16673052227

Committed 01 Aug 2025 10:44AM UTC coverage: 67.016% (-0.03%) from 67.047%

Build # 16673052227

Build Type

Pull #9888

github

Committed by

web-flow

Commit Message

Merge 1dd8765d7 into 37523b6cb

Pull Request Pull Request #9888: Attributable failures

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78.43

/peer/brontide.go

package peer

import (
        "bytes"
        "container/list"
        "context"
        "errors"
        "fmt"
        "math/rand"
        "net"
        "strings"
        "sync"
        "sync/atomic"
        "time"

        "github.com/btcsuite/btcd/btcec/v2"
        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/btcsuite/btcd/connmgr"
        "github.com/btcsuite/btcd/txscript"
        "github.com/btcsuite/btcd/wire"
        "github.com/btcsuite/btclog/v2"
        "github.com/davecgh/go-spew/spew"
        sphinx "github.com/lightningnetwork/lightning-onion"
        "github.com/lightningnetwork/lnd/buffer"
        "github.com/lightningnetwork/lnd/chainntnfs"
        "github.com/lightningnetwork/lnd/channeldb"
        "github.com/lightningnetwork/lnd/channelnotifier"
        "github.com/lightningnetwork/lnd/contractcourt"
        "github.com/lightningnetwork/lnd/discovery"
        "github.com/lightningnetwork/lnd/feature"
        "github.com/lightningnetwork/lnd/fn/v2"
        "github.com/lightningnetwork/lnd/funding"
        graphdb "github.com/lightningnetwork/lnd/graph/db"
        "github.com/lightningnetwork/lnd/graph/db/models"
        "github.com/lightningnetwork/lnd/htlcswitch"
        "github.com/lightningnetwork/lnd/htlcswitch/hodl"
        "github.com/lightningnetwork/lnd/htlcswitch/hop"
        "github.com/lightningnetwork/lnd/input"
        "github.com/lightningnetwork/lnd/invoices"
        "github.com/lightningnetwork/lnd/keychain"
        "github.com/lightningnetwork/lnd/lnpeer"
        "github.com/lightningnetwork/lnd/lntypes"
        "github.com/lightningnetwork/lnd/lnutils"
        "github.com/lightningnetwork/lnd/lnwallet"
        "github.com/lightningnetwork/lnd/lnwallet/chainfee"
        "github.com/lightningnetwork/lnd/lnwallet/chancloser"
        "github.com/lightningnetwork/lnd/lnwire"
        "github.com/lightningnetwork/lnd/msgmux"
        "github.com/lightningnetwork/lnd/netann"
        "github.com/lightningnetwork/lnd/pool"
        "github.com/lightningnetwork/lnd/protofsm"
        "github.com/lightningnetwork/lnd/queue"
        "github.com/lightningnetwork/lnd/subscribe"
        "github.com/lightningnetwork/lnd/ticker"
        "github.com/lightningnetwork/lnd/tlv"
        "github.com/lightningnetwork/lnd/watchtower/wtclient"
)

const (
        // pingInterval is the interval at which ping messages are sent.
        pingInterval = 1 * time.Minute

        // pingTimeout is the amount of time we will wait for a pong response
        // before considering the peer to be unresponsive.
        //
        // This MUST be a smaller value than the pingInterval.
        pingTimeout = 30 * time.Second

        // idleTimeout is the duration of inactivity before we time out a peer.
        idleTimeout = 5 * time.Minute

        // writeMessageTimeout is the timeout used when writing a message to the
        // peer.
        writeMessageTimeout = 5 * time.Second

        // readMessageTimeout is the timeout used when reading a message from a
        // peer.
        readMessageTimeout = 5 * time.Second

        // handshakeTimeout is the timeout used when waiting for the peer's init
        // message.
        handshakeTimeout = 15 * time.Second

        // ErrorBufferSize is the number of historic peer errors that we store.
        ErrorBufferSize = 10

        // pongSizeCeiling is the upper bound on a uniformly distributed random
        // variable that we use for requesting pong responses. We don't use the
        // MaxPongBytes (upper bound accepted by the protocol) because it is
        // needlessly wasteful of precious Tor bandwidth for little to no gain.
        pongSizeCeiling = 4096

        // torTimeoutMultiplier is the scaling factor we use on network timeouts
        // for Tor peers.
        torTimeoutMultiplier = 3

        // msgStreamSize is the size of the message streams.
        msgStreamSize = 50
)

var (
        // ErrChannelNotFound is an error returned when a channel is queried and
        // either the Brontide doesn't know of it, or the channel in question
        // is pending.
        ErrChannelNotFound = fmt.Errorf("channel not found")
)

// outgoingMsg packages an lnwire.Message to be sent out on the wire, along with
// a buffered channel which will be sent upon once the write is complete. This
// buffered channel acts as a semaphore to be used for synchronization purposes.
type outgoingMsg struct {
        priority bool
        msg      lnwire.Message
        errChan  chan error // MUST be buffered.
}

// newChannelMsg packages a channeldb.OpenChannel with a channel that allows
// the receiver of the request to report when the channel creation process has
// completed.
type newChannelMsg struct {
        // channel is used when the pending channel becomes active.
        channel *lnpeer.NewChannel

        // channelID is used when there's a new pending channel.
        channelID lnwire.ChannelID

        err chan error
}

type customMsg struct {
        peer [33]byte
        msg  lnwire.Custom
}

// closeMsg is a wrapper struct around any wire messages that deal with the
// cooperative channel closure negotiation process. This struct includes the
// raw channel ID targeted along with the original message.
type closeMsg struct {
        cid lnwire.ChannelID
        msg lnwire.Message
}

// PendingUpdate describes the pending state of a closing channel.
type PendingUpdate struct {
        // Txid is the txid of the closing transaction.
        Txid []byte

        // OutputIndex is the output index of our output in the closing
        // transaction.
        OutputIndex uint32

        // FeePerVByte is an optional field, that is set only when the new RBF
        // coop close flow is used. This indicates the new closing fee rate on
        // the closing transaction.
        FeePerVbyte fn.Option[chainfee.SatPerVByte]

        // IsLocalCloseTx is an optional field that indicates if this update is
        // sent for our local close txn, or the close txn of the remote party.
        // This is only set if the new RBF coop close flow is used.
        IsLocalCloseTx fn.Option[bool]
}

// ChannelCloseUpdate contains the outcome of the close channel operation.
type ChannelCloseUpdate struct {
        ClosingTxid []byte
        Success     bool

        // LocalCloseOutput is an optional, additional output on the closing
        // transaction that the local party should be paid to. This will only be
        // populated if the local balance isn't dust.
        LocalCloseOutput fn.Option[chancloser.CloseOutput]

        // RemoteCloseOutput is an optional, additional output on the closing
        // transaction that the remote party should be paid to. This will only
        // be populated if the remote balance isn't dust.
        RemoteCloseOutput fn.Option[chancloser.CloseOutput]

        // AuxOutputs is an optional set of additional outputs that might be
        // included in the closing transaction. These are used for custom
        // channel types.
        AuxOutputs fn.Option[chancloser.AuxCloseOutputs]
}

// TimestampedError is a timestamped error that is used to store the most recent
// errors we have experienced with our peers.
type TimestampedError struct {
        Error     error
        Timestamp time.Time
}

// Config defines configuration fields that are necessary for a peer object
// to function.
type Config struct {
        // Conn is the underlying network connection for this peer.
        Conn MessageConn

        // ConnReq stores information related to the persistent connection request
        // for this peer.
        ConnReq *connmgr.ConnReq

        // PubKeyBytes is the serialized, compressed public key of this peer.
        PubKeyBytes [33]byte

        // Addr is the network address of the peer.
        Addr *lnwire.NetAddress

        // Inbound indicates whether or not the peer is an inbound peer.
        Inbound bool

        // Features is the set of features that we advertise to the remote party.
        Features *lnwire.FeatureVector

        // LegacyFeatures is the set of features that we advertise to the remote
        // peer for backwards compatibility. Nodes that have not implemented
        // flat features will still be able to read our feature bits from the
        // legacy global field, but we will also advertise everything in the
        // default features field.
        LegacyFeatures *lnwire.FeatureVector

        // OutgoingCltvRejectDelta defines the number of blocks before expiry of
        // an htlc where we don't offer it anymore.
        OutgoingCltvRejectDelta uint32

        // ChanActiveTimeout specifies the duration the peer will wait to request
        // a channel reenable, beginning from the time the peer was started.
        ChanActiveTimeout time.Duration

        // ErrorBuffer stores a set of errors related to a peer. It contains error
        // messages that our peer has recently sent us over the wire and records of
        // unknown messages that were sent to us so that we can have a full track
        // record of the communication errors we have had with our peer. If we
        // choose to disconnect from a peer, it also stores the reason we had for
        // disconnecting.
        ErrorBuffer *queue.CircularBuffer

        // WritePool is the task pool that manages reuse of write buffers. Write
        // tasks are submitted to the pool in order to conserve the total number of
        // write buffers allocated at any one time, and decouple write buffer
        // allocation from the peer life cycle.
        WritePool *pool.Write

        // ReadPool is the task pool that manages reuse of read buffers.
        ReadPool *pool.Read

        // Switch is a pointer to the htlcswitch. It is used to setup, get, and
        // tear-down ChannelLinks.
        Switch messageSwitch

        // InterceptSwitch is a pointer to the InterceptableSwitch, a wrapper around
        // the regular Switch. We only export it here to pass ForwardPackets to the
        // ChannelLinkConfig.
        InterceptSwitch *htlcswitch.InterceptableSwitch

        // ChannelDB is used to fetch opened channels, and closed channels.
        ChannelDB *channeldb.ChannelStateDB

        // ChannelGraph is a pointer to the channel graph which is used to
        // query information about the set of known active channels.
        ChannelGraph *graphdb.ChannelGraph

        // ChainArb is used to subscribe to channel events, update contract signals,
        // and force close channels.
        ChainArb *contractcourt.ChainArbitrator

        // AuthGossiper is needed so that the Brontide impl can register with the
        // gossiper and process remote channel announcements.
        AuthGossiper *discovery.AuthenticatedGossiper

        // ChanStatusMgr is used to set or un-set the disabled bit in channel
        // updates.
        ChanStatusMgr *netann.ChanStatusManager

        // ChainIO is used to retrieve the best block.
        ChainIO lnwallet.BlockChainIO

        // FeeEstimator is used to compute our target ideal fee-per-kw when
        // initializing the coop close process.
        FeeEstimator chainfee.Estimator

        // Signer is used when creating *lnwallet.LightningChannel instances.
        Signer input.Signer

        // SigPool is used when creating *lnwallet.LightningChannel instances.
        SigPool *lnwallet.SigPool

        // Wallet is used to publish transactions and generates delivery
        // scripts during the coop close process.
        Wallet *lnwallet.LightningWallet

        // ChainNotifier is used to receive confirmations of a coop close
        // transaction.
        ChainNotifier chainntnfs.ChainNotifier

        // BestBlockView is used to efficiently query for up-to-date
        // blockchain state information
        BestBlockView chainntnfs.BestBlockView

        // RoutingPolicy is used to set the forwarding policy for links created by
        // the Brontide.
        RoutingPolicy models.ForwardingPolicy

        // Sphinx is used when setting up ChannelLinks so they can decode sphinx
        // onion blobs.
        Sphinx *hop.OnionProcessor

        // WitnessBeacon is used when setting up ChannelLinks so they can add any
        // preimages that they learn.
        WitnessBeacon contractcourt.WitnessBeacon

        // Invoices is passed to the ChannelLink on creation and handles all
        // invoice-related logic.
        Invoices *invoices.InvoiceRegistry

        // ChannelNotifier is used by the link to notify other sub-systems about
        // channel-related events and by the Brontide to subscribe to
        // ActiveLinkEvents.
        ChannelNotifier *channelnotifier.ChannelNotifier

        // HtlcNotifier is used when creating a ChannelLink.
        HtlcNotifier *htlcswitch.HtlcNotifier

        // TowerClient is used to backup revoked states.
        TowerClient wtclient.ClientManager

        // DisconnectPeer is used to disconnect this peer if the cooperative close
        // process fails.
        DisconnectPeer func(*btcec.PublicKey) error

        // GenNodeAnnouncement is used to send our node announcement to the remote
        // on startup.
        GenNodeAnnouncement func(...netann.NodeAnnModifier) (
                lnwire.NodeAnnouncement, error)

        // PrunePersistentPeerConnection is used to remove all internal state
        // related to this peer in the server.
        PrunePersistentPeerConnection func([33]byte)

        // FetchLastChanUpdate fetches our latest channel update for a target
        // channel.
        FetchLastChanUpdate func(lnwire.ShortChannelID) (*lnwire.ChannelUpdate1,
                error)

        // FundingManager is an implementation of the funding.Controller interface.
        FundingManager funding.Controller

        // Hodl is used when creating ChannelLinks to specify HodlFlags as
        // breakpoints in dev builds.
        Hodl *hodl.Config

        // UnsafeReplay is used when creating ChannelLinks to specify whether or
        // not to replay adds on its commitment tx.
        UnsafeReplay bool

        // MaxOutgoingCltvExpiry is used when creating ChannelLinks and is the max
        // number of blocks that funds could be locked up for when forwarding
        // payments.
        MaxOutgoingCltvExpiry uint32

        // MaxChannelFeeAllocation is used when creating ChannelLinks and is the
        // maximum percentage of total funds that can be allocated to a channel's
        // commitment fee. This only applies for the initiator of the channel.
        MaxChannelFeeAllocation float64

        // MaxAnchorsCommitFeeRate is the maximum fee rate we'll use as an
        // initiator for anchor channel commitments.
        MaxAnchorsCommitFeeRate chainfee.SatPerKWeight

        // CoopCloseTargetConfs is the confirmation target that will be used
        // to estimate the fee rate to use during a cooperative channel
        // closure initiated by the remote peer.
        CoopCloseTargetConfs uint32

        // ServerPubKey is the serialized, compressed public key of our lnd node.
        // It is used to determine which policy (channel edge) to pass to the
        // ChannelLink.
        ServerPubKey [33]byte

        // ChannelCommitInterval is the maximum time that is allowed to pass between
        // receiving a channel state update and signing the next commitment.
        // Setting this to a longer duration allows for more efficient channel
        // operations at the cost of latency.
        ChannelCommitInterval time.Duration

        // PendingCommitInterval is the maximum time that is allowed to pass
        // while waiting for the remote party to revoke a locally initiated
        // commitment state. Setting this to a longer duration if a slow
        // response is expected from the remote party or large number of
        // payments are attempted at the same time.
        PendingCommitInterval time.Duration

        // ChannelCommitBatchSize is the maximum number of channel state updates
        // that is accumulated before signing a new commitment.
        ChannelCommitBatchSize uint32

        // HandleCustomMessage is called whenever a custom message is received
        // from the peer.
        HandleCustomMessage func(peer [33]byte, msg *lnwire.Custom) error

        // GetAliases is passed to created links so the Switch and link can be
        // aware of the channel's aliases.
        GetAliases func(base lnwire.ShortChannelID) []lnwire.ShortChannelID

        // RequestAlias allows the Brontide struct to request an alias to send
        // to the peer.
        RequestAlias func() (lnwire.ShortChannelID, error)

        // AddLocalAlias persists an alias to an underlying alias store.
        AddLocalAlias func(alias, base lnwire.ShortChannelID,
                gossip, liveUpdate bool) error

        // AuxLeafStore is an optional store that can be used to store auxiliary
        // leaves for certain custom channel types.
        AuxLeafStore fn.Option[lnwallet.AuxLeafStore]

        // AuxSigner is an optional signer that can be used to sign auxiliary
        // leaves for certain custom channel types.
        AuxSigner fn.Option[lnwallet.AuxSigner]

        // AuxResolver is an optional interface that can be used to modify the
        // way contracts are resolved.
        AuxResolver fn.Option[lnwallet.AuxContractResolver]

        // AuxTrafficShaper is an optional auxiliary traffic shaper that can be
        // used to manage the bandwidth of peer links.
        AuxTrafficShaper fn.Option[htlcswitch.AuxTrafficShaper]

        // PongBuf is a slice we'll reuse instead of allocating memory on the
        // heap. Since only reads will occur and no writes, there is no need
        // for any synchronization primitives. As a result, it's safe to share
        // this across multiple Peer struct instances.
        PongBuf []byte

        // Adds the option to disable forwarding payments in blinded routes
        // by failing back any blinding-related payloads as if they were
        // invalid.
        DisallowRouteBlinding bool

        // DisallowQuiescence is a flag that indicates whether the Brontide
        // should have the quiescence feature disabled.
        DisallowQuiescence bool

        // QuiescenceTimeout is the max duration that the channel can be
        // quiesced. Any dependent protocols (dynamic commitments, splicing,
        // etc.) must finish their operations under this timeout value,
        // otherwise the node will disconnect.
        QuiescenceTimeout time.Duration

        // MaxFeeExposure limits the number of outstanding fees in a channel.
        // This value will be passed to created links.
        MaxFeeExposure lnwire.MilliSatoshi

        // MsgRouter is an optional instance of the main message router that
        // the peer will use. If None, then a new default version will be used
        // in place.
        MsgRouter fn.Option[msgmux.Router]

        // AuxChanCloser is an optional instance of an abstraction that can be
        // used to modify the way the co-op close transaction is constructed.
        AuxChanCloser fn.Option[chancloser.AuxChanCloser]

        // ShouldFwdExpEndorsement is a closure that indicates whether
        // experimental endorsement signals should be set.
        ShouldFwdExpEndorsement func() bool

        // NoDisconnectOnPongFailure indicates whether the peer should *not* be
        // disconnected if a pong is not received in time or is mismatched.
        NoDisconnectOnPongFailure bool

        // Quit is the server's quit channel. If this is closed, we halt operation.
        Quit chan struct{}
}

// chanCloserFsm is a union-like type that can hold the two versions of co-op
// close we support: negotiation, and RBF based.
//
// TODO(roasbeef): rename to chancloser.Negotiator and chancloser.RBF?
type chanCloserFsm = fn.Either[*chancloser.ChanCloser, *chancloser.RbfChanCloser] //nolint:ll

// makeNegotiateCloser creates a new negotiate closer from a
// chancloser.ChanCloser.
func makeNegotiateCloser(chanCloser *chancloser.ChanCloser) chanCloserFsm {
        return fn.NewLeft[*chancloser.ChanCloser, *chancloser.RbfChanCloser](
                chanCloser,
        )
}

// makeRbfCloser creates a new RBF closer from a chancloser.RbfChanCloser.
func makeRbfCloser(rbfCloser *chancloser.RbfChanCloser) chanCloserFsm {
        return fn.NewRight[*chancloser.ChanCloser](
                rbfCloser,
        )
}

// Brontide is an active peer on the Lightning Network. This struct is responsible
// for managing any channel state related to this peer. To do so, it has
// several helper goroutines to handle events such as HTLC timeouts, new
// funding workflow, and detecting an uncooperative closure of any active
// channels.
type Brontide struct {
        // MUST be used atomically.
        started    int32
        disconnect int32

        // MUST be used atomically.
        bytesReceived uint64
        bytesSent     uint64

        // isTorConnection is a flag that indicates whether or not we believe
        // the remote peer is a tor connection. It is not always possible to
        // know this with certainty but we have heuristics we use that should
        // catch most cases.
        //
        // NOTE: We judge the tor-ness of a connection by if the remote peer has
        // ".onion" in the address OR if it's connected over localhost.
        // This will miss cases where our peer is connected to our clearnet
        // address over the tor network (via exit nodes). It will also misjudge
        // actual localhost connections as tor. We need to include this because
        // inbound connections to our tor address will appear to come from the
        // local socks5 proxy. This heuristic is only used to expand the timeout
        // window for peers so it is OK to misjudge this. If you use this field
        // for any other purpose you should seriously consider whether or not
        // this heuristic is good enough for your use case.
        isTorConnection bool

        pingManager *PingManager

        // lastPingPayload stores an unsafe pointer wrapped as an atomic
        // variable which points to the last payload the remote party sent us
        // as their ping.
        //
        // MUST be used atomically.
        lastPingPayload atomic.Value

        cfg Config

        // activeSignal when closed signals that the peer is now active and
        // ready to process messages.
        activeSignal chan struct{}

        // startTime is the time this peer connection was successfully established.
        // It will be zero for peers that did not successfully call Start().
        startTime time.Time

        // sendQueue is the channel which is used to queue outgoing messages to be
        // written onto the wire. Note that this channel is unbuffered.
        sendQueue chan outgoingMsg

        // outgoingQueue is a buffered channel which allows second/third party
        // objects to queue messages to be sent out on the wire.
        outgoingQueue chan outgoingMsg

        // activeChannels is a map which stores the state machines of all
        // active channels. Channels are indexed into the map by the txid of
        // the funding transaction which opened the channel.
        //
        // NOTE: On startup, pending channels are stored as nil in this map.
        // Confirmed channels have channel data populated in the map. This means
        // that accesses to this map should nil-check the LightningChannel to
        // see if this is a pending channel or not. The tradeoff here is either
        // having two maps everywhere (one for pending, one for confirmed chans)
        // or having an extra nil-check per access.
        activeChannels *lnutils.SyncMap[
                lnwire.ChannelID, *lnwallet.LightningChannel]

        // addedChannels tracks any new channels opened during this peer's
        // lifecycle. We use this to filter out these new channels when the time
        // comes to request a reenable for active channels, since they will have
        // waited a shorter duration.
        addedChannels *lnutils.SyncMap[lnwire.ChannelID, struct{}]

        // newActiveChannel is used by the fundingManager to send fully opened
        // channels to the source peer which handled the funding workflow.
        newActiveChannel chan *newChannelMsg

        // newPendingChannel is used by the fundingManager to send pending open
        // channels to the source peer which handled the funding workflow.
        newPendingChannel chan *newChannelMsg

        // removePendingChannel is used by the fundingManager to cancel pending
        // open channels to the source peer when the funding flow is failed.
        removePendingChannel chan *newChannelMsg

        // activeMsgStreams is a map from channel id to the channel streams that
        // proxy messages to individual, active links.
        activeMsgStreams map[lnwire.ChannelID]*msgStream

        // activeChanCloses is a map that keeps track of all the active
        // cooperative channel closures. Any channel closing messages are directed
        // to one of these active state machines. Once the channel has been closed,
        // the state machine will be deleted from the map.
        activeChanCloses *lnutils.SyncMap[lnwire.ChannelID, chanCloserFsm]

        // localCloseChanReqs is a channel in which any local requests to close
        // a particular channel are sent over.
        localCloseChanReqs chan *htlcswitch.ChanClose

        // linkFailures receives all reported channel failures from the switch,
        // and instructs the channelManager to clean remaining channel state.
        linkFailures chan linkFailureReport

        // chanCloseMsgs is a channel that any message related to channel
        // closures are sent over. This includes lnwire.Shutdown message as
        // well as lnwire.ClosingSigned messages.
        chanCloseMsgs chan *closeMsg

        // remoteFeatures is the feature vector received from the peer during
        // the connection handshake.
        remoteFeatures *lnwire.FeatureVector

