18915193695

Committed 29 Oct 2025 04:31PM UTC coverage: 66.644% (+0.005%) from 66.639%

Build # 18915193695

Build Type

Pull #10329

github

Committed by

web-flow

Commit Message

Merge 1c46ace26 into f938e40af

Pull Request Pull Request #10329: Gossiper - Bugfix context check

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83.12

/discovery/syncer.go

package discovery

import (
        "context"
        "errors"
        "fmt"
        "iter"
        "math"
        "math/rand"
        "sort"
        "sync"
        "sync/atomic"
        "time"

        "github.com/btcsuite/btcd/chaincfg/chainhash"
        "github.com/lightningnetwork/lnd/fn/v2"
        "github.com/lightningnetwork/lnd/graph"
        graphdb "github.com/lightningnetwork/lnd/graph/db"
        "github.com/lightningnetwork/lnd/lnpeer"
        "github.com/lightningnetwork/lnd/lnwire"
        "golang.org/x/time/rate"
)

// SyncerType encapsulates the different types of syncing mechanisms for a
// gossip syncer.
type SyncerType uint8

const (
        // ActiveSync denotes that a gossip syncer:
        //
        // 1. Should not attempt to synchronize with the remote peer for
        //    missing channels.
        // 2. Should respond to queries from the remote peer.
        // 3. Should receive new updates from the remote peer.
        //
        // They are started in a chansSynced state in order to accomplish their
        // responsibilities above.
        ActiveSync SyncerType = iota

        // PassiveSync denotes that a gossip syncer:
        //
        // 1. Should not attempt to synchronize with the remote peer for
        //    missing channels.
        // 2. Should respond to queries from the remote peer.
        // 3. Should not receive new updates from the remote peer.
        //
        // They are started in a chansSynced state in order to accomplish their
        // responsibilities above.
        PassiveSync

        // PinnedSync denotes an ActiveSync that doesn't count towards the
        // default active syncer limits and is always active throughout the
        // duration of the peer's connection. Each pinned syncer will begin by
        // performing a historical sync to ensure we are well synchronized with
        // their routing table.
        PinnedSync
)

const (
        // defaultTimestampQueueSize is the size of the timestamp range queue
        // used.
        defaultTimestampQueueSize = 1
)

// String returns a human readable string describing the target SyncerType.
func (t SyncerType) String() string {
        switch t {
        case ActiveSync:
                return "ActiveSync"
        case PassiveSync:
                return "PassiveSync"
        case PinnedSync:
                return "PinnedSync"
        default:
                return fmt.Sprintf("unknown sync type %d", t)
        }
}

// IsActiveSync returns true if the SyncerType should set a GossipTimestampRange
// allowing new gossip messages to be received from the peer.
func (t SyncerType) IsActiveSync() bool {
        switch t {
        case ActiveSync, PinnedSync:
                return true
        default:
                return false
        }
}

// syncerState is an enum that represents the current state of the GossipSyncer.
// As the syncer is a state machine, we'll gate our actions based off of the
// current state and the next incoming message.
type syncerState uint32

const (
        // syncingChans is the default state of the GossipSyncer. We start in
        // this state when a new peer first connects and we don't yet know if
        // we're fully synchronized.
        syncingChans syncerState = iota

        // waitingQueryRangeReply is the second main phase of the GossipSyncer.
        // We enter this state after we send out our first QueryChannelRange
        // reply. We'll stay in this state until the remote party sends us a
        // ReplyShortChanIDsEnd message that indicates they've responded to our
        // query entirely. After this state, we'll transition to
        // waitingQueryChanReply after we send out requests for all the new
        // chan ID's to us.
        waitingQueryRangeReply

        // queryNewChannels is the third main phase of the GossipSyncer.  In
        // this phase we'll send out all of our QueryShortChanIDs messages in
        // response to the new channels that we don't yet know about.
        queryNewChannels

        // waitingQueryChanReply is the fourth main phase of the GossipSyncer.
        // We enter this phase once we've sent off a query chink to the remote
        // peer.  We'll stay in this phase until we receive a
        // ReplyShortChanIDsEnd message which indicates that the remote party
        // has responded to all of our requests.
        waitingQueryChanReply

        // chansSynced is the terminal stage of the GossipSyncer. Once we enter
        // this phase, we'll send out our update horizon, which filters out the
        // set of channel updates that we're interested in. In this state,
        // we'll be able to accept any outgoing messages from the
        // AuthenticatedGossiper, and decide if we should forward them to our
        // target peer based on its update horizon.
        chansSynced

        // syncerIdle is a state in which the gossip syncer can handle external
        // requests to transition or perform historical syncs. It is used as the
        // initial state for pinned syncers, as well as a fallthrough case for
        // chansSynced allowing fully synced peers to facilitate requests.
        syncerIdle
)

// String returns a human readable string describing the target syncerState.
func (s syncerState) String() string {
        switch s {
        case syncingChans:
                return "syncingChans"

        case waitingQueryRangeReply:
                return "waitingQueryRangeReply"

        case queryNewChannels:
                return "queryNewChannels"

        case waitingQueryChanReply:
                return "waitingQueryChanReply"

        case chansSynced:
                return "chansSynced"

        case syncerIdle:
                return "syncerIdle"

        default:
                return "UNKNOWN STATE"
        }
}

const (
        // maxQueryChanRangeReplies specifies the default limit of replies to
        // process for a single QueryChannelRange request.
        maxQueryChanRangeReplies = 500

        // maxQueryChanRangeRepliesZlibFactor specifies the factor applied to
        // the maximum number of replies allowed for zlib encoded replies.
        maxQueryChanRangeRepliesZlibFactor = 4

        // chanRangeQueryBuffer is the number of blocks back that we'll go when
        // asking the remote peer for their any channels they know of beyond
        // our highest known channel ID.
        chanRangeQueryBuffer = 144

        // syncTransitionTimeout is the default timeout in which we'll wait up
        // to when attempting to perform a sync transition.
        syncTransitionTimeout = 5 * time.Second

        // requestBatchSize is the maximum number of channels we will query the
        // remote peer for in a QueryShortChanIDs message.
        requestBatchSize = 500

        // syncerBufferSize is the size of the syncer's buffers.
        syncerBufferSize = 50
)

var (
        // encodingTypeToChunkSize maps an encoding type, to the max number of
        // short chan ID's using the encoding type that we can fit into a
        // single message safely.
        encodingTypeToChunkSize = map[lnwire.QueryEncoding]int32{
                lnwire.EncodingSortedPlain: 8000,
        }

        // ErrGossipSyncerExiting signals that the syncer has been killed.
        ErrGossipSyncerExiting = errors.New("gossip syncer exiting")

        // ErrSyncTransitionTimeout is an error returned when we've timed out
        // attempting to perform a sync transition.
        ErrSyncTransitionTimeout = errors.New("timed out attempting to " +
                "transition sync type")

        // zeroTimestamp is the timestamp we'll use when we want to indicate to
        // peers that we do not want to receive any new graph updates.
        zeroTimestamp time.Time
)

// syncTransitionReq encapsulates a request for a gossip syncer sync transition.
type syncTransitionReq struct {
        newSyncType SyncerType
        errChan     chan error
}

// historicalSyncReq encapsulates a request for a gossip syncer to perform a
// historical sync.
type historicalSyncReq struct {
        // doneChan is a channel that serves as a signal and is closed to ensure
        // the historical sync is attempted by the time we return to the caller.
        doneChan chan struct{}
}

// gossipSyncerCfg is a struct that packages all the information a GossipSyncer
// needs to carry out its duties.
type gossipSyncerCfg struct {
        // chainHash is the chain that this syncer is responsible for.
        chainHash chainhash.Hash

        // peerPub is the public key of the peer we're syncing with, serialized
        // in compressed format.
        peerPub [33]byte

        // channelSeries is the primary interface that we'll use to generate
        // our queries and respond to the queries of the remote peer.
        channelSeries ChannelGraphTimeSeries

        // encodingType is the current encoding type we're aware of. Requests
        // with different encoding types will be rejected.
        encodingType lnwire.QueryEncoding

