discovery: adhere to proper channel chunk splitting for ReplyChannelRange

channeldb/graph.go

@@ -10,6 +10,7 @@ import (
 	"io"
 	"math"
 	"net"
+	"sort"
 	"sync"
 	"time"
 
@@ -1704,12 +1705,25 @@ func (c *ChannelGraph) FilterKnownChanIDs(chanIDs []uint64) ([]uint64, error) {
 	return newChanIDs, nil
 }
 
+// BlockChannelRange represents a range of channels for a given block height.
+type BlockChannelRange struct {
+	// Height is the height of the block all of the channels below were
+	// included in.
+	Height uint32
+
+	// Channels is the list of channels identified by their short ID
+	// representation known to us that were included in the block height
+	// above.
+	Channels []lnwire.ShortChannelID
+}
+
 // FilterChannelRange returns the channel ID's of all known channels which were
-// mined in a block height within the passed range. This method can be used to
-// quickly share with a peer the set of channels we know of within a particular
-// range to catch them up after a period of time offline.
-func (c *ChannelGraph) FilterChannelRange(startHeight, endHeight uint32) ([]uint64, error) {
-	var chanIDs []uint64
+// mined in a block height within the passed range. The channel IDs are grouped
+// by their common block height. This method can be used to quickly share with a
+// peer the set of channels we know of within a particular range to catch them
+// up after a period of time offline.
+func (c *ChannelGraph) FilterChannelRange(startHeight,
+	endHeight uint32) ([]BlockChannelRange, error) {
 
 	startChanID := &lnwire.ShortChannelID{
 		BlockHeight: startHeight,
@@ -1728,6 +1742,7 @@ func (c *ChannelGraph) FilterChannelRange(startHeight, endHeight uint32) ([]uint
 	byteOrder.PutUint64(chanIDStart[:], startChanID.ToUint64())
 	byteOrder.PutUint64(chanIDEnd[:], endChanID.ToUint64())
 
+	var channelsPerBlock map[uint32][]lnwire.ShortChannelID
 	err := kvdb.View(c.db, func(tx kvdb.RTx) error {
 		edges := tx.ReadBucket(edgeBucket)
 		if edges == nil {
@@ -1742,33 +1757,51 @@ func (c *ChannelGraph) FilterChannelRange(startHeight, endHeight uint32) ([]uint
 
 		// We'll now iterate through the database, and find each
 		// channel ID that resides within the specified range.
-		var cid uint64
 		for k, _ := cursor.Seek(chanIDStart[:]); k != nil &&
 			bytes.Compare(k, chanIDEnd[:]) <= 0; k, _ = cursor.Next() {
 
 			// This channel ID rests within the target range, so
-			// we'll convert it into an integer and add it to our
-			// returned set.
-			cid = byteOrder.Uint64(k)
-			chanIDs = append(chanIDs, cid)
+			// we'll add it to our returned set.
+			rawCid := byteOrder.Uint64(k)
+			cid := lnwire.NewShortChanIDFromInt(rawCid)
+			channelsPerBlock[cid.BlockHeight] = append(
+				channelsPerBlock[cid.BlockHeight], cid,
+			)
 		}
 
 		return nil
 	}, func() {
-		chanIDs = nil
+		channelsPerBlock = make(map[uint32][]lnwire.ShortChannelID)
 	})
 
 	switch {
 	// If we don't know of any channels yet, then there's nothing to
 	// filter, so we'll return an empty slice.
-	case err == ErrGraphNoEdgesFound:
-		return chanIDs, nil
+	case err == ErrGraphNoEdgesFound || len(channelsPerBlock) == 0:
+		return nil, nil
 
 	case err != nil:
 		return nil, err
 	}
 
-	return chanIDs, nil
+	// Return the channel ranges in ascending block height order.
+	blocks := make([]uint32, 0, len(channelsPerBlock))
+	for block := range channelsPerBlock {
+		blocks = append(blocks, block)
+	}
+	sort.Slice(blocks, func(i, j int) bool {
+		return blocks[i] < blocks[j]
+	})
+
+	channelRanges := make([]BlockChannelRange, 0, len(channelsPerBlock))
+	for _, block := range blocks {
+		channelRanges = append(channelRanges, BlockChannelRange{
+			Height:   block,
+			Channels: channelsPerBlock[block],
+		})
+	}
+
+	return channelRanges, nil
 }
 
