the prefix key we need to obtain the invoice information:
        // invoiceNum || setID.
        var invoiceSetIDKey [invoiceSetIDKeyLen]byte
        copy(invoiceSetIDKey[:], invoiceNum)
        copy(invoiceSetIDKey[len(invoiceNum):], setID)

        return invoiceSetIDKey
}

// delAMPInvoices attempts to delete all the "sub" invoices associated with a
// greater AMP invoices. We do this by deleting the set of keys that share the
// invoice number as a prefix.
func delAMPInvoices(invoiceNum []byte, invoiceBucket kvdb.RwBucket) error {
        // Since it isn't safe to delete using an active cursor, we'll use the
        // cursor simply to collect the set of keys we need to delete, _then_
        // delete them in another pass.
        var keysToDel [][]byte
        err := forEachAMPInvoice(
                invoiceBucket, invoiceNum,
                func(cursorKey, v []byte) error {
                        keysToDel = append(keysToDel, cursorKey)
                        return nil
                },
        )
        if err != nil {
                return err
        }

        // In this next phase, we'll then delete all the relevant invoices.
        for _, keyToDel := range keysToDel {
                if err := invoiceBucket.Delete(keyToDel); err != nil {
                        return err
                }
        }

        return nil
}

// delAMPSettleIndex removes all the entries in the settle index associated
// with a given AMP invoice.
func delAMPSettleIndex(invoiceNum []byte, invoices,
        settleIndex kvdb.RwBucket) error {

        // First, we need to grab the AMP invoice state to see if there's
        // anything that we even need to delete.
        ampState, err := fetchInvoiceStateAMP(invoiceNum, invoices)
        if err != nil {
                return err
        }

        // If there's no AMP state at all (non-AMP invoice), then we can return
        // early.
        if len(ampState) == 0 {
                return nil
        }

        // Otherwise, we'll need to iterate and delete each settle index within
        // the set of returned entries.
        var settleIndexKey [8]byte
        for _, subState := range ampState {
                byteOrder.PutUint64(
                        settleIndexKey[:], subState.SettleIndex,
                )

                if err := settleIndex.Delete(settleIndexKey[:]); err != nil {
                        return err
                }
        }

        return nil
}

// DeleteCanceledInvoices deletes all canceled invoices from the database.
func (d *DB) DeleteCanceledInvoices(_ context.Context) error {
        return kvdb.Update(d, func(tx kvdb.RwTx) error {
                invoices := tx.ReadWriteBucket(invoiceBucket)
                if invoices == nil {
                        return nil
                }

                invoiceIndex := invoices.NestedReadWriteBucket(
                        invoiceIndexBucket,
                )
                if invoiceIndex == nil {
                        return nil
                }

                invoiceAddIndex := invoices.NestedReadWriteBucket(
                        addIndexBucket,
                )
                if invoiceAddIndex == nil {
                        return nil
                }

                payAddrIndex := tx.ReadWriteBucket(payAddrIndexBucket)

                return invoiceIndex.ForEach(func(k, v []byte) error {
                        // Skip the special numInvoicesKey as that does not
                        // point to a valid invoice.
                        if bytes.Equal(k, numInvoicesKey) {
                                return nil
                        }

                        // Skip sub-buckets.
                        if v == nil {
                                return nil
                        }

                        invoice, err := fetchInvoice(v, invoices, nil, false)
                        if err != nil {
                                return err
                        }

                        if invoice.State != invpkg.ContractCanceled {
                                return nil
                        }

                        // Delete the payment hash from the invoice index.
                        err = invoiceIndex.Delete(k)
                        if err != nil {
                                return err
                        }

                        // Delete payment address index reference if there's a
                        // valid payment address.
                        if invoice.Terms.PaymentAddr != invpkg.BlankPayAddr {
                                // To ensure consistency check that the already
                                // fetched invoice key matches the one in the
                                // payment address index.
                                key := payAddrIndex.Get(
                                        invoice.Terms.PaymentAddr[:],
                                )
                                if bytes.Equal(key, k) {
                                        // Delete from the payment address
                                        // index.
                                        if err := payAddrIndex.Delete(
                                                invoice.Terms.PaymentAddr[:],
                                        ); err != nil {
                                                return err
                                        }
                                }
                        }

                        // Remove from the add index.
                        var addIndexKey [8]byte
                        byteOrder.PutUint64(addIndexKey[:], invoice.AddIndex)
                        err = invoiceAddIndex.Delete(addIndexKey[:])
                        if err != nil {
                                return err
                        }

                        // Note that we don't need to delete the invoice from
                        // the settle index as it is not added until the
                        // invoice is settled.