        // chunkSize is the max number of short chan IDs using the syncer's
        // encoding type that we can fit into a single message safely.
        chunkSize int32

        // batchSize is the max number of channels the syncer will query from
        // the remote node in a single QueryShortChanIDs request.
        batchSize int32

        // sendMsg sends a variadic number of messages to the remote peer.
        // The boolean indicates whether this method should be blocked or not
        // while waiting for sends to be written to the wire.
        sendMsg func(context.Context, bool, ...lnwire.Message) error

        // noSyncChannels will prevent the GossipSyncer from spawning a
        // channelGraphSyncer, meaning we will not try to reconcile unknown
        // channels with the remote peer.
        noSyncChannels bool

        // noReplyQueries will prevent the GossipSyncer from spawning a
        // replyHandler, meaning we will not reply to queries from our remote
        // peer.
        noReplyQueries bool

        // noTimestampQueryOption will prevent the GossipSyncer from querying
        // timestamps of announcement messages from the peer, and it will
        // prevent it from responding to timestamp queries.
        noTimestampQueryOption bool

        // ignoreHistoricalFilters will prevent syncers from replying with
        // historical data when the remote peer sets a gossip_timestamp_range.
        // This prevents ranges with old start times from causing us to dump the
        // graph on connect.
        ignoreHistoricalFilters bool

        // bestHeight returns the latest height known of the chain.
        bestHeight func() uint32

        // markGraphSynced updates the SyncManager's perception of whether we
        // have completed at least one historical sync.
        markGraphSynced func()

        // maxQueryChanRangeReplies is the maximum number of replies we'll allow
        // for a single QueryChannelRange request.
        maxQueryChanRangeReplies uint32

        // isStillZombieChannel takes the timestamps of the latest channel
        // updates for a channel and returns true if the channel should be
        // considered a zombie based on these timestamps.
        isStillZombieChannel func(time.Time, time.Time) bool

        // timestampQueueSize is the size of the timestamp range queue. If not
        // set, defaults to the global timestampQueueSize constant.
        timestampQueueSize int

        // msgBytesPerSecond is the allotted bandwidth rate, expressed in
        // bytes/second that this gossip syncer can consume. Once we exceed this
        // rate, message sending will block until we're below the rate.
        msgBytesPerSecond uint64
}

// GossipSyncer is a struct that handles synchronizing the channel graph state
// with a remote peer. The GossipSyncer implements a state machine that will
// progressively ensure we're synchronized with the channel state of the remote
// node. Once both nodes have been synchronized, we'll use an update filter to
// filter out which messages should be sent to a remote peer based on their
// update horizon. If the update horizon isn't specified, then we won't send
// them any channel updates at all.
type GossipSyncer struct {
        started sync.Once
        stopped sync.Once

        // state is the current state of the GossipSyncer.
        //
        // NOTE: This variable MUST be used atomically.
        state uint32

        // syncType denotes the SyncerType the gossip syncer is currently
        // exercising.
        //
        // NOTE: This variable MUST be used atomically.
        syncType uint32

        // remoteUpdateHorizon is the update horizon of the remote peer. We'll
        // use this to properly filter out any messages.
        remoteUpdateHorizon *lnwire.GossipTimestampRange

        // localUpdateHorizon is our local update horizon, we'll use this to
        // determine if we've already sent out our update.
        localUpdateHorizon *lnwire.GossipTimestampRange

        // syncTransitions is a channel through which new sync type transition
        // requests will be sent through. These requests should only be handled
        // when the gossip syncer is in a chansSynced state to ensure its state
        // machine behaves as expected.
        syncTransitionReqs chan *syncTransitionReq

        // historicalSyncReqs is a channel that serves as a signal for the
        // gossip syncer to perform a historical sync. These can only be done
        // once the gossip syncer is in a chansSynced state to ensure its state
        // machine behaves as expected.
        historicalSyncReqs chan *historicalSyncReq

        // genHistoricalChanRangeQuery when true signals to the gossip syncer
        // that it should request the remote peer for all of its known channel
        // IDs starting from the genesis block of the chain. This can only
        // happen if the gossip syncer receives a request to attempt a
        // historical sync. It can be unset if the syncer ever transitions from
        // PassiveSync to ActiveSync.
        genHistoricalChanRangeQuery bool

        // gossipMsgs is a channel that all responses to our queries from the
        // target peer will be sent over, these will be read by the
        // channelGraphSyncer.
        gossipMsgs chan lnwire.Message

        // queryMsgs is a channel that all queries from the remote peer will be
        // received over, these will be read by the replyHandler.
        queryMsgs chan lnwire.Message

        // curQueryRangeMsg keeps track of the latest QueryChannelRange message
        // we've sent to a peer to ensure we've consumed all expected replies.
        // This field is primarily used within the waitingQueryChanReply state.
        curQueryRangeMsg *lnwire.QueryChannelRange

        // prevReplyChannelRange keeps track of the previous ReplyChannelRange
        // message we've received from a peer to ensure they've fully replied to
        // our query by ensuring they covered our requested block range. This
        // field is primarily used within the waitingQueryChanReply state.
        prevReplyChannelRange *lnwire.ReplyChannelRange

        // bufferedChanRangeReplies is used in the waitingQueryChanReply to
        // buffer all the chunked response to our query.
        bufferedChanRangeReplies []graphdb.ChannelUpdateInfo

        // numChanRangeRepliesRcvd is used to track the number of replies
        // received as part of a QueryChannelRange. This field is primarily used
        // within the waitingQueryChanReply state.
        numChanRangeRepliesRcvd uint32

        // newChansToQuery is used to pass the set of channels we should query
        // for from the waitingQueryChanReply state to the queryNewChannels
        // state.
        newChansToQuery []lnwire.ShortChannelID

        cfg gossipSyncerCfg

        // syncedSignal is a channel that, if set, will be closed when the
        // GossipSyncer reaches its terminal chansSynced state.
        syncedSignal chan struct{}

        // syncerSema is used to more finely control the syncer's ability to
        // respond to gossip timestamp range messages.
        syncerSema chan struct{}

        // timestampRangeQueue is a buffered channel for queuing timestamp range
        // messages that need to be processed asynchronously. This prevents the
        // gossiper from blocking when ApplyGossipFilter is called.
        timestampRangeQueue chan *lnwire.GossipTimestampRange

        // isSendingBacklog is an atomic flag that indicates whether a goroutine
        // is currently sending the backlog of messages. This ensures only one
        // goroutine is active at a time.
        isSendingBacklog atomic.Bool

        sync.Mutex

        // 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

        // rateLimiter dictates the frequency with which we will reply to gossip
        // queries to this peer.
        rateLimiter *rate.Limiter
}

// newGossipSyncer returns a new instance of the GossipSyncer populated using
// the passed config.
func newGossipSyncer(cfg gossipSyncerCfg, sema chan struct{}) *GossipSyncer {
        // Use the configured queue size if set, otherwise use the default.
        queueSize := cfg.timestampQueueSize
        if queueSize == 0 {
                queueSize = defaultTimestampQueueSize
        }

        bytesPerSecond := cfg.msgBytesPerSecond
        if bytesPerSecond == 0 {
                bytesPerSecond = DefaultPeerMsgBytesPerSecond
        }
        bytesBurst := 2 * bytesPerSecond

        // We'll use this rate limiter to limit this single peer.
        rateLimiter := rate.NewLimiter(
                rate.Limit(bytesPerSecond), int(bytesBurst),
        )

        return &GossipSyncer{
                cfg:                cfg,
                syncTransitionReqs: make(chan *syncTransitionReq),
                historicalSyncReqs: make(chan *historicalSyncReq),
                gossipMsgs:         make(chan lnwire.Message, syncerBufferSize),
                queryMsgs:          make(chan lnwire.Message, syncerBufferSize),
                timestampRangeQueue: make(
                        chan *lnwire.GossipTimestampRange, queueSize,
                ),
                syncerSema:  sema,
                cg:          fn.NewContextGuard(),
                rateLimiter: rateLimiter,
        }
}

