13211764208

Committed 08 Feb 2025 03:08AM UTC coverage: 49.288% (-9.5%) from 58.815%

Build # 13211764208

Build Type

Pull #9489

github

Committed by

calvinrzachman

Commit Message

itest: verify switchrpc server enforces send then track

We prevent the rpc server from allowing onion dispatches for
attempt IDs which have already been tracked by rpc clients.

This helps protect the client from leaking a duplicate onion
attempt. NOTE: This is not the only method for solving this
issue! The issue could be addressed via careful client side
programming which accounts for the uncertainty and async
nature of dispatching onions to a remote process via RPC.
This would require some lnd ChannelRouter changes for how
we intend to use these RPCs though.

Pull Request Pull Request #9489: multi: add BuildOnion, SendOnion, and TrackOnion RPCs

Run Details

474 of 990 new or added lines in 11 files covered. (47.88%)

27321 existing lines in 435 files now uncovered.

101192 of 205306 relevant lines covered (49.29%)

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Source File
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41.62

/contractcourt/utxonursery.go

package contractcourt

import (
        "bytes"
        "encoding/binary"
        "errors"
        "fmt"
        "io"
        "sync"
        "sync/atomic"

        "github.com/btcsuite/btcd/btcutil"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
        "github.com/davecgh/go-spew/spew"
        "github.com/lightningnetwork/lnd/chainntnfs"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/fn/v2"
        graphdb "github.com/lightningnetwork/lnd/graph/db"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/labels"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/sweep"
        "github.com/lightningnetwork/lnd/tlv"
)

//                          SUMMARY OF OUTPUT STATES
//
//  - CRIB
//    - SerializedType: babyOutput
//    - OriginalOutputType: HTLC
//    - Awaiting: First-stage HTLC CLTV expiry
//    - HeightIndexEntry: Absolute block height of CLTV expiry.
//    - NextState: KNDR
//  - PSCL
//    - SerializedType: kidOutput
//    - OriginalOutputType: Commitment
//    - Awaiting: Confirmation of commitment txn
//    - HeightIndexEntry: None.
//    - NextState: KNDR
//  - KNDR
//    - SerializedType: kidOutput
//    - OriginalOutputType: Commitment or HTLC
//    - Awaiting: Commitment CSV expiry or second-stage HTLC CSV expiry.
//    - HeightIndexEntry: Input confirmation height + relative CSV delay
//    - NextState: GRAD
//  - GRAD:
//    - SerializedType: kidOutput
//    - OriginalOutputType: Commitment or HTLC
//    - Awaiting: All other outputs in channel to become GRAD.
//    - NextState: Mark channel fully closed in channeldb and remove.
//
//                        DESCRIPTION OF OUTPUT STATES
//
// TODO(roasbeef): update comment with both new output types
//
//  - CRIB (babyOutput) outputs are two-stage htlc outputs that are initially
//    locked using a CLTV delay, followed by a CSV delay. The first stage of a
//    crib output requires broadcasting a presigned htlc timeout txn generated
//    by the wallet after an absolute expiry height. Since the timeout txns are
//    predetermined, they cannot be batched after-the-fact, meaning that all
//    CRIB outputs are broadcast and confirmed independently. After the first
//    stage is complete, a CRIB output is moved to the KNDR state, which will
//    finishing sweeping the second-layer CSV delay.
//
//  - PSCL (kidOutput) outputs are commitment outputs locked under a CSV delay.
//    These outputs are stored temporarily in this state until the commitment
//    transaction confirms, as this solidifies an absolute height that the
//    relative time lock will expire. Once this maturity height is determined,
//    the PSCL output is moved into KNDR.
//
//  - KNDR (kidOutput) outputs are CSV delayed outputs for which the maturity
//    height has been fully determined. This results from having received
//    confirmation of the UTXO we are trying to spend, contained in either the
//    commitment txn or htlc timeout txn. Once the maturity height is reached,
//    the utxo nursery will sweep all KNDR outputs scheduled for that height
//    using a single txn.
//
//  - GRAD (kidOutput) outputs are KNDR outputs that have successfully been
//    swept into the user's wallet. A channel is considered mature once all of
//    its outputs, including two-stage htlcs, have entered the GRAD state,
//    indicating that it safe to mark the channel as fully closed.
//
//
//                     OUTPUT STATE TRANSITIONS IN UTXO NURSERY
//
//      ┌────────────────┐            ┌──────────────┐
//      │ Commit Outputs │            │ HTLC Outputs │
//      └────────────────┘            └──────────────┘
//               │                            │
//               │                            │
//               │                            │               UTXO NURSERY
//   ┌───────────┼────────────────┬───────────┼───────────────────────────────┐
//   │           │                            │                               │
//   │           │                │           │                               │
//   │           │                            │           CLTV-Delayed        │
//   │           │                │           V            babyOutputs        │
//   │           │                        ┌──────┐                            │
//   │           │                │       │ CRIB │                            │
//   │           │                        └──────┘                            │
//   │           │                │           │                               │
//   │           │                            │                               │
//   │           │                │           |                               │
//   │           │                            V    Wait CLTV                  │
//   │           │                │          [ ]       +                      │
//   │           │                            |   Publish Txn                 │
//   │           │                │           │                               │
//   │           │                            │                               │
//   │           │                │           V ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┐        │
//   │           │                           ( )  waitForTimeoutConf          │
//   │           │                │           | └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┘        │
//   │           │                            │                               │
//   │           │                │           │                               │
//   │           │                            │                               │
//   │           V                │           │                               │
//   │       ┌──────┐                         │                               │
//   │       │ PSCL │             └  ──  ──  ─┼  ──  ──  ──  ──  ──  ──  ──  ─┤
//   │       └──────┘                         │                               │
//   │           │                            │                               │
//   │           │                            │                               │
//   │           V ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┐     │            CSV-Delayed        │
//   │          ( )  waitForCommitConf        │             kidOutputs        │
//   │           | └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─┘     │                               │
//   │           │                            │                               │
//   │           │                            │                               │
//   │           │                            V                               │
//   │           │                        ┌──────┐                            │
//   │           └─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─▶│ KNDR │                            │
//   │                                    └──────┘                            │
//   │                                        │                               │
//   │                                        │                               │
//   │                                        |                               │
//   │                                        V     Wait CSV                  │
//   │                                       [ ]       +                      │
//   │                                        |   Publish Txn                 │
//   │                                        │                               │
//   │                                        │                               │
//   │                                        V ┌ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┐         │
//   │                                       ( )  waitForSweepConf            │
//   │                                        | └ ─ ─ ─ ─ ─ ─ ─ ─ ─ ┘         │
//   │                                        │                               │
//   │                                        │                               │
//   │                                        V                               │
//   │                                     ┌──────┐                           │
//   │                                     │ GRAD │                           │
//   │                                     └──────┘                           │
//   │                                        │                               │
//   │                                        │                               │
//   │                                        │                               │
//   └────────────────────────────────────────┼───────────────────────────────┘
//                                            │
//                                            │
//                                            │
//                                            │
//                                            V
//                                   ┌────────────────┐
//                                   │ Wallet Outputs │
//                                   └────────────────┘

var byteOrder = binary.BigEndian

const (
        // kgtnOutputConfTarget is the default confirmation target we'll use for
        // sweeps of CSV delayed outputs.
        kgtnOutputConfTarget = 6
)

var (
        // ErrContractNotFound is returned when the nursery is unable to
        // retrieve information about a queried contract.
        ErrContractNotFound = fmt.Errorf("unable to locate contract")
)