 // FetchChanInfos returns the set of channel edges that correspond to the passed

channeldb/graph_test.go

@@ -1848,24 +1848,32 @@ func TestFilterChannelRange(t *testing.T) {
 		t.Fatalf("expected zero chans, instead got %v", len(resp))
 	}
 
-	// To start, we'll create a set of channels, each mined in a block 10
+	// To start, we'll create a set of channels, two mined in a block 10
 	// blocks after the prior one.
 	startHeight := uint32(100)
 	endHeight := startHeight
 	const numChans = 10
-	chanIDs := make([]uint64, 0, numChans)
-	for i := 0; i < numChans; i++ {
+	channelRanges := make([]BlockChannelRange, 0, numChans/2)
+	for i := 0; i < numChans/2; i++ {
 		chanHeight := endHeight
-		channel, chanID := createEdge(
-			uint32(chanHeight), uint32(i+1), 0, 0, node1, node2,
+		channel1, chanID1 := createEdge(
+			chanHeight, uint32(i+1), 0, 0, node1, node2,
 		)
-
-		if err := graph.AddChannelEdge(&channel); err != nil {
+		if err := graph.AddChannelEdge(&channel1); err != nil {
 			t.Fatalf("unable to create channel edge: %v", err)
 		}
 
-		chanIDs = append(chanIDs, chanID.ToUint64())
+		channel2, chanID2 := createEdge(
+			chanHeight, uint32(i+2), 0, 0, node1, node2,
+		)
+		if err := graph.AddChannelEdge(&channel2); err != nil {
+			t.Fatalf("unable to create channel edge: %v", err)
+		}
 
+		channelRanges = append(channelRanges, BlockChannelRange{
+			Height:   chanHeight,
+			Channels: []lnwire.ShortChannelID{chanID1, chanID2},
+		})
 		endHeight += 10
 	}
 
@@ -1876,7 +1884,7 @@ func TestFilterChannelRange(t *testing.T) {
 		startHeight uint32
 		endHeight   uint32
 
-		resp []uint64
+		resp []BlockChannelRange
 	}{
 		// If we query for the entire range, then we should get the same
 		// set of short channel IDs back.
@@ -1884,7 +1892,7 @@ func TestFilterChannelRange(t *testing.T) {
 			startHeight: startHeight,
 			endHeight:   endHeight,
 
-			resp: chanIDs,
+			resp: channelRanges,
 		},
 
 		// If we query for a range of channels right before our range, we
@@ -1900,7 +1908,7 @@ func TestFilterChannelRange(t *testing.T) {
 			startHeight: endHeight - 10,
 			endHeight:   endHeight - 10,
 
-			resp: chanIDs[9:],
+			resp: channelRanges[4:],
 		},
 
 		// If we query for just the first height, we should only get a
@@ -1909,7 +1917,14 @@ func TestFilterChannelRange(t *testing.T) {
 			startHeight: startHeight,
 			endHeight:   startHeight,
 
-			resp: chanIDs[:1],
+			resp: channelRanges[:1],
+		},
+
+		{
+			startHeight: startHeight + 10,
+			endHeight:   endHeight - 10,
+
+			resp: channelRanges[1:5],
 		},
 	}
 	for i, queryCase := range queryCases {

discovery/chan_series.go

@@ -39,10 +39,11 @@ type ChannelGraphTimeSeries interface {
 		superSet []lnwire.ShortChannelID) ([]lnwire.ShortChannelID, error)
 
 	// FilterChannelRange returns the set of channels that we created
-	// between the start height and the end height. We'll use this to to a
-	// remote peer's QueryChannelRange message.
+	// between the start height and the end height. The channel IDs are
+	// grouped by their common block height. We'll use this to to a remote
+	// peer's QueryChannelRange message.
 	FilterChannelRange(chain chainhash.Hash,
-		startHeight, endHeight uint32) ([]lnwire.ShortChannelID, error)
+		startHeight, endHeight uint32) ([]channeldb.BlockChannelRange, error)
 