// Start starts the GossipSyncer and any goroutines that it needs to carry out
// its duties.
func (g *GossipSyncer) Start() {
        g.started.Do(func() {
                log.Debugf("Starting GossipSyncer(%x)", g.cfg.peerPub[:])

                ctx, _ := g.cg.Create(context.Background())

                // TODO(conner): only spawn channelGraphSyncer if remote
                // supports gossip queries, and only spawn replyHandler if we
                // advertise support
                if !g.cfg.noSyncChannels {
                        g.cg.WgAdd(1)
                        go g.channelGraphSyncer(ctx)
                }
                if !g.cfg.noReplyQueries {
                        g.cg.WgAdd(1)
                        go g.replyHandler(ctx)
                }

                // Start the timestamp range queue processor to handle gossip
                // filter applications asynchronously.
                if !g.cfg.noTimestampQueryOption {
                        g.cg.WgAdd(1)
                        go g.processTimestampRangeQueue(ctx)
                }
        })
}

// Stop signals the GossipSyncer for a graceful exit, then waits until it has
// exited.
func (g *GossipSyncer) Stop() {
        g.stopped.Do(func() {
                log.Debugf("Stopping GossipSyncer(%x)", g.cfg.peerPub[:])
                defer log.Debugf("GossipSyncer(%x) stopped", g.cfg.peerPub[:])

                g.cg.Quit()
        })
}

// handleSyncingChans handles the state syncingChans for the GossipSyncer. When
// in this state, we will send a QueryChannelRange msg to our peer and advance
// the syncer's state to waitingQueryRangeReply.
func (g *GossipSyncer) handleSyncingChans(ctx context.Context) {
        // Prepare the query msg.
        queryRangeMsg, err := g.genChanRangeQuery(
                ctx, g.genHistoricalChanRangeQuery,
        )
        if err != nil {
                log.Errorf("Unable to gen chan range query: %v", err)
                return
        }

        // Acquire a lock so the following state transition is atomic.
        //
        // NOTE: We must lock the following steps as it's possible we get an
        // immediate response (ReplyChannelRange) after sending the query msg.
        // The response is handled in ProcessQueryMsg, which requires the
        // current state to be waitingQueryRangeReply.
        g.Lock()
        defer g.Unlock()

        // Send the msg to the remote peer, which is non-blocking as
        // `sendToPeer` only queues the msg in Brontide.
        err = g.sendToPeer(ctx, queryRangeMsg)
        if err != nil {
                log.Errorf("Unable to send chan range query: %v", err)
                return
        }

        // With the message sent successfully, we'll transition into the next
        // state where we wait for their reply.
        g.setSyncState(waitingQueryRangeReply)
}

// channelGraphSyncer is the main goroutine responsible for ensuring that we
// properly channel graph state with the remote peer, and also that we only
// send them messages which actually pass their defined update horizon.
func (g *GossipSyncer) channelGraphSyncer(ctx context.Context) {
        defer g.cg.WgDone()

        for {
                // Check cancellation before processing any state.
                select {
                case <-ctx.Done():
                        log.Debugf("GossipSyncer(%x): context canceled, "+
                                "exiting", g.cfg.peerPub[:])

                        return
                case <-g.cg.Done():
                        log.Debugf("GossipSyncer(%x): shutting down",
                                g.cfg.peerPub[:])

                        return
                default:
                }

                state := g.syncState()
                syncType := g.SyncType()

                log.Debugf("GossipSyncer(%x): state=%v, type=%v",
                        g.cfg.peerPub[:], state, syncType)

                switch state {
                // When we're in this state, we're trying to synchronize our
                // view of the network with the remote peer. We'll kick off
                // this sync by asking them for the set of channels they
                // understand, as we'll as responding to any other queries by
                // them.
                case syncingChans:
                        g.handleSyncingChans(ctx)

                // In this state, we've sent out our initial channel range
                // query and are waiting for the final response from the remote
                // peer before we perform a diff to see with channels they know
                // of that we don't.
                case waitingQueryRangeReply:
                        // We'll wait to either process a new message from the
                        // remote party, or exit due to the gossiper exiting,
                        // or us being signalled to do so.
                        select {
                        case msg := <-g.gossipMsgs:
                                // The remote peer is sending a response to our
                                // initial query, we'll collate this response,
                                // and see if it's the final one in the series.
                                // If so, we can then transition to querying
                                // for the new channels.
                                queryReply, ok := msg.(*lnwire.ReplyChannelRange)
                                if ok {
                                        err := g.processChanRangeReply(
                                                ctx, queryReply,
                                        )
                                        if err != nil {
                                                log.Errorf("Unable to "+
                                                        "process chan range "+
                                                        "query: %v", err)
                                                return
                                        }
                                        continue
                                }

                                log.Warnf("Unexpected message: %T in state=%v",
                                        msg, state)

                        case <-g.cg.Done():
                                return

                        case <-ctx.Done():
                                return
                        }

                // We'll enter this state once we've discovered which channels
                // the remote party knows of that we don't yet know of
                // ourselves.
                case queryNewChannels:
                        // First, we'll attempt to continue our channel
                        // synchronization by continuing to send off another
                        // query chunk.
                        done := g.synchronizeChanIDs(ctx)

                        // If this wasn't our last query, then we'll need to
                        // transition to our waiting state.
                        if !done {
                                continue
                        }

                        // If we're fully synchronized, then we can transition
                        // to our terminal state.
                        g.setSyncState(chansSynced)

                        // Ensure that the sync manager becomes aware that the
                        // historical sync completed so synced_to_graph is
                        // updated over rpc.
                        g.cfg.markGraphSynced()

                // In this state, we've just sent off a new query for channels
                // that we don't yet know of. We'll remain in this state until
                // the remote party signals they've responded to our query in
                // totality.
                case waitingQueryChanReply:
                        // Once we've sent off our query, we'll wait for either
                        // an ending reply, or just another query from the
                        // remote peer.
                        select {
                        case msg := <-g.gossipMsgs:
                                // If this is the final reply to one of our
                                // queries, then we'll loop back into our query
                                // state to send of the remaining query chunks.
                                _, ok := msg.(*lnwire.ReplyShortChanIDsEnd)
                                if ok {
                                        g.setSyncState(queryNewChannels)
                                        continue
                                }

                                log.Warnf("Unexpected message: %T in state=%v",
                                        msg, state)

                        case <-g.cg.Done():
                                return

                        case <-ctx.Done():
                                return
                        }

                // This is our final terminal state where we'll only reply to
                // any further queries by the remote peer.
                case chansSynced:
                        g.Lock()
                        if g.syncedSignal != nil {
                                close(g.syncedSignal)
                                g.syncedSignal = nil
                        }
                        g.Unlock()

                        // If we haven't yet sent out our update horizon, and
                        // we want to receive real-time channel updates, we'll
                        // do so now.
                        if g.localUpdateHorizon == nil &&
                                syncType.IsActiveSync() {

                                err := g.sendGossipTimestampRange(
                                        ctx, time.Now(), math.MaxUint32,
                                )
                                if err != nil {
                                        log.Errorf("Unable to send update "+
                                                "horizon to %x: %v",
                                                g.cfg.peerPub, err)
                                }
                        }
                        // With our horizon set, we'll simply reply to any new
                        // messages or process any state transitions and exit if
                        // needed.
                        fallthrough

                // Pinned peers will begin in this state, since they will
                // immediately receive a request to perform a historical sync.
                // Otherwise, we fall through after ending in chansSynced to
                // facilitate new requests.
                case syncerIdle:
                        select {
                        case req := <-g.syncTransitionReqs:
                                req.errChan <- g.handleSyncTransition(ctx, req)

                        case req := <-g.historicalSyncReqs:
                                g.handleHistoricalSync(req)

                        case <-g.cg.Done():
                                return

                        case <-ctx.Done():
                                return
                        }
                }
        }
}

