routing: add support for detection+processing of premature announcements

This commit fixes a prior block propagation race-condition by detecting
and properly processing “premature” announcements. A premature
announcement is one that’s received with an anchored block height which
is beyond our chain tip. Once received, we now store these
announcements in a special map that’s caches them in memory. Once a new
block arrives, we check the map for the existence of any entries,
processing them as normal if so.

routing/router.go

@@ -96,8 +96,13 @@ type Config struct {
 type ChannelRouter struct {
 	sync.RWMutex
 
+	// cfg is a copy of the configuration struct that the ChannelRouter was
+	// initialized with.
 	cfg *Config
 
+	// selfNode is the center of the star-graph centered around the
+	// ChannelRouter. The ChannelRouter uses this node as a starting point
+	// when doing any path finding.
 	selfNode *channeldb.LightningNode
 
 	// TODO(roasbeef): make LRU, invalidate upon new block connect
@@ -105,12 +110,31 @@ type ChannelRouter struct {
 	nodeCache         map[[33]byte]*channeldb.LightningNode
 	edgeCache         map[wire.OutPoint]*channeldb.ChannelEdge
 
+	// newBlocks is a channel in which new blocks connected to the end of
+	// the main chain are sent over.
 	newBlocks chan *chainntnfs.BlockEpoch
 
+	// networkMsgs is a channel that carries new network messages from
+	// outside the ChannelRouter to be processed by the networkHandler.
 	networkMsgs chan *routingMsg
 
+	// syncRequests is a channel that carries requests to synchronize newly
+	// connected peers to the state of the channel graph from our PoV.
 	syncRequests chan *syncRequest
 
+	// prematureAnnouncements maps a blockheight to a set of announcements
+	// which are "premature" from our PoV. An announcement is premature if
+	// it claims to be anchored in a block which is beyond the current
+	// mainchain tip as we know it. Premature announcements will be
+	// processed once the chain tip as we know it extends to/past the
+	// premature height.
+	// TODO(roasbeef): limit premature announcements to N
+	prematureAnnouncements map[uint32][]lnwire.Message
+
+	// bestHeight is the height of the block at the tip of the main chain
+	// as we know it.
+	bestHeight uint32
+
 	fakeSig *btcec.Signature
 
 	started uint32
@@ -150,6 +174,7 @@ func New(cfg Config) (*ChannelRouter, error) {
 		fakeSig:                fakeSig,
 		networkMsgs:            make(chan *routingMsg),
 		syncRequests:           make(chan *syncRequest),
+		prematureAnnouncements: make(map[uint32][]lnwire.Message),
 		quit: make(chan struct{}),
 	}, nil
 }
@@ -174,6 +199,12 @@ func (r *ChannelRouter) Start() error {
 	}
 	r.newBlocks = blockEpochs.Epochs
 
+	_, height, err := r.cfg.Chain.GetBestBlock()
+	if err != nil {
+		return err
+	}
+	r.bestHeight = uint32(height)
+
 	// Before we begin normal operation of the router, we first need to
 	// synchronize the channel graph to the latest state of the UTXO set.
 	if err := r.syncGraphWithChain(); err != nil {
@@ -304,6 +335,7 @@ func (r *ChannelRouter) networkHandler() {
 
 	var announcementBatch []lnwire.Message
 
+	// TODO(roasbeef): parametrize the above
 	trickleTimer := time.NewTicker(time.Millisecond * 300)
 	defer trickleTimer.Stop()
 
@@ -316,11 +348,8 @@ func (r *ChannelRouter) networkHandler() {
 		// result we'll modify the channel graph accordingly depending
 		// on the exact type of the message.
 		case netMsg := <-r.networkMsgs:
-			// TODO(roasbeef): this loop would mostly be moved to
+			// Process the network announcement to determine if
-			// the discovery service
+			// this is either a new announcement from our PoV or an
-
-			// Process the network announcement to determine if this
-			// is either a new announcement from our PoV or an
 			// update to a prior vertex/edge we previously
 			// accepted.
 			accepted := r.processNetworkAnnouncement(netMsg.msg)
@@ -345,15 +374,34 @@ func (r *ChannelRouter) networkHandler() {
 				return
 			}
 