// NurseryConfig abstracts the required subsystems used by the utxo nursery. An
// instance of NurseryConfig is passed to newUtxoNursery during instantiation.
type NurseryConfig struct {
        // ChainIO is used by the utxo nursery to determine the current block
        // height, which drives the incubation of the nursery's outputs.
        ChainIO lnwallet.BlockChainIO

        // ConfDepth is the number of blocks the nursery store waits before
        // determining outputs in the chain as confirmed.
        ConfDepth uint32

        // FetchClosedChannels provides access to a user's channels, such that
        // they can be marked fully closed after incubation has concluded.
        FetchClosedChannels func(pendingOnly bool) (
                []*channeldb.ChannelCloseSummary, error)

        // FetchClosedChannel provides access to the close summary to extract a
        // height hint from.
        FetchClosedChannel func(chanID *wire.OutPoint) (
                *channeldb.ChannelCloseSummary, error)

        // Notifier provides the utxo nursery the ability to subscribe to
        // transaction confirmation events, which advance outputs through their
        // persistence state transitions.
        Notifier chainntnfs.ChainNotifier

        // PublishTransaction facilitates the process of broadcasting a signed
        // transaction to the appropriate network.
        PublishTransaction func(*wire.MsgTx, string) error

        // Store provides access to and modification of the persistent state
        // maintained about the utxo nursery's incubating outputs.
        Store NurseryStorer

        // Sweep sweeps an input back to the wallet.
        SweepInput func(input.Input, sweep.Params) (chan sweep.Result, error)

        // Budget is the configured budget for the nursery.
        Budget *BudgetConfig
}

// UtxoNursery is a system dedicated to incubating time-locked outputs created
// by the broadcast of a commitment transaction either by us, or the remote
// peer. The nursery accepts outputs and "incubates" them until they've reached
// maturity, then sweep the outputs into the source wallet. An output is
// considered mature after the relative time-lock within the pkScript has
// passed. As outputs reach their maturity age, they're swept in batches into
// the source wallet, returning the outputs so they can be used within future
// channels, or regular Bitcoin transactions.
type UtxoNursery struct {
        started uint32 // To be used atomically.
        stopped uint32 // To be used atomically.

        cfg *NurseryConfig

        mu         sync.Mutex
        bestHeight uint32

        quit chan struct{}
        wg   sync.WaitGroup
}

// NewUtxoNursery creates a new instance of the UtxoNursery from a
// ChainNotifier and LightningWallet instance.
func NewUtxoNursery(cfg *NurseryConfig) *UtxoNursery {
        return &UtxoNursery{
                cfg:  cfg,
                quit: make(chan struct{}),
        }
}

// Start launches all goroutines the UtxoNursery needs to properly carry out
// its duties.
func (u *UtxoNursery) Start() error {
        if !atomic.CompareAndSwapUint32(&u.started, 0, 1) {
                return nil
        }

        utxnLog.Info("UTXO nursery starting")

        // Retrieve the currently best known block. This is needed to have the
        // state machine catch up with the blocks we missed when we were down.
        bestHash, bestHeight, err := u.cfg.ChainIO.GetBestBlock()
        if err != nil {
                return err
        }

        // Set best known height to schedule late registrations properly.
        atomic.StoreUint32(&u.bestHeight, uint32(bestHeight))

        // 2. Flush all fully-graduated channels from the pipeline.

        // Load any pending close channels, which represents the super set of
        // all channels that may still be incubating.
        pendingCloseChans, err := u.cfg.FetchClosedChannels(true)
        if err != nil {
                return err
        }

        // Ensure that all mature channels have been marked as fully closed in
        // the channeldb.
        for _, pendingClose := range pendingCloseChans {
                err := u.closeAndRemoveIfMature(&pendingClose.ChanPoint)
                if err != nil {
                        return err
                }
        }

        // TODO(conner): check if any fully closed channels can be removed from
        // utxn.

        // 2. Restart spend ntfns for any preschool outputs, which are waiting
        // for the force closed commitment txn to confirm, or any second-layer
        // HTLC success transactions.
        //
        // NOTE: The next two steps *may* spawn go routines, thus from this
        // point forward, we must close the nursery's quit channel if we detect
        // any failures during startup to ensure they terminate.
        if err := u.reloadPreschool(); err != nil {
                close(u.quit)
                return err
        }

        // 3. Replay all crib and kindergarten outputs up to the current best
        // height.
        if err := u.reloadClasses(uint32(bestHeight)); err != nil {
                close(u.quit)
                return err
        }

        // Start watching for new blocks, as this will drive the nursery store's
        // state machine.
        newBlockChan, err := u.cfg.Notifier.RegisterBlockEpochNtfn(&chainntnfs.BlockEpoch{
                Height: bestHeight,
                Hash:   bestHash,
        })
        if err != nil {
                close(u.quit)
                return err
        }

        u.wg.Add(1)
        go u.incubator(newBlockChan)

        return nil
}

// Stop gracefully shuts down any lingering goroutines launched during normal
// operation of the UtxoNursery.
func (u *UtxoNursery) Stop() error {
        if !atomic.CompareAndSwapUint32(&u.stopped, 0, 1) {
                return nil
        }

        utxnLog.Infof("UTXO nursery shutting down...")
        defer utxnLog.Debug("UTXO nursery shutdown complete")

        close(u.quit)
        u.wg.Wait()

        return nil
}

// IncubateOutputs sends a request to the UtxoNursery to incubate a set of
// outputs from an existing commitment transaction. Outputs need to incubate if
// they're CLTV absolute time locked, or if they're CSV relative time locked.
// Once all outputs reach maturity, they'll be swept back into the wallet.
func (u *UtxoNursery) IncubateOutputs(chanPoint wire.OutPoint,
        outgoingHtlc fn.Option[lnwallet.OutgoingHtlcResolution],
        incomingHtlc fn.Option[lnwallet.IncomingHtlcResolution],
        broadcastHeight uint32, deadlineHeight fn.Option[int32]) error {

        // Add to wait group because nursery might shut down during execution of
        // this function. Otherwise it could happen that nursery thinks it is
        // shut down, but in this function new goroutines were started and stay
        // around.
        u.wg.Add(1)
        defer u.wg.Done()

        // Check quit channel for the case where the waitgroup wait was finished
        // right before this function's add call was made.
        select {
        case <-u.quit:
                return fmt.Errorf("nursery shutting down")
        default:
        }

        var (
                // Kid outputs can be swept after an initial confirmation
                // followed by a maturity period.Baby outputs are two stage and
                // will need to wait for an absolute time out to reach a
                // confirmation, then require a relative confirmation delay.
                kidOutputs  = make([]kidOutput, 0)
                babyOutputs = make([]babyOutput, 0)
        )

        // 1. Build all the spendable outputs that we will try to incubate.