// replyHandler is an event loop whose sole purpose is to reply to the remote
// peers queries. Our replyHandler will respond to messages generated by their
// channelGraphSyncer, and vice versa. Each party's channelGraphSyncer drives
// the other's replyHandler, allowing the replyHandler to operate independently
// from the state machine maintained on the same node.
//
// NOTE: This method MUST be run as a goroutine.
func (g *GossipSyncer) replyHandler(ctx context.Context) {
        defer g.cg.WgDone()

        for {
                select {
                case msg := <-g.queryMsgs:
                        err := g.replyPeerQueries(ctx, msg)
                        switch {
                        case err == ErrGossipSyncerExiting:
                                return

                        case err == lnpeer.ErrPeerExiting:
                                return

                        case err != nil:
                                log.Errorf("Unable to reply to peer "+
                                        "query: %v", err)
                        }

                case <-g.cg.Done():
                        return

                case <-ctx.Done():
                        return
                }
        }
}

// processTimestampRangeQueue handles timestamp range messages from the queue
// asynchronously. This prevents blocking the gossiper when rate limiting is
// active and multiple peers are trying to apply gossip filters.
func (g *GossipSyncer) processTimestampRangeQueue(ctx context.Context) {
        defer g.cg.WgDone()

        for {
                select {
                case msg := <-g.timestampRangeQueue:
                        // Process the timestamp range message. If we hit an
                        // error, log it but continue processing to avoid
                        // blocking the queue.
                        err := g.ApplyGossipFilter(ctx, msg)
                        switch {
                        case errors.Is(err, ErrGossipSyncerExiting):
                                return

                        case errors.Is(err, lnpeer.ErrPeerExiting):
                                return

                        case err != nil:
                                log.Errorf("Unable to apply gossip filter: %v",
                                        err)
                        }

                case <-g.cg.Done():
                        return

                case <-ctx.Done():
                        return
                }
        }
}

// QueueTimestampRange attempts to queue a timestamp range message for
// asynchronous processing. If the queue is full, it returns false to indicate
// the message was dropped.
func (g *GossipSyncer) QueueTimestampRange(
        msg *lnwire.GossipTimestampRange) bool {

        // If timestamp queries are disabled, don't queue the message.
        if g.cfg.noTimestampQueryOption {
                return false
        }

        select {
        case g.timestampRangeQueue <- msg:
                return true

        // Queue is full, drop the message to prevent blocking.
        default:
                log.Warnf("Timestamp range queue full for peer %x, "+
                        "dropping message", g.cfg.peerPub[:])
                return false
        }
}

// sendGossipTimestampRange constructs and sets a GossipTimestampRange for the
// syncer and sends it to the remote peer.
func (g *GossipSyncer) sendGossipTimestampRange(ctx context.Context,
        firstTimestamp time.Time, timestampRange uint32) error {

        endTimestamp := firstTimestamp.Add(
                time.Duration(timestampRange) * time.Second,
        )

        log.Infof("GossipSyncer(%x): applying gossipFilter(start=%v, end=%v)",
                g.cfg.peerPub[:], firstTimestamp, endTimestamp)

        localUpdateHorizon := &lnwire.GossipTimestampRange{
                ChainHash:      g.cfg.chainHash,
                FirstTimestamp: uint32(firstTimestamp.Unix()),
                TimestampRange: timestampRange,
        }

        if err := g.sendToPeer(ctx, localUpdateHorizon); err != nil {
                return err
        }

        if firstTimestamp.Equal(zeroTimestamp) && timestampRange == 0 {
                g.localUpdateHorizon = nil
        } else {
                g.localUpdateHorizon = localUpdateHorizon
        }

        return nil
}

// synchronizeChanIDs is called by the channelGraphSyncer when we need to query
// the remote peer for its known set of channel IDs within a particular block
// range. This method will be called continually until the entire range has
// been queried for with a response received. We'll chunk our requests as
// required to ensure they fit into a single message. We may re-renter this
// state in the case that chunking is required.
func (g *GossipSyncer) synchronizeChanIDs(ctx context.Context) bool {
        // If we're in this state yet there are no more new channels to query
        // for, then we'll transition to our final synced state and return true
        // to signal that we're fully synchronized.
        if len(g.newChansToQuery) == 0 {
                log.Infof("GossipSyncer(%x): no more chans to query",
                        g.cfg.peerPub[:])

                return true
        }

        // Otherwise, we'll issue our next chunked query to receive replies
        // for.
        var queryChunk []lnwire.ShortChannelID

        // If the number of channels to query for is less than the chunk size,
        // then we can issue a single query.
        if int32(len(g.newChansToQuery)) < g.cfg.batchSize {
                queryChunk = g.newChansToQuery
                g.newChansToQuery = nil

        } else {
                // Otherwise, we'll need to only query for the next chunk.
                // We'll slice into our query chunk, then slide down our main
                // pointer down by the chunk size.
                queryChunk = g.newChansToQuery[:g.cfg.batchSize]
                g.newChansToQuery = g.newChansToQuery[g.cfg.batchSize:]
        }

        log.Infof("GossipSyncer(%x): querying for %v new channels",
                g.cfg.peerPub[:], len(queryChunk))

        // Change the state before sending the query msg.
        g.setSyncState(waitingQueryChanReply)

        // With our chunk obtained, we'll send over our next query, then return
        // false indicating that we're net yet fully synced.
        err := g.sendToPeer(ctx, &lnwire.QueryShortChanIDs{
                ChainHash:    g.cfg.chainHash,
                EncodingType: lnwire.EncodingSortedPlain,
                ShortChanIDs: queryChunk,
        })
        if err != nil {
                log.Errorf("Unable to sync chan IDs: %v", err)
        }

        return false
}

// isLegacyReplyChannelRange determines where a ReplyChannelRange message is
// considered legacy. There was a point where lnd used to include the same query
// over multiple replies, rather than including the portion of the query the
// reply is handling. We'll use this as a way of detecting whether we are
// communicating with a legacy node so we can properly sync with them.
func isLegacyReplyChannelRange(query *lnwire.QueryChannelRange,
        reply *lnwire.ReplyChannelRange) bool {

        return (reply.ChainHash == query.ChainHash &&
                reply.FirstBlockHeight == query.FirstBlockHeight &&
                reply.NumBlocks == query.NumBlocks)
}

// processChanRangeReply is called each time the GossipSyncer receives a new
// reply to the initial range query to discover new channels that it didn't
// previously know of.
func (g *GossipSyncer) processChanRangeReply(_ context.Context,
        msg *lnwire.ReplyChannelRange) error {

        // isStale returns whether the timestamp is too far into the past.
        isStale := func(timestamp time.Time) bool {
                return time.Since(timestamp) > graph.DefaultChannelPruneExpiry
        }

        // isSkewed returns whether the timestamp is too far into the future.
        isSkewed := func(timestamp time.Time) bool {
                return time.Until(timestamp) > graph.DefaultChannelPruneExpiry
        }

        // If we're not communicating with a legacy node, we'll apply some
        // further constraints on their reply to ensure it satisfies our query.
        if !isLegacyReplyChannelRange(g.curQueryRangeMsg, msg) {
                // The first block should be within our original request.
                if msg.FirstBlockHeight < g.curQueryRangeMsg.FirstBlockHeight {
                        return fmt.Errorf("reply includes channels for height "+
                                "%v prior to query %v", msg.FirstBlockHeight,
                                g.curQueryRangeMsg.FirstBlockHeight)
                }

                // The last block should also be. We don't need to check the
                // intermediate ones because they should already be in sorted
                // order.
                replyLastHeight := msg.LastBlockHeight()
                queryLastHeight := g.curQueryRangeMsg.LastBlockHeight()
                if replyLastHeight > queryLastHeight {
                        return fmt.Errorf("reply includes channels for height "+
                                "%v after query %v", replyLastHeight,
                                queryLastHeight)
                }

                // If we've previously received a reply for this query, look at
                // its last block to ensure the current reply properly follows
                // it.
                if g.prevReplyChannelRange != nil {
                        prevReply := g.prevReplyChannelRange
                        prevReplyLastHeight := prevReply.LastBlockHeight()

                        // The current reply can either start from the previous
                        // reply's last block, if there are still more channels
                        // for the same block, or the block after.
                        if msg.FirstBlockHeight != prevReplyLastHeight &&
                                msg.FirstBlockHeight != prevReplyLastHeight+1 {