+			// Once a new block arrives, we update our running
+			// track of the height of the chain tip.
+			blockHeight := uint32(newBlock.Height)
+			r.bestHeight = blockHeight
+
+			// Next we check if we have any premature announcements
+			// for this height, if so, then we process them once
+			// more as normal announcements.
+			prematureAnns := r.prematureAnnouncements[uint32(newBlock.Height)]
+			log.Infof("Re-processing %v premature announcements for "+
+				"height %v", len(prematureAnns), blockHeight)
+
+			for _, ann := range prematureAnns {
+				if ok := r.processNetworkAnnouncement(ann); ok {
+					announcementBatch = append(announcementBatch, ann)
+				}
+			}
+			delete(r.prematureAnnouncements, blockHeight)
+
+			log.Infof("Pruning channel graph using block %v (height=%v)",
+				newBlock.Hash, blockHeight)
+
 			block, err := r.cfg.Chain.GetBlock(newBlock.Hash)
 			if err != nil {
 				log.Errorf("unable to get block: %v", err)
 				continue
 			}
 
-			log.Infof("Pruning channel graph using block %v (height=%v)",
-				newBlock.Hash, newBlock.Height)
-
 			// We're only interested in all prior outputs that've
 			// been spent in the block, so collate all the
 			// referenced previous outpoints within each tx and
@@ -371,14 +419,14 @@ func (r *ChannelRouter) networkHandler() {
 			// of the block being pruned so the prune tip can be
 			// updated.
 			numClosed, err := r.cfg.Graph.PruneGraph(spentOutputs,
-				newBlock.Hash, uint32(newBlock.Height))
+				newBlock.Hash, blockHeight)
 			if err != nil {
 				log.Errorf("unable to prune routing table: %v", err)
 				continue
 			}
 
 			log.Infof("Block %v (height=%v) closed %v channels",
-				newBlock.Hash, newBlock.Height, numClosed)
+				newBlock.Hash, blockHeight, numClosed)
 
 		// The retransmission timer has ticked which indicates that we
 		// should broadcast our personal channel sot the network. This
@@ -481,9 +529,13 @@ func (r *ChannelRouter) networkHandler() {
 // channel or node announcement. If the update didn't affect the internal state
 // of the draft due to either being out of date, invalid, or redundant, then
 // false is returned. Otherwise, true is returned indicating that the caller
-// may want to batch this request to be broadcast to immediate peers during th
+// may want to batch this request to be broadcast to immediate peers during the
 // next announcement epoch.
 func (r *ChannelRouter) processNetworkAnnouncement(msg lnwire.Message) bool {
+	isPremature := func(chanID *lnwire.ChannelID) bool {
+		return chanID.BlockHeight > r.bestHeight
+	}
+
 	switch msg := msg.(type) {
 
 	// A new node announcement has arrived which either presents a new
@@ -545,10 +597,22 @@ func (r *ChannelRouter) processNetworkAnnouncement(msg lnwire.Message) bool {
 			return false
 		}
 
-		// TODO(roasbeef): check if height > then our known height and
+		// If the advertised inclusionary block is beyond our knowledge
-		// wait for next epoch based on that?
+		// of the chain tip, then we'll put the announcement in limbo
-		//  * or add to "premature" announcement bucket
+		// to be fully verified once we advance forward in the chain.
-		//  * bucket gets checked on each new incoming block
+		if isPremature(&msg.ChannelID) {
+			blockHeight := msg.ChannelID.BlockHeight
+			log.Infof("Announcement for chan_id=(%v), is "+
+				"premature: advertises height %v, only height "+
+				"%v is known", channelID,
+				msg.ChannelID.BlockHeight, r.bestHeight)
+
+			r.prematureAnnouncements[blockHeight] = append(
+				r.prematureAnnouncements[blockHeight],
+				msg,
+			)
+			return false
+		}
 
 		// Before we can add the channel to the channel graph, we need
 		// to obtain the full funding outpoint that's encoded within
@@ -597,6 +661,23 @@ func (r *ChannelRouter) processNetworkAnnouncement(msg lnwire.Message) bool {
 			return false
 		}
 
+		// If the advertised inclusionary block is beyond our knowledge
+		// of the chain tip, then we'll put the announcement in limbo
+		// to be fully verified once we advance forward in the chain.
+		if isPremature(&msg.ChannelID) {
+			blockHeight := msg.ChannelID.BlockHeight
+			log.Infof("Update announcement for chan_id=(%v), is "+
+				"premature: advertises height %v, only height "+
+				"%v is known", chanID, blockHeight,
+				r.bestHeight)
+
+			r.prematureAnnouncements[blockHeight] = append(
+				r.prematureAnnouncements[blockHeight],
+				msg,
+			)
+			return false
+		}
+
 		// As edges are directional edge node has a unique policy for
 		// the direction of the edge they control. Therefore we first
 		// check if we already have the most up to date information for