 	// FetchChanAnns returns a full set of channel announcements as well as
 	// their updates that match the set of specified short channel ID's.
@@ -203,26 +204,15 @@ func (c *ChanSeries) FilterKnownChanIDs(chain chainhash.Hash,
 }
 
 // FilterChannelRange returns the set of channels that we created between the
-// start height and the end height. We'll use this respond to a remote peer's
-// QueryChannelRange message.
+// start height and the end height. The channel IDs are grouped by their common
+// block height. We'll use this respond to a remote peer's QueryChannelRange
+// message.
 //
 // NOTE: This is part of the ChannelGraphTimeSeries interface.
 func (c *ChanSeries) FilterChannelRange(chain chainhash.Hash,
-	startHeight, endHeight uint32) ([]lnwire.ShortChannelID, error) {
+	startHeight, endHeight uint32) ([]channeldb.BlockChannelRange, error) {
 
-	chansInRange, err := c.graph.FilterChannelRange(startHeight, endHeight)
-	if err != nil {
-		return nil, err
-	}
-
-	chanResp := make([]lnwire.ShortChannelID, 0, len(chansInRange))
-	for _, chanID := range chansInRange {
-		chanResp = append(
-			chanResp, lnwire.NewShortChanIDFromInt(chanID),
-		)
-	}
-
-	return chanResp, nil
+	return c.graph.FilterChannelRange(startHeight, endHeight)
 }
 
 // FetchChanAnns returns a full set of channel announcements as well as their

discovery/sync_manager.go

@@ -426,6 +426,7 @@ func (m *SyncManager) createGossipSyncer(peer lnpeer.Peer) *GossipSyncer {
 		maxUndelayedQueryReplies:  DefaultMaxUndelayedQueryReplies,
 		delayedQueryReplyInterval: DefaultDelayedQueryReplyInterval,
 		bestHeight:                m.cfg.BestHeight,
+		maxQueryChanRangeReplies:  maxQueryChanRangeReplies,
 	})
 
 	// Gossip syncers are initialized by default in a PassiveSync type

discovery/sync_manager_test.go

@@ -11,6 +11,7 @@ import (
 	"github.com/lightningnetwork/lnd/lntest/wait"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/ticker"
+	"github.com/stretchr/testify/require"
 )
 
 // randPeer creates a random peer.
@@ -537,10 +538,14 @@ func assertTransitionToChansSynced(t *testing.T, s *GossipSyncer, peer *mockPeer
 	}
 	assertMsgSent(t, peer, query)
 
-	s.ProcessQueryMsg(&lnwire.ReplyChannelRange{
+	require.Eventually(t, func() bool {
+		return s.syncState() == waitingQueryRangeReply
+	}, time.Second, 500*time.Millisecond)
+
+	require.NoError(t, s.ProcessQueryMsg(&lnwire.ReplyChannelRange{
 		QueryChannelRange: *query,
 		Complete:          1,
-	}, nil)
+	}, nil))
 
 	chanSeries := s.cfg.channelSeries.(*mockChannelGraphTimeSeries)
 

discovery/syncer.go

@@ -4,6 +4,8 @@ import (
 	"errors"
 	"fmt"
 	"math"
+	"math/rand"
+	"sort"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -128,6 +130,14 @@ const (
 	// maxUndelayedQueryReplies queries.
 	DefaultDelayedQueryReplyInterval = 5 * time.Second
 
+	// 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.
@@ -240,6 +250,10 @@ type gossipSyncerCfg struct {
 
 	// bestHeight returns the latest height known of the chain.
 	bestHeight func() uint32
+
+	// maxQueryChanRangeReplies is the maximum number of replies we'll allow
+	// for a single QueryChannelRange request.
+	maxQueryChanRangeReplies uint32
 }
 