                                return fmt.Errorf("first block of reply %v "+
                                        "does not continue from last block of "+
                                        "previous %v", msg.FirstBlockHeight,
                                        prevReplyLastHeight)
                        }
                }
        }

        g.prevReplyChannelRange = msg

        for i, scid := range msg.ShortChanIDs {
                info := graphdb.NewChannelUpdateInfo(
                        scid, time.Time{}, time.Time{},
                )

                if len(msg.Timestamps) != 0 {
                        t1 := time.Unix(int64(msg.Timestamps[i].Timestamp1), 0)
                        info.Node1UpdateTimestamp = t1

                        t2 := time.Unix(int64(msg.Timestamps[i].Timestamp2), 0)
                        info.Node2UpdateTimestamp = t2

                        // Sort out all channels with outdated or skewed
                        // timestamps. Both timestamps need to be out of
                        // boundaries for us to skip the channel and not query
                        // it later on.
                        switch {
                        case isStale(info.Node1UpdateTimestamp) &&
                                isStale(info.Node2UpdateTimestamp):

                                continue

                        case isSkewed(info.Node1UpdateTimestamp) &&
                                isSkewed(info.Node2UpdateTimestamp):

                                continue

                        case isStale(info.Node1UpdateTimestamp) &&
                                isSkewed(info.Node2UpdateTimestamp):

                                continue

                        case isStale(info.Node2UpdateTimestamp) &&
                                isSkewed(info.Node1UpdateTimestamp):

                                continue
                        }
                }

                g.bufferedChanRangeReplies = append(
                        g.bufferedChanRangeReplies, info,
                )
        }

        switch g.cfg.encodingType {
        case lnwire.EncodingSortedPlain:
                g.numChanRangeRepliesRcvd++
        case lnwire.EncodingSortedZlib:
                g.numChanRangeRepliesRcvd += maxQueryChanRangeRepliesZlibFactor
        default:
                return fmt.Errorf("unhandled encoding type %v", g.cfg.encodingType)
        }

        log.Infof("GossipSyncer(%x): buffering chan range reply of size=%v",
                g.cfg.peerPub[:], len(msg.ShortChanIDs))

        // If this isn't the last response and we can continue to receive more,
        // then we can exit as we've already buffered the latest portion of the
        // streaming reply.
        maxReplies := g.cfg.maxQueryChanRangeReplies
        switch {
        // If we're communicating with a legacy node, we'll need to look at the
        // complete field.
        case isLegacyReplyChannelRange(g.curQueryRangeMsg, msg):
                if msg.Complete == 0 && g.numChanRangeRepliesRcvd < maxReplies {
                        return nil
                }

        // Otherwise, we'll look at the reply's height range.
        default:
                replyLastHeight := msg.LastBlockHeight()
                queryLastHeight := g.curQueryRangeMsg.LastBlockHeight()

                // TODO(wilmer): This might require some padding if the remote
                // node is not aware of the last height we sent them, i.e., is
                // behind a few blocks from us.
                if replyLastHeight < queryLastHeight &&
                        g.numChanRangeRepliesRcvd < maxReplies {

                        return nil
                }
        }

        log.Infof("GossipSyncer(%x): filtering through %v chans",
                g.cfg.peerPub[:], len(g.bufferedChanRangeReplies))

        // Otherwise, this is the final response, so we'll now check to see
        // which channels they know of that we don't.
        newChans, err := g.cfg.channelSeries.FilterKnownChanIDs(
                g.cfg.chainHash, g.bufferedChanRangeReplies,
                g.cfg.isStillZombieChannel,
        )
        if err != nil {
                return fmt.Errorf("unable to filter chan ids: %w", err)
        }

        // As we've received the entirety of the reply, we no longer need to
        // hold on to the set of buffered replies or the original query that
        // prompted the replies, so we'll let that be garbage collected now.
        g.curQueryRangeMsg = nil
        g.prevReplyChannelRange = nil
        g.bufferedChanRangeReplies = nil
        g.numChanRangeRepliesRcvd = 0

        // If there aren't any channels that we don't know of, then we can
        // switch straight to our terminal state.
        if len(newChans) == 0 {
                log.Infof("GossipSyncer(%x): remote peer has no new chans",
                        g.cfg.peerPub[:])

                g.setSyncState(chansSynced)

                // Ensure that the sync manager becomes aware that the
                // historical sync completed so synced_to_graph is updated over
                // rpc.
                g.cfg.markGraphSynced()
                return nil
        }

        // Otherwise, we'll set the set of channels that we need to query for
        // the next state, and also transition our state.
        g.newChansToQuery = newChans
        g.setSyncState(queryNewChannels)

        log.Infof("GossipSyncer(%x): starting query for %v new chans",
                g.cfg.peerPub[:], len(newChans))

        return nil
}

// genChanRangeQuery generates the initial message we'll send to the remote
// party when we're kicking off the channel graph synchronization upon
// connection. The historicalQuery boolean can be used to generate a query from
// the genesis block of the chain.
func (g *GossipSyncer) genChanRangeQuery(ctx context.Context,
        historicalQuery bool) (*lnwire.QueryChannelRange, error) {

        // First, we'll query our channel graph time series for its highest
        // known channel ID.
        newestChan, err := g.cfg.channelSeries.HighestChanID(
                ctx, g.cfg.chainHash,
        )
        if err != nil {
                return nil, err
        }

        // Once we have the chan ID of the newest, we'll obtain the block height
        // of the channel, then subtract our default horizon to ensure we don't
        // miss any channels. By default, we go back 1 day from the newest
        // channel, unless we're attempting a historical sync, where we'll
        // actually start from the genesis block instead.
        var startHeight uint32
        switch {
        case historicalQuery:
                fallthrough
        case newestChan.BlockHeight <= chanRangeQueryBuffer:
                startHeight = 0
        default:
                startHeight = newestChan.BlockHeight - chanRangeQueryBuffer
        }

        // Determine the number of blocks to request based on our best height.
        // We'll take into account any potential underflows and explicitly set
        // numBlocks to its minimum value of 1 if so.
        bestHeight := g.cfg.bestHeight()
        numBlocks := bestHeight - startHeight
        if int64(numBlocks) < 1 {
                numBlocks = 1
        }

        log.Infof("GossipSyncer(%x): requesting new chans from height=%v "+
                "and %v blocks after", g.cfg.peerPub[:], startHeight, numBlocks)

        // Finally, we'll craft the channel range query, using our starting
        // height, then asking for all known channels to the foreseeable end of
        // the main chain.
        query := &lnwire.QueryChannelRange{
                ChainHash:        g.cfg.chainHash,
                FirstBlockHeight: startHeight,
                NumBlocks:        numBlocks,
        }

        if !g.cfg.noTimestampQueryOption {
                query.QueryOptions = lnwire.NewTimestampQueryOption()
        }

        g.curQueryRangeMsg = query

        return query, nil
}

// replyPeerQueries is called in response to any query by the remote peer.
// We'll examine our state and send back our best response.
func (g *GossipSyncer) replyPeerQueries(ctx context.Context,
        msg lnwire.Message) error {

        switch msg := msg.(type) {

        // In this state, we'll also handle any incoming channel range queries
        // from the remote peer as they're trying to sync their state as well.
        case *lnwire.QueryChannelRange:
                return g.replyChanRangeQuery(ctx, msg)

        // If the remote peer skips straight to requesting new channels that
        // they don't know of, then we'll ensure that we also handle this case.
        case *lnwire.QueryShortChanIDs:
                return g.replyShortChanIDs(ctx, msg)

        default:
                return fmt.Errorf("unknown message: %T", msg)
        }
}

// replyChanRangeQuery will be dispatched in response to a channel range query
// by the remote node. We'll query the channel time series for channels that
// meet the channel range, then chunk our responses to the remote node. We also
// ensure that our final fragment carries the "complete" bit to indicate the
// end of our streaming response.
func (g *GossipSyncer) replyChanRangeQuery(ctx context.Context,
        query *lnwire.QueryChannelRange) error {