        // TODO(roasbeef): query and see if we already have, if so don't add?

        // For each incoming HTLC, we'll register a kid output marked as a
        // second-layer HTLC output. We effectively skip the baby stage (as the
        // timelock is zero), and enter the kid stage.
        incomingHtlc.WhenSome(func(htlcRes lnwallet.IncomingHtlcResolution) {
                // Based on the input pk script of the sign descriptor, we can
                // determine if this is a taproot output or not. This'll
                // determine the witness type we try to set below.
                isTaproot := txscript.IsPayToTaproot(
                        htlcRes.SweepSignDesc.Output.PkScript,
                )

                var witType input.StandardWitnessType
                if isTaproot {
                        witType = input.TaprootHtlcAcceptedSuccessSecondLevel
                } else {
                        witType = input.HtlcAcceptedSuccessSecondLevel
                }

                htlcOutput := makeKidOutput(
                        &htlcRes.ClaimOutpoint, &chanPoint, htlcRes.CsvDelay,
                        witType, &htlcRes.SweepSignDesc, 0, deadlineHeight,
                )

                if htlcOutput.Amount() > 0 {
                        kidOutputs = append(kidOutputs, htlcOutput)
                }
        })

        // For each outgoing HTLC, we'll create a baby output. If this is our
        // commitment transaction, then we'll broadcast a second-layer
        // transaction to transition to a kid output. Otherwise, we'll directly
        // spend once the CLTV delay us up.
        outgoingHtlc.WhenSome(func(htlcRes lnwallet.OutgoingHtlcResolution) {
                // If this HTLC is on our commitment transaction, then it'll be
                // a baby output as we need to go to the second level to sweep
                // it.
                if htlcRes.SignedTimeoutTx != nil {
                        htlcOutput := makeBabyOutput(
                                &chanPoint, &htlcRes, deadlineHeight,
                        )

                        if htlcOutput.Amount() > 0 {
                                babyOutputs = append(babyOutputs, htlcOutput)
                        }

                        return
                }

                // Based on the input pk script of the sign descriptor, we can
                // determine if this is a taproot output or not. This'll
                // determine the witness type we try to set below.
                isTaproot := txscript.IsPayToTaproot(
                        htlcRes.SweepSignDesc.Output.PkScript,
                )

                var witType input.StandardWitnessType
                if isTaproot {
                        witType = input.TaprootHtlcOfferedRemoteTimeout
                } else {
                        witType = input.HtlcOfferedRemoteTimeout
                }

                // Otherwise, this is actually a kid output as we can sweep it
                // once the commitment transaction confirms, and the absolute
                // CLTV lock has expired. We set the CSV delay what the
                // resolution encodes, since the sequence number must be set
                // accordingly.
                htlcOutput := makeKidOutput(
                        &htlcRes.ClaimOutpoint, &chanPoint, htlcRes.CsvDelay,
                        witType, &htlcRes.SweepSignDesc, htlcRes.Expiry,
                        deadlineHeight,
                )
                kidOutputs = append(kidOutputs, htlcOutput)
        })

        // TODO(roasbeef): if want to handle outgoing on remote commit
        //  * need ability to cancel in the case that we learn of pre-image or
        //    remote party pulls

        numHtlcs := len(babyOutputs) + len(kidOutputs)
        utxnLog.Infof("Incubating Channel(%s) num-htlcs=%d",
                chanPoint, numHtlcs)

        u.mu.Lock()
        defer u.mu.Unlock()

        // 2. Persist the outputs we intended to sweep in the nursery store
        if err := u.cfg.Store.Incubate(kidOutputs, babyOutputs); err != nil {
                utxnLog.Errorf("unable to begin incubation of Channel(%s): %v",
                        chanPoint, err)
                return err
        }

        // As an intermediate step, we'll now check to see if any of the baby
        // outputs has actually _already_ expired. This may be the case if
        // blocks were mined while we processed this message.
        _, bestHeight, err := u.cfg.ChainIO.GetBestBlock()
        if err != nil {
                return err
        }

        // We'll examine all the baby outputs just inserted into the database,
        // if the output has already expired, then we'll *immediately* sweep
        // it. This may happen if the caller raced a block to call this method.
        for i, babyOutput := range babyOutputs {
                if uint32(bestHeight) >= babyOutput.expiry {
                        err = u.sweepCribOutput(
                                babyOutput.expiry, &babyOutputs[i],
                        )
                        if err != nil {
                                return err
                        }
                }
        }

        // 3. If we are incubating any preschool outputs, register for a
        // confirmation notification that will transition it to the
        // kindergarten bucket.
        if len(kidOutputs) != 0 {
                for i := range kidOutputs {
                        err := u.registerPreschoolConf(
                                &kidOutputs[i], broadcastHeight,
                        )
                        if err != nil {
                                return err
                        }
                }
        }

        return nil
}

// NurseryReport attempts to return a nursery report stored for the target
// outpoint. A nursery report details the maturity/sweeping progress for a
// contract that was previously force closed. If a report entry for the target
// chanPoint is unable to be constructed, then an error will be returned.
func (u *UtxoNursery) NurseryReport(
        chanPoint *wire.OutPoint) (*ContractMaturityReport, error) {

        u.mu.Lock()
        defer u.mu.Unlock()

        utxnLog.Debugf("NurseryReport: building nursery report for channel %v",
                chanPoint)

        var report *ContractMaturityReport

        if err := u.cfg.Store.ForChanOutputs(chanPoint, func(k, v []byte) error {
                switch {
                case bytes.HasPrefix(k, cribPrefix):
                        // Cribs outputs are the only kind currently stored as
                        // baby outputs.
                        var baby babyOutput
                        err := baby.Decode(bytes.NewReader(v))
                        if err != nil {
                                return err
                        }

                        // Each crib output represents a stage one htlc, and
                        // will contribute towards the limbo balance.
                        report.AddLimboStage1TimeoutHtlc(&baby)

                case bytes.HasPrefix(k, psclPrefix),
                        bytes.HasPrefix(k, kndrPrefix),
                        bytes.HasPrefix(k, gradPrefix):

                        // All others states can be deserialized as kid outputs.
                        var kid kidOutput
                        err := kid.Decode(bytes.NewReader(v))
                        if err != nil {
                                return err
                        }

                        // Now, use the state prefixes to determine how the
                        // this output should be represented in the nursery
                        // report.  An output's funds are always in limbo until
                        // reaching the graduate state.
                        switch {
                        case bytes.HasPrefix(k, psclPrefix):
                                // Preschool outputs are awaiting the
                                // confirmation of the commitment transaction.
                                switch kid.WitnessType() {