 // GossipSyncer is a struct that handles synchronizing the channel graph state
@@ -316,6 +330,11 @@ type GossipSyncer struct {
 	// buffer all the chunked response to our query.
 	bufferedChanRangeReplies []lnwire.ShortChannelID
 
+	// 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.
@@ -741,17 +760,27 @@ func (g *GossipSyncer) processChanRangeReply(msg *lnwire.ReplyChannelRange) erro
 	g.bufferedChanRangeReplies = append(
 		g.bufferedChanRangeReplies, msg.ShortChanIDs...,
 	)
+	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, then we can exit as we've already
-	// buffered the latest portion of the streaming reply.
+	// 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 {
+		if msg.Complete == 0 && g.numChanRangeRepliesRcvd < maxReplies {
 			return nil
 		}
 
@@ -763,7 +792,8 @@ func (g *GossipSyncer) processChanRangeReply(msg *lnwire.ReplyChannelRange) erro
 		// 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 {
+		if replyLastHeight < queryLastHeight &&
+			g.numChanRangeRepliesRcvd < maxReplies {
 			return nil
 		}
 	}
@@ -786,6 +816,7 @@ func (g *GossipSyncer) processChanRangeReply(msg *lnwire.ReplyChannelRange) erro
 	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.
@@ -930,7 +961,7 @@ func (g *GossipSyncer) replyChanRangeQuery(query *lnwire.QueryChannelRange) erro
 	// channel ID's that match their query.
 	startBlock := query.FirstBlockHeight
 	endBlock := query.LastBlockHeight()
-	channelRange, err := g.cfg.channelSeries.FilterChannelRange(
+	channelRanges, err := g.cfg.channelSeries.FilterChannelRange(
 		query.ChainHash, startBlock, endBlock,
 	)
 	if err != nil {
@@ -940,102 +971,98 @@ func (g *GossipSyncer) replyChanRangeQuery(query *lnwire.QueryChannelRange) erro
 	// TODO(roasbeef): means can't send max uint above?
 	//  * or make internal 64
 
-	// In the base case (no actual response) the first block and last block
-	// will match those of the query. In the loop below, we'll update these
-	// two variables incrementally with each chunk to properly compute the
-	// starting block for each response and the number of blocks in a
-	// response.
-	firstBlockHeight := startBlock
-	lastBlockHeight := endBlock
+	// 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 []lnwire.ShortChannelID,
+		firstHeight, lastHeight uint32, finalChunk bool) error {
 
-	numChannels := int32(len(channelRange))
-	numChansSent := int32(0)
-	for {
-		// We'll send our this 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.
-		var channelChunk []lnwire.ShortChannelID
-
-		// We know this is the final chunk, if the difference between
-		// the total number of channels, and the number of channels
-		// we've sent is less-than-or-equal to the chunk size.
-		isFinalChunk := (numChannels - numChansSent) <= g.cfg.chunkSize
-
-		// If this is indeed the last chunk, then we'll send the
-		// remainder of the channels.
-		if isFinalChunk {
-			channelChunk = channelRange[numChansSent:]
-
-			log.Infof("GossipSyncer(%x): sending final chan "+
-				"range chunk, size=%v", g.cfg.peerPub[:],
-				len(channelChunk))
-		} else {
-			// Otherwise, we'll only send off a fragment exactly
-			// sized to the proper chunk size.
-			channelChunk = channelRange[numChansSent : numChansSent+g.cfg.chunkSize]
-
-			log.Infof("GossipSyncer(%x): sending range chunk of "+
-				"size=%v", g.cfg.peerPub[:], len(channelChunk))
-		}
-
-		// If we have any channels at all to return, then we need to
-		// update our pointers to the first and last blocks for each
-		// response.
-		if len(channelChunk) > 0 {
-			// If this is the first response we'll send, we'll point
-			// the first block to the first block in the query.
-			// Otherwise, we'll continue from the block we left off
-			// at.
-			if numChansSent == 0 {
-				firstBlockHeight = startBlock
-			} else {
-				firstBlockHeight = lastBlockHeight
-			}
-
-			// If this is the last response we'll send, we'll point
-			// the last block to the last block of the query.
-			// Otherwise, we'll set it to the height of the last
-			// channel in the chunk.
-			if isFinalChunk {
-				lastBlockHeight = endBlock
-			} else {
-				lastBlockHeight = channelChunk[len(channelChunk)-1].BlockHeight
-			}
-		}
-
-		// The number of blocks contained in this response (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
+		// 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.
-		numBlocksInResp := lastBlockHeight - firstBlockHeight + 1
+		numBlocks := lastHeight - firstHeight + 1
+		complete := uint8(0)
+		if finalChunk {
+			complete = 1
+		}
 