        // resentChanSyncMsg is a set that keeps track of which channels we
        // have re-sent channel reestablishment messages for. This is done to
        // avoid getting into loop where both peers will respond to the other
        // peer's chansync message with its own over and over again.
        resentChanSyncMsg map[lnwire.ChannelID]struct{}

        // channelEventClient is the channel event subscription client that's
        // used to assist retry enabling the channels. This client is only
        // created when the reenableTimeout is no greater than 1 minute. Once
        // created, it is canceled once the reenabling has been finished.
        //
        // NOTE: we choose to create the client conditionally to avoid
        // potentially holding lots of un-consumed events.
        channelEventClient *subscribe.Client

        // msgRouter is an instance of the msgmux.Router which is used to send
        // off new wire messages for handing.
        msgRouter fn.Option[msgmux.Router]

        // globalMsgRouter is a flag that indicates whether we have a global
        // msg router. If so, then we don't worry about stopping the msg router
        // when a peer disconnects.
        globalMsgRouter bool

        startReady chan struct{}

        // cg is a helper that encapsulates a wait group and quit channel and
        // allows contexts that either block or cancel on those depending on
        // the use case.
        cg *fn.ContextGuard

        // log is a peer-specific logging instance.
        log btclog.Logger
}

// A compile-time check to ensure that Brontide satisfies the lnpeer.Peer
// interface.
var _ lnpeer.Peer = (*Brontide)(nil)

// NewBrontide creates a new Brontide from a peer.Config struct.
func NewBrontide(cfg Config) *Brontide {
        logPrefix := fmt.Sprintf("Peer(%x):", cfg.PubKeyBytes)

        // We have a global message router if one was passed in via the config.
        // In this case, we don't need to attempt to tear it down when the peer
        // is stopped.
        globalMsgRouter := cfg.MsgRouter.IsSome()

        // We'll either use the msg router instance passed in, or create a new
        // blank instance.
        msgRouter := cfg.MsgRouter.Alt(fn.Some[msgmux.Router](
                msgmux.NewMultiMsgRouter(),
        ))

        p := &Brontide{
                cfg:           cfg,
                activeSignal:  make(chan struct{}),
                sendQueue:     make(chan outgoingMsg),
                outgoingQueue: make(chan outgoingMsg),
                addedChannels: &lnutils.SyncMap[lnwire.ChannelID, struct{}]{},
                activeChannels: &lnutils.SyncMap[
                        lnwire.ChannelID, *lnwallet.LightningChannel,
                ]{},
                newActiveChannel:     make(chan *newChannelMsg, 1),
                newPendingChannel:    make(chan *newChannelMsg, 1),
                removePendingChannel: make(chan *newChannelMsg),

                activeMsgStreams: make(map[lnwire.ChannelID]*msgStream),
                activeChanCloses: &lnutils.SyncMap[
                        lnwire.ChannelID, chanCloserFsm,
                ]{},
                localCloseChanReqs: make(chan *htlcswitch.ChanClose),
                linkFailures:       make(chan linkFailureReport),
                chanCloseMsgs:      make(chan *closeMsg),
                resentChanSyncMsg:  make(map[lnwire.ChannelID]struct{}),
                startReady:         make(chan struct{}),
                log:                peerLog.WithPrefix(logPrefix),
                msgRouter:          msgRouter,
                globalMsgRouter:    globalMsgRouter,
                cg:                 fn.NewContextGuard(),
        }

        if cfg.Conn != nil && cfg.Conn.RemoteAddr() != nil {
                remoteAddr := cfg.Conn.RemoteAddr().String()
                p.isTorConnection = strings.Contains(remoteAddr, ".onion") ||
                        strings.Contains(remoteAddr, "127.0.0.1")
        }

        var (
                lastBlockHeader           *wire.BlockHeader
                lastSerializedBlockHeader [wire.MaxBlockHeaderPayload]byte
        )
        newPingPayload := func() []byte {
                // We query the BestBlockHeader from our BestBlockView each time
                // this is called, and update our serialized block header if
                // they differ.  Over time, we'll use this to disseminate the
                // latest block header between all our peers, which can later be
                // used to cross-check our own view of the network to mitigate
                // various types of eclipse attacks.
                header, err := p.cfg.BestBlockView.BestBlockHeader()
                if err != nil && header == lastBlockHeader {
                        return lastSerializedBlockHeader[:]
                }

                buf := bytes.NewBuffer(lastSerializedBlockHeader[0:0])
                err = header.Serialize(buf)
                if err == nil {
                        lastBlockHeader = header
                } else {
                        p.log.Warn("unable to serialize current block" +
                                "header for ping payload generation." +
                                "This should be impossible and means" +
                                "there is an implementation bug.")
                }

                return lastSerializedBlockHeader[:]
        }

        // TODO(roasbeef): make dynamic in order to create fake cover traffic.
        //
        // NOTE(proofofkeags): this was changed to be dynamic to allow better
        // pong identification, however, more thought is needed to make this
        // actually usable as a traffic decoy.
        randPongSize := func() uint16 {
                return uint16(
                        // We don't need cryptographic randomness here.
                        /* #nosec */
                        rand.Intn(pongSizeCeiling) + 1,
                )
        }

        p.pingManager = NewPingManager(&PingManagerConfig{
                NewPingPayload:   newPingPayload,
                NewPongSize:      randPongSize,
                IntervalDuration: p.scaleTimeout(pingInterval),
                TimeoutDuration:  p.scaleTimeout(pingTimeout),
                SendPing: func(ping *lnwire.Ping) {
                        p.queueMsg(ping, nil)
                },
                OnPongFailure: func(reason error,
                        timeWaitedForPong time.Duration,
                        lastKnownRTT time.Duration) {

                        logMsg := fmt.Sprintf("pong response "+
                                "failure for %s: %v. Time waited for this "+
                                "pong: %v. Last successful RTT: %v.",
                                p, reason, timeWaitedForPong, lastKnownRTT)

                        // If NoDisconnectOnPongFailure is true, we don't
                        // disconnect. Otherwise (if it's false, the default),
                        // we disconnect.
                        if p.cfg.NoDisconnectOnPongFailure {
                                p.log.Warnf("%s -- not disconnecting "+
                                        "due to config", logMsg)
                                return
                        }

                        p.log.Warnf("%s -- disconnecting", logMsg)

                        go p.Disconnect(fmt.Errorf("pong failure: %w", reason))
                },
        })

        return p
}

// Start starts all helper goroutines the peer needs for normal operations.  In
// the case this peer has already been started, then this function is a noop.
func (p *Brontide) Start() error {
        if atomic.AddInt32(&p.started, 1) != 1 {
                return nil
        }

        // Once we've finished starting up the peer, we'll signal to other
        // goroutines that the they can move forward to tear down the peer, or
        // carry out other relevant changes.
        defer close(p.startReady)

        p.log.Tracef("starting with conn[%v->%v]",
                p.cfg.Conn.LocalAddr(), p.cfg.Conn.RemoteAddr())

        // Fetch and then load all the active channels we have with this remote
        // peer from the database.
        activeChans, err := p.cfg.ChannelDB.FetchOpenChannels(
                p.cfg.Addr.IdentityKey,
        )
        if err != nil {
                p.log.Errorf("Unable to fetch active chans "+
                        "for peer: %v", err)
                return err
        }

        if len(activeChans) == 0 {
                go p.cfg.PrunePersistentPeerConnection(p.cfg.PubKeyBytes)
        }

        // Quickly check if we have any existing legacy channels with this
        // peer.
        haveLegacyChan := false
        for _, c := range activeChans {
                if c.ChanType.IsTweakless() {
                        continue
                }

                haveLegacyChan = true
                break
        }

        // Exchange local and global features, the init message should be very
        // first between two nodes.
        if err := p.sendInitMsg(haveLegacyChan); err != nil {
                return fmt.Errorf("unable to send init msg: %w", err)
        }

        // Before we launch any of the helper goroutines off the peer struct,
        // we'll first ensure proper adherence to the p2p protocol. The init
        // message MUST be sent before any other message.
        readErr := make(chan error, 1)
        msgChan := make(chan lnwire.Message, 1)
        p.cg.WgAdd(1)
        go func() {
                defer p.cg.WgDone()

                msg, err := p.readNextMessage()
                if err != nil {
                        readErr <- err
                        msgChan <- nil
                        return
                }
                readErr <- nil
                msgChan <- msg
        }()

        select {
        // In order to avoid blocking indefinitely, we'll give the other peer
        // an upper timeout to respond before we bail out early.
        case <-time.After(handshakeTimeout):
                return fmt.Errorf("peer did not complete handshake within %v",
                        handshakeTimeout)
        case err := <-readErr:
                if err != nil {
                        return fmt.Errorf("unable to read init msg: %w", err)
                }
        }

        // Once the init message arrives, we can parse it so we can figure out
        // the negotiation of features for this session.
        msg := <-msgChan
        if msg, ok := msg.(*lnwire.Init); ok {
                if err := p.handleInitMsg(msg); err != nil {
                        p.storeError(err)
                        return err
                }
        } else {
                return errors.New("very first message between nodes " +
                        "must be init message")
        }

        // Next, load all the active channels we have with this peer,
        // registering them with the switch and launching the necessary
        // goroutines required to operate them.
        p.log.Debugf("Loaded %v active channels from database",
                len(activeChans))

        // Conditionally subscribe to channel events before loading channels so
        // we won't miss events. This subscription is used to listen to active
        // channel event when reenabling channels. Once the reenabling process
        // is finished, this subscription will be canceled.
        //
        // NOTE: ChannelNotifier must be started before subscribing events
        // otherwise we'd panic here.
        if err := p.attachChannelEventSubscription(); err != nil {
                return err
        }

        // Register the message router now as we may need to register some
        // endpoints while loading the channels below.
        p.msgRouter.WhenSome(func(router msgmux.Router) {
                router.Start(context.Background())
        })

        msgs, err := p.loadActiveChannels(activeChans)
        if err != nil {
                return fmt.Errorf("unable to load channels: %w", err)
        }

        p.startTime = time.Now()

        // Before launching the writeHandler goroutine, we send any channel
        // sync messages that must be resent for borked channels. We do this to
        // avoid data races with WriteMessage & Flush calls.
        if len(msgs) > 0 {
                p.log.Infof("Sending %d channel sync messages to peer after "+
                        "loading active channels", len(msgs))

                // Send the messages directly via writeMessage and bypass the
                // writeHandler goroutine.
                for _, msg := range msgs {
                        if err := p.writeMessage(msg); err != nil {
                                return fmt.Errorf("unable to send "+
                                        "reestablish msg: %v", err)
                        }
                }
        }

        err = p.pingManager.Start()
        if err != nil {
                return fmt.Errorf("could not start ping manager %w", err)
        }

        p.cg.WgAdd(4)
        go p.queueHandler()
        go p.writeHandler()
        go p.channelManager()
        go p.readHandler()

        // Signal to any external processes that the peer is now active.
        close(p.activeSignal)

        // Node announcements don't propagate very well throughout the network
        // as there isn't a way to efficiently query for them through their
        // timestamp, mostly affecting nodes that were offline during the time
        // of broadcast. We'll resend our node announcement to the remote peer
        // as a best-effort delivery such that it can also propagate to their
        // peers. To ensure they can successfully process it in most cases,
        // we'll only resend it as long as we have at least one confirmed
        // advertised channel with the remote peer.
        //
        // TODO(wilmer): Remove this once we're able to query for node
        // announcements through their timestamps.
        p.cg.WgAdd(2)
        go p.maybeSendNodeAnn(activeChans)
        go p.maybeSendChannelUpdates()

        return nil
}

// initGossipSync initializes either a gossip syncer or an initial routing
// dump, depending on the negotiated synchronization method.
func (p *Brontide) initGossipSync() {
        // If the remote peer knows of the new gossip queries feature, then
        // we'll create a new gossipSyncer in the AuthenticatedGossiper for it.
        if p.remoteFeatures.HasFeature(lnwire.GossipQueriesOptional) {
                p.log.Info("Negotiated chan series queries")

                if p.cfg.AuthGossiper == nil {
                        // This should only ever be hit in the unit tests.
                        p.log.Warn("No AuthGossiper configured. Abandoning " +
                                "gossip sync.")
                        return
                }

                // Register the peer's gossip syncer with the gossiper.
                // This blocks synchronously to ensure the gossip syncer is
                // registered with the gossiper before attempting to read
                // messages from the remote peer.
                //
                // TODO(wilmer): Only sync updates from non-channel peers. This
                // requires an improved version of the current network
                // bootstrapper to ensure we can find and connect to non-channel
                // peers.
                p.cfg.AuthGossiper.InitSyncState(p)
        }
}

// taprootShutdownAllowed returns true if both parties have negotiated the
// shutdown-any-segwit feature.
func (p *Brontide) taprootShutdownAllowed() bool {
        return p.RemoteFeatures().HasFeature(lnwire.ShutdownAnySegwitOptional) &&
                p.LocalFeatures().HasFeature(lnwire.ShutdownAnySegwitOptional)
}

// rbfCoopCloseAllowed returns true if both parties have negotiated the new RBF
// coop close feature.
func (p *Brontide) rbfCoopCloseAllowed() bool {
        bothHaveBit := func(bit lnwire.FeatureBit) bool {
                return p.RemoteFeatures().HasFeature(bit) &&
                        p.LocalFeatures().HasFeature(bit)
        }

        return bothHaveBit(lnwire.RbfCoopCloseOptional) ||
                bothHaveBit(lnwire.RbfCoopCloseOptionalStaging)
}

// QuitSignal is a method that should return a channel which will be sent upon
// or closed once the backing peer exits. This allows callers using the
// interface to cancel any processing in the event the backing implementation
// exits.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) QuitSignal() <-chan struct{} {
        return p.cg.Done()
}

// addrWithInternalKey takes a delivery script, then attempts to supplement it
// with information related to the internal key for the addr, but only if it's
// a taproot addr.
func (p *Brontide) addrWithInternalKey(
        deliveryScript []byte) (*chancloser.DeliveryAddrWithKey, error) {

        // Currently, custom channels cannot be created with external upfront
        // shutdown addresses, so this shouldn't be an issue. We only require
        // the internal key for taproot addresses to be able to provide a non
        // inclusion proof of any scripts.
        internalKeyDesc, err := lnwallet.InternalKeyForAddr(
                p.cfg.Wallet, &p.cfg.Wallet.Cfg.NetParams, deliveryScript,
        )
        if err != nil {
                return nil, fmt.Errorf("unable to fetch internal key: %w", err)
        }

        return &chancloser.DeliveryAddrWithKey{
                DeliveryAddress: deliveryScript,
                InternalKey: fn.MapOption(
                        func(desc keychain.KeyDescriptor) btcec.PublicKey {
                                return *desc.PubKey
                        },
                )(internalKeyDesc),
        }, nil
}

// loadActiveChannels creates indexes within the peer for tracking all active
// channels returned by the database. It returns a slice of channel reestablish
// messages that should be sent to the peer immediately, in case we have borked
// channels that haven't been closed yet.
func (p *Brontide) loadActiveChannels(chans []*channeldb.OpenChannel) (
        []lnwire.Message, error) {

        // Return a slice of messages to send to the peers in case the channel
        // cannot be loaded normally.
        var msgs []lnwire.Message

        scidAliasNegotiated := p.hasNegotiatedScidAlias()

        for _, dbChan := range chans {
                hasScidFeature := dbChan.ChanType.HasScidAliasFeature()
                if scidAliasNegotiated && !hasScidFeature {
                        // We'll request and store an alias, making sure that a
                        // gossiper mapping is not created for the alias to the
                        // real SCID. This is done because the peer and funding
                        // manager are not aware of each other's states and if
                        // we did not do this, we would accept alias channel
                        // updates after 6 confirmations, which would be buggy.
                        // We'll queue a channel_ready message with the new
                        // alias. This should technically be done *after* the
                        // reestablish, but this behavior is pre-existing since
                        // the funding manager may already queue a
                        // channel_ready before the channel_reestablish.
                        if !dbChan.IsPending {
                                aliasScid, err := p.cfg.RequestAlias()
                                if err != nil {
                                        return nil, err
                                }

                                err = p.cfg.AddLocalAlias(
                                        aliasScid, dbChan.ShortChanID(), false,
                                        false,
                                )
                                if err != nil {
                                        return nil, err
                                }

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

                                // Fetch the second commitment point to send in
                                // the channel_ready message.
                                second, err := dbChan.SecondCommitmentPoint()
                                if err != nil {
                                        return nil, err
                                }

                                channelReadyMsg := lnwire.NewChannelReady(
                                        chanID, second,
                                )
                                channelReadyMsg.AliasScid = &aliasScid

                                msgs = append(msgs, channelReadyMsg)
                        }

                        // If we've negotiated the option-scid-alias feature
                        // and this channel does not have ScidAliasFeature set
                        // to true due to an upgrade where the feature bit was
                        // turned on, we'll update the channel's database
                        // state.
                        err := dbChan.MarkScidAliasNegotiated()
                        if err != nil {
                                return nil, err
                        }
                }

                var chanOpts []lnwallet.ChannelOpt
                p.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
                        chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
                })
                p.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
                        chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
                })
                p.cfg.AuxResolver.WhenSome(
                        func(s lnwallet.AuxContractResolver) {
                                chanOpts = append(
                                        chanOpts, lnwallet.WithAuxResolver(s),
                                )
                        },
                )

                lnChan, err := lnwallet.NewLightningChannel(
                        p.cfg.Signer, dbChan, p.cfg.SigPool, chanOpts...,
                )
                if err != nil {
                        return nil, fmt.Errorf("unable to create channel "+
                                "state machine: %w", err)
                }

                chanPoint := dbChan.FundingOutpoint

                chanID := lnwire.NewChanIDFromOutPoint(chanPoint)

                p.log.Infof("Loading ChannelPoint(%v), isPending=%v",
                        chanPoint, lnChan.IsPending())

                // Skip adding any permanently irreconcilable channels to the
                // htlcswitch.
                if !dbChan.HasChanStatus(channeldb.ChanStatusDefault) &&
                        !dbChan.HasChanStatus(channeldb.ChanStatusRestored) {

                        p.log.Warnf("ChannelPoint(%v) has status %v, won't "+
                                "start.", chanPoint, dbChan.ChanStatus())

                        // To help our peer recover from a potential data loss,
                        // we resend our channel reestablish message if the
                        // channel is in a borked state. We won't process any
                        // channel reestablish message sent from the peer, but
                        // that's okay since the assumption is that we did when
                        // marking the channel borked.
                        chanSync, err := dbChan.ChanSyncMsg()
                        if err != nil {
                                p.log.Errorf("Unable to create channel "+
                                        "reestablish message for channel %v: "+
                                        "%v", chanPoint, err)
                                continue
                        }

                        msgs = append(msgs, chanSync)

                        // Check if this channel needs to have the cooperative
                        // close process restarted. If so, we'll need to send
                        // the Shutdown message that is returned.
                        if dbChan.HasChanStatus(
                                channeldb.ChanStatusCoopBroadcasted,
                        ) {

                                shutdownMsg, err := p.restartCoopClose(lnChan)
                                if err != nil {
                                        p.log.Errorf("Unable to restart "+
                                                "coop close for channel: %v",
                                                err)
                                        continue
                                }

                                if shutdownMsg == nil {
                                        continue
                                }

                                // Append the message to the set of messages to
                                // send.
                                msgs = append(msgs, shutdownMsg)
                        }

                        continue
                }

                // Before we register this new link with the HTLC Switch, we'll
                // need to fetch its current link-layer forwarding policy from
                // the database.
                graph := p.cfg.ChannelGraph
                info, p1, p2, err := graph.FetchChannelEdgesByOutpoint(
                        &chanPoint,
                )
                if err != nil && !errors.Is(err, graphdb.ErrEdgeNotFound) {
                        return nil, err
                }

                // We'll filter out our policy from the directional channel
                // edges based whom the edge connects to. If it doesn't connect
                // to us, then we know that we were the one that advertised the
                // policy.
                //
                // TODO(roasbeef): can add helper method to get policy for
                // particular channel.
                var selfPolicy *models.ChannelEdgePolicy
                if info != nil && bytes.Equal(info.NodeKey1Bytes[:],
                        p.cfg.ServerPubKey[:]) {

                        selfPolicy = p1
                } else {
                        selfPolicy = p2
                }

                // If we don't yet have an advertised routing policy, then
                // we'll use the current default, otherwise we'll translate the
                // routing policy into a forwarding policy.
                var forwardingPolicy *models.ForwardingPolicy
                if selfPolicy != nil {
                        forwardingPolicy = &models.ForwardingPolicy{
                                MinHTLCOut:    selfPolicy.MinHTLC,
                                MaxHTLC:       selfPolicy.MaxHTLC,
                                BaseFee:       selfPolicy.FeeBaseMSat,
                                FeeRate:       selfPolicy.FeeProportionalMillionths,
                                TimeLockDelta: uint32(selfPolicy.TimeLockDelta),
                        }
                        selfPolicy.InboundFee.WhenSome(func(fee lnwire.Fee) {
                                inboundFee := models.NewInboundFeeFromWire(fee)
                                forwardingPolicy.InboundFee = inboundFee
                        })
                } else {
                        p.log.Warnf("Unable to find our forwarding policy "+
                                "for channel %v, using default values",
                                chanPoint)
                        forwardingPolicy = &p.cfg.RoutingPolicy
                }

                p.log.Tracef("Using link policy of: %v",
                        spew.Sdump(forwardingPolicy))

                // If the channel is pending, set the value to nil in the
                // activeChannels map. This is done to signify that the channel
                // is pending. We don't add the link to the switch here - it's
                // the funding manager's responsibility to spin up pending
                // channels. Adding them here would just be extra work as we'll
                // tear them down when creating + adding the final link.
                if lnChan.IsPending() {
                        p.activeChannels.Store(chanID, nil)

                        continue
                }

                shutdownInfo, err := lnChan.State().ShutdownInfo()
                if err != nil && !errors.Is(err, channeldb.ErrNoShutdownInfo) {
                        return nil, err
                }

                isTaprootChan := lnChan.ChanType().IsTaproot()

                var (
                        shutdownMsg     fn.Option[lnwire.Shutdown]
                        shutdownInfoErr error
                )
                shutdownInfo.WhenSome(func(info channeldb.ShutdownInfo) {
                        // If we can use the new RBF close feature, we don't
                        // need to create the legacy closer. However for taproot
                        // channels, we'll continue to use the legacy closer.
                        if p.rbfCoopCloseAllowed() && !isTaprootChan {
                                return
                        }

                        // Compute an ideal fee.
                        feePerKw, err := p.cfg.FeeEstimator.EstimateFeePerKW(
                                p.cfg.CoopCloseTargetConfs,
                        )
                        if err != nil {
                                shutdownInfoErr = fmt.Errorf("unable to "+
                                        "estimate fee: %w", err)