        // Before responding, we'll check to ensure that the remote peer is
        // querying for the same chain that we're on. If not, we'll send back a
        // response with a complete value of zero to indicate we're on a
        // different chain.
        if g.cfg.chainHash != query.ChainHash {
                log.Warnf("Remote peer requested QueryChannelRange for "+
                        "chain=%v, we're on chain=%v", query.ChainHash,
                        g.cfg.chainHash)

                return g.sendToPeerSync(ctx, &lnwire.ReplyChannelRange{
                        ChainHash:        query.ChainHash,
                        FirstBlockHeight: query.FirstBlockHeight,
                        NumBlocks:        query.NumBlocks,
                        Complete:         0,
                        EncodingType:     g.cfg.encodingType,
                        ShortChanIDs:     nil,
                })
        }

        log.Infof("GossipSyncer(%x): filtering chan range: start_height=%v, "+
                "num_blocks=%v", g.cfg.peerPub[:], query.FirstBlockHeight,
                query.NumBlocks)

        // Check if the query asked for timestamps. We will only serve
        // timestamps if this has not been disabled with
        // noTimestampQueryOption.
        withTimestamps := query.WithTimestamps() &&
                !g.cfg.noTimestampQueryOption

        // Next, we'll consult the time series to obtain the set of known
        // channel ID's that match their query.
        startBlock := query.FirstBlockHeight
        endBlock := query.LastBlockHeight()
        channelRanges, err := g.cfg.channelSeries.FilterChannelRange(
                query.ChainHash, startBlock, endBlock, withTimestamps,
        )
        if err != nil {
                return err
        }

        // TODO(roasbeef): means can't send max uint above?
        //  * or make internal 64

        // We'll send our response in a streaming manner, chunk-by-chunk. We do
        // this as there's a transport message size limit which we'll need to
        // adhere to. We also need to make sure all of our replies cover the
        // expected range of the query.
        sendReplyForChunk := func(channelChunk []graphdb.ChannelUpdateInfo,
                firstHeight, lastHeight uint32, finalChunk bool) error {

                // The number of blocks contained in the current chunk (the
                // total span) is the difference between the last channel ID and
                // the first in the range. We add one as even if all channels
                // returned are in the same block, we need to count that.
                numBlocks := lastHeight - firstHeight + 1
                complete := uint8(0)
                if finalChunk {
                        complete = 1
                }

                var timestamps lnwire.Timestamps
                if withTimestamps {
                        timestamps = make(lnwire.Timestamps, len(channelChunk))
                }

                scids := make([]lnwire.ShortChannelID, len(channelChunk))
                for i, info := range channelChunk {
                        scids[i] = info.ShortChannelID

                        if !withTimestamps {
                                continue
                        }

                        timestamps[i].Timestamp1 = uint32(
                                info.Node1UpdateTimestamp.Unix(),
                        )

                        timestamps[i].Timestamp2 = uint32(
                                info.Node2UpdateTimestamp.Unix(),
                        )
                }

                return g.sendToPeerSync(ctx, &lnwire.ReplyChannelRange{
                        ChainHash:        query.ChainHash,
                        NumBlocks:        numBlocks,
                        FirstBlockHeight: firstHeight,
                        Complete:         complete,
                        EncodingType:     g.cfg.encodingType,
                        ShortChanIDs:     scids,
                        Timestamps:       timestamps,
                })
        }

        var (
                firstHeight  = query.FirstBlockHeight
                lastHeight   uint32
                channelChunk []graphdb.ChannelUpdateInfo
        )

        // chunkSize is the maximum number of SCIDs that we can safely put in a
        // single message. If we also need to include timestamps though, then
        // this number is halved since encoding two timestamps takes the same
        // number of bytes as encoding an SCID.
        chunkSize := g.cfg.chunkSize
        if withTimestamps {
                chunkSize /= 2
        }

        for _, channelRange := range channelRanges {
                channels := channelRange.Channels
                numChannels := int32(len(channels))
                numLeftToAdd := chunkSize - int32(len(channelChunk))

                // Include the current block in the ongoing chunk if it can fit
                // and move on to the next block.
                if numChannels <= numLeftToAdd {
                        channelChunk = append(channelChunk, channels...)
                        continue
                }

                // Otherwise, we need to send our existing channel chunk as is
                // as its own reply and start a new one for the current block.
                // We'll mark the end of our current chunk as the height before
                // the current block to ensure the whole query range is replied
                // to.
                log.Infof("GossipSyncer(%x): sending range chunk of size=%v",
                        g.cfg.peerPub[:], len(channelChunk))

                lastHeight = channelRange.Height - 1
                err := sendReplyForChunk(
                        channelChunk, firstHeight, lastHeight, false,
                )
                if err != nil {
                        return err
                }

                // With the reply constructed, we'll start tallying channels for
                // our next one keeping in mind our chunk size. This may result
                // in channels for this block being left out from the reply, but
                // this isn't an issue since we'll randomly shuffle them and we
                // assume a historical gossip sync is performed at a later time.
                firstHeight = channelRange.Height
                finalChunkSize := numChannels
                exceedsChunkSize := numChannels > chunkSize
                if exceedsChunkSize {
                        rand.Shuffle(len(channels), func(i, j int) {
                                channels[i], channels[j] = channels[j], channels[i]
                        })
                        finalChunkSize = chunkSize
                }
                channelChunk = channels[:finalChunkSize]

                // Sort the chunk once again if we had to shuffle it.
                if exceedsChunkSize {
                        sort.Slice(channelChunk, func(i, j int) bool {
                                id1 := channelChunk[i].ShortChannelID.ToUint64()
                                id2 := channelChunk[j].ShortChannelID.ToUint64()

                                return id1 < id2
                        })
                }
        }

        // Send the remaining chunk as the final reply.
        log.Infof("GossipSyncer(%x): sending final chan range chunk, size=%v",
                g.cfg.peerPub[:], len(channelChunk))

        return sendReplyForChunk(
                channelChunk, firstHeight, query.LastBlockHeight(), true,
        )
}

// replyShortChanIDs will be dispatched in response to a query by the remote
// node for information concerning a set of short channel ID's. Our response
// will be sent in a streaming chunked manner to ensure that we remain below
// the current transport level message size.
func (g *GossipSyncer) replyShortChanIDs(ctx context.Context,
        query *lnwire.QueryShortChanIDs) error {

        // Before responding, we'll check to ensure that the remote peer is
        // querying for the same chain that we're on. If not, we'll send back a
        // response with a complete value of zero to indicate we're on a
        // different chain.
        if g.cfg.chainHash != query.ChainHash {
                log.Warnf("Remote peer requested QueryShortChanIDs for "+
                        "chain=%v, we're on chain=%v", query.ChainHash,
                        g.cfg.chainHash)

                return g.sendToPeerSync(ctx, &lnwire.ReplyShortChanIDsEnd{
                        ChainHash: query.ChainHash,
                        Complete:  0,
                })
        }

        if len(query.ShortChanIDs) == 0 {
                log.Infof("GossipSyncer(%x): ignoring query for blank short chan ID's",
                        g.cfg.peerPub[:])
                return nil
        }

        log.Infof("GossipSyncer(%x): fetching chan anns for %v chans",
                g.cfg.peerPub[:], len(query.ShortChanIDs))

        // Now that we know we're on the same chain, we'll query the channel
        // time series for the set of messages that we know of which satisfies
        // the requirement of being a chan ann, chan update, or a node ann
        // related to the set of queried channels.
        replyMsgs, err := g.cfg.channelSeries.FetchChanAnns(
                query.ChainHash, query.ShortChanIDs,
        )
        if err != nil {
                return fmt.Errorf("unable to fetch chan anns for %v..., %w",
                        query.ShortChanIDs[0].ToUint64(), err)
        }

        // Reply with any messages related to those channel ID's, we'll write
        // each one individually and synchronously to throttle the sends and
        // perform buffering of responses in the syncer as opposed to the peer.
        for _, msg := range replyMsgs {
                err := g.sendToPeerSync(ctx, msg)
                if err != nil {
                        return err
                }
        }