                                //nolint:ll
                                case input.TaprootHtlcAcceptedSuccessSecondLevel:
                                        fallthrough
                                case input.HtlcAcceptedSuccessSecondLevel:
                                        // An HTLC output on our commitment
                                        // transaction where the second-layer
                                        // transaction hasn't
                                        // yet confirmed.
                                        report.AddLimboStage1SuccessHtlc(&kid)

                                case input.HtlcOfferedRemoteTimeout,
                                        input.TaprootHtlcOfferedRemoteTimeout:
                                        // This is an HTLC output on the
                                        // commitment transaction of the remote
                                        // party. We are waiting for the CLTV
                                        // timelock expire.
                                        report.AddLimboDirectHtlc(&kid)
                                }

                        case bytes.HasPrefix(k, kndrPrefix):
                                // Kindergarten outputs may originate from
                                // either the commitment transaction or an htlc.
                                // We can distinguish them via their witness
                                // types.
                                switch kid.WitnessType() {

                                case input.HtlcOfferedRemoteTimeout,
                                        input.TaprootHtlcOfferedRemoteTimeout:
                                        // This is an HTLC output on the
                                        // commitment transaction of the remote
                                        // party. The CLTV timelock has
                                        // expired, and we only need to sweep
                                        // it.
                                        report.AddLimboDirectHtlc(&kid)

                                //nolint:ll
                                case input.TaprootHtlcAcceptedSuccessSecondLevel:
                                        fallthrough
                                case input.TaprootHtlcOfferedTimeoutSecondLevel:
                                        fallthrough
                                case input.HtlcAcceptedSuccessSecondLevel:
                                        fallthrough
                                case input.HtlcOfferedTimeoutSecondLevel:
                                        // The htlc timeout or success
                                        // transaction has confirmed, and the
                                        // CSV delay has begun ticking.
                                        report.AddLimboStage2Htlc(&kid)
                                }

                        case bytes.HasPrefix(k, gradPrefix):
                                // Graduate outputs are those whose funds have
                                // been swept back into the wallet. Each output
                                // will contribute towards the recovered
                                // balance.
                                switch kid.WitnessType() {

                                //nolint:ll
                                case input.TaprootHtlcAcceptedSuccessSecondLevel:
                                        fallthrough
                                case input.TaprootHtlcOfferedTimeoutSecondLevel:
                                        fallthrough
                                case input.HtlcAcceptedSuccessSecondLevel:
                                        fallthrough
                                case input.HtlcOfferedTimeoutSecondLevel:
                                        fallthrough
                                case input.TaprootHtlcOfferedRemoteTimeout:
                                        fallthrough
                                case input.HtlcOfferedRemoteTimeout:
                                        // This htlc output successfully
                                        // resides in a p2wkh output belonging
                                        // to the user.
                                        report.AddRecoveredHtlc(&kid)
                                }
                        }

                default:
                }

                return nil
        }, func() {
                report = &ContractMaturityReport{}
        }); err != nil {
                return nil, err
        }

        return report, nil
}

// reloadPreschool re-initializes the chain notifier with all of the outputs
// that had been saved to the "preschool" database bucket prior to shutdown.
func (u *UtxoNursery) reloadPreschool() error {
        psclOutputs, err := u.cfg.Store.FetchPreschools()
        if err != nil {
                return err
        }

        // For each of the preschool outputs stored in the nursery store, load
        // its close summary from disk so that we can get an accurate height
        // hint from which to start our range for spend notifications.
        for i := range psclOutputs {
                kid := &psclOutputs[i]
                chanPoint := kid.OriginChanPoint()

                // Load the close summary for this output's channel point.
                closeSummary, err := u.cfg.FetchClosedChannel(chanPoint)
                if err == channeldb.ErrClosedChannelNotFound {
                        // This should never happen since the close summary
                        // should only be removed after the channel has been
                        // swept completely.
                        utxnLog.Warnf("Close summary not found for "+
                                "chan_point=%v, can't determine height hint"+
                                "to sweep commit txn", chanPoint)
                        continue

                } else if err != nil {
                        return err
                }

                // Use the close height from the channel summary as our height
                // hint to drive our spend notifications, with our confirmation
                // depth as a buffer for reorgs.
                heightHint := closeSummary.CloseHeight - u.cfg.ConfDepth
                err = u.registerPreschoolConf(kid, heightHint)
                if err != nil {
                        return err
                }
        }

        return nil
}

// reloadClasses reinitializes any height-dependent state transitions for which
// the utxonursery has not received confirmation, and replays the graduation of
// all kindergarten and crib outputs for all heights up to the current block.
// This allows the nursery to reinitialize all state to continue sweeping
// outputs, even in the event that we missed blocks while offline. reloadClasses
// is called during the startup of the UTXO Nursery.
func (u *UtxoNursery) reloadClasses(bestHeight uint32) error {
        // Loading all active heights up to and including the current block.
        activeHeights, err := u.cfg.Store.HeightsBelowOrEqual(
                uint32(bestHeight))
        if err != nil {
                return err
        }

        // Return early if nothing to sweep.
        if len(activeHeights) == 0 {
                return nil
        }

        utxnLog.Infof("(Re)-sweeping %d heights below height=%d",
                len(activeHeights), bestHeight)

        // Attempt to re-register notifications for any outputs still at these
        // heights.
        for _, classHeight := range activeHeights {
                utxnLog.Debugf("Attempting to sweep outputs at height=%v",
                        classHeight)

                if err = u.graduateClass(classHeight); err != nil {
                        utxnLog.Errorf("Failed to sweep outputs at "+
                                "height=%v: %v", classHeight, err)
                        return err
                }
        }

        utxnLog.Infof("UTXO Nursery is now fully synced")

        return nil
}

// incubator is tasked with driving all state transitions that are dependent on
// the current height of the blockchain. As new blocks arrive, the incubator
// will attempt spend outputs at the latest height. The asynchronous
// confirmation of these spends will either 1) move a crib output into the
// kindergarten bucket or 2) move a kindergarten output into the graduated
// bucket.
func (u *UtxoNursery) incubator(newBlockChan *chainntnfs.BlockEpochEvent) {
        defer u.wg.Done()
        defer newBlockChan.Cancel()

        for {
                select {
                case epoch, ok := <-newBlockChan.Epochs:
                        // If the epoch channel has been closed, then the
                        // ChainNotifier is exiting which means the daemon is
                        // as well. Therefore, we exit early also in order to
                        // ensure the daemon shuts down gracefully, yet
                        // swiftly.
                        if !ok {
                                return
                        }

                        // TODO(roasbeef): if the BlockChainIO is rescanning
                        // will give stale data

                        // A new block has just been connected to the main
                        // chain, which means we might be able to graduate crib
                        // or kindergarten outputs at this height. This involves
                        // broadcasting any presigned htlc timeout txns, as well
                        // as signing and broadcasting a sweep txn that spends
                        // from all kindergarten outputs at this height.
                        height := uint32(epoch.Height)

                        // Update best known block height for late registrations
                        // to be scheduled properly.
                        atomic.StoreUint32(&u.bestHeight, height)