                                return
                        }

                        addr, err := p.addrWithInternalKey(
                                info.DeliveryScript.Val,
                        )
                        if err != nil {
                                shutdownInfoErr = fmt.Errorf("unable to make "+
                                        "delivery addr: %w", err)
                                return
                        }
                        negotiateChanCloser, err := p.createChanCloser(
                                lnChan, addr, feePerKw, nil,
                                info.Closer(),
                        )
                        if err != nil {
                                shutdownInfoErr = fmt.Errorf("unable to "+
                                        "create chan closer: %w", err)

                                return
                        }

                        chanID := lnwire.NewChanIDFromOutPoint(
                                lnChan.State().FundingOutpoint,
                        )

                        p.activeChanCloses.Store(chanID, makeNegotiateCloser(
                                negotiateChanCloser,
                        ))

                        // Create the Shutdown message.
                        shutdown, err := negotiateChanCloser.ShutdownChan()
                        if err != nil {
                                p.activeChanCloses.Delete(chanID)
                                shutdownInfoErr = err

                                return
                        }

                        shutdownMsg = fn.Some(*shutdown)
                })
                if shutdownInfoErr != nil {
                        return nil, shutdownInfoErr
                }

                // Subscribe to the set of on-chain events for this channel.
                chainEvents, err := p.cfg.ChainArb.SubscribeChannelEvents(
                        chanPoint,
                )
                if err != nil {
                        return nil, err
                }

                err = p.addLink(
                        &chanPoint, lnChan, forwardingPolicy, chainEvents,
                        true, shutdownMsg,
                )
                if err != nil {
                        return nil, fmt.Errorf("unable to add link %v to "+
                                "switch: %v", chanPoint, err)
                }

                p.activeChannels.Store(chanID, lnChan)

                // We're using the old co-op close, so we don't need to init
                // the new RBF chan closer. If we have a taproot chan, then
                // we'll also use the legacy type, so we don't need to make the
                // new closer.
                if !p.rbfCoopCloseAllowed() || isTaprootChan {
                        continue
                }

                // Now that the link has been added above, we'll also init an
                // RBF chan closer for this channel, but only if the new close
                // feature is negotiated.
                //
                // Creating this here ensures that any shutdown messages sent
                // will be automatically routed by the msg router.
                if _, err := p.initRbfChanCloser(lnChan); err != nil {
                        p.activeChanCloses.Delete(chanID)

                        return nil, fmt.Errorf("unable to init RBF chan "+
                                "closer during peer connect: %w", err)
                }

                // If the shutdown info isn't blank, then we should kick things
                // off by sending a shutdown message to the remote party to
                // continue the old shutdown flow.
                restartShutdown := func(s channeldb.ShutdownInfo) error {
                        return p.startRbfChanCloser(
                                newRestartShutdownInit(s),
                                lnChan.ChannelPoint(),
                        )
                }
                err = fn.MapOptionZ(shutdownInfo, restartShutdown)
                if err != nil {
                        return nil, fmt.Errorf("unable to start RBF "+
                                "chan closer: %w", err)
                }
        }

        return msgs, nil
}

// addLink creates and adds a new ChannelLink from the specified channel.
func (p *Brontide) addLink(chanPoint *wire.OutPoint,
        lnChan *lnwallet.LightningChannel,
        forwardingPolicy *models.ForwardingPolicy,
        chainEvents *contractcourt.ChainEventSubscription,
        syncStates bool, shutdownMsg fn.Option[lnwire.Shutdown]) error {

        // onChannelFailure will be called by the link in case the channel
        // fails for some reason.
        onChannelFailure := func(chanID lnwire.ChannelID,
                shortChanID lnwire.ShortChannelID,
                linkErr htlcswitch.LinkFailureError) {

                failure := linkFailureReport{
                        chanPoint:   *chanPoint,
                        chanID:      chanID,
                        shortChanID: shortChanID,
                        linkErr:     linkErr,
                }

                select {
                case p.linkFailures <- failure:
                case <-p.cg.Done():
                case <-p.cfg.Quit:
                }
        }

        updateContractSignals := func(signals *contractcourt.ContractSignals) error {
                return p.cfg.ChainArb.UpdateContractSignals(*chanPoint, signals)
        }

        notifyContractUpdate := func(update *contractcourt.ContractUpdate) error {
                return p.cfg.ChainArb.NotifyContractUpdate(*chanPoint, update)
        }

        //nolint:ll
        linkCfg := htlcswitch.ChannelLinkConfig{
                Peer:                p,
                DecodeHopIterators:  p.cfg.Sphinx.DecodeHopIterators,
                ExtractSharedSecret: p.cfg.Sphinx.ExtractSharedSecret,
                CreateErrorEncrypter: func(ephemeralKey *btcec.PublicKey,
                        sharedSecret sphinx.Hash256, isIntroduction,
                        hasBlindingPoint bool) hop.ErrorEncrypter {

                        switch {
                        case isIntroduction:
                                return hop.NewIntroductionErrorEncrypter(
                                        ephemeralKey, sharedSecret,
                                )

                        case hasBlindingPoint:
                                return hop.NewRelayingErrorEncrypter(
                                        ephemeralKey, sharedSecret,
                                )

                        default:
                                return hop.NewSphinxErrorEncrypter(
                                        ephemeralKey, sharedSecret,
                                )
                        }
                }, FetchLastChannelUpdate: p.cfg.FetchLastChanUpdate,
                HodlMask:              p.cfg.Hodl.Mask(),
                Registry:              p.cfg.Invoices,
                BestHeight:            p.cfg.Switch.BestHeight,
                Circuits:              p.cfg.Switch.CircuitModifier(),
                ForwardPackets:        p.cfg.InterceptSwitch.ForwardPackets,
                FwrdingPolicy:         *forwardingPolicy,
                FeeEstimator:          p.cfg.FeeEstimator,
                PreimageCache:         p.cfg.WitnessBeacon,
                ChainEvents:           chainEvents,
                UpdateContractSignals: updateContractSignals,
                NotifyContractUpdate:  notifyContractUpdate,
                OnChannelFailure:      onChannelFailure,
                SyncStates:            syncStates,
                BatchTicker:           ticker.New(p.cfg.ChannelCommitInterval),
                FwdPkgGCTicker:        ticker.New(time.Hour),
                PendingCommitTicker: ticker.New(
                        p.cfg.PendingCommitInterval,
                ),
                BatchSize:               p.cfg.ChannelCommitBatchSize,
                UnsafeReplay:            p.cfg.UnsafeReplay,
                MinUpdateTimeout:        htlcswitch.DefaultMinLinkFeeUpdateTimeout,
                MaxUpdateTimeout:        htlcswitch.DefaultMaxLinkFeeUpdateTimeout,
                OutgoingCltvRejectDelta: p.cfg.OutgoingCltvRejectDelta,
                TowerClient:             p.cfg.TowerClient,
                MaxOutgoingCltvExpiry:   p.cfg.MaxOutgoingCltvExpiry,
                MaxFeeAllocation:        p.cfg.MaxChannelFeeAllocation,
                MaxAnchorsCommitFeeRate: p.cfg.MaxAnchorsCommitFeeRate,
                NotifyActiveLink:        p.cfg.ChannelNotifier.NotifyActiveLinkEvent,
                NotifyActiveChannel:     p.cfg.ChannelNotifier.NotifyActiveChannelEvent,
                NotifyInactiveChannel:   p.cfg.ChannelNotifier.NotifyInactiveChannelEvent,
                NotifyInactiveLinkEvent: p.cfg.ChannelNotifier.NotifyInactiveLinkEvent,
                HtlcNotifier:            p.cfg.HtlcNotifier,
                GetAliases:              p.cfg.GetAliases,
                PreviouslySentShutdown:  shutdownMsg,
                DisallowRouteBlinding:   p.cfg.DisallowRouteBlinding,
                MaxFeeExposure:          p.cfg.MaxFeeExposure,
                ShouldFwdExpEndorsement: p.cfg.ShouldFwdExpEndorsement,
                DisallowQuiescence: p.cfg.DisallowQuiescence ||
                        !p.remoteFeatures.HasFeature(lnwire.QuiescenceOptional),
                AuxTrafficShaper:  p.cfg.AuxTrafficShaper,
                QuiescenceTimeout: p.cfg.QuiescenceTimeout,
        }

        // Before adding our new link, purge the switch of any pending or live
        // links going by the same channel id. If one is found, we'll shut it
        // down to ensure that the mailboxes are only ever under the control of
        // one link.
        chanID := lnwire.NewChanIDFromOutPoint(*chanPoint)
        p.cfg.Switch.RemoveLink(chanID)

        // With the channel link created, we'll now notify the htlc switch so
        // this channel can be used to dispatch local payments and also
        // passively forward payments.
        return p.cfg.Switch.CreateAndAddLink(linkCfg, lnChan)
}

// maybeSendNodeAnn sends our node announcement to the remote peer if at least
// one confirmed public channel exists with them.
func (p *Brontide) maybeSendNodeAnn(channels []*channeldb.OpenChannel) {
        defer p.cg.WgDone()

        hasConfirmedPublicChan := false
        for _, channel := range channels {
                if channel.IsPending {
                        continue
                }
                if channel.ChannelFlags&lnwire.FFAnnounceChannel == 0 {
                        continue
                }

                hasConfirmedPublicChan = true
                break
        }
        if !hasConfirmedPublicChan {
                return
        }

        ourNodeAnn, err := p.cfg.GenNodeAnnouncement()
        if err != nil {
                p.log.Debugf("Unable to retrieve node announcement: %v", err)
                return
        }

        if err := p.SendMessageLazy(false, &ourNodeAnn); err != nil {
                p.log.Debugf("Unable to resend node announcement: %v", err)
        }
}

// maybeSendChannelUpdates sends our channel updates to the remote peer if we
// have any active channels with them.
func (p *Brontide) maybeSendChannelUpdates() {
        defer p.cg.WgDone()

        // If we don't have any active channels, then we can exit early.
        if p.activeChannels.Len() == 0 {
                return
        }

        maybeSendUpd := func(cid lnwire.ChannelID,
                lnChan *lnwallet.LightningChannel) error {

                // Nil channels are pending, so we'll skip them.
                if lnChan == nil {
                        return nil
                }

                dbChan := lnChan.State()
                scid := func() lnwire.ShortChannelID {
                        switch {
                        // Otherwise if it's a zero conf channel and confirmed,
                        // then we need to use the "real" scid.
                        case dbChan.IsZeroConf() && dbChan.ZeroConfConfirmed():
                                return dbChan.ZeroConfRealScid()

                        // Otherwise, we can use the normal scid.
                        default:
                                return dbChan.ShortChanID()
                        }
                }()

                // Now that we know the channel is in a good state, we'll try
                // to fetch the update to send to the remote peer. If the
                // channel is pending, and not a zero conf channel, we'll get
                // an error here which we'll ignore.
                chanUpd, err := p.cfg.FetchLastChanUpdate(scid)
                if err != nil {
                        p.log.Debugf("Unable to fetch channel update for "+
                                "ChannelPoint(%v), scid=%v: %v",
                                dbChan.FundingOutpoint, dbChan.ShortChanID, err)

                        return nil
                }

                p.log.Debugf("Sending channel update for ChannelPoint(%v), "+
                        "scid=%v", dbChan.FundingOutpoint, dbChan.ShortChanID)

                // We'll send it as a normal message instead of using the lazy
                // queue to prioritize transmission of the fresh update.
                if err := p.SendMessage(false, chanUpd); err != nil {
                        err := fmt.Errorf("unable to send channel update for "+
                                "ChannelPoint(%v), scid=%v: %w",
                                dbChan.FundingOutpoint, dbChan.ShortChanID(),
                                err)
                        p.log.Errorf(err.Error())

                        return err
                }

                return nil
        }

        p.activeChannels.ForEach(maybeSendUpd)
}

// WaitForDisconnect waits until the peer has disconnected. A peer may be
// disconnected if the local or remote side terminates the connection, or an
// irrecoverable protocol error has been encountered. This method will only
// begin watching the peer's waitgroup after the ready channel or the peer's
// quit channel are signaled. The ready channel should only be signaled if a
// call to Start returns no error. Otherwise, if the peer fails to start,
// calling Disconnect will signal the quit channel and the method will not
// block, since no goroutines were spawned.
func (p *Brontide) WaitForDisconnect(ready chan struct{}) {
        // Before we try to call the `Wait` goroutine, we'll make sure the main
        // set of goroutines are already active.
        select {
        case <-p.startReady:
        case <-p.cg.Done():
                return
        }

        select {
        case <-ready:
        case <-p.cg.Done():
        }

        p.cg.WgWait()
}

// Disconnect terminates the connection with the remote peer. Additionally, a
// signal is sent to the server and htlcSwitch indicating the resources
// allocated to the peer can now be cleaned up.
//
// NOTE: Be aware that this method will block if the peer is still starting up.
// Therefore consider starting it in a goroutine if you cannot guarantee that
// the peer has finished starting up before calling this method.
func (p *Brontide) Disconnect(reason error) {
        if !atomic.CompareAndSwapInt32(&p.disconnect, 0, 1) {
                return
        }

        // Make sure initialization has completed before we try to tear things
        // down.
        //
        // NOTE: We only read the `startReady` chan if the peer has been
        // started, otherwise we will skip reading it as this chan won't be
        // closed, hence blocks forever.
        if atomic.LoadInt32(&p.started) == 1 {
                p.log.Debugf("Peer hasn't finished starting up yet, waiting " +
                        "on startReady signal before closing connection")

                select {
                case <-p.startReady:
                case <-p.cg.Done():
                        return
                }
        }

        err := fmt.Errorf("disconnecting %s, reason: %v", p, reason)
        p.storeError(err)

        p.log.Infof(err.Error())

        // Stop PingManager before closing TCP connection.
        p.pingManager.Stop()

        // Ensure that the TCP connection is properly closed before continuing.
        p.cfg.Conn.Close()

        p.cg.Quit()

        // If our msg router isn't global (local to this instance), then we'll
        // stop it. Otherwise, we'll leave it running.
        if !p.globalMsgRouter {
                p.msgRouter.WhenSome(func(router msgmux.Router) {
                        router.Stop()
                })
        }
}

// String returns the string representation of this peer.
func (p *Brontide) String() string {
        return fmt.Sprintf("%x@%s", p.cfg.PubKeyBytes, p.cfg.Conn.RemoteAddr())
}

// readNextMessage reads, and returns the next message on the wire along with
// any additional raw payload.
func (p *Brontide) readNextMessage() (lnwire.Message, error) {
        noiseConn := p.cfg.Conn
        err := noiseConn.SetReadDeadline(time.Time{})
        if err != nil {
                return nil, err
        }

        pktLen, err := noiseConn.ReadNextHeader()
        if err != nil {
                return nil, fmt.Errorf("read next header: %w", err)
        }

        // First we'll read the next _full_ message. We do this rather than
        // reading incrementally from the stream as the Lightning wire protocol
        // is message oriented and allows nodes to pad on additional data to
        // the message stream.
        var (
                nextMsg lnwire.Message
                msgLen  uint64
        )
        err = p.cfg.ReadPool.Submit(func(buf *buffer.Read) error {
                // Before reading the body of the message, set the read timeout
                // accordingly to ensure we don't block other readers using the
                // pool. We do so only after the task has been scheduled to
                // ensure the deadline doesn't expire while the message is in
                // the process of being scheduled.
                readDeadline := time.Now().Add(
                        p.scaleTimeout(readMessageTimeout),
                )
                readErr := noiseConn.SetReadDeadline(readDeadline)
                if readErr != nil {
                        return readErr
                }

                // The ReadNextBody method will actually end up re-using the
                // buffer, so within this closure, we can continue to use
                // rawMsg as it's just a slice into the buf from the buffer
                // pool.
                rawMsg, readErr := noiseConn.ReadNextBody(buf[:pktLen])
                if readErr != nil {
                        return fmt.Errorf("read next body: %w", readErr)
                }
                msgLen = uint64(len(rawMsg))

                // Next, create a new io.Reader implementation from the raw
                // message, and use this to decode the message directly from.
                msgReader := bytes.NewReader(rawMsg)
                nextMsg, err = lnwire.ReadMessage(msgReader, 0)
                if err != nil {
                        return err
                }

                // At this point, rawMsg and buf will be returned back to the
                // buffer pool for re-use.
                return nil
        })
        atomic.AddUint64(&p.bytesReceived, msgLen)
        if err != nil {
                return nil, err
        }

        p.logWireMessage(nextMsg, true)

        return nextMsg, nil
}

// msgStream implements a goroutine-safe, in-order stream of messages to be
// delivered via closure to a receiver. These messages MUST be in order due to
// the nature of the lightning channel commitment and gossiper state machines.
// TODO(conner): use stream handler interface to abstract out stream
// state/logging.
type msgStream struct {
        streamShutdown int32 // To be used atomically.

        peer *Brontide

        apply func(lnwire.Message)

        startMsg string
        stopMsg  string

        msgCond *sync.Cond
        msgs    []lnwire.Message

        mtx sync.Mutex

        producerSema chan struct{}

        wg   sync.WaitGroup
        quit chan struct{}
}

// newMsgStream creates a new instance of a chanMsgStream for a particular
// channel identified by its channel ID. bufSize is the max number of messages
// that should be buffered in the internal queue. Callers should set this to a
// sane value that avoids blocking unnecessarily, but doesn't allow an
// unbounded amount of memory to be allocated to buffer incoming messages.
func newMsgStream(p *Brontide, startMsg, stopMsg string, bufSize uint32,
        apply func(lnwire.Message)) *msgStream {

        stream := &msgStream{
                peer:         p,
                apply:        apply,
                startMsg:     startMsg,
                stopMsg:      stopMsg,
                producerSema: make(chan struct{}, bufSize),
                quit:         make(chan struct{}),
        }
        stream.msgCond = sync.NewCond(&stream.mtx)

        // Before we return the active stream, we'll populate the producer's
        // semaphore channel. We'll use this to ensure that the producer won't
        // attempt to allocate memory in the queue for an item until it has
        // sufficient extra space.
        for i := uint32(0); i < bufSize; i++ {
                stream.producerSema <- struct{}{}
        }

        return stream
}

// Start starts the chanMsgStream.
func (ms *msgStream) Start() {
        ms.wg.Add(1)
        go ms.msgConsumer()
}

// Stop stops the chanMsgStream.
func (ms *msgStream) Stop() {
        // TODO(roasbeef): signal too?

        close(ms.quit)

        // Now that we've closed the channel, we'll repeatedly signal the msg
        // consumer until we've detected that it has exited.
        for atomic.LoadInt32(&ms.streamShutdown) == 0 {
                ms.msgCond.Signal()
                time.Sleep(time.Millisecond * 100)
        }

        ms.wg.Wait()
}

// msgConsumer is the main goroutine that streams messages from the peer's
// readHandler directly to the target channel.
func (ms *msgStream) msgConsumer() {
        defer ms.wg.Done()
        defer peerLog.Tracef(ms.stopMsg)
        defer atomic.StoreInt32(&ms.streamShutdown, 1)

        peerLog.Tracef(ms.startMsg)

        for {
                // First, we'll check our condition. If the queue of messages
                // is empty, then we'll wait until a new item is added.
                ms.msgCond.L.Lock()
                for len(ms.msgs) == 0 {
                        ms.msgCond.Wait()

                        // If we woke up in order to exit, then we'll do so.
                        // Otherwise, we'll check the message queue for any new
                        // items.
                        select {
                        case <-ms.peer.cg.Done():
                                ms.msgCond.L.Unlock()
                                return
                        case <-ms.quit:
                                ms.msgCond.L.Unlock()
                                return
                        default:
                        }
                }

                // Grab the message off the front of the queue, shifting the
                // slice's reference down one in order to remove the message
                // from the queue.
                msg := ms.msgs[0]
                ms.msgs[0] = nil // Set to nil to prevent GC leak.
                ms.msgs = ms.msgs[1:]

                ms.msgCond.L.Unlock()

                ms.apply(msg)

                // We've just successfully processed an item, so we'll signal
                // to the producer that a new slot in the buffer. We'll use
                // this to bound the size of the buffer to avoid allowing it to
                // grow indefinitely.
                select {
                case ms.producerSema <- struct{}{}:
                case <-ms.peer.cg.Done():
                        return
                case <-ms.quit:
                        return
                }
        }
}

// AddMsg adds a new message to the msgStream. This function is safe for
// concurrent access.
func (ms *msgStream) AddMsg(msg lnwire.Message) {
        // First, we'll attempt to receive from the producerSema struct. This
        // acts as a semaphore to prevent us from indefinitely buffering
        // incoming items from the wire. Either the msg queue isn't full, and
        // we'll not block, or the queue is full, and we'll block until either
        // we're signalled to quit, or a slot is freed up.
        select {
        case <-ms.producerSema:
        case <-ms.peer.cg.Done():
                return
        case <-ms.quit:
                return
        }

        // Next, we'll lock the condition, and add the message to the end of
        // the message queue.
        ms.msgCond.L.Lock()
        ms.msgs = append(ms.msgs, msg)
        ms.msgCond.L.Unlock()

        // With the message added, we signal to the msgConsumer that there are
        // additional messages to consume.
        ms.msgCond.Signal()
}

// waitUntilLinkActive waits until the target link is active and returns a
// ChannelLink to pass messages to. It accomplishes this by subscribing to
// an ActiveLinkEvent which is emitted by the link when it first starts up.
func waitUntilLinkActive(p *Brontide,
        cid lnwire.ChannelID) htlcswitch.ChannelUpdateHandler {

        p.log.Tracef("Waiting for link=%v to be active", cid)

        // Subscribe to receive channel events.
        //
        // NOTE: If the link is already active by SubscribeChannelEvents, then
        // GetLink will retrieve the link and we can send messages. If the link
        // becomes active between SubscribeChannelEvents and GetLink, then GetLink
        // will retrieve the link. If the link becomes active after GetLink, then
        // we will get an ActiveLinkEvent notification and retrieve the link. If
        // the call to GetLink is before SubscribeChannelEvents, however, there
        // will be a race condition.
        sub, err := p.cfg.ChannelNotifier.SubscribeChannelEvents()
        if err != nil {
                // If we have a non-nil error, then the server is shutting down and we
                // can exit here and return nil. This means no message will be delivered
                // to the link.
                return nil
        }
        defer sub.Cancel()

        // The link may already be active by this point, and we may have missed the
        // ActiveLinkEvent. Check if the link exists.
        link := p.fetchLinkFromKeyAndCid(cid)
        if link != nil {
                return link
        }

        // If the link is nil, we must wait for it to be active.
        for {
                select {
                // A new event has been sent by the ChannelNotifier. We first check
                // whether the event is an ActiveLinkEvent. If it is, we'll check
                // that the event is for this channel. Otherwise, we discard the
                // message.
                case e := <-sub.Updates():
                        event, ok := e.(channelnotifier.ActiveLinkEvent)
                        if !ok {
                                // Ignore this notification.
                                continue
                        }

                        chanPoint := event.ChannelPoint

                        // Check whether the retrieved chanPoint matches the target
                        // channel id.
                        if !cid.IsChanPoint(chanPoint) {
                                continue
                        }