                        // Now remove all sub invoices.
                        err = delAMPInvoices(k, invoices)
                        if err != nil {
                                return err
                        }

                        // Finally remove the serialized invoice from the
                        // invoice bucket.
                        return invoices.Delete(k)
                })
        }, func() {})
}

// DeleteInvoice attempts to delete the passed invoices from the database in
// one transaction. The passed delete references hold all keys required to
// delete the invoices without also needing to deserialize them.
func (d *DB) DeleteInvoice(_ context.Context,
        invoicesToDelete []invpkg.InvoiceDeleteRef) error {

        err := kvdb.Update(d, func(tx kvdb.RwTx) error {
                invoices := tx.ReadWriteBucket(invoiceBucket)
                if invoices == nil {
                        return invpkg.ErrNoInvoicesCreated
                }

                invoiceIndex := invoices.NestedReadWriteBucket(
                        invoiceIndexBucket,
                )
                if invoiceIndex == nil {
                        return invpkg.ErrNoInvoicesCreated
                }

                invoiceAddIndex := invoices.NestedReadWriteBucket(
                        addIndexBucket,
                )
                if invoiceAddIndex == nil {
                        return invpkg.ErrNoInvoicesCreated
                }

                // settleIndex can be nil, as the bucket is created lazily
                // when the first invoice is settled.
                settleIndex := invoices.NestedReadWriteBucket(settleIndexBucket)

                payAddrIndex := tx.ReadWriteBucket(payAddrIndexBucket)

                for _, ref := range invoicesToDelete {
                        // Fetch the invoice key for using it to check for
                        // consistency and also to delete from the invoice
                        // index.
                        invoiceKey := invoiceIndex.Get(ref.PayHash[:])
                        if invoiceKey == nil {
                                return invpkg.ErrInvoiceNotFound
                        }

                        err := invoiceIndex.Delete(ref.PayHash[:])
                        if err != nil {
                                return err
                        }

                        // Delete payment address index reference if there's a
                        // valid payment address passed.
                        if ref.PayAddr != nil {
                                // To ensure consistency check that the already
                                // fetched invoice key matches the one in the
                                // payment address index.
                                key := payAddrIndex.Get(ref.PayAddr[:])
                                if bytes.Equal(key, invoiceKey) {
                                        // Delete from the payment address
                                        // index. Note that since the payment
                                        // address index has been introduced
                                        // with an empty migration it may be
                                        // possible that the index doesn't have
                                        // an entry for this invoice.
                                        // ref: https://github.com/lightningnetwork/lnd/pull/4285/commits/cbf71b5452fa1d3036a43309e490787c5f7f08dc#r426368127
                                        if err := payAddrIndex.Delete(
                                                ref.PayAddr[:],
                                        ); err != nil {
                                                return err
                                        }
                                }
                        }

                        var addIndexKey [8]byte
                        byteOrder.PutUint64(addIndexKey[:], ref.AddIndex)

                        // To ensure consistency check that the key stored in
                        // the add index also matches the previously fetched
                        // invoice key.
                        key := invoiceAddIndex.Get(addIndexKey[:])
                        if !bytes.Equal(key, invoiceKey) {
                                return fmt.Errorf("unknown invoice " +
                                        "in add index")
                        }

                        // Remove from the add index.
                        err = invoiceAddIndex.Delete(addIndexKey[:])
                        if err != nil {
                                return err
                        }

                        // Remove from the settle index if available and
                        // if the invoice is settled.
                        if settleIndex != nil && ref.SettleIndex > 0 {
                                var settleIndexKey [8]byte
                                byteOrder.PutUint64(
                                        settleIndexKey[:], ref.SettleIndex,
                                )

                                // To ensure consistency check that the already
                                // fetched invoice key matches the one in the
                                // settle index
                                key := settleIndex.Get(settleIndexKey[:])
                                if !bytes.Equal(key, invoiceKey) {
                                        return fmt.Errorf("unknown invoice " +
                                                "in settle index")
                                }

                                err = settleIndex.Delete(settleIndexKey[:])
                                if err != nil {
                                        return err
                                }
                        }

                        // In addition to deleting the main invoice state, if
                        // this is an AMP invoice, then we'll also need to
                        // delete the set HTLC set stored as a key prefix. For
                        // non-AMP invoices, this'll be a noop.
                        err = delAMPSettleIndex(
                                invoiceKey, invoices, settleIndex,
                        )
                        if err != nil {
                                return err
                        }
                        err = delAMPInvoices(invoiceKey, invoices)
                        if err != nil {
                                return err
                        }

                        // Finally remove the serialized invoice from the
                        // invoice bucket.
                        err = invoices.Delete(invoiceKey)
                        if err != nil {
                                return err
                        }
                }

                return nil
        }, func() {})

        return err
}

lightningnetwork / lnd / 13153965138

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