                        if err := u.graduateClass(height); err != nil {
                                utxnLog.Errorf("error while graduating "+
                                        "class at height=%d: %v", height, err)

                                // TODO(conner): signal fatal error to daemon
                        }

                case <-u.quit:
                        return
                }
        }
}

// graduateClass handles the steps involved in spending outputs whose CSV or
// CLTV delay expires at the nursery's current height. This method is called
// each time a new block arrives, or during startup to catch up on heights we
// may have missed while the nursery was offline.
func (u *UtxoNursery) graduateClass(classHeight uint32) error {
        // Record this height as the nursery's current best height.
        u.mu.Lock()
        defer u.mu.Unlock()

        // Fetch all information about the crib and kindergarten outputs at
        // this height.
        kgtnOutputs, cribOutputs, err := u.cfg.Store.FetchClass(
                classHeight,
        )
        if err != nil {
                return err
        }

        utxnLog.Debugf("Attempting to graduate height=%v: num_kids=%v, "+
                "num_babies=%v", classHeight, len(kgtnOutputs), len(cribOutputs))

        // Offer the outputs to the sweeper and set up notifications that will
        // transition the swept kindergarten outputs and cltvCrib into graduated
        // outputs.
        if len(kgtnOutputs) > 0 {
                if err := u.sweepMatureOutputs(classHeight, kgtnOutputs); err != nil {
                        utxnLog.Errorf("Failed to sweep %d kindergarten "+
                                "outputs at height=%d: %v",
                                len(kgtnOutputs), classHeight, err)
                        return err
                }
        }

        // Now, we broadcast all pre-signed htlc txns from the csv crib outputs
        // at this height.
        for i := range cribOutputs {
                err := u.sweepCribOutput(classHeight, &cribOutputs[i])
                if err != nil {
                        utxnLog.Errorf("Failed to sweep first-stage HTLC "+
                                "(CLTV-delayed) output %v",
                                cribOutputs[i].OutPoint())
                        return err
                }
        }

        return nil
}

// decideDeadlineAndBudget returns the deadline and budget for a given output.
func (u *UtxoNursery) decideDeadlineAndBudget(k kidOutput) (fn.Option[int32],
        btcutil.Amount) {

        // Assume this is a to_local output and use a None deadline.
        deadline := fn.None[int32]()

        // Exit early if this is not HTLC.
        if !k.isHtlc {
                budget := calculateBudget(
                        k.amt, u.cfg.Budget.ToLocalRatio, u.cfg.Budget.ToLocal,
                )

                return deadline, budget
        }

        // Otherwise it's the first-level HTLC output, we'll use the
        // time-sensitive settings for it.
        budget := calculateBudget(
                k.amt, u.cfg.Budget.DeadlineHTLCRatio,
                u.cfg.Budget.DeadlineHTLC,
        )

        return k.deadlineHeight, budget
}

// sweepMatureOutputs generates and broadcasts the transaction that transfers
// control of funds from a prior channel commitment transaction to the user's
// wallet. The outputs swept were previously time locked (either absolute or
// relative), but are not mature enough to sweep into the wallet.
func (u *UtxoNursery) sweepMatureOutputs(classHeight uint32,
        kgtnOutputs []kidOutput) error {

        utxnLog.Infof("Sweeping %v CSV-delayed outputs with sweep tx for "+
                "height %v", len(kgtnOutputs), classHeight)

        for _, output := range kgtnOutputs {
                // Create local copy to prevent pointer to loop variable to be
                // passed in with disastrous consequences.
                local := output

                // Calculate the deadline height and budget for this output.
                deadline, budget := u.decideDeadlineAndBudget(local)

                resultChan, err := u.cfg.SweepInput(&local, sweep.Params{
                        DeadlineHeight: deadline,
                        Budget:         budget,
                })
                if err != nil {
                        return err
                }
                u.wg.Add(1)
                go u.waitForSweepConf(classHeight, &local, resultChan)
        }

        return nil
}

// waitForSweepConf watches for the confirmation of a sweep transaction
// containing a batch of kindergarten outputs. Once confirmation has been
// received, the nursery will mark those outputs as fully graduated, and proceed
// to mark any mature channels as fully closed in channeldb.
// NOTE(conner): this method MUST be called as a go routine.
func (u *UtxoNursery) waitForSweepConf(classHeight uint32,
        output *kidOutput, resultChan chan sweep.Result) {

        defer u.wg.Done()

        select {
        case result, ok := <-resultChan:
                if !ok {
                        utxnLog.Errorf("Notification chan closed, can't" +
                                " advance graduating output")
                        return
                }

                // In case of a remote spend, still graduate the output. There
                // is no way to sweep it anymore.
                if result.Err == sweep.ErrRemoteSpend {
                        utxnLog.Infof("Output %v was spend by remote party",
                                output.OutPoint())
                        break
                }

                if result.Err != nil {
                        utxnLog.Errorf("Failed to sweep %v at "+
                                "height=%d", output.OutPoint(),
                                classHeight)
                        return
                }

        case <-u.quit:
                return
        }

        u.mu.Lock()
        defer u.mu.Unlock()

        // TODO(conner): add retry utxnLogic?

        // Mark the confirmed kindergarten output as graduated.
        if err := u.cfg.Store.GraduateKinder(classHeight, output); err != nil {
                utxnLog.Errorf("Unable to graduate kindergarten output %v: %v",
                        output.OutPoint(), err)
                return
        }

        utxnLog.Infof("Graduated kindergarten output from height=%d",
                classHeight)

        // Attempt to close the channel, only doing so if all of the channel's
        // outputs have been graduated.
        chanPoint := output.OriginChanPoint()
        if err := u.closeAndRemoveIfMature(chanPoint); err != nil {
                utxnLog.Errorf("Failed to close and remove channel %v",
                        *chanPoint)
                return
        }
}

// sweepCribOutput broadcasts the crib output's htlc timeout txn, and sets up a
// notification that will advance it to the kindergarten bucket upon
// confirmation.
func (u *UtxoNursery) sweepCribOutput(classHeight uint32, baby *babyOutput) error {
        utxnLog.Infof("Publishing CLTV-delayed HTLC output using timeout tx "+
                "(txid=%v): %v", baby.timeoutTx.TxHash(),
                lnutils.SpewLogClosure(baby.timeoutTx))

        // We'll now broadcast the HTLC transaction, then wait for it to be
        // confirmed before transitioning it to kindergarten.
        label := labels.MakeLabel(labels.LabelTypeSweepTransaction, nil)
        err := u.cfg.PublishTransaction(baby.timeoutTx, label)