                        // The link shouldn't be nil as we received an
                        // ActiveLinkEvent. If it is nil, we return nil and the
                        // calling function should catch it.
                        return p.fetchLinkFromKeyAndCid(cid)

                case <-p.cg.Done():
                        return nil
                }
        }
}

// newChanMsgStream is used to create a msgStream between the peer and
// particular channel link in the htlcswitch. We utilize additional
// synchronization with the fundingManager to ensure we don't attempt to
// dispatch a message to a channel before it is fully active. A reference to the
// channel this stream forwards to is held in scope to prevent unnecessary
// lookups.
func newChanMsgStream(p *Brontide, cid lnwire.ChannelID) *msgStream {
        var chanLink htlcswitch.ChannelUpdateHandler

        apply := func(msg lnwire.Message) {
                // This check is fine because if the link no longer exists, it will
                // be removed from the activeChannels map and subsequent messages
                // shouldn't reach the chan msg stream.
                if chanLink == nil {
                        chanLink = waitUntilLinkActive(p, cid)

                        // If the link is still not active and the calling function
                        // errored out, just return.
                        if chanLink == nil {
                                p.log.Warnf("Link=%v is not active", cid)
                                return
                        }
                }

                // In order to avoid unnecessarily delivering message
                // as the peer is exiting, we'll check quickly to see
                // if we need to exit.
                select {
                case <-p.cg.Done():
                        return
                default:
                }

                chanLink.HandleChannelUpdate(msg)
        }

        return newMsgStream(p,
                fmt.Sprintf("Update stream for ChannelID(%x) created", cid[:]),
                fmt.Sprintf("Update stream for ChannelID(%x) exiting", cid[:]),
                msgStreamSize,
                apply,
        )
}

// newDiscMsgStream is used to setup a msgStream between the peer and the
// authenticated gossiper. This stream should be used to forward all remote
// channel announcements.
func newDiscMsgStream(p *Brontide) *msgStream {
        apply := func(msg lnwire.Message) {
                // TODO(elle): thread contexts through the peer system properly
                // so that a parent context can be passed in here.
                ctx := context.TODO()

                // Processing here means we send it to the gossiper which then
                // decides whether this message is processed immediately or
                // waits for dependent messages to be processed. It can also
                // happen that the message is not processed at all if it is
                // premature and the LRU cache fills up and the message is
                // deleted.
                p.log.Debugf("Processing remote msg %T", msg)

                // TODO(ziggie): ProcessRemoteAnnouncement returns an error
                // channel, but we cannot rely on it being written to.
                // Because some messages might never be processed (e.g.
                // premature channel updates). We should change the design here
                // and use the actor model pattern as soon as it is available.
                // So for now we should NOT use the error channel.
                // See https://github.com/lightningnetwork/lnd/pull/9820.
                p.cfg.AuthGossiper.ProcessRemoteAnnouncement(ctx, msg, p)
        }

        return newMsgStream(
                p,
                "Update stream for gossiper created",
                "Update stream for gossiper exited",
                msgStreamSize,
                apply,
        )
}

// readHandler is responsible for reading messages off the wire in series, then
// properly dispatching the handling of the message to the proper subsystem.
//
// NOTE: This method MUST be run as a goroutine.
func (p *Brontide) readHandler() {
        defer p.cg.WgDone()

        // We'll stop the timer after a new messages is received, and also
        // reset it after we process the next message.
        idleTimer := time.AfterFunc(idleTimeout, func() {
                err := fmt.Errorf("peer %s no answer for %s -- disconnecting",
                        p, idleTimeout)
                p.Disconnect(err)
        })

        // Initialize our negotiated gossip sync method before reading messages
        // off the wire. When using gossip queries, this ensures a gossip
        // syncer is active by the time query messages arrive.
        //
        // TODO(conner): have peer store gossip syncer directly and bypass
        // gossiper?
        p.initGossipSync()

        discStream := newDiscMsgStream(p)
        discStream.Start()
        defer discStream.Stop()
out:
        for atomic.LoadInt32(&p.disconnect) == 0 {
                nextMsg, err := p.readNextMessage()
                if !idleTimer.Stop() {
                        select {
                        case <-idleTimer.C:
                        default:
                        }
                }
                if err != nil {
                        p.log.Infof("unable to read message from peer: %v", err)

                        // If we could not read our peer's message due to an
                        // unknown type or invalid alias, we continue processing
                        // as normal. We store unknown message and address
                        // types, as they may provide debugging insight.
                        switch e := err.(type) {
                        // If this is just a message we don't yet recognize,
                        // we'll continue processing as normal as this allows
                        // us to introduce new messages in a forwards
                        // compatible manner.
                        case *lnwire.UnknownMessage:
                                p.storeError(e)
                                idleTimer.Reset(idleTimeout)
                                continue

                        // If they sent us an address type that we don't yet
                        // know of, then this isn't a wire error, so we'll
                        // simply continue parsing the remainder of their
                        // messages.
                        case *lnwire.ErrUnknownAddrType:
                                p.storeError(e)
                                idleTimer.Reset(idleTimeout)
                                continue

                        // If the NodeAnnouncement has an invalid alias, then
                        // we'll log that error above and continue so we can
                        // continue to read messages from the peer. We do not
                        // store this error because it is of little debugging
                        // value.
                        case *lnwire.ErrInvalidNodeAlias:
                                idleTimer.Reset(idleTimeout)
                                continue

                        // If the error we encountered wasn't just a message we
                        // didn't recognize, then we'll stop all processing as
                        // this is a fatal error.
                        default:
                                break out
                        }
                }

                // If a message router is active, then we'll try to have it
                // handle this message. If it can, then we're able to skip the
                // rest of the message handling logic.
                err = fn.MapOptionZ(p.msgRouter, func(r msgmux.Router) error {
                        return r.RouteMsg(msgmux.PeerMsg{
                                PeerPub: *p.IdentityKey(),
                                Message: nextMsg,
                        })
                })

                // No error occurred, and the message was handled by the
                // router.
                if err == nil {
                        continue
                }

                var (
                        targetChan   lnwire.ChannelID
                        isLinkUpdate bool
                )

                switch msg := nextMsg.(type) {
                case *lnwire.Pong:
                        // When we receive a Pong message in response to our
                        // last ping message, we send it to the pingManager
                        p.pingManager.ReceivedPong(msg)

                case *lnwire.Ping:
                        // First, we'll store their latest ping payload within
                        // the relevant atomic variable.
                        p.lastPingPayload.Store(msg.PaddingBytes[:])

                        // Next, we'll send over the amount of specified pong
                        // bytes.
                        pong := lnwire.NewPong(p.cfg.PongBuf[0:msg.NumPongBytes])
                        p.queueMsg(pong, nil)

                case *lnwire.OpenChannel,
                        *lnwire.AcceptChannel,
                        *lnwire.FundingCreated,
                        *lnwire.FundingSigned,
                        *lnwire.ChannelReady:

                        p.cfg.FundingManager.ProcessFundingMsg(msg, p)

                case *lnwire.Shutdown:
                        select {
                        case p.chanCloseMsgs <- &closeMsg{msg.ChannelID, msg}:
                        case <-p.cg.Done():
                                break out
                        }
                case *lnwire.ClosingSigned:
                        select {
                        case p.chanCloseMsgs <- &closeMsg{msg.ChannelID, msg}:
                        case <-p.cg.Done():
                                break out
                        }

                case *lnwire.Warning:
                        targetChan = msg.ChanID
                        isLinkUpdate = p.handleWarningOrError(targetChan, msg)

                case *lnwire.Error:
                        targetChan = msg.ChanID
                        isLinkUpdate = p.handleWarningOrError(targetChan, msg)

                case *lnwire.ChannelReestablish:
                        targetChan = msg.ChanID
                        isLinkUpdate = p.hasChannel(targetChan)

                        // If we failed to find the link in question, and the
                        // message received was a channel sync message, then
                        // this might be a peer trying to resync closed channel.
                        // In this case we'll try to resend our last channel
                        // sync message, such that the peer can recover funds
                        // from the closed channel.
                        if !isLinkUpdate {
                                err := p.resendChanSyncMsg(targetChan)
                                if err != nil {
                                        // TODO(halseth): send error to peer?
                                        p.log.Errorf("resend failed: %v",
                                                err)
                                }
                        }

                // For messages that implement the LinkUpdater interface, we
                // will consider them as link updates and send them to
                // chanStream. These messages will be queued inside chanStream
                // if the channel is not active yet.
                case lnwire.LinkUpdater:
                        targetChan = msg.TargetChanID()
                        isLinkUpdate = p.hasChannel(targetChan)

                        // Log an error if we don't have this channel. This
                        // means the peer has sent us a message with unknown
                        // channel ID.
                        if !isLinkUpdate {
                                p.log.Errorf("Unknown channel ID: %v found "+
                                        "in received msg=%s", targetChan,
                                        nextMsg.MsgType())
                        }

                case *lnwire.ChannelUpdate1,
                        *lnwire.ChannelAnnouncement1,
                        *lnwire.NodeAnnouncement,
                        *lnwire.AnnounceSignatures1,
                        *lnwire.GossipTimestampRange,
                        *lnwire.QueryShortChanIDs,
                        *lnwire.QueryChannelRange,
                        *lnwire.ReplyChannelRange,
                        *lnwire.ReplyShortChanIDsEnd:

                        discStream.AddMsg(msg)

                case *lnwire.Custom:
                        err := p.handleCustomMessage(msg)
                        if err != nil {
                                p.storeError(err)
                                p.log.Errorf("%v", err)
                        }

                default:
                        // If the message we received is unknown to us, store
                        // the type to track the failure.
                        err := fmt.Errorf("unknown message type %v received",
                                uint16(msg.MsgType()))
                        p.storeError(err)

                        p.log.Errorf("%v", err)
                }

                if isLinkUpdate {
                        // If this is a channel update, then we need to feed it
                        // into the channel's in-order message stream.
                        p.sendLinkUpdateMsg(targetChan, nextMsg)
                }

                idleTimer.Reset(idleTimeout)
        }

        p.Disconnect(errors.New("read handler closed"))

        p.log.Trace("readHandler for peer done")
}

// handleCustomMessage handles the given custom message if a handler is
// registered.
func (p *Brontide) handleCustomMessage(msg *lnwire.Custom) error {
        if p.cfg.HandleCustomMessage == nil {
                return fmt.Errorf("no custom message handler for "+
                        "message type %v", uint16(msg.MsgType()))
        }

        return p.cfg.HandleCustomMessage(p.PubKey(), msg)
}

// isLoadedFromDisk returns true if the provided channel ID is loaded from
// disk.
//
// NOTE: only returns true for pending channels.
func (p *Brontide) isLoadedFromDisk(chanID lnwire.ChannelID) bool {
        // If this is a newly added channel, no need to reestablish.
        _, added := p.addedChannels.Load(chanID)
        if added {
                return false
        }

        // Return false if the channel is unknown.
        channel, ok := p.activeChannels.Load(chanID)
        if !ok {
                return false
        }

        // During startup, we will use a nil value to mark a pending channel
        // that's loaded from disk.
        return channel == nil
}

// isActiveChannel returns true if the provided channel id is active, otherwise
// returns false.
func (p *Brontide) isActiveChannel(chanID lnwire.ChannelID) bool {
        // The channel would be nil if,
        // - the channel doesn't exist, or,
        // - the channel exists, but is pending. In this case, we don't
        //   consider this channel active.
        channel, _ := p.activeChannels.Load(chanID)

        return channel != nil
}

// isPendingChannel returns true if the provided channel ID is pending, and
// returns false if the channel is active or unknown.
func (p *Brontide) isPendingChannel(chanID lnwire.ChannelID) bool {
        // Return false if the channel is unknown.
        channel, ok := p.activeChannels.Load(chanID)
        if !ok {
                return false
        }

        return channel == nil
}

// hasChannel returns true if the peer has a pending/active channel specified
// by the channel ID.
func (p *Brontide) hasChannel(chanID lnwire.ChannelID) bool {
        _, ok := p.activeChannels.Load(chanID)
        return ok
}

// storeError stores an error in our peer's buffer of recent errors with the
// current timestamp. Errors are only stored if we have at least one active
// channel with the peer to mitigate a dos vector where a peer costlessly
// connects to us and spams us with errors.
func (p *Brontide) storeError(err error) {
        var haveChannels bool

        p.activeChannels.Range(func(_ lnwire.ChannelID,
                channel *lnwallet.LightningChannel) bool {

                // Pending channels will be nil in the activeChannels map.
                if channel == nil {
                        // Return true to continue the iteration.
                        return true
                }

                haveChannels = true

                // Return false to break the iteration.
                return false
        })

        // If we do not have any active channels with the peer, we do not store
        // errors as a dos mitigation.
        if !haveChannels {
                p.log.Trace("no channels with peer, not storing err")
                return
        }

        p.cfg.ErrorBuffer.Add(
                &TimestampedError{Timestamp: time.Now(), Error: err},
        )
}

// handleWarningOrError processes a warning or error msg and returns true if
// msg should be forwarded to the associated channel link. False is returned if
// any necessary forwarding of msg was already handled by this method. If msg is
// an error from a peer with an active channel, we'll store it in memory.
//
// NOTE: This method should only be called from within the readHandler.
func (p *Brontide) handleWarningOrError(chanID lnwire.ChannelID,
        msg lnwire.Message) bool {

        if errMsg, ok := msg.(*lnwire.Error); ok {
                p.storeError(errMsg)
        }

        switch {
        // Connection wide messages should be forwarded to all channel links
        // with this peer.
        case chanID == lnwire.ConnectionWideID:
                for _, chanStream := range p.activeMsgStreams {
                        chanStream.AddMsg(msg)
                }

                return false

        // If the channel ID for the message corresponds to a pending channel,
        // then the funding manager will handle it.
        case p.cfg.FundingManager.IsPendingChannel(chanID, p):
                p.cfg.FundingManager.ProcessFundingMsg(msg, p)
                return false

        // If not we hand the message to the channel link for this channel.
        case p.isActiveChannel(chanID):
                return true

        default:
                return false
        }
}

// messageSummary returns a human-readable string that summarizes a
// incoming/outgoing message. Not all messages will have a summary, only those
// which have additional data that can be informative at a glance.
func messageSummary(msg lnwire.Message) string {
        switch msg := msg.(type) {
        case *lnwire.Init:
                // No summary.
                return ""

        case *lnwire.OpenChannel:
                return fmt.Sprintf("temp_chan_id=%x, chain=%v, csv=%v, amt=%v, "+
                        "push_amt=%v, reserve=%v, flags=%v",
                        msg.PendingChannelID[:], msg.ChainHash,
                        msg.CsvDelay, msg.FundingAmount, msg.PushAmount,
                        msg.ChannelReserve, msg.ChannelFlags)

        case *lnwire.AcceptChannel:
                return fmt.Sprintf("temp_chan_id=%x, reserve=%v, csv=%v, num_confs=%v",
                        msg.PendingChannelID[:], msg.ChannelReserve, msg.CsvDelay,
                        msg.MinAcceptDepth)

        case *lnwire.FundingCreated:
                return fmt.Sprintf("temp_chan_id=%x, chan_point=%v",
                        msg.PendingChannelID[:], msg.FundingPoint)

        case *lnwire.FundingSigned:
                return fmt.Sprintf("chan_id=%v", msg.ChanID)

        case *lnwire.ChannelReady:
                return fmt.Sprintf("chan_id=%v, next_point=%x",
                        msg.ChanID, msg.NextPerCommitmentPoint.SerializeCompressed())

        case *lnwire.Shutdown:
                return fmt.Sprintf("chan_id=%v, script=%x", msg.ChannelID,
                        msg.Address[:])

        case *lnwire.ClosingComplete:
                return fmt.Sprintf("chan_id=%v, fee_sat=%v, locktime=%v",
                        msg.ChannelID, msg.FeeSatoshis, msg.LockTime)

        case *lnwire.ClosingSig:
                return fmt.Sprintf("chan_id=%v", msg.ChannelID)

        case *lnwire.ClosingSigned:
                return fmt.Sprintf("chan_id=%v, fee_sat=%v", msg.ChannelID,
                        msg.FeeSatoshis)

        case *lnwire.UpdateAddHTLC:
                var blindingPoint []byte
                msg.BlindingPoint.WhenSome(
                        func(b tlv.RecordT[lnwire.BlindingPointTlvType,
                                *btcec.PublicKey]) {

                                blindingPoint = b.Val.SerializeCompressed()
                        },
                )

                return fmt.Sprintf("chan_id=%v, id=%v, amt=%v, expiry=%v, "+
                        "hash=%x, blinding_point=%x, custom_records=%v",
                        msg.ChanID, msg.ID, msg.Amount, msg.Expiry,
                        msg.PaymentHash[:], blindingPoint, msg.CustomRecords)

        case *lnwire.UpdateFailHTLC:
                return fmt.Sprintf("chan_id=%v, id=%v, reason=%x", msg.ChanID,
                        msg.ID, msg.Reason)

        case *lnwire.UpdateFulfillHTLC:
                return fmt.Sprintf("chan_id=%v, id=%v, preimage=%x, "+
                        "custom_records=%v", msg.ChanID, msg.ID,
                        msg.PaymentPreimage[:], msg.CustomRecords)

        case *lnwire.CommitSig:
                return fmt.Sprintf("chan_id=%v, num_htlcs=%v", msg.ChanID,
                        len(msg.HtlcSigs))

        case *lnwire.RevokeAndAck:
                return fmt.Sprintf("chan_id=%v, rev=%x, next_point=%x",
                        msg.ChanID, msg.Revocation[:],
                        msg.NextRevocationKey.SerializeCompressed())

        case *lnwire.UpdateFailMalformedHTLC:
                return fmt.Sprintf("chan_id=%v, id=%v, fail_code=%v",
                        msg.ChanID, msg.ID, msg.FailureCode)

        case *lnwire.Warning:
                return fmt.Sprintf("%v", msg.Warning())

        case *lnwire.Error:
                return fmt.Sprintf("%v", msg.Error())

        case *lnwire.AnnounceSignatures1:
                return fmt.Sprintf("chan_id=%v, short_chan_id=%v", msg.ChannelID,
                        msg.ShortChannelID.ToUint64())

        case *lnwire.ChannelAnnouncement1:
                return fmt.Sprintf("chain_hash=%v, short_chan_id=%v",
                        msg.ChainHash, msg.ShortChannelID.ToUint64())

        case *lnwire.ChannelUpdate1:
                return fmt.Sprintf("chain_hash=%v, short_chan_id=%v, "+
                        "mflags=%v, cflags=%v, update_time=%v", msg.ChainHash,
                        msg.ShortChannelID.ToUint64(), msg.MessageFlags,
                        msg.ChannelFlags, time.Unix(int64(msg.Timestamp), 0))

        case *lnwire.NodeAnnouncement:
                return fmt.Sprintf("node=%x, update_time=%v",
                        msg.NodeID, time.Unix(int64(msg.Timestamp), 0))

        case *lnwire.Ping:
                return fmt.Sprintf("ping_bytes=%x", msg.PaddingBytes[:])

        case *lnwire.Pong:
                return fmt.Sprintf("len(pong_bytes)=%d", len(msg.PongBytes[:]))

        case *lnwire.UpdateFee:
                return fmt.Sprintf("chan_id=%v, fee_update_sat=%v",
                        msg.ChanID, int64(msg.FeePerKw))

        case *lnwire.ChannelReestablish:
                return fmt.Sprintf("chan_id=%v, next_local_height=%v, "+
                        "remote_tail_height=%v", msg.ChanID,
                        msg.NextLocalCommitHeight, msg.RemoteCommitTailHeight)

        case *lnwire.ReplyShortChanIDsEnd:
                return fmt.Sprintf("chain_hash=%v, complete=%v", msg.ChainHash,
                        msg.Complete)

        case *lnwire.ReplyChannelRange:
                return fmt.Sprintf("start_height=%v, end_height=%v, "+
                        "num_chans=%v, encoding=%v", msg.FirstBlockHeight,
                        msg.LastBlockHeight(), len(msg.ShortChanIDs),
                        msg.EncodingType)

        case *lnwire.QueryShortChanIDs:
                return fmt.Sprintf("chain_hash=%v, encoding=%v, num_chans=%v",
                        msg.ChainHash, msg.EncodingType, len(msg.ShortChanIDs))

        case *lnwire.QueryChannelRange:
                return fmt.Sprintf("chain_hash=%v, start_height=%v, "+
                        "end_height=%v", msg.ChainHash, msg.FirstBlockHeight,
                        msg.LastBlockHeight())

        case *lnwire.GossipTimestampRange:
                return fmt.Sprintf("chain_hash=%v, first_stamp=%v, "+
                        "stamp_range=%v", msg.ChainHash,
                        time.Unix(int64(msg.FirstTimestamp), 0),
                        msg.TimestampRange)

        case *lnwire.Stfu:
                return fmt.Sprintf("chan_id=%v, initiator=%v", msg.ChanID,
                        msg.Initiator)

        case *lnwire.Custom:
                return fmt.Sprintf("type=%d", msg.Type)
        }

        return fmt.Sprintf("unknown msg type=%T", msg)
}

// logWireMessage logs the receipt or sending of particular wire message. This
// function is used rather than just logging the message in order to produce
// less spammy log messages in trace mode by setting the 'Curve" parameter to
// nil. Doing this avoids printing out each of the field elements in the curve
// parameters for secp256k1.
func (p *Brontide) logWireMessage(msg lnwire.Message, read bool) {
        summaryPrefix := "Received"
        if !read {
                summaryPrefix = "Sending"
        }

        p.log.Debugf("%v", lnutils.NewLogClosure(func() string {
                // Debug summary of message.
                summary := messageSummary(msg)
                if len(summary) > 0 {
                        summary = "(" + summary + ")"
                }

                preposition := "to"
                if read {
                        preposition = "from"
                }

                var msgType string
                if msg.MsgType() < lnwire.CustomTypeStart {
                        msgType = msg.MsgType().String()
                } else {
                        msgType = "custom"
                }

                return fmt.Sprintf("%v %v%s %v %s", summaryPrefix,
                        msgType, summary, preposition, p)
        }))

        prefix := "readMessage from peer"
        if !read {
                prefix = "writeMessage to peer"
        }

        p.log.Tracef(prefix+": %v", lnutils.SpewLogClosure(msg))
}

// writeMessage writes and flushes the target lnwire.Message to the remote peer.
// If the passed message is nil, this method will only try to flush an existing
// message buffered on the connection. It is safe to call this method again
// with a nil message iff a timeout error is returned. This will continue to
// flush the pending message to the wire.
//
// NOTE:
// Besides its usage in Start, this function should not be used elsewhere
// except in writeHandler. If multiple goroutines call writeMessage at the same
// time, panics can occur because WriteMessage and Flush don't use any locking
// internally.
func (p *Brontide) writeMessage(msg lnwire.Message) error {
        // Only log the message on the first attempt.
        if msg != nil {
                p.logWireMessage(msg, false)
        }

        noiseConn := p.cfg.Conn

        flushMsg := func() error {
                // Ensure the write deadline is set before we attempt to send
                // the message.
                writeDeadline := time.Now().Add(
                        p.scaleTimeout(writeMessageTimeout),
                )
                err := noiseConn.SetWriteDeadline(writeDeadline)
                if err != nil {
                        return err
                }