-		// With our chunk assembled, we'll now send to the remote peer
-		// the current chunk.
-		replyChunk := lnwire.ReplyChannelRange{
+		return g.cfg.sendToPeerSync(&lnwire.ReplyChannelRange{
 			QueryChannelRange: lnwire.QueryChannelRange{
 				ChainHash:        query.ChainHash,
-				NumBlocks:        numBlocksInResp,
-				FirstBlockHeight: firstBlockHeight,
+				NumBlocks:        numBlocks,
+				FirstBlockHeight: firstHeight,
 			},
-			Complete:     0,
+			Complete:     complete,
 			EncodingType: g.cfg.encodingType,
 			ShortChanIDs: channelChunk,
+		})
+	}
+
+	var (
+		firstHeight  = query.FirstBlockHeight
+		lastHeight   uint32
+		channelChunk []lnwire.ShortChannelID
+	)
+	for _, channelRange := range channelRanges {
+		channels := channelRange.Channels
+		numChannels := int32(len(channels))
+		numLeftToAdd := g.cfg.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
 		}
-		if isFinalChunk {
-			replyChunk.Complete = 1
-		}
-		if err := g.cfg.sendToPeerSync(&replyChunk); err != nil {
+
+		// 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
 		}
 
-		// If this was the final chunk, then we'll exit now as our
-		// response is now complete.
-		if isFinalChunk {
-			return nil
+		// 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
+		chunkSize := numChannels
+		exceedsChunkSize := numChannels > g.cfg.chunkSize
+		if exceedsChunkSize {
+			rand.Shuffle(len(channels), func(i, j int) {
+				channels[i], channels[j] = channels[j], channels[i]
+			})
+			chunkSize = g.cfg.chunkSize
+		}
+		channelChunk = channels[:chunkSize]
+
+		// Sort the chunk once again if we had to shuffle it.
+		if exceedsChunkSize {
+			sort.Slice(channelChunk, func(i, j int) bool {
+				return channelChunk[i].ToUint64() <
+					channelChunk[j].ToUint64()
+			})
 		}
-
-		numChansSent += int32(len(channelChunk))
 	}
+
+	// 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
@@ -1285,11 +1312,23 @@ func (g *GossipSyncer) FilterGossipMsgs(msgs ...msgWithSenders) {
 
 // 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{}) {
+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:
+		syncState := g.syncState()
+		if syncState != waitingQueryRangeReply &&
+			syncState != waitingQueryChanReply {
+			return fmt.Errorf("received unexpected query reply "+
+				"message %T", msg)
+		}
+		msgChan = g.gossipMsgs
+
 	default:
 		msgChan = g.gossipMsgs
 	}
@@ -1299,6 +1338,8 @@ func (g *GossipSyncer) ProcessQueryMsg(msg lnwire.Message, peerQuit <-chan struc
 	case <-peerQuit:
 	case <-g.quit:
 	}
+
+	return nil
 }
 
 // setSyncState sets the gossip syncer's state to the given state.

discovery/syncer_test.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"math"
 	"reflect"
+	"sort"
 	"sync"
 	"testing"
 	"time"
@@ -12,7 +13,9 @@ import (
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
 	"github.com/davecgh/go-spew/spew"
+	"github.com/lightningnetwork/lnd/channeldb"
 	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/stretchr/testify/require"
 )
 
 const (
@@ -95,11 +98,36 @@ func (m *mockChannelGraphTimeSeries) FilterKnownChanIDs(chain chainhash.Hash,
 	return <-m.filterResp, nil
 }
 func (m *mockChannelGraphTimeSeries) FilterChannelRange(chain chainhash.Hash,
-	startHeight, endHeight uint32) ([]lnwire.ShortChannelID, error) {
+	startHeight, endHeight uint32) ([]channeldb.BlockChannelRange, error) {
 
 	m.filterRangeReqs <- filterRangeReq{startHeight, endHeight}
+	reply := <-m.filterRangeResp
 