        // Regardless of whether we had any messages to reply with, send over
        // the sentinel message to signal that the stream has terminated.
        return g.sendToPeerSync(ctx, &lnwire.ReplyShortChanIDsEnd{
                ChainHash: query.ChainHash,
                Complete:  1,
        })
}

// ApplyGossipFilter applies a gossiper filter sent by the remote node to the
// state machine. Once applied, we'll ensure that we don't forward any messages
// to the peer that aren't within the time range of the filter.
func (g *GossipSyncer) ApplyGossipFilter(ctx context.Context,
        filter *lnwire.GossipTimestampRange) error {

        g.Lock()

        g.remoteUpdateHorizon = filter

        startTime := time.Unix(int64(g.remoteUpdateHorizon.FirstTimestamp), 0)
        endTime := startTime.Add(
                time.Duration(g.remoteUpdateHorizon.TimestampRange) * time.Second,
        )

        g.Unlock()

        // If requested, don't reply with historical gossip data when the remote
        // peer sets their gossip timestamp range.
        if g.cfg.ignoreHistoricalFilters {
                return nil
        }

        // Check if a goroutine is already sending the backlog. If so, return
        // early without attempting to acquire the semaphore.
        if g.isSendingBacklog.Load() {
                log.Debugf("GossipSyncer(%x): skipping ApplyGossipFilter, "+
                        "backlog send already in progress", g.cfg.peerPub[:])
                return nil
        }

        select {
        case <-g.syncerSema:
        case <-g.cg.Done():
                return ErrGossipSyncerExiting
        case <-ctx.Done():
                return ctx.Err()
        }

        // We don't put this in a defer because if the goroutine is launched,
        // it needs to be called when the goroutine is stopped.
        returnSema := func() {
                g.syncerSema <- struct{}{}
        }

        // Now that the remote peer has applied their filter, we'll query the
        // database for all the messages that are beyond this filter.
        newUpdatestoSend := g.cfg.channelSeries.UpdatesInHorizon(
                g.cfg.chainHash, startTime, endTime,
        )

        // Create a pull-based iterator so we can check if there are any
        // updates before launching the goroutine.
        next, stop := iter.Pull2(newUpdatestoSend)

        // Check if we have any updates to send by attempting to get the first
        // message.
        firstMsg, firstErr, ok := next()
        if firstErr != nil {
                stop()
                returnSema()
                return firstErr
        }

        log.Infof("GossipSyncer(%x): applying new remote update horizon: "+
                "start=%v, end=%v, has_updates=%v", g.cfg.peerPub[:],
                startTime, endTime, ok)

        // If we don't have any to send, then we can return early.
        if !ok {
                stop()
                returnSema()
                return nil
        }

        // Set the atomic flag to indicate we're starting to send the backlog.
        // If the swap fails, it means another goroutine is already active, so
        // we return early.
        if !g.isSendingBacklog.CompareAndSwap(false, true) {
                returnSema()
                log.Debugf("GossipSyncer(%x): another goroutine already "+
                        "sending backlog, skipping", g.cfg.peerPub[:])

                return nil
        }

        // We'll conclude by launching a goroutine to send out any updates.
        // The goroutine takes ownership of the iterator.
        g.cg.WgAdd(1)
        go func() {
                defer g.cg.WgDone()
                defer returnSema()
                defer g.isSendingBacklog.Store(false)
                defer stop()

                // Send the first message we already pulled.
                err := g.sendToPeerSync(ctx, firstMsg)
                switch {
                case errors.Is(err, ErrGossipSyncerExiting):
                        return

                case errors.Is(err, lnpeer.ErrPeerExiting):
                        return

                case err != nil:
                        log.Errorf("Unable to send message for "+
                                "peer catch up: %v", err)
                }

                // Continue with the rest of the messages using the same pull
                // iterator.
                for {
                        select {
                        case <-ctx.Done():
                                log.Debugf("GossipSyncer(%x): context "+
                                        "canceled, exiting", g.cfg.peerPub[:])

                                return
                        case <-g.cg.Done():
                                log.Debugf("GossipSyncer(%x): shutting down, "+
                                        "exiting", g.cfg.peerPub[:])

                                return
                        default:
                        }

                        msg, err, ok := next()
                        if !ok {
                                return
                        }

                        // If the iterator yielded an error, log it and
                        // continue.
                        if err != nil {
                                log.Errorf("Error fetching update for peer "+
                                        "catch up: %v", err)
                                continue
                        }

                        err = g.sendToPeerSync(ctx, msg)
                        switch {
                        case err == ErrGossipSyncerExiting:
                                return

                        case err == lnpeer.ErrPeerExiting:
                                return

                        case err != nil:
                                log.Errorf("Unable to send message for "+
                                        "peer catch up: %v", err)
                        }
                }
        }()

        return nil
}

// FilterGossipMsgs takes a set of gossip messages, and only send it to a peer
// iff the message is within the bounds of their set gossip filter. If the peer
// doesn't have a gossip filter set, then no messages will be forwarded.
func (g *GossipSyncer) FilterGossipMsgs(ctx context.Context,
        msgs ...msgWithSenders) {

        // If the peer doesn't have an update horizon set, then we won't send
        // it any new update messages.
        if g.remoteUpdateHorizon == nil {
                log.Tracef("GossipSyncer(%x): skipped due to nil "+
                        "remoteUpdateHorizon", g.cfg.peerPub[:])
                return
        }

        // If we've been signaled to exit, or are exiting, then we'll stop
        // short.
        select {
        case <-g.cg.Done():
                return
        case <-ctx.Done():
                return
        default:
        }

        // TODO(roasbeef): need to ensure that peer still online...send msg to
        // gossiper on peer termination to signal peer disconnect?

        var err error

        // Before we filter out the messages, we'll construct an index over the
        // set of channel announcements and channel updates. This will allow us
        // to quickly check if we should forward a chan ann, based on the known
        // channel updates for a channel.
        chanUpdateIndex := make(
                map[lnwire.ShortChannelID][]*lnwire.ChannelUpdate1,
        )
        for _, msg := range msgs {
                chanUpdate, ok := msg.msg.(*lnwire.ChannelUpdate1)
                if !ok {
                        continue
                }

                chanUpdateIndex[chanUpdate.ShortChannelID] = append(
                        chanUpdateIndex[chanUpdate.ShortChannelID], chanUpdate,
                )
        }

        // We'll construct a helper function that we'll us below to determine
        // if a given messages passes the gossip msg filter.
        g.Lock()
        startTime := time.Unix(int64(g.remoteUpdateHorizon.FirstTimestamp), 0)
        endTime := startTime.Add(
                time.Duration(g.remoteUpdateHorizon.TimestampRange) * time.Second,
        )
        g.Unlock()

        passesFilter := func(timeStamp uint32) bool {
                t := time.Unix(int64(timeStamp), 0)
                return t.Equal(startTime) ||
                        (t.After(startTime) && t.Before(endTime))
        }

        msgsToSend := make([]lnwire.Message, 0, len(msgs))
        for _, msg := range msgs {
                // If the target peer is the peer that sent us this message,
                // then we'll exit early as we don't need to filter this
                // message.
                if _, ok := msg.senders[g.cfg.peerPub]; ok {
                        continue
                }

                switch msg := msg.msg.(type) {

                // For each channel announcement message, we'll only send this
                // message if the channel updates for the channel are between
                // our time range.
                case *lnwire.ChannelAnnouncement1:
                        // First, we'll check if the channel updates are in
                        // this message batch.
                        chanUpdates, ok := chanUpdateIndex[msg.ShortChannelID]
                        if !ok {
                                // If not, we'll attempt to query the database
                                // to see if we know of the updates.
                                chanUpdates, err = g.cfg.channelSeries.FetchChanUpdates(
                                        g.cfg.chainHash, msg.ShortChannelID,
                                )
                                if err != nil {
                                        log.Warnf("no channel updates found for "+
                                                "short_chan_id=%v",
                                                msg.ShortChannelID)
                                        continue
                                }
                        }

                        for _, chanUpdate := range chanUpdates {
                                if passesFilter(chanUpdate.Timestamp) {
                                        msgsToSend = append(msgsToSend, msg)
                                        break
                                }
                        }