                // Flush the pending message to the wire. If an error is
                // encountered, e.g. write timeout, the number of bytes written
                // so far will be returned.
                n, err := noiseConn.Flush()

                // Record the number of bytes written on the wire, if any.
                if n > 0 {
                        atomic.AddUint64(&p.bytesSent, uint64(n))
                }

                return err
        }

        // If the current message has already been serialized, encrypted, and
        // buffered on the underlying connection we will skip straight to
        // flushing it to the wire.
        if msg == nil {
                return flushMsg()
        }

        // Otherwise, this is a new message. We'll acquire a write buffer to
        // serialize the message and buffer the ciphertext on the connection.
        err := p.cfg.WritePool.Submit(func(buf *bytes.Buffer) error {
                // Using a buffer allocated by the write pool, encode the
                // message directly into the buffer.
                _, writeErr := lnwire.WriteMessage(buf, msg, 0)
                if writeErr != nil {
                        return writeErr
                }

                // Finally, write the message itself in a single swoop. This
                // will buffer the ciphertext on the underlying connection. We
                // will defer flushing the message until the write pool has been
                // released.
                return noiseConn.WriteMessage(buf.Bytes())
        })
        if err != nil {
                return err
        }

        return flushMsg()
}

// writeHandler is a goroutine dedicated to reading messages off of an incoming
// queue, and writing them out to the wire. This goroutine coordinates with the
// queueHandler in order to ensure the incoming message queue is quickly
// drained.
//
// NOTE: This method MUST be run as a goroutine.
func (p *Brontide) writeHandler() {
        // We'll stop the timer after a new messages is sent, and also reset it
        // after we process the next message.
        idleTimer := time.AfterFunc(idleTimeout, func() {
                err := fmt.Errorf("peer %s no write for %s -- disconnecting",
                        p, idleTimeout)
                p.Disconnect(err)
        })

        var exitErr error

out:
        for {
                select {
                case outMsg := <-p.sendQueue:
                        // Record the time at which we first attempt to send the
                        // message.
                        startTime := time.Now()

                retry:
                        // Write out the message to the socket. If a timeout
                        // error is encountered, we will catch this and retry
                        // after backing off in case the remote peer is just
                        // slow to process messages from the wire.
                        err := p.writeMessage(outMsg.msg)
                        if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
                                p.log.Debugf("Write timeout detected for "+
                                        "peer, first write for message "+
                                        "attempted %v ago",
                                        time.Since(startTime))

                                // If we received a timeout error, this implies
                                // that the message was buffered on the
                                // connection successfully and that a flush was
                                // attempted. We'll set the message to nil so
                                // that on a subsequent pass we only try to
                                // flush the buffered message, and forgo
                                // reserializing or reencrypting it.
                                outMsg.msg = nil

                                goto retry
                        }

                        // The write succeeded, reset the idle timer to prevent
                        // us from disconnecting the peer.
                        if !idleTimer.Stop() {
                                select {
                                case <-idleTimer.C:
                                default:
                                }
                        }
                        idleTimer.Reset(idleTimeout)

                        // If the peer requested a synchronous write, respond
                        // with the error.
                        if outMsg.errChan != nil {
                                outMsg.errChan <- err
                        }

                        if err != nil {
                                exitErr = fmt.Errorf("unable to write "+
                                        "message: %v", err)
                                break out
                        }

                case <-p.cg.Done():
                        exitErr = lnpeer.ErrPeerExiting
                        break out
                }
        }

        // Avoid an exit deadlock by ensuring WaitGroups are decremented before
        // disconnect.
        p.cg.WgDone()

        p.Disconnect(exitErr)

        p.log.Trace("writeHandler for peer done")
}

// queueHandler is responsible for accepting messages from outside subsystems
// to be eventually sent out on the wire by the writeHandler.
//
// NOTE: This method MUST be run as a goroutine.
func (p *Brontide) queueHandler() {
        defer p.cg.WgDone()

        // priorityMsgs holds an in order list of messages deemed high-priority
        // to be added to the sendQueue. This predominately includes messages
        // from the funding manager and htlcswitch.
        priorityMsgs := list.New()

        // lazyMsgs holds an in order list of messages deemed low-priority to be
        // added to the sendQueue only after all high-priority messages have
        // been queued. This predominately includes messages from the gossiper.
        lazyMsgs := list.New()

        for {
                // Examine the front of the priority queue, if it is empty check
                // the low priority queue.
                elem := priorityMsgs.Front()
                if elem == nil {
                        elem = lazyMsgs.Front()
                }

                if elem != nil {
                        front := elem.Value.(outgoingMsg)

                        // There's an element on the queue, try adding
                        // it to the sendQueue. We also watch for
                        // messages on the outgoingQueue, in case the
                        // writeHandler cannot accept messages on the
                        // sendQueue.
                        select {
                        case p.sendQueue <- front:
                                if front.priority {
                                        priorityMsgs.Remove(elem)
                                } else {
                                        lazyMsgs.Remove(elem)
                                }
                        case msg := <-p.outgoingQueue:
                                if msg.priority {
                                        priorityMsgs.PushBack(msg)
                                } else {
                                        lazyMsgs.PushBack(msg)
                                }
                        case <-p.cg.Done():
                                return
                        }
                } else {
                        // If there weren't any messages to send to the
                        // writeHandler, then we'll accept a new message
                        // into the queue from outside sub-systems.
                        select {
                        case msg := <-p.outgoingQueue:
                                if msg.priority {
                                        priorityMsgs.PushBack(msg)
                                } else {
                                        lazyMsgs.PushBack(msg)
                                }
                        case <-p.cg.Done():
                                return
                        }
                }
        }
}

// PingTime returns the estimated ping time to the peer in microseconds.
func (p *Brontide) PingTime() int64 {
        return p.pingManager.GetPingTimeMicroSeconds()
}

// queueMsg adds the lnwire.Message to the back of the high priority send queue.
// If the errChan is non-nil, an error is sent back if the msg failed to queue
// or failed to write, and nil otherwise.
func (p *Brontide) queueMsg(msg lnwire.Message, errChan chan error) {
        p.queue(true, msg, errChan)
}

// queueMsgLazy adds the lnwire.Message to the back of the low priority send
// queue. If the errChan is non-nil, an error is sent back if the msg failed to
// queue or failed to write, and nil otherwise.
func (p *Brontide) queueMsgLazy(msg lnwire.Message, errChan chan error) {
        p.queue(false, msg, errChan)
}

// queue sends a given message to the queueHandler using the passed priority. If
// the errChan is non-nil, an error is sent back if the msg failed to queue or
// failed to write, and nil otherwise.
func (p *Brontide) queue(priority bool, msg lnwire.Message,
        errChan chan error) {

        select {
        case p.outgoingQueue <- outgoingMsg{priority, msg, errChan}:
        case <-p.cg.Done():
                p.log.Tracef("Peer shutting down, could not enqueue msg: %v.",
                        spew.Sdump(msg))
                if errChan != nil {
                        errChan <- lnpeer.ErrPeerExiting
                }
        }
}

// ChannelSnapshots returns a slice of channel snapshots detailing all
// currently active channels maintained with the remote peer.
func (p *Brontide) ChannelSnapshots() []*channeldb.ChannelSnapshot {
        snapshots := make(
                []*channeldb.ChannelSnapshot, 0, p.activeChannels.Len(),
        )

        p.activeChannels.ForEach(func(_ lnwire.ChannelID,
                activeChan *lnwallet.LightningChannel) error {

                // If the activeChan is nil, then we skip it as the channel is
                // pending.
                if activeChan == nil {
                        return nil
                }

                // We'll only return a snapshot for channels that are
                // *immediately* available for routing payments over.
                if activeChan.RemoteNextRevocation() == nil {
                        return nil
                }

                snapshot := activeChan.StateSnapshot()
                snapshots = append(snapshots, snapshot)

                return nil
        })

        return snapshots
}

// genDeliveryScript returns a new script to be used to send our funds to in
// the case of a cooperative channel close negotiation.
func (p *Brontide) genDeliveryScript() ([]byte, error) {
        // We'll send a normal p2wkh address unless we've negotiated the
        // shutdown-any-segwit feature.
        addrType := lnwallet.WitnessPubKey
        if p.taprootShutdownAllowed() {
                addrType = lnwallet.TaprootPubkey
        }

        deliveryAddr, err := p.cfg.Wallet.NewAddress(
                addrType, false, lnwallet.DefaultAccountName,
        )
        if err != nil {
                return nil, err
        }
        p.log.Infof("Delivery addr for channel close: %v",
                deliveryAddr)

        return txscript.PayToAddrScript(deliveryAddr)
}

// channelManager is goroutine dedicated to handling all requests/signals
// pertaining to the opening, cooperative closing, and force closing of all
// channels maintained with the remote peer.
//
// NOTE: This method MUST be run as a goroutine.
func (p *Brontide) channelManager() {
        defer p.cg.WgDone()

        // reenableTimeout will fire once after the configured channel status
        // interval has elapsed. This will trigger us to sign new channel
        // updates and broadcast them with the "disabled" flag unset.
        reenableTimeout := time.After(p.cfg.ChanActiveTimeout)

out:
        for {
                select {
                // A new pending channel has arrived which means we are about
                // to complete a funding workflow and is waiting for the final
                // `ChannelReady` messages to be exchanged. We will add this
                // channel to the `activeChannels` with a nil value to indicate
                // this is a pending channel.
                case req := <-p.newPendingChannel:
                        p.handleNewPendingChannel(req)

                // A new channel has arrived which means we've just completed a
                // funding workflow. We'll initialize the necessary local
                // state, and notify the htlc switch of a new link.
                case req := <-p.newActiveChannel:
                        p.handleNewActiveChannel(req)

                // The funding flow for a pending channel is failed, we will
                // remove it from Brontide.
                case req := <-p.removePendingChannel:
                        p.handleRemovePendingChannel(req)

                // We've just received a local request to close an active
                // channel. It will either kick of a cooperative channel
                // closure negotiation, or be a notification of a breached
                // contract that should be abandoned.
                case req := <-p.localCloseChanReqs:
                        p.handleLocalCloseReq(req)

                // We've received a link failure from a link that was added to
                // the switch. This will initiate the teardown of the link, and
                // initiate any on-chain closures if necessary.
                case failure := <-p.linkFailures:
                        p.handleLinkFailure(failure)

                // We've received a new cooperative channel closure related
                // message from the remote peer, we'll use this message to
                // advance the chan closer state machine.
                case closeMsg := <-p.chanCloseMsgs:
                        p.handleCloseMsg(closeMsg)

                // The channel reannounce delay has elapsed, broadcast the
                // reenabled channel updates to the network. This should only
                // fire once, so we set the reenableTimeout channel to nil to
                // mark it for garbage collection. If the peer is torn down
                // before firing, reenabling will not be attempted.
                // TODO(conner): consolidate reenables timers inside chan status
                // manager
                case <-reenableTimeout:
                        p.reenableActiveChannels()

                        // Since this channel will never fire again during the
                        // lifecycle of the peer, we nil the channel to mark it
                        // eligible for garbage collection, and make this
                        // explicitly ineligible to receive in future calls to
                        // select. This also shaves a few CPU cycles since the
                        // select will ignore this case entirely.
                        reenableTimeout = nil

                        // Once the reenabling is attempted, we also cancel the
                        // channel event subscription to free up the overflow
                        // queue used in channel notifier.
                        //
                        // NOTE: channelEventClient will be nil if the
                        // reenableTimeout is greater than 1 minute.
                        if p.channelEventClient != nil {
                                p.channelEventClient.Cancel()
                        }

                case <-p.cg.Done():
                        // As, we've been signalled to exit, we'll reset all
                        // our active channel back to their default state.
                        p.activeChannels.ForEach(func(_ lnwire.ChannelID,
                                lc *lnwallet.LightningChannel) error {

                                // Exit if the channel is nil as it's a pending
                                // channel.
                                if lc == nil {
                                        return nil
                                }

                                lc.ResetState()

                                return nil
                        })

                        break out
                }
        }
}

// reenableActiveChannels searches the index of channels maintained with this
// peer, and reenables each public, non-pending channel. This is done at the
// gossip level by broadcasting a new ChannelUpdate with the disabled bit unset.
// No message will be sent if the channel is already enabled.
func (p *Brontide) reenableActiveChannels() {
        // First, filter all known channels with this peer for ones that are
        // both public and not pending.
        activePublicChans := p.filterChannelsToEnable()

        // Create a map to hold channels that needs to be retried.
        retryChans := make(map[wire.OutPoint]struct{}, len(activePublicChans))

        // For each of the public, non-pending channels, set the channel
        // disabled bit to false and send out a new ChannelUpdate. If this
        // channel is already active, the update won't be sent.
        for _, chanPoint := range activePublicChans {
                err := p.cfg.ChanStatusMgr.RequestEnable(chanPoint, false)

                switch {
                // No error occurred, continue to request the next channel.
                case err == nil:
                        continue

                // Cannot auto enable a manually disabled channel so we do
                // nothing but proceed to the next channel.
                case errors.Is(err, netann.ErrEnableManuallyDisabledChan):
                        p.log.Debugf("Channel(%v) was manually disabled, "+
                                "ignoring automatic enable request", chanPoint)

                        continue

                // If the channel is reported as inactive, we will give it
                // another chance. When handling the request, ChanStatusManager
                // will check whether the link is active or not. One of the
                // conditions is whether the link has been marked as
                // reestablished, which happens inside a goroutine(htlcManager)
                // after the link is started. And we may get a false negative
                // saying the link is not active because that goroutine hasn't
                // reached the line to mark the reestablishment. Thus we give
                // it a second chance to send the request.
                case errors.Is(err, netann.ErrEnableInactiveChan):
                        // If we don't have a client created, it means we
                        // shouldn't retry enabling the channel.
                        if p.channelEventClient == nil {
                                p.log.Errorf("Channel(%v) request enabling "+
                                        "failed due to inactive link",
                                        chanPoint)

                                continue
                        }

                        p.log.Warnf("Channel(%v) cannot be enabled as " +
                                "ChanStatusManager reported inactive, retrying")

                        // Add the channel to the retry map.
                        retryChans[chanPoint] = struct{}{}
                }
        }

        // Retry the channels if we have any.
        if len(retryChans) != 0 {
                p.retryRequestEnable(retryChans)
        }
}

// fetchActiveChanCloser attempts to fetch the active chan closer state machine
// for the target channel ID. If the channel isn't active an error is returned.
// Otherwise, either an existing state machine will be returned, or a new one
// will be created.
func (p *Brontide) fetchActiveChanCloser(chanID lnwire.ChannelID) (
        *chanCloserFsm, error) {

        chanCloser, found := p.activeChanCloses.Load(chanID)
        if found {
                // An entry will only be found if the closer has already been
                // created for a non-pending channel or for a channel that had
                // previously started the shutdown process but the connection
                // was restarted.
                return &chanCloser, nil
        }

        // First, we'll ensure that we actually know of the target channel. If
        // not, we'll ignore this message.
        channel, ok := p.activeChannels.Load(chanID)

        // If the channel isn't in the map or the channel is nil, return
        // ErrChannelNotFound as the channel is pending.
        if !ok || channel == nil {
                return nil, ErrChannelNotFound
        }

        // We'll create a valid closing state machine in order to respond to
        // the initiated cooperative channel closure. First, we set the
        // delivery script that our funds will be paid out to. If an upfront
        // shutdown script was set, we will use it. Otherwise, we get a fresh
        // delivery script.
        //
        // TODO: Expose option to allow upfront shutdown script from watch-only
        // accounts.
        deliveryScript := channel.LocalUpfrontShutdownScript()
        if len(deliveryScript) == 0 {
                var err error
                deliveryScript, err = p.genDeliveryScript()
                if err != nil {
                        p.log.Errorf("unable to gen delivery script: %v",
                                err)
                        return nil, fmt.Errorf("close addr unavailable")
                }
        }

        // In order to begin fee negotiations, we'll first compute our target
        // ideal fee-per-kw.
        feePerKw, err := p.cfg.FeeEstimator.EstimateFeePerKW(
                p.cfg.CoopCloseTargetConfs,
        )
        if err != nil {
                p.log.Errorf("unable to query fee estimator: %v", err)
                return nil, fmt.Errorf("unable to estimate fee")
        }

        addr, err := p.addrWithInternalKey(deliveryScript)
        if err != nil {
                return nil, fmt.Errorf("unable to parse addr: %w", err)
        }
        negotiateChanCloser, err := p.createChanCloser(
                channel, addr, feePerKw, nil, lntypes.Remote,
        )
        if err != nil {
                p.log.Errorf("unable to create chan closer: %v", err)
                return nil, fmt.Errorf("unable to create chan closer")
        }

        chanCloser = makeNegotiateCloser(negotiateChanCloser)

        p.activeChanCloses.Store(chanID, chanCloser)

        return &chanCloser, nil
}

// filterChannelsToEnable filters a list of channels to be enabled upon start.
// The filtered channels are active channels that's neither private nor
// pending.
func (p *Brontide) filterChannelsToEnable() []wire.OutPoint {
        var activePublicChans []wire.OutPoint

        p.activeChannels.Range(func(chanID lnwire.ChannelID,
                lnChan *lnwallet.LightningChannel) bool {

                // If the lnChan is nil, continue as this is a pending channel.
                if lnChan == nil {
                        return true
                }

                dbChan := lnChan.State()
                isPublic := dbChan.ChannelFlags&lnwire.FFAnnounceChannel != 0
                if !isPublic || dbChan.IsPending {
                        return true
                }

                // We'll also skip any channels added during this peer's
                // lifecycle since they haven't waited out the timeout. Their
                // first announcement will be enabled, and the chan status
                // manager will begin monitoring them passively since they exist
                // in the database.
                if _, ok := p.addedChannels.Load(chanID); ok {
                        return true
                }

                activePublicChans = append(
                        activePublicChans, dbChan.FundingOutpoint,
                )

                return true
        })

        return activePublicChans
}

// retryRequestEnable takes a map of channel outpoints and a channel event
// client. It listens to the channel events and removes a channel from the map
// if it's matched to the event. Upon receiving an active channel event, it
// will send the enabling request again.
func (p *Brontide) retryRequestEnable(activeChans map[wire.OutPoint]struct{}) {
        p.log.Debugf("Retry enabling %v channels", len(activeChans))

        // retryEnable is a helper closure that sends an enable request and
        // removes the channel from the map if it's matched.
        retryEnable := func(chanPoint wire.OutPoint) error {
                // If this is an active channel event, check whether it's in
                // our targeted channels map.
                _, found := activeChans[chanPoint]

                // If this channel is irrelevant, return nil so the loop can
                // jump to next iteration.
                if !found {
                        return nil
                }

                // Otherwise we've just received an active signal for a channel
                // that's previously failed to be enabled, we send the request
                // again.
                //
                // We only give the channel one more shot, so we delete it from
                // our map first to keep it from being attempted again.
                delete(activeChans, chanPoint)

                // Send the request.
                err := p.cfg.ChanStatusMgr.RequestEnable(chanPoint, false)
                if err != nil {
                        return fmt.Errorf("request enabling channel %v "+
                                "failed: %w", chanPoint, err)
                }

                return nil
        }

        for {
                // If activeChans is empty, we've done processing all the
                // channels.
                if len(activeChans) == 0 {
                        p.log.Debug("Finished retry enabling channels")
                        return
                }

                select {
                // A new event has been sent by the ChannelNotifier. We now
                // check whether it's an active or inactive channel event.
                case e := <-p.channelEventClient.Updates():
                        // If this is an active channel event, try enable the
                        // channel then jump to the next iteration.
                        active, ok := e.(channelnotifier.ActiveChannelEvent)
                        if ok {
                                chanPoint := *active.ChannelPoint

                                // If we received an error for this particular
                                // channel, we log an error and won't quit as
                                // we still want to retry other channels.
                                if err := retryEnable(chanPoint); err != nil {
                                        p.log.Errorf("Retry failed: %v", err)
                                }

                                continue
                        }

                        // Otherwise check for inactive link event, and jump to
                        // next iteration if it's not.
                        inactive, ok := e.(channelnotifier.InactiveLinkEvent)
                        if !ok {
                                continue
                        }

                        // Found an inactive link event, if this is our
                        // targeted channel, remove it from our map.
                        chanPoint := *inactive.ChannelPoint
                        _, found := activeChans[chanPoint]
                        if !found {
                                continue
                        }

                        delete(activeChans, chanPoint)
                        p.log.Warnf("Re-enable channel %v failed, received "+
                                "inactive link event", chanPoint)

                case <-p.cg.Done():
                        p.log.Debugf("Peer shutdown during retry enabling")
                        return
                }
        }
}

// chooseDeliveryScript takes two optionally set shutdown scripts and returns
// a suitable script to close out to. This may be nil if neither script is
// set. If both scripts are set, this function will error if they do not match.
func chooseDeliveryScript(upfront, requested lnwire.DeliveryAddress,
        genDeliveryScript func() ([]byte, error),
) (lnwire.DeliveryAddress, error) {

        switch {
        // If no script was provided, then we'll generate a new delivery script.
        case len(upfront) == 0 && len(requested) == 0:
                return genDeliveryScript()

        // If no upfront shutdown script was provided, return the user
        // requested address (which may be nil).
        case len(upfront) == 0:
                return requested, nil

        // If an upfront shutdown script was provided, and the user did not
        // request a custom shutdown script, return the upfront address.
        case len(requested) == 0:
                return upfront, nil

        // If both an upfront shutdown script and a custom close script were
        // provided, error if the user provided shutdown script does not match
        // the upfront shutdown script (because closing out to a different
        // script would violate upfront shutdown).
        case !bytes.Equal(upfront, requested):
                return nil, chancloser.ErrUpfrontShutdownScriptMismatch

        // The user requested script matches the upfront shutdown script, so we
        // can return it without error.
        default:
                return upfront, nil
        }
}

// restartCoopClose checks whether we need to restart the cooperative close
// process for a given channel.
func (p *Brontide) restartCoopClose(lnChan *lnwallet.LightningChannel) (
        *lnwire.Shutdown, error) {

        isTaprootChan := lnChan.ChanType().IsTaproot()

        // If this channel has status ChanStatusCoopBroadcasted and does not
        // have a closing transaction, then the cooperative close process was
        // started but never finished. We'll re-create the chanCloser state
        // machine and resend Shutdown. BOLT#2 requires that we retransmit
        // Shutdown exactly, but doing so would mean persisting the RPC
        // provided close script. Instead use the LocalUpfrontShutdownScript
        // or generate a script.
        c := lnChan.State()
        _, err := c.BroadcastedCooperative()
        if err != nil && err != channeldb.ErrNoCloseTx {
                // An error other than ErrNoCloseTx was encountered.
                return nil, err
        } else if err == nil && !p.rbfCoopCloseAllowed() {
                // This is a channel that doesn't support RBF coop close, and it
                // already had a coop close txn broadcast. As a result, we can
                // just exit here as all we can do is wait for it to confirm.
                return nil, nil
        }

        chanID := lnwire.NewChanIDFromOutPoint(c.FundingOutpoint)

        var deliveryScript []byte

        shutdownInfo, err := c.ShutdownInfo()
        switch {
        // We have previously stored the delivery script that we need to use
        // in the shutdown message. Re-use this script.
        case err == nil:
                shutdownInfo.WhenSome(func(info channeldb.ShutdownInfo) {
                        deliveryScript = info.DeliveryScript.Val
                })