        // In case the tx does not meet mempool fee requirements we continue
        // because the tx is rebroadcasted in the background and there is
        // nothing we can do to bump this transaction anyways.
        if err != nil && !errors.Is(err, lnwallet.ErrDoubleSpend) &&
                !errors.Is(err, lnwallet.ErrMempoolFee) {

                utxnLog.Errorf("Unable to broadcast baby tx: "+
                        "%v, %v", err, spew.Sdump(baby.timeoutTx))
                return err
        }

        return u.registerTimeoutConf(baby, classHeight)
}

// registerTimeoutConf is responsible for subscribing to confirmation
// notification for an htlc timeout transaction. If successful, a goroutine
// will be spawned that will transition the provided baby output into the
// kindergarten state within the nursery store.
func (u *UtxoNursery) registerTimeoutConf(baby *babyOutput,
        heightHint uint32) error {

        birthTxID := baby.timeoutTx.TxHash()

        // Register for the confirmation of presigned htlc txn.
        confChan, err := u.cfg.Notifier.RegisterConfirmationsNtfn(
                &birthTxID, baby.timeoutTx.TxOut[0].PkScript, u.cfg.ConfDepth,
                heightHint,
        )
        if err != nil {
                return err
        }

        utxnLog.Infof("Htlc output %v registered for promotion "+
                "notification.", baby.OutPoint())

        u.wg.Add(1)
        go u.waitForTimeoutConf(baby, confChan)

        return nil
}

// waitForTimeoutConf watches for the confirmation of an htlc timeout
// transaction, and attempts to move the htlc output from the crib bucket to the
// kindergarten bucket upon success.
func (u *UtxoNursery) waitForTimeoutConf(baby *babyOutput,
        confChan *chainntnfs.ConfirmationEvent) {

        defer u.wg.Done()

        select {
        case txConfirmation, ok := <-confChan.Confirmed:
                if !ok {
                        utxnLog.Debugf("Notification chan "+
                                "closed, can't advance baby output %v",
                                baby.OutPoint())
                        return
                }

                baby.SetConfHeight(txConfirmation.BlockHeight)

        case <-u.quit:
                return
        }

        u.mu.Lock()
        defer u.mu.Unlock()

        // TODO(conner): add retry utxnLogic?

        err := u.cfg.Store.CribToKinder(baby)
        if err != nil {
                utxnLog.Errorf("Unable to move htlc output from "+
                        "crib to kindergarten bucket: %v", err)
                return
        }

        utxnLog.Infof("Htlc output %v promoted to "+
                "kindergarten", baby.OutPoint())
}

// registerPreschoolConf is responsible for subscribing to the confirmation of
// a commitment transaction, or an htlc success transaction for an incoming
// HTLC on our commitment transaction.. If successful, the provided preschool
// output will be moved persistently into the kindergarten state within the
// nursery store.
func (u *UtxoNursery) registerPreschoolConf(kid *kidOutput, heightHint uint32) error {
        txID := kid.OutPoint().Hash

        // TODO(roasbeef): ensure we don't already have one waiting, need to
        // de-duplicate
        //  * need to do above?

        pkScript := kid.signDesc.Output.PkScript
        confChan, err := u.cfg.Notifier.RegisterConfirmationsNtfn(
                &txID, pkScript, u.cfg.ConfDepth, heightHint,
        )
        if err != nil {
                return err
        }

        var outputType string
        if kid.isHtlc {
                outputType = "HTLC"
        } else {
                outputType = "Commitment"
        }

        utxnLog.Infof("%v outpoint %v registered for "+
                "confirmation notification.", outputType, kid.OutPoint())

        u.wg.Add(1)
        go u.waitForPreschoolConf(kid, confChan)

        return nil
}

// waitForPreschoolConf is intended to be run as a goroutine that will wait until
// a channel force close commitment transaction, or a second layer HTLC success
// transaction has been included in a confirmed block. Once the transaction has
// been confirmed (as reported by the Chain Notifier), waitForPreschoolConf
// will delete the output from the "preschool" database bucket and atomically
// add it to the "kindergarten" database bucket.  This is the second step in
// the output incubation process.
func (u *UtxoNursery) waitForPreschoolConf(kid *kidOutput,
        confChan *chainntnfs.ConfirmationEvent) {

        defer u.wg.Done()

        select {
        case txConfirmation, ok := <-confChan.Confirmed:
                if !ok {
                        utxnLog.Errorf("Notification chan "+
                                "closed, can't advance output %v",
                                kid.OutPoint())
                        return
                }

                kid.SetConfHeight(txConfirmation.BlockHeight)

        case <-u.quit:
                return
        }

        u.mu.Lock()
        defer u.mu.Unlock()

        // TODO(conner): add retry utxnLogic?

        var outputType string
        if kid.isHtlc {
                outputType = "HTLC"
        } else {
                outputType = "Commitment"
        }

        bestHeight := atomic.LoadUint32(&u.bestHeight)
        err := u.cfg.Store.PreschoolToKinder(kid, bestHeight)
        if err != nil {
                utxnLog.Errorf("Unable to move %v output "+
                        "from preschool to kindergarten bucket: %v",
                        outputType, err)
                return
        }
}

// RemoveChannel channel erases all entries from the channel bucket for the
// provided channel point.
func (u *UtxoNursery) RemoveChannel(op *wire.OutPoint) error {
        return u.cfg.Store.RemoveChannel(op)
}

// ContractMaturityReport is a report that details the maturity progress of a
// particular force closed contract.
type ContractMaturityReport struct {
        // limboBalance is the total number of frozen coins within this
        // contract.
        LimboBalance btcutil.Amount

        // recoveredBalance is the total value that has been successfully swept
        // back to the user's wallet.
        RecoveredBalance btcutil.Amount

        // htlcs records a maturity report for each htlc output in this channel.
        Htlcs []HtlcMaturityReport
}

// HtlcMaturityReport provides a summary of a single htlc output, and is
// embedded as party of the overarching ContractMaturityReport.
type HtlcMaturityReport struct {
        // Outpoint is the final output that will be swept back to the wallet.
        Outpoint wire.OutPoint

        // Amount is the final value that will be swept in back to the wallet.
        Amount btcutil.Amount

        // MaturityHeight is the absolute block height that this output will
        // mature at.
        MaturityHeight uint32

        // Stage indicates whether the htlc is in the CLTV-timeout stage (1) or
        // the CSV-delay stage (2). A stage 1 htlc's maturity height will be set
        // to its expiry height, while a stage 2 htlc's maturity height will be
        // set to its confirmation height plus the maturity requirement.
        Stage uint32
}

// AddLimboStage1TimeoutHtlc adds an htlc crib output to the maturity report's
// htlcs, and contributes its amount to the limbo balance.
func (c *ContractMaturityReport) AddLimboStage1TimeoutHtlc(baby *babyOutput) {
        c.LimboBalance += baby.Amount()

        // TODO(roasbeef): bool to indicate stage 1 vs stage 2?
        c.Htlcs = append(c.Htlcs, HtlcMaturityReport{
                Outpoint:       baby.OutPoint(),
                Amount:         baby.Amount(),
                MaturityHeight: baby.expiry,
                Stage:          1,
        })
}