-	return <-m.filterRangeResp, nil
+	channelsPerBlock := make(map[uint32][]lnwire.ShortChannelID)
+	for _, cid := range reply {
+		channelsPerBlock[cid.BlockHeight] = append(
+			channelsPerBlock[cid.BlockHeight], cid,
+		)
+	}
+
+	// Return the channel ranges in ascending block height order.
+	blocks := make([]uint32, 0, len(channelsPerBlock))
+	for block := range channelsPerBlock {
+		blocks = append(blocks, block)
+	}
+	sort.Slice(blocks, func(i, j int) bool {
+		return blocks[i] < blocks[j]
+	})
+
+	channelRanges := make([]channeldb.BlockChannelRange, 0, len(channelsPerBlock))
+	for _, block := range blocks {
+		channelRanges = append(channelRanges, channeldb.BlockChannelRange{
+			Height:   block,
+			Channels: channelsPerBlock[block],
+		})
+	}
+
+	return channelRanges, nil
 }
 func (m *mockChannelGraphTimeSeries) FetchChanAnns(chain chainhash.Hash,
 	shortChanIDs []lnwire.ShortChannelID) ([]lnwire.Message, error) {
@@ -161,6 +189,7 @@ func newTestSyncer(hID lnwire.ShortChannelID,
 		bestHeight: func() uint32 {
 			return latestKnownHeight
 		},
+		maxQueryChanRangeReplies: maxQueryChanRangeReplies,
 	}
 	syncer := newGossipSyncer(cfg)
 
@@ -828,6 +857,7 @@ func TestGossipSyncerReplyChanRangeQuery(t *testing.T) {
 	// reply. We should get three sets of messages as two of them should be
 	// full, while the other is the final fragment.
 	const numExpectedChunks = 3
+	var prevResp *lnwire.ReplyChannelRange
 	respMsgs := make([]lnwire.ShortChannelID, 0, 5)
 	for i := 0; i < numExpectedChunks; i++ {
 		select {
@@ -855,14 +885,14 @@ func TestGossipSyncerReplyChanRangeQuery(t *testing.T) {
 			// channels.
 			case i == 0:
 				expectedFirstBlockHeight = startingBlockHeight
-				expectedNumBlocks = chunkSize + 1
+				expectedNumBlocks = 4
 
 			// The last reply should range starting from the next
 			// block of our previous reply up until the ending
 			// height of the query. It should also have the Complete
 			// bit set.
 			case i == numExpectedChunks-1:
-				expectedFirstBlockHeight = respMsgs[len(respMsgs)-1].BlockHeight
+				expectedFirstBlockHeight = prevResp.LastBlockHeight() + 1
 				expectedNumBlocks = endingBlockHeight - expectedFirstBlockHeight + 1
 				expectedComplete = 1
 
@@ -870,8 +900,8 @@ func TestGossipSyncerReplyChanRangeQuery(t *testing.T) {
 			// the next block of our previous reply up until it
 			// reaches its maximum capacity of channels.
 			default:
-				expectedFirstBlockHeight = respMsgs[len(respMsgs)-1].BlockHeight
-				expectedNumBlocks = 5
+				expectedFirstBlockHeight = prevResp.LastBlockHeight() + 1
+				expectedNumBlocks = 4
 			}
 
 			switch {
@@ -889,9 +919,10 @@ func TestGossipSyncerReplyChanRangeQuery(t *testing.T) {
 			case rangeResp.Complete != expectedComplete:
 				t.Fatalf("Complete in resp #%d incorrect: "+
 					"expected %v, got %v", i+1,
-					expectedNumBlocks, rangeResp.Complete)
+					expectedComplete, rangeResp.Complete)
 			}
 