        // An error other than ErrNoShutdownInfo was returned
        case !errors.Is(err, channeldb.ErrNoShutdownInfo):
                return nil, err

        case errors.Is(err, channeldb.ErrNoShutdownInfo):
                deliveryScript = c.LocalShutdownScript
                if len(deliveryScript) == 0 {
                        var err error
                        deliveryScript, err = p.genDeliveryScript()
                        if err != nil {
                                p.log.Errorf("unable to gen delivery script: "+
                                        "%v", err)

                                return nil, fmt.Errorf("close addr unavailable")
                        }
                }
        }

        // If the new RBF co-op close is negotiated, then we'll init and start
        // that state machine, skipping the steps for the negotiate machine
        // below. We don't support this close type for taproot channels though.
        if p.rbfCoopCloseAllowed() && !isTaprootChan {
                _, err := p.initRbfChanCloser(lnChan)
                if err != nil {
                        return nil, fmt.Errorf("unable to init rbf chan "+
                                "closer during restart: %w", err)
                }

                shutdownDesc := fn.MapOption(
                        newRestartShutdownInit,
                )(shutdownInfo)

                err = p.startRbfChanCloser(
                        fn.FlattenOption(shutdownDesc), lnChan.ChannelPoint(),
                )

                return nil, err
        }

        // Compute an ideal fee.
        feePerKw, err := p.cfg.FeeEstimator.EstimateFeePerKW(
                p.cfg.CoopCloseTargetConfs,
        )
        if err != nil {
                p.log.Errorf("unable to query fee estimator: %v", err)
                return nil, fmt.Errorf("unable to estimate fee")
        }

        // Determine whether we or the peer are the initiator of the coop
        // close attempt by looking at the channel's status.
        closingParty := lntypes.Remote
        if c.HasChanStatus(channeldb.ChanStatusLocalCloseInitiator) {
                closingParty = lntypes.Local
        }

        addr, err := p.addrWithInternalKey(deliveryScript)
        if err != nil {
                return nil, fmt.Errorf("unable to parse addr: %w", err)
        }
        chanCloser, err := p.createChanCloser(
                lnChan, addr, feePerKw, nil, closingParty,
        )
        if err != nil {
                p.log.Errorf("unable to create chan closer: %v", err)
                return nil, fmt.Errorf("unable to create chan closer")
        }

        p.activeChanCloses.Store(chanID, makeNegotiateCloser(chanCloser))

        // Create the Shutdown message.
        shutdownMsg, err := chanCloser.ShutdownChan()
        if err != nil {
                p.log.Errorf("unable to create shutdown message: %v", err)
                p.activeChanCloses.Delete(chanID)
                return nil, err
        }

        return shutdownMsg, nil
}

// createChanCloser constructs a ChanCloser from the passed parameters and is
// used to de-duplicate code.
func (p *Brontide) createChanCloser(channel *lnwallet.LightningChannel,
        deliveryScript *chancloser.DeliveryAddrWithKey,
        fee chainfee.SatPerKWeight, req *htlcswitch.ChanClose,
        closer lntypes.ChannelParty) (*chancloser.ChanCloser, error) {

        _, startingHeight, err := p.cfg.ChainIO.GetBestBlock()
        if err != nil {
                p.log.Errorf("unable to obtain best block: %v", err)
                return nil, fmt.Errorf("cannot obtain best block")
        }

        // The req will only be set if we initiated the co-op closing flow.
        var maxFee chainfee.SatPerKWeight
        if req != nil {
                maxFee = req.MaxFee
        }

        chanCloser := chancloser.NewChanCloser(
                chancloser.ChanCloseCfg{
                        Channel:      channel,
                        MusigSession: NewMusigChanCloser(channel),
                        FeeEstimator: &chancloser.SimpleCoopFeeEstimator{},
                        BroadcastTx:  p.cfg.Wallet.PublishTransaction,
                        AuxCloser:    p.cfg.AuxChanCloser,
                        DisableChannel: func(op wire.OutPoint) error {
                                return p.cfg.ChanStatusMgr.RequestDisable(
                                        op, false,
                                )
                        },
                        MaxFee: maxFee,
                        Disconnect: func() error {
                                return p.cfg.DisconnectPeer(p.IdentityKey())
                        },
                        ChainParams: &p.cfg.Wallet.Cfg.NetParams,
                },
                *deliveryScript,
                fee,
                uint32(startingHeight),
                req,
                closer,
        )

        return chanCloser, nil
}

// initNegotiateChanCloser initializes the channel closer for a channel that is
// using the original "negotiation" based protocol. This path is used when
// we're the one initiating the channel close.
//
// TODO(roasbeef): can make a MsgEndpoint for existing handling logic to
// further abstract.
func (p *Brontide) initNegotiateChanCloser(req *htlcswitch.ChanClose,
        channel *lnwallet.LightningChannel) error {

        // First, we'll choose a delivery address that we'll use to send the
        // funds to in the case of a successful negotiation.

        // An upfront shutdown and user provided script are both optional, but
        // must be equal if both set  (because we cannot serve a request to
        // close out to a script which violates upfront shutdown). Get the
        // appropriate address to close out to (which may be nil if neither are
        // set) and error if they are both set and do not match.
        deliveryScript, err := chooseDeliveryScript(
                channel.LocalUpfrontShutdownScript(), req.DeliveryScript,
                p.genDeliveryScript,
        )
        if err != nil {
                return fmt.Errorf("cannot close channel %v: %w",
                        req.ChanPoint, err)
        }

        addr, err := p.addrWithInternalKey(deliveryScript)
        if err != nil {
                return fmt.Errorf("unable to parse addr for channel "+
                        "%v: %w", req.ChanPoint, err)
        }

        chanCloser, err := p.createChanCloser(
                channel, addr, req.TargetFeePerKw, req, lntypes.Local,
        )
        if err != nil {
                return fmt.Errorf("unable to make chan closer: %w", err)
        }

        chanID := lnwire.NewChanIDFromOutPoint(channel.ChannelPoint())
        p.activeChanCloses.Store(chanID, makeNegotiateCloser(chanCloser))

        // Finally, we'll initiate the channel shutdown within the
        // chanCloser, and send the shutdown message to the remote
        // party to kick things off.
        shutdownMsg, err := chanCloser.ShutdownChan()
        if err != nil {
                // As we were unable to shutdown the channel, we'll return it
                // back to its normal state.
                defer channel.ResetState()

                p.activeChanCloses.Delete(chanID)

                return fmt.Errorf("unable to shutdown channel: %w", err)
        }

        link := p.fetchLinkFromKeyAndCid(chanID)
        if link == nil {
                // If the link is nil then it means it was already removed from
                // the switch or it never existed in the first place. The
                // latter case is handled at the beginning of this function, so
                // in the case where it has already been removed, we can skip
                // adding the commit hook to queue a Shutdown message.
                p.log.Warnf("link not found during attempted closure: "+
                        "%v", chanID)
                return nil
        }

        if !link.DisableAdds(htlcswitch.Outgoing) {
                p.log.Warnf("Outgoing link adds already "+
                        "disabled: %v", link.ChanID())
        }

        link.OnCommitOnce(htlcswitch.Outgoing, func() {
                p.queueMsg(shutdownMsg, nil)
        })

        return nil
}

// chooseAddr returns the provided address if it is non-zero length, otherwise
// None.
func chooseAddr(addr lnwire.DeliveryAddress) fn.Option[lnwire.DeliveryAddress] {
        if len(addr) == 0 {
                return fn.None[lnwire.DeliveryAddress]()
        }

        return fn.Some(addr)
}

// observeRbfCloseUpdates observes the channel for any updates that may
// indicate that a new txid has been broadcasted, or the channel fully closed
// on chain.
func (p *Brontide) observeRbfCloseUpdates(chanCloser *chancloser.RbfChanCloser,
        closeReq *htlcswitch.ChanClose,
        coopCloseStates chancloser.RbfStateSub) {

        newStateChan := coopCloseStates.NewItemCreated.ChanOut()
        defer chanCloser.RemoveStateSub(coopCloseStates)

        var (
                lastTxids    lntypes.Dual[chainhash.Hash]
                lastFeeRates lntypes.Dual[chainfee.SatPerVByte]
        )

        maybeNotifyTxBroadcast := func(state chancloser.AsymmetricPeerState,
                party lntypes.ChannelParty) {

                // First, check to see if we have an error to report to the
                // caller. If so, then we''ll return that error and exit, as the
                // stream will exit as well.
                if closeErr, ok := state.(*chancloser.CloseErr); ok {
                        // We hit an error during the last state transition, so
                        // we'll extract the error then send it to the
                        // user.
                        err := closeErr.Err()

                        peerLog.Warnf("ChannelPoint(%v): encountered close "+
                                "err: %v", closeReq.ChanPoint, err)

                        select {
                        case closeReq.Err <- err:
                        case <-closeReq.Ctx.Done():
                        case <-p.cg.Done():
                        }

                        return
                }

                closePending, ok := state.(*chancloser.ClosePending)

                // If this isn't the close pending state, we aren't at the
                // terminal state yet.
                if !ok {
                        return
                }

                // Only notify if the fee rate is greater.
                newFeeRate := closePending.FeeRate
                lastFeeRate := lastFeeRates.GetForParty(party)
                if newFeeRate <= lastFeeRate {
                        peerLog.Debugf("ChannelPoint(%v): remote party made "+
                                "update for fee rate %v, but we already have "+
                                "a higher fee rate of %v", closeReq.ChanPoint,
                                newFeeRate, lastFeeRate)

                        return
                }

                feeRate := closePending.FeeRate
                lastFeeRates.SetForParty(party, feeRate)

                // At this point, we'll have a txid that we can use to notify
                // the client, but only if it's different from the last one we
                // sent. If the user attempted to bump, but was rejected due to
                // RBF, then we'll send a redundant update.
                closingTxid := closePending.CloseTx.TxHash()
                lastTxid := lastTxids.GetForParty(party)
                if closeReq != nil && closingTxid != lastTxid {
                        select {
                        case closeReq.Updates <- &PendingUpdate{
                                Txid:        closingTxid[:],
                                FeePerVbyte: fn.Some(closePending.FeeRate),
                                IsLocalCloseTx: fn.Some(
                                        party == lntypes.Local,
                                ),
                        }:

                        case <-closeReq.Ctx.Done():
                                return

                        case <-p.cg.Done():
                                return
                        }
                }

                lastTxids.SetForParty(party, closingTxid)
        }

        peerLog.Infof("Observing RBF close updates for channel %v",
                closeReq.ChanPoint)

        // We'll consume each new incoming state to send out the appropriate
        // RPC update.
        for {
                select {
                case newState := <-newStateChan:

                        switch closeState := newState.(type) {
                        // Once we've reached the state of pending close, we
                        // have a txid that we broadcasted.
                        case *chancloser.ClosingNegotiation:
                                peerState := closeState.PeerState

                                // Each side may have gained a new co-op close
                                // tx, so we'll examine both to see if they've
                                // changed.
                                maybeNotifyTxBroadcast(
                                        peerState.GetForParty(lntypes.Local),
                                        lntypes.Local,
                                )
                                maybeNotifyTxBroadcast(
                                        peerState.GetForParty(lntypes.Remote),
                                        lntypes.Remote,
                                )

                        // Otherwise, if we're transition to CloseFin, then we
                        // know that we're done.
                        case *chancloser.CloseFin:
                                // To clean up, we'll remove the chan closer
                                // from the active map, and send the final
                                // update to the client.
                                closingTxid := closeState.ConfirmedTx.TxHash()
                                if closeReq != nil {
                                        closeReq.Updates <- &ChannelCloseUpdate{
                                                ClosingTxid: closingTxid[:],
                                                Success:     true,
                                        }
                                }
                                chanID := lnwire.NewChanIDFromOutPoint(
                                        *closeReq.ChanPoint,
                                )
                                p.activeChanCloses.Delete(chanID)

                                return
                        }

                case <-closeReq.Ctx.Done():
                        return

                case <-p.cg.Done():
                        return
                }
        }
}

// chanErrorReporter is a simple implementation of the
// chancloser.ErrorReporter. This is bound to a single channel by the channel
// ID.
type chanErrorReporter struct {
        chanID lnwire.ChannelID
        peer   *Brontide
}

// newChanErrorReporter creates a new instance of the chanErrorReporter.
func newChanErrorReporter(chanID lnwire.ChannelID,
        peer *Brontide) *chanErrorReporter {

        return &chanErrorReporter{
                chanID: chanID,
                peer:   peer,
        }
}

// ReportError is a method that's used to report an error that occurred during
// state machine execution. This is used by the RBF close state machine to
// terminate the state machine and send an error to the remote peer.
//
// This is a part of the chancloser.ErrorReporter interface.
func (c *chanErrorReporter) ReportError(chanErr error) {
        c.peer.log.Errorf("coop close error for channel %v: %v",
                c.chanID, chanErr)

        var errMsg []byte
        if errors.Is(chanErr, chancloser.ErrInvalidStateTransition) {
                errMsg = []byte("unexpected protocol message")
        } else {
                errMsg = []byte(chanErr.Error())
        }

        err := c.peer.SendMessageLazy(false, &lnwire.Error{
                ChanID: c.chanID,
                Data:   errMsg,
        })
        if err != nil {
                c.peer.log.Warnf("unable to send error message to peer: %v",
                        err)
        }

        // After we send the error message to the peer, we'll re-initialize the
        // coop close state machine as they may send a shutdown message to
        // retry the coop close.
        lnChan, ok := c.peer.activeChannels.Load(c.chanID)
        if !ok {
                return
        }

        if lnChan == nil {
                c.peer.log.Debugf("channel %v is pending, not "+
                        "re-initializing coop close state machine",
                        c.chanID)

                return
        }

        if _, err := c.peer.initRbfChanCloser(lnChan); err != nil {
                c.peer.activeChanCloses.Delete(c.chanID)

                c.peer.log.Errorf("unable to init RBF chan closer after "+
                        "error case: %v", err)
        }
}

// chanFlushEventSentinel is used to send the RBF coop close state machine the
// channel flushed event. We'll wait until the state machine enters the
// ChannelFlushing state, then request the link to send the event once flushed.
//
// NOTE: This MUST be run as a goroutine.
func (p *Brontide) chanFlushEventSentinel(chanCloser *chancloser.RbfChanCloser,
        link htlcswitch.ChannelUpdateHandler,
        channel *lnwallet.LightningChannel) {

        defer p.cg.WgDone()

        // If there's no link, then the channel has already been flushed, so we
        // don't need to continue.
        if link == nil {
                return
        }

        coopCloseStates := chanCloser.RegisterStateEvents()
        defer chanCloser.RemoveStateSub(coopCloseStates)

        newStateChan := coopCloseStates.NewItemCreated.ChanOut()

        sendChanFlushed := func() {
                chanState := channel.StateSnapshot()

                peerLog.Infof("ChannelPoint(%v) has been flushed for co-op "+
                        "close, sending event to chan closer",
                        channel.ChannelPoint())

                chanBalances := chancloser.ShutdownBalances{
                        LocalBalance:  chanState.LocalBalance,
                        RemoteBalance: chanState.RemoteBalance,
                }
                ctx := context.Background()
                chanCloser.SendEvent(ctx, &chancloser.ChannelFlushed{
                        ShutdownBalances: chanBalances,
                        FreshFlush:       true,
                })
        }

        // We'll wait until the channel enters the ChannelFlushing state. We
        // exit after a success loop. As after the first RBF iteration, the
        // channel will always be flushed.
        for {
                select {
                case newState, ok := <-newStateChan:
                        if !ok {
                                return
                        }

                        if _, ok := newState.(*chancloser.ChannelFlushing); ok {
                                peerLog.Infof("ChannelPoint(%v): rbf coop "+
                                        "close is awaiting a flushed state, "+
                                        "registering with link..., ",
                                        channel.ChannelPoint())

                                // Request the link to send the event once the
                                // channel is flushed. We only need this event
                                // sent once, so we can exit now.
                                link.OnFlushedOnce(sendChanFlushed)

                                return
                        }

                case <-p.cg.Done():
                        return
                }
        }
}

// initRbfChanCloser initializes the channel closer for a channel that
// is using the new RBF based co-op close protocol. This only creates the chan
// closer, but doesn't attempt to trigger any manual state transitions.
func (p *Brontide) initRbfChanCloser(
        channel *lnwallet.LightningChannel) (*chancloser.RbfChanCloser, error) {

        chanID := lnwire.NewChanIDFromOutPoint(channel.ChannelPoint())

        link := p.fetchLinkFromKeyAndCid(chanID)

        _, startingHeight, err := p.cfg.ChainIO.GetBestBlock()
        if err != nil {
                return nil, fmt.Errorf("cannot obtain best block: %w", err)
        }

        defaultFeePerKw, err := p.cfg.FeeEstimator.EstimateFeePerKW(
                p.cfg.CoopCloseTargetConfs,
        )
        if err != nil {
                return nil, fmt.Errorf("unable to estimate fee: %w", err)
        }

        thawHeight, err := channel.AbsoluteThawHeight()
        if err != nil {
                return nil, fmt.Errorf("unable to get thaw height: %w", err)
        }

        peerPub := *p.IdentityKey()

        msgMapper := chancloser.NewRbfMsgMapper(
                uint32(startingHeight), chanID, peerPub,
        )

        initialState := chancloser.ChannelActive{}

        scid := channel.ZeroConfRealScid().UnwrapOr(
                channel.ShortChanID(),
        )

        env := chancloser.Environment{
                ChainParams:    p.cfg.Wallet.Cfg.NetParams,
                ChanPeer:       peerPub,
                ChanPoint:      channel.ChannelPoint(),
                ChanID:         chanID,
                Scid:           scid,
                ChanType:       channel.ChanType(),
                DefaultFeeRate: defaultFeePerKw.FeePerVByte(),
                ThawHeight:     fn.Some(thawHeight),
                RemoteUpfrontShutdown: chooseAddr(
                        channel.RemoteUpfrontShutdownScript(),
                ),
                LocalUpfrontShutdown: chooseAddr(
                        channel.LocalUpfrontShutdownScript(),
                ),
                NewDeliveryScript: func() (lnwire.DeliveryAddress, error) {
                        return p.genDeliveryScript()
                },
                FeeEstimator: &chancloser.SimpleCoopFeeEstimator{},
                CloseSigner:  channel,
                ChanObserver: newChanObserver(
                        channel, link, p.cfg.ChanStatusMgr,
                ),
        }

        spendEvent := protofsm.RegisterSpend[chancloser.ProtocolEvent]{
                OutPoint:   channel.ChannelPoint(),
                PkScript:   channel.FundingTxOut().PkScript,
                HeightHint: channel.DeriveHeightHint(),
                PostSpendEvent: fn.Some[chancloser.RbfSpendMapper](
                        chancloser.SpendMapper,
                ),
        }

        daemonAdapters := NewLndDaemonAdapters(LndAdapterCfg{
                MsgSender:     newPeerMsgSender(peerPub, p),
                TxBroadcaster: p.cfg.Wallet,
                ChainNotifier: p.cfg.ChainNotifier,
        })

        protoCfg := chancloser.RbfChanCloserCfg{
                Daemon:        daemonAdapters,
                InitialState:  &initialState,
                Env:           &env,
                InitEvent:     fn.Some[protofsm.DaemonEvent](&spendEvent),
                ErrorReporter: newChanErrorReporter(chanID, p),
                MsgMapper: fn.Some[protofsm.MsgMapper[chancloser.ProtocolEvent]]( //nolint:ll
                        msgMapper,
                ),
        }

        ctx := context.Background()
        chanCloser := protofsm.NewStateMachine(protoCfg)
        chanCloser.Start(ctx)

        // Finally, we'll register this new endpoint with the message router so
        // future co-op close messages are handled by this state machine.
        err = fn.MapOptionZ(p.msgRouter, func(r msgmux.Router) error {
                _ = r.UnregisterEndpoint(chanCloser.Name())

                return r.RegisterEndpoint(&chanCloser)
        })
        if err != nil {
                chanCloser.Stop()

                return nil, fmt.Errorf("unable to register endpoint for co-op "+
                        "close: %w", err)
        }

        p.activeChanCloses.Store(chanID, makeRbfCloser(&chanCloser))

        // Now that we've created the rbf closer state machine, we'll launch a
        // new goroutine to eventually send in the ChannelFlushed event once
        // needed.
        p.cg.WgAdd(1)
        go p.chanFlushEventSentinel(&chanCloser, link, channel)

        return &chanCloser, nil
}

// shutdownInit describes the two ways we can initiate a new shutdown. Either we
// got an RPC request to do so (left), or we sent a shutdown message to the
// party (for w/e reason), but crashed before the close was complete.
//
//nolint:ll
type shutdownInit = fn.Option[fn.Either[*htlcswitch.ChanClose, channeldb.ShutdownInfo]]

// shutdownStartFeeRate returns the fee rate that should be used for the
// shutdown.  This returns a doubly wrapped option as the shutdown info might
// be none, and the fee rate is only defined for the user initiated shutdown.
func shutdownStartFeeRate(s shutdownInit) fn.Option[chainfee.SatPerKWeight] {
        feeRateOpt := fn.MapOption(func(init fn.Either[*htlcswitch.ChanClose,
                channeldb.ShutdownInfo]) fn.Option[chainfee.SatPerKWeight] {

                var feeRate fn.Option[chainfee.SatPerKWeight]
                init.WhenLeft(func(req *htlcswitch.ChanClose) {
                        feeRate = fn.Some(req.TargetFeePerKw)
                })

                return feeRate
        })(s)

        return fn.FlattenOption(feeRateOpt)
}

// shutdownStartAddr returns the delivery address that should be used when
// restarting the shutdown process.  If we didn't send a shutdown before we
// restarted, and the user didn't initiate one either, then None is returned.
func shutdownStartAddr(s shutdownInit) fn.Option[lnwire.DeliveryAddress] {
        addrOpt := fn.MapOption(func(init fn.Either[*htlcswitch.ChanClose,
                channeldb.ShutdownInfo]) fn.Option[lnwire.DeliveryAddress] {

                var addr fn.Option[lnwire.DeliveryAddress]
                init.WhenLeft(func(req *htlcswitch.ChanClose) {
                        if len(req.DeliveryScript) != 0 {
                                addr = fn.Some(req.DeliveryScript)
                        }
                })
                init.WhenRight(func(info channeldb.ShutdownInfo) {
                        addr = fn.Some(info.DeliveryScript.Val)
                })

                return addr
        })(s)

        return fn.FlattenOption(addrOpt)
}

// whenRPCShutdown registers a callback to be executed when the shutdown init
// type is and RPC request.
func whenRPCShutdown(s shutdownInit, f func(r *htlcswitch.ChanClose)) {
        s.WhenSome(func(init fn.Either[*htlcswitch.ChanClose,
                channeldb.ShutdownInfo]) {

                init.WhenLeft(f)
        })
}

// newRestartShutdownInit creates a new shutdownInit for the case where we need
// to restart the shutdown flow after a restart.
func newRestartShutdownInit(info channeldb.ShutdownInfo) shutdownInit {
        return fn.Some(fn.NewRight[*htlcswitch.ChanClose](info))
}