// AddLimboDirectHtlc adds a direct HTLC on the commitment transaction of the
// remote party to the maturity report. This a CLTV time-locked output that
// has or hasn't expired yet.
func (c *ContractMaturityReport) AddLimboDirectHtlc(kid *kidOutput) {
        c.LimboBalance += kid.Amount()

        htlcReport := HtlcMaturityReport{
                Outpoint:       kid.OutPoint(),
                Amount:         kid.Amount(),
                MaturityHeight: kid.absoluteMaturity,
                Stage:          2,
        }

        c.Htlcs = append(c.Htlcs, htlcReport)
}

// AddLimboStage1SuccessHtlcHtlc adds an htlc crib output to the maturity
// report's set of HTLC's. We'll use this to report any incoming HTLC sweeps
// where the second level transaction hasn't yet confirmed.
func (c *ContractMaturityReport) AddLimboStage1SuccessHtlc(kid *kidOutput) {
        c.LimboBalance += kid.Amount()

        c.Htlcs = append(c.Htlcs, HtlcMaturityReport{
                Outpoint: kid.OutPoint(),
                Amount:   kid.Amount(),
                Stage:    1,
        })
}

// AddLimboStage2Htlc adds an htlc kindergarten output to the maturity report's
// htlcs, and contributes its amount to the limbo balance.
func (c *ContractMaturityReport) AddLimboStage2Htlc(kid *kidOutput) {
        c.LimboBalance += kid.Amount()

        htlcReport := HtlcMaturityReport{
                Outpoint: kid.OutPoint(),
                Amount:   kid.Amount(),
                Stage:    2,
        }

        // If the confirmation height is set, then this means the first stage
        // has been confirmed, and we know the final maturity height of the CSV
        // delay.
        if kid.ConfHeight() != 0 {
                htlcReport.MaturityHeight = kid.ConfHeight() + kid.BlocksToMaturity()
        }

        c.Htlcs = append(c.Htlcs, htlcReport)
}

// AddRecoveredHtlc adds a graduate output to the maturity report's htlcs, and
// contributes its amount to the recovered balance.
func (c *ContractMaturityReport) AddRecoveredHtlc(kid *kidOutput) {
        c.RecoveredBalance += kid.Amount()

        c.Htlcs = append(c.Htlcs, HtlcMaturityReport{
                Outpoint:       kid.OutPoint(),
                Amount:         kid.Amount(),
                MaturityHeight: kid.ConfHeight() + kid.BlocksToMaturity(),
        })
}

// closeAndRemoveIfMature removes a particular channel from the channel index
// if and only if all of its outputs have been marked graduated. If the channel
// still has ungraduated outputs, the method will succeed without altering the
// database state.
func (u *UtxoNursery) closeAndRemoveIfMature(chanPoint *wire.OutPoint) error {
        isMature, err := u.cfg.Store.IsMatureChannel(chanPoint)
        if err == ErrContractNotFound {
                return nil
        } else if err != nil {
                utxnLog.Errorf("Unable to determine maturity of "+
                        "channel=%s", chanPoint)
                return err
        }

        // Nothing to do if we are still incubating.
        if !isMature {
                return nil
        }

        // Now that the channel is fully closed, we remove the channel from the
        // nursery store here. This preserves the invariant that we never remove
        // a channel unless it is mature, as this is the only place the utxo
        // nursery removes a channel.
        if err := u.cfg.Store.RemoveChannel(chanPoint); err != nil {
                utxnLog.Errorf("Unable to remove channel=%s from "+
                        "nursery store: %v", chanPoint, err)
                return err
        }

        utxnLog.Infof("Removed channel %v from nursery store", chanPoint)

        return nil
}

// babyOutput represents a two-stage CSV locked output, and is used to track
// htlc outputs through incubation. The first stage requires broadcasting a
// presigned timeout txn that spends from the CLTV locked output on the
// commitment txn. A babyOutput is treated as a subset of CsvSpendableOutputs,
// with the additional constraint that a transaction must be broadcast before
// it can be spent. Each baby transaction embeds the kidOutput that can later
// be used to spend the CSV output contained in the timeout txn.
//
// TODO(roasbeef): re-rename to timeout tx
//   - create CltvCsvSpendableOutput
type babyOutput struct {
        // expiry is the absolute block height at which the secondLevelTx
        // should be broadcast to the network.
        //
        // NOTE: This value will be zero if this is a baby output for a prior
        // incoming HTLC.
        expiry uint32

        // timeoutTx is a fully-signed transaction that, upon confirmation,
        // transitions the htlc into the delay+claim stage.
        timeoutTx *wire.MsgTx

        // kidOutput represents the CSV output to be swept from the
        // secondLevelTx after it has been broadcast and confirmed.
        kidOutput
}

// makeBabyOutput constructs a baby output that wraps a future kidOutput. The
// provided sign descriptors and witness types will be used once the output
// reaches the delay and claim stage.
func makeBabyOutput(chanPoint *wire.OutPoint,
        htlcResolution *lnwallet.OutgoingHtlcResolution,
        deadlineHeight fn.Option[int32]) babyOutput {

        htlcOutpoint := htlcResolution.ClaimOutpoint
        blocksToMaturity := htlcResolution.CsvDelay

        isTaproot := txscript.IsPayToTaproot(
                htlcResolution.SweepSignDesc.Output.PkScript,
        )

        var witnessType input.StandardWitnessType
        if isTaproot {
                witnessType = input.TaprootHtlcOfferedTimeoutSecondLevel
        } else {
                witnessType = input.HtlcOfferedTimeoutSecondLevel
        }

        kid := makeKidOutput(
                &htlcOutpoint, chanPoint, blocksToMaturity, witnessType,
                &htlcResolution.SweepSignDesc, 0, deadlineHeight,
        )

        return babyOutput{
                kidOutput: kid,
                expiry:    htlcResolution.Expiry,
                timeoutTx: htlcResolution.SignedTimeoutTx,
        }
}

// Encode writes the baby output to the given io.Writer.
func (bo *babyOutput) Encode(w io.Writer) error {
        var scratch [4]byte
        byteOrder.PutUint32(scratch[:], bo.expiry)
        if _, err := w.Write(scratch[:]); err != nil {
                return err
        }

        if err := bo.timeoutTx.Serialize(w); err != nil {
                return err
        }

        return bo.kidOutput.Encode(w)
}

// Decode reconstructs a baby output using the provided io.Reader.
func (bo *babyOutput) Decode(r io.Reader) error {
        var scratch [4]byte
        if _, err := r.Read(scratch[:]); err != nil {
                return err
        }
        bo.expiry = byteOrder.Uint32(scratch[:])

        bo.timeoutTx = new(wire.MsgTx)
        if err := bo.timeoutTx.Deserialize(r); err != nil {
                return err
        }

        return bo.kidOutput.Decode(r)
}

// kidOutput represents an output that's waiting for a required blockheight
// before its funds will be available to be moved into the user's wallet.  The
// struct includes a WitnessGenerator closure which will be used to generate
// the witness required to sweep the output once it's mature.
//
// TODO(roasbeef): rename to immatureOutput?
type kidOutput struct {
        breachedOutput

        originChanPoint wire.OutPoint

        // isHtlc denotes if this kid output is an HTLC output or not. This
        // value will be used to determine how to report this output within the
        // nursery report.
        isHtlc bool