                        if len(chanUpdates) == 0 {
                                msgsToSend = append(msgsToSend, msg)
                        }

                // For each channel update, we'll only send if it the timestamp
                // is between our time range.
                case *lnwire.ChannelUpdate1:
                        if passesFilter(msg.Timestamp) {
                                msgsToSend = append(msgsToSend, msg)
                        }

                // Similarly, we only send node announcements if the update
                // timestamp ifs between our set gossip filter time range.
                case *lnwire.NodeAnnouncement1:
                        if passesFilter(msg.Timestamp) {
                                msgsToSend = append(msgsToSend, msg)
                        }
                }
        }

        log.Tracef("GossipSyncer(%x): filtered gossip msgs: set=%v, sent=%v",
                g.cfg.peerPub[:], len(msgs), len(msgsToSend))

        if len(msgsToSend) == 0 {
                return
        }

        if err = g.sendToPeer(ctx, msgsToSend...); err != nil {
                log.Errorf("unable to send gossip msgs: %v", err)
        }

}

// ProcessQueryMsg is used by outside callers to pass new channel time series
// queries to the internal processing goroutine.
func (g *GossipSyncer) ProcessQueryMsg(msg lnwire.Message, peerQuit <-chan struct{}) error {
        var msgChan chan lnwire.Message
        switch msg.(type) {
        case *lnwire.QueryChannelRange, *lnwire.QueryShortChanIDs:
                msgChan = g.queryMsgs

        // Reply messages should only be expected in states where we're waiting
        // for a reply.
        case *lnwire.ReplyChannelRange, *lnwire.ReplyShortChanIDsEnd:
                g.Lock()
                syncState := g.syncState()
                g.Unlock()

                if syncState != waitingQueryRangeReply &&
                        syncState != waitingQueryChanReply {

                        return fmt.Errorf("unexpected msg %T received in "+
                                "state %v", msg, syncState)
                }
                msgChan = g.gossipMsgs

        default:
                msgChan = g.gossipMsgs
        }

        select {
        case msgChan <- msg:
        case <-peerQuit:
        case <-g.cg.Done():
        }

        return nil
}

// setSyncState sets the gossip syncer's state to the given state.
func (g *GossipSyncer) setSyncState(state syncerState) {
        atomic.StoreUint32(&g.state, uint32(state))
}

// syncState returns the current syncerState of the target GossipSyncer.
func (g *GossipSyncer) syncState() syncerState {
        return syncerState(atomic.LoadUint32(&g.state))
}

// ResetSyncedSignal returns a channel that will be closed in order to serve as
// a signal for when the GossipSyncer has reached its chansSynced state.
func (g *GossipSyncer) ResetSyncedSignal() chan struct{} {
        g.Lock()
        defer g.Unlock()

        syncedSignal := make(chan struct{})

        syncState := syncerState(atomic.LoadUint32(&g.state))
        if syncState == chansSynced {
                close(syncedSignal)
                return syncedSignal
        }

        g.syncedSignal = syncedSignal
        return g.syncedSignal
}

// ProcessSyncTransition sends a request to the gossip syncer to transition its
// sync type to a new one.
//
// NOTE: This can only be done once the gossip syncer has reached its final
// chansSynced state.
func (g *GossipSyncer) ProcessSyncTransition(newSyncType SyncerType) error {
        errChan := make(chan error, 1)
        select {
        case g.syncTransitionReqs <- &syncTransitionReq{
                newSyncType: newSyncType,
                errChan:     errChan,
        }:
        case <-time.After(syncTransitionTimeout):
                return ErrSyncTransitionTimeout
        case <-g.cg.Done():
                return ErrGossipSyncerExiting
        }

        select {
        case err := <-errChan:
                return err
        case <-g.cg.Done():
                return ErrGossipSyncerExiting
        }
}

// handleSyncTransition handles a new sync type transition request.
//
// NOTE: The gossip syncer might have another sync state as a result of this
// transition.
func (g *GossipSyncer) handleSyncTransition(ctx context.Context,
        req *syncTransitionReq) error {

        // Return early from any NOP sync transitions.
        syncType := g.SyncType()
        if syncType == req.newSyncType {
                return nil
        }

        log.Debugf("GossipSyncer(%x): transitioning from %v to %v",
                g.cfg.peerPub, syncType, req.newSyncType)

        var (
                firstTimestamp time.Time
                timestampRange uint32
        )

        switch req.newSyncType {
        // If an active sync has been requested, then we should resume receiving
        // new graph updates from the remote peer.
        case ActiveSync, PinnedSync:
                firstTimestamp = time.Now()
                timestampRange = math.MaxUint32

        // If a PassiveSync transition has been requested, then we should no
        // longer receive any new updates from the remote peer. We can do this
        // by setting our update horizon to a range in the past ensuring no
        // graph updates match the timestamp range.
        case PassiveSync:
                firstTimestamp = zeroTimestamp
                timestampRange = 0

        default:
                return fmt.Errorf("unhandled sync transition %v",
                        req.newSyncType)
        }

        err := g.sendGossipTimestampRange(ctx, firstTimestamp, timestampRange)
        if err != nil {
                return fmt.Errorf("unable to send local update horizon: %w",
                        err)
        }

        g.setSyncType(req.newSyncType)

        return nil
}

// setSyncType sets the gossip syncer's sync type to the given type.
func (g *GossipSyncer) setSyncType(syncType SyncerType) {
        atomic.StoreUint32(&g.syncType, uint32(syncType))
}

// SyncType returns the current SyncerType of the target GossipSyncer.
func (g *GossipSyncer) SyncType() SyncerType {
        return SyncerType(atomic.LoadUint32(&g.syncType))
}

// historicalSync sends a request to the gossip syncer to perofmr a historical
// sync.
//
// NOTE: This can only be done once the gossip syncer has reached its final
// chansSynced state.
func (g *GossipSyncer) historicalSync() error {
        done := make(chan struct{})

        select {
        case g.historicalSyncReqs <- &historicalSyncReq{
                doneChan: done,
        }:
        case <-time.After(syncTransitionTimeout):
                return ErrSyncTransitionTimeout
        case <-g.cg.Done():
                return ErrGossiperShuttingDown
        }

        select {
        case <-done:
                return nil
        case <-g.cg.Done():
                return ErrGossiperShuttingDown
        }
}

// handleHistoricalSync handles a request to the gossip syncer to perform a
// historical sync.
func (g *GossipSyncer) handleHistoricalSync(req *historicalSyncReq) {
        // We'll go back to our initial syncingChans state in order to request
        // the remote peer to give us all of the channel IDs they know of
        // starting from the genesis block.
        g.genHistoricalChanRangeQuery = true
        g.setSyncState(syncingChans)
        close(req.doneChan)
}

// sendToPeer sends a variadic number of messages to the remote peer. This
// method should not block while waiting for sends to be written to the wire.
func (g *GossipSyncer) sendToPeer(ctx context.Context,
        msgs ...lnwire.Message) error {

        return g.sendMsgRateLimited(ctx, false, msgs...)
}

// sendToPeerSync sends a variadic number of messages to the remote peer,
// blocking until all messages have been sent successfully or a write error is
// encountered.
func (g *GossipSyncer) sendToPeerSync(ctx context.Context,
        msgs ...lnwire.Message) error {

        return g.sendMsgRateLimited(ctx, true, msgs...)
}

// sendMsgRateLimited sends a variadic number of messages to the remote peer,
// applying our per-peer rate limit before each send. The sync boolean
// determines if the send is blocking or not.
func (g *GossipSyncer) sendMsgRateLimited(ctx context.Context, sync bool,
        msgs ...lnwire.Message) error {

        for _, msg := range msgs {
                err := maybeRateLimitMsg(
                        ctx, g.rateLimiter, g.cfg.peerPub, msg, g.cg.Done(),
                )
                if err != nil {
                        return err
                }

                err = g.cfg.sendMsg(ctx, sync, msg)
                if err != nil {
                        return err
                }
        }

        return nil
}

lightningnetwork / lnd / 18915193695

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