// newRPCShutdownInit creates a new shutdownInit for the case where we
// initiated the shutdown via an RPC client.
func newRPCShutdownInit(req *htlcswitch.ChanClose) shutdownInit {
        return fn.Some(
                fn.NewLeft[*htlcswitch.ChanClose, channeldb.ShutdownInfo](req),
        )
}

// waitUntilRbfCoastClear waits until the RBF co-op close state machine has
// advanced to a terminal state before attempting another fee bump.
func waitUntilRbfCoastClear(ctx context.Context,
        rbfCloser *chancloser.RbfChanCloser) error {

        coopCloseStates := rbfCloser.RegisterStateEvents()
        newStateChan := coopCloseStates.NewItemCreated.ChanOut()
        defer rbfCloser.RemoveStateSub(coopCloseStates)

        isTerminalState := func(newState chancloser.RbfState) bool {
                // If we're not in the negotiation sub-state, then we aren't at
                // the terminal state yet.
                state, ok := newState.(*chancloser.ClosingNegotiation)
                if !ok {
                        return false
                }

                localState := state.PeerState.GetForParty(lntypes.Local)

                // If this isn't the close pending state, we aren't at the
                // terminal state yet.
                _, ok = localState.(*chancloser.ClosePending)

                return ok
        }

        // Before we enter the subscription loop below, check to see if we're
        // already in the terminal state.
        rbfState, err := rbfCloser.CurrentState()
        if err != nil {
                return err
        }
        if isTerminalState(rbfState) {
                return nil
        }

        peerLog.Debugf("Waiting for RBF iteration to complete...")

        for {
                select {
                case newState := <-newStateChan:
                        if isTerminalState(newState) {
                                return nil
                        }

                case <-ctx.Done():
                        return fmt.Errorf("context canceled")
                }
        }
}

// startRbfChanCloser kicks off the co-op close process using the new RBF based
// co-op close protocol. This is called when we're the one that's initiating
// the cooperative channel close.
//
// TODO(roasbeef): just accept the two shutdown pointer params instead??
func (p *Brontide) startRbfChanCloser(shutdown shutdownInit,
        chanPoint wire.OutPoint) error {

        // Unlike the old negotiate chan closer, we'll always create the RBF
        // chan closer on startup, so we can skip init here.
        chanID := lnwire.NewChanIDFromOutPoint(chanPoint)
        chanCloser, found := p.activeChanCloses.Load(chanID)
        if !found {
                return fmt.Errorf("rbf chan closer not found for channel %v",
                        chanPoint)
        }

        defaultFeePerKw, err := shutdownStartFeeRate(
                shutdown,
        ).UnwrapOrFuncErr(func() (chainfee.SatPerKWeight, error) {
                return p.cfg.FeeEstimator.EstimateFeePerKW(
                        p.cfg.CoopCloseTargetConfs,
                )
        })
        if err != nil {
                return fmt.Errorf("unable to estimate fee: %w", err)
        }

        chanCloser.WhenRight(func(rbfCloser *chancloser.RbfChanCloser) {
                peerLog.Infof("ChannelPoint(%v): rbf-coop close requested, "+
                        "sending shutdown", chanPoint)

                rbfState, err := rbfCloser.CurrentState()
                if err != nil {
                        peerLog.Warnf("ChannelPoint(%v): unable to get "+
                                "current state for rbf-coop close: %v",
                                chanPoint, err)

                        return
                }

                coopCloseStates := rbfCloser.RegisterStateEvents()

                // Before we send our event below, we'll launch a goroutine to
                // watch for the final terminal state to send updates to the RPC
                // client. We only need to do this if there's an RPC caller.
                var rpcShutdown bool
                whenRPCShutdown(shutdown, func(req *htlcswitch.ChanClose) {
                        rpcShutdown = true

                        p.cg.WgAdd(1)
                        go func() {
                                defer p.cg.WgDone()

                                p.observeRbfCloseUpdates(
                                        rbfCloser, req, coopCloseStates,
                                )
                        }()
                })

                if !rpcShutdown {
                        defer rbfCloser.RemoveStateSub(coopCloseStates)
                }

                ctx, _ := p.cg.Create(context.Background())
                feeRate := defaultFeePerKw.FeePerVByte()

                // Depending on the state of the state machine, we'll either
                // kick things off by sending shutdown, or attempt to send a new
                // offer to the remote party.
                switch rbfState.(type) {
                // The channel is still active, so we'll now kick off the co-op
                // close process by instructing it to send a shutdown message to
                // the remote party.
                case *chancloser.ChannelActive:
                        rbfCloser.SendEvent(
                                context.Background(),
                                &chancloser.SendShutdown{
                                        IdealFeeRate: feeRate,
                                        DeliveryAddr: shutdownStartAddr(
                                                shutdown,
                                        ),
                                },
                        )

                // If we haven't yet sent an offer (didn't have enough funds at
                // the prior fee rate), or we've sent an offer, then we'll
                // trigger a new offer event.
                case *chancloser.ClosingNegotiation:
                        // Before we send the event below, we'll wait until
                        // we're in a semi-terminal state.
                        err := waitUntilRbfCoastClear(ctx, rbfCloser)
                        if err != nil {
                                peerLog.Warnf("ChannelPoint(%v): unable to "+
                                        "wait for coast to clear: %v",
                                        chanPoint, err)

                                return
                        }

                        event := chancloser.ProtocolEvent(
                                &chancloser.SendOfferEvent{
                                        TargetFeeRate: feeRate,
                                },
                        )
                        rbfCloser.SendEvent(ctx, event)

                default:
                        peerLog.Warnf("ChannelPoint(%v): unexpected state "+
                                "for rbf-coop close: %T", chanPoint, rbfState)
                }
        })

        return nil
}

// handleLocalCloseReq kicks-off the workflow to execute a cooperative or
// forced unilateral closure of the channel initiated by a local subsystem.
func (p *Brontide) handleLocalCloseReq(req *htlcswitch.ChanClose) {
        chanID := lnwire.NewChanIDFromOutPoint(*req.ChanPoint)

        channel, ok := p.activeChannels.Load(chanID)

        // Though this function can't be called for pending channels, we still
        // check whether channel is nil for safety.
        if !ok || channel == nil {
                err := fmt.Errorf("unable to close channel, ChannelID(%v) is "+
                        "unknown", chanID)
                p.log.Errorf(err.Error())
                req.Err <- err
                return
        }

        isTaprootChan := channel.ChanType().IsTaproot()

        switch req.CloseType {
        // A type of CloseRegular indicates that the user has opted to close
        // out this channel on-chain, so we execute the cooperative channel
        // closure workflow.
        case contractcourt.CloseRegular:
                var err error
                switch {
                // If this is the RBF coop state machine, then we'll instruct
                // it to send the shutdown message. This also might be an RBF
                // iteration, in which case we'll be obtaining a new
                // transaction w/ a higher fee rate.
                //
                // We don't support this close type for taproot channels yet
                // however.
                case !isTaprootChan && p.rbfCoopCloseAllowed():
                        err = p.startRbfChanCloser(
                                newRPCShutdownInit(req), channel.ChannelPoint(),
                        )
                default:
                        err = p.initNegotiateChanCloser(req, channel)
                }

                if err != nil {
                        p.log.Errorf(err.Error())
                        req.Err <- err
                }

        // A type of CloseBreach indicates that the counterparty has breached
        // the channel therefore we need to clean up our local state.
        case contractcourt.CloseBreach:
                // TODO(roasbeef): no longer need with newer beach logic?
                p.log.Infof("ChannelPoint(%v) has been breached, wiping "+
                        "channel", req.ChanPoint)
                p.WipeChannel(req.ChanPoint)
        }
}

// linkFailureReport is sent to the channelManager whenever a link reports a
// link failure, and is forced to exit. The report houses the necessary
// information to clean up the channel state, send back the error message, and
// force close if necessary.
type linkFailureReport struct {
        chanPoint   wire.OutPoint
        chanID      lnwire.ChannelID
        shortChanID lnwire.ShortChannelID
        linkErr     htlcswitch.LinkFailureError
}

// handleLinkFailure processes a link failure report when a link in the switch
// fails. It facilitates the removal of all channel state within the peer,
// force closing the channel depending on severity, and sending the error
// message back to the remote party.
func (p *Brontide) handleLinkFailure(failure linkFailureReport) {
        // Retrieve the channel from the map of active channels. We do this to
        // have access to it even after WipeChannel remove it from the map.
        chanID := lnwire.NewChanIDFromOutPoint(failure.chanPoint)
        lnChan, _ := p.activeChannels.Load(chanID)

        // We begin by wiping the link, which will remove it from the switch,
        // such that it won't be attempted used for any more updates.
        //
        // TODO(halseth): should introduce a way to atomically stop/pause the
        // link and cancel back any adds in its mailboxes such that we can
        // safely force close without the link being added again and updates
        // being applied.
        p.WipeChannel(&failure.chanPoint)

        // If the error encountered was severe enough, we'll now force close
        // the channel to prevent reading it to the switch in the future.
        if failure.linkErr.FailureAction == htlcswitch.LinkFailureForceClose {
                p.log.Warnf("Force closing link(%v)", failure.shortChanID)

                closeTx, err := p.cfg.ChainArb.ForceCloseContract(
                        failure.chanPoint,
                )
                if err != nil {
                        p.log.Errorf("unable to force close "+
                                "link(%v): %v", failure.shortChanID, err)
                } else {
                        p.log.Infof("channel(%v) force "+
                                "closed with txid %v",
                                failure.shortChanID, closeTx.TxHash())
                }
        }

        // If this is a permanent failure, we will mark the channel borked.
        if failure.linkErr.PermanentFailure && lnChan != nil {
                p.log.Warnf("Marking link(%v) borked due to permanent "+
                        "failure", failure.shortChanID)

                if err := lnChan.State().MarkBorked(); err != nil {
                        p.log.Errorf("Unable to mark channel %v borked: %v",
                                failure.shortChanID, err)
                }
        }

        // Send an error to the peer, why we failed the channel.
        if failure.linkErr.ShouldSendToPeer() {
                // If SendData is set, send it to the peer. If not, we'll use
                // the standard error messages in the payload. We only include
                // sendData in the cases where the error data does not contain
                // sensitive information.
                data := []byte(failure.linkErr.Error())
                if failure.linkErr.SendData != nil {
                        data = failure.linkErr.SendData
                }

                var networkMsg lnwire.Message
                if failure.linkErr.Warning {
                        networkMsg = &lnwire.Warning{
                                ChanID: failure.chanID,
                                Data:   data,
                        }
                } else {
                        networkMsg = &lnwire.Error{
                                ChanID: failure.chanID,
                                Data:   data,
                        }
                }

                err := p.SendMessage(true, networkMsg)
                if err != nil {
                        p.log.Errorf("unable to send msg to "+
                                "remote peer: %v", err)
                }
        }

        // If the failure action is disconnect, then we'll execute that now. If
        // we had to send an error above, it was a sync call, so we expect the
        // message to be flushed on the wire by now.
        if failure.linkErr.FailureAction == htlcswitch.LinkFailureDisconnect {
                p.Disconnect(fmt.Errorf("link requested disconnect"))
        }
}

// fetchLinkFromKeyAndCid fetches a link from the switch via the remote's
// public key and the channel id.
func (p *Brontide) fetchLinkFromKeyAndCid(
        cid lnwire.ChannelID) htlcswitch.ChannelUpdateHandler {

        var chanLink htlcswitch.ChannelUpdateHandler

        // We don't need to check the error here, and can instead just loop
        // over the slice and return nil.
        links, _ := p.cfg.Switch.GetLinksByInterface(p.cfg.PubKeyBytes)
        for _, link := range links {
                if link.ChanID() == cid {
                        chanLink = link
                        break
                }
        }

        return chanLink
}

// finalizeChanClosure performs the final clean up steps once the cooperative
// closure transaction has been fully broadcast. The finalized closing state
// machine should be passed in. Once the transaction has been sufficiently
// confirmed, the channel will be marked as fully closed within the database,
// and any clients will be notified of updates to the closing state.
func (p *Brontide) finalizeChanClosure(chanCloser *chancloser.ChanCloser) {
        closeReq := chanCloser.CloseRequest()

        // First, we'll clear all indexes related to the channel in question.
        chanPoint := chanCloser.Channel().ChannelPoint()
        p.WipeChannel(&chanPoint)

        // Also clear the activeChanCloses map of this channel.
        cid := lnwire.NewChanIDFromOutPoint(chanPoint)
        p.activeChanCloses.Delete(cid) // TODO(roasbeef): existing race

        // Next, we'll launch a goroutine which will request to be notified by
        // the ChainNotifier once the closure transaction obtains a single
        // confirmation.
        notifier := p.cfg.ChainNotifier

        // If any error happens during waitForChanToClose, forward it to
        // closeReq. If this channel closure is not locally initiated, closeReq
        // will be nil, so just ignore the error.
        errChan := make(chan error, 1)
        if closeReq != nil {
                errChan = closeReq.Err
        }

        closingTx, err := chanCloser.ClosingTx()
        if err != nil {
                if closeReq != nil {
                        p.log.Error(err)
                        closeReq.Err <- err
                }
        }

        closingTxid := closingTx.TxHash()

        // If this is a locally requested shutdown, update the caller with a
        // new event detailing the current pending state of this request.
        if closeReq != nil {
                closeReq.Updates <- &PendingUpdate{
                        Txid: closingTxid[:],
                }
        }

        localOut := chanCloser.LocalCloseOutput()
        remoteOut := chanCloser.RemoteCloseOutput()
        auxOut := chanCloser.AuxOutputs()
        go WaitForChanToClose(
                chanCloser.NegotiationHeight(), notifier, errChan,
                &chanPoint, &closingTxid, closingTx.TxOut[0].PkScript, func() {
                        // Respond to the local subsystem which requested the
                        // channel closure.
                        if closeReq != nil {
                                closeReq.Updates <- &ChannelCloseUpdate{
                                        ClosingTxid:       closingTxid[:],
                                        Success:           true,
                                        LocalCloseOutput:  localOut,
                                        RemoteCloseOutput: remoteOut,
                                        AuxOutputs:        auxOut,
                                }
                        }
                },
        )
}

// WaitForChanToClose uses the passed notifier to wait until the channel has
// been detected as closed on chain and then concludes by executing the
// following actions: the channel point will be sent over the settleChan, and
// finally the callback will be executed. If any error is encountered within
// the function, then it will be sent over the errChan.
func WaitForChanToClose(bestHeight uint32, notifier chainntnfs.ChainNotifier,
        errChan chan error, chanPoint *wire.OutPoint,
        closingTxID *chainhash.Hash, closeScript []byte, cb func()) {

        peerLog.Infof("Waiting for confirmation of close of ChannelPoint(%v) "+
                "with txid: %v", chanPoint, closingTxID)

        // TODO(roasbeef): add param for num needed confs
        confNtfn, err := notifier.RegisterConfirmationsNtfn(
                closingTxID, closeScript, 1, bestHeight,
        )
        if err != nil {
                if errChan != nil {
                        errChan <- err
                }
                return
        }

        // In the case that the ChainNotifier is shutting down, all subscriber
        // notification channels will be closed, generating a nil receive.
        height, ok := <-confNtfn.Confirmed
        if !ok {
                return
        }

        // The channel has been closed, remove it from any active indexes, and
        // the database state.
        peerLog.Infof("ChannelPoint(%v) is now closed at "+
                "height %v", chanPoint, height.BlockHeight)

        // Finally, execute the closure call back to mark the confirmation of
        // the transaction closing the contract.
        cb()
}

// WipeChannel removes the passed channel point from all indexes associated with
// the peer and the switch.
func (p *Brontide) WipeChannel(chanPoint *wire.OutPoint) {
        chanID := lnwire.NewChanIDFromOutPoint(*chanPoint)

        p.activeChannels.Delete(chanID)

        // Instruct the HtlcSwitch to close this link as the channel is no
        // longer active.
        p.cfg.Switch.RemoveLink(chanID)
}

// handleInitMsg handles the incoming init message which contains global and
// local feature vectors. If feature vectors are incompatible then disconnect.
func (p *Brontide) handleInitMsg(msg *lnwire.Init) error {
        // First, merge any features from the legacy global features field into
        // those presented in the local features fields.
        err := msg.Features.Merge(msg.GlobalFeatures)
        if err != nil {
                return fmt.Errorf("unable to merge legacy global features: %w",
                        err)
        }

        // Then, finalize the remote feature vector providing the flattened
        // feature bit namespace.
        p.remoteFeatures = lnwire.NewFeatureVector(
                msg.Features, lnwire.Features,
        )

        // Now that we have their features loaded, we'll ensure that they
        // didn't set any required bits that we don't know of.
        err = feature.ValidateRequired(p.remoteFeatures)
        if err != nil {
                return fmt.Errorf("invalid remote features: %w", err)
        }

        // Ensure the remote party's feature vector contains all transitive
        // dependencies. We know ours are correct since they are validated
        // during the feature manager's instantiation.
        err = feature.ValidateDeps(p.remoteFeatures)
        if err != nil {
                return fmt.Errorf("invalid remote features: %w", err)
        }

        // Now that we know we understand their requirements, we'll check to
        // see if they don't support anything that we deem to be mandatory.
        if !p.remoteFeatures.HasFeature(lnwire.DataLossProtectRequired) {
                return fmt.Errorf("data loss protection required")
        }

        return nil
}

// LocalFeatures returns the set of global features that has been advertised by
// the local node. This allows sub-systems that use this interface to gate their
// behavior off the set of negotiated feature bits.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) LocalFeatures() *lnwire.FeatureVector {
        return p.cfg.Features
}

// RemoteFeatures returns the set of global features that has been advertised by
// the remote node. This allows sub-systems that use this interface to gate
// their behavior off the set of negotiated feature bits.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) RemoteFeatures() *lnwire.FeatureVector {
        return p.remoteFeatures
}

// hasNegotiatedScidAlias returns true if we've negotiated the
// option-scid-alias feature bit with the peer.
func (p *Brontide) hasNegotiatedScidAlias() bool {
        peerHas := p.remoteFeatures.HasFeature(lnwire.ScidAliasOptional)
        localHas := p.cfg.Features.HasFeature(lnwire.ScidAliasOptional)
        return peerHas && localHas
}

// sendInitMsg sends the Init message to the remote peer. This message contains
// our currently supported local and global features.
func (p *Brontide) sendInitMsg(legacyChan bool) error {
        features := p.cfg.Features.Clone()
        legacyFeatures := p.cfg.LegacyFeatures.Clone()

        // If we have a legacy channel open with a peer, we downgrade static
        // remote required to optional in case the peer does not understand the
        // required feature bit. If we do not do this, the peer will reject our
        // connection because it does not understand a required feature bit, and
        // our channel will be unusable.
        if legacyChan && features.RequiresFeature(lnwire.StaticRemoteKeyRequired) {
                p.log.Infof("Legacy channel open with peer, " +
                        "downgrading static remote required feature bit to " +
                        "optional")

                // Unset and set in both the local and global features to
                // ensure both sets are consistent and merge able by old and
                // new nodes.
                features.Unset(lnwire.StaticRemoteKeyRequired)
                legacyFeatures.Unset(lnwire.StaticRemoteKeyRequired)

                features.Set(lnwire.StaticRemoteKeyOptional)
                legacyFeatures.Set(lnwire.StaticRemoteKeyOptional)
        }

        msg := lnwire.NewInitMessage(
                legacyFeatures.RawFeatureVector,
                features.RawFeatureVector,
        )

        return p.writeMessage(msg)
}

// resendChanSyncMsg will attempt to find a channel sync message for the closed
// channel and resend it to our peer.
func (p *Brontide) resendChanSyncMsg(cid lnwire.ChannelID) error {
        // If we already re-sent the mssage for this channel, we won't do it
        // again.
        if _, ok := p.resentChanSyncMsg[cid]; ok {
                return nil
        }

        // Check if we have any channel sync messages stored for this channel.
        c, err := p.cfg.ChannelDB.FetchClosedChannelForID(cid)
        if err != nil {
                return fmt.Errorf("unable to fetch channel sync messages for "+
                        "peer %v: %v", p, err)
        }

        if c.LastChanSyncMsg == nil {
                return fmt.Errorf("no chan sync message stored for channel %v",
                        cid)
        }

        if !c.RemotePub.IsEqual(p.IdentityKey()) {
                return fmt.Errorf("ignoring channel reestablish from "+
                        "peer=%x", p.IdentityKey().SerializeCompressed())
        }

        p.log.Debugf("Re-sending channel sync message for channel %v to "+
                "peer", cid)

        if err := p.SendMessage(true, c.LastChanSyncMsg); err != nil {
                return fmt.Errorf("failed resending channel sync "+
                        "message to peer %v: %v", p, err)
        }

        p.log.Debugf("Re-sent channel sync message for channel %v to peer ",
                cid)

        // Note down that we sent the message, so we won't resend it again for
        // this connection.
        p.resentChanSyncMsg[cid] = struct{}{}

        return nil
}

// SendMessage sends a variadic number of high-priority messages to the remote
// peer. The first argument denotes if the method should block until the
// messages have been sent to the remote peer or an error is returned,
// otherwise it returns immediately after queuing.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) SendMessage(sync bool, msgs ...lnwire.Message) error {
        return p.sendMessage(sync, true, msgs...)
}

// SendMessageLazy sends a variadic number of low-priority messages to the
// remote peer. The first argument denotes if the method should block until
// the messages have been sent to the remote peer or an error is returned,
// otherwise it returns immediately after queueing.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) SendMessageLazy(sync bool, msgs ...lnwire.Message) error {
        return p.sendMessage(sync, false, msgs...)
}

// sendMessage queues a variadic number of messages using the passed priority
// to the remote peer. If sync is true, this method will block until the
// messages have been sent to the remote peer or an error is returned, otherwise
// it returns immediately after queueing.
func (p *Brontide) sendMessage(sync, priority bool, msgs ...lnwire.Message) error {
        // Add all incoming messages to the outgoing queue. A list of error
        // chans is populated for each message if the caller requested a sync
        // send.
        var errChans []chan error
        if sync {
                errChans = make([]chan error, 0, len(msgs))
        }
        for _, msg := range msgs {
                // If a sync send was requested, create an error chan to listen
                // for an ack from the writeHandler.
                var errChan chan error
                if sync {
                        errChan = make(chan error, 1)
                        errChans = append(errChans, errChan)
                }

                if priority {
                        p.queueMsg(msg, errChan)
                } else {
                        p.queueMsgLazy(msg, errChan)
                }
        }