        // blocksToMaturity is the relative CSV delay required after initial
        // confirmation of the commitment transaction before we can sweep this
        // output.
        //
        // NOTE: This will be set for: commitment outputs, and incoming HTLC's.
        // Otherwise, this will be zero. It will also be non-zero for
        // commitment types which requires confirmed spends.
        blocksToMaturity uint32

        // absoluteMaturity is the absolute height that this output will be
        // mature at. In order to sweep the output after this height, the
        // locktime of sweep transaction will need to be set to this value.
        //
        // NOTE: This will only be set for: outgoing HTLC's on the commitment
        // transaction of the remote party.
        absoluteMaturity uint32

        // deadlineHeight is the absolute height that this output should be
        // confirmed at. For an incoming HTLC, this is the CLTV expiry height.
        // For outgoing HTLC, this is its corresponding incoming HTLC's CLTV
        // expiry height.
        deadlineHeight fn.Option[int32]
}

func makeKidOutput(outpoint, originChanPoint *wire.OutPoint,
        blocksToMaturity uint32, witnessType input.StandardWitnessType,
        signDescriptor *input.SignDescriptor, absoluteMaturity uint32,
        deadlineHeight fn.Option[int32]) kidOutput {

        // This is an HTLC either if it's an incoming HTLC on our commitment
        // transaction, or is an outgoing HTLC on the commitment transaction of
        // the remote peer.
        isHtlc := (witnessType == input.HtlcAcceptedSuccessSecondLevel ||
                witnessType == input.TaprootHtlcAcceptedSuccessSecondLevel ||
                witnessType == input.TaprootHtlcOfferedRemoteTimeout ||
                witnessType == input.HtlcOfferedRemoteTimeout)

        // heightHint can be safely set to zero here, because after this
        // function returns, nursery will set a proper confirmation height in
        // waitForTimeoutConf or waitForPreschoolConf.
        heightHint := uint32(0)

        return kidOutput{
                breachedOutput: makeBreachedOutput(
                        outpoint, witnessType, nil, signDescriptor, heightHint,
                        fn.None[tlv.Blob](),
                ),
                isHtlc:           isHtlc,
                originChanPoint:  *originChanPoint,
                blocksToMaturity: blocksToMaturity,
                absoluteMaturity: absoluteMaturity,
                deadlineHeight:   deadlineHeight,
        }
}

func (k *kidOutput) OriginChanPoint() *wire.OutPoint {
        return &k.originChanPoint
}

func (k *kidOutput) BlocksToMaturity() uint32 {
        return k.blocksToMaturity
}

func (k *kidOutput) SetConfHeight(height uint32) {
        k.confHeight = height
}

func (k *kidOutput) ConfHeight() uint32 {
        return k.confHeight
}

func (k *kidOutput) RequiredLockTime() (uint32, bool) {
        return k.absoluteMaturity, k.absoluteMaturity > 0
}

// Encode converts a KidOutput struct into a form suitable for on-disk database
// storage. Note that the signDescriptor struct field is included so that the
// output's witness can be generated by createSweepTx() when the output becomes
// spendable.
func (k *kidOutput) Encode(w io.Writer) error {
        var scratch [8]byte
        byteOrder.PutUint64(scratch[:], uint64(k.Amount()))
        if _, err := w.Write(scratch[:]); err != nil {
                return err
        }

        op := k.OutPoint()
        if err := graphdb.WriteOutpoint(w, &op); err != nil {
                return err
        }
        if err := graphdb.WriteOutpoint(w, k.OriginChanPoint()); err != nil {
                return err
        }

        if err := binary.Write(w, byteOrder, k.isHtlc); err != nil {
                return err
        }

        byteOrder.PutUint32(scratch[:4], k.BlocksToMaturity())
        if _, err := w.Write(scratch[:4]); err != nil {
                return err
        }

        byteOrder.PutUint32(scratch[:4], k.absoluteMaturity)
        if _, err := w.Write(scratch[:4]); err != nil {
                return err
        }

        byteOrder.PutUint32(scratch[:4], k.ConfHeight())
        if _, err := w.Write(scratch[:4]); err != nil {
                return err
        }

        byteOrder.PutUint16(scratch[:2], uint16(k.witnessType))
        if _, err := w.Write(scratch[:2]); err != nil {
                return err
        }

        if err := input.WriteSignDescriptor(w, k.SignDesc()); err != nil {
                return err
        }

        if k.SignDesc().ControlBlock == nil {
                return nil
        }

        // If this is a taproot output, then it'll also have a control block,
        // so we'll go ahead and write that now.
        return wire.WriteVarBytes(w, 1000, k.SignDesc().ControlBlock)
}

// Decode takes a byte array representation of a kidOutput and converts it to an
// struct. Note that the witnessFunc method isn't added during deserialization
// and must be added later based on the value of the witnessType field.
func (k *kidOutput) Decode(r io.Reader) error {
        var scratch [8]byte

        if _, err := r.Read(scratch[:]); err != nil {
                return err
        }
        k.amt = btcutil.Amount(byteOrder.Uint64(scratch[:]))

        err := graphdb.ReadOutpoint(io.LimitReader(r, 40), &k.outpoint)
        if err != nil {
                return err
        }

        err = graphdb.ReadOutpoint(io.LimitReader(r, 40), &k.originChanPoint)
        if err != nil {
                return err
        }

        if err := binary.Read(r, byteOrder, &k.isHtlc); err != nil {
                return err
        }

        if _, err := r.Read(scratch[:4]); err != nil {
                return err
        }
        k.blocksToMaturity = byteOrder.Uint32(scratch[:4])

        if _, err := r.Read(scratch[:4]); err != nil {
                return err
        }
        k.absoluteMaturity = byteOrder.Uint32(scratch[:4])

        if _, err := r.Read(scratch[:4]); err != nil {
                return err
        }
        k.confHeight = byteOrder.Uint32(scratch[:4])

        if _, err := r.Read(scratch[:2]); err != nil {
                return err
        }
        k.witnessType = input.StandardWitnessType(byteOrder.Uint16(scratch[:2]))

        if err := input.ReadSignDescriptor(r, &k.signDesc); err != nil {
                return err
        }

        // If there's anything left in the reader, then this is a taproot
        // output that also wrote a control block.
        ctrlBlock, err := wire.ReadVarBytes(r, 0, 1000, "control block")
        switch {
        // If there're no bytes remaining, then we'll return early.
        case errors.Is(err, io.EOF):
                fallthrough
        case errors.Is(err, io.ErrUnexpectedEOF):
                return nil

        case err != nil:
                return err
        }

        k.signDesc.ControlBlock = ctrlBlock

        return nil
}

// Compile-time constraint to ensure kidOutput implements the
// Input interface.

var _ input.Input = (*kidOutput)(nil)

lightningnetwork / lnd / 13211764208

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