+			prevResp = rangeResp
 			respMsgs = append(respMsgs, rangeResp.ShortChanIDs...)
 		}
 	}
@@ -1498,10 +1529,12 @@ func TestGossipSyncerDelayDOS(t *testing.T) {
 	// inherently disjoint.
 	var syncer2Chans []lnwire.ShortChannelID
 	for i := 0; i < numTotalChans; i++ {
-		syncer2Chans = append(syncer2Chans, lnwire.ShortChannelID{
-			BlockHeight: highestID.BlockHeight - 1,
-			TxIndex:     uint32(i),
-		})
+		syncer2Chans = append([]lnwire.ShortChannelID{
+			{
+				BlockHeight: highestID.BlockHeight - uint32(i) - 1,
+				TxIndex:     uint32(i),
+			},
+		}, syncer2Chans...)
 	}
 
 	// We'll kick off the test by asserting syncer1 sends over the
@@ -2305,3 +2338,80 @@ func TestGossipSyncerSyncedSignal(t *testing.T) {
 		t.Fatal("expected to receive chansSynced signal")
 	}
 }
+
+// TestGossipSyncerMaxChannelRangeReplies ensures that a gossip syncer
+// transitions its state after receiving the maximum possible number of replies
+// for a single QueryChannelRange message, and that any further replies after
+// said limit are not processed.
+func TestGossipSyncerMaxChannelRangeReplies(t *testing.T) {
+	t.Parallel()
+
+	msgChan, syncer, chanSeries := newTestSyncer(
+		lnwire.ShortChannelID{BlockHeight: latestKnownHeight},
+		defaultEncoding, defaultChunkSize,
+	)
+
+	// We'll tune the maxQueryChanRangeReplies to a more sensible value for
+	// the sake of testing.
+	syncer.cfg.maxQueryChanRangeReplies = 100
+
+	syncer.Start()
+	defer syncer.Stop()
+
+	// Upon initialization, the syncer should submit a QueryChannelRange
+	// request.
+	var query *lnwire.QueryChannelRange
+	select {
+	case msgs := <-msgChan:
+		require.Len(t, msgs, 1)
+		require.IsType(t, &lnwire.QueryChannelRange{}, msgs[0])
+		query = msgs[0].(*lnwire.QueryChannelRange)
+
+	case <-time.After(time.Second):
+		t.Fatal("expected query channel range request msg")
+	}
+
+	// We'll send the maximum number of replies allowed to a
+	// QueryChannelRange request with each reply consuming only one block in
+	// order to transition the syncer's state.
+	for i := uint32(0); i < syncer.cfg.maxQueryChanRangeReplies; i++ {
+		reply := &lnwire.ReplyChannelRange{
+			QueryChannelRange: *query,
+			ShortChanIDs: []lnwire.ShortChannelID{
+				{
+					BlockHeight: query.FirstBlockHeight + i,
+				},
+			},
+		}
+		reply.FirstBlockHeight = query.FirstBlockHeight + i
+		reply.NumBlocks = 1
+		require.NoError(t, syncer.ProcessQueryMsg(reply, nil))
+	}
+
+	// We should receive a filter request for the syncer's local channels
+	// after processing all of the replies. We'll send back a nil response
+	// indicating that no new channels need to be synced, so it should
+	// transition to its final chansSynced state.
+	select {
+	case <-chanSeries.filterReq:
+	case <-time.After(time.Second):
+		t.Fatal("expected local filter request of known channels")
+	}
+	select {
+	case chanSeries.filterResp <- nil:
+	case <-time.After(time.Second):
+		t.Fatal("timed out sending filter response")
+	}
+	assertSyncerStatus(t, syncer, chansSynced, ActiveSync)
+
+	// Finally, attempting to process another reply for the same query
+	// should result in an error.
+	require.Error(t, syncer.ProcessQueryMsg(&lnwire.ReplyChannelRange{
+		QueryChannelRange: *query,
+		ShortChanIDs: []lnwire.ShortChannelID{
+			{
+				BlockHeight: query.LastBlockHeight() + 1,
+			},
+		},
+	}, nil))
+}