        // Wait for all replies from the writeHandler. For async sends, this
        // will be a NOP as the list of error chans is nil.
        for _, errChan := range errChans {
                select {
                case err := <-errChan:
                        return err
                case <-p.cg.Done():
                        return lnpeer.ErrPeerExiting
                case <-p.cfg.Quit:
                        return lnpeer.ErrPeerExiting
                }
        }

        return nil
}

// PubKey returns the pubkey of the peer in compressed serialized format.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) PubKey() [33]byte {
        return p.cfg.PubKeyBytes
}

// IdentityKey returns the public key of the remote peer.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) IdentityKey() *btcec.PublicKey {
        return p.cfg.Addr.IdentityKey
}

// Address returns the network address of the remote peer.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) Address() net.Addr {
        return p.cfg.Addr.Address
}

// AddNewChannel adds a new channel to the peer. The channel should fail to be
// added if the cancel channel is closed.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) AddNewChannel(newChan *lnpeer.NewChannel,
        cancel <-chan struct{}) error {

        errChan := make(chan error, 1)
        newChanMsg := &newChannelMsg{
                channel: newChan,
                err:     errChan,
        }

        select {
        case p.newActiveChannel <- newChanMsg:
        case <-cancel:
                return errors.New("canceled adding new channel")
        case <-p.cg.Done():
                return lnpeer.ErrPeerExiting
        }

        // We pause here to wait for the peer to recognize the new channel
        // before we close the channel barrier corresponding to the channel.
        select {
        case err := <-errChan:
                return err
        case <-p.cg.Done():
                return lnpeer.ErrPeerExiting
        }
}

// AddPendingChannel adds a pending open channel to the peer. The channel
// should fail to be added if the cancel channel is closed.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) AddPendingChannel(cid lnwire.ChannelID,
        cancel <-chan struct{}) error {

        errChan := make(chan error, 1)
        newChanMsg := &newChannelMsg{
                channelID: cid,
                err:       errChan,
        }

        select {
        case p.newPendingChannel <- newChanMsg:

        case <-cancel:
                return errors.New("canceled adding pending channel")

        case <-p.cg.Done():
                return lnpeer.ErrPeerExiting
        }

        // We pause here to wait for the peer to recognize the new pending
        // channel before we close the channel barrier corresponding to the
        // channel.
        select {
        case err := <-errChan:
                return err

        case <-cancel:
                return errors.New("canceled adding pending channel")

        case <-p.cg.Done():
                return lnpeer.ErrPeerExiting
        }
}

// RemovePendingChannel removes a pending open channel from the peer.
//
// NOTE: Part of the lnpeer.Peer interface.
func (p *Brontide) RemovePendingChannel(cid lnwire.ChannelID) error {
        errChan := make(chan error, 1)
        newChanMsg := &newChannelMsg{
                channelID: cid,
                err:       errChan,
        }

        select {
        case p.removePendingChannel <- newChanMsg:
        case <-p.cg.Done():
                return lnpeer.ErrPeerExiting
        }

        // We pause here to wait for the peer to respond to the cancellation of
        // the pending channel before we close the channel barrier
        // corresponding to the channel.
        select {
        case err := <-errChan:
                return err

        case <-p.cg.Done():
                return lnpeer.ErrPeerExiting
        }
}

// StartTime returns the time at which the connection was established if the
// peer started successfully, and zero otherwise.
func (p *Brontide) StartTime() time.Time {
        return p.startTime
}

// handleCloseMsg is called when a new cooperative channel closure related
// message is received from the remote peer. We'll use this message to advance
// the chan closer state machine.
func (p *Brontide) handleCloseMsg(msg *closeMsg) {
        link := p.fetchLinkFromKeyAndCid(msg.cid)

        // We'll now fetch the matching closing state machine in order to
        // continue, or finalize the channel closure process.
        chanCloserE, err := p.fetchActiveChanCloser(msg.cid)
        if err != nil {
                // If the channel is not known to us, we'll simply ignore this
                // message.
                if err == ErrChannelNotFound {
                        return
                }

                p.log.Errorf("Unable to respond to remote close msg: %v", err)

                errMsg := &lnwire.Error{
                        ChanID: msg.cid,
                        Data:   lnwire.ErrorData(err.Error()),
                }
                p.queueMsg(errMsg, nil)
                return
        }

        if chanCloserE.IsRight() {
                // TODO(roasbeef): assert?
                return
        }

        // At this point, we'll only enter this call path if a negotiate chan
        // closer was used. So we'll extract that from the either now.
        //
        // TODO(roabeef): need extra helper func for either to make cleaner
        var chanCloser *chancloser.ChanCloser
        chanCloserE.WhenLeft(func(c *chancloser.ChanCloser) {
                chanCloser = c
        })

        handleErr := func(err error) {
                err = fmt.Errorf("unable to process close msg: %w", err)
                p.log.Error(err)

                // As the negotiations failed, we'll reset the channel state
                // machine to ensure we act to on-chain events as normal.
                chanCloser.Channel().ResetState()
                if chanCloser.CloseRequest() != nil {
                        chanCloser.CloseRequest().Err <- err
                }

                p.activeChanCloses.Delete(msg.cid)

                p.Disconnect(err)
        }

        // Next, we'll process the next message using the target state machine.
        // We'll either continue negotiation, or halt.
        switch typed := msg.msg.(type) {
        case *lnwire.Shutdown:
                // Disable incoming adds immediately.
                if link != nil && !link.DisableAdds(htlcswitch.Incoming) {
                        p.log.Warnf("Incoming link adds already disabled: %v",
                                link.ChanID())
                }

                oShutdown, err := chanCloser.ReceiveShutdown(*typed)
                if err != nil {
                        handleErr(err)
                        return
                }

                oShutdown.WhenSome(func(msg lnwire.Shutdown) {
                        // If the link is nil it means we can immediately queue
                        // the Shutdown message since we don't have to wait for
                        // commitment transaction synchronization.
                        if link == nil {
                                p.queueMsg(&msg, nil)
                                return
                        }

                        // Immediately disallow any new HTLC's from being added
                        // in the outgoing direction.
                        if !link.DisableAdds(htlcswitch.Outgoing) {
                                p.log.Warnf("Outgoing link adds already "+
                                        "disabled: %v", link.ChanID())
                        }

                        // When we have a Shutdown to send, we defer it till the
                        // next time we send a CommitSig to remain spec
                        // compliant.
                        link.OnCommitOnce(htlcswitch.Outgoing, func() {
                                p.queueMsg(&msg, nil)
                        })
                })

                beginNegotiation := func() {
                        oClosingSigned, err := chanCloser.BeginNegotiation()
                        if err != nil {
                                handleErr(err)
                                return
                        }

                        oClosingSigned.WhenSome(func(msg lnwire.ClosingSigned) {
                                p.queueMsg(&msg, nil)
                        })
                }

                if link == nil {
                        beginNegotiation()
                } else {
                        // Now we register a flush hook to advance the
                        // ChanCloser and possibly send out a ClosingSigned
                        // when the link finishes draining.
                        link.OnFlushedOnce(func() {
                                // Remove link in goroutine to prevent deadlock.
                                go p.cfg.Switch.RemoveLink(msg.cid)
                                beginNegotiation()
                        })
                }

        case *lnwire.ClosingSigned:
                oClosingSigned, err := chanCloser.ReceiveClosingSigned(*typed)
                if err != nil {
                        handleErr(err)
                        return
                }

                oClosingSigned.WhenSome(func(msg lnwire.ClosingSigned) {
                        p.queueMsg(&msg, nil)
                })

        default:
                panic("impossible closeMsg type")
        }

        // If we haven't finished close negotiations, then we'll continue as we
        // can't yet finalize the closure.
        if _, err := chanCloser.ClosingTx(); err != nil {
                return
        }

        // Otherwise, we've agreed on a closing fee! In this case, we'll wrap up
        // the channel closure by notifying relevant sub-systems and launching a
        // goroutine to wait for close tx conf.
        p.finalizeChanClosure(chanCloser)
}

// HandleLocalCloseChanReqs accepts a *htlcswitch.ChanClose and passes it onto
// the channelManager goroutine, which will shut down the link and possibly
// close the channel.
func (p *Brontide) HandleLocalCloseChanReqs(req *htlcswitch.ChanClose) {
        select {
        case p.localCloseChanReqs <- req:
                p.log.Info("Local close channel request is going to be " +
                        "delivered to the peer")
        case <-p.cg.Done():
                p.log.Info("Unable to deliver local close channel request " +
                        "to peer")
        }
}

// NetAddress returns the network of the remote peer as an lnwire.NetAddress.
func (p *Brontide) NetAddress() *lnwire.NetAddress {
        return p.cfg.Addr
}

// Inbound is a getter for the Brontide's Inbound boolean in cfg.
func (p *Brontide) Inbound() bool {
        return p.cfg.Inbound
}

// ConnReq is a getter for the Brontide's connReq in cfg.
func (p *Brontide) ConnReq() *connmgr.ConnReq {
        return p.cfg.ConnReq
}

// ErrorBuffer is a getter for the Brontide's errorBuffer in cfg.
func (p *Brontide) ErrorBuffer() *queue.CircularBuffer {
        return p.cfg.ErrorBuffer
}

// SetAddress sets the remote peer's address given an address.
func (p *Brontide) SetAddress(address net.Addr) {
        p.cfg.Addr.Address = address
}

// ActiveSignal returns the peer's active signal.
func (p *Brontide) ActiveSignal() chan struct{} {
        return p.activeSignal
}

// Conn returns a pointer to the peer's connection struct.
func (p *Brontide) Conn() net.Conn {
        return p.cfg.Conn
}

// BytesReceived returns the number of bytes received from the peer.
func (p *Brontide) BytesReceived() uint64 {
        return atomic.LoadUint64(&p.bytesReceived)
}

// BytesSent returns the number of bytes sent to the peer.
func (p *Brontide) BytesSent() uint64 {
        return atomic.LoadUint64(&p.bytesSent)
}

// LastRemotePingPayload returns the last payload the remote party sent as part
// of their ping.
func (p *Brontide) LastRemotePingPayload() []byte {
        pingPayload := p.lastPingPayload.Load()
        if pingPayload == nil {
                return []byte{}
        }

        pingBytes, ok := pingPayload.(lnwire.PingPayload)
        if !ok {
                return nil
        }

        return pingBytes
}

// attachChannelEventSubscription creates a channel event subscription and
// attaches to client to Brontide if the reenableTimeout is no greater than 1
// minute.
func (p *Brontide) attachChannelEventSubscription() error {
        // If the timeout is greater than 1 minute, it's unlikely that the link
        // hasn't yet finished its reestablishment. Return a nil without
        // creating the client to specify that we don't want to retry.
        if p.cfg.ChanActiveTimeout > 1*time.Minute {
                return nil
        }

        // When the reenable timeout is less than 1 minute, it's likely the
        // channel link hasn't finished its reestablishment yet. In that case,
        // we'll give it a second chance by subscribing to the channel update
        // events. Upon receiving the `ActiveLinkEvent`, we'll then request
        // enabling the channel again.
        sub, err := p.cfg.ChannelNotifier.SubscribeChannelEvents()
        if err != nil {
                return fmt.Errorf("SubscribeChannelEvents failed: %w", err)
        }

        p.channelEventClient = sub

        return nil
}

// updateNextRevocation updates the existing channel's next revocation if it's
// nil.
func (p *Brontide) updateNextRevocation(c *channeldb.OpenChannel) error {
        chanPoint := c.FundingOutpoint
        chanID := lnwire.NewChanIDFromOutPoint(chanPoint)

        // Read the current channel.
        currentChan, loaded := p.activeChannels.Load(chanID)

        // currentChan should exist, but we perform a check anyway to avoid nil
        // pointer dereference.
        if !loaded {
                return fmt.Errorf("missing active channel with chanID=%v",
                        chanID)
        }

        // currentChan should not be nil, but we perform a check anyway to
        // avoid nil pointer dereference.
        if currentChan == nil {
                return fmt.Errorf("found nil active channel with chanID=%v",
                        chanID)
        }

        // If we're being sent a new channel, and our existing channel doesn't
        // have the next revocation, then we need to update the current
        // existing channel.
        if currentChan.RemoteNextRevocation() != nil {
                return nil
        }

        p.log.Infof("Processing retransmitted ChannelReady for "+
                "ChannelPoint(%v)", chanPoint)

        nextRevoke := c.RemoteNextRevocation

        err := currentChan.InitNextRevocation(nextRevoke)
        if err != nil {
                return fmt.Errorf("unable to init next revocation: %w", err)
        }

        return nil
}

// addActiveChannel adds a new active channel to the `activeChannels` map. It
// takes a `channeldb.OpenChannel`, creates a `lnwallet.LightningChannel` from
// it and assembles it with a channel link.
func (p *Brontide) addActiveChannel(c *lnpeer.NewChannel) error {
        chanPoint := c.FundingOutpoint
        chanID := lnwire.NewChanIDFromOutPoint(chanPoint)

        // If we've reached this point, there are two possible scenarios.  If
        // the channel was in the active channels map as nil, then it was
        // loaded from disk and we need to send reestablish. Else, it was not
        // loaded from disk and we don't need to send reestablish as this is a
        // fresh channel.
        shouldReestablish := p.isLoadedFromDisk(chanID)

        chanOpts := c.ChanOpts
        if shouldReestablish {
                // If we have to do the reestablish dance for this channel,
                // ensure that we don't try to call InitRemoteMusigNonces twice
                // by calling SkipNonceInit.
                chanOpts = append(chanOpts, lnwallet.WithSkipNonceInit())
        }

        p.cfg.AuxLeafStore.WhenSome(func(s lnwallet.AuxLeafStore) {
                chanOpts = append(chanOpts, lnwallet.WithLeafStore(s))
        })
        p.cfg.AuxSigner.WhenSome(func(s lnwallet.AuxSigner) {
                chanOpts = append(chanOpts, lnwallet.WithAuxSigner(s))
        })
        p.cfg.AuxResolver.WhenSome(func(s lnwallet.AuxContractResolver) {
                chanOpts = append(chanOpts, lnwallet.WithAuxResolver(s))
        })

        // If not already active, we'll add this channel to the set of active
        // channels, so we can look it up later easily according to its channel
        // ID.
        lnChan, err := lnwallet.NewLightningChannel(
                p.cfg.Signer, c.OpenChannel, p.cfg.SigPool, chanOpts...,
        )
        if err != nil {
                return fmt.Errorf("unable to create LightningChannel: %w", err)
        }

        // Store the channel in the activeChannels map.
        p.activeChannels.Store(chanID, lnChan)

        p.log.Infof("New channel active ChannelPoint(%v) with peer", chanPoint)

        // Next, we'll assemble a ChannelLink along with the necessary items it
        // needs to function.
        chainEvents, err := p.cfg.ChainArb.SubscribeChannelEvents(chanPoint)
        if err != nil {
                return fmt.Errorf("unable to subscribe to chain events: %w",
                        err)
        }

        // We'll query the channel DB for the new channel's initial forwarding
        // policies to determine the policy we start out with.
        initialPolicy, err := p.cfg.ChannelDB.GetInitialForwardingPolicy(chanID)
        if err != nil {
                return fmt.Errorf("unable to query for initial forwarding "+
                        "policy: %v", err)
        }

        // Create the link and add it to the switch.
        err = p.addLink(
                &chanPoint, lnChan, initialPolicy, chainEvents,
                shouldReestablish, fn.None[lnwire.Shutdown](),
        )
        if err != nil {
                return fmt.Errorf("can't register new channel link(%v) with "+
                        "peer", chanPoint)
        }

        isTaprootChan := c.ChanType.IsTaproot()

        // We're using the old co-op close, so we don't need to init the new RBF
        // chan closer. If this is a taproot channel, then we'll also fall
        // through, as we don't support this type yet w/ rbf close.
        if !p.rbfCoopCloseAllowed() || isTaprootChan {
                return nil
        }

        // Now that the link has been added above, we'll also init an RBF chan
        // closer for this channel, but only if the new close feature is
        // negotiated.
        //
        // Creating this here ensures that any shutdown messages sent will be
        // automatically routed by the msg router.
        if _, err := p.initRbfChanCloser(lnChan); err != nil {
                p.activeChanCloses.Delete(chanID)

                return fmt.Errorf("unable to init RBF chan closer for new "+
                        "chan: %w", err)
        }

        return nil
}

// handleNewActiveChannel handles a `newChannelMsg` request. Depending on we
// know this channel ID or not, we'll either add it to the `activeChannels` map
// or init the next revocation for it.
func (p *Brontide) handleNewActiveChannel(req *newChannelMsg) {
        newChan := req.channel
        chanPoint := newChan.FundingOutpoint
        chanID := lnwire.NewChanIDFromOutPoint(chanPoint)

        // Only update RemoteNextRevocation if the channel is in the
        // activeChannels map and if we added the link to the switch. Only
        // active channels will be added to the switch.
        if p.isActiveChannel(chanID) {
                p.log.Infof("Already have ChannelPoint(%v), ignoring",
                        chanPoint)

                // Handle it and close the err chan on the request.
                close(req.err)

                // Update the next revocation point.
                err := p.updateNextRevocation(newChan.OpenChannel)
                if err != nil {
                        p.log.Errorf(err.Error())
                }

                return
        }

        // This is a new channel, we now add it to the map.
        if err := p.addActiveChannel(req.channel); err != nil {
                // Log and send back the error to the request.
                p.log.Errorf(err.Error())
                req.err <- err

                return
        }

        // Close the err chan if everything went fine.
        close(req.err)
}

// handleNewPendingChannel takes a `newChannelMsg` request and add it to
// `activeChannels` map with nil value. This pending channel will be saved as
// it may become active in the future. Once active, the funding manager will
// send it again via `AddNewChannel`, and we'd handle the link creation there.
func (p *Brontide) handleNewPendingChannel(req *newChannelMsg) {
        defer close(req.err)

        chanID := req.channelID

        // If we already have this channel, something is wrong with the funding
        // flow as it will only be marked as active after `ChannelReady` is
        // handled. In this case, we will do nothing but log an error, just in
        // case this is a legit channel.
        if p.isActiveChannel(chanID) {
                p.log.Errorf("Channel(%v) is already active, ignoring "+
                        "pending channel request", chanID)

                return
        }

        // The channel has already been added, we will do nothing and return.
        if p.isPendingChannel(chanID) {
                p.log.Infof("Channel(%v) is already added, ignoring "+
                        "pending channel request", chanID)

                return
        }

        // This is a new channel, we now add it to the map `activeChannels`
        // with nil value and mark it as a newly added channel in
        // `addedChannels`.
        p.activeChannels.Store(chanID, nil)
        p.addedChannels.Store(chanID, struct{}{})
}

// handleRemovePendingChannel takes a `newChannelMsg` request and removes it
// from `activeChannels` map. The request will be ignored if the channel is
// considered active by Brontide. Noop if the channel ID cannot be found.
func (p *Brontide) handleRemovePendingChannel(req *newChannelMsg) {
        defer close(req.err)

        chanID := req.channelID

        // If we already have this channel, something is wrong with the funding
        // flow as it will only be marked as active after `ChannelReady` is
        // handled. In this case, we will log an error and exit.
        if p.isActiveChannel(chanID) {
                p.log.Errorf("Channel(%v) is active, ignoring remove request",
                        chanID)
                return
        }

        // The channel has not been added yet, we will log a warning as there
        // is an unexpected call from funding manager.
        if !p.isPendingChannel(chanID) {
                p.log.Warnf("Channel(%v) not found, removing it anyway", chanID)
        }

        // Remove the record of this pending channel.
        p.activeChannels.Delete(chanID)
        p.addedChannels.Delete(chanID)
}

// sendLinkUpdateMsg sends a message that updates the channel to the
// channel's message stream.
func (p *Brontide) sendLinkUpdateMsg(cid lnwire.ChannelID, msg lnwire.Message) {
        p.log.Tracef("Sending link update msg=%v", msg.MsgType())

        chanStream, ok := p.activeMsgStreams[cid]
        if !ok {
                // If a stream hasn't yet been created, then we'll do so, add
                // it to the map, and finally start it.
                chanStream = newChanMsgStream(p, cid)
                p.activeMsgStreams[cid] = chanStream
                chanStream.Start()

                // Stop the stream when quit.
                go func() {
                        <-p.cg.Done()
                        chanStream.Stop()
                }()
        }

        // With the stream obtained, add the message to the stream so we can
        // continue processing message.
        chanStream.AddMsg(msg)
}

// scaleTimeout multiplies the argument duration by a constant factor depending
// on variious heuristics. Currently this is only used to check whether our peer
// appears to be connected over Tor and relaxes the timout deadline. However,
// this is subject to change and should be treated as opaque.
func (p *Brontide) scaleTimeout(timeout time.Duration) time.Duration {
        if p.isTorConnection {
                return timeout * time.Duration(torTimeoutMultiplier)
        }

        return timeout
}

// CoopCloseUpdates is a struct used to communicate updates for an active close
// to the caller.
type CoopCloseUpdates struct {
        UpdateChan chan interface{}

        ErrChan chan error
}

// ChanHasRbfCoopCloser returns true if the channel as identifier by the channel
// point has an active RBF chan closer.
func (p *Brontide) ChanHasRbfCoopCloser(chanPoint wire.OutPoint) bool {
        chanID := lnwire.NewChanIDFromOutPoint(chanPoint)
        chanCloser, found := p.activeChanCloses.Load(chanID)
        if !found {
                return false
        }

        return chanCloser.IsRight()
}

// TriggerCoopCloseRbfBump given a chan ID, and the params needed to trigger a
// new RBF co-op close update, a bump is attempted. A channel used for updates,
// along with one used to o=communicate any errors is returned. If no chan
// closer is found, then false is returned for the second argument.
func (p *Brontide) TriggerCoopCloseRbfBump(ctx context.Context,
        chanPoint wire.OutPoint, feeRate chainfee.SatPerKWeight,
        deliveryScript lnwire.DeliveryAddress) (*CoopCloseUpdates, error) {

        // If RBF coop close isn't permitted, then we'll an error.
        if !p.rbfCoopCloseAllowed() {
                return nil, fmt.Errorf("rbf coop close not enabled for " +
                        "channel")
        }

        closeUpdates := &CoopCloseUpdates{
                UpdateChan: make(chan interface{}, 1),
                ErrChan:    make(chan error, 1),
        }

        // We'll re-use the existing switch struct here, even though we're
        // bypassing the switch entirely.
        closeReq := htlcswitch.ChanClose{
                CloseType:      contractcourt.CloseRegular,
                ChanPoint:      &chanPoint,
                TargetFeePerKw: feeRate,
                DeliveryScript: deliveryScript,
                Updates:        closeUpdates.UpdateChan,
                Err:            closeUpdates.ErrChan,
                Ctx:            ctx,
        }

        err := p.startRbfChanCloser(newRPCShutdownInit(&closeReq), chanPoint)
        if err != nil {
                return nil, err
        }

        return closeUpdates, nil
}

lightningnetwork / lnd / 16